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Old 25th Nov 2017, 14:57   #1 (permalink)
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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?
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Old 25th Nov 2017, 21:20   #2 (permalink)
 
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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
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Old 26th Nov 2017, 14:51   #3 (permalink)
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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.
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Old 26th Nov 2017, 16:16   #4 (permalink)
 
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You also need to consider that to be useful to a customer the aeroplane has to have performance over a range of missions - different leg lengths, different cruise altitudes, different load capacities etc. You also can't consider the wing design in isolation - the optimum wing design varies with engine choice, structural concept, intended control system etc. I know of one aeroplane design where a "more efficient" set of wing sections had to be abandoned when it came to light that the pitching moment characteristics of those airfoils would need an additional 800kg of fuselage structure to make it stiff enough to avoid phase-lag resonances between wing and tail.

Also consider that "wing section" is a two-dimensional thing that's only used for initial . Real wings are 3-dimensional objects over which the air almost never flows directly parallel to the velocity vector. So the 2D section data is only really useful to schoolboys!

In other words - the design of aeroplanes is never just a "throw a set of numbers into a database and let it get on with it" thing - it needs engineers to do teh hard stuff.

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Old 26th Nov 2017, 19:53   #5 (permalink)
 
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Originally Posted by Downwind Lander View Post
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
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.

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Old 26th Nov 2017, 22:06   #6 (permalink)
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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.
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Old 26th Nov 2017, 22:24   #7 (permalink)
 
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And of course, every inspection panel also has structural implications.

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Old 26th Nov 2017, 23:21   #8 (permalink)
 
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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
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Old 27th Nov 2017, 00:41   #9 (permalink)
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And of course, every inspection panel also has structural implications.
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.
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Old 27th Nov 2017, 06:14   #10 (permalink)
 
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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!
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Old 27th Nov 2017, 08:28   #11 (permalink)
 
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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
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Old 27th Nov 2017, 15:56   #12 (permalink)
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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.
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Old 27th Nov 2017, 18:55   #13 (permalink)
 
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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
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Old 28th Nov 2017, 15:48   #14 (permalink)
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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.
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Last edited by Downwind Lander; 28th Nov 2017 at 16:23.
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Old 29th Nov 2017, 14:02   #15 (permalink)
 
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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).

Last edited by Genghis the Engineer; 29th Nov 2017 at 14:15.
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Old 29th Nov 2017, 15:20   #16 (permalink)
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I'm going to hazard a guess you are doing this as a dissertation exercise in a university somewhere?
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.
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Old 29th Nov 2017, 16:05   #17 (permalink)
 
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I'm busy flying other stuff right now).
Posting to PPRuNe while acting as P1 is highly dangerous!



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Old 29th Nov 2017, 16:08   #18 (permalink)
 
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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.
Look at the two in terms of draggy bits - the P&M has lots of external bracing, sticky-out wheels, open cockpit etc etc. All that makes for a marked relictance to slip thropugh fluids like a well-buttered eel.

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Old 29th Nov 2017, 17:10   #19 (permalink)
 
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Multitasking is at the root of successful piloting skills

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Old 29th Nov 2017, 17:13   #20 (permalink)
 
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Look at the two in terms of draggy bits - the P&M has lots of external bracing, sticky-out wheels, open cockpit etc etc. All that makes for a marked relictance to slip thropugh fluids like a well-buttered eel.

PDR
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.

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