[the4ork]

haha was toying around last night and made these... they look pretty cool

one is original spitfire, and the other the spit16 clipped wings... i was thinking maybe when i get bored again of making some 109 style wings...

the Hershey bar wing just doesnt do it for me... thought about making some elliptical wing tips for it, that might be cool... performance wise? dunno what that would do for ya

 

[gmcjetpilot]

Cool photo work

Richard: Yep the true elliptical wing is a beauty. Put them on almost any plane and you think of the spitfire. They where works of art.


I do think its a cool idea. Now for a little rain on the parade, sorry, this is my opinion. A spitfire wing would likely weigh more! When you taper the spar and make more contours and curves, you'll add more weight. It'll be WAY more complicated to make. Performance will not increase substantially if at all IMHO. If not done very carefully, as the original wing design was done, chances are performance will be poorer. Spitfires had the spit and fire from +2000 HP.

You did not mention performance, but part of the RV joy is how RV's handle to any GA plane. Anyone that has flown a RV knows they fly like no other plane.

I'd also guess performance of a RV4 with a spitfire wing would not improve much, if at all, with an elliptical plan-form wing. Engineers have learned how to approximate the ideal lift distribution of an elliptical wing with out using an elliptical wing shape.

The key to the great performance of the stock RV wing is in airfoil selection, wing loading, power loading and light simple construction with awesome ailerons (more on that below). With the extra weight of a custom new wing, which I predict the spitfire/RV wing will have, there's will be no net gain. I understand you did not mention performance, you're more on looks, but the NACA 230xx (23013.5 exactly) airfoil, with low wing loading and attention to detail is hard to beat.

Performance:
You may gain some top speed but your stall speed would go up, no doubt, unless you get some fancy flaps (more weight, cost and complexity).

Here is a good analogy to what you want to do. Look at team Rockets F-1. Its a RV-4 derived plane with a 540 engine. They offer two wings, the Sport (classic RV wing clipped) and a new tapered wing they call the "Evo" wing. The latter tapered "Evo" wing has high lift flaps to make up for lost slow speed performance. They did get a top speed gain (15 mph) which is good while they actually got lower stall, but at the added cost and complexity of the Evo wings high lift slotted flaps. The cost is higher with the new wing, but it's nice.

Don't get me wrong the Evo wing is nice, but it illustrates how hard it is to make a better wing than the stock RV wing. The complex flap did lower stall, but climb is reported to be the same. Not sure about how it feels. They had some flight test / pilot evaluation reports that where fair and honest posted. The Evo flys nice but different. Van did a real good job with all the compromises needed in any design, making an easy to build, light, low drag wing that can stall in the low 50's and go over 210-220 mph on a small 4-banger engine.


I would rather a homely Hershey bar wing, than a pretty elliptical "spitfire" wannabe, if the spitfire wing performed and handle worse. I suspect if not real careful you would be all show no go with new wing.

Team Rocket F-1 Sport (classic wing)
http://www.teamrocketaircraft.com/spec/spec.html

Team Rocket F-1 Evo wing
http://www.teamrocketaircraft.com/evospec/evo.html


When you consider how good performance is with the RV wing (even though its not elliptical) and how easy it's to build, (every rib the same, constant cord no tapper) it's amazing. Also the fact that the RV's has very little adverse yaw with it's beautiful "Frise Aileron's". The RV is a real joy to fly. I say RV's make pilots think they are better than they are, mainly from the wing and flight controls. If you change the wing you will no doubt lose the wonderful RV feel.

The Hershey bar wing may not be elegantly curved like a Spitfire, but beauty is in the eye of the beholder. The way a RV flys is the beauty.

I would not want to build a spitfire wing in metal. You would have to use wood like the original or dare I say it composites, eweee glue and string! Plastic wings on a RV? Horrors of horrors. With any material it would be hard wing to build right with tappers and curves. A jig would be a must.

Bottom line I think it would be a cool project and challenge anyone. It would be a real show stopper. Would you go retract? That would be another wrinkle. The engineering, design, building and integration into the RV airframe would be some work (understatement). I gave all the negatives but would LOVE to see it. If you need help with basic structural design and analysis let me know I can point you.

