How to design a new wing (apols if OT)
 

Once in a while one comes across a wing that seems so bad that anyone could improve upon it.


There is a massive NACA database of aerofoil (airfoil if googling in US) sections and NASA has more tucked away somewhere.


It should be possible to start with:


MTOW
Intended cruising speed
Engine power
Take off, landing, stall speeds
Wing loading, wing span
No. of seats
Maybe more criteria


and, as if by magic, get referred to a suitable aerofoil section.


I have tried writing to my old professor, a junior reader, NASA department of s/w assistance, and all have thrown my approaches into the ether.


Does anyone have any ideas?

I think one of the clues is in your use of the word 'magic'. Choosing a wing profile, as well as sorting out all the other variables in designing a wing, can be an incredibly difficult task. Have a read of this, it will give you an idea of the parameters that are involved: Wing Design Parameters

Thanks for a very interesting page - and web site.

But this is what computers and so called AI are good at. For instance, a statement of cruising speed would, in my case, rule out the paragraph on sweep - but, of course, the Rutan Long EZ has plenty of it, nonetheless. So, back to square one. I'll have a good read of that site. Thanks again.

Structural reserve factors
Technology used on company existing products and available for reuse
Available manufacturing techniques and capacity
Structural reserve factors
Data on latest available materials.
Size and mass of available actuators
Fuel tank requirements
Mach number limits
Latest certification requirements
Lessons learned from previous designs
Projections for future development
The market and operational requirement to minimise excess structure

Those are some of the "maybe more criteria".

And in that context major manufacturers maybe design a new wing every 15-20 years, and minor manufacturers perhaps every 5-10 years. So anybody leading the activity is as likely as not, never have to have had a senior role in wind development before - and if they did, it was almost certainly with the use of different design techniques.

This is not to say that it's impossible, or that it's not done well in most cases. But it's extremely inaccurate to presume that you can just plug the numbers into a bit of software or standard set of algorithms and get the right answer out of the box. That is what happens on undergraduate degree courses because of the need to massively simplify problems to get the basic principles across to students - but not in the real world.

G

In service inspectability, and reparability. Very unwise to allow a design which incorporates areas which cannot be inspected by normal means, and the possibility that damage cannot be repaired due to access/complexity/special processes/aerodynamic smoothness.

Avoid producing products which cannot be easily maintained.

And of course, every inspection panel also has structural implications.

G

Not forgetting handling qualities and low speed/stall behaviour.
Wing twist/wash out
Flutter considerations
Location of engines or weapon pylons
Any low observable demands

In practice in low speed aircraft aerofoil section is not always significant. As speeds increase the choice of section becomes more important, and probably more open to compromise. Bear in mind a thicker section will be lighter, have greater internal volume for fuel, but slower. Everything is a compromise - the skill is where to pitch the compromise ... Many choices will work, but what will make money?

Phil

Indeed. Cessna, the masters of adequate aircraft thought of this too. The 100/200 series of their aircraft have numerous inspection panels on the underside of the wing. However, it could be required to repair in an area to which inspection panel access is not possible. The wing may have up to five additional inspection panels, as long as it is no more than one per bay. Very forward thinking on Cessna's part.

This sort of maintenance "ease" is not generally considered by civil aircraft buyers, but it certainly saves a lot of repair or maintenance cost later in the life of the aircraft. Sometimes, it's much cheaper to remove the wing from the aircraft to work on it.

The ease with which a Cessna or Piper wing may be removed from the fuselage is also very pleasing. By comparison, single through spar wings (like a Found Bush Hawk or Islander) become really challenging when the aircraft has to be disassembled for transport.

As soon as trying to extract the most performance out of a wing is attempted, you will find even small changes can produce large effects. I'm not an aerodynamicist but had to reprogram the Stall Protection Computer on a Regional Jet after the wing was found to have less than optimum performance. I eventually filled a whole filing cabinet with change documentation & bench test results before the final solution was found by our Flight Sciences group - and that was without making any major changes to the airfoil or planform!

And so far we've all only really mentioned the wing.

