Okay - maybe I'm going about it the wrong way. *DIsclaimer - No 2 strokes are discussed here so all the engines referred to by me are 4 strokes.

I've seen a lot of mention of props that in my opinion under prop an engine. For example - I recently read of a fella using a 14x4 on a saito 91. Now - I've also heard that this is agreat prop on the saito 72/82 and I have used it on my Magnum 61 4stroke.

I've got a 91 in a Funtana 40 now and I am trying to make the best prop choice for it.

So...what do you use on your plane?

A 15x4W apc worked well in a buddy's Funtana 40/Mag .91 combo.

Hi, submikestar, your opinion is wrong i,m afraid. The reason you state there SEEMS to be many engines underproped is because were 3Ders, we dont need and dont want the torque of a big prop. We need 'throtteability' for control (80% of the skill is with the throttle - thats when 3D!) and you get this from a slightly smaller dia. prop. Also preferable is a lightweight prop, wood being lightest.
A heavy prop has more momentum, I.E. slows down slower, and speeds up slower, it is AMAZING the difference a prop can make.

Hey, how ya doing??

all i can say is the 14x4W doesn't have enough pull and slows the motor down too much in the case of my 70 4 stroker....
that is why this spring i am sealing the aileron hinge area of the wing and putting a 13x8 on the monster.....

that should do the job....

cheers, and good luck finding the right prop......

Andrew

Hello,

I'd say for Funtana 40 w/ 91 4-stroke, a 14x6 is best match. It will give enough thrust: 10+ lb., so you don't need additional thrust of a 15x4W. It will also spool up/down a lot quicker than an APC 15x4W.

I use Pro Zinger 15x4 on a fun fly on Saito 82. But I think Funtana could use a little more speed for the IMAC type moves. Besides, Funtana 40's stock landing gear is a little short for 15" props.

Ok heres the skinny. The difference between a 4W prop and a 6 prop is obviously pitch and width you can prop a saito 100 with a variety of props in their range say the smallest prop is a 14X6 thats listed just as an example. In writing a 14X4W equates to a 14x6 in loading terms. They will swing the same rpm's ( or close) but your difference is power and torque vs. Speed. If you are finding that your plane is taking too long to spool up doesnt mean you need to ditch the W prop and go to a 6. There are other options, a std 4 pitch without the W or even 1" dia smaller say 13x4W. All of the manufactures lited props can be thrown out the window when it comes to 3D there is a different approach to it. Some people perfer a 6 or 8 to a 4 or 4W but thats because they want that slower response time in power. But the purpose of a 4 or 4W prop is to slow the plane down. 3D planes were not meant to go a million miles an hour but more like being able to pull a house, which is what a 4W prop does vs a 6 or 8 and up. In wingmans case he is going for a 13X8 from a 14X4W personally it may give you a slightly higer RPM but it will not pull harder than the 14x4W. you will gain speed no doubt but not the power you are looking for. You will see that your pull out in a hover will still be lacking. Try a 13X4W. point is you dont want to get away from that power prop and rule of thumb is low pitch large diameter for power. Once you get it narrowed to the approx lenght and pitch size its a delicate balance in there to get it to your liking. Then there is always a curve point you can dial into your Computer radio if you have one that can. It can broaden or narrow the throttle band to help with your spool time and and or thottle response.

In terms of peak RPM load, my tach data says that APC 13x4W will peak 500 rpm higher than APC 13x6 on the same engine/fuel. So APC 14x4W is still not quite the same "load" as APC 14x6; perhaps 14x5.

On the same token, I have tried the APC 14x5N, and it peaks the same rpm as the APC 13x6, both at 10500 rpm on Saito 72.

