Majorpayne317641
Well Known Member
For anyone who uses cowl flaps like me on my RV8A, be aware of an unknown induced spin tendency my instructor and I discovered in my plane.
I am practicing for my commercial today, the instructor began to demo a power on stall from the back seat, being a hot day I elected to leave my cowl flaps open for the air work. At about 60kts 50ish degrees nose high the aircraft rapidly breaks for a right spin. We tried it again this time me in the front seat, it did the same thing. He at first was puzzled because his 8 does not do this. I then realized I had my cowl flaps open and decided to try with them closed. The following power on stall maneuver was a predictable straight ahead break into a stall.
This is not uncommon in supersonic aircraft, as the first few inches of the nose is checked for any defects greater than a particular size. This affects maneuvers at high AOA. I suppose the RV8A has this same tendency if you have laminar airflow along the bottom of the cowl disturbed by open cowl flaps.
I have a IO360M1B fixed pitch sensenich prop set to a cruise pitch. Everything else is pretty much a standard RV8A aside from the cowl flaps.
I will change my immediate action items to reflect checking cowl flaps closed in a spin recovery. I will also be mindful of open cowl flaps on takeoff, 60kts is way below Vx/y but it's much higher than the normal power on stall. I wanted the rest of the community to be aware of our discovery in my aircraft today.
I am practicing for my commercial today, the instructor began to demo a power on stall from the back seat, being a hot day I elected to leave my cowl flaps open for the air work. At about 60kts 50ish degrees nose high the aircraft rapidly breaks for a right spin. We tried it again this time me in the front seat, it did the same thing. He at first was puzzled because his 8 does not do this. I then realized I had my cowl flaps open and decided to try with them closed. The following power on stall maneuver was a predictable straight ahead break into a stall.
This is not uncommon in supersonic aircraft, as the first few inches of the nose is checked for any defects greater than a particular size. This affects maneuvers at high AOA. I suppose the RV8A has this same tendency if you have laminar airflow along the bottom of the cowl disturbed by open cowl flaps.
I have a IO360M1B fixed pitch sensenich prop set to a cruise pitch. Everything else is pretty much a standard RV8A aside from the cowl flaps.
I will change my immediate action items to reflect checking cowl flaps closed in a spin recovery. I will also be mindful of open cowl flaps on takeoff, 60kts is way below Vx/y but it's much higher than the normal power on stall. I wanted the rest of the community to be aware of our discovery in my aircraft today.
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