Delivery of acceptable longitudinal stability and control criteria mean integrating the wing's innate stability characteristics with the broader aeroplane longstab behaviour as determined by the tailplane and fuselage shapes. You really can't design a wing in isolation in that regard.

G

Gordon Bennett! - What a tsunami of wisdom.

But I am not in the market for a new1000 seater airliner or a new generation stealth vehicle: - Two seats and under 450Kg MTOW.

The existing bar is low - very low.

The aircraft is fine, in its way, but the wing could have been designed by Laurence Llewelyn Bowen. I can't find the pic that I am looking for - give me a day or so. I just reckon that if it were to be given a wing designed by Burt Rutan, then that would turn it on its head.

If it's in that class, I have considerable industry knowledge - are you able to tell us what it is? I will point out however that in that class manufacturing and certification costs have to be extremely low, not all that many people in the community are particularly highly skilled engineers (albeit that the best are world leading), and there's usually an absolute requirement to keep Vso below 35kCAS.

G

Well, you've guessed, Ghenghis.

I can't find the image I was looking for; it looked like a French cathedral stained glass window. Here is a bread & butter one.

It doesn't need to be high wing; it could be mid or low level - even, possibly adjustable. Obviously, the thrust/drag couple will have something to say.

Of course, this is a flexwing design and so, to get 3 axis control back, further thought will be needed. Certain composite designs might be bendable - a slightly scary thought. Wing loading needs consideration to keep within the rules. But the scope for improvement is there - big time.

A Rogallo wing is an extremely complex exercise in aeroelasticity, understood well by far fewer people than "conventional" wings. What they're not is crude or necessarily poorly designed. The specific wing you're describing sounds to me like an Air Creation Tanarg wing, or close relative, imported into the UK by Flylight at Northampton Sywell.

The concept of the use of a Rogallo wing within a 3-axis control system was tried by a few manufacturers in the 1980s, and generally speaking abandoned. I can't offhand think of anything that's happened since to change that conclusion - although the elimination of top rigging in some of the most modern designs may make it possible to mount the wing below structure - not previously attempted. Checking the usual databases it doesn't look like any of those hybrids made it through the mandatory imposition of BCAR Section S in the UK between 1984 and 1987, or the similar BFU-95 in Germany a little later so data will be sketchy in the extreme. Almost certainly the best source of information will be a long out of print book called "Microlight and Ultralight Aircraft of the World" by Berger & Burr.

On basic characteristics of Rogallo wings, these are probably the most authoritative sources, some you can download, some you may need to buy, or quite possibly just use a library (the National Aerospace Library in Farnborough may be your best resource here!).

http://citeseerx.ist.psu.edu/viewdoc...=rep1&type=pdf

https://www.amazon.co.uk/dp/18403728..._sl_anerc182_e

Book Review: Tailless Aircraft in Theory & Practice | UAV and Model Airplane Design, Building and Flying | RCadvisor.com

http://citeseerx.ist.psu.edu/viewdoc...=rep1&type=pdf

You might also see if any talks by Dr. Billy Brooks of P&M Aviation in Wiltshire are on the web somewhere - he's certainly the cleverest man in the field in the UK, and quite possibly the world.


I'm going to hazard a guess you are doing this as a dissertation exercise in a university somewhere?

Will a microlight or hang-glider Rogallo wing be improved by the addition of 3-axis controls? I doubt it very much, but it's an interesting academic exercise, and I wish you well with it. There are discussions from time to time about whether the use of an external horizontal stabiliser may reduce the risk of a tumbling departure, but that's unproven and all current work on tumble resistance lies elsewhere so far as I know.


G

(Checking my logbook, 350hrs under a Rogallo wing, although no current plans to increase that as I'm busy flying other stuff right now).

I did all that back in the 60s.


You have given me much to think about. But what makes me think that it is an inefficient wing is a comparison of the engine power and top/cruising speeds of a P & M and the Long EZ, which certainly looks like the ultimate in both elegance and good aerodynamic design - which pays off in performance.

Multitasking is at the root of successful piloting skills :}

G

Yes. If you want a tailless delta that's efficient it wants to look something like a Horton or early Northrop, not a flexwing microlight.

