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RV-7 Speed Increase

jetblackaircraft

jetblackaircraft

Member
So, this is a little bit out there.... but what would you guys say if I told you that when you build your RV-7, if instead of buying Van's wing kit you buy the spars, shear web, ailerons and flaps, and other miscellaneous parts from Van's, but you buy ribs and skins from Jet Black Aircraft and it'll make your RV-7 go 10 to 15 knots faster.

Same or similar cost (Van's wing kit is $6110, depending on what they would charge for the above mentioned parts, I would say between $6500 and $7500 for the Jet Black version.)

Same type of construction. Ribs would be stamped and have predrilled holes. Skins are drilled, cut, and bent. You just drill to size, dimple, cleco, and rivet.

Now for the downside...

The stall speed would increase slightly from 58mph to around 64 or 65mph.

The takeoff run would increase from 500 ft to around 625 to 650 (still respectable).

Just throwing around ideas here. But, by changing the airfoil the drag can be reduced at high speeds to allow another 10 to 15 knots with the same powerplant.

This would increase your range to over 800 statute miles with 200HP.

Anyway, just a thought....

Mike
 
My interest is peaked....

hmmmmm.... sounds interesting..... any more data to be had? Any structural tests? Any flying?
Best
Brian
 
Preliminary stages

Don't get the wrong idea. This is all just on paper (well on the computer) for now. I understand your situation though, I wouldn't want to be the guinea pig either if it wasn't my design.

Sounds like the consensus is that if it were proven and had a good track record people would be interested.

Who knows, maybe you'll see it at Oshkosh in 09.
 
I'd be down for trying it out, if you need a guinea pig, of course I'm at the mercy of my budget for completion time, but for the record, i'm building a -7 tailwheel, with whatever engine I can afford :). When are you thinking of having the stuff ready, and will the be a discount to be a tester?

I totally believe in the 'experimental' side of aviation. While your at it, increase the fuel capacity to 50+ gallons for more range :)
 
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If you develop it and prove it people will buy it

I have an RV-6A that I have modified a lot for speed without touching the engine or propeller. I just got home an hour ago from the Big Country Air Fest at Abilene, Texas. From this event I can assure you that there are people out there that will pay for speed. I think 10kts is a magic number. The small increase in stall and landing speeds do not mean squat to these folks. As a previous poster has stated there is continuing interest in increased fuel capacity. I fly with two configurations a 24.5 ft wing span and a 21.5 ft wingspan. The 24.5 ft configuration carries 55 gallons of fuel and the 21.5 ft configuration is 3 kts faster. For short races like the one in Abilene this morning I fly with the short wing.

Bob Axsom
 
Clip wing?

jetblackaircraft said:
So, this is a little bit out there.... but what would you guys say if I told you that when you build your RV-7, if instead of buying Van's wing kit you buy the spars, shear web, ailerons and flaps, and other miscellaneous parts from Van's, but you buy ribs and skins from Jet Black Aircraft and it'll make your RV-7 go 10 to 15 knots faster.

Same or similar cost (Van's wing kit is $6110, depending on what they would charge for the above mentioned parts, I would say between $6500 and $7500 for the Jet Black version.)

Same type of construction. Ribs would be stamped and have predrilled holes. Skins are drilled, cut, and bent. You just drill to size, dimple, cleco, and rivet.

Now for the downside...

The stall speed would increase slightly from 58mph to around 64 or 65mph.

The takeoff run would increase from 500 ft to around 625 to 650 (still respectable).

Just throwing around ideas here. But, by changing the airfoil the drag can be reduced at high speeds to allow another 10 to 15 knots with the same powerplant.

This would increase your range to over 800 statute miles with 200HP.

Anyway, just a thought....

Mike
Click to expand...

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
 
"Yankee" wing

I've always wondered about using a wing similar to the old American Yankee AA-1. When they changed the wing for the trainer, or AA-1A, the stall speed dropped, but the cruise airspeed also dropped by around ten knots. If you could put this airfoil on the Vans, should be a good performer with 180 hp.
 
Bob Axsom...

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?
 
Jerry Cochran said:
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
Click to expand...

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!
 
Well I don't think so

N941WR said:
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?
Click to expand...

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
 
Experimental is the name of the game.

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!
 
N941WR said:
Yep, it's called a Rocket.
Click to expand...

Or a Mustang II

M40.jpg
 
Modifying and RV

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.
 
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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!
 
More on the "Yankee" wing

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
 
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?

:confused: CJ
 
Span down 3 ft (1.5 under Stock)speed increased 3 kts





This is my short wing configuration. The span is 1.5 ft less than stock and 3 ft less than my tip tank and stock tip configuration. It flies a little different in every mode. Roll rate and speed are improved. There is little float in the landing flare, climb rate is probably less but well over 1,000 fpm, and the take off roll seems longer. Yesterday in the BCAF Air Race at Dyess AFB in Abilene I made three turns in the vicinity of 120 degrees at over 180 kts (around 193 on one) going into each one and it didn't give me any trouble. I do not typically go over 10,000 ft on trips so I have no information on high altitude performance.

