Most manufacturers design propellers in the same way and they read the old books and reports and the prop gets no more than 80-85% efficiency at best. It is written in books that propeller efficiency will be about that at best and it is left often open how low it can be at worst.

Here is an interesting article about a guy that made a prop that was 90 percent efficient by not abiding the "old truths" but thinking out of the box:

http://www.eaa.org/experimenter/articles/2020-02_elippse.asp

Having a strong taper certainly makes sense since the propeller tip travels very much faster than the root through the air. Also the old saying that single blade prop is most efficient does not make sense if you think it in detail: the air that enters in the next blade is not the same air that went through the previous blade because of the forward movement of the aircraft. This could be extrapolated in a such way, that the faster the aircraft travels, the more blades the propeller can have without sacrificing the propeller efficiency. This should not actually require very high mathematics, but I am quite sure that it could be estimated with simple calculations where the downwash of the previous blade goes in relation to the next blade on the speed range intended for the aircraft being designed.

High altitude propeller will require some additional thinking for the tip chord because the Reynolds number will become low if the chord is this short. The TAS is much higher at high altitude, therefore the air travels faster through the prop, that would mean that the prop could have more blades. The high altitude propeller does not require full efficiency at low altitude because to be able to operate at high altitude, there needs to be a lots of excess thrust available regardless.

I have been ranting about that personal aviation is starving and struggling at best to stay alive. But there is no such reason it has to stay that way. If nothing is done, ever increasing regulation and bureaucracy and the increasing expenses will make personal aviation extinct sooner rather than later. And in my opinion, sportplanes/LSA are not the right answer. They are substitute for something else that would be really needed instead - airplanes are most useful when they are used to get somewhere - with fun and with style. Let's face it, flying traffic pattern is such hardcore fun that only dedicated pilots like me and maybe the readers of this blog will enjoy about. And to get somewhere, there is the blocker, which is weather. And I think there is a solution for that:

What is missing in general currently in current general aviation market is simply:
- affordable mass produced aircraft that are so simple to fly that much greater portion of population can do that, and with less training than currently is required for pilot's license.

Lets address this simple to fly thing: mechanically controlled aircraft can be easy to fly to an extent. For example Diamond DA40 is very easy airplane to fly. However, it still requires a lot of training to fly one. To make airplanes more accessible to people, controls should be extremely simple to learn, should not be any harder to get it than learn to ride a motorcycle, or ideally, it should be easier. So what would be the cure then?

In my opinion the answer is in fly-by-wire. No control rods, cables and the like, but instead a (doubled for redundancy) computer that controls all control surfaces and specially purpose built brushless DC servo motors which are directly connected to control surfaces. User uses a fully electronic stick that only gives input to the computer which then decides what control surfaces to move and how much to respond to the input the way user wanted. Pushrod assemblies are very complicated, have many parts, of which many are expensive. To make the plane less expensive, all expensive parts should be designed out of it. Servo motors can be made in large quantities quite inexpensive and the control system will not be super expensive either as it would use off-the-shelf hardware. Doubling that for redundancy would not be very expensive as the hardware in question is similar than what controls all quadro copters and toys like that.

Second enabler will be avionics which displays only important information to the user. E.g. user does not need to know oil pressure, oil temperature, EGT, CHT etc. values if they are all well and optimal, ECU is controlling the engine without bothering you about mixture controls or other obsolete things, and trend analysis done by the computer concludes that trends are not alarming and user does not need to worry about engine failure. Only when something would fail, or something suspicious would be found from analysed trends, the computer would inform the user about the problem. If things are ok and green, why to bother user with 100 gauge displays on a cluttered control panel. User would be left with much less workload and he or she could concentrate on looking for other traffic and flying the plane rather than trying to watch all the engine monitoring etc. values.

The system could communicate automatically with ATC and would display the pilot a very easy path to follow to make a IFR approach without needing any of the workload that is the burden for IFR-pilots. The plane would do things automatically, a bit like a copilot that would be helping you on the right seat. You would not need to worry about what is ILS alpha approach as all the necessary information would be presented you automatically and the display would show you in very clear way which way to turn your plane. You would still be able to control the plane to not lose the fun of flying, but the hard and messy parts would be handled by automation. And for pilot going to weather he or she is not able to fly through, there could be a panic button that would direct the plane to the next airport and land automatically if the pilot so wishes.

And one more enabler would be nice to have. It takes awful lot of time to pre-flight a modern high performance aircraft such as Cirrus SR22. You open the checklist and start checking this and that and that and that and there are zillion items to check before you can even start the engine. What if there would be a computer with sophisticated sensors wired everywhere in the plane and it could do the pre-flight automatically without user needing to care about it unless he or she wants. Sometimes, in case of a short trip, due to the long time spent to pre-flighting the plane, one could reach the destination by car faster by driving rather than getting to airport, pre-flighting plane, filing flight plan etc. There surely should be a faster way to do it with some technology.

It would not be the thing how fast the plane would be. That would be secondary after the plane would be fast enough. How economic the plane would be has greater importance. But how easy it is has greatest importance. Not everybody is skilled enough to ever become IFR-pilots and let's face it, single pilot IFR is a quite dangerous thing to do in hard IMC to the minimums alone without second pilot as helper. The second pilot would need to be replaced with very intelligent computer system that would take off the workload from the pilot so the pilot could concentrate on flying a perfect approach.

Since the plane would be fly-by-wire, it could be made more stable and the ride could be augmented to be less bumpy by automation. So that the plane would be always rock solid, in perfect trim etc. in all flight conditions that would make flying the IFR-approaches very easy and safe. This would enable really this pre-requisite of getting somewhere. Who would want to drive 1000 km with a car slowly averaging 80 km/h at best if there was a way to do it with airplane with no more expense, as easily as with the car, and much more conveniently and certainly with a lot more style. That would make airplanes desirable again to general public, that they currently are not. Only hardcore pilots (like myself) have a desire for the current selection of airplanes.

None of these things I presented here are technically impossible to do and neither they would or should cost much. Everything presented above is doable with even a less sophisticated hardware than a typical smartphone that costs no more than 400 euros. The authorities with ancient rules, regulations and bureaucracy is a thing that makes everything expensive, and I could imagine that some certification process could kill this idea for starters even before it began and this kind of installed system would cost due to certification costs, millions per one single unit. But lets assume that this would not happen and things would go the right way for a change.

To get somewhere, regulation should be largely reinvented in order to not kill personal aviation. Well it is already killed by certification requirements and regulations, it is more like a zombie now, but I would be really happy the GA to be reanimated and to be a real business again, and this time reinvented to be better than ever before. This is a market that would exist if it was not overregulated and that would employ a lot of people and would revolutionize how people travel from point A to B - instead of sitting in Boeing or Airbus and licking their knees in tourist class, they could enjoy similar freedom as driving a family car and getting to the destination with their own schedule without queues, waiting, walking kilometers in huge terminals of huge airports, and without associated anxiety etc. Instead of a large jumbo-jet now and then, there would be demand for hundreds of thousands to millions of small inexpensive and easy to fly aircraft that would be designed for serious transportation and not to be toys like LSAs. Current airplane market is more like a joke. To make it a real market, it would need to be completely reinvented and revolutionized, otherwise it is a dead end that leads to nowhere else than the gradually reduced amount of pilots and the remaining pilots facing more and more ridiculous expenses which will further reduce their interest and numbers which is no good for the individuals nor businesses.

In addition to the RC batteries from http://www.hobbyking.com, you can also get more robust packaged batteries from for example here:

http://www.ev-power.eu/

They also have high power motor controllers which are at or exceeding power class of a big hybrid aircraft.

XFLR5 is the most sophisticated easy to use free tool currently for modelling aircraft. I found some interesting articles about how to use it. They are covering old versions, but you may find them helpful.

