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Propeller weights
I'm starting this thread to post some figures on how much props weigh. While maybe it isn't incredibly important for the 50cc++ gassers, I have found that on most glow engines (and probably smaller gassers as well), the weight can actually have a significant impact on engine/plane performance, especially as it regards spooling up or down. I believe that the weight of the prop should be taken into consideration, not just it's maximum static thrust etc.
I used a reasonably accurate scale from WalMart, though someone with a nice postal scale or something similiar will obviously produce better results. I encourage whoever has a few extra minutes to go and weigh a few props and post the results here for all to see. ------ Xoar 15x6 laminated wood : 52g/1.75oz. APC 14x6 : 76g/2.75oz. APC 15x6 : 76g/2.75oz. APC 15x4w : 70g/2.5oz. Master Airscrew Wood Scimitar 14x6 : 30g/1.1oz. That's all I've got on hand. |
RE: Propeller weights
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Robert, please, please, don't make me do it.
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RE: Propeller weights
ORIGINAL: Hobbsy Robert, please, please, don't make me do it. |
RE: Propeller weights
ORIGINAL: RVM I'm starting this thread to post some figures on how much props weigh. ..... especially as it regards spooling up, or down. It is not the weight that matters. It is the tangential inertia of the prop, that affects the amount of work the engine must do, in order to increase, or to decrease the speed at which is spins. Spool-up is what the spools in turbine engine do - not props. Let's not make a 3-D pilot with a .46 feel like he has a real turbine ;):D That 15x6 Xoar prop, at only 52 grams, may have more inertia than the 76 gram 14x6 APC, just because it has a larger diameter. The weight to be accelerated is further from the shaft. Increasing the spinning speed of a shaft weighing 76 grams takes but an instant, because its weight is close to the center and the linear change in its tangential speed is relatively small as a result. An annulus with the same weight, with spokes connecting it to the shaft, will require much more work to reach the same RPM, since its tangential speed must be made much greater. This is the main reason only a few are using props 16" and greater in diameter, which are made of heavy GFN. Most use wood and props made of carbon fibre are middle-weight... |
RE: Propeller weights
I've flown some 120 size 3D planes with 17 to 18 inch apc props and found spool up to be a minor nuisance. A bigger nuisance was the feeling that I was flying a gyroscope rather than a plane.
Denis |
RE: Propeller weights
How did you notice the gyroscopic effects?
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RE: Propeller weights
ORIGINAL: djlyon ...A bigger nuisance was the feeling that I was flying a gyroscope rather than a plane. |
RE: Propeller weights
Adverse yaw or pitch with sharp pitch or yaw inputs. It seemed to be a lot less with a lighter prop, wood or mejzlik. Could have been my imagination or a wrong conclusion (adverse condition being caused by something else).
Denis |
RE: Propeller weights
True gyroscopic effects are minimal and probably very difficult to really pinpoint unless in a controlled environment like a test stand with sensors. That is why I asked. P factor effects account for probably 99.9% of similar effects. Also, a slow pitching up would skew things as the engine probably leans and RPMs increase. Angle of attack would change things, so it would be confusing if you were looking for pure gyroscopic effect tendencies. Yaw (or roll) has its own set of problems mixing together. The V-22 would probably have to have a swashplate sort of system to apply the force 90 degrees before the desired effect since those blades are very long. It would be interesting to look into on that full scale plane.
Helicopters do have to compensate for it due to very long blades and the mass at the end of them. Same thing with bicycle tires when we hold them as they spin. The swashplate on helicopters is where this is compensated for. You can also feel some gyroscopic effects from aerodynamic forces such as blowback when the helicopter has a slight left roll and pitch up as it accelerates. The pilot has to apply right roll to cancel the slight rolling tendency for a second or two. This is also called transverse flow effect. |
RE: Propeller weights
bwa ha ha haha I think you would be exempt! :D
Nice collection by the way! ORIGINAL: Hobbsy Robert, please, please, don't make me do it. |
RE: Propeller weights
Well, obviously distance from the center is extremely important, but I don't have a way to measure that. I figured one could look at the length, look at the weight and draw some conclusions.
I have always used the term "spool" rather loosely, though I do understand that there is a definite technical difference. ORIGINAL: DarZeelon Robert, It is not the weight that matters. It is the tangential inertia of the prop, that affects the amount of work the engine must do, in order to increase, or to decrease the speed at which is spins. Spool-up is what the spools in turbine engine do - not props. Let's not make a 3-D pilot with a .46 feel like he has a real turbine ;):D That 15x6 Xoar prop, at only 52 grams, may have more inertia than the 76 gram 14x6 APC, just because it has a larger diameter. The weight to be accelerated is further from the shaft. Increasing the spinning speed of a shaft weighing 76 grams takes but an instant, because its weight is close to the center and the linear change in its tangential speed is relatively small as a result. An annulus with the same weight, with spokes connecting it to the shaft, will require much more work to reach the same RPM, since its tangential speed must be made much greater. This is the main reason only a few are using props 16" and greater in diameter, which are made of heavy GFN. Most use wood and props made of carbon fibre are middle-weight... |
RE: Propeller weights
Take another look at Hobbsy's stash.