Why do most so called small scale replica WWII fighters have lousy performance? (Here's a beautiful looking Pacific AeroSport "Twister" single seat kit with an elliptical wing. Its imported from German, sold by a distributor North of Seattle. It's slower than a RV (but only 80hp) and cost is not cheap, but it is pretty. The cost is about $35,000 for the basic kit ($40k with retract gear) with out engine, engine installation kit, prop, lights, instruments. This single seat-er could easily end up costing more than a RV. The kit is $20,000 more than a RV. I would love to have one. The detachable wing and trailer is a cool idea, no doubt.

Richard, I am not sending you away from the RV airforce, we want you to be a RV pilot, but just showing it for design ideas.

P-51 verses the Spitfire? Got to go Yankee

 

[smokyray]

Laminar Flo Fo...

My F14 buddy (and Aeronautical Engineer) RV4 builder "Trout" Falley began building his RV4 10 years ago with a modified P-51 type wing and retractable gear. He had John Roncz review his design and give it a thumbs up and proceeded to build the wings. He engineered the landing gear himself in his fabrication business. Meanwhile, he bought a stock flying RV4 to have fun with.
Having seen the almost finished product I have to say it is very cool! When it flies, Trout will truly have a unique RV4.

Rob Ray

 

[AntiGravity]

Or just build one...

...my heart looked at this before my brain chose the RV!!

http://www.supermarineaircraft.com/

 

[the4ork]

it would be pretty neat to make a 109 style wing... just angle the trailing edge from fuselage to wingtip foward, but doing so by keeping the wing loading as close to the same as possible....

some flush 109 style wing slats would be cool too but complex...

one day when im old i can experiment with this kind of stuff... but now i just need to build an RV already, ordering a tail kit SOON

 

[Andy_RR]

I would like to know why Vans chose to design no washout in the RV wing (at least I think that is the case).

Surely if you are going to have anything close to optimum lift distribution for minimum induced drag (ellipses and all that), you will need at least some towards the wing tip?

What is the background to this? Anyone know or care to guess?

A

 

[gmcjetpilot]

Washout, Because RV's don't need it

I would like to know why Vans chose to design no washout in the RV wing (at least I think that is the case).

Surely if you are going to have anything close to optimum lift distribution for minimum induced drag (ellipses and all that), you will need at least some towards the wing tip?

What is the background to this? Anyone know or care to guess?

A

Guess as usual, but I am pretty sure I have the answer, because it does not need it.

So we are all talking the same thing, washout is wing twist where the outboard part of the wing is intentionally built twisted down, to be at a lower angle of attack than the inboard wing. The intent is so the inboard wing is suppose to stall first and the outboard last, which helps maintain aileron (roll) control if the outboard wing is not fully stalled yet. Some time the same thing is accomplished with "stall strips" on the inboard wing leading edge.

With the inboard wing stalling earlier you get natural stall warning or feel from the burble hitting the tail. This is all good to fix planes with lousy ailerons and not so good natural stall warning characteristics. These methods tend to not help lower stall speed but actually some times raise them a little. Therefore washout or stall strips are not automatic design features like dihedral or angle of incidence on a low wing plane.

RV's don't have huge natural pre-stall indicator (like buffeting) but you can tell you are about to stall. RV's are very honest and not scary stall airplanes. You really have to be sleeping not to notice the plane is thinking about stop flying. The real joy is the fact RV's, even without washout, have incredible roll control at slow speed and into the stall. A Piper, Cessna or most planes for that matter wishes they had slow speed roll control like a RV.

Normal generic stall recovery is break the stall with elevator and keep the ailerons neutral. The reason is most ailerons will make it worse because of adverse yaw or will just not be effective. However with the RV, you have roll control in the stall with the aileron. You don't want to be ham handed and use full left or right stick, but you can input some aileron while breaking the stall with elevator at the same time. There is no doubt you need to unload the wing and get the AOA back down to fly before maneuvering if you stall, but RV's have incredible ailerons that remain effective at min speed at stall speed. I recall UK RV-8 pilots did some nice spin testing and recovery techniques with and without aileron. It was well documented and published in the RVator in the last few years. It was interesting.

