Propeller FAQ's
Choosing a Prop for best performance
(Best for .15-1.2 engines!)
Of course you will need a Tach., a spread sheet (or other software for
calculating thrust, HP, and speed ) to determine the “holy trinity” of model
performance. (Speed, Acceleration, Vertical).
To prop for speed
Choose the highest pitch prop between 6 and 8 pitch that produces at
least a 1:1 thrust to weight ratio, and runs at the bottom of the RPM range
on the ground. *
To prop for extreme aerobatic performance
Prop for a speed of 65 MPH - 80 MPH. Bias the speed according to your
model type and personal preferences. Choose a prop between 4 and 6
pitch that produces maximum thrust within the above speed range, and
runs near the upper RPM limit.
To prop for a good compromise
Prop for 10%-15% more thrust than model weight, use the highest pitch
prop possible between 5 and 7 pitch. Prop for the middle of the RPM
range.
That’s it! It works every time! You have my personal guarantee.
Tips and a few thoughts on prop selection.
1.Speed, acceleration, and vertical are the Holy Trinity of performance. All
3 must be in balance.
2.A good spreadsheet and Tach are very handy for figuring max
performance.
3.Knowing the speed, thrust, and HP a motor/ prop combo produce are
keys to propping correctly.
4.Knowing the model’s weight within 2 or 3 Oz is a key to propping
correctly and choosing the right engine.
5.It’s a very common mistake to over pitch. This hurts speed, acceleration,
and vertical.
6.Under propping is not as harmful to an engine as most modelers think.
7.There’s no use propping for more than 10 MPH greater than the model’s
flutter speed.
8.10-15 MPH speed headroom helps acceleration look impressive. You
don't have to use it.
9.Acceleration is rarely considered but important. Good acceleration is a
must for a fun, responsive model.
10.8 pitch prop are rarely correct for smaller models, but often needed on
larger ones.
11.4 pitch props are best for high performance engines. Otherwise they're
too slow, and look sluggish in flight.
12.HP is a great way to predict performance. It translates directly into speed,
acceleration, and vertical.
13.Props that extract highest HP always produce the most exciting
performance.
14.Don’t worry about unloading in the air, etc. Models fly too slowly for this
to matter.
15.To have pleasing acceleration, your max speed must be at least 65 MPH.
16.Accelerating instantly from 20 MPH to 45 MPH is not impressive.
17.Unlimited vertical at 5 MPH is not impressive. At 15 MPH, it is!
18.A very fast plane is no fun if it has less thrust than weight.
19.Always give up 5-6 MPH of top speed in favor of needed acceleration.
20.Speed, acceleration, and vertical are a compromise, and can be biased any
way you wish.
21.Don't totally sell out any of the Holy Trinity. Your performance will suffer
badly if you do.
22.4 Pitch props hurt speed and acceleration, but help vertical for heavy
models.
23.5 Pitch props are usually a great balance of speed, acceleration, and
vertical.
24.6 pitch props are good for speed and acceleration, but vertical suffers
somewhat.
25.7 pitch props are good for speed, but acceleration and vertical both suffer.
26.8 pitch props are only useful for larger models or restricted noise
situations.
27.See suggested RPM envelope for 2 stroke engines below.
Suggested RPM (2 stroke)
15-.36 14000-18000
.40-.53 13500-16000
.61-.90 9500-13000
1.08-1.20 8000-10000
* If you can’t get this level of performance, the engine is not powerful enough.
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