3 blade prop...help!
 

Howy everybody..
hope-in you can help me with a thought I have with my 74" cessna 310q Im finishing up.I would like to go to a three blade prop on my twin o.s.46 la's in order to keep my spinner size down.I think the plane look's better with a smaller,pointy spinner.Fits my engine nacelle outline better too.It's a big,heavy plane!.I did a poor job of planking and have tried to make up for it with fiberglass so I don't want to down grade the engine any.O.S. call's for a 11x6 or 11x7.It's a 16,000 rpm engine.I would appreciate any input! thanks Bob

RE: 3 blade prop...help!
 

If you're worried about the plane being overweight, you'd be better off maximizing the efficiency of the props than minimizing the size of the spinners. It's pretty widely accepted that a 3 bladed prop is less efficient than a 2 blade.

RE: 3 blade prop...help!
 

http://www.hobby-lobby.com/grprop.htm#3%20Blade

These guys will look good and pull hard, either the 9x7 or 10x7.

RE: 3 blade prop...help!
 

Look I don't believe in that way less efficent stuff. If they are so inefficent why are dropped down 1 size and 1 pitch. Use the dubro pointed colored aluminum spinners and a 9x6 or 9x7 3 blade and go fly. You'll have good RPM and at 1/2 to 3/4 throttle they will have great effincency. OH by the way don't tell your engine he's 3 bladed , CAUSE HE WON"T KNOW THAT, THEY will love those props. 9x7 will be a little bit better than 9x6

RE: 3 blade prop...help!
 

They do have less efficiency, but an insignicant amount. The problem with multi blade props is the poor selection of size and pitch.

RE: 3 blade prop...help!
 

There is no real aerodynamic rule on props for what we are doing. Generally, a 3 bladed prop may be less efficient. But, there are advantages. They may have better vertical pull. They do have better braking action with throttle reduction. Pattern flyers like the braking on vertical downlines. This is something you just have to try out and see for yourself and your particular plane and engine(s). You may find the ideal prop for the model but it sucks because the engine doesn't like it. You may have to try several different pitch/diameter variations before you hit upon the ideal prop. Sometimes you can suggest a certain prop and it works great, but sometimes it doesn't.

RE: 3 blade prop...help!
 

Hi!
As You have OS .46 engines the proper 3-blade prop would be a 10x6 , that if you fly at sea level. I don't recommend 3-blade props though as these are always inferior to two bladed ones.

I flew a Marutaka Cessna 310, 25 years ago with Enya .40 X engines and these were much to strong for it. But the airplane was very easy to fly.

Regards!
Jan K
Sweden

RE: 3 blade prop...help!
 

The 46 LA is not a 16,000 RPM engine -- that is just OS advertising (like the imaginary 1.2 HP). It develops peak power (~1 HP)@~13,500 RPM. An 11-6 2-blade is far too big for that engine to develop peak power -- it will turn ~ 11,000 with that prop & an 11-7 is the far side of the moon. A more realistic prop on that engine for peak power would be an 11-4 2-blade, or a 10-6 2-blade -- they will spin at ~13,000 -- right where that engine needs to be with a heavy model.

If you can find one, a 10-4 3b would be the right size for ~13,000 RPM, but realistically the 46 LA is not well-suited to 3-blade applications -- it just doesn't have enough grunt.

RE: 3 blade prop...help!
 

Jaka it's an OS 46 LA not an FX or AX.

RE: 3 blade prop...help!
 

Jaka- you should say that a 10x6 *MAY* be the ideal prop. Comments like this have little value as you don't know if he wants to fly sport, pattern, or 3D.

Also, saying that 3 bladed props are always inferior shows a lack of understanding of how props work.

RE: 3 blade prop...help!
 

This is a Cessna 310 -- it isn't going to be doing 3D, or pattern flying. It may, however, have to fly on one engine -- reaching peak power & efficiency with those weak engines is going to be important in that nasty scenario.

