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RE: Torque and P factor, why do we continually confuse them?
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This thread is like the Energizer bunny... I think I hear the horse whinnying... http://www.rcuniverse.com/forum/js/f...wink_smile.gif rmh, nice bird! Got plans? |
RE: Torque and P factor, why do we continually confuse them?
ORIGINAL: speedracerntrixie ORIGINAL: iron eagel ORIGINAL: rmh I just drop it and hit the power Now the reason I mentioned my plane is; if this spiral effect was so pronounced, with the leading edge being between 1/8 an 3/4 of an inch behind the prop, this plane should want to heel to the right and it doesn't. Now on the flip side of all this (which lead me to think motor torque is more of an issue) is that she will roll left a lot faster than she will roll right. NO I haven't fixed that yet, I just hope it holds together long enough to get some real flight testing done (this bird isn't really built for aerobatic flight). The plane is not an arf :D (scratch built) and seems to have a pretty big envelope. (check out stingray 2nd flight on YT). Throws seem pretty good, and using elevons the elevator action doesn't cause any roll that we've noticed (but the elevator is really sensitive, I needed to add 30%expo). I hope I've got it set up right. I was concerned what effect p-factor would have on this plane where the prop is so close to the leading edge. Thus far it doe not appear to be an issue but it only has two flights on it, who knows what other things may crop up. |
RE: Torque and P factor, why do we continually confuse them?
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ORIGINAL: rmh 4.5 degrees offset? That is a BUNCH! It does swing a 14" prop which is pretty huge for a 40" span model so that probably explains the need for more right thrust than usual. It doesn't have any down thrust. ***Edited due to my stupidity***http://www.rcuniverse.com/forum/js/f.../red_smile.gif |
RE: Torque and P factor, why do we continually confuse them?
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Offensive ? why?
It is a bunch of offset. None of the bipes I have done required more than a couple of degrees - Some of the foamies DO require offset tho. If you like the setup then it's the right one for you. PS foamies arenot our only models -some are a wee bit larger |
RE: Torque and P factor, why do we continually confuse them?
ORIGINAL: Jet_Plane ORIGINAL: rmh 4.5 degrees offset? That is a BUNCH! The model is a Precision Aerobatics Ultimate AMR. It comes stock with 3Deg right thrust but when doing the standard vertical up-line test i consistently had the model yawing away left soI added an extra shim that took the right thrust to about 4.5deg (give ar take half a degree). She now goes vertical without any use of rudder. Increased right thrust also sorted out other areas such as a slight sideways drift through consecutive loops, now eliminated. CG is spot of by the way. As for the model being underpowered or overweight nothing could be further from the truth. This is a 40" span 3D aerobatic biplane weighing under 40oz with a wing loading of 9.5oz/sq ft. It's got about 200W per lb power loading and a thrust:weight ratio of 2:1.. overweight and underpowered it isn't... However it does swing a 14" prop which is pretty huge for a 40" span model so that probably explains the need for more right thrust than usual. It doesn't have any down thrust. As you might still think I'm talking 'a BUNCH' then here's a photo, put a protractor on it if you wish. I'm pretty sure Rich did not mean to offend. 4.5 degrees is a little more then what we usually see but it does go to prove a point of mine. I tell people all the time to listen and watch your airplane, she will tell you what she needs. Often I am asked where my needle settings are, where my CG is. How many PRMs do I get. My answer is usually " Beats me". Not 100% true statement as when I get these adjusted to where I like them I do omake a note for future reference. Lets take CG for example. I usually set it for a safe maiden then fly the airplane. Do a couple of tests and then adjust by moving batteries around or switching some components until I fet the flight performance I want. Pulling to a 45, doing a 1/2 roll to invert and letting off the sticks. Over the next 6 to 7 seconds I want the airplane to arc to level invert. For your high power, draggy bibe, I would expect it to require more right thrust as you have that big prop under more load then with a cleaner mono. You listened to the airplane and gave her what she wanted...........Bravo! |
RE: Torque and P factor, why do we continually confuse them?
ORIGINAL: rmh Offensive ? why? It is a bunch of offset. None of the bipes I have done required more than a couple of degrees - Some of the foamies DO require offset tho. If you like the setup then it's the right one for you. PS foamies arenot our only models -some are a wee bit larger by a common language they sayhttp://www.rcuniverse.com/forum/js/f.../red_smile.gif Once again sorry for taking it the wrong way.. Steve |
RE: Torque and P factor, why do we continually confuse them?
ORIGINAL: fledermaus FWIW: [link=http://www.nrc-cnrc.gc.ca/eng/multimedia/cavitation-tunnel.html]http://www.nrc-cnrc.gc.ca/eng/multimedia/cavitation-tunnel.html[/link] showing the spiral cavitation pattern caused by a ship propeller in water, in the National Research Council of Canada's experimental water tunnel. [link=http://www.flightglobal.com/airspace/media/mokkel/propeller-vortices-2-7104.aspx]In this picture of a C-130 taking off[/link] one can see condensation vortices behind the props which are similar to the cavitation in water. The pressure changes around the prop blades cause water vapour to condense along the path of the blade. One thought I have, however, is that these helical patterns do not necessarily mirror the airflow. The axial velocity of the air in the propwash is much greater than the tangential velocity (if it wasn't, it would be a pretty crappy propeller) and there is not that much momentum transferred tangentially as a result. This suggests that the prop wash effects might not be that substantial, but I'm not sure about that conclusion. Maybe I'm just blowing smoke...:eek: The sprial smoke trail doesn't prove there is spiral flow. If the air is moving straight back you will get a sprial smoke trail simply because the source is at a fixed point and rotating. Not saying there is none, there is, but it is not a strong force. Certainly not as strong as the smoke trail would seem to indicate. |
RE: Torque and P factor, why do we continually confuse them?
ORIGINAL: Sport_Pilot The sprial smoke trail doesn't prove there is spiral flow. If the air is moving straight back you will get a sprial smoke trail simply because the source is at a fixed point and rotating. Not saying there is none, there is, but it is not a strong force. Certainly not as strong as the smoke trail would seem to indicate. There are a number of photos of recip-airplanes taxiing and producing beautiful corkscrew condensation trails that surround the fuselage. A couple of those showing Hellcats on carriers come to mind. Those photos often pop up as proof that prop blast spirals aft. In fact, as you mention, the source (prop tip) is rotating and the visible particles produced simply remain pretty much where each was produced, and the continued propogation builds the visible corkscrew. If each particle was moving in a spiral, it would probably dissipate as it moved. Those pretty corkscrews got their picture took mostly because they weren't moving and neither was the air around them. The plane was moving slowly forward in quite calm air. Very probably the air wasn't moving or the corkscrews would have been blown apart. Those condensentaion trails aren't moving anywhere much. |
RE: Torque and P factor, why do we continually confuse them?
The biggest confusion point is the word "torque." P-Factor is a "torque effect." Too many people get into flying and try to apply common definitions to words that in flying have varied or even different definitions. Torque for the average person is from the engine, transmitted through various transmissions and shafts. In flying the definition " the moment of a force or system of forces tending to cause rotation" is the most appropriate and can be applied to the roll moment caused by engine torque, or the yaw moment caused by P-Factor. Torque, therefore will cause both roll and yaw, but the effect is from different sources.
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