RV-9 flaps on a -7?

[N941WR]

I was talking to a -7 builder the other day regarding the landing speeds of the -7 & -9. I made the comment the flaps were different between the two and that I didn't think it would be difficult to install shortened RV-9 fowler flaps on a -7.

Has anyone done this?

The expected benefits would be lower landing and stall speeds. The drawback is longer build time. I also wonder if the leading edge on the -9 flaps would fit the -7 wing.

 

[wingtime]

Airfoil

The airfoil on the 9 is Roncz which is totally differnt than the 7 so I think it would be easier to just change the hinge style on the 7. I would consider that as a major modification that could end up biting ya in the backside.

 

[RBurn]

There are a few important things to consider. Some of these will sound obvious, but I think they should still be listed...

1) Will they even fit? The 9 wing is longer than the 7 so the flap and aileron lengths are going to be different. If you put a 9 flap on a 7 wing then you'll have to shorten your ailerons. This will reduce your roll control. Reducing the roll control leads to a whole host of issues such as: x-wind landing handling, trimming during unbalanced fuel/passenger load, formation keeping, etc.

2) How do the aerodynamics work out? As previously mentioned the 7 and 9 have different airfoils. So if you stick the flap of the 9 onto a 7 wing you're going to create a new airfoil. Will it fly...probably. Will it fly the same as the 7 that everyone has come to know and love...probably NOT. You are correct that the larger flaps would result in a lower landing/stalling speed. However, the biggest issue about adujsting the flap size will be if you have enough elevator authority to stall the airplane at foward CG with the flaps all the way down. That would require some analysis/testing to figure out. I think this is a case of, "if it ain't broke don't fix it."

 

[kentb]

I don't think that it is the flap.

I think the lower landing speed has more to do with the airfoil then the flaps.

Even without flaps being used the 9 stall a lot slower then the 7.

Kent

 

[Mel]

Like Ron said. Putting the -9 flaps on the -7 would require a complete redesign. Nothing is compatible between the -7 and -9 wing.