Resources for getting started with XFLR5:

1. Get XFLR5 here (for Mac): http://sourceforge.net/projects/xflr5/files/v6.09.06/XFLR5-6.09.06-MacOSX.dmg/download

Read some instructions (covers old version of XFLR5 though):

http://www.v0id.at/downloads/XFLR5-tut-v1.pdf

https://engineering.purdue.edu/~aerodyn/AAE333/FALL10/HOMEWORKS/HW13/XFLR5_v6.01_Beta_Win32(2)/Release/Guidelines.pdf

Then something from this magazine (covers old version of XFLR5 though):

http://www.rcsoaringdigest.com/pdfs/RCSD-2020/RCSD-2020-02.pdf

The moment curve especially in wing analysis is great tool for making your plane stable.

The Reynolds number at very high altitude is very low. Here is an article about airfoil study for 60000 ft altitude flight. My previous airfoils are not very suitable in a small aircraft at 60000 ft, they require longer chord to be efficient. I made series of new airfoils for short chord and high altitude and ended up with the KS415/14.3.

Example:
altitude = 20000 m
velocity = 80 m/s
wing chord = 0.8 m (80 cm)
=>
Re = 396331.94
M = 0.2711

Therefore it is beneficial that the airfoil used in this kind of aircraft is such that provides maximum L/D at low Re, here around 400000.

Here are some simulations:

Then some airfoils that I created:
http://www.katix.org/karoliina/airfoils/KS414.dat
http://www.katix.org/karoliina/airfoils/KS415%2014.3.dat
http://www.katix.org/karoliina/airfoils/KS416%2014.20.dat

KS416:

More simulation at low Re, two conditions: 80 m/s at 600000 ft and 111 m/s (400 km/h) at 60000 ft:

Added case 154 m/2 (300 kts) at 60000 ft:

Of these, the KS415 exhibits the lowest drag. Here is the geometry of the KS415:

Here is a smoothed version of KS415/14.3:
http://www.katix.org/karoliina/airfoils/KS415_14_3sm.dat

And simulation for a Reynolds number range:

I was thinking one day about the Bohannon B1. It is basically a modified RV (Harmon rocket something) with very high power to weight ratio and that's it. This plane climbed to something like 14 km.

So consider this (high excess power) case hypothetically:
- Airplane with high aspect ratio (low span loading) with high power engines with high power to weight ratio. Example: Chevrolet LS9 (600 hp).
- If the plane can maintain level flight with minimal power. 35000 ft we have remaining power 0.2 * 600 = 120 hp.
- Diamond flies nicely with 120 hp, actually 90 hp is quite sufficient for it for normal cruise speed. With lower span loading much less should keep the plane level.

So now the naysay would be "nah, LS9 can not sustain 600 hp continuous without breaking". However, 120 hp is hardly 600 hp continuous even if the engine is at full throttle and giving all it can at the altitude. It is still stressed only for the 20 percent power.

Same engine, with single stage turbocharger, it should be possible to extend this quite a bit further. With two stage turbocharger even higher altitude should be possible, 70000 ft might be feasible given that the other challenges that come with the altitude are solved somehow.

So you could have a 1200 hp airplane with 240 hp used at altitude for cruise (in case of twin). This should give a quite generous cruise speed at the altitude given that the props are big enough (disc loading low enough).

Airfoil



KS400 wing at altitude 20 km, speed = 155 kts



Here is the dat-file. Download it here: KS400.dat

Works from Re 500 000 up.

More simulations to follow later.

If you are into flying wings like me, this PowerPoint slideset might interest you. It compares the basics of conventional airliner and flying wing airliner. Much bigger planes in other words, than my interest area. However, some of the pros and cons findings for each configuration also apply for the small version. Not all though as the starting point does not have engine nacelles and engines sticking out of the wing. http://www.engbrasil.eng.br/index_arquivos/ap23.pdf I haven't done yet comparison for the wetted area of a flying wing compared to a sailplane like structure. Logic tells that the flying wing in this size category might have more wetted area. But I am not sure. I need to design both and then measure the wetted area of both and compare. I am not a big fan of wing twist and the amount of wing twist on PUL-10 causes me shivers (wing tip twisted 10 degrees). That can't be good for cruise, simply can not. Ten degrees is insane amount of twist - on cruise the tips are on negative angle of attack and cause a lots of negative lift. The wing tips act as rather poor tails this way - it is very short coupled and if you have tail deflected that much on that close, the wing center section will need to lift also the negative lift of the tips which will make the plane to perform poorer. I am quite sure that a flying wing should be made stable without that much twist. I have a related idea for a flying wing: - one problem with flying wing is that flaps can not be used - what if you had small trim tails that look like the ones in SpaceShipOne. When flaps would be down, the trim tail, would cause opposing pitching moment to negate the pitching moment of the flap - The elevator control otherwise would be like on a flying wing, with elevons. - I haven't tried this out yet but it can be tested with RC model.

I am progressing forwards from concentrating on aerodynamics to also fabrication and optimizing the fabrication process. Been doing hand layups for a quite long time now, but I need to start doing shape accurate parts. Testing aerodynamics requires very high accuracy.

I have been doing several molds lately. One was almost successful, but it was a lot of work and it still had non-sharp edges.

So what I am trying to do is a wing mold with CNC fabrication. I have a CNC mill that can carve blue styrofoam, wood, MDF, Corecell etc. and is large enough for producing a half (lower or upper) of a wing section (with the limitation of the length, have to glue a big mold from ~1.2 meter pieces together).

I would need a rapid prototyping technique to produce shape accurate molds with glossy or at least almost glossy surface. So that manual work would be minimal. This is especially pronounced in case of making wing molds.

The problem I am facing is this:
- if I carve the plug to blue styrofoam, and then paint it and polish it, there is the downside:
- the styrofoam can be only painted with a paint that does not have solvent in it, and the only paint that will fill the surface is solvent free epoxy primer. The problem with that is that it also makes sharp edges round, and especially in a small scale (RC scale) the roundness becomes way too big to be acceptable. The edges where the lower and upper half meet, should be also absolutely accurate and sharp. Doesn't happen with this technique.

Has any reader used molding epoxy? I saw some picture of a mold being filled with a molding epoxy and then milled with CNC again to shiny surface directly (?). Would that be viable option for my use? As it would be for rapid prototyping and for fabricating many wings (and not just one pair), it should be somewhat reasonably cost effective. Making the mold from wood is not completely inexpensive either - requires a very thick perfect wood block (or MDF block). I could not afford consider replacing the styrofoam with a huge solid mold plastic block (that is used in industry for prototyping shapes with CNC), because the same volume is much more expensive, would be possibly fine for a CNC model of a small device, but for making a mold for large wing the cost hikes out of the roof very quickly. Styrofoam is cheap and very easy for the machine to carve, but that's the best part of it, otherwise it is really poor material.

Any first hand experiences on this?

I referred to the AR-drone in previous article about flying car. We produced a short video about Ar-drone flying:
http://www.vimeo.com/16147472

iPad provides control input (which direction one wants to go) and the computer inside the AR-drone provides artificial stability (so it is very easy to fly unlike RC-helicopters).

There are many considerations where to put a propellers in a small aircraft or RPV. The common place to put them is at the nose. The biggest reason and driver for this placement is that it is advantageous for CG location. However, from aerodynamic standpoint that is not very optimal. There was discussion at HBA Forums about propeller placement and this document was linked (it studies difference of prop placed in pusher and tractor configuration):

http://www.icas.org/ICAS_ARCHIVE_CD1998-2019/ICAS2000/PAPERS/ICA0344.PDF

Optimal place is behind the wing, a bit above the wing centerline (only small part of the prop circle goes below the wing). This placement has the typical CG challenges with it. And it will require either pylon on the wing, or a pylon on the fuselage (assuming a single fuselage). There is then the question about the effect of the body to the prop located near the fuselage behind the trailing edge of the wing. There might be unfavorable flow due to the effects of the wing-fuselage joint that this study did not take in account.

According to the article, it was possible to increase quite significantly the Clmax of the wing with the rear placement of the propeller due to the suction effect to the wing. This leads to interesting thought about a line-thruster - multiple small electric motors turning multiple relatively small props behind the trailing edge of the wing, providing suction to the whole wing surface, or at least large part of it. Interesting question then would be that would a varying thrust angle be beneficial, should the pylons be actually mounted on the flaps? Downside of this is that this may lead to flap mechanism that is not very lightweight as the flaps have to take all the torque and push from the motors. Normal flap mechanisms would not like that.