RV Flight test: Get into slow or min control speed flight, flaps up, level flight. Now roll with generous aileron input. The plane will roll very nicely with no additional rudder input. It will not be lightning fast but get use to what it feels like at slow speed. Now go fly a C-172 and do the same thing and you will get almost no or very slow, lazy rolls out of it with lots of adverse yaw. Of course the control will fill like its in molasses.


I've done tons of slow flight, stalls, min control flight in and out of stall with RV's and you have roll control, which is amazing. Not only does Van use "Frise" ailerons, he uses deferential movement where the down aileron deflection less than up aileron. This minimizes adverse yaw and increases control. Than he is a good designer and picked excellent aileron length, chord and hinge point. Some credit goes to the NACA 230xx airfoil Van picked for the RV. The list of famous planes that have used this airfoil is very long. Here are a few notable ones: (DC-4, DC-6, DC-7, Helio Stallion, Shrike Aero Commander's, Beech KingAir/1900/Baron/Bonanza/Staggerwing, Cessna Caravan/400 series twins/Citation jets, Grumman: wildcat/tigercat/hellcat/bearcat/albatross, B-25, P-38, Lockheed Constillation/Electra. Basically everything from GA single/twin engine, Airliners, WWII fighter/bombers, STOL, Turboprops and jets, plus one kick tail line of experimental kit planes.)


Washout is really a "fix" to make bad behaving wings and planes be semi controllable at slow speed. The RV is amazing in that it's slow speed control is excellent. Can you tell I like RV's?

 

[Andy_RR]

Washout is really a "fix" to make bad behaving wings and planes be semi controllable at slow speed. The RV is amazing in that it's slow speed control is excellent. Can you tell I like RV's?

I like RV's too, but i thought washout was also used to reduce lift at the wingtips to allow a hershey-bar wing to generate an ellipsoidal (or optimal) span-wise lift distribution that minimizes induced drag.

Given that the RV's have no washout and no variation in chord, one must assume they have relatively constant lift distribution across the span and therefore large wingtip vorticies?

A

 

[gmcjetpilot]

Calling Aero guys?

I like RV's too, but i thought washout was also used to reduce lift at the wingtips to allow a hershey-bar wing to generate an ellipsoidal (or optimal) span-wise lift distribution that minimizes induced drag.

Given that the RV's have no washout and no variation in chord, one must assume they have relatively constant lift distribution across the span and therefore large wingtip vorticies?

A

I was not aware that was the reason for washout, you could be right, but I think job # one is to help aileron control at slow speed to give better control into the stall region. I doubled checked and googled "washout" and did not see that description you mention, but it could be. Hard core Aero guys out there?

You are right lift distribution could be more efficient with the "bar". I see how the washout might help as you say intuitively, but my guess (and it is a guess) there's a down side to doing it, like less total lift. Therefore you may need more span, which in turn makes more drag. Point, trade offs and no free lunch. You do one thing and affect a dozen other things. Of course the word "twisted" does not conjure goodness.

However all the other non Aero stuff factors in, ease of construction, weight and cost trade off's. There are ways to cut down on the wing tip vortices's with a "top secret" modification to Van's symmetric wing tips.

Here is an interesting quote from Wikipedia
http://en.wikipedia.org/wiki/Elliptical_wing

- furthermore, the wing's (elliptical) uniform lift distribution causes the entire span of the wing to stall simultaneously, potentially causing loss of control with little warning. To compensate, aircraft such as the Supermarine Spitfire used a modified elliptical wing with washout, though such compromises increase induced drag and reduce a wing?s efficiency.

So there you have it, washout adds induced drag and lowers wings efficiency? So the statement RV wings don't need washout looks correct, but I'm open to correction. I have no dog in the fight.

But than I found this (for airplane model guys) which backs you up
http://yarchive.net/air/washout.html

Since the lovely elliptical wing of the spitfire could NOT and DID not
have any washout (which contradicts Wikipeda), the wing TIPs always stalled first, causing a loss
of roll control near stall and the unpredictable stall behavior that
we associate with a "wicked" stall characteristic.

