RV-7 Speed Increase

[N941WR]

Originally Posted by Jerry Cochran

has anyone done a "Clipped Wing" RV?

Yep, it's called a Rocket.

[N941WR]

I know nothing about airplane racing but would changing the wing on an RV put you in a different race class? Maybe with the Rockets?

[elippse]

Originally Posted by Jerry Cochran

While we're talking about modifying the wings, has anyone done a "Clipped Wing" RV? I'm thinkin' 70kt stall, 220Kt cruise, 2000' for landing and takeoff...
Chopping 3' of each wing of an RV-8 should do it... Yeah, that's the ticket...
It would give those plastic guys heartburn for sure...

Who will be first? (large smiley here)

Jerry

Keep in mind that if you do that your induced loss at altitude will go up a lot causing you to go slower up there. You'll go much faster at low altitudes 'though! The plastic ones usually have much higher aspect ratios and will not drop off much in speed at higher altitudes.Clipping a -9 wing, with its higher initial AR should be a hoot!

[Bob Axsom]

Originally Posted by N941WR

I know nothing about airplane racing but would changing the wing on an RV put you in a different race class? Maybe with the Rockets?

One of the stated objectives in the Airventure Cup Race is to stimulate people to experiment with their planes to increase performance. I have effectively clipped 1.5 ft off of my RV-6A but all of the "clipping" (I actually made totally different tips) has been in the fiberglass tip area. When it sits out on the ramp with other RVs in it's short wing configuration it is noticeably more compact than the rest. No doubt a point will be reached when an official line will have to be drawn but it doesn't exist at this time in the Sport Air Racing League or EAA AirVenture Cup Rules. Maybe they will then have to come up with another class like RV-Supermodified. RVs with larger engines than 360 cu. in. can and do run in the FX-red, FX-Blue and Sport classes.

Bob Axsom

[panhandler1956]

Mike,

I like the idea. I'm no aerodynamicist, but we must be giving up some top end speed based on how well the aircraft does in the short field department. I think there are practical limits for a 200hp fixed gear airplane, but I can see 10-15 kts like you said should be very achievable.
Now tooling up to make all those prepunched holes line up perfectly with the rest of the wing - well that blows my mind, which is why I'm a pilot and not a machinist!


Good luck with your venture and keep us posted!


PS If my wings weren't already done, I'd jump on this!

[aerial]

Originally Posted by N941WR

Yep, it's called a Rocket.

Or a Mustang II

[Aden Rich]

This had already been done on an RV-6. A guy by the name of Dave Freid put a tapered wing on a RV-6. He lives up in Ont, Canada.-Check Vans Ont wing website.
A little history lesson: a long time ago back in the 80's Van's faced off with a guy in a Mustang II with the same horsepower. The guy claimed he would beat Van's fat wing RV-6 all over the place. Well, Van spanked this guys behind all over the place, in every field. The tapered wing Mustang lost and went back in the barn in defeat.
There have been several people that have changed the airfoil of the wing and it did not do all that much in speed and made the airplane less desirable to fly comparative to an RV.
I love to modify RV's myself but they are pretty darn good all around airplanes for the wing they have. You can buy a lot of aftermarket parts like cowlings, fairings, props, spinners, exhausts..ect to make an RV go faster.
I am working on my RV-6 right now and I will get 10-15 knots out of it over the top speed. My last 180hp went 218mph, not to shabby. If I can get to 230 on the same power, why mess with the wing? If you like to tinker, then it would be great. What needs to be done it design a set of wings that goes 20knots faster and lands 15knot slower and carries more gas. I am building a set of 47 gal tanks for my RV-6 that are for a Rocket III.
I worked on a set of Rocket EVO tapered wings for a while. All I have to say is complex and heavy. There was over 500 screws in the wing to take off the leading edge and wing tanks. If you thought putting in nutplates in the floor boards was bad, well think again. The wing was a PITA to work on.
For the money, time to build and the performance we get out these airplanes, they're pretty hard to beat.
I have seen one to many Glasairs and Lancairs use up too much runway on hot days to want something like that to go a few knots faster.

[elippse]

You can assign a co-efficient times the wing area to account for the equivalent parasite drag area; this is apart from the induced loss. The RV-6 has an EPG of about 2.15-2.35 sq. ft. with 110 sq.ft. of wing area, for an overal co-efficient of 0.02. When you decrease the wing area for a given coefficient, the EPG will go down about the same amount as the wing area, however the induced loss will go up slightly because of the lower AR. This is of little consequence when flying flat-out at low altitudes, but is of more concern when flying higher and/or at higher gross weight or in pulling g's around a race course. Watch the biplanes with low AR wings when they take the turns at Reno, and see how they slow down and mush around. Then watch Mike Dacey in his high AR Questair Venture how he maintains speed around the pylons! Biplanes have an even higher induced loss due to the Munk factor which relates the crossover of the induced flow of the two wings. The biplanes typically will have about 50% more induced loss because of this. So roughly, at low altitudes, you will go about the cube-root of the wing area ratio faster, or, with a constant-chord wing, about the cube-root of the span ratio. So in going from 23' span to 20', you'll go roughly 4.8% faster as long as you keep the tip shape's Oswald efficiency factor the same!

[captainron]

Here is a link to Wikipedia's take on the original Yankee, later followed by the Trainer. While the Yankee was fun to fly, it certainly wasn't the most forgiving of airspeed errors and stall practice mistakes, and hence was sometimes "exciting" for newbies (myself included) to learn primary flight training in. There used to be a joke back then that if you were qualified in the F-104, you could probably hop right into a Yankee! American Aviation saw the need to re-work the original Bede designed wing to make the airplane more appealing to flight schools (think lots of VA loan money pouring in back then) and launched the AA-1A. The Trainer wing is just a re-work of the leading edge, which lowered stall speed, but also lowered top, or cruise speed. I'm sure this lesson wasn't lost on Van when he was designing the RV to be suitable for everyone from novices to F-16 jocks. I believe the RV wing is a compromise towards safety, and the plane simply has enough muscle to make it go fast enough.
To have a wing like the original AA-1 probably wouldn't be too difficult to design and produce, and kits could probably made to convert the leading edge while you are constructing the wings. I don't see the tapered design to be much of an advantage; it really didn't help the Arrow that much and they're harder to manufacture.
If you have a chance to look at a Yankee wing and the AA-1A wing, you'll see why the Yankee is the speed winner.
http://en.wikipedia.org/wiki/Grumman_American_AA-1

[Captain_John]

Let me start off by saying that I have been watching this thread with great interest.

These changes are exactly what Experimental Amateur-Built is all about! The RV series is so tried and true, it would be the perfect platform to alter with reasonable consistency in predictable performance.

Buuuut,

Not being a real en-ga-near, only an armchair en-ga-near... I have to wonder about control surface flutter in the face of such changes.

Am is incorrect in thinking that to make such changes to the 'foil (and use standard Van's control surfaces) without considering flutter would be an incomplete analysis of the complete modification?

Maybe set of ailerons with solid ribs and possibly counterweights would be on the list of considerations?

Sorry to bring up the "F" word, but flutter is really scary sounding and I would try not to push that limit!

What is your take on it?

CJ