Any comments on this?

The Joby Motors seems to have good enough KV-values for running slow turning props (especially JM2S and JM2):
http://www.jobymotors.com/public/views/pages/products.php

Electric Lazair uses these motors. Standard windings are available for up to 700 volt system!

I have been thinking what would make "flying cars" feasible. I think the answer is pretty much that it needs to be VTOL. Anything that lands on runway will become very complex design mechanically. A real solution would be to land on the car anywhere, e.g. shop parking lot - otherwise it would be just a clumsy non-optimal airplane.

So what are the breakthroughs needed for this? I doubt that the internal combustion engines can do this ever very well and turbines are out of question as well because nobody can afford flying to shop with turbine power. So I think this will require electric motors and advanced battery technology. Hybrid design could possibly work too.

Large helicopter propeller blades will become a problem when landing on congested place and it would cause also safety issues. You could hit something with the rotating prop and newspapers would be full of horrific accidents very soon. Someone sliced somebody or sliced somebody's house or whatever. The props should be shrouded for safety of general public. Then how many props? One prop and it will require tail and tail rotor. Not so nice. Coaxial rotors, that would be better but still will require one to be helicopter pilot. I think the case of how it would work is very simple, and the case example already exists in small scale as sort of "RC copter":
http://ardrone.parrot.com/parrot-ar-drone/usa/

So computer controlled fly by wire and the user would be just selecting to go forward or backward or up or down or to rotate. Computer handles the rest. Each prop would have electric motors, big ones instead of the small ones found from the little thing. This plane could even have small wings, which could be optimized for cruise only (and not for landing at all) and could be possibly pivoting - when airspeed increases less vertical thrust would be needed. This could be "the flying car" that everybody can control. Not everybody can become a helicopter pilot or even airplane pilot - requirements are all the time becoming more and more and less and less will ever succeed to become pilots (from those who dared to start the training), but anybody that can drive a car, can select up, down, turn left, turn right, go forward, go backwards. This thing could be done so that all "flying cars" would have a data link to other "flying cars" nearby. The computer could automatically avoid collisions without the need of centralized air traffic control at all. Actually air traffic control is a system that can not scale to the level of cars are used on the roads, no matter what. The only way to manage the huge amount of traffic is to not have centralized control at all, but the control would need to be between the aircraft and it would need to be automatic data link, not this antiquated AM radio we are using to call ATC. I think it would be reasonable to make the system such that there could be as many flying cars in the air than there are cars on the ground now. Traffic congestions could be easily avoided because there is lots of space in the vertical plane in the air (when we forget about airspace altitudes and minimum altitudes etc.).

The four rotor configuration would also solve the problem of placing ballistic parachute. It could be directly at the CG and it could be even made automatic, if something fails, parachute would be pulled right away.

So what would be needed:
- lightweight electric motors with high power (already possible with today's technology)
- fly by wire system (already possible with today's technology)
- data link to other aircraft (would be already possible with today's technology)
- combustion engine to charge batteries (already possible with today's technology)
- high capacity light weight batteries (this might require next generation batteries to have good enough usefulness)

For these to be good for mass market, the following points must be considered:
- it must not require pilot's license
- it must not require medical of any kind
- it must not be over-regulated, otherwise it will never gain any popularity
- it needs to be very much automatic and very easy
- there must not be super-restrictive regulation where one can land and take off, the usefulness of this concept depends on possibility take off and land from and to everywhere, it would make no sense to take off from airport and to land to airport
- it would not replace airplane, instead one could fly with this kind of machine to airport to get far away with the airplane, I don't see that this kind of design could be made ultra long range and super fast.
- it is unavoidable that this design actually requires more space still than a car, quite large diameter props needs to be used for efficiency. However, each of them would be more reasonable size compared to one helicopter rotor and less expensive to manufacture. Also four rotors provide more thrust and lower disc loading than a single rotor.

Then how these could be manufactured?
- For mass market I think they should be pressed with 3d molds from aluminium with monococue type construction like cars are made of steel. This should be feasible with today's technology because Piaggio P-180 Avanti is manufactured from this type of aluminium construction.
- There could be no rivets and there could be no hand layup in anywhere in the structure to make the price down
- The price of high capacity batteries must drop to get the price down
- the electric motors are inexpensive to manufacture in great volumes
- prototype could be composite construction

So I don't believe in Möller's design as such (combustion engines driving ducted fans), but this slightly different version (with helicopter like but shrouded rotors) could possibly be feasible. And these could be made aesthetically to look very stylish unlike helicopters, and they could have bigger mass market appeal also because of that.

The previous article received lots of very good comments, and since my reply to one comment became too long, I decided to post a new article about it.

One reader proposed either push-pull hybrid where one engine would be diesel and the other would be electric motor. There was another possibility also considered, with coaxial propellers the same thing. This is a valid point and would work. There are some challenges on it therefore here is some cons I considered and hereby listed for this setup:

I may post this as a separate article also because otherwise it possibly does not get read by that many:

This is reply to a commenter for the earlier article:
There is a little incompatibility here that I don't see how to overcome:
- the diesel engine operates at medium rpm which requires reduction drive
- the electric motor can designed to be direct drive and low rpm without need for reduction unit

Having series hybrid there is weight penalty of two brushless DC motors and the engine and the battery, but no other systems. The engine runs the brushless DC motor without reduction gear and the motor that is used as generator can be designed to operate at the rpm the engine operates. The other motor which drives the prop can be made to operate at low rpm.
-> this sytem has NO:
- weight penalty of reduction gear unit
- reliability penalty of reduction gear unit
- need for propeller clutch and the associated reliability penalty and weight penalty
- need for drive shaft to achieve aerodynamic cowling shape

You already listed the most of the pros for the diesel direct drive. I list the cons:
The diesel direct drive cons:
- would not work without clutch, the power pulses would make the prop come off in flight if it did not fail on ground testing already
- does not get necessary power to weight ratio from the engine because of the need to run it at low rpm because of the prop requires low rpm
- weight penalty of the additional gear reduction unit
- reliability penalty of the additional gear reduction unit
- weight penalty of the clutch
- reliability penalty of the clutch (in Thielert engines they have failed now and then, especially in the original design, the latest engine models might have addressed this issue but I am not sure)
- added complexity for the conversion, this is a major consideration in homebuilt experimental since added complexity can add lots of cost in terms of labor if it goes very much beyond "I can do that myself".
- aerodynamic cowling shape may require drive shaft, and reliable drive shaft has been proven to be hard to design and manufacture such way that it would be 100% reliable
- the diesel engine is harder for the prop than a electric motor because of power pulses (even with clutch) and more expensive propeller is needed than would be needed with the electric motor alone.


There is however a case what has not been talked about for your case:
- planetary gear system for driving the electric motor and the diesel engine at the same time - Toyota Prius hybrid synergy drive thing. That is about bullet proof and single point of failure will not stop the prop, one motor is enough to continue driving the prop.
- This of course has associated weight penalty. On Toyota Prius it does not matter, but on aircraft it does matter.

Case for push-pull:
- To avoid drive shaft, the diesel engine would need to be the front engine.
- case for achieving any kind of laminar flow to the fuselage would be pretty much lost
- inefficiency problems on the rear prop because of the front prop. I have not quantified this on the other hand, apparently nobody is able to answer how much is the penalty, it is not even exact in literature.

HD-link: http://youtu.be/HSwkY5M4pPo?hd=1

I was shocked to read the bad news about Steve Jobs. He is surely one of the few persons in the Wolrd that have inspired me a lot. The World has now lost one of the guiding lights and Steve is no more.

His legacy should not die. In whatever you do (his wisdom is not limited to computers and mobile phones, but also apply for aircraft, space technology and everywhere) - live your each day like it was your last day. Ask yourself, that what you would want to give to the world if this was your last day. Don't tolerate being mediocre, but create something that will change the World.