That said, internal structural cleverness and use of fairings and simplified shapes certainly has potential to remove a lot of the easily identifiable profile drag generators in the way of cables, struts, pilots, etc... The best such at the moment is probably the P&M PulsR?...

https://www.youtube.com/watch?v=1RbDVS-0XTE

Which if nothing else, is very clever, and very pretty. Designed by the aforementioned Bill Brooks.

G

... and of course, we all admire the fluids properties of the well buttered eel.


I accept what you say but it also has a low frontal area, albeit cluttered, with a silly bit of streaming which could be improved upon. The coefficient of drag of the Rogallo wing would be good to know.

Glide ratio and best glide speed will give you Cd with a few back of envelope calcs.

Looking at my personal notes, I have data for a Quik, which is last generation but still quite high performance. That gives a glide ratio of 7.7:1 with MTOW=409kg and best glide speed of 50mph IAS. You should get something to 2ish significant figures from that.

Generation before that would be a Quantum: 8.5:1, 40mph, 390kg.

Generation before that an XL-Q: 8.7:1, 40mph, 365kg

And if you really want to go back into pre-history, Pegasus XL-R, 7.5:1, 41mph, 350kg.

That's for the whole aeroplane of course. I had data once for a few wings on a test rig, but unfortunately that's mostly buried now in a previous employers archives. Looking at the one graph I have tucked away in an old report, it really isn't good enough to tell you much. But for a wing of the same generation as the XL-Q, *indicates* Total drag below 400N in the range -10 to +20° AoA, with Total lift about 6500N at 20AoA (stall) and about 4400N at 10AoA, and zero at -5AoA (just blame the datum there). that was at 44±3kts.

G

...and we all admire the fluids properties of the well buttered eel.


I take your point but the frontal area is low, if somewhat cluttered. The key to the Rogallo wing would be its coefficient of drag.

Most of the world uses microlight definitions that include Vso<=35kCAS, that is clearly a very important design driver and tends to deliver low speed aircraft. The newest designs are achieving 80-90kCAS in level flight, which impresses microlight pilots, but in real terms is still very low speed.

And being low speed, form drag is a bit less problematic than it would on a higher speed aeroplane - but clearly not trivial, and all the cables and cantilevers create very draggy airframes. Billy did a great job with the PulsR but it's still, well, a flexwing!

There have been attempts to achieve much lower drag with a similar wingform in, say, the Dyke Delta or Verhees Delta. But they are using much more conventional structures, and don't use aeroelastic deformation to achieve stability in the way a Rogallo wing does.

G

Don't get me wrong, G, the wing is an incredible achievement - incorporating all control surfaces in one mathematically horrifically complex 3D shape. What i am saying is that it isn't efficient and this could be improved on ... somehow.

As a generator of low speed lift, or as a generator of lift for low structural mass, it's extremely efficient. Ditto achieving a functional wing for very few parts.

If I understand you correctly - you basically want to reduce profile drag? That means the short of exercise Bill Brooks did when he created the PulsR, *or* incorporate the basic wing structure into a conventionally controlled aeroplane - a bit like the Verhees Delta?

If you can do that, and retain the foldability for transport and storage of a current Rogallo wing, you might do something quite worthwhile.

G

Let me put it this way.

If you compare the power requirements and the cruising speeds of Rogallo wing a/c and the Long EZ, there is a big discrepancy.

If you take a good look at these two, it seems obvious why - but because it "seems obvious", it doesn't follow that the conclusion is correct.

Protecting myself with the Edward Debono "Po" concept, here is a Po suggestion: rip the wings off a EZ and nail them on a microlight - quickly glossing over the fact that there are control surface issues, with a few tweaks, how much better/worse would it do?

Run the numbers, let us know :)

My guess is, not as well if you leave all the struts and fittings in place. Both are designs optimised to the wing they have. But I'd be the first to read with rapt interest your proof that I'm wrong.

G

1. That's the thing - could it happen? maybe Yes, maybe No. At the moment, No, but - see below -

2. Yes, this is so and also there is a wing loading problem to solve, possibly both with a larger wing area.

Do you mean "Fluid Dynamic Drag" or is that a completely different book?

