Hey all:


Pls help me remember. " I did a search but cant find it "

when doing a knife edge, the craft pulls to the landing gear. If I remember I need ot adjust the right elevator, is this correct ?


thanks

It means you are tail heavy. The plane needs down trim to fly level because of the tail heavy situation, but when you go into KE flight the down trim then causes the plane to pitch to the belly (or gear).

they have a app for this , follow the app will help you tune out the airframe

http://www.mini-iac.com/Forums/tabid...c/Default.aspx

It's just coupling and most planes have it. That's why radios today generally have a rudder to aeileron/elevator mix. You want to use the mix to program in a small amount of up elevator when giving rudder so that all you end up with is pure yaw. You can add in some aileron as well if needed. Leave the mix on 24/7.

I just want to add on to what they are saying about the P mix or mixing elevator to rudder to remove coupling


the P-mix is just like sub trim. It’s a great tool future, but you should really have the physical, mechicnaly set up done complete before using the sub trim or P-mix... for the vary last fine tuning...


so if you P-mixed a great deal of coupling out of your plane, that P-mix would affect other flight aspec's

like if you had a high percent of rudder to elevator mix,, that's great you can do a hands off Knife edge pass but.. If you did a flat spin or something where you Pined the rudder full over you' have a much greater percentage of elevator movement active at that time. So ideally a small percentage of mix for some fine tuning wouldn't affect the spin... or pining hte rudder full over but the Higher precent of compsition to make up for physical and mechicanly set up... would be over excergrated in that Flat spin ..

So ideally get your physical and mechicnaly set up pretty darn close then do some P-mix Fine tuning at the very end

and do P-mix mulitable ways... like my buddys edge we did right to left left to right .. Gear in... Gear out, it required. A very small amount Rudder to elevator, and a little bit of aileron mix in there

It is no mystery.. usually less than a 10% mix of Rudder to UP elev is needed.... set it, leave it on all the time and forget about it..... it will NOT adversely affect other aspects of the flight regime...

One thing you can do to determine if CG or trim is a significant influence is to pull the plane up to a 45 degree climb, roll it to KE and let it go (NO RUDDER..just a trajectory).. chances are it will only pull a very slight amount to the canopy as it is very slightly pitch positively stable....

now repeat and gradually apply rudder (with no compensation mixing) and you will prolly observe as you add more rudder, it will pitch to the gear harder...

Originally Posted by AeroSheldon

It means you are tail heavy. The plane needs down trim to fly level because of the tail heavy situation, but when you go into KE flight the down trim then causes the plane to pitch to the belly (or gear).

This is not likely... as what you describe above is a pitch unstable condition... easy to determine by just going up high and doing a straight down dive at idle... if the plane pulls.. it is pitch stable... if the plane "Tucks".. it is pitch UNstable...
I am assuming the OP's plane is at worst "Neutral"...

the IMAC app will really help you .. just download it .. IMAC trim application i think its for iphone dorid

IMAC app >>mith ~!

I did some flight testing with tufting.... as can bee seen here....

Yaw Tuft (14 min 21 sec)

At about 3 minutes...on the down line, I yaw right and then left....
if you pause it right at 3:03 you can see the tufts are wrapped around the fuselage....
at the top and bottom... but right at the center of the fuse.. the tufts are essentially straight... this is sort of like
a "Stagnation" line .... and also notice.. the stab is on this line....
If the stab is mounted above this line... the induced angle of the airflow strikes the tail at an angle and induces a
"Down" or Pitch towards the wheels force.... if the stab is located below this line, the induced angle of the airflow
will cause an "Up" or canopy direction force.... the effect is small and primarilly focused near the root of the tail...

This flight testing with tufts is consistant with the CFD I did on a YAK 55 model 2 years ago....

FF... whatever

Originally Posted by Cerus98

It's just coupling and most planes have it. That's why radios today generally have a rudder to aeileron/elevator mix. You want to use the mix to program in a small amount of up elevator when giving rudder so that all you end up with is pure yaw. You can add in some aileron as well if needed. Leave the mix on 24/7.

Once you take the time to KE mix your plane, you will wonder why you never did it, and you will always do it from there out. After maiden, once I have my CG where I like to fly the plane....I immediately do the mixing. Keep in mind if you change your CG you will need to re-mix. Best to do with a buddy to help remember which way the plane is rolling and / or pulling because it will likely be different with left and right rudder. I set mine for half throttle hands free KE on a calm day. Good luck.

Originally Posted by terryscustom

Once you take the time to KE mix your plane, you will wonder why you never did it, and you will always do it from there out. After maiden, once I have my CG where I like to fly the plane....I immediately do the mixing. Keep in mind if you change your CG you will need to re-mix. Best to do with a buddy to help remember which way the plane is rolling and / or pulling because it will likely be different with left and right rudder. I set mine for half throttle hands free KE on a calm day. Good luck.

YES, thanks I think this is where I'm at. I do change the CG and then other things change. " DUH "

Ah yes - thanks for adding the CG info terry, totally forgot.

FF - the amounts used in the mix are minimal as Mith stated. I run mine all the time and they cause no issues in any maneuvers. Opposite in fact because you now have pure yaw when applying rudder. Also, what happens in knife edge is generally going to happen in straight and level flight too.

So imagine a plane that pitches up or down and/or rolls when rudder is applied. What's going to happen during a landing when correcting your heading with rudder only as you should be doing? It's going to do more than just yaw and you'll be fighting it all the way. I've seen many guys have so much trouble landing and it wasn't even their fault. They were using the rudder and then fighting the plane. Mixing it out solved the problem.

ya i agree with mith i am just saying the IMAC app for your smart phone makes quick easy work of triming

and not to overly use the P -mix to compensate for physical issue . just like sub trim ..

I use P mixes just like anyone eles .. i learned from Andrew Jeskey video he did a great job of explaining things and then demoing them

Originally Posted by futile flight

I use P mixes just like anyone eles .. i learned from Andrew Jeskey video he did a great job of explaining things and then demoing them

That's kinda where I started too, saw his vid and tried it....amazing. Normally everything is very small amounts as stated. I think the most I've got even on a couple of "dirty" flying ARF's is 6% Most will be 2-5%. I even did KE mixing on my BH cub and it is only 7-8%. Crap, I think I'm obsessive compulsive, I even mixed out my foamies and my little BNF Edge540QQ

Anyway, if you are further out than 5-6% I would look for setup or other problems.

Another useful mix to do is throttle to rudder for nice straight full throttle up-lines, but that is a completely separate deal that others will debate should only be addressed with thrust angle alone. For slight adjustment a mix is fine.

I have a mix for full idle downlines.... my flight idle switch activates the mixer (ON and OFF)...only 1 or 2% DOWN with IDLE mix... mostly a step that occurs at idle...

Oh yeaaaa, the app is GREAT.... at least there is a starting point. and NOW I can remember what I did, and didn't do

thanks ev1