Steve is one of the rare people who had realized that statements like "maybe after 100 years we have the technology..." are simply failed logic. It does not take any period of time for something that would be like given from somebody. Nothing is given. Everybody has to work hard to make the dreams come true. There are no dreams coming true, if you don't work for what you dream for. This after 100 years never comes if everybody is just waiting for the time to make its work. Time will not make its work, it is the passionate people who do it. Stop dreaming, do what you want to do, and show to the World that you can do it. Do what you are passionate about, it is the passion that will change the world. Even if it is something market does not even consider to exist, but if you are passionate about it and find others who are too, just do it.

My sincere respect to Steve Jobs and my condolences to the family and fans world wide. But please everybody make his legacy to live on. Stay foolish. Stay hungry.

Here is a yet another collection of tech papers, however, in this time in a quite hand-picked manner - those most interesting ones (Voyager liquid cooled engines, Rotary engines, three lifting surfaces papers etc.):

http://www.protonet.org/doc/

Go to get them, good stuff.

I recorded this highly interesting presentation at Oshkosh 2019. John Roncz is telling inside story what happened with various designs he had teamed up with Burt Rutan. Link: http://youtu.be/E9eEwyVrAps?hd=1

I also had a chance to record the speech of John Roncz at Airventure 2019. John Roncz Presentation Airventure 2019

I recorded Dr. Pete Gall's presentation at Oshkosh 2019 about Designing Light Aircraft. This presentation explains with a case example of Beech Bonanza how the wing affects the drag of the whole aircraft. In the presentation a new more efficient wing is designed for the Bonanza and the results are compared to the original aircraft. This presentation is rather interesting and worth to watch. Pete Gall's merit list is rather long (see the end titles from the video). Here is the link to the event recording I made: YouTube: Dr. Pete Gall: Designing Light Aircraft. Oshkosh Airventure 2019

Someone was lucky in Oshkosh and took this short video clip from inside the Boomerang while it was doing takeoff. I find it rather interesting, especially because I am interested how this kind of window layout works. Here is the clip from some lucky person who got as a passenger to the plane: http://www.youtube.com/watch?v=QD8Cz0Sw44Q&feature=related

Rockets lifting off from the ground are inefficient and require enormous amount of fuel and especially oxidizer despite there is plenty of oxygen in the low atmosphere. Rocket engine is very inefficient too, and to save fuel, the best way is to limit the time the rocket engine is needed => more reasonable amount of fuel needs to be carried and subsequently smaller rocket is needed.

To launch microsatellites, a similar approach than Burt Rutan's WhiteKnightTwo (or Stratolauncher) is the best way to go. The difference for a microsatellite rocket is that the payload is much more modest and a much smaller and much less expensive airplane can be used. The airplane can be either UAV or optionally piloted aircraft. If it is just pure UAV, it can be made smaller and less expensive.

The principle of this airplane would be series hybrid propulsion. There would be a small but powerful modified series turbo liquid cooled motorcycle engine turning a generator (which is also a brushless DC electric motor, but bigger than the propulsion units). The actual propulsion would be provided with several smaller electric motors which would turn relatively modest size propellers (vs. the need for prop size in the high altitude). The large number of the propulsion units would compensate for the diameter. Very large diameter in the prop would cause severe geometric problems for the aircraft (landing gear, wing placement etc. as evidenced by Grob's high altitude aircraft), but instead lowering the disc loading of the prop by increasing the number of the props, is much less expensive and much less complicated way to do it, especially since the construction with electric motors approaches trivial.

The aerodynamics of the aircraft would be based on a high aspect ratio long wing and conventional tail placed aft of a ideal laminar pod-shaped fuselage (for UAV pod-shape would be even easier because there is no need for seating people inside and no bumps / deviations of the ideal shape are needed). The airfoil designed for the purpose would be obviously a low Re airfoil with maximized L/D at moderately high Cl (unlike the cruise-oriented airfoils presented earlier on this site).

The airplane would lift the rocket with the hybrid electric propulsion to 50000-80000 ft like e.g. the Stratolauncher does, but with the difference that the aircraft would be very inexpensive. Even 80000 feet should be possible with hybrid propulsion since when the dual turbo can not provide enough power anymore (it would cut out pretty much after 60000 according to some studies done for HALE-UAVs), it can continue climb purely by using batteries. There is a limit though how much batteries can be carried along with the plane to not lose too much of the payload (the rocket). This is a compromise that needs to be optimized carefully to maximize benefits.

The airplane would be obviously fully reusable and good for a long long time. Different kind of payloads could be accommodated, depending on the need. E.g. rocket carrying multiple microsatellites or a rocket carrying one payload or a equipment that would study higher atmosphere (without rocket) or possibly a pressurized pod housing a human (as alternative to the rocket). It would be highly interesting concept to design & implement. It requires some budget, but can be done with quite modest budget not commonly considered in the aircraft/spacecraft circles.

Marching order would be this:
First study items for this would be:
1. Determine how large rocket would be needed for reaching orbit from case 1) 50000 ft and case 2) 80000 ft. Someone familiar with rocket equations could contribute if you would be interested. Please note comments are unfortunately moderated due to spam-comment problem, and may not appear immediately (only when I have time to go to press approve).
2. Then the size of the aircraft that will lift the rocket can be determined by requirements set by 1).
3. Determine the propulsion system needed for lifting the 2) to case 1) 50000 ft and case 2) 80000 ft.

Conservative assumption would be that the aircraft would reach 50000 ft and horizontal speed would be negligible at launch altitude, and the size of the rocket would need to be determined based on that altitude (and initial speed). Then if the aircraft could be made to reach 80000 ft, it would be all plus, bigger payload could be accommodated to the rocket.

The configuration for the aircraft could be quite simple:
- 2 small pods with two tails (or interconnected tail) like Burt Rutan's high altitude lifters leaving the center section for the payload
- one pod could house the piston engine + fuel
- another pod could house the batteries
- four wheel landing gear would be located to both pods, similarly than White Knight

We got interesting ideas at Oshkosh and I think we have a plan now

So the concept is about high efficiency, high altitude and long range. In other words, these are called as HALR. None of these concepts have been designed yet. But I think we have now defined a goal that can be used as a target where to aim at. And what is the motivation for this? For fun of course. And because we can.

The plan now has the following steps:

 1. Develop, test fly, measure scale model aircraft of the full size concept. Electric propulsion is going to be used. The aircraft shall model the full size aircraft in configuration and prototype control mechanisms of the model 2 aircraft. Possibly more than 1 RC model needs to be built to validate feasibility of different configuration features. This step is very likely to succeed. There are no impediments for executing this plan.

 2. Develop, test fly, measure a human piloted scale model of the full size concept. The plane is intended to utilize electric propulsion. The aircraft shall be able to carry at least 100 kg payload, stay at least tens of minutes in air and then safely land on a grass runway. This requires some feasibility analysis - this one needs to be super-light because the full size one needs to be light as well, and needs to be able carry substantial amount of fuel (300-400 kg). I will blog about what I will learn about structural design and also can validate the feasibility of the concept along the way. We saw that single place CriCri size small aircraft is ideal test bed for testing configurations, technologies etc. for the full size aircraft. This one must work from our summer cottage neighbor's airfield, in other words, needs to be relatively STOL. This has good chance to succeed but there are few impediments to clear out before this can succeed.

 3. Develop, test fly the full size plane, and then fly it to Oshkosh. The plane is intended to have hybrid propulsion. The aircraft shall be able to fly at high altitude non-stop from Helsinki to Kangerlussuaq, refuel, and continue and fly next leg non-stop to Oshkosh. The plane shall be practical efficient transportation tool that can partially replace using commercial aviation. The plane shall carry at least two persons plus rescue equipment plus baggage plus full fuel, and must defeat Toyota Prius 2019 model in transportation efficiency. Some serious problem solving is required before this will succeed.

The plane shall be able to fly long distances non-stop to avoid cost of landing fees and other costs associated by stopping on places of no interest. There are no guarantees of success of any of the mentioned steps, but this is the intent. The intent is subject to change. But this is where we are at today. We are very limited by the budget unfortunately and it can affect to the timing and success of each step. If we had substantial budget for this available, we would like to work on this full time, but unfortunately this is not the case.
  