Notice all the Graupner props? The engine gurus know how good those suckers are - even if they ARE heavy |
RE: Propeller weights
They don't make them in the sizes I want to use. The few I've seen at the field also turned up slow, which is not good for 3d. They did seem to pull really hard though.
ORIGINAL: MinnFlyer Take another look at Hobbsy's stash. Notice all the Graupner props? The engine gurus know how good those suckers are - even if they ARE heavy |
RE: Propeller weights
ORIGINAL: RVM The few I've seen at the field also turned up slow, which is not good for 3d. They did seem to pull really hard though. Jens Eirik |
RE: Propeller weights
ORIGINAL: Hobbsy Robert, please, please, don't make me do it. 'Tis true - one can never have enough props........or engines.........or planes [8D] |
RE: Propeller weights
Heavy props may help the idle characteristics of an engine too.
Personally, I think Hobbsy should weigh all of those props and post the results here.[>:] |
RE: Propeller weights
I dunno, ah'm purty tard tonite.
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RE: Propeller weights
It's easy Hobbsy. Just throw them all in a box, weigh them and devide by the estimated number of props. Then leave them in the box under a table.
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RE: Propeller weights
What I want to know about in Hobbsy's room is that Rascal Forty with the 4-blade prop. http://www.fototime.com/24380C8ED7B05D5/orig.gif
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RE: Propeller weights
ORIGINAL: DarZeelon It is not the weight that matters. It is the tangential inertia of the prop, Gyroscopic precession also follows the same moment of inertia and combined weight deal. It's noticeable in CL stunt where very tight turns are done and causes the nose to yaw out with up elevator and vice versa. This is one reason why either wood or CF props are preferable but can be counteracted by using what's called a Rabe rudder linked to the elevator so the rudder turns in the direction needed to oppose the precession yaw. For props of a roughly similar size... APC 11x6...40 grams Taipan 11.5x8...18 grams (narrow blade) Taipan 11x5...27 grams MA 11x5...26 grams Zinger wood 12x6...17 grams Bolly 11.75x4.25 CF 2 blade...32 grams Bolly 12x4.25 CF 3 blade...36 grams Eather 11.25x4 CF 3 blade..24 grams Grish 7x10 nylon...8 grams :D |
RE: Propeller weights
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Tom, it is powered by a PAW .40 Diesel mounted inverted. I had to dis-assemble the engine to get it in there, then re-assemble it in place. The prop is a 10x7 three blade that it turns at 9,000 rpm. I used to run a 12x6 three blade that it turned at 8,300 but it flew slugginsh with the tail kinda hangin low. Now it jumps into the air and flies with some spirit.
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RE: Propeller weights
ORIGINAL: downunder Taipan 11.5x8...18 grams (narrow blade) Could you please post a couple of photos of this particular prop? I have a whole package of unused, orange, GFN Taipan 11x7 props, those with blades that are pretty wide at their roots. They are from about 24 years ago and wouldn't possibly fit into any normal spinner (except a back-plate-less Kavan). They are also much heavier. |
RE: Propeller weights
ORIGINAL: blw True gyroscopic effects are minimal and probably very difficult to really pinpoint unless in a controlled environment like a test stand with sensors. That is why I asked. P factor effects account for probably 99.9% of similar effects. Also, a slow pitching up would skew things as the engine probably leans and RPMs increase. Angle of attack would change things, so it would be confusing if you were looking for pure gyroscopic effect tendencies. Yaw (or roll) has its own set of problems mixing together. The V-22 would probably have to have a swashplate sort of system to apply the force 90 degrees before the desired effect since those blades are very long. It would be interesting to look into on that full scale plane. Helicopters do have to compensate for it due to very long blades and the mass at the end of them. Same thing with bicycle tires when we hold them as they spin. The swashplate on helicopters is where this is compensated for. You can also feel some gyroscopic effects from aerodynamic forces such as blowback when the helicopter has a slight left roll and pitch up as it accelerates. The pilot has to apply right roll to cancel the slight rolling tendency for a second or two. This is also called transverse flow effect. It depends on the flight mode. P-Factor is strongest on take off, in flight it is usually very very small except when changing pitch. http://en.wikipedia.org/wiki/P_factor Grysocopic effects or precession is very small except when changing the torque of the propeller then there is a momentary yaw to the left. http://en.wikipedia.org/wiki/Precess...ced_precession In nomal steady state flight the predominate force causing the plane to yaw left is most likely the spiriling slipstream. http://en.wikipedia.org/wiki/Spiral_slipstream |
RE: Propeller weights
{Quote}
Grysocopic effects or precession is very small except when changing the torque of the propeller then there is a momentary yaw to the left. {Quote} BUT, the precession is what induces a Lomcevak (full scale not model----by definition a models precession is not great enough so our "Lomcevaks" are truly NOT Lomcevaks.) Visually they will pass for one but in truth they are not. |
RE: Propeller weights
onewasp,
That is true. They look like one but the entry isn't the same for that reason. The Wikipedia links are very vague. There are better sites that explain both rc and control line gyroscopic precession effects. |
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