I purchased a plane hanging from the ceiling of my lhs ( a 4 stroke). Whoever built it put 0 right thrust in it, WOW I never would have thought it would have made that much of a difference. At times, on low rate it takes full right rudder to make up for it. This is my first 4 stroke maybe even with proper right thrust angle it will still pull. What do you think? I'm going to shim the motor mount and see how much it helps.

Is the plane a tail dragger or tricycle gear. Is the problem during take off only or in flight? If only on the ground, check to see that the sterring wheel is properly aligned. If problem in flight, make sure all the flight surfaces are properly aligned.

I have two planes with no right thrust and it only affects take off roll to any degree. Once in the air see no difference.

Gary

And the mystery plane with the mystery engine may or may not have called for thrust?? MOst planes I build for myself never get thrust added until I test fly the plane to see if it needs it or not. If the plans call for it then I put it in. Right now on my bench I have a 4* 60 going together.[kit] It calls for no right thrust and 2 degrees down plus 1/2+wing incidence. Some kits and ARFs the thrust is already set by the fire wall.

Are you sure? Most Arfs now come with right thrust already built into the firewall. When the engine and cowl are mounted, you really won't know unless you stand over it and look down.

Its a Sig Mayhem (a taildragger) with a Saito 56 on it. The specs call out 2 deg rt thrust and its at 0. The cowl was my first clue before I measured it. You can see in the picture its designed for it in the cowl. I dont think its in the firewall in this kit you can usually see it. The motor is square with the mount and with a 12 inch prop sitting level its the exact same measurement from the vertical stab to both blade tips. 2 degrees should give about .21 inches difference.

I notice it most on full throttle vertical flight, initial climb, and take off roll, in that order.

The cowl doesn't mean much. It could be mounted a little off by it's self. Also I wouldn't necessarily trust measuring from prop tips unless I averaged the measurements with the prop rotated 180. Ever look edge on at a prop when the engine idling? A quarter inch wobble is not uncommon on a 10 to 14 inch props.

Itried to maiden a Twist 150 Monday. It has a Saito 180 in it. Iwent out on the runway and taxied it around, getting a feel for it and the, it was time for the take off. I've only flown tail dragger's for the last three years and all have been four strokes. Easing on the throttle while using some right rudder, until the plane has air speed and the rudder can control it is kind of second nature now. HOWEVER. Monday was an experience. I started my roll our and when I went to about half throttle, it was pulling pretty good to the left and I had to use a bit more right rudder than normal, however when I kicked the throttle some more, the rudder really took control and the plane did a 90 degree right turn and was off the runway before I could shut it down. No damage, but it left me kind of shaky. Ihaven't lost a plane like that in three years. My conclusion was that the 180 is a brute when it comes to torque. It required a lot of right rudder to keep it straight, but when the huge rudder took over, it was pointed in a much different direction than the plane and off into the weeds I went. Throttle control is something I'm going to have to really practice with this plane.

Don



Four strokes have a lot of low end torque.

If you feel it needs it then put it in - if it flies better then leave it - if it flies worst then just take it out again.

The amount of right thrust needed is usually determined by pulling up into a vertical climb. But even with the correct amount, it does not prevent the pilot from having to use rudder on take-offs or in maneuvers where the aircraft is changing direction in pitch.

For instance, when doing inside loops, the model will track better with a touch of right rudder.
Outside loops, will require a touch of left rudder. Now loops are the most basic maneuver, and yet hard to do well since all four basic controls are involved.

That's my thinking. If they used a GP adjustable mount you can even slide the mount/engine over to get the shaft centered again. Engine thrust angle is something I decide on with in flight testing. I add or remove it as needed. For testing I just use washers but when I hit the magic spot I make a hardwood shim when I get home.

Agreed. The cowl is set to be true to the engine/spinner thrust ring whether it has engine offset or not. The prop shaft should always be centered in the cowl opening for appearance.

The only guarantee you get with test flights, is that they are seldom boring !

In the last few years I have had a GeeBee R2 that test flew easy as heck on takeoff, and a trainer that turned into a slightly tail heavy 3d wannabee !

Both were checked over and balanced to plans..but its what makes it exciting, and frustrating !

The cowl is on the plane true and of course the propshaft is supposed to be centered thats not what where talking about here???. Its obvious if you look at the picture the cowl was designed to have an even gap around the spinner when the motor is installed with a few degrees of right thrust. Look at how its extended on the left side.
I recently put togeather a Hangar 9 Saratoga and the cowl was the same way a slight angle so the gap is even around the spinner, it had the same angle built into the firewall which was nice cause the motor is installed at about 45 degree from inverted. That would have been a pain to shim the right thrust angle.

Anyway as I mentioned in my original post I going to shim the motor up to have the proper right thrust and see how much it helps. may be a little bit but I will report back.

I once broke a firewall off of a plane when it deadsticked at a very low speed and at low altitude. I spoke to a guy at the LHS regarding thrust angle etc. He told me something interesting which I will try someday. What he did on one of his planes was to build and bolt a separate firewall onto the original of the fuse. He bolted it in such a way that he could adjust thrust angles easily without removing the engine. In other words, he basically had the second firewall which you could adjust just by bolting down or "loosening" the bolts which goes into the original firewall. This allowed him to make quick changes at the field without the hassle of removing the engine, putting in a washer etc etc.

After putting in 2 plus degrees of right thrust the plane handles much better. It was a bit of a suprise how much of a differance it made, I guess I just never flew a plane that wasn't right.