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-   -   Clipped wing RV-8 (https://vansairforce.net/community/showthread.php?t=84187)

Bob Axsom 03-23-2012 01:20 AM

They are faster but not the fastest and they are ugly
 
Faster than stock:




Fastest for me so far:



Bob Axsom

N941WR 03-23-2012 03:58 AM

On the HR, the same number of ribs are retained but the wing is shorter.

To do this with the -8 you will want to order a custom spar and wing skins, parts without the pre-punched holes.

Then your options are less flaps or less aileron. Either way it will land faster and roll quicker than a stock -8 due to the shorter wing. Pick the compromise you want.

Vlad 03-23-2012 04:20 AM

Quote:

Originally Posted by jenatepilot (Post 642073)
I love what Harmon did for the RV4 giving it a shorter and stiffer wing and coincidentally a higher G tolerance. Is there ANYONE who has done the same favor for the RV8???


Several years ago I spoke to a gentleman who was designing different wing for RV8. Great engineering brainpower was behind it. Since then I've never heard of any progress.

F1Boss 03-23-2012 07:55 AM

Look at the whole equation
 
The Rocket can get away with a shorter wing (which REQUIRES a higher IAS, all else being equal) because the ship has a larger engine. If you do not add a serious upgrade in HP to a clipped 8, the ship is gonna be significantly slower at higher altitudes, as in above 5000MSL, which is not very high.
Remember, every design is a compromise. To get something, you are likely to give up something, unless a wing redesign is also in your plans.
Carry on!
Mark

smokyray 03-23-2012 09:31 AM

The long and short of it...
 
Quote:

Originally Posted by jenatepilot (Post 642073)
I love what Harmon did for the RV4 giving it a shorter and stiffer wing and coincidentally a higher G tolerance. Is there ANYONE who has done the same favor for the RV8???

Well said Mark! Furthermore and in conclusion, the RV7 and 8 have longer and significantly different constructed wings than the RV4. As you mentioned the HR2 is built from the RV4 wing kit with all the original RV4 ribs moved closer together. Big difference? The 6 and 4 have a laminated spar vs a billeted single chunk of aluminum for the 7/8. (laminated is stronger in my humble opinion) There has never been an HR2, RV4 or 6 in-flight wing failure that I know of. There has however been an RV8 in-flight wing failure, a Van's demonstrator RV8 several years ago. Shortening the billeted spar in the 8 would require stress testing since the billeting changes thickness from fuse to tip.

V/R
Smokey

PS:My RVX wingspan is identical to the RV6 but with RV4 ailerons. (51" vs 48") Essentially the span and aileron length of a HR2 on a 6 fuselage. I trimmed the RV4 flaps to match the remaining room left on the wing! The span from fuse to tip on the X is within 1/4" of my Harmon Rocket wing span and identical to any stock RV6. Result, best aerobatic RV I have flown yet!

rocketbob 03-23-2012 11:32 AM

Quote:

Originally Posted by DRBuilder (Post 642424)
JM Out of Indy?

Yep that's correct!

Bob Axsom 03-23-2012 12:27 PM

Thanks F1 Boss
 
Quote:

Originally Posted by F1Boss (Post 642511)
The Rocket can get away with a shorter wing (which REQUIRES a higher IAS, all else being equal) because the ship has a larger engine. If you do not add a serious upgrade in HP to a clipped 8, the ship is gonna be significantly slower at higher altitudes, as in above 5000MSL, which is not very high.
Remember, every design is a compromise. To get something, you are likely to give up something, unless a wing redesign is also in your plans.
Carry on!
Mark

That adds weight to the conclusion I came to with our airplane in flight recently. Although my 21.5' wing span configuration is faster than my 24.5' cruise configuration (tip tanks remember) at 6,000 ft dalt I noticed a slight nose high hanging on the prop condition. I decided then that going shorter would risk performance everything else remaining equal. The flat metal tip configuration is 21' and if I went shorter I could use those with tip plates ... I seldom go above 3,000' in the short races and the tip tanks would get most of it back for me in cruise. Heck, If I put the old stock tips back on the wing span would go all the way back up to 22.5' which is just 0.5' below RV-6 stock span. Depends on how things go at Texoma and beyond. I don't want to do it so it will take some big motivation like finishing last to push me in that direction.

