Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

Props Less Pitch more RPM or More pitch LessRPM

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Old 09-11-2003, 09:28 PM
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LUDS96
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Default Props Less Pitch more RPM or More pitch LessRPM

I'm trying to make a prop decision! If I run an 11x9 it turns 11,700 That works out to be 105,300 inch's per minute! It would take an 11x8 13,162 to turn the same distance! I'm runnig a super tiger ninty with a pipe. Should I try to get it to turn 14,000? It may with the 11x8 if I can get the pipe to come in! Thats 112,000 inches per minute! Or theoretically 106.06 Miles per hour! In a perfect atmosphere no drag!
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Old 09-11-2003, 10:49 PM
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Default RE: Props Less Pitch more RPM or More pitch LessRPM

Here is a quick formula for calculating speed for a pitch at rpm.

RPM X Pitch Inches X .000947 = Speed (MPH)

I would try to get it to turn up a bit more and get some more power out of the engine.

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Old 09-12-2003, 12:08 PM
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Default RE: Props Less Pitch more RPM or More pitch LessRPM

I don't know if you'll get 14,000 out of a super tiger 90, I'd be very surprised if you break 12,500. You might with a pipe, but the 90 wasn't really ported for that, you may need to raise the exhaust timing to do that but I'm not sure. All I know is that my ST 90 blew the rod at 11,900 when I was running it
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Old 09-12-2003, 03:00 PM
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Default RE: Props Less Pitch more RPM or More pitch LessRPM

So Jeremy maybe I should be happy with 11,700 and tune up from there and keep away from the 11X8
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Old 09-12-2003, 03:05 PM
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Default RE: Props Less Pitch more RPM or More pitch LessRPM

Nice quick formula! Same results less work!
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Old 09-12-2003, 03:08 PM
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Default RE: Props Less Pitch more RPM or More pitch LessRPM

I would actually try a higher pitch, say an 11x11 narrow. I doubt you'd lose much if any RPM but it would give you a higher top speed in the air, it will make take off's take a little more distance though.

The thing you have to remember is that it will unload quite a bit in the air, specifically in a dive, that's when I blew the rod in mine. The ST90 wasn't developed for speed unfortunately, it's a great sport engine, but not a speed a engine.
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Old 09-12-2003, 03:32 PM
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Default RE: Props Less Pitch more RPM or More pitch LessRPM

I think I will work around the 11X9 for now! I have the 11x8 but I agree it will unload in the sky!

Super Tiger Ninty:

SPECS: Bore: 1.803" (27.5mm)
Stroke: 0.976" (24.8mm)
Weight w/o muffler: 589g (20.66oz)
Weight with muffler: 765g (27oz)
Displacement: .90 cu in (14.73cc)
Output: 2.5 bhp at 14,800 rpm
RPM Range: 2,500-16,000
Width between centers of mounting holes: 50mm (1.97")
Length between center of mounting holes: 20mm (.79")
Width of crankcase excluding mounting flanges: 42mm (1.65")
Length from backplate to front of drive washer: 97mm (3.82")
Height from bottom of crankcase to top of head: 108mm (4.24")
Crankshaft size: 5/16"-24
Suggested prop size: 12x8, 13x6
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Old 09-12-2003, 03:40 PM
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Default RE: Props Less Pitch more RPM or More pitch LessRPM

I have looked at their practical RPM range too, I just can't see that engine turning that high in all honesty. I used to typically run a 14x6 for sport flying, but tried 11x10's and stuff as well with some success. I would try to keep it proped for no more than 12,000 on the ground and let it do it's think in the air
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Old 09-12-2003, 04:07 PM
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Default RE: Props Less Pitch more RPM or More pitch LessRPM

Advice not taken should not be asked for!!!! I'll try to get twelve out of it with the 11X9 if it rev's higher I'll go with 11X10
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Old 09-12-2003, 06:27 PM
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Default RE: Props Less Pitch more RPM or More pitch LessRPM

Well tuning session over! Cut a few more pieces off the pipe about 3/4 of and inch! Turning 12,600 with the 11X9 got six hundred out of the last 1/8 inch! I can hear the engine changing it's note! I'm sure if I trim it some more it would crank higher! But enough is enough! That's 107.39 more than I could hope for with the 11X8 at 14,000! So I'll save the engine some stress and hopfully it will last!
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Old 09-12-2003, 08:14 PM
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Default RE: Props Less Pitch more RPM or More pitch LessRPM

Nah- keep going! [8D]

Go until the RPM's do not increase-

Have fun,
james
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Old 09-12-2003, 08:21 PM
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Default RE: Props Less Pitch more RPM or More pitch LessRPM

Jeremy and Razor you don't agree! I don't want to break it! Thats what I read keep cutting till it slows down. Jeremy says it will slow to Sudden Stop! I'm trying something different in my Later years. If it works don't break it! But I feel the need! To much Top Gun
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Old 09-12-2003, 09:23 PM
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Default RE: Props Less Pitch more RPM or More pitch LessRPM

If it were me, I would prop it to run about 13 - 14K on the ground and let it rip.