Here is a updated list of some of the books I have:
Rating, Book


***** Aircraft Design: A Conceptual Approach. Fourth Edition. Daniel P. Raymer
Great standard book for everyone. A bit different equations than the Anderson's book. This + Anderson's book is a great combination.


*** Simplified Aircraft Design for Homebuilders. Daniel P. Raymer
This covers only basics. Does not take very long before the Aircraft Design: A Conceptual Approach is very much required. Not bad, but is not enough information for getting started with aircraft design alone. Can be a good introductory book if someone starts from scratch, sort of "soft landing" to the world of aerodynamics.


***** Aircraft Performance and Design. John D. Anderson, Jr.
Great overall book, similar to Raymer's book. I use this book very often.


* Aerodynamics for Engineers
Concentrates too much on transsonic and hypersonic and jets rather than subsonic design. I rarely open this book, I am not designing a Space Shuttle and even if I would, this is like phone book in the depth, depth of the book is rather small. Everything covered, but just very little.


** Aerodynamics for Engineering Students
Quite similar than the Aerodynamics for Engineers. But more basic. And nothing special here.


***** Fundamentals of Aerodynamics, by John Anderson
John D. Anderson's books are great. This one is no exception. Highly recommended.


** MODERN AIRCRAFT DESIGN, Volume 1 5th Edition, by Martin Hollmann.
You have to look at the source code of the basic programs to get something valuable of this book. Otherwise you will not be so much enlightened. I have been converting the programs to C++. It also has the Oshkosh airfoil program source code. Real vintage.


** MODERN AIRCRAFT DESIGN, Volume 2 4th Edition, by Martin Hollmann.You have to look at the source code of the basic programs to get something valuable of this book. Otherwise you will not be so much enlightened. I have been converting the programs to C++.


** COMPOSITE AIRCRAFT DESIGN. REVISED 2003. By Dr. Hal Loken and Martin Hollmann.You have to look at the source code of the basic programs to get something valuable of this book. Otherwise you will not be so much enlightened. I have been converting the programs to C++. There is some information on creating pressurized fuselage for Lancair IV if I remember the book right and also about lightning protection on composite aircraft (not sure, could be also in Advanced Aircraft Design, I do not have the book at hand when typing this). The information in general is not very deep, just listed how it can be done and that's it.


** MODERN AIRCRAFT DRAFTING by Eric and Martin Hollmann.You have to look at the source code of the basic programs to get something valuable of this book. Otherwise you will not be so much enlightened. I have been converting the programs to C++. And also if you use Rhino, the lofting programs presented on this book do not have so much importance. You can do the same more conveniently with 3D CAD.  The information in general is not very deep, just listed how it can be done and that's it.


** ADVANCED AIRCRAFT DESIGN by Martin Hollmann.
You have to look at the source code of the basic programs to get something valuable of this book. Otherwise you will not be so much enlightened. I have been converting the programs to C++.  The information in general is not very deep, just listed how it can be done and that's it.


***** BRUCE CARMICHAEL'S PERSONAL AIRCRAFT DRAG REDUCTION
Excellent book on drag, laminar flow and laminar bodies. No other book covers these. Old one, availability nowadays poor, but I have it. I am feeling lucky. 


*** Model Aircraft Design
This covers basics from different perspective.


Jan Roskam: Aircraft Design parts 1-7
Jan Roskam: Airplane Flight Dynamics and Automated Flight Controls
Jan Roskam: Airplane Aerodynamics and Performance
Theory of Flight
Smith: Illustrated guide to aerodynamics
Ron Wanttaja: Kit airplane construction
Bingelis: Sportplane construction techniques
Synthesis of Subsonic Aircraft Design
Theoretical Aerodynamics
Hoerner: Fluid Dynamic Drag
Flight Performance of Aircraft
Design of the Airplane
Burt Rutan: Moldless composite sandwitch aircraft consrtuction




I am considering getting Theory of Wing sections. I heard in Oshkosh that actually the first part of it has interesting equations before the airfoil data, and that's where John Roncz program codes are largely based on. I did not buy it before because I thought that I do not need the NACA foil data. Now I have incentive to get that too.

We were discussing with Kate about possibilities to use tip propellers, in tractor configuration. Tractor configuration would cause a swirling motion to the opposite direction of the tip vortex before the tip wortex forms and it would reduce the tip vortex. Therefore the propeller at the wing tip would give more efficient dynamic thrust for the plane than propeller at some other location in the aircraft. In cruise condition when the tip vortex is low with low span loading wing, this could eliminate significantly the unfavorable tip vortex. With electric motors, additional tip propellers would be fairly easy to arrange.

Some analysis would be needed how much this would help. Of course it would depend on the weight of the plane. The heavier the plane, the more leakage to the tip, the more tip vortex would form. The bigger the benefit of having a opposite direction swirling motion to nullify the tip vortex formation.

I was listening to John Roncz's presentation in Oshkosh 2019. We had just talked with few aerodynamics people about the induced drag and that it is actually tangent of downwash angle (except for the tip vortex which forms from leakage of pressure over the tip and due to the movement of the plane, a swirling motion is created).

John Roncz was talking in his presentation about wing span, and finally noted about wing area, that he does not care about wing area, because induced drag has nothing to do with aspect ratio. That's why gliders have not only skinny wings, but also very long wings. That's why Rutan's aircraft have long wings, not only skinny wings. Lots of span is needed for low induced drag.

However, there is a geometrical relation about AR to the drag: The lower the AR, the higher is the wetted area for the given span. Wetted area is bad, it causes drag, you don't want extra wetted area. So the wing becomes skinny by definition. But now the wing is skinny (high AR) but also very long, and not only skinny.

There is another problem: I would think then that I want 20 meters long wing span, but very very narrow chord. The chord can not be infinitely narrow in order it to be structurally any sound, especially in speed. Therefore the higher the AR gets, and the lower the wetted area gets, the heavier the wing becomes. And the heavier it becomes, the worse gets the span loading if this is added to the weight of the plane. Then there is the another consideration, where I could taxi such plane which would have 20 meter span? On our airport even the Diamond's comparatively modest wing span is in some places a bit tricky.

Interesting dilemma. This also answers why there are multiple pods on some Rutan's aircrafts, along the span. The reason is to reduce induced drag, by moving the weight from the center more along the span. Then the lift required on the center where the lift given by the wing is worst does not give that unfavorable dip to lift distribution. And it reduces induced drag. On planes, like Globalflyer, induced drag plays major role in how much range the Brequet's equation gives.

But there is even more to this: the higher the AR gets, the lower the Re gets. The higher the altitude, also the lower the Re is again. The lower the Re, the higher is the profile drag. To get high L/D and thus efficiency one has to get also the profile drag down. And airplane efficiency is all about L/D (lift/drag), no less.

So my basic concept remains and does not need to be revised for another configuration alternatives:
- conventional (to be able to use efficient flaps)
- large span, low span loading (to reduce induced drag)
- high aspect ratio, relatively high wing loading (to avoid extra wetted area and that way to reduce drag and AR also to have steep lift curve slope (in other words, closer to the 2D airfoil simulations of infinite wings)
- larger than minimum size elevator for larger CG allowance - this is for practicality rather than minimum trim drag
- The large AR is also needed for this: cruising with high wing loading causes need for high Cl for cruise, which in turn causes high alpha. To reduce alpha, the steepness of the lift curve slope is your friend. The lift curve slope steepness will make the plane to cruise fairly low angle of attack despite of flying at high Cl at high altitude with high wing loading.

Sorry for not being very active on this blog lately because I have been busy (work, summer vacation (I have been busy (work, current airplane, summer vacation etc.). I noticed that there were plenty of not yet approved comments. Sorry for the delay, I have been busy. Your comments are now approved and after you have been approved once, I think you can comment without prior approval in the future. Thanks for writing comments!

