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US 40 - Jett 60LX radar numbers - Prop Question.

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US 40 - Jett 60LX radar numbers - Prop Question.

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Old 05-05-2009, 10:47 AM
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dithersail
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Default US 40 - Jett 60LX radar numbers - Prop Question.

Hi All,

question regarding my hyped up US 40 that I built last winter that I have now flown some. Jett 60 LX power. Details of plane can be found in this thread

http://www.rcuniverse.com/forum/m_31...2Csport/tm.htm

Finally was able to get some radar numbers yesterday at field. Friend with gun was there and we got a bunch of readings both up and downwind. Conditions, 60 degrees, wind 0-8mph. APC 9x9 standard pattern prop, 10% nitro cool power. Running just slightly rich, I already burned up a glow plug after a couple flights leaning out too much. Even tweaked slightly rich it gets on the pipe and screams.

We got some truly impressive readings. Upwind in the 122-123 range consistently. Top of 129, average of 126. These numbers we expect are pretty close (we have used gun a lot - especially lately a lot of messing with EDF jets) and may be a little low - we never got a reading with the plane coming directly at gunner - I can't blame my friend the thing is a missile.

So we decided to put on a 9x8 APC just to see what we would get, speed dropped into the 115 range.

So my question is for all you speed guys, I think the 9x9 is about right (?). But should I get a APC racing prop or other brand to play with. And with a "better" prop how much more speed could I squeeze out of the setup?

It's plenty fun to fly, makes me LOL while it's up. It sounds and looks so good when it streaks by. But maybe I can get it to blur just a little more.
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Old 05-05-2009, 10:57 AM
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Default RE: US 40 - Jett 60LX radar numbers - Prop Question.

send Dub and email and ask what he thinks, or Bob27s here. Both should be able to give you the proper prop for that combo.

I would suggest at least running Omega instead of the Cruel Power. A little castor is good for these things.
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Old 05-05-2009, 11:09 AM
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Default RE: US 40 - Jett 60LX radar numbers - Prop Question.


ORIGINAL: dithersail

So we decided to put on a 9x8 APC just to see what we would get, speed dropped into the 115 range.

So my question is for all you speed guys, I think the 9x9 is about right (?). But should I get a APC racing prop or other brand to play with. And with a "better" prop how much more speed could I squeeze out of the setup?
Some will take you to task for running Cool Power aka Cruel Power in your nice Jett. (Ah, DaveN already did while I was slowly typing I see..)

APC sport props are actually very efficient. One issue you may run into is that the US40 has more frontal area than most or all racers. In order to make use of the thinner pylon props you need low frontal area. Otherwise, it is quite common that the sport props can perform better on many aircraft die to greater blade area. Unless someone chimes in and says "I did this to my US40 and it works" my suggestion would be to try one, simple as that - 8.8" x 8.5/8.75/9.0" I'd say would be the starting range. Just keep those ground rpm up where Jett says to and don't bake it lean. What was static rpm on those two props you tried?

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Old 05-05-2009, 01:32 PM
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Default RE: US 40 - Jett 60LX radar numbers - Prop Question.

APC makes some 9 1/2" Narrow pylon props, I'd start there, get several pitch sizes and experiment.
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Old 05-05-2009, 01:35 PM
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Default RE: US 40 - Jett 60LX radar numbers - Prop Question.

Cruel Power - Amen! Yes I have heard this, let's just say I will add a splash of castor for next time LOL. I do have some cooper's 10%, which I know has castor - I'll run that next time.

Static RPM on the 9x9 was 17,300. I don't have numbers on the 9x8.

I'll see if I can dig up some of the prop sizes and types you indicate and see what happens.

Soon after I posted I emailed Dub directly - he answered almost immediately. He indicates that if the motor seems to like the 9x9 on the plane, then try cutting it down gradually to see if it can attain 18,000 static. I have heard of this being done - Have you or anyone tried this? Maybe a thread on how to do it properly?

I did mention that I was using Cruel Power, he didn't say anything about that.
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Old 05-05-2009, 02:39 PM
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Default RE: US 40 - Jett 60LX radar numbers - Prop Question.


ORIGINAL: dithersail

Cruel Power - Amen! Yes I have heard this, let's just say I will add a splash of castor for next time LOL. I do have some cooper's 10%, which I know has castor - I'll run that next time.

Static RPM on the 9x9 was 17,300. I don't have numbers on the 9x8.

I'll see if I can dig up some of the prop sizes and types you indicate and see what happens.

Soon after I posted I emailed Dub directly - he answered almost immediately. He indicates that if the motor seems to like the 9x9 on the plane, then try cutting it down gradually to see if it can attain 18,000 static. I have heard of this being done - Have you or anyone tried this? Maybe a thread on how to do it properly?

I did mention that I was using Cruel Power, he didn't say anything about that.
Don't be scared of doing this, just be safe and methodical. For small amounts of trimming you can simply cut square and sand off the fuzzies with 600 grit paper. Devise a way to do it symmetrically and consistently and you should be fine - like a bolt in a board with the cutter/sander/whatever device you use at the appropriate radius from the bolt center. You should rebalance if you have a balancer. If not you ought to invest in one. Try reducing the diameter by 1/4" and note the change. Then extrapolate from there, maybe home in by 1/8" steps. You could trim the prop to 7-1/2" and pin the throttle and the engine probably wouldn't give a hoot. But don't.

Once you learn something about the pitch and diameter combination that seems to work well, you could look to see if there is something closer to that configuration in box stock form, in the same line of props preferably, but if not experiment with other brands of trusted quality. The prop blade design is a package from root to tip, so the more you trim the greater the potential for messing up efficiency. Obviously not all clipping jobs are equal, and the compound curvature of APC props esp. for example makes them a challenge to reshape. But minor changes aren't worth lying awake at night over.

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Old 05-06-2009, 02:31 PM
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Default RE: US 40 - Jett 60LX radar numbers - Prop Question.

With the stack of exhaust spacers in there, about 17,300 ground peak is pretty much perfect. Without the spacers, target is indeed 18,000 rpm.

Try and keep that target. Engine should unload up around 18,500 in flight.

The smaller prop cant really unload. Likely why the 9x8 slowed down.

Next step, try a 10x7, 9.5x7.5 D-1
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