Hi guys,

I have a TT91 FS with about 2 gallons through, i've tried several props but none seem to be just "right" for the engine/plane (Seagull Extra 300), I think it's a heavy plane!

Zinger 11x10-> Not enough pull, not a lot of prop showing on the sides of the cowl
MAS 12x5 -> Too small, didn't even try it
MAS 13x5 -> Not enough speed, too small and too low pitch maybe?
APC 14x4W -> Engine revs nice and good thrust but no speed, this is a heavy plane and I need some speed
MAS 14x8 -> I feel it's just too much prop for this engine

I tried a Zinger 13x8 (wood) this morning, the high speed needle is very touchy and had a deadstick because of detonation, but if I use it richer the engine hesitates too much.

WIth this prop I tune it on the ground but when I take off, the RPMs drop when I go pass 3/4 throttle.

The timing is where it should and the valves have the right clearance

I noticed there is a small dent, VERY small, on the high speed needle (see attachment).

So...

a) Use a 2-Stroke on this airplane (I have a ST G61 that I used with this airplane with "good" results)
b) The high speed needle dent is the cause of my problems
c) That 4 stroke will never give me speed (speed is what I want)

Thanks for any advice
Joseph

Joseph,

Try 12 -8 Master Airscrew, or 12-8 wood zinger and see how well they will
perform on your .91 These props will allow full rpm from your engine,
plus great speed with the #8 pitch. The wide blade MAS performs really well,
it is designed expressly for the four stroke.

I have four planes with .91 four stroke engines on them, they all run the 12-8
MAS, except the YS .91 uses a 14-8 Zinger.

FBD.

A 14-6 is my favorite for this size engine.

Enjoy,

Jim

Gracias señor Dave

I have at hand a 13x8 MAS, what do you think? Is it too much? I don't have any 12x8 right now and my LHS doesn't have any in stock now [:'(]

I have a plane without prop clearance and I use a 13-8 MAS it seems fine.

I assume you are using a TT91 FS too

The 13-8 is on a Saito 91. But the engine's power characteristics is not that much different.

Enjoy,

Jim

Thanks Jim

How are your tach readings on that prop?

Tell you the truth, I don't do much taching anymore. If it sounds good, away it goes.

Enjoy,

Jim

I found the 12-8 MAS works better for me. It will give you around 9500
on the ground. The 13-8 will lug it down some. []

In theory the 12-8 and the 14-6 give about the same load, however the
12-8 will allow higher RPM, and more speed due to the increase in pitch.

FBD.

Thanks Dave

Called the LHS, they only have APC 12x7 [&o] will it do?

No, the MAS wide blade is made expressly for the four stroke. Trust me,
order a couple 12-8 MAS props for it. You will love the performance and
the speed.

The two props you should try are the 13-8 and 14-6, preferably APC but all brands and types should work. I would think the 14-6 should work well. If you are haveing detonation problems with a 13-8 then either you are using too much nitro, too hot a plug, or you do not have the choke adaptor attached. Without the choke adaptor the engine will lean out in the air, and have problems with running too lean and if you richen it up will have strange transition problems, smaller propes will increase engine speed and velocity through the carb, resulting in better fuel draw, but to use the props you need for this engine you will need to use the choke adaptor. This is not the same as on other four stroke models. If you look at the choke adaptor on an OS or Saito you will find that it is the same or larger size than the carb bore, but on the TT the choke adaptor has a smaller size than the carb bore and this restriction allow's the carb to draw fuel.

Thanks Sport Pilot

I'm using PowerMaster 10/18, OS Type-F plug, choke adaptor ON since the 1st run.

I'll try to get a couple of 12/8 MAS to see how it flies

Thanks all, and sorry for asking so many questions in about 60 minutes [&:]

I don't know what 10-18 is but if its 18% nitro you might have better luck with a Fox Miricle or K&B 4S plug. For 10% nitro the OS should do fine. Doubt it woule cause detonation though. Sounds like it got too lean to me.

Oh, sorry for the misunderstood

10/18 = 10% Nitro, 18% Castor/Syn Blend

I was too lean, almost spit the prop [&:]

I run a 14/6 Master airscrew on my TT91FS. It turns about 10200 on 15% nitro 18% oil. It does very nice towing around my Deweyville special.


Denis

Hi Denis

I think a MAS 14x6 will give you a lot of thrust, but I think what I want is speed, i'm flying a heavy plane which will feel slugish when slowed down so i'll try a 12x8 as Dave suggested to take up the RPMs and take advantage of the 8" pitch

I don't think you should be thinking about speed in a heavy Seagull Extra. It will go fast enough with a 14-6. Not that much faster with a 13-8. If it were light it might be another matter.

Well, I'll try both and see which one "feels" better

Thanks for the advice

Some actual numbers for you:

APC 14x6 @ 10300 rpm
Thrust = 9.5 lb.
Speed = 60 mph

This is good pull and speed for the Seagull Extra.

I've gone through a slew of different prop make and sizes. APC 14x6 is the one to use.

Geez, i'm getting confused [sm=confused.gif], so many props, just 1 plane... oh dear, my life sucks [:'(]

The sad part is that whatever prop I choose, be it 12x8 as dave suggested, or 14x6 as seanychen suggests, i'll have to order them from Tower and wait about 2 weeks before I can test them [&o]

[:@][:@][:@][:@]

I have set one TT .91 up for a guy at the field. The APC 13x8 worked really well, as did the APC 14x6. This engine did just under 10 grand with both.

Those are the first two I'd start with if I were you.

The TT .91 I worked with was a really sweet engine by the way - totally reliable from tank number one.

The prop you choose will depend not only on your plane but also your flying style.

If you want to fly smooth pattern type aerobatics then a 14x6 should be perfect. It'll give you *lots* of thrust for those uplines and good braking on the downlines.

However, if you want more speed (ie: you really wanted a pylon racer :-) then a 13x8 or even a 12x10 will be more to your liking.

I have a P51 Mustang with a TT91FS and found that the 14x6 gave me unlimited vertical but the plane flew too slow to be scale. The 13x8 was better but still too slow for my liking

The 12.5x10 I'm using now is nice and fast, but I don't have the unlimited vertical I got from the other two props.

The MAS K-series props look good and sound sweet but to be honest, they're not as efficient as the APC or even the Master Scimitar series. My 12.5x10 is actually a 13x10 Scimitar that I've taken a 1/4" off each tip. It's the *perfect* size for this engine in this plane.

I'll just toss my 2 cents in and say...
I saw 10,300 R.P.M. w/ a 14X6 APC leaned right out, and then I richen it to about 9,800 give or take a few, for flight.
(that's with PM 15% fuel, O.S. type F plug )

Mine's in a H9 P-40 and flys it quite well...actually a little fast to be scale speed, but...