FlyRatz Posted May 28, 2012 Report Share Posted May 28, 2012 Hi friends out there, Today I would like to discuss a problem with the aerodynamical behaviour with one of our CTSWs and because I am at the end of my knowledge I would appreciate your thoughts very much. It is a 2007 CTSW with 100 hp engine and a in-flight adjustable prop. Compared to our other 2 CTSW, this one is consiberable slower and does not go faster than about 114 knots. Even not with WOT and 5500 RPM. Our other CTSW with fixed prop runs 135 knots with WOT (5500 RPM). The slow CTSW climbs with 1200 ft/min out of the field so I presume that the speed problem has aerodynamical causes and is not a problem with engine power. I took a test ride and found the following strange behaviour: If I go horizontal with WOT, trimm the plane to fly straight and level, hands off all controls and pull back the power-throttle to idle, the plane raises its nose high above the horizon and banks to the right (about 20 degree). After this test-ride, I measured the down-thrust-angle of the engine and compared it to the faster CTSW. No considerable difference! The traction angle ist the same as well. Now, I am out of ideas. Do you fellows have some ideas what to check/measure to isolate the problem?? Thanks in advance and many greetings Markus Link to comment Share on other sites More sharing options...
N89WD Posted May 28, 2012 Report Share Posted May 28, 2012 I'd like to know how your fixed pitch(ground adjustable)prop at 5500 RPM WOT is giving yiu 135 knots true air speed? Link to comment Share on other sites More sharing options...
coppercity Posted May 28, 2012 Report Share Posted May 28, 2012 How does the weight and CG compare between the other CTSW's? If you trim it WOT, keep the trim setting the same until your back on the ground is there a significant difference between the anti servo tab position of the slow CT vs the fast one. Does the -12 reflex flap position look different between them? Link to comment Share on other sites More sharing options...
FlyRatz Posted May 28, 2012 Author Report Share Posted May 28, 2012 Hi Mike, the 135 knots are IAS not TAS. Yes, this one is very fast and the GPS readings seem to confirm the high speed. To be honest, I never did exact measurements because nobody wants to go that fast. Sometimes the two CTSWs fly in formation and then it is obvious, that the fixed prop CT is up and away if the throttle moves forward. @Eric: Until now, I did not measure the angle of the flaps in -12 position. I will do that asap. The comparision of the trim tab position is a very good idea. I will do that. Thank you. Thank you for your posts Markus Link to comment Share on other sites More sharing options...
FlyRatz Posted June 4, 2012 Author Report Share Posted June 4, 2012 News from measurement. I did a measurement of the -12 flap position at both planes. To get a accurate measurement I used this device I set the flaps in 0° position, placed the BevelBox on top of the flap, calibrated it to zero and switched then to -12°. Results: Lame duck CTSW: -12° exactly Fast running CTSW: -10.7° As you can see, the results are the opposite from the expected. As soon as weather and time allows it, I will do the trim test coppercity suggests. Safe landings Markus Link to comment Share on other sites More sharing options...
coppercity Posted June 5, 2012 Report Share Posted June 5, 2012 News from measurement. I did a measurement of the -12 flap position at both planes. To get a accurate measurement I used this device I set the flaps in 0° position, placed the BevelBox on top of the flap, calibrated it to zero and switched then to -12°. Results: Lame duck CTSW: -12° exactly Fast running CTSW: -10.7° As you can see, the results are the opposite from the expected. As soon as weather and time allows it, I will do the trim test coppercity suggests. Safe landings Markus Interesting. On both CTs is the 0 position in line with the fuselage filet? Link to comment Share on other sites More sharing options...
mocfly Posted June 5, 2012 Report Share Posted June 5, 2012 Wonder if you took a -6 plane and made it go to -10.7 what the result would be? Do you plan to make it go to -12 and record results? Link to comment Share on other sites More sharing options...
FredG Posted June 5, 2012 Report Share Posted June 5, 2012 I would check the alignment of the turn and bank "ball". Some planes have the ball out of alignment (i.e., ball is centered when wings are not level). When this happens, the plane will be in a slight slip when the ball is centered (leading the pilot to believe that flight is coordinated). Such uncoordinated flight is inefficient and will reduce true (and indicated) air speed at any given engine (propeller) speed. A question for you - when the throttle is pulled to idle from WOT, does the plane bank right or yaw right, or both? My plane will yaw right when power is decreased (after being trimmed for hands-off straight and level flight with power), which seems correct (but it does not pitch up when power is decreased as described in your post). Good luck. Fred Link to comment Share on other sites More sharing options...
FlyRatz Posted June 5, 2012 Author Report Share Posted June 5, 2012 Thank you for your thoughts :-) Yes, the 0 position is in line with the fuselage filet at both planes. If I pull the throttle at WOT the plane banks considerable to the right while the nose rises up in the blue. Mybe there is a little yaw as well. But the bank is much more. Greetings Markus Link to comment Share on other sites More sharing options...
Jim Meade Posted June 6, 2012 Report Share Posted June 6, 2012 I don't have any magic ideas, but it sounds considerably out of rig. The nose pitching right with a decrease in power is logical. The plane banking puzzles me, especially 20°. Some yaw I could understand. What would you find if you optimized the controls for best speed flying level? Don't worry if it is straight, yaws, or is in a bank, simple gently adjust the aeliron and rudder trim until the plane flies as fast as you can get it to go - is that straight or is it in a turn? Obviously, you'll have to keep it at the same altitude. If the plane flies faster in a bank or yaw than it does straight, you have a rigging problem. Have you tried an accelerated power off stall? You could do it straight ahead if you watch your speed. I'd be curious if one wing really drops hard. Link to comment Share on other sites More sharing options...
FlyRatz Posted June 28, 2012 Author Report Share Posted June 28, 2012 OK guys, here are some news from the testride. With my friend in the lame duck, i flew side by side with the faster CTSW. As suggested, we trimmed straight and level, ensuring both planes running the same airspeed (side by side). After trimming we landed without touching the trim-wheel anymore. Back on the ground, we compared the angle of the elevator trim. The angles I give you here, are relative to the ground of the co-pilot compartment (where your feets are and the cover of the small trunk resides). This means, the higher the angle, the higher the trailing edge of the elevator, the higher the AOA was). Here are the numbers: | LAME DUCK | FAST RUNNER -------------+-------------------+--------------- Elev angle | 9° | 7° CG | 308,97 mm | 292,33 mm As you can see, the CG of the lame plane is 1,5 cm behind the other and the AOA is 2° more at the same airspeed. This confuses me totally. Best to you Markus Link to comment Share on other sites More sharing options...
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