I was reading http://www.eaa.org/news/2019/2019-08-11_bipod.asp
I also listened Burt Rutan's presentations about Bipod in Oshkosh 2019.

This article on the EAA news tells that some carplane designer thinks Burt's Bipod is "too slippery". I really wonder what is the definition of too slippery. There is a group of misguided people who want airplanes to have lots of drag for them to "not be too slippery", in other words have aerodynamics of brick. I have bumped into Cessna pilots who think like that and they look for example our Diamond that "oh that is too slipperly plane for me". From my standpoint, that is not too clever.

Drag is always unfavorable and waste of resources. There can never be too little drag (except in landing configuration when drag is helpful to land the plane in a meaningful distance). Low drag when plane is cruising, has absolutely nothing to do with the flying qualities of the plane. Having more drag does not make the plane any easier to fly. Having more drag just means you have to burn more fuel, you have to have bigger engine, you have to beef up structure, to compensate, you have to put even bigger engine, and have even more fuel on board. Airplane being slippery is a myth. Some Cessna pilots think our Diamond is "slippery" or "too slippery for them". Yeah right, the truth is that the Diamond has better flying qualities than the C172, is easier to land and especially flare and it also stalls softer.

I wholeheartedly agree with Burt [about his Bipod]:  "Gee, he complains that we have too much drag as a car but not enough drag as an airplane!"

I think the US LSA specification is deeply flawed as they have introduced the top speed limit. It will limit the category of LSA planes to such that it is not worth to make efficient planes and high drag has been made a standard. That is not too clever either. Apparently the rules have been set by non-pilots who do not have slightest clue on what makes airplanes safe and what makes them easy to fly [and land]... It is all about stability, stall speed, stall charasteristics and inertia. Europeans have understood that better since there is no top speed limit in Europe but there is a stringent stall speed requirement. Low inertia, low stall speed and gentle handling qualities, and no matter what is the top speed, the plane will be easy to fly.

Read about Burt Rutan's Bipod here:
http://www.airventure.org/news/2019/110727_bipod.html

I arrived back from Oshkosh and got lots of new ideas. I had a privilege to talk to many aerodynamics people and also aircraft designers. I met professors, homebuilders etc. It was awesome. I was listening to John Roncz's presentation about how high L/D he achieved in this and that airfoil and attempted the same. I did not get yet 75% laminar flow, but quite close - 70% with thickness 15.72%. I think there could be opportunity for even higher L/D by reducing the thickness but I wanted it to be as thick as I could make it as possible for structural reasons. Thick airfoil also has more volume for storing e.g. fuel.

I created this new airfoil which has 70% laminar flow according to the simulation (please note, this is not tested in wind tunnel). It has a little larger pitching moment than the other airfoils I have done, but the L/D at low angle of attack (zero degrees angle of attack is Cl 0.35) reaches L/D over 100 at Re 5000000. The minimum drag count is 30 (Cd = 0.0030) at Re 7000000. At 5000000 the drag count increases to 31.

The airfoil can be downloaded here: KS-70PLAMINAR.dat.

Simulation results at Re 500 000, 1 000 000, 5 000 000, 7 000 000, 10 000 000 (Cl-Cd polar):

Simulation results at 500 000, 1 000 000, 5 000 000, 7 000 000, 10 000 000 (L/D polar):

Airfoil shape

Pitching moment polar. NACA 2412 and NACA 4412 included for comparison. The pitching moment is between NACA 2412 and 4412 airfoils. Not as good as NACA 23-series airfoils. This airfoil requires aircraft configuration with two surfaces and is not suitable for flying wing.

I will build RC scale model of this airfoil and test it with RC plane. At RC scale it will be a bit worse than best thin turbulent airfoils, but according to simulations, the polars are smooth to low Re which is desirable of course and this airfoil reaches at least the same Cd at the low Re than NACA 2415 unlike some other laminar airfoils.

I was just thinking about Curtis channel wing. I have a concern that this kind of design will result in tip stall in addition to the other problems there could be if something would fail.

However, what if you use electric motors instead and place that channel as a C on the tip of a wing? There is this 3D effect that flow tends to want to slip towards the tip and it causes wake turbulence and reduces Clmax. However, what if there is this C and then there is a prop inside the C. The flow comes to the prop and the prop sends it away and causes even bigger pressure differential between lower side of the wing and the upper side of the wing. With brushless DC electric motor it could be technically doable - one could not think about putting a Lycosaurus to the wing tip. You could even add redundancy by adding two motors in cascade. Should one fail, the another one would still be operational.

I think there are two kinds of aircraft that would be needed to cover the needs of personal air transportation: super stol/vtol for flying to airport from home to the pressurized long range plane that can cover large distances. I think today's general aviation falls in the middle of these, but I think it could be obsolete with these new two categories. I think the today's GA is not popular exactly because it falls between these two categories and does not fit in either purpose properly. And they are neither good toys nor good tools. This first VSTOL would cover the toy part and day to day short distance travel, and the HALE the serious transportation case.


I will write another blog entry about this split of concepts later because I believe I have - as a GA customer - found what's wrong with it. What are the needs and what is the gap. I think I have the answer.

I found some interesting videos from Youtube describing the new Pipistrel Panthera four seat aircraft that has incredible performance and economy compared to competition in the similar class:

Roughly 4 hours ago, John McGinnis succeeded to raise the goal for funding his Synergy aircraft on Kickstarter. The funding exceeded the goal by couple of tens of thousands. I think this is a remarkable achievement and it proves that also aircraft projects can be crowd-sourced. Congratulations to John and good luck with his project. Now it is his turn to finish the plane and get it on the air. This is now on critical path since as the plane is funded, the reputation of crowd-funding aircraft projects in the future will have this as a case example, so he better succeed. Looking forward to seeing Synergy to fly to Oshkosh! Please make it happen!

These calculations might interest you if you are wondering what is the Clmax in those little aircraft. Rule of thumb from Daniel Raymer et all says it is impossible, but flight data from MCR proves that ULC R has nothing short of extraordinary high Clmax.

Read more here: http://www.homebuiltairplanes.com/forums/aircraft-design-aerodynamics-new-technology/10349-specifications-coefficient-lift-dyn-aero-lafayette-mcr-ban-bi.html

I met John McGinnis in Oshkosh and he is a humble homebuilder guy with a dream and passion bigger and stronger than most of the aircraft fellas and he has unorthodox design that will be one of the coolest looking homebuilt aircraft when finished & successfully in the air. It is a kind of like flying wing but elevons placed in a box tail in the wing tips -  a configuration which is supposed to reduce drag. This is combined with very aerodynamic pod shape fuselage and laminar flow airfoil wings. And on top of that the plane will run on Deltahawk diesel engine and will work in places where AVGAS is no longer available and can just fill the tanks with JET-A, even in places like Kuujjuaq or Pangnirtung if he chooses to go for that kind of adventure. You can help this project getting this bird to the air by backing John's Kickstarter project:

http://www.kickstarter.com/projects/launchsynergy/synergy-aircraft-project?ref=live

Lets face the facts: general aviation is starving. Or it could be said that general aviation is even dying. There are many signs to that: less and less people are getting pilot's license, regulations are becoming more and more unreasonable (especially in Europe for general aviation as they have been designed for airline companies, with all the standards drawn to such level where there is no business) and hardcore hobbyists (like myself) are flying with from aging and poor to mediocre flying machines that are very expensive to operate and that are not enough capable (there are few exceptions, but there would still be very much room for improvement) to be useful for serious transportation. Years come and go and nothing changes, and every new year comes with no progress and all new things come without learning anything new but rather on evolution which is not very steep but rather very shallow. Very small amount of people are interested anymore in subsonic flight and the breakthroughs needs to happen exactly on this subsonic flight this new renaissance to happen.

Yes, I am myself flying airplanes for fun, and the fun is very important. And the fun will need to remain important in the future as well. The fun part should therefore not be taken away. Airliners are taking the fun away, sitting in economy class is more like suffering than fun and business class is not fun either, everything has been made to take the attention away from the aviation, people are eating and drinking and not looking out of the window. Windows even are ridiculously small, even in business class.