In modern designs we use a straight taper and then wash out the tip
to reduce the lift near the tips to approximate the elliptical lift
distribution with a straight tapered wing. This gives us close to
the aerodynamic ideal distribution along with a more docile stall
characteristic. However, some aircraft with straight taper wings and
washout, such at the Beechcraft Bonanza and those aircraft based on
its design and wing, that use the 23012 airfoil still tend to be a
bit twitchy near the stall. (Don't know about Bonznza stall but its not the airfoils fault)

Two things are in discrepancy with the above quote in my opinion, one whether the Spitfire had washout or not, two, the NACA 230xx is inherently "twitchy" (may be on the Bonanza?).

It seems both quotes indicate wicked stall to be a common factor with a elliptical wing lift distribution. He says washout changes the lift distribution as you say and seems to make sense, but he does seem to point to the reason for washout as modifying stall/roll characteristic, not better performance or efficiency of an eliptical lift distribution. The Wikipedia entry says it has negative effect on efficiency and adds drag. I guess there is controversy here?

The last quote also says that the Bonanza stalls twitchy because of the NACA 23012 airfoil. I disagree its the airfoil, most airfoils stop flying when they stall. The RV "Fat" 23013.5 wing is not twitchy in the stall. I have stalled a lot of planes and the RV is mild but solid (feeling of more control). The Bonanza wing has a tapered wing in chord and thickness, plus aileron design differs from a RV, so that makes a big difference. The NACA 230XX is a honest wing airfoil and why its so popular. Talk about wicked stall, try some of the laminar flow jobs like what's on the Glasair III for example.

Another reason NOT to washout a wing, is if you have an acro plane, you would like the plane to fly the same upside down. Although most RV'ers tend not to explore the negative G stuff, you probably want a non twisted wing on a sport acro plane.

 

[Andy_RR]

Here is a NACA/NASA paper on the subject, which takes the assumed elliptical lift-distribution profile on to the next level.

I thought that the reason the elliptical wing planform was chosen was to achieve optimum lift distribution only by varying chord. Since lift and drag are proportional to chord length, it makes sense to vary chord and maintain best L/D angle of attack to achieve the most efficient wing.

...but as you say, a constant AoA wing gives a viscious stall characterstics as the entire wing stalls simultaneously. Maybe this isn't the case so much on the RV because the airfoil stalls very gently, compared to some sections.

Note that in the above paper, it suggests you can improve induced drag by 15% with a 15% increase in span, so the washout reduction in lift causing extra span may not be an issue.

Big question is, if you gave the RV a closer-to-elliptical (or optimum, depending on who's theory you believe) lift distribution with a new (elliptical?) wing, would it be faster?

BTW, would the Mk26 Spitfire wings fit an RV4? Would be the ultimate hybrid kit and you would perhaps need to do a whole lot less engineering...

Oh dear, worms, can, open...

 

[penguin]

I like RV's too, but i thought washout was also used to reduce lift at the wingtips to allow a hershey-bar wing to generate an ellipsoidal (or optimal) span-wise lift distribution that minimizes induced drag.

Given that the RV's have no washout and no variation in chord, one must assume they have relatively constant lift distribution across the span and therefore large wingtip vorticies?

A

One of the reasons for washout is to ensure that the root stalls before the tip and so promote good low speed/stall behaviour. Tapered wings without twist will tend to stall at the tip first giving rather exciting low speed handling. An other reason to go with a straight straight wing is much much easier & quicker to build. Although an eliptical planform is theoretically the best you have to consider the penalty for using a straight straight wing. At the angles of attack that an RV wing operates at when cruising I suspect that there would be little advantage. However, if you are continually yanking and banking (or dogfighting as in the Spitfire) and operating at higher AoAs, then an eliptical planform becomes more advantageous.

Pete

 

[gmcjetpilot]

The NACA 230XX series airfoil rules LOVE the Hershey Bar!

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930082889_1993082889.pdf
is a NACA/NASA paper on the subject, which takes the assumed elliptical lift-distribution profile on to the next level.

Oh dear, worms, can, open...

