Could it be that, due to the prop spinning the other way, the so far well proven "0.5° stab up" rule holds no longer true?
At first glance I wouldnt think up and up will work to well together....
Did you say you have the Stab up and the Motor up?? Typically with the tractor props stab up and engine down works well together. Or engine at 0 and stab up. If you can set the motor at 0 try it out and see what happens. At first glance I wouldnt think up and up will work to well together....
Hello Peter,
I think that since we use models with landing gears down, thrust line over center of drag (over the wing) and also over the CG, the tractor prop will always get more symetric flight.
If you want use pusher, I would expect also motor up and also stab down configuration, but I can say that I never got as good trim with pusher as I had with tractor. May be "all in line" will be better configuration for pushers, but still, landing gear is on opposite side as precession and p-factor need to be ballanced.
I find the resulting nose-out moment in outside loops quite helpful and I am willing to trade-in the resulting increase of line pull in the upper loops of the vertical eights and the upper corners of the hourglass against a (slight) lack of symmetry. The reason for this being that as a pilot I can deal, up to a certain degree, with assymmetry but there is not too much I can do for line pull.I do not mean symmetry as reaction to handle, I mean symmetry as tendency to pitch up or down without elevator input, because it could be a reason for hunting. Yes, asymetric reaction can be cured either with elevator to flaps position or handle leodouts etc, but it can add another troubles while trimming. Simply since you have landig gears down and wing also, you will need less elevator deflection to fly straight with tractor compared to pusher. That kind of asymmetry I mean.
Rabe rudder being coupled to elevator up seems to help against the slight loss of tension resulting from pusher induced nose-in moment in inside loops.Yes that is the way I solved probles in second corner of hourglass with tractor. And not only, Max Bee has wing located little under CG, it means CG moment tends to roll model out and motor moment and aslo flaps must ballance it ... and now, in situation when model goes up to second corner of houglass, when the gravity kills little of line tension, model with tractor tends to roll in - what makes that secon hourglass corner safer (like little more tip weight) ... pusher will do it just opposite :-))) ... whole that model is simply designed around tractor, pusher cannot help him(theoretically - with straight model without any other issues).
When I did a couple of test flights with the Meizlik 11.5 x 5.5 3-blade tractor, the most significant effect, besides considerably higher current drain, was the airplane rapidly turning inwards during spool-up in take-off run.Yes, it is illness of such small prop front of so large asymetric nose. Pusher helps in that case. However model must keep its position to lines also with change of power or thrust. If you will move leadouts little back and if you give little more rudder out offset, it will be cured. Model MUST keep its position regardless of prop thrust. You can check it when motor stops, if model yaws somewhere, then you have something not so well trimmed - either rudder, or LO position or motor out offset. And in that case it will be magnified at startup. However there is one important thing at startup, many people tend to pull elevator UP at startup, tractor prop Rabe rudder will move rudder in, and that will do just that what you explored.
Have a similar problem on a .46 ship at the moment
Any chance of a picture or two of youre aeroplane . ? .
For airplane specs see: "List your Set Up", reply 127 march 6 2012
Peter
THEREFORE this bothersome ship is going to get reamed in the Elevator Horn . To achieve 5 m.m. free play at the trailing edge of the elevator .
THINKING ABOUT IT . Your pusher set up will be enhaceing elevator responce , and lowering Thrust ' power assistance ' to the FLAPS .
%^@ Small incremental alterations in lift through the flaps achive steady course . Where elevator action alters track .
Tailplane offset from wing , affects induced tailplane A.o.A. , as its in wingwash , proportional to load . So incorrect can get it weaveing in rounds due to
varying force requireing further correction for trim . Thus ' the Trim wheel ' setting @ various loads / speeds , on F.S. Aircraft . n~
At this point in in time, I am about to do flight tests with an 1/8 x 1 in balsa strip taped to the front bottom side of the stab, kind of "simulating" a smaller AoA (approx. 0° as per the Robart Model Incidence Meter).
Here is what I, perhaps naive, flew yesterday. No effect whatsoever. Seems I have to cut into the airplane to get something like 0.25° negative (LE down) stab AoA...
