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Jan 24, 2009, 12:01 AM
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atmk's Avatar
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Question

what prop for max thrust for OS61fx


I'm trying to get the absolute most thrust form an unmodified O.S. 61FX engine
price and speed are not issues. is there some company that makes extra low pitch props? is wood better than apc? is there some stupidly expensive German carbon fiber prop that kicks everything ass? I'm open to any suggestions...
and of course in the interest of public knowledge i will post thrust numbers for all the props i try.

thanks in advance
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Jan 24, 2009, 09:34 AM
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Wayne V's Avatar
Well i'm sure you could get away with a 20x1 prop to make tons of thrust but at a estimated 10mph pitch speed it won't fly a plane, what kinda goals are you after?, what prop/rpm combo are you using now?
Jan 24, 2009, 08:45 PM
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downunder's Avatar
I don't know about stupidly expensive German CF props but the type of prop you're looking for is much the same as the type of prop used for CL stunt where high thrust is very important. Probably the best CF props in the world for CL stunt are made here in Australia by Brian Eather and come in a huge range of sizes in 2, 3 and 4 blade. Prices are extremely reasonable but you'd have to contact him for the latest prices.

The only link to him is from this page. Click on the Brian Eather button at the top which takes you to a page where you can check out all his props. If you want a particular pitch the Brian will repitch it for you. Likewise, if you tell him exactly what your use will be he'll suggest the ideal prop.
Jan 24, 2009, 08:48 PM
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atmk's Avatar
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right now there is a 14x6 that was got around 9 pounds but it only got to 10,000rpm out of 16,000rpm rating for max power so it over propped.

ok so there is limitations on speed and price but the budget can cover any rc prop i've ever seen as for speed as long as it can pull a really heavy airplane faster than stall its good enough.

i cant even find a 14x4 let alone a 20X1 so if you know of someone that makes a 20x1 please tell me where i can find them maybe they'll make a 16x2 but the point is to focus on propellers that actually exist
Jan 24, 2009, 08:57 PM
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atmk's Avatar
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thanks!! downunder thats something i would have never found on my own
and an awesome selection with pitch increments of a 1/4" so it can really be dialed in
Jan 24, 2009, 10:10 PM
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rodneygt's Avatar
Quote:
Originally Posted by atmk
. . . i cant even find a 14x4 let alone a 20X1 . . .
I bought an APC 14x4W at hobbypeople.net - sometimes my hobby shop has them, sometimes they don't. I run it on a Saito .82 and get about 10K rpm and if I attach my plane to my fish scales, it will pull around 8.5lbs on the scale. I would think you could get more out of it with a .61 2 stroke.

You've still not indicated your application or what you're shooting for.
Jan 24, 2009, 10:37 PM
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atmk's Avatar
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its for SAE areodesign competition. we have to use an unmodified os61fx(no tuned pipe or anything) and there's a bunch of airframe restrictions but the goal is to lift as much weight as possible our goal is to lift 29-31 pounds(not including airframe). so of course thrust = good and speed doesn't matter it just has to get up(take off speed) do a circle and get down
Jan 24, 2009, 10:57 PM
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atmk's Avatar
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Quote:
Originally Posted by rodneygt
I bought an APC 14x4W at hobbypeople.net
cool, so 14x4's do exist, i even found a couple wood 15x4's at tower (both of those are defiantly on the "testing wish list")

so does nay one have opinions of different brands and types of props?
how the wood props like zinger and topflight stack up against APC?
is master aircrew even worth considering?(i've heard they're less efficient)

and of course suggestions for less known high performance props are much appreciated.
Jan 25, 2009, 08:07 AM
Registered User Wannabe
rodneygt's Avatar
Here are some xoar props that include 12 - 17 x 4 : http://www.swanyshouse.com/xoar/props.aspx I've bought a mojo 40 from that site - Paul Swany who owns it is a straight up guy. Some of the probros like these props allot. You might want to look around at theprofilebrotherhood.com and see what they are saying about props - generally they just want thrust.
Mar 05, 2009, 12:29 PM
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atmk's Avatar
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ok we finally did prop testing last night.
we tested some props like 13x7 13x6 even found a 13.5somthing but i forget the numbers. we tried a 14x6 which was way to big
anyway the three best props were:
apc14x4w at 7lbs2oz
apc14x5n at 7lbs2oz
zinger 14x4 at 8lbs 4oz!!!!!

the apc 13x4w did very well also but i forget the number maybe 7lbs1oz

unfortunately we never got any of the Ausi CF props or xoar and we only had the one zinger

so heres a Question WHY IS THE ZINGER WOOD PROP SO AWESOME!?!?!?!!?
most of us still don't believe it can be THAT much better to produce more than a pound of extra thrust.
Mar 05, 2009, 12:57 PM
Registered User
Im sure your realize that this is that this is static thrust. Is this for the AIAA DBF competition? Thrust drops with speed so you may want to optimize for thrust at your cruising speed or takeoff speed or something other than zero speed since planes do not fly at zero speed.

You may want to take a look at how much thrust these props produce at speed. Does your school have a big enough wind tunnel to test the motor? If not does someone on the team have a pickup truck? Mount the test cell somewhere on the truck where the airflow is smooth and measure the airspeed at the test stand. Dont go by the spedometer since carspeed does not equal airspeed.
Mar 07, 2009, 02:50 AM
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atmk's Avatar
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its for sae areo design competition and we are actually at competition as of now so its a little late for wind tunnel testing the numbers previously posted were done by a fish scale on the back of the airplane. we figured that static thrust was the best (and easiest)measure of prop performance because we are at relatively low speeds as long as it get us off the ground (past stall) its fast enough. the dynamic thrust is not out of ou minds it just out of our ability to measure.
Mar 07, 2009, 08:26 PM
Registered User
You may want to try an APC 14x4 from tower hobbies or hobby town. Just modify it. If you reduce the weight by filling down the thickness of the inner sides it will turn faster and therefore produce more thrust. Just make sure you don't change the pitch of the prop. I do this all of the time with my .46AX and a 13x4 APC it works very well.

Let me know if it works for you.

Sorry I don't have any numbers at this time but I will measure the thrust difference and post them.
Mar 07, 2009, 08:30 PM
Registered User
oh and make sure you don't change the camber of the airfoil on the prop. It will destroy the thrust numbers.
Mar 08, 2009, 12:13 AM
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atmk's Avatar
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sorry to disappoint but we managed to crash three times (many others crashed to these are notoriously unstable aircraft)
the first time we snapped a wing which we fixed last night (cause horrible cg placement) the plane took off in about 5' with 5pound of ballast and immediately turned strait up then fell
our first official flight today was with no load it took off with no effort at only partial throttle with a 13x7 (chosen for lower thrust) started rolling and the tailerons(yes tailerons our horizontal tail planes were full flying and differential with no ailerons) didn't have enough authority to do almost anything at such a lw speed it cartwheeled damaging the wings snapping the fuselage in half and ripping off the nose of the plane

we got it looking almost as good as new for for the last run of the day loaded it up with 18.6 pounds the cg was marginal but we went froward anyway. we hoped that the weight would push our take off speed up enough to give the tailerons some role authority well... it took of as if it were a moderately powered normal airplane no effort at all got about 20 up and started to roll a little the correction from the ailerons in the still relatively low speed and tail heavy condition caused tail to stall and the airplane to point up and tumble down resulting in a catastrophic crash

as you can see we wern't in a position to worry about squeasing the last pit of thrust out of our engine but thank you very much for your helpful suggestions


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