Tucking in Knife edge flight

[flierbk]

Many planes tuck to the wheels in KE flight, I know that C of G effects this but have also heard the placement of the horizontal stab ( higher or lower on the plane) has a great effect on this, can someone comment on this please? If this is correct I would like to know why the location effects this so much.

Thanks,

WRK

[GremlinX]

I have asked this before on here.... I got very little for answers. I will be curious to see the answer. Tony and the other guys at Aero-Tech are regulars here on FG. I had hoped to learn but they did not comment...

[TimDavie]

WRK, It's mostly Asymmetrical Disk Loading....but a little of everything else.

[Stu_D]

The easy way to put it is every thing below the thrust line pulls the plane in that
direction .

Easy fix is add up thrust ( to the engine)until it stops or do a rudder to ele
mix or even do both .

Stu

[tommy321]

If you're up to it George Hicks wrote an interesting article on KE flight that has been circling around the discussion boards for quite some time.

I think it shows that there's alot more than meets the eye ... which is probably why it's so hard to get a straight answer on the subject.

Tom

[Stu_D]

Thanks Tommy , I got most of it .

Now I know why I fly a yak 55 .

Stu .

[GremlinX]

Why the Yak 55?

[TeamFlatout]

I dont know why it happens either but I can tell you you wont like to fly a Cap on knife edge to much with out elevator to rudder mix. I could do a knife edge circle without any elevator input and the plane will come back to where I started just by holding the rudder.

[Dangerous Dan]

My planes are set up just for precision I do my ruder coupling from straight and level since there is no knife edge in sequence

[Tired Old Man]

There's a whole bunch of different influences on the airframe in knife edge. The CG and horizontal stab location are two of the biggies, but also involved are engine thrust line, shape of the fuselage, location and shape of the canopy, propeller type and pitch, rudder size, location of the main wing relative to the horizontal stab, wing and stab relative incidence,and a few other things.

Just go for the mix that works the best after the cg and engine thrust are established. You can also reflex the ailerons up a little.

The George Hicks article was very good reading if you can find it.

Reason for a Yak 55 or a Sukhoi?

They both have the least amount of natural pitch coupling in knife. The 55 is a little better in a few other things as well because the rudder extends a bit below the fuselage.

[toprudder]

	Quote: Originally Posted by TeamFlatout
	I dont know why it happens either but I can tell you you wont like to fly a Cap on knife edge to much with out elevator to rudder mix. I could do a knife edge circle without any elevator input and the plane will come back to where I started just by holding the rudder.

I had a Cap 21 I flew for two years in pattern that would do that. I had something like 30% mix between rudder and elevator to correct it.

Yes, there are a lot of things that cause it, but the best way to fix it (aerodynamically) is to move the stab towards the direction it tends to pitch.

Simple explaination - In knife edge flight, the air spills around the fuselage from one side to the other. There is a line -- a "continental divide" -- that forms on the fuselage, above this line the air tends to spill around the top, below this line the air spills around the bottom. If the stab is not placed on this line, it will tend to pitch. Look at a Cap, the stab is on the very top of the fuselage.

There is also the shape of the fuselage. A fuselage with a round top and a square bottom will tend to pitch down more than a completely round fuselage. Guess what, a Cap has both, a Yak does not.

JMHO.

Bob R.

[buttface]

	Quote: Originally Posted by flierbk
	Many planes tuck to the wheels in KE flight, I know that C of G effects this but have also heard the placement of the horizontal stab ( higher or lower on the plane) has a great effect on this, can someone comment on this please? If this is correct I would like to know why the location effects this so much. Thanks, WRK

Buy a Yak!!!!Or an Edge and fuhgetabout it....