Bob Axsom
 
If the wing is changed (camber,chord or both) would that not change the center of lift for which the RV is designed and then necessitate a change in the position of the spar attach point? Not trying to throw cold water on the thread cause I like the way you guys are thinking but just wandering if it is really possible w/o re-engineering everything else.

Hey Bob...about your wing tips...have you considered or tried a simple flat plate with the top edge extended above the upper wing surface creating a flow fence...seems there may be some possibility with that.

Glenn Wilkinson
 
No I haven't

I am familiar with tip plates but I don't think I need to go there. Others have suggested that and I looked at Tom Martin's flat tips (no tip plates) but I am very happy with what I have now and I don't plan any more wing work except to fill the recessed ends of the control surfaces and look at ways to close the attach access openings.

Bob Axsom
 
Flutter and Airfoil shapes

glenn654 said:
If the wing is changed (camber,chord or both) would that not change the center of lift for which the RV is designed and then necessitate a change in the position of the spar attach point? Not trying to throw cold water on the thread cause I like the way you guys are thinking but just wandering if it is really possible w/o re-engineering everything else.

Hey Bob...about your wing tips...have you considered or tried a simple flat plate with the top edge extended above the upper wing surface creating a flow fence...seems there may be some possibility with that.

Glenn Wilkinson
Click to expand...

Glenn,

The change that I have in mind would at worst only require a slight change in CG fore and aft limit. The changes in pitching moment could be accounted for by slightly adjusting where the spar is located in the airfoil section of the new wing. They should be fairly similar. There also might be a slight adjustment in horizontal stablizer incidence as well as wing incidence.

About FLUTTER: I put it in bold to get everyone who's worrided about it's attention.... This is probably one of the most important things to discuss when talking about any speed increase. There is an article which Ken Kruger has written regarding the Vne speed of Van's airplanes. He talks about the many factors which contribute to calculating Vne. In the Van's airplanes, aerodynamic flutter is a key factor in determining Vne. Now, I haven't been able to find in my brief research what Vne is for the various Van's kits... If anyone has that data it would be greatly appreciated.

But, as Ken will probably tell you, an aircrafts flutter characteristics will change depending on a lot of things. So, when a person modifies the wing tips, adds horsepower, etc., the flutter speed can change.

What is flutter? Flutter, or aeroelasticity (http://en.wikipedia.org/wiki/Aeroelasticity), is when the aerodynamic loading on a structure cause it to deflect to a new position in which the aerodynamic loading has changed and causes a change in deflection resulting in a cyclic or oscillatory movment of the structure. A good example would be the airplane goes fast enough to create a very strong nose down pitching moment on the wing. So, the wing begins to twist leading edge down at the tip (because the tip is unsupported by the fuselage). Then, the tip is at a lower angle of attack than the root causing the tip to lose lift and deflect downward. When the tip twists downward and there is a loss of lift there is a simultaneous reduction in pitching moment (lift and pitching moment are somewhat coupled) and the structure is no longer loaded as much and twists back to normal which then causes the lift to increase again and the wing deflects back upward. The cycle then starts again.

This only happens at speeds high enough to cause a significant deflection to the wing so that the vibrations occur at a slow enough time constant to where the natural frequency of the structure is excited.

Anyway, the point is, flutter will have to be addressed with a modification such as this, but can be reduced by doing things like increasing skin thickness to reduce twisting, etc. The question will be, can it be done without a large weight penalty.

I am amazed at the response to this thread. It is encouraging. I will continue developing this idea and let you all know if it seems like it is worth testing on an aircraft.

This would help me... I have been guessing at airfoil sections based on drawings that I have borrowed of the kits. Does anyone know what airfoil is used on the different Van's aircraft? Some common ones are the NACA series (NACA 2412, etc.), Eppler, Clark, there are many others.

Thanks,
Mike
www.jetblackaircraft.com
 
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jetblackaircraft said:
Does anyone know what airfoil is used on the different Van's aircraft? Some common ones are the NACA series (NACA 2412, etc.), Eppler, Clark, there are many others.
Click to expand...

Van's RV-3 NACA 23013.5
Van's RV-4 NACA 23013.5
Van's RV-6 NACA 23013.5
Van's RV-7 NACA 23013.5
Van's RV-8 NACA 23013.5
Van's RV-9 Roncz RV6T
from http://strategywiki.org/wiki/X-Plane/Developing/PlaneMaker/Airfoils

RV-10:
"The airfoil section we have chosen will (heh, heh,) remain a secret at this time." from http://www.vansaircraft.com/public/rv-10int1.htm

But I would verify that data. :eek:
 
Pirkka said:
Van's RV-3 NACA 23013.5
Van's RV-4 NACA 23013.5
Van's RV-6 NACA 23013.5
Van's RV-7 NACA 23013.5
Van's RV-8 NACA 23013.5
Van's RV-9 Roncz RV6T
from http://strategywiki.org/wiki/X-Plane/Developing/PlaneMaker/Airfoils

RV-10:
"The airfoil section we have chosen will (heh, heh,) remain a secret at this time." from http://www.vansaircraft.com/public/rv-10int1.htm

But I would verify that data. :eek:
Click to expand...