Then if we look road transportation. How many people prefer traveling in bus rather than in a private car or taxi? Are you a bus-fan? At least I am not. We drive with our Prius to work everyday and my carbon emissions are less than they would be if we would drive with the 1/3 filled bus. You could argue that the bus drives anyway, but that is not the point. Bus travel is like being in the economy class, it does not have anything that I could describe with fun or enjoyable. However driving with own car or sitting in taxi can be much better experience.

So I think here is the cure for general aviation:
1) Diesel piston engine based efficient air taxis that can carry 5-6 persons. Requirement for the aircraft would be that they would need to be efficient (leading to low passenger mile cost), safe and comfortable. Low passenger mile cost means cost comparable to airline ticket price. This cost should be able to include the whole thing: aircraft cost, insurance, pilot, everything. I think this is doable, but requires some novel engineering and not doing things like they have been always done. These planes would look more like Burt Rutan's special machines with very long wings or they could be possibly also blended flying wings but one could not expect these to look like Cessna C150.

2) Personal aircraft (I am not repeating what cafe is saying about PAV, this is my personal view on this) intended for serious transportation with large level of automation. This calls for fly-by-wire and stability augmentation. Pilot would rather choose to which direction to drive rather than correcting for bumpy air or cross wind. It would be different from autopilot, you could still drive the plane, but the plane would make driving a lot more convenient and so much easier that most car drivers could learn it. There could be additional aids, such as landing aid which would automatically line up the plane with the runway. It could use machine vision to be able to help the landing path all the way to full stop on runway independently from navigation aids. It would be still fun to fly even if it would be much easier. Why the definition of fun has to be hard? These aircraft geared for personal transportation would be at least 4 place machines making them comparable to family car capability.

Lots of people are shouting that "more entry level planes are needed". I do not fully agree. There are lots of planes which are very suitable for flight training. For example the LSA planes, Diamonds, Cirruses etc. Of course if the intention was to fly a fly-by-wire PAV-machine, there could be a different path that would be trained with these PAV machines. Logical step in that direction would be to drop all medical, currency etc. requirements, but rather make the flying with these with similar requirements than driving a car. If flying these would be so easy, you simply would not need check rides now and then, BFRs etc. And then planes are made with unreliable parts which were certified 40 years ago while cars almost never break with parts that were designed one year ago.

In personal aircraft you fly with the computer the flying machine. This license should be upgradeable to a normal pilot's license which would require then learning to fly with planes with traditional controls and avionics. Some could argue that this would be so expensive as the computers would be so heavy and they would cost more than a plane and what not. I don't think so. Computer that can run this kind of algorithms in real time does not need to cost a fortune. In mass production, a reasonable price is hundreds of dollars, not tens of thousands or hundreds of thousands. Such computer weights less than 0.3 kg and while it would need some more weight for all the control hardware, it would not be that complicated. Actually telephones are so much more complicated today than any electronics in aircraft, in fact, these things are so low hanging fruits that they are waiting for somebody to implement.

What slows down the progress on this area in my opinion, is very conservative thinking in the aviation circles, not thinking out of the box and at least in Finland there seems to be a tendency to repeat old beliefs like they would be teachings in a church and even clever people may take silly things for granted. Of course that is all they can do, as there are no alternatives, but that does not mean it would be right. In fact, the situation with aviation is so desperate that this feels like some alternate universe in Stargate TV-series where things have gone real badly wrong. We are that dystopic parallel universe and someone needs to do something to fix it. So aviation in general needs a major overhaul. New kind of airplanes are needed, new kind of regulations are needed (while dropping old obsolete ones), new kind of air traffic control system is needed (when there are millions of personal planes in the air, there is no way for the current system to work, it is a dinosaur already, you can not have centralized system in a case where traffic is so huge, car traffic already has hard data about that) and new kind of attitudes are needed. New more efficient and less expensive mass produced planes and regulations are necessary enablers for the attitudes becoming more positive towards flying.

So what I am complaining about attitudes? Consider this: I was one day few years ago in cafeteria of the Malmi airport. There was a some mother with her child there. The little boy said that he wants to drive airplanes. The little boy spoke out the truth of what he wants. His mother then replied that "No, you can't fly planes, they are so expensive that only richest of the rich people can afford that and these planes are just fancy toys for yuppies". I was sorry to hear that. The no-way-you-can-fly attitude seems to be brainwashed to children at young age and their dreams are severed "ah that was the thing I can't do, so I don't consider about it". This must change, personal and air taxi -like flying needs to become common practice to get from point A to point B. Not something that is for only rich people, but something that is for everyone.

No densely packed people in huge planes like in cattle car. No queues in security checks. No limitations on liquids, take as much Coca Cola you like. And you just pack your gear to the plane and make departure and arrive shortly after to your destination. No flight planning, you just drive the plane and all your plan is almost automatic. No radio communications with air traffic control unless you are in trouble for some reason. It would all be automatic that computer would do for you.

Personal and air taxi style travel can augment or even replace domestic travel and also part of the travel to neighboring countries in Europe. Busses and trains are still needed despite there are personal cars and taxis, but this what I described above is the breakthrough that needs to happen. It does not happen by itself. It does not happen by government (FAA, CAA, LAA etc.) making it readily available for you. No it does not happen without lots of work. It requires you. When I was little child, I was thinking that "what kind of technology there is in year 2019". Later I realized that no, the technology is not given, it has to be done by people like you and me. Nothing is given, someone is always needed to invent, plan, design and implement it. Breakthroughs can be made by thinking out of the box and not just improving the envelope of the old. You can help by doing your part on that.

Thanks for reading and happy rest of the week.

I have been thinking about the series hybrid and it may not be ideal for conventional aircraft configuration. The weight penalty is rather high and it needs to be accounted with wing area. It seems that best way to achieve more wing area is to make the plane a wing itself. Flying wing design ends up with large wing area very easily and this can be used to account for the weight penalty.

Therefore I am proposing now this series hybrid idea to flying wing instead. It would also save the long drive shafts and the associated problems which are in the Northrop early designs there.

The engine that drives the generator could reside in CG inside the wing and the electrical drive which is light could be distributed in the trailing edge to several motors and propellers.

This way also it would be possible to get lower disc loading for the same power for high altitude flight by distributing the power to several propellers which would be distributed in the trailing edge. This would work as alternative for using large propellers as these many props would move as much air as the two large props which would make the landing gear unbearably tall. These smaller props could also be inside the wake getting drag reduction benefit from the Goldschmied wake propeller idea but in a bit different form. These props would be easier to manufacture because of the lower power per prop and also smaller diameter for aeroelasticity considerations and it would also enable optimizing the prop planform to reynolds number on the rotation speed meaning very drastic taper ratio (very pointy blades with thick roots, and high curvature).

Interesting case example for poor power to weight ratio flying wing is Northrop N1M. 120 hp takeoff power for 1750 kg plane. That is enormously low power figure. The plane was upgraded later to a bit higher power, but it flew with that power, indicating that it would be realistic to design a rather heavy plane as a flying wing without needing to ending up using enormously big engines.

I have apparently so many ideas that they can not be incorporated in one aircraft. Therefore I have concluded that there needs to be several steps or tiers with a slightly different themes.

So these are now:
Tier 1: Conventional simplicity: Low drag low power low cost twin. Small wing but high aspect ratio. Compromise: Medium power to weight ratio required. Concept usable for personal aviation.
Potential outcomes: RC-models, UAVs, Private aircraft.
Budget: Shoe-string

Tier 2: Flying wing: Suitable for diesel power, series hybrid and other non-optimal power/weight ratio powerplants. Large wing. Compromise: Poor power to weight ratio is ok.
Potential outcome: Plane with long range and diesel economy. UAV applications possible.
Budget: Shoe-string, external funding possibly needed for the large craft

Tier 3: Ladder: Large aspect ratio, climb machine. Compromise: High power to weight ratio beneficial, has impact in fuel consumption. Interference drag from multi-fuselage configuration.
Budget: External funding required. Implementation requires substantial investments in infrastructure and machinery.