No worms, its interesting. We kind of have an answer based on Team Rocket's F-1 and the "evo" wing, per my first post on this thread.

The standard RV based F-1 wing top speed is 250 mph and the new "Evo" wing (tapered chord/thickness and laminar flow airfoil) reports a 265 mph top speed. It's about a 6% gain in speed.

I know Mark of Team Rocket from airshows; He's a super nice guy, but I think they made mistake with the airfoil on the Evo wing. It is a similar series airfoil the Glasair III uses, a NASA LS(1)-0413.

"The new airfoil is an MS(1)-313. This airfoil series, along with the LS(1)-xxx series, and the NLF series, developed by NASA in the seventies. Their testing shows a potential 20% decrease in wing drag through use of these air foils. A secondary positive side of these air foils is that surface degradation through rain, or insect leading edge contamination, does not cause a significant problems: a contaminated airfoil still provides drag equal to our current air foil, the NACA 23013.5."​

Read this article, interesting opinion about the NASA LS airfoils the Glasair III and Evo wings use.

http://www.oriontechnologies.net/Documents/Airfoil.htm

"....when the kit of the Questair Venture was becoming popular, Stoddard-Hamilton (Glasair) was desperately trying to figure out why the Questair (NACA 230xx) configuration was so much more efficient than their Glasair III. It was not uncommon for the new aircraft to easily outdistance the Glasair, on substantially less horsepower. In an industry where an extra mile per hour can result in bragging rights and a few extra sales, this difference in performance was hurting some of the company?s projected sales figures.

Looking at the published performance and geometry figures for both aircraft (Jane?s 1993 ? 1994) and extrapolating where necessary to get the sea level values, we can determine the lift coefficients for each of the aircrafts? cruise condition. For the Questair Venture this yields a value of .208. (the Questair use a 23015 at the root and a 23010 at the tip) so approximate performance assumed with the (NACA) 23012 section, we see that the "l/d" comes to 33.55.

For the Glasair, the same calculation yields a cruise lift coefficient value of .13. The aircraft used the LS(1)-0413 section, so for the same flight condition, its wing generates an "l/d" value of 16.56 or less than half of the Venture. To compound the problem, to counter the heavy stick forces of the selected airfoil, early in the development the company filled in the trailing edge cusp, thus decreasing the lift performance further. In short, this was a terrible selection on the part of the original designer.​

Look @ Questair wing: (span 27'6", wing area 72.75 ft2, cruise speed 276 mph, stall (wt?) 70 mph ) Uses same NACA 230xx airfoil as RV's and Piper Malibu

The Glasair III (span 23'4" (optional 2' extension), wing area 81.3 ft2, cruise speed 258 mph, stall solo std 80 mph/optional slotted flap 73 mph)

RV-7: (span 25', wing area 121 ft2, cruise speed 207 mph, stall solo 51/gross 58 mph) Pretty wing to me

Rocket with Evo Wing: (span 24'10", wing area 102 ft2, cruise speed 240 mph. stall (wt?) 50 mph)

Obvious relation with top speed, wing area, stall speed and aspect ratio, no secret. Put a big enough engine on and no wing is needed?

-There's always greener grass & sometimes greener grass has dog stuff in it.
-Nothing wrong w/ chocolate or Hersey bar wings (they taste good & make pretty wing shapes).
-Not using washout is in fact goodness, if you achieve excellent low speed performance & roll control with out.
-You can change wing shape, area or airfoils but Van came up with a sweet spot for sport plane pilots to fly fast & safely.**
-(Ecclesiastes 1:9-14 NIV) What has been will be again, what has been done will be done again; there is nothing new under the sun.

**The Lancair IV, Glasair III have a poor safety record and its proportional to stall speed. A Glasair III at gross, has a stall speed of approx 90 mph; Vso x 1.3 = gives an approx 115 mph approach speed!

Dreaming of the ideal wing is great, but practical experience, balance of all factors of design, performance and structure makes the NACA 23013.5 airfoil pretty darn good. It works on the Questair. Trivia: The guy who designed the Questair also designed the Piper PA-46 Malibu, which also uses the same NACA 230xx airfoil. An intersting article on the Questair and people behind it with insight to aviation design and Piper is HERE. Van can't be accused of being stuck in his ways since the RV-9 and RV-10 use different airfoils (Roncz) and higher aspect ratios.

