Prop load data
10-19-2015, 12:11 PM
#1
Thread Starter
Prop load data
Just a little heads up for those who like to get into the details of different props and engine power numbers etc.
I've had a closer look at the data from APC themselves (https://www.apcprop.com/v/PERFILES_W...tDatafiles.asp) and there is something strange with the 7x4 prop. Don't know about the other props (there could be similar errors) but here is a plot that illustrates the problem. The red curve is from their data base and it doesn't follow an rpm^3 curve after about 17000rpm.
So these numbers seem more accurate (power in HP = P x rpm^3), and replicate the APC data file for revs below 17000rpm (also shown in the blue curve above);
I've had a closer look at the data from APC themselves (https://www.apcprop.com/v/PERFILES_W...tDatafiles.asp) and there is something strange with the 7x4 prop. Don't know about the other props (there could be similar errors) but here is a plot that illustrates the problem. The red curve is from their data base and it doesn't follow an rpm^3 curve after about 17000rpm.
So these numbers seem more accurate (power in HP = P x rpm^3), and replicate the APC data file for revs below 17000rpm (also shown in the blue curve above);
Last edited by Mr Cox; 10-19-2015 at 12:21 PM.
10-19-2015, 12:20 PM
#2
Thread Starter
Forgot to mention the reason for getting into the details of the APC 7x4 prop...
I have used that as a reference prop for .10-.15 engines, and it has been working fine until a Picco .12 engine spins it at 22000rpm. This would be around 1.15 hp (!) if one were to trust the data file, but a little more reasonable 0.68 hp if one uses the rpm^3 formula.
I have used that as a reference prop for .10-.15 engines, and it has been working fine until a Picco .12 engine spins it at 22000rpm. This would be around 1.15 hp (!) if one were to trust the data file, but a little more reasonable 0.68 hp if one uses the rpm^3 formula.
10-19-2015, 01:15 PM
#4
Thread Starter
Yes, I'm not complaining... 
Here it is with an MVVS muffler making close to 19000rpm:
http://www.youtube.com/watch?v=n7YEtP5cEbI I somehow messed up the video though with the Rossy pipe on it (did around 22000rpm) and only got an image;
Here it is with an MVVS muffler making close to 19000rpm:
http://www.youtube.com/watch?v=n7YEtP5cEbI I somehow messed up the video though with the Rossy pipe on it (did around 22000rpm) and only got an image;
10-19-2015, 07:05 PM
#5
I read 18,491 but you seemed to be doing more of a idle test in this vid, the engine didn't run wide open for long.
Looks good with the tuned pipe 22k static, so unloaded perhaps 24.8
Looks good with the tuned pipe 22k static, so unloaded perhaps 24.8
10-19-2015, 09:59 PM
#6
Thread Starter
Yes, the engine is set a little rich in the video rather than squeezing everything out of it, and it would creep up towards 18900rpm when left longer at full throttle. The video was more for my own documentation of throttle response etc in order to compare with the running with the pipe on it, but then I somehow screwed that up when I used the camera.
Back to prop loads, I plotted the data for the APC 5.7x3 prop in a similar way, and there the data file seems to be correct up to 23000rpm at least (didn't plot higher). There is only a slight discrepancy in the constant I guess;
Back to prop loads, I plotted the data for the APC 5.7x3 prop in a similar way, and there the data file seems to be correct up to 23000rpm at least (didn't plot higher). There is only a slight discrepancy in the constant I guess;
10-19-2015, 10:29 PM
#7
After finding the APC data chart I have been using it for all the APC props seems like good ball park data.
I have a MA 5.5x4 will try for speed with the GS V12RR could do 120mph with it.
Engine system is 214g with pipe and prop / spinner.
Next project is to build a plane for the 10 to 15 size aluminum case engines.
Kris you should try the APC 6.3x4 nice robust prop and should make good thrust with the Picco. Perhaps 24k static with 15% nitro.
I have a MA 5.5x4 will try for speed with the GS V12RR could do 120mph with it.
Engine system is 214g with pipe and prop / spinner.
Next project is to build a plane for the 10 to 15 size aluminum case engines.
Kris you should try the APC 6.3x4 nice robust prop and should make good thrust with the Picco. Perhaps 24k static with 15% nitro.
10-20-2015, 12:13 PM
#8
I may email APC and ask them what they use to test their props I can assume some sort of dyno machine.
It is possible they are using pure base line math per prop type, shape, airfoil, surface area, dia. and pitch.
It is possible they are using pure base line math per prop type, shape, airfoil, surface area, dia. and pitch.
10-24-2015, 11:27 AM
#9
Tested my GS Pro V12RR today with the Russian .09 pipe
APC 6x3 for a closer unloaded est. with a 6.3x4
.6hp / 448w
3.4lbs thrust
28,270 / 80.31mph static.
Estimate 29.6k unloaded APC 6.3x4 / 112 mph -will use for test flights.
6x5 should do around 130 mph - after the plane is trimmed up and flown a few times.
MA 7x5 cut down to 6x5
The engine had no problem instantly spinning the prop up to max rpm the acceleration was clearly
ridiculous and wont test with the 6x3 ever again.
APC 6x3 for a closer unloaded est. with a 6.3x4
.6hp / 448w
3.4lbs thrust
28,270 / 80.31mph static.
Estimate 29.6k unloaded APC 6.3x4 / 112 mph -will use for test flights.
6x5 should do around 130 mph - after the plane is trimmed up and flown a few times.
MA 7x5 cut down to 6x5
The engine had no problem instantly spinning the prop up to max rpm the acceleration was clearly
ridiculous and wont test with the 6x3 ever again.
