Rate1

Guys help me out.

First of all, I understand that one should try out different props to find the performance wanted. However the cost for a CF scale prop is high and buying 10 different props seams a tad unnecessary with all the combined experience found here at RCU. I'm instead hoping for some advice to guide me to a starting point in the 3-blade CF scale prop market for my engine.

This will be my first warbird project, ESM Corsair 74" approx 16-17,5 lbs, and will put on my OS200FS non pump with a Perry vib pump. I wish to use a big 3-blade prop on it for scale reasons and still be a good performer. I found the Biela 18x10 3-blade Corsair scale prop that I'm hoping I could use. My engine is all new and has never been runned so i know little about it.
Q: Do you think the Biela 18x10 3-blade is too much for this engine?
Q: Which 3-blade scale prop do you think I should go for?
Q: What fuel offer the best power for this engine and could the engine be damaged?
Q: which pitch is commonly used on 74" warbirds? Been flying aerobats earlier I'm used to 6-8 pitch.

OS Recommended props: 16x12N-15, 16.5x12-14, 17x10N-13, 18x6W-12 and 20x8.

In addition, I found a general rule of thumb for props; going from a 2-blade to a 3-blade reduce the diameter by 10%, hence the 20" 2-b becomes a 18" 3-b. I have also found a recommendation that if adding another blade one should increase the pitch with one unit as the additional blade is shading the blade next to it.
Q: does that mean the load will stay the same as the prop is shading itself, or does that mean that you increase the pitch to avoid shading and also as a consequence get bigger load?

If going from 2-b to a 4-b one is recommended to reduce the diameter by 15% and again increase the pitch with one unit, meaning that a 20x8 2-blade would equal a 17x6-7 4-blade. I understand that for the optimal performance one should stick with 2-blad props within the model world due the effect of Raynolds number.

If increase the pitch one should decrease the diameter.

I'm looking for warbird style flying and would be happy with 7500RPM'ish as I understand it would be a good number for this engine which has good torque but not so good revs. I am ready to increase the percentage of nitro if that would help me. Any advice?

Hobbsy

My Feedback: (102)

http://www.zingerpropeller.com/_2_blade_.htm

Here is a chart to help you some, I'll be back.

Another for engine to prop size
http://www.zingerpropeller.com/Convert.htm

Rate1

Thanks, these are usefull charts. To bad it is indicating that the Biela 18x10 3-blade might be a notch too big for this engine.

blw

My Feedback: (3)

Please tell Capt Morgan that you always end up with some percentage of guesswork and experimentation. However, the undesirable props you check out on the Corsair can be used somewhere else one day.

Hobbsy

My Feedback: (102)

Rate, that shaded blade business is part of an Old Wives Tale that was de-mythed many years ago. Since the blades are constantly moving forward into new air, there is no shading/ineffeciency etc. When it comes to power absorbtion a well chosen 3 blade is more effecient.

Rate1

Thanks guys, well too much or not that darn prop is so beautiful I just got to have it anyway. I can always just hang it up for display untill I find a motor big enough for it. Order placed.
I got an APC 18x8 for first running of engine and for maiden flight anyhow.

Emil The Swede

Hobbsy

My Feedback: (102)

http://www3.towerhobbies.com/cgi-bin...?&I=LXCW95&P=Z

The intake spring is 20mm in length with a 6mm ID the exhaust spring is 18mm in length with 6mm ID, the above link is the longer/stronger intake spring.

Emil The Swede

I found that Xoar also have som 3-blades, both 17x8 and 18x8. Not scale, but very good looking. Ad the Hamilton Standard Prop Decal and you are close...

http://magnumrc.com/xoar-m-5.html

magnumrc.com/hamilton-standard-prop-decal-set-p-242.html

Emil The Swede

Rate, How did it go with the prop size? Can you share the test result?