medicap

My Feedback: (11)

The pinch test worked!! Oh my word, what a smooth running engine. Life is good.

Thank you for all the advice. I ordered some 15x6 props too so will really be in business.

Steve

medicap

My Feedback: (11)

An addendum to all this. I went from a 14x6 prop to a 15x6 prop and A) got a bit more thrust B) the engine even idled better I suppose the extra mass helps keep it rotating? Anyway, the only downside was the APC 15x6 did not fit in my aluminum spinner without modifying the spinner and enlarging the openings a bit. I did equal on both sides to keep it in balance.
In the future, are there spnners that fit the larger blades like this? I am sure that there are......... Also, what advantage if any does a 3 blade prop have over a 2 blade. What size would you recommend if I got one? I own a Cessna 210 and have 3 blade prop on it but there are people adamant on both sides of the question about if a 3 blade prop should go on a Mooney for instance ionstead of the stock 2 blade. More climb but less speed? Anyone have any data for R/C?


Thanks for the advice

da Rock

Glad you tried the larger prop. Consider that you increased the area the prop sweeps by a whopping 15% with that one change.

What advantages do 3 blades give? The problem we have is a deathly lack of 3 bladed props in any size. The combinations of engine to airplane are vast so we really need even more props than we already have to have a chance to match whatever engine we happen to be running on whatever plane we've got. For my 91FXs right now, I've got a grand total of 3 three bladers that come close to being worth testing. For my 75AX on the Extra300, I've got two. The 61 has one. Yet, my prop testing on all 3 engines (on the planes they're on right now) has proven at least one 3 blader ranks in the top couple of props that work "best". OK, sermon over................

3 bladers are quieter.

If your engine/plane combination has the power loading, very often a 3 blader will provide the extra blade area the combination can use but can't get from the two bladers that fit the combination.

They solve ground clearance problems.

Testing shows they're very often equal or better than the 2 bladers available. So in practice they're basically like having another 2 blader to try, and the theoretical differences really don't mean much in our limited model world.

You're going to hear that 2 are more efficient than 3. That is true. It also misses the point that the difference is slight and the variance in performance in model props is significantly greater. We ran some tests on a batch of props the other day. All were identical diameter. All were "identical" pitch rating. The difference we got in rpm and power draw (on a brushless motor) were fairly large. The differences were far greater than the slight efficiency loss an extra blade gives. So if a batch of "the same" props varies so much, and you were lucky enough to even find a 3 to test, don't be surprised when the 3 performs better than most (or all) the 2s. It's just luck that you could find a 3.

Kostas1

Nice Steve !!

Show us your airframe , where you use the O.S. !

da Rock

Matching ANY prop to your model (or Mooney) is a search to find enough blade area to absorb the power of your choice of engine efficiently, to operate in the rpm range your engine is going to give based on the airframe you happen to want it to pull around at the speed you're wanting.

I've found over the last few years that my 91FXs all have done great with a Master Airscrew 14x7(3). Their 14x9(3) did ok in winter but was too fast, and did ok in summer but not as good in summer as the 7" pitch. The 9"pitch in summer wasn't even as good as some of the 2 bladers. Guess that proves the efficiency BS. yeah, right

BTW, don't let MAS's recommendations cause you to try too small a 3-blader. They say their 14"ers work on 1.5-1.8 engines. Jeez, they work great on my 91FXs. I'm guessing they wrote those recommendations some years back.

I've not gotten around to trying a Graupner I found some months back. It's got appreciably more blade area than the MASs, so I'm expecting the one I found to be too much load. That'll hurt rpm probably. But I know that I won't know about that until I get around to testing it. The pitch numbers so many of us take as gospel often are just words of the devil.

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hi are you still up for giving some of your expert advise

j.duncker

My Feedback: (2)

First of all welcome to RCU.

You have replied to 4 year old thread. It would be better to start a new thread and describe your problem in detail. Someone will come along with an answer, that is what RCU is about.