One more example of "looked good on paper", Long ago I happily flew a Piper PA-38 Tomahawk many hours, which has a NASA GA(W)-1 airfoil. This GA airfoil was then a new NASA laminar airfoil series developed for General Aviation (GA). They promised a lot but it did not deliver. It also had some bad traits (stall and spin recovery characteristics). They tried to fix them with band aids like stall strips, but it was not a great trainer. Flying it was fine, but it was truly squirrely at in stalls and at low speed. (T-tail did not help)

The RV-9A & Tomahawk have lots in common. Both have the same wing area w/ higher aspect ratio, fairly long span, constant chord & thickness wing. They both have the same engine, a Lyc O-235. The Tommyhawk rated it at 112 hp, which gave 108 kts/124 mph cruise; not bad for a trainer, but the RV-9A is almost 40 kts faster, with a 118 hp version of the same O-235. Why? That's a lot. To be fair the PA-38 is not a bad flying plane and visibility/seating position is way better than a C-152. The C-152 book says it flys @ the same speed as a PA-38, but the Piper is faster. The C-152 did stall slower at 43 kts/50 mph, about RV stall speed, but RV's are twice as fast.

Piper PA-38 / Van's RV-9A
Top Speed: 109 kts / 147 kts
Cruise Speed: 108 kts / 143 kts
Stall Speed (dirty): 49 kts / 42 kts
Gross Weight: 1670 lbs / 1600 lbs
Empty Weight: 1128 lbs / 1028 lbs
Wing span: 34 ft / 28 ft
Wing area: 125 ft2 / 124 ft2
Fuel Capacity: 30 gal / 36 gal

Obviously longer span, high aspect ratio = less induced drag. However per that NACA TN-2249 report, wing bending moment changes. The RV-9 is not aerobatic and a 28 foot wing span does not help. This is why winglets are not always an automatic goodness. When you add them, you change the wing root bending (a lot), which means added structural weight. The truth is winglets laid out flat are better, ie more wing span is better than winglets any day. On airliners winglets help get them into smaller gates, or it's a good place for a logo.

That is the circle of life or circle of design, trade-offs, "Hakuna matata " (Lion King). If designing planes was easy than they would all fly like RV's.

 

[Andy_RR]

George - interesting post - fascinating study, as you say.

The RV-9 looks very impressive when you line it up against the Traumahawk. In fact it is a classic case study of where the devil is in the detail.

To the untrained eye, the two aircraft 'look pretty much the same thing', but the massive performance differential tells the true story.

You've written a lot about airfoil sections, but whatever section you choose, I still wonder whether manipulating the lift-distribution further towards optimum wouldn't liberate some extra drag power for you.

I think though, maybe a small clue to the answer is in Penguin Pete's post. From http://cafefoundation.org/v2/pdf_cafe_reports/ZTGT.pdf you see the that the induced drag at cruise speeds of around 180mph is less than 10% of the total drag, so maybe the wing isn't the place to start looking for breakthroughs in speed-related drag reductions. It's probably the reason that Van's 'gets away with' a hershey-bar wing, yet still delivers a fair turn of speed.

A

 

[gmcjetpilot]

Don't know, its PFM, pure freaking magic

I really don't know anything about airfoils like Aero guys, but I sat next to one once. They think different. The real question is where do great plane designs or great designers come from, like: Kelly Johnson, Burt Rutan, ?Jack? Northrop, Steve Whitman, Clyde Cessna, Walter H. Beech, Orville and Wilbur Wright. It's more than science & engineering. There seems to be a bit of magic involved in designing a plane. It takes a vision and countless decisions that affect countless other decisions. There is a little magic.

By looking at a RV you are right, you would think there is a little something to be gained by improving the lift distribution. Team Rocket tried it with some success ($5,000 more or 12% for the Evo wing over Std). However that change may come at great cost, effort and affect 20 other major and minor things. Worst of all you might lose the magic.