You are quite correct that a 10-6 3-b MAY be a good choice (personally, I doubt it, it won't let those 46 LA's reach peak power), however, I'm quite sure that Jaka knows very well how a prop works -- like a lot of us -- yourself included.

RE: 3 blade prop...help!
 

I'd use 10-7 Master Airscrews on it, and spinner nuts like this one. ;)
I wouldn't use three bladed props until I had the plane completely sorted
out. I found that three bladers are not as efficient as a regulat two blade.
You don't want a twin hanging on the props. [X(]

FBD. :D

RE: 3 blade prop...help!
 

I use three bladers almost exclusively and have never had a plane fail to fly. Not even close. That less effeciency stuff is a load of it.

RE: 3 blade prop...help!
 

Britbrat- I'll reiterate...he sounds like he doesn't know much about props from the rash comments that he made. Maybe reading them again would help.

I'll agree with the single engine problem but I'm not sure about ruling out 3 bladed props for that possibility alone. You don't think someone would want to do rolls, loops, and maybe try a hammerhead stall with the Cessna 310 model? Those would be pattern type things. I would try it.

RE: 3 blade prop...help!
 

I tried a three blade once, and I mean once. It was a Super Kaos with a K&B .61
in it. It took-off OK....I flew it two laps, and brought her down....it was barely
flying....I'm not kidding. I still have the prop, it did look cool. I put the normal
11-7 1/2 MAS on it, and it was great. That was about 15 years ago, I never
bought another three blader since. The performance of the three blader was so
poor, I thought it was in danger of falling out of the sky. [:-]

I wouldn't say it if it wasn't true. :D

FBD.

RE: 3 blade prop...help!
 

Me neither too.

RE: 3 blade prop...help!
 

Yes you can tell I like 3 blades .You right the choices are limited and more pricey.I like the looks and like the ground clearence. Not as much mowing to do. They are a little less efficent at screaming high RPM. The OS 46LA is good less powerful engine . A 10x6 3 blade as JAKA stated is too much prop. He has to keep the noise down:D The 9x6 would be the perfect choice.

RE: 3 blade prop...help!
 

Hey Dave What size and brand is your museum 3 blade prop?:D

RE: 3 blade prop...help!
 

Here it is....a Zingali ????[sm=stupid.gif]

I think I had a special three blade spinner on it too. I think the Guy that
sold me that junk still gets a chuckle out of it from time to time. :)

RE: 3 blade prop...help!
 

LOL, too much flex with that prop? Though 3 blades are less efficient, the differance is just a percent or three. Not enough to cause it to almost not fly. A 10-6 three blade is a bit light for a K&B .61, coupled with too much flexing, could have been the problem.

RE: 3 blade prop...help!
 

Dave Thanks for sharing. Think that was made buy Zinger propellers. I 've used the zinger 3 blades but I like the MAS better. 3 blades are not for every plane.

RE: 3 blade prop...help!
 

Hey Flyboy Dave I just had a pregnet idea. Your the perfect test subject . You need to get a 11x7 MAS 3 blade and put on your 90's and give us your opinion. Should be the right size for 12x8 2blade .Down 1" down 1 pitch!!!!!!!!!!!!!!!!!!!!!!!

RE: 3 blade prop...help!
 

....here's a good test plane too, but it flys too good with the 12-8. :)

In fact, it's way too fast....maybe a doggy three blade would be better. :eek:

RE: 3 blade prop...help!
 

Thats the spirit DAVE This should be perfect and we are all waiting for the results............

RE: 3 blade prop...help!
 

Hi!
No! we don't have any noise regulations over here in my club, nor are we limited to fly at certain hours. So noise isn't an issue here. I'm only recommending what gives best performance, from my own experience.
Remember that the OS .46LA engine are quiet powerful at low rpm, I would expect the rpm to be around 10000 -11000 with a 10x6 3-blade prop...it's no point propping it for max power (at 16000 rpm).
Of course 3-blade props are inferior two two blade ones, this is a knowledge accepted world wide.
Remember this concerns small model engine propellers like 6" up to 18-20"props.

Regards!
Jan K
Sweden