Knife Edge Questions - RC Groups
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Dec 24, 2016, 11:25 PM
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Knife Edge Questions


When I try to go smoothly from upright flight to knife edge, the plane starts to roll immediately, so by the time I start thinking about getting top rudder in, the heading is lost. I was wondering if I needed to roll to ninety faster, feed in down elevator as I roll, or something else entirely. Any pointers for me to practice? Thanks.
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Dec 24, 2016, 11:55 PM
Closed Account
Your airplane is simply out of trim. What airplane specifically are we talking about? What advanced trimming have you done to this point?
Dec 25, 2016, 12:28 AM
Registered User
Super Chipmunk. Plane trimmed pretty well. Flies inverted with little to no elevator. Tracks straight when level, pulling through loops, etc. Not a perfect plane, but pretty good. I think my technique is just lacking is why I was asking.
Dec 25, 2016, 08:47 AM
Closed Account
It could be your aileron differential is off causing a cork screw when rolling to knife or you are still carrying some elevator trim that shows up at knife when the wing is unloaded. Impossible with a Chippy but a properly trimmed pattern airplane can be rolled to knife edge with only aileron input and held there with only rudder input. With further trimming your Chippy can get 90% there.
Last edited by exf3bguy; Jan 08, 2017 at 11:40 AM.
Jan 08, 2017, 11:35 AM
Chef Pilot: Planes vs Butter
ChinoDiablo's Avatar
IMO, the dihedral in the Super Chipmunk's wing makes more likely that you're going to have a moderate degree of coupling with the Rudder in KE.
Also, your CG plays a part in all of this as well.
If you're nose heavy, the plane is going to pull towards the canopy.
If you're tail heavy, the plane will likely pull to towards the gear.
This effect is exaggerated with dihedral and a non symmetrical airfoil, which if like most Chipmunks, it has.
Jan 10, 2017, 11:07 PM
Registered User
Unless you modify it you will have to maintain heading using the elevator, and ailerons.
Jan 19, 2017, 10:48 AM
Aerofox74
I'd suggest to look up Peter Goldsmith's Trimming Method, and trim your plane in to that. You will be amazed if to take the time (and the many flights it will take) to get it trimmed right of how easy knife edge and anything else you what to try will be. Goldsmith covers balance, vertical, differential, mixing and more.