pocatosaras

I have an old OS 40 FP engine lying around. I'm currently building a 40ARF and plan on using this engine to keep project costs down.

I'd like to get the most out of this engine, specifically thrust (11X5) vs. pure speed (10X7) (using the 11X5 to accelerate & climb faster, but decelerate faster & be slower in level flight vs. engine reving somewhat higher with the 10X7 increasing the model's speed -- from the effects of both the rev increase & the steeper pitch)

So in effect I'm thinking of going to an 11X5. Am I correct in this assumption or does someone have a better recommendation for this engine?

CliffordH

My Feedback: (9)

I have had FP40s for years and found them to be a solid and pretty much trouble free engine. Not a power house but trouble free and have always used a 10/6 wood prop on them.

Will be interesting to hear what some of the others run on them.

Cliff

burgh_guy61

My Feedback: (11)

As stated they are not power house engines but mine was/is very reliable. I used mainly 11x4, 11x5 or 10x6 i found the 10x7 to be to much pitch for the motor unless it was on a scat cat and it still never seemed to like it. In a smaller 40 size model the 11's seemed to be the ticket.

Timoteo

My Feedback: (3)

11x5, 11x6.

jaka

Hi!
At sea-level, a 11x5 or 11x6 prop works best in a high winged trainer model (Kyosho trainer or Calmato). A 10x6 prop is to small. APC is a good choice.

Regards!

Jan K

Dzlstunter

I ran an FP40 for several years on APC 10X6 props. Easy to needle, nice idle, good enough for an overweight LT-40 or later on a SIG 4* 40 and a SIG Fazer, too. Good luck, Dzl

jaka

Hi!
Yeah! But a 11x5 -11x6 APC is better for a highwinged trainer. An 11" prop will bite the air better than a "small " 10" prop. ...and the sound will be a lot less annoying.
Regards!
Jan K

britbrat

I suggest an 11-4. The FP is not a powerhouse & the 11-4 will give you the efficiency gains from a larger diameter prop, yet allow the engine to spool up to its best operating range. You can expect 12,000 + with an 11-4 (right in the optimum RPM range), but only ~11,000 with an 11-5 & ~10,500 with an 11-6 --well below peak power & torque.

fredscz

My Feedback: (47)

I've used several FP 40's on different planes the last three years. . The 11x5 and 11x6 were way too big. Tried an 11x4, 11x5, 11x6,10x6,and 10x5 on the same trainer type plane on the same day and the 10x5 was the best on that plane that day. You could do the same experiment as props that size are not very expensive.
FEB

jaka

Hi!
As I said earlier...At sea level at around - 20+40 degrees centigrade ...nothing beats an 11x5-11x6 APC when using 0-10% nitro! Then you get a very quiet engine with perfect throttle response and very good pulling power. RPM will be around 9000-10500 rpm. Perfect on a highwinged trainer aircraft weighting around 2,2-2,5kg. These props will not deliver the best speed, but I asume you are not after speed but good stable flying charateristics?!
A 10x6 will not pull it as good making take-offs worse and a 11x4 will pull as good and rew too much (too much noise), and it's not suitable for a trainer...at least not at sea level...

Regards!
Jan K

pocatosaras

Thanks to all for your responses. I went to the LHS and picked up two 11X4 and two 11X5 wood props. Once the plane is built I'll experiment a bit. It'll be a while before the ARF is done though!!

I'll be putting it on a CMPro Staudacher 300. Here's the start of another cruel relationship -- builder/pilot vs aerodynamics/gravity.

britbrat

Sorry Jaka -- I really disagree with you. Pocatosaras said he wanted to get the most out of the engine, particularly thrust. The 11-4 revs the engine right at its torque peak (it is also perfect for a trainer at sea level), while the 11-5 & 11-6 just won't cut it.

jaka

Hi!
I don't want you to be disappointed but the OS LA.40 is not the right engine for this airplane.
It doesn't have the power! My propeller recommendations earlier were for a highwinged trainer airplane ...not for a semi-scale aerobatic airplane...but never the less ..the OS LA .40 hasn't got the power for that model.
You would be better of with a ball bearinged engine.
Ofcourse your OS LA .40 will fly it... but the performance will be so marginal that you will soon be disappointed especially if using a wood prop...as those are inferior to APC:s
You would be better off with a .40-.46 ballbearinged engine.

Regards!
Jan K
Sweden

britbrat

This time I agree with you -- a 46 LA is not really the best choice for that model. Neither is the 40FP that he actually has.

However, considering that he has it, & is going to use it, an APC 11-4 is probably the best choice for vertical work. If the model sags too much from insufficient airspeed, I think that the only realistic options remaining would be either a 10-5 APC (~ 12,500 RPM), or a 10-6 APC (12,000 RPM).

A 9-6 prop would probably achieve peak engine performance (~13,500 RPM), but the small diameter would really hinder vertical flight performance.