I have a great planes extra 300 s and I gotta os 46 engine in int. I am getting full rudder throw. I had no problem doing a knife edge with the sig something extra but with this plane, it wont do a knife edge that good. I read a review in great planes website that you can do a knife edge loop. What can be the problem? when i go up elevator the plane seems to wanna roll to the left with no rudder input and not roll much to the right with full right rudder input.

The planes are quite different. The Sig SE has the wing in the fuselage center and the GP Extra has the wing at the bottom of the fuselage. This causes a considerable amount of roll-pitch coupling with rudder application in the low wing plane. Also the larger fuselage causes more drag. The roll-pitch can be mixed out with a computer radio. It seems as if lack of power may be a problem. You shouldn't need full rudder throw to maintian knife edge flight as it will just slow the plane. Center of gravity location can also effect the knife edge flight. Knife edge needs side area and speed to maintian flight as the fuselage is now the wing (flying surface).

EXCAP232

Hey, Thats what I thought it was lack of power but reading the review this is what it said.

"It is the most confidence-inspiring aircraft I have ever flown, and I can only give one example to truly validate that—I had never done a knife edge loop, but the knife edge was so smooth, so stable "

The guy had a OS 46 AX engine during the review.

Did it by chance tell you what magazine did the review? You have to take most of those reviews with a few grains a salt. Nowadays, most of the time it seems that if a company throws enough advertising money to a magazine, their products will get raving reviews, even if it flies like a broken brick. I agree that you might be just a tad bit underpowered, but you should be able to take care of most of the problem by mixing it out on your radio. I've seen two of the Extras that you have, and they flew very well, but both had 4 stroke engines on them.

I got that info from here http://www.greatplanes.com/reviews/gpma0235-srcm.html . I know they over react in the review but where do you draw the line? If the plane cant do a knife edge loop with a 46 dont say it can. I mean it can barely do a knife edge never mind a knife edge loop.

You have to get the plane really stable in knife edge before it will do a KE Loop. You also need a LOT of power, at least 2:1 to really make them symmetrical.
There are SO many things that can help or hurt with coupling issues due to thrust, incidence and cg.
Heres a start to simply mix out what you now have,,,, on a day when there is <5mph wind fly straight into the wind on knife edge with just rudder and see what the plane does. Do NOT correct with the right stick while you are testing for trim, just watch what it does.
1. Rudder to Elevator- Its either going to fly straight, pitch to the belly, or to the canopy. Put in a Rudder to elevator mix that is always on that puts in the appropriate elevator input to counteract the pitch coupling so that the plane flies on a straight line in KE. DO this on both knife edges. Dont make assumptions, check both left and right KE. The mix may be totally different of left and right KE. No switches to activate, leave the mix on all the time. Play with it till you can fly straight into the wind with only the rudder. No elevator or aileron.
2. Rudder to Aileron- Its going to fly straight or its going to roll to the left or right. Put in a rudder to aileron mix that puts opposite aileron to couteract the roll. Set each side seperately and be thorough. Same as the other mix do not put it on a switch, leave it on all the time.

On both mixes you will probably not need more than 10% mix to correct. Work in increments of 2 until you get it close and then tweek it down till you can fly on KE straight into the wind with only the rudder and the plane tracks arrow straight.

Once you get this right it will do better flat turns and anything that involves the rudder. The things the coupling screws up in KE it also screws up the rest of the time, you are just trimming it out.

Once you get this done you will be able to do better KE loops but even with a well trimmed plane you STILL have to correct with elevator and aileron a little as you progress through the loop. The only way to minimize this is with a rudder to elevator mix on a curve and a perfectly balanced plane with the right type of rudder.


Here are some other things to consider on KE that are about the fundamental setup of the plane.

1. Pulls to the wheels, could be noseheavy
2. Pulls to the canopy, could be a little tailheavy
3. Has roll coupling, may need to be laterally balanced. (Add weight to on wingtip or the other to truly balance the plane from tip to tip, this is very important by the way if you want a a plane that flies true.)

I notice when I read the review you are talking about, that the reviewer states that she did add 5% mix for the knife edge loop she is talking about.

You really do need power. My Florio Flyer 60 weighs 7 lb & has a GMS 76 dragging it around -- it can manage a KE loop, but it isn't a nice round one -- not enough power.

hey, Ya i thought it was the power too. I'm going to put a os 91 2 stroke I think that might do the job.

Yup, my 37% Ultimate weighs about 26 pounds and my BME 110 which I estimate generates about 80# of thrust with a 27x10 is just enough to make em nice and round. Ive seen guys do it with a DA100 on a plane of the same weight but its not really enough authority to really drive through the upline part of the loop with gusto. The plane wobbles a little as it slowly decelerates as it climbs. Thats by no means a shot at DA engines it just drive home the point that the maneuver takes mega power in the upline,,,,, and MEGA rudder authority in the downline.[8D]

Hey, Okay so what would be better a OS O.S. FS-91 II Surpass or a OS 91 FX 2 Stroke? I would like something that can also be used on other planes down the road.

You just have to figure out what prop engine combo will give you at least a 2:1 power to weight ratio. If you are below 2:1 you are going to regret it if you are wanting bigtime 3D or aerobatic power.

Where's the loop????????????????????

1.5:1 thrust to weight is more than enough for a KE loop. You don't need 2:1, but 2:1 is nice. Anything more is silly unless you are doing extreme fun fly/ 3D. I think the problem is with your plane setup. You mention the plane barely does knife edge in post 5. You don't even need 1:1 power to hold KE, so there is something wrong with plane setup. Where is your CG? Throws? How much does the plane weigh? How much is it supposed to weigh?

As for elevator causing roll but no roll with right rudder business. Your initial post is confusing. I can't figure out what you are asking. Does your plane roll when you make pitch changes?