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.