I feel that APC 14x4W is not enough load for 91 4-stroke. You have to be careful during level or downward flight that you never go to full throttle unless your engine is point upwards. Low pitch props unload A WHOLE LOT MORE during level flight, because at 40 MPH air speed, a 4" pitch prop swinging at 10000 rpm is actually 0" pitch (so there's very little load at this point). So expect the 4" pitch prop to unload up to 1500 rpm in the air for a low pitch prop, and make sure the ground rpm + 1500 will not exceed the max recommended rpm of the engine. I think max for OS 91 4-stroke is like 12000 rpm. If you use 14x4W on a 91 4-stroke, you might get 11000 on the ground. That's pushing your luck.

My friend over-revved a Saito 80 by flying with a Master Airscrew 12x6 full throttle during level flight and damaged the engine.

Speaking in terms of actual RPM's from one prop to the other is not acurate IMO. You are talking about you specific engine a lot varys from one engine to the other and not just fuel type the diffence in 500 rpms higher or lower to be should be considered a buffer. In all practical circumstances it is quite safe to say that the 13X4W and 13x6 have the same loads imprressed upon them on a specific make and size engine. Just MO

From RPM readings that I have seen people post ,seanychen's readings are typical across motors and fuel. That is to say that a 13x4w APC will spin faster than a 13x6apc(static). This is also the case with the 14,15, 16 and 17 inch respective 4W's to 6's. And yes unloading is a much bigger factor with 4 pitch.

Hey guys sorry to but in but I have a quick question,

I have been flying a supersportser 60 with a .61 webra. Initially I had a 12 x 6 on it. I have been looking at getting in to 3d and thought I would try a 13 x 4 wide. I asked around and people seemed to think that it could handle it. I know the supersportser will not 3d I just wanted to see how the prop performed.

Well the engined seemed to be reving pretty high. I did cut the throttle in the downlines. The uplines seemed to have less vertical then the 12 X 6 and the engine really seemed to bog at the apex of an upline.

Now here is the kicker. After several minutes into the flight I deadsticked. No damage to the airframe with soft landing. But I have almost no compression on the engine now and it will not run. Yuck.

So the question is do you think it was the unloading and over revving.

By the way the props are all APC.

cstewa, I don't think you hurt your 2-stroke by over-revving, but possibly from operating too lean.

Friends,
I have a Funtana 90 with TT 120 2 Cycle, what prop you recomend me to 3D flight?

Thanks.

Juan

I am going to take the head off tonight and she what she looks like.

Maybe a 15 or a 16 4W.

Ive found no matter what prop i try i allways end up coming back to the 15X4w on a 91 4 stroke. a 6 pitch gives me a little more pullout but i dont like how hot or touchy it gets when doing rolling harriers,, there is a fine line for the sweet spot in a hover with the 6 pitch. the 4W gives me a few more clicks in either direction of throttle before it either pulls or falls backwards.same reason the rolling harriers are touchy. In other words not as touchy trying to keep it in one spot in the hover. or to keep your angle in a rolling harrier.. Im on 30%

If it can spin it 9500 or so I would say a 17 x6 apc. Some 120 TT's can.---what prop & RPM are you getting now with the TT?
If not than 17 x4w or 16x6.

For 2-stroke .61 (other than OS 61 SF long stroke), over-revving is not a concern unless you are above 15000 rpm. It sounds like your high end mixture is too lean, or you don't get enough fuel draw. 12x6 is right for Webra 61, you maybe want even a little smaller prop, since Webra 2-strokes like to rev.

I would recommend APC 13x4 Sport (not wide). It will gain about 500 rpm from APC 12x6, whereas the APC 13x4W will drop 500 rpm. You should get 12000 to 13000 peak to keep a .61 2-stroke happy.

Thanks,
I am in the building process of my F90 and the engine TT120 is in the box.
I need to buy the prop to fly the plane, in want 3D flight.
The big problem is the Nitro Fuel, because in my country we canot fin this fuel.
I will use fuel with 20% of syntethic oil.
Then, What prop?

Regards.

I have a webra 1.20 2C and the APC 17x6 works fine for me.