can't find the recommended 11x10 break in prop anywhere
 

According to the owners' manual, the recommended break in prop for the TT.91FS is an 11x10. I checked three of the local shops here in town and no one has it. I hate to have to mail order it due to time and shipping costs. The owner of the most recent shop I visited told me it would be ok to break it in with the prop I plan to fly with: apc 14x6. What do you all think?

can't find the recommended 11x10 break in prop anywhere
 

I try to use as short and high pitch as possible. If no 11-10 which is not that uncommon then how bout 12-12 or 12-10? or at least a 12-9. Even a 13-8 would be better than a 14-6 to keep that engine cool.

can't find the recommended 11x10 break in prop anywhere
 

According to ThrustHP, an 11x10 prop has a loading of ~ 150000 (sorry I don't know the units).

Approximately equivalent loading, again according to ThrustHP, is provided by: 11.5x6, 12x5

14x6 might be too big, it has a loading of 346000.

can't find the recommended 11x10 break in prop anywhere
 

Loading doesn't matter the bench will move at the same speed with any of the props.:p

can't find the recommended 11x10 break in prop anywhere
 

If I had to lean one way between load vs. cooling, which would be better?

can't find the recommended 11x10 break in prop anywhere
 

The engine will run at about the same the speed with props of similar loading. That was the point.

can't find the recommended 11x10 break in prop anywhere
 

11-10 is a fairly low load for this engine so I guess a higher load would be better. 14-6 will be the best prop for most planes when broken in.

can't find the recommended 11x10 break in prop anywhere
 

But you have to throttle back to 5,000 RPM for the initial break in anyway. Also this is a light prop. It will turn it over 11,000 RPM. You don't want to put something lighter.

can't find the recommended 11x10 break in prop anywhere
 

http://www2.towerhobbies.com/cgi-bin...?&I=LXZ976&P=7


TOWER HOBBIES MASTER AIRSCREW 11X10 2.29

can't find the recommended 11x10 break in prop anywhere
 

try a 13/8 it will rev pretty good wide open with this but you are breaking in rich so over revs won't be a problem. it is also within the useful range of many engines so it may not end up as clutter.

can't find the recommended 11x10 break in prop anywhere
 

Hello!

A 14x6 APC or a 13x8 is what you should use ...the manufactureres recomendations is not a law carved in stone....
A 11" prop is too small for both running-in or sportflying

Regards!
Jan K
Sweden

Break-in prop
 

Cruzomatic,

The intention of that prop size for break-in, is to give the engine a relatively light load, but at the same time to have the highest possible flow of cooling air over the engine.

That is why a different, larger diameter prop with a similar load factor, would not suffice. A larger diameter prop with a similar load factor will need to have a much smaller pitch.
The smaller pitch will "pitch" too little cooling air at the engine, causing it to run hotter than its OEM intended, for a good break-in procedure.

Also, starting a new engine is easier with a larger diameter prop, especially for people who still use their fingers, or a "chicken stick". So it is tempting, but don't you dare do it.

Sincerely,

can't find the recommended 11x10 break in prop anywhere
 

You can certainly break in an engine with a 14-6. But you won't have any extra insurance if you accidentally run it too lean. I know I have done that. And the 11-10 is not too small. The engine will not over rev with it. But there is not as much margin from the 11,000+ rev to the 12,000 or so max recommended revs. Actually this may be a good prop for say the WM Midget Mustang. Though a 11-11, 12-11, or 12-12 might be better. This would give high speed but the climb out would be slow.

TT .91
 

You can break it in on a 14x6 APC. I never use a light loading prop on 4 strokes to break them in.

Chancer of overheating? Nope, if I recall correctly from the 4 TT 91s I broke in, you are supposed to run the engine about 5000 rpm for a while at a very rich mixture setting.

Use a fuel which contains some castor in it. It won't hurt one bit and once you are broken in, switch to a low castor, high synthetic fuel.

Re: TT .91
 

On the latest TT 91, I overheated it after I switched from the 11-10 to the 14-6, this was a couple of tanks after running at 5,000 RPM. I switched back to the 11-10 and ran it slightly richer. Ruined a plug, but no damage to the engine. Waited till about 5 tanks to switch back to the 14-6.

can't find the recommended 11x10 break in prop anywhere
 

When breaking in a 4 stroke it is more the needle valve which lowers RPM than throttle. (At least that is my understanding.) In other words start the engine, open throttle to full, and back out the needle valve until the engine is running so rich it will only spin at 5K RPM-thus the reason the manual expects you to have to leave the glow starter on. This ensures a very low running temp and a LOT of lubrication. It is the excessive amount of fuel/lubrication which allows the engine to run cool, not so much the prop or lower throttle settings. If it were the prop that mainly cools the engine during break in why does the TT .54's manual only call for an 11x5 for break in?
If you just run it a little rich at lower throttle settings to maintain the 5K RPM limit the engine may not get what the manufacturer deemed to be sufficient lubrication. Without sufficient lubrication the engine will run hotter which may possibly shorten it's life span and increase the wear of mating parts.
Owning a TT .91 myself, my first 4 stroke, I wish I had enlisted the help of someone more experienced for the break in procedure. The manual doesn't describe it very well and 2 1/2 turns out resulted in a very LEAN run. Phone calls to the service dept resulted in an average needle valve setting of 5 1/4 turns out. For break in the needle valve will need to be MORE than 5 1/4 turns out-unless they've altered the carb in the last 4 years.

This is what I've learned through research and trial and error.

Good luck with your 4 strokes!:)

can't find the recommended 11x10 break in prop anywhere
 

If you open the throttle to WOT and richen it down to 5,000, then you will have broken the 5,000 limit. I could not get it to run at 5000 with a WOT. Maybe my glow ignitor was weak. But as I said, the problem is later when you lean it out for the first time. And as you have noticed it is possible to get it to lean even whe trying to go for a very rich mixture. Needle valves vary a lot! A