Pusher: I've seen the pusher in your photograph in a Stockholm, Sweden, museum perhaps 25 years ago. Staff there said it was not a really successful airplane. Which is why mine is not a real pusher.
Peter I do not thing that this modiffication will do anything. If you modify arfoil by lowering its LE, you will do something like negative AoA, that is true, but you will also make little chamber and it will make little extra lift, so I expect that 0 lift AoA will not change too much. May be not at all :- )))
...easier then cut whole plane
... Motor is still at 1° up as changing this to 1° down is a bit tricky ...
rgds. Peter
You have to get that "UP" out of the motor offset. Get it level or a little down but NO up. It wont track with that in the configuration.Thank you, Doug. The motor is now adjusted 1 degree down. Tractor prop trim and test to be flown when I will be back from FAI/CIAM Plenary Meeting next week.
Thank you, Doug. The motor is now adjusted 1 degree down. Tractor prop trim and test to be flown when I will be back from FAI/CIAM Plenary Meeting next week.
rgds, Peter
Peter this is a beautiful aeroplane.Nice model Peter H^^(http://stunthanger.com/smf/index.php?action=dlattach;topic=31117.0;attach=125152;image)
Cant wait to hear how it goes!
Here what I've done so far:
Switched to tractor APC 13 x 4 E, repitched plus 1 in at station No. 7 (9'340 RPM / 5.3 sec)
Motor thrust axis 1° down
Left unchanged stab AoA +1° (LE up)
Set C.G. at: 13.5% MAC
Added turbulators on stab; 0.4 x 3 mm (15/1000 x1/8) tape, 5/16 forward of hingeline, top & bottom sides.
Results are:
Sensitivity: high
Accuracy in manoeuvre: sufficient
Corner:tight, exits flat
Rounds: might need a bit of smoothing
Tracking in level flight: barely usable
Tracking in inverted flight: poor
As the elevators LE are of the same thickness as the stab TE, I will next replace the sharp TE elevators by significantly thinner flat plates with rounded trailing edges. This will take a bit of time and I will report findings when done.
Meanwhile, as our contest season has started yesterday, I will use last year's Max Bee (one) to compete.
rgds, Peter
PeterKind of sharp, i.e. a radius of approx. 1/8"
Is the stab LE sharp or blunt?
Randy
May be there is something you can test without too much effort, Rabe rudder can also cause or solve hunting, may be you can try to switch it off and try, if something changes. If not (if pusher/tractor does not make any change), then it is definitelly elevator.When I switched to tractor the (pusher) rabe rudder (coupled to elevator up) was switched off and replaced by an adjustable rudder now being set to approx. 5° out.
Kind of sharp, i.e. a radius of approx. 1/8"
Peter
I was curious, I have found the stab LE being sharp makes the plane groove better.
Randy
I was thinking, just a thought before you go and make new elevators and all that work, could you or have you tried adjusting the length of the elevator pushrod Since you went to the tractor prop? Shorter or longer? Typically I try to go shorter first and see if it worsens or helps the situation.
I've cranked in as much as 1/4" elevator up (at the TE, with flaps neutral) w/o noticable influence on tracking... Contests coming up (next: http://www.mgbreitenbach.ch/) keep me from working at the new airplane now, so its back to last years pretty stright forward Max Bee.
rgds, Peter
Right, that would make sense. With the elevator up and flap neutral when you go to fly the plane you will need to level the elevator to get it to fly level. This would then give you a up flap, or negative AoA, and the plane would want to sink, and probably pretty badly as well.
With down elevator at flap neutral when you level elevator in flight you get a positive AoA and the plane will fly level.
At least this is what I have encountered over the years.
Hi PeterTwo (with 66 oz kind of heavy) airplanes later, and still flying pushers, I am now back to 0° incidence for both, motor and stab. As Randy suggests, elevator slightly (1°) out of neutral seems to help.
Doug is correct with the standard rotation prop try to set the elevators at about 1/32 inch down, when flaps are dead level. Have you tried it that way yet? and not only will it fly more level, it tracks better
Randy