The RV-3 used the thinner NACA 23012

From the very first iteration the RV-3 has always used the 23012 airfoil. All the two-seat short wing RVs (-4, -6, -7 and -8) use the 23013.5. All the 23000 series airfoils have the same basic shape, the only difference in these airfoils is the thickness. The thickness is given by the last digits. The 23012 airfoil is 12% thick (i.e. the maximum thickness is 12% of the wing chord) while the 23013.5 is 13.5% thick.

From Randy's excellent site
 
Airfoils

Pirkka said:
Van's RV-3 NACA 23013.5
Van's RV-4 NACA 23013.5
Van's RV-6 NACA 23013.5
Van's RV-7 NACA 23013.5
Van's RV-8 NACA 23013.5
Van's RV-9 Roncz RV6T
from http://strategywiki.org/wiki/X-Plane/Developing/PlaneMaker/Airfoils

RV-10:
"The airfoil section we have chosen will (heh, heh,) remain a secret at this time." from http://www.vansaircraft.com/public/rv-10int1.htm

But I would verify that data. :eek:
Click to expand...

Following the Grumman posting above, the later Grummans after the AA-1A use basically the same wing panels (2 per side on the 2 seaters, and 3 per side on the 4 seaters) and a NACA 64-415 airfoil.

At 15% thick, it's a little thicker than the RVs.

Even Ironflight's boss has one....:)

http://www.nasa.gov/centers/langley/news/researchernews/rn_nacaopening.html

Our RVs look like this.. just stretch the picture in a vertical direction by a factor of 13.5/12....:)

naca23012.gif


The later Grumman one is a bit different with some undercamber... similar to this...

naca642415.gif


gil A
 
Grumman airfoil

From what I can find, Grumman claims the same airfoil for both the AA-1 and the AA-1A, with the latter having a "redsigned leading edge". You can certainly spot an original Yankee (AA-1) a good distance away by its rather sharp leading edge as opposed to the AA-1A's bug-smasher profile. The resultant 10 kts. or so speed difference between the two was accomplished on the same 108 hp..
The AA-1 was indeed a ground-lover compared to the later models, but if you consider this wing now through the perspective of having 180 hp. available, takeoff shouldn't be much of a problem. As far as flutter, observe speed limitations and you'll be fine. The point here is, why not go the same speed by using a faster wing, while using less hp. and fuel? Or is nobody worried by the price of Avgas now?:eek:
 
A new wing project can be a lot of fun. I was involved in the design and development project for the new laminar flow wing for the KR-2S. We achieved an honest ten percent improvement as demonstrated in the University of Illinois' wind tunnel and verified by many Krs that are now flying the new wing.

We went the full route getting the University involved in designing an optimized airfoil and testing it in their wind tunnel followed by retrofitting an existing KR-2 for flight testing.

If handled professionally it can be a great project.

http://www.krnet.org/as504x/
 
newtech said:
A new wing project can be a lot of fun. I was involved in the design and development project for the new laminar flow wing for the KR-2S. We achieved an honest ten percent improvement as demonstrated in the University of Illinois' wind tunnel and verified by many Krs that are now flying the new wing.

We went the full route getting the University involved in designing an optimized airfoil and testing it in their wind tunnel followed by retrofitting an existing KR-2 for flight testing.

If handled professionally it can be a great project.

http://www.krnet.org/as504x/
Click to expand...

Sure! That's my thinking as well! For as great as the Vans is, what was the price of Avgas when this wing was chosen? I think this was part of the rational behind the RV-9 with the O-235. I know it can present problems for a manufacturer these days to want to increase performance if there is any way that it could be perceived to affect safety, but I think that, like the Rockets, there would be an interest in kits to modify these wings.
 
New Numbers

So, after using airfoil data on the actual airfoil Van's is using... It apprears I can only get between 7.5 to 10 knots.... But, I'm going to make some changes to the airfoil I am planning to use. I think I can get back up to around 15 knots. I'll keep you guys posted and post some performance figures later.
 
It's an interesting idea, Mike. Good luck with it.
While takeoff numbers of 275'-575' are really nice, few of us operate out of really short fields. Stall speeds can be raised several knots and still remain well within Category A.
New leading edge kits can incorporate a reasonable increase in fuel capacity while keeping that fuel at the same CG location. No more extra tanks and their associated valves and plumbing to deal with.
If you can keep your original cruise speeds, but throttled back to save even one gallon per hour, you can save $10,000 over a two-thousand hour period with Avgas at $5.00/gallon. Range would be improved significantly.
There would probably be lots of interest in something like this.
 
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