Tier 4: Scissor wing delta: Aircraft that are optimized for speed and altitude.
Budget: Requires substantial investments.

Tier 5: Will happen only if tier 1-4 succeed. Idea not announced. Not all of these will be guaranteed to produce real flying aircraft, these are just categorization for a family of concepts.

I have noticed (well, might be that it is a usual way to use it but I just haven't heard of it) that Teknodur polyurethane paint that can be used to paint composite structures like those on experimental aircraft, can be applied with brush and then perfected with sanding like on applying topcoat (/gelcoat) on a sailplane.

This just works for me, please do not follow if you are not willing to take the responsibility of potentially ruining your paint:
0. Do not use base paint or raw epoxy method, you don't need to fill pinholes, just forget about pinholes with this method! In other words, you can directly apply like this on top of smooth sanded dry micro or automotive polyester filler!
1. Apply thick layer of Teknodur 2 component polyurethane paint (e.g. white) on top of the composite structure. Any other similar polyurethane paint works too (I have also tested with Hempel 2-component boat polyurethane paint). Base paint is not necessary, the Teknodur takes on a bare epoxy surface which is sanded to dull (be sure it is sanded to dull, if it is not, then it will not take, but peels off). Do not use solvent to make the paint thinner, the thick property is desirable. The thick paint blocks the pinholes on the surface below.
2. Let it cure and then inspect. Look, 1 layer of paint and no pinholes! There may be runs, but you can get rid of the runs easily!
3. Wet sand the surface smooth. Use quite coarse grit at this point.
4. Add second layer of Teknodur paint. You can use a bit solvent now, and you will get no pinholes. Try to avoid runs more carefully at this time.
5. Wet sand to completely smooth finish.
Use all available wet sand paper grits up to 2000 if you can find 2000 grit. 1200 grit is fine though.
6. Use polishing compounds to finish the surface to high gloss.
7. Add vax and polish.

A little bit tedious with all the wet sanding, but on the other hand: full control over pinholes, no base needed, and most sanding goes to the paint without harming the critical glass/carbon fabric under it.

I am just in middle of painting a little composite part this way and I have noticed that it works. Before you ruin any large parts by using a method where the paint is misused and done differently than all painters will teach you, please try it to some scrap part first. I have finished two scrap parts like this and they have been in the snow and ice the whole winter without any harm done to the paint surface, so I would guess that this sanding method does not ruin the paint.

I am not sure, but it could be that:
- You would be even better off if you first apply a very thin layer of paint that enters the pinholes. Sand dull. Then don't care about the pinholes, just add the thick layer of paint on top of the thin layer.

On the base and on the first layer, the sanding result does not need to be smoother than 240 grit. Anything more than that is waste of time because the thick paint rounds the minor irregularities.

Pros:
- Polyurethane paint is easy to sand, very very very very easy compared to sanding epoxy
- Runs on polyurethane paint is no big deal, just sand them off in a minute and you are done!
- Quick to finish
- The thick paint is very weather resistant and is as smooth as you sand it

Cons:
- The layer of paint becomes pretty thick and it is heavy, and in some cases might be undesirable.

I have been thinking this back and forth now quite some time. This idea is quite simple, the purpose is to fix the most critical problem with auto conversions, achieve better aerodynamics, propeller placement and mass and inertia distribution.

Auto conversions most often fail, no surprise, because of the reduction gear or belt. The core engine is not the root cause in the problems and many problems with the reduction belt or gear system can not be seen beforehand because the dynamics of the vibrations of the engine, propeller and their inertia forces affecting each other is a bit more complicated than one could think at first - it is not that simple to make these parts to last for hundreds or thousands of hours.

So we came up (with Kate, we usually talk with Kate about these things and we kind of invent these things together, I usually happen to be the one who writes them down - and it is usually so that Kate is the opponent into which I test my idea's feasibility before I write it here) with the idea of having a auto engine, possibly a diesel engine, running at constant power, most likely exactly at the optimum point of the engine, always. Then all the power variation would come from the electric motors which would drive the propellers. The idea is that the diesel engine only runs a generator.

The downside of this idea is the additional weight from the generator, batteries, motor controllers, electric motors and the props (depending how many electric motors are used, it is also possible to use just one if that is preferred). However, there are two several things possibly good about this:

- First the diesel engine burns less fuel, resulting smaller fuel tanks.
- Secondly the gearbox system is saved. The gearbox system can be very heavy duty in a high power aircraft engine and they still have tendency to fail. Possibly something like 40-50 kg is saved straight away.
- Thirdly the aerodynamic advantage - optimal aerodynamic shape without using long extension shafts and couplings to deal with the dynamics of the rotating shaft connected to a non-optimally rotating propeller and the power pulses of the diesel engine. Now there is the chance to put the engine anywhere in the airframe where it best fits and propeller drive don't need to be considered at all.

Then there is the redundancy thing. Brushless DC electric motors usually never fail, but the prop can still fail in bad circumstances. Therefore having two independent props for the one diesel engine could be advantageous. Same thing with the batteries - if the diesel engine fails, the batteries could be sized such that the aircraft can fly without the diesel engine for example for 30 minutes in level flight. That might be enough in most cases to get safely on the ground, except on middle of an ocean. The most likely place for the engine to fail is the takeoff. This takeoff stress would never happen with this engine configuration - the engine would be run always at optimum and safe power, never on takeoff power. The extra power for the takeoff can be easily taken from the batteries if they have proper capacity and the electric motors are powerful enough. On takeoff the batteries at full power are not discharging that quickly, because the diesel engine is recharging the batteries at the same time. The takeoff power can be rarely used for longer than 5 minutes on an aircraft equipped with Lycoming engine either, so having a limited period of time for the full power is not that big problem.

Generator and electric motor can have very high efficiency, and the gap to a efficiency of a reduction belt system is not that great. Best electric motors (though heavy ones) are around 98% efficient.

On descent the diesel engine could be shut down providing there was enough battery capacity. The motors could actually regenerate also batteries when the pilot wants to decelerate the plane.

Maintenance cost would be like a single engine aircraft, but the reliability geared towards a twin. Of course there is the one little fine print: the battery pack is expensive and it has an expiration time and date, unfortunately. But nothing is perfect and without compromises.

Any comments about this idea? This surely would not be a racer as the power to weight ratio would be rather poor, but anyhow I am thinking, providing it would be efficient enough to climb adequately, this would be a quite economical thing to fly and also easy conversion-wise, almost stock auto engine would be okay, no reduction gear and prop installation and an assembly that takes the push or pulling loads, would be needed. Also waiting on the airport would not waste any energy, since props can be completely stopped when the plane does not need to move. For example Lycoming IO-360 consumes about the same amount of gasoline per hour when waiting on IFR clearance on the ground than our Toyota Prius car on highway. Consuming zero amount of fuel when still on the ground, but still being ready, would save some liters.

And answer to the question, why diesel and not gasoline when gasoline engines can be run very lean and quite great specific fuel consumption values can be achieved in optimal conditions - it is quite simple: availability of the 100LL/Avgas seems to be becoming poor. There has been three 100LL operators in Finland, but two of them decided to discontinue this year. There is only one left. When that only one decides that it is not profitable enough, there is no 100LL available for anybody and the whole country's fleet of Lycoming and Continental based planes are grounded. The Jet-A1 is not going anywhere, so engine that can burn the jet fuel would be a safe bet. Jet engine, turboprop, or turbofan are out of the question because those are not available in meaningful sizes and power classes - there is not a small turbofan that would have high pressure ratio and bypass ratio available, nobody manufactures such a thing. And it is unlikely anybody will in the future because this personal flying all is a very niche market unfortunately until it changes for better (if it ever does).

The implementation possibilities have challenges; namely no such electric motor available (would require custom motors possibly), etc. And the weight also causes penalty for the efficiency and speed of the plane. But the power to weight ratio will be with this arrangement a lot better than on a pure electric aircraft. And pure electric aircraft is feasible, why an electric aircraft with a generator and a fueltank added would not be.

And by the way, even if it is first of April at the time of writing this, this blog post is not an April fool.