Francis Rogallo
 

My father, who was the Executive Vice President of Aetna Life and Casualty, a/k/a "Mother Aetna", was a friend of Frank Rogallo. Though Dad was a Mechanical Engineer (Georgia Tech) and a Masters of Marine Architect (U.S. Naval Academy Annapolis), he was fascinated by and loved every aspect of flight. The Aetna insured the U.S. Space Program from Mercury through Apollo, and when the Gemini Program was first on the drawing board, the Rogallo "Parawing" was considered as a recovery system. Dad (and the astronauts!) were entirely in favor of the concept: a steerable vehicle with a glide ratio would preclude the danger-ridden parachute landing in the ocean. Unfortunately, the engineers could not find a weight-economic way to stow the wing during launch and orbit. Deployment on orbit prior to re-entry presented its own set of problems.

On Christmas Day 1964 I was presented with a real Rogallo-winged kite powered by an .049 engine. The trailing edge of the device, which spanned about four feet, was autographed by Mr. Rogallo and his wife, Gertrude. My father, younger brother, and I took this high-viz orange-winged beauty to a nearby elementary school's playground for a test flight. The engine started on the first try and we released the kite into a calm, severe clear azure sky. Up, up, up she went, ascending in a slow left-handed turn toward heaven. The engine's fuel tank was relatively large; the Rogallo was but a speck (~ 3,000 feet?) when, as soon as the engine was fuel-exhausted, a straight ahead course became evident. She flew for miles and miles and out of sight on an eastward course - I like to think she made England...

Fast forward to 2004. My wife was the Assistant Curator of the Outer Banks History Center in Manteo, North Carolina on Roanoke Island. (You know, the first British attempt at colonization of North America. Virginia Dare, etc.) She had archived maps and notes dating back to 1583! I was visiting one spring day when she said "Come back into (the temperature, light, and humidity controlled vault, occupying about 10,000 square feet) my parlor, she smiled and beckoned. I have something I know you will like!" Thinking I might have lucked into a little "afternoon delight", I was not disappointed. Before me lay the entire compendium of notes and drawings of Francis Rogallo. He lived in Southern Shores, North Carolina, next door to a big sand dune in a place called Kitty Hawk, where he would often fly his own man-carrying designs. He had come home to test the same winds that his heroes, the Brothers Wright, had spent the Fall and Winter of 1903 mastering powered, sustained, and controlled flight.

My wife and I lived across Roanoke Sound, a mile from the tall and imposing Wright Brothers Memorial. It features a very bright rotating beacon that cycles around every eight seconds. It serves as a warning to sailors of the treacherous coast of North Carolina and a beckoning candle to aviators. It stands where our species first took flight. My wife learned to fly there. She would return from a flying lesson, give me a hug and a kiss, and say "I just flew in the same airspace as Orv and Will!" Our Golden Retriever would join the hug with his cold nose and wagging feathered tail. He was nearly the color of my Rogallo that had flown out of sight all those years ago... :p

- Ed

Excellent story, thank you very much.


On a light-hearted note, as both a Yorkshireman and an engineer involved with buoyant flight, I might change "our species first took flight" to "our species first took powered, sustained, controlled flight". (For the avoidance of doubt, I put the Wright brothers on the highest of pedestals for that achievement and the science that they performed to reach it.)

Dear JOE-FBS,

Your suggestions are correct, accurate, and appreciated! I have edited my story incorporating them. Thank you as well, my friend; I am glad you enjoyed my story.

- Ed

Very interesting PD. I see that the author was treated to an extended American working holiday under Operation Paperclip, presumably in 1946, when he wrote your book which he self published in 1951. Then the other one comes out fifteen years later.

I wonder if material was removed between the volumes on the grounds of military secrecy. A comparison of your book, which must be pretty valuable, to the available Fluid Dynamics could be intriguing.

cavuman - thank you, that is really interesting.

May I ask something: I've flown a few Rogallo winged aircraft, and studied them fairly extensively. What I have often wondered about is the relationship between Francis and Gertrude. To what extent where they a true working team of two engineers, and to what extent was Francis in the lead and Gertrude essentially his assistant?

History tends to assume the latter, but I've always rather believed the former. If you were around people who knew them, I'd be really interested in your views.

G