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Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Carbon_Rod wrote ...
@Andrew... this needs more cow bell.... much more...
lol!
Carbon_Rod wrote ...
Thrust bending and centrifugal twisting forces aside, In general there will usually be a small fan cut into the motor housing itself to keep the copper insulation from burning off.
the FW-190 has a 12 blade impeller that spins at 3.12 times the props rpm, just becuase the engine cowl was so tight around its radial engine...
on my DT750's the stator is stationary (duh) and the rotor rotates (duh) and that helps cool the motor supposedly.
Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837
Found a nice dissertation on ducting which answered most of my questions ... it turns out only a small amount of gains are from the tip losses and most are from the diffusion gains (ie. the duct widens and spreads the flow relatively smoothly and you benefit according to momentum theory as Bigbad mentioned). For a given diffusion you're always better off just using a larger prop the size of the duct exhaust though, making that almost useless for a quadrotor.
That leaves using a very small duct to remove tip losses, if you can make them light enough, but you'll probably lose all you gain there in horizontal flight because of drag.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Pinky's Brain wrote ...
Found a nice dissertation on ducting which answered most of my questions ... it turns out only a small amount of gains are from the tip losses and most are from the diffusion gains (ie. the duct widens and spreads the flow relatively smoothly and you benefit according to momentum theory as Bigbad mentioned). For a given diffusion you're always better off just using a larger prop the size of the duct exhaust though, making that almost useless for a quadrotor.
That leaves using a very small duct to remove tip losses, if you can make them light enough, but you'll probably lose all you gain there in horizontal flight because of drag.
The Embry Riddle team closed their ducts to within a 1/16 (2mm) of the prop tip and they calculated and found in trials that it gained them 5-8% greater battery life in a hover, but all of our maximum speeds are in the 0.2m/s range for horizontal flight.
Registered Member #2529
Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600
Another thing that could help, given the size constraint is a wingtip device:
They generally do well when you cannot extend the span for any reason, and this would seem to be a classic case of that, but I am uncertain as to how well they really work in practice, they seem quite marginal.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
i wonder if spiroids could be used on the tips slow flyer prop...
spiroid wingtip it does put more loading on the wing tip, the weakest part of a wing or prop, and most prone to unbalance and flutter.
if a normal winglet were used on a small RC prop, i wonder if we could get 8-10% improvement over the same tip on a 747, since our smalll models move larger volumes of air per unit of mass than a 747 which gains only 5% from a winglet.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
pinky, you mean a box wing...
heres a vid of the spiroid... 10% better fuel economy, supposedly.
pics: APC prop, 10x3.8 slow-flyer, for testing.
a winglet!!! using heat. (glass fiber and nylon prop)
first, i wonder if i can make uniform, well balanced prop winglets using a positive and negative mold clamped together....
second, i wonder if i could clip a half inch of the 10" prop, then add 2 inches of carbon fiber curved over like in the spiroid design... this way we multi rotor operators would have a 10" physical diameter, but a 13" aerodynamic diameter!?!?
Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837
How about a 3D printed prop? I see CSU has an ABS FDM printer, ideally you'd use PC ... but if you have the carbon fiber material thin enough to make the spiroid you could just add it to the 3D printed prop as well if the ABS is too flexible.
Do you have a prop balancer?
PS. I don't think trying this with prototypes is going to get you very far, you just can't have enough design iterations ... unless by chance you have a good design on your first try. CFD is the obvious solution, but again you're looking at an awful lot of time investment.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Pinky's Brain wrote ...
Do you have a prop balancer?
PS. I don't think trying this with prototypes is going to get you very far, you just can't have enough design iterations ... unless by chance you have a good design on your first try. CFD is the obvious solution, but again you're looking at an awful lot of time investment.
dont have prop balancer, and i think you maybe right, also teh winglet may just unbend or shred due to rotating forces.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Patrick wrote ...
Does anyone see what i mean or is all this just trivial?
Propellers (certainly marine screw propellers) are measured in diameter and pitch. The pitch is the theoretical distance the prop 'moves' in one revolution, so as the diameter increases, the blade angle must decrease for uniform pitch.
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The Physics Of Propellers (And Electrical Motors).
