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.