Bob Axsom

DRBuilder 03-23-2012 07:30 PM

Quote:

Originally Posted by rocketbob (Post 642592)
Yep that's correct!

John built the engine mount for my Super-7. Did an AWESOME job. Just over 44 hours on it now and loving it! John definitely knows RV's.

rvmills 03-24-2012 01:48 AM

Nate,

I have a Super Six with clipped wings (7" per side, same number of ribs in the shorter span...much like the HRII wings). What others have said rings very true (as you'd expect from this smart bunch!)

Concur with Smokey's recommendation to consult with Van's engineering folks before diving in. Proven concept on the 4/6 wing, not sure if its been done on an 8 wing.

My set up is slightly different than Smokey's, in that I have full size flaps and lost the span in the ailerons (guess that means Smokey would be trying to lure me into a rolling scissors, and I'd be pulling into the vertical or trying to drag him up into a flat scissors...eh Rob! ;))

As far as performance goes, as was mentioned, the g limits remain the same with my higher gross weight. That was a key element of the design feature, from what I've been told. If you're not going heavy (big motor), not sure you need to go that route. If just seeking higher g limits, I'd also find out from the engineers if other parts of the plane will tolerate higher g (tail, etc). If you're just seeking more safety margin at max g...perhaps that's a valid reason...but I think there is a good safety margin there if well built and maintained.

I've found that the clipped wing g-limit-saving design feature does cost in high altitude performance. At Airventure Cup 2010, Mark, Wayne Hadath and I climbed to 15.5K, then Wayne went up to 17.5K. At 15.5K, Mark (with his EVO Wings) slowly walked away from me (at that time we were very evenly matched at SL). Wayne (with the same wing as me) lost even more top end at 17.5K and fell back, then descended. I tend to cruise at 12.5 to 13.5 for best effeciency...and that sweet spot altitude would likely be higher with stock wings. So I pay a little in specific fuel consumption there.

Flat tips will likely buy you some speed (mine added 3 kts, and upped the stall 5 knots); should add roll rate (as Bill said) but cost in highter bleed rates in a turn or vertical maneuver. I use the flat tips for SL racing with fewer turns. I'm intrigued by Bill's fences...if they preserve stall speed, that's a bonus (Bill, how are they at bleed rates under g, and did they add any top end?)

The good news on flat tips, is you can go back to stock, which I did for the turning races at Reno (still bleeds some there though).

Here's a few pics. First is Mark and I at Reno, me with stock tips:


Here's a pic of us at Macho Grande (Marks place near Taylor, TX):


Pretty stubby with clipped wings and flat tips, eh! Its a bit skewed because I'm a little closer to the camera in the first pic, and a little further away in the second, but it gives some perspective.

Just for fun, check out this tip design, by a guy here in Reno:


They are called Scimitar tips, and Eric's website is here. Eric said they are optimized for turning...very little bleed under g. Would they work at RV speeds?...not sure. Eric thinks there may be some benefit. Bet I get Bob Axsom's juices flowing with that one though! :D

Finally, of the Super 8's I know of, I don't believe any have been clipped. Kahuna has those long-range tanks in his :), and I imagine standard-length wings keeps his maneuvering wing performance closer to that of the other Team RV aircraft as well. Kahuna, any structural mods to the wings, other than the tanks?

Interesting topic Nate!

Cheers,
Bob

pierre smith 03-24-2012 05:08 AM

Say Bob...
 
...are our tips on my -10 not fairly close to being of Scimitar design? Those and also the two seaters with the "batwing" type tips?

Best,


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