FMS P-51 4 blade vs 2 blade - RC Groups
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This thread is privately moderated by LICobra, who may elect to delete unwanted replies.
Jun 24, 2012, 11:17 AM
Warbird Enthusiast
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FMS P-51 4 blade vs 2 blade

Because of the discussions about speed of the FMS 1450mm P-51...or the lack of....I decided to test the FMS version 6 (500kv motor) with the stock 4 blade against an APC 14X12 2 blade.

I know alot of people say it sure looks like it's going XX miles per hour....and there usually way off as I would have thought different also.....but I will say this....a Parkzone P-51 going an actual 70 mph looks so much faster on a low fly by then an FMS P-51 going by at the same 70 the much larger airframe makes it look so much with that said...

I took my V6 out this morning at 7am as it was already hot but there was zero wind, so I thought it was perfect for a prop speed test using the Voltron GPS data logger which gives accurate top speed , highest altitude, flight time and duration.

I static tested, then (GPS) flight tested both stock V6 4 blade and an APC 14X12 2 blade with the stock 500 motor and a 3600 4S 25C lipo....each test consisted of flying a 2 direction full throttle pass using 2 lipos for each prop.
I recorded the average of both lipos.

The stock 4 blade static tested 58.92 amps, 5900 rpms @925 watts with a calculated pitch speed of 55
The stock 4 blade actual in-flight GPS test logged an average of 62 mph

The APC 14X12 2 blade elecrtic prop static tested 42.62 amps, 6300 rpms @ 672 watts, with a calculated pitch speed of 71.
The APC 14X12 actual in flight GPS test logged an average of 73 mph...

The 4 blade seems to unload and gain some speed over the static test. and now we know if we remove the 4 blade and replace it with a 14X12 you'll get an instant 10+ mile per hour increase along with less amp consumption.

I know I can hear the skeptics now....and I agree....the stock 4 blade looks like its going 40 mph....but it's not.
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Jul 31, 2012, 07:34 AM
Head NEAT geek
Tom Hunt's Avatar

one cannot test deep pitch props statically. Pitch/Diameter ratios above .8 (14 x 12 = .85) are partially to fully stalled giving one false power and rpm readings than if they were moving just a few MPH through the air.

That is whay it is omportant to FLY the props and get power, RPM and airspeed data from either an Eagletree system, or at least an ICE controller and a radar gun (on a clam day or do upwind/downwind averages).

Aug 20, 2012, 01:19 PM
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I like what you're doing LICobra! I'm highly interested in the FMS P-51 prop and also any comparison between multi-blade props and standard 2 bladed props for that matter. However, I keep hearing things like what Tom is saying.... that high pitched props are stalled or nearly so doing static tests. I don't know for sure this is a fact (although I'm inclined to believe it is) and I also don't know exactly what that means. Did you get any in flight data other than the airspeed? I am very curious to how a static test compares to an in flight test, primarily what the Amp Draw difference is. I do like how you had the pitch speed and real speed recorded... thats cool, but I'm wondering if say the FMS prop is pulling 60A static, will is pull 70A in flight because its stalled, or is it pulling more on the ground? Kind of a big deal when you're pulling 55A static on a 60A ESC.... (Although I flew mine and it didn't explode so I'm drawing conclusions that the static test was higher than in flight amp draw or close to the same )

Aug 23, 2012, 05:01 PM
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Eric...I think the testing is fun, but like you I question it's accuracy. Tom tested his FMS back in the early days with his Castle Creations ICE ESC in-flight data recorder and recorded basically the same rpms static and he did in level flight.....only the amp draw and watts were lower as the prop unloaded in flight.

I doubt the amps will be higher in flight then they would be in static testing. Since I don't have in flight testing capabilities, I took my static rpms and converted them to pitch speed.....the Voltron gps only gives highest achieved speed and height....but the speed was very close to static calculated pitch speed on several of my like you...I'd really like to know more with the in-flight data...and compare at least my level top speed to the GPS.
Dec 02, 2012, 05:42 AM
Registered User
How did you get the 2 blades to fit into the original spinner? I have version 8 of the P51 and trying with an APC 14x10 / APC 15x8 and the motor axle is too short to mount the prop securely.
Dec 07, 2012, 03:12 PM
Registered User
Adapter styles original and what is needed

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