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SJ50, need to slow that plane down.

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Old 05-25-2008, 07:41 PM
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still4given
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Default SJ50, need to slow that plane down.

You probably don't get this request too often, but I'm looking for a little advice as to the best way to approach this.
I am flying my SJ50 in a Phoenix Strega in our warbird racing. It is not quite fast enough to be competitive in Silver class but it breaks out too easily in Bronze. I tried playing cat-n-mouse at the last race but still ended up breaking out twice. I'm running an APC 9x9. Would you stay with 9" and go to a smaller pitch or switch to a 10" prop?

Thanks, Terry
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Old 05-26-2008, 02:14 PM
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Default RE: SJ50, need to slow that plane down.

Well... that is understandable

It is sorta like bracket racing.

Put a 10x6 on it. Engien will run fine, and your lap speed will probably drop just a bit.

The other side is... try a 9x7 on it.. and see if you can break clean into silver class with it. might just hit that special note and take off on ya. (although I think you tried that once..)
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Old 05-26-2008, 05:55 PM
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Default RE: SJ50, need to slow that plane down.

To be honest, I haven't tried the 9x7 since I got the gold pipe. It seemed slower before with the red pipe. Is the gold pipe tuned for higher RPM? Worth a try I suppose.

Thanks, Terry
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Old 05-26-2008, 10:23 PM
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Default RE: SJ50, need to slow that plane down.

yes, the gold pipe will really let that thing turn.

give it a try both ways

I am pleased that things seem to be running well now.....

Bob
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Old 05-26-2008, 10:46 PM
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Default RE: SJ50, need to slow that plane down.

I'll try it next weekend. I have a few props I can try. The tough part is flying identical laps so the time means something. I have a few props I can try. It is turning the 9x9 at 16,400. I bet it will pull the turns better with a lower pitch if I don't lose too much top end.

I have been using a CMPro Zero with a YS 1.10 for Silver but I lost it last race. It would be nice if I can get the Jett Strega up to Silver speed. Looking forward to trying a few different props now.

Yes, the SJ50 is really running well. Thanks for all your help.

Blessings, Terry
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Old 05-27-2008, 10:45 AM
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Default RE: SJ50, need to slow that plane down.

Good deal.....

At 16,400 the engine is barely staging on the gold muffler. Probably hitting good rpm in the air, but chances are the plane is slowing down a bunch in the turns, the engine lugs down, and you lose performance/rpm exiting the turns. Then it takes a period of time for the plane and engine to get back up to speed.

For the gold muffler look for ground rpm up over 17,500 at peak ..... even more is better

Keep in mind, about 1/3 of the race (even your event course) is spent turning in the corners.

The 9x7 turning that high will outperform the 9x9 out of the turns on exit speed, and will hold speed well in the straights. If your racing line is a bit... inconsistant? ....... this will minimize mistakes and will recover more quickly. You may see the lap times drop even if it looks like speed is the same.

The 10x6 will give you pretty consistant speed all around the course.

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Old 05-27-2008, 12:18 PM
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Default RE: SJ50, need to slow that plane down.

Hey Bob, sounds good. I'm sure the 9x7 will get up there. I just wasn't sure about the drag of the plane.

My son flies the same model Strega with a TT .46Pro w/Ultra Thrust racing muffler and an APC 9x8 and he is breaking out of Bronze too. He needed the extra speed at first but now he's getting too good in the turns. I'm thinking about throwing a GMS muffler on that TT 46 to slow it down a bit.

I'm thinking of clipping the wings on the Strega with the SJ50. I can lose 9 inches in span and still be legal. That and the smaller prop may just get me to the front of Silver. I'll report back after this weekend and let you know how it does.

Blessings, Terry
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Old 05-31-2008, 04:48 PM
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Default RE: SJ50, need to slow that plane down.

Well I flew it this morning. I didn't get a chance to time it with the 9x9 but I did time it with the 9x7. I was pleasantly surprised. It turned in a 1:58 for 10 laps. Then I tried the 9x8 and turn a 1:59. Just for kicks I threw on a 10x6 and much to my surprise, it turned a 1:55. The weird thing was that the 9x7 spun 17,400 and the 10x6 was only turning about 16,400 on the ground. Of course, these are all so close that just flying better turns could make the difference but I do believe that the 10x6 was better through the turns and that made the difference.

Blessings, Terry
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Old 06-02-2008, 09:41 AM
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Default RE: SJ50, need to slow that plane down.

Now that is more like it

Yeah, the corner exit speed is everything. Especially with a big plane. Looks like you found a good match up. Flying better helps too [&:]

I am pleased to see that the differences were apparent. I think you saw how the 10x6 and 9x9 basically turned the same rpm, but how the "6" pitch was effectively quicker than the "9" pitch in this application. And importantly I think you have found the boundaries you will want to work with.

what you found there is the muffler "shelf" - where the pipe stages. See how it jumps from 16,400 to 17,400 ? It is ok to run down at 16,400..... as you saw as long as you are not greedy tweeking the needle for rpm. In the air the engine will quickly unload up to 17,000....., fully stage on the muffler, and from there will build some torque and take off even higher.

The gold muffler has a higher rpm band than the regular muffler, so you see that step/shelf/peak higher.
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Old 06-03-2008, 05:47 PM
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Default RE: SJ50, need to slow that plane down.

I was quite amazed at how fast it was with the 10x6. It kind of went against all the logic I had heard about speed vs torque. Seemed odd that a 9" pitch turning the same RPM as a 6" pitch would not be faster but the proof is in the pudding. I will rely on trial and error from now on when it comes to props. This SJ50 just keeps on amazing me.

Thanks for everything.

Blessings, Terry
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