Another knife-edge qn

[stuartaw]

Since we're getting good answers to knife-edge questions....

What angle-of-attack (of the fuz) does a plane typically use during knife-edge in order to maintain height?

Stuart

[Bill Glover]

It varies enormously depending on the speed and the fus side area. My IC pylon racers would knife edge with the fus. practically horizontal, but my Panic required quite a nose-up attitude (and a lot of the lift on that came from the flat plate struts at the wingtips and centre-section).

Never tried a knife-edge loop with a pylon racer, but no problem for a Panic with plenty of power and a huge rudder :D

I don't (yet) have an e-flight model that will sustain knife-edge :(

[stuartaw]

Originally posted by Bill Glover
It varies enormously depending ...


Thought you might say that :)


I don't (yet) have an e-flight model that will sustain knife-edge :(

Me neither. The limbo dancer was sort of close at about 45+deg up - but its got no side area, and huge roll-coupling - i guess it was doing more of a falling-sideways hover than knife-edge.

But my Nightmare (a twin) with lots of rudder->throttle mixing can at least be made to hold its nose straight. It's only had about 7 minutes of flying time so far and my one KE attempt maintained attitude but lost altitude. When (if?) the weather clears I need to try holding it at different angles to see if any will fly.

Thanks for the reply Bill,

Stuart

PS - are you the only person that reads this forum?

[Bill Glover]

Yup :D

[Dereck]

Hi Stuart
The other thing is that, just like wings, fuselages fly differently at different speeds. As I only fly e-power these days, I go for a run run at it so I can fly with the body fairly level - slow KE with a high AOA requires more power than I have right now.

KE with a high winger inevitably means you have to hold stacks of aileron to offset the top rudder trying to roll the thing out, and often some elevator to keep on heading. The drag is 'orrible! The only way I can do a passable KE with my high winged Embat is to really pour on the coal, flip onto a wing tip from a slightly nose high attitude and not stay there too long.

OTOH, the GP CAP 232 - onto a wing tip, bit of top rudder - and watch it fly KE as long as your eyesight holds!

There used to be a good website around for trimming pattern ships out for FAI work - anyone recall its location?

[stuartaw]

Originally posted by Dereck
Hi Stuart
The other thing is that, just like wings, fuselages fly differently at different speeds. As I only fly e-power these days, I go for a run run at it so I can fly with the body fairly level - slow KE with a high AOA requires more power than I have right now.

Hi Dereck thanks for the reply. It also leads rather neatly on to my next question. After about 3 weeks of wind and rain, I've been idly running numbers thru motocalc - and it definitely likes the idea of gearboxes on the nightmare.

But - does anyone know which is more important - thrust or speed for knife-edge? My instinct is usually to go for thrust, but is that wrong in this case? I know this is very subjective, but any advice anyone? Motocalc is suggesting something like 80% more static thrust for 25% less speed, so guessing at 50% more thrust in the real world would this help KE or make it worse?


....There used to be a good website around for trimming pattern ships out for FAI work - anyone recall its location?
I can't remember the site either. There's basically the same thing in the Futaba FF8 manual, which is the copy I use.

Stuart

[Norm]

Dereck, not all high wingers have a roll coupling problem. My Sundancer has zero roll coupling in knife edge, but does require some elevator mix which I have programed into my 8UAFS.

Norm

[Dereck]

Hi Norm
Now there's a thing. All my high-wingers have - or right now, "the' high winger".

The fleet of shoulder wing things I designed back in my oily days, with everything on the centreline, would all do a slow roll on rudder / elevator, though they were pretty axial rolling on ailerons. That was pre-computer radio too - they all got a little differential built in, to take out a tendency to barrell roll a little too