MY .46fx is turns 15800 on the ground and has been singing in the air @ 20k for two years.

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Old 09-12-2003, 11:07 PM
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Default RE: Props Less Pitch more RPM or More pitch LessRPM

IT's a Super Tiger 90 From the orient
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Old 09-13-2003, 02:00 AM
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Default RE: Props Less Pitch more RPM or More pitch LessRPM

Just because mine blew up doesn't mean yours will, I could have had a bad one, I could have ingested something, I don't really know. I'm honestly surprised at the amount you're getting out of a ST90, but all the better! Just be sure to keep it rich (just at that point before it goes off the pipe) on the ground so that it won't lean out in the air, you don't want to seize it or blow a bearing either.

As I say, I could have had a bad engine, or maybe even just one to many runs, I guess my personal opinion is I don't try to use non speed engines for intense speed, but if it's working, then work it!
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Old 09-13-2003, 11:13 AM
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Default RE: Props Less Pitch more RPM or More pitch LessRPM

46FX is probably the sweetest motor I've ever owned! but this ST 90 is looking Real Good. I have one resting waiting for as new projectile to ride on! Patriot is under the bench!!!!!
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Old 09-13-2003, 12:44 PM
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Default RE: Props Less Pitch more RPM or More pitch LessRPM

MY .46fx is turns 15800 on the ground and has been singing in the air @ 20k for two years.
with what prop are you getting these numbers at? Unloading to 20 K in air? Thats almost a 5000 rpm unload...... Are you talking about a 46 FX basic sport engine or a Jett 40? Not saying it wont but the numbers just dont add up.
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Old 09-13-2003, 04:31 PM
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Default RE: Props Less Pitch more RPM or More pitch LessRPM

.46fx, 9x7

the plane is clean and really unloads in a dive. the rpm is just a quess. what do you think it it reving too?

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Old 09-13-2003, 05:33 PM
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Default RE: Props Less Pitch more RPM or More pitch LessRPM

I doubt the .46 unloads nearly that much, but 16,000 on the ground is quite realistic. We prop this engine to run in the mid 15,000 range with a variety of props in the 8 3/4" x 8.5 range.
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Old 09-14-2003, 08:49 AM
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Default RE: Props Less Pitch more RPM or More pitch LessRPM

I am not so sure that it does not unload that much.

My Sonerai turns 3400 static on the ground, but drops to 3200 during the takeoff roll when the prop unstalls. Full throttle straight and level it will turn 4K. Thats 800 rpm just running level. If I pointed the nose a the ground full power for 1000', not only would my wings depart, but the engine would overspeed several thousand rpms.

How could I practically measure how much the .46 unloads. BTW, I have switched to an 8.5x8 but have not had a chance to tach it yet.
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Old 09-14-2003, 10:12 PM
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Default RE: Props Less Pitch more RPM or More pitch LessRPM

Great Day 11X9 Worked Awsome! Pipe worked Great! Sealed the control surfaces NO Flutter at all even in a Power dive! This thing was COOKING
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Old 09-15-2003, 06:46 PM
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Default RE: Props Less Pitch more RPM or More pitch LessRPM

If you take a stock 46 fx and start it up without a prop (you can use a disc as a flywheel or something)... it will not go to 25 or 30 Krpm or something like that, because it is not ported like that. The power curve goes down quite abrupt once you pass the point of maximum power... this is because scavenging suffers at higher rpm with an engine ported for lower rpm... it suffers so badly that at a certain point the engine will not go any faster and all the power is needed just to keep going...

PS: if you don't believe me, and decide to test this... don't run your engine for 5 minutes without a prop...

PPS: and I don't think your Sonerai will overspeed several thousand rpm... your valves will start to float before it comes to that I think...
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Old 09-15-2003, 08:42 PM
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Default RE: Props Less Pitch more RPM or More pitch LessRPM

Ah, did not realize the porting was the issue. How do I change the porting? hehe.

As far as the sonerai goes, it will rev till about 5.5k - 6k before the valves will float )but I would have to look into that), and even if they do, the air rushing past the prop will continue to spool up the little VW till it goes k-boom. I can tell you that taxi power in a fairly shallow dive gets it up to 180mph without a problem.

I am considering trying a 10x6 but don't want to give up the extra speed the 9x7 gives. At 5.5 pounds, it will almost go straight up with the 9x7.

That does it, how do I port the FX to rev better?

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Old 10-05-2003, 09:33 PM
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Default RE: Props Less Pitch more RPM or More pitch LessRPM

Super Tiger Ninety Breaking in! WOOW Tached 12,600 Static today! Sounds Awsome with the Pipe!!!
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Old 10-05-2003, 10:08 PM
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Default RE: Props Less Pitch more RPM or More pitch LessRPM

Based on that formula my Patriot swinging a Jett-50 16.5K (9x9) puts it about 140MPH (??)

Didn't think I was anywhere near that-
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