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-8 wings the same as -7?

Roy Thoma

Roy Thoma

Well Known Member
I’ve read, been told and always believed that the RV-7 and RV-8 wings are the same. Not interchangeable because of subtle mounting differences or something? The specs on the Vans website say the RV-7 has 121 square*feet of wing while the RV-8 has 116 square*feet of wing. Can someone explain the difference?

Regards,
 
The wing area measurement includes the wing area projected inside the fuselage. The extra area comes from the wider fuse. The chord of both wings is the same, (4'10") the -8 has a 24 foot span and the -7 has a 25 foot span adding the extra not quite 5 square feet.

Don't know if the wings are exactly the same, but I do believe they share many common parts.
 
bifft said:
The wing area measurement includes the wing area projected inside the fuselage. The extra area comes from the wider fuse. The chord of both wings is the same, (4'10") the -8 has a 24 foot span and the -7 has a 25 foot span adding the extra not quite 5 square feet.

Don't know if the wings are exactly the same, but I do believe they share many common parts.
Click to expand...

This is correct.
Wing area measurement typically includes the surface area of the fuselage belly.

The wings are nearly the same but there is very suttle differences in the attach bolt pattern and the inboard end of the flap where it interfaces with the fuselage.
 
wing area measurement includes the wing area projected inside the fuselage
Click to expand...

Which makes me once more wonder as to why this is so…
In my over simplistic view, the wings are producing the lift, the fuse is producing… a lot of drag, maybe some lift, but certainly not in the same relation as the wings themselves.

Anyone with a historical or scientific explanation?
 
I have no idea why we include the wing area within the fuselage, maybe something to do with biplanes or when people literally sat on the wing to fly it?

However, fuselages do produce quite a lot of lift in themselves, if you look closely, most of them are an aerofoil shape.
 
fuse lift

Yeah, it really doesn't seem that the fuselage should count as wing area since it by itself would have to be at maybe 30 degrees to generate much lift.

But when there is a wing on each side, the fuselage gets very enthusiastic about lifting, sometimes overdoing it.

Ideally, the fuse lift should be designed to lift exactly the same as a wing extended through its position would. That will give the highest span efficiency.

In fact, if the fuse did not lift, there would be a drastic hole in the middle of the span lift distribution and the induced drag would be sky high with the plane still on the ground trying to lift off.

An example of this, amusing to recall, is a Breezy type photo plane that was designed to to do some Hollywood stuff at Flabob airport years ago. The 2 j3 wing panels were connected with a 3 foot gap in the middle. It would not fly. When a wing center section, as I had originally suggested was added to replace the missing fuselage, it flew like a bird, a drafty, slow one that did its job well.

So, yes, fuselages do their share of lifting as part of the wing system and including the projected area is perfectly justified.

Ron
 
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Many years ago, Van wrote an article for the RVator in which he talked about fuselage-generated lift in the context of Delmar Benjamin flying the GeeBee in knife edge.
 
Yes, fuselages do produce lift, no question about it.
Flying knife edge, the fuse produces lift too, we do a lot of it in 3D RC flying (see Jase here: https://www.youtube.com/watch?v=t-2TZbh5dW0)...

But this ought to be very dirty lift, as say compared to a wing, no? And a good reason lots of people tried to get rid of the fuselage in itself, as in flying wings, the name of the game being efficiency, as in max lift for min drag...

  • How does an engineer calculate the polar of a fuselage?
  • The lift it produces?
  • The fuselage's max AOA?
  • And finally, since the lifting characteristics of a fuselage body will most probably not be as good as the wing itself, why is it included in its total surface in a 1:1 relation?
 
Intersting... does the fuselage of a high wing aircraft generate less lift in general than a low wing plane?
 
The fuselage generates much less lift per square foot than the wing does, but it's usually about the same area as the wing (give or take), so the lift from the fuselage does end up being roughly equivalent to the lift that would be generated by the "imaginary" wing area that is "buried" in the fuselage.

For hershey-bar wings like on our airplanes, that's a straightforward calculation. For tapered wings, especially when the taper is not constant (e.g. for airplanes with a Yehudi like most jet transports) it gets more interesting: There are actually different ways to calculate the "equivalent" wing area; Airbus has a way to do it, Boeing has their way...

https://leehamnews.com/2015/04/28/fundamentals-of-airliner-performance-part-7-the-wing/

The funniest implication of this is John Cook's Parker Air Racer from 1977. Formula 1 rules required 66 square feet of wing area including the area in the fuselage, so he designed and built and raced an airplane with a compound-tapered wing with tons of "area in the fuselage" and reduced actual wing area. They apparently let him get away with it, the airplane was not disqualified due to this loophole.

http://www.westernnorthcarolinaairmuseum.com/1977-parker-air-racer.html
 

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Ok, now I’ve learned two “somethings” in the same day. Interestingly, I had queried my IF1 buddy in between “somethings” and he had said it’s not as simple as it sounds. Clearly. Thx for the links.
 
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So, outside of considering the area of the fuselage, coming back to the OP's question, my -8- wing has W-709, W-710, W-711, & W-712 ribs, then W-701, W-702, W-703, W-704 & W-705 skins.
The tank has T-703 & T-704 ribs & T-701 skins.

Flaps are FL-704 & FL-705 ribs,
Ailerons are A-705 ribs and A-710 stiffeners
Many other parts have -7XX as numbers.
That would say that both 7 & 8 share the same wing parts ???

The flap and aileron skin have -801 numbers, indicating slight differences as Scott mentionned
 
Also the rear spar is the same on the -8 and the -7, but you cut more material off it on the -7 I believe.. making them different after the cut.
 
Thanks for that link AeroEngineer, excellent article, and series of.
This goes well towards answering some of the stuff I was scratching my head for :)
 
I believe Jay Pratt had a set of -7 wings for his latest -8 project originally 'because they were (supposed to be) essentially the same'. He ended up having to sell the -7 set and build an actual -8 set because the modifications to make them fit were not possible/feasible.

Just in case anybody was looking to interchange...
 
flaps won't fit

I can tell you from experience that the flaps are different lengths. The 8s flaps are about an inch and half longer than the 7s. I was shipped there wrong flaps with my kit.

Ailerons are identical.

tool man
 
It’s called flat plate lift. You can get lift from any flat surface presented to the airflow at a positive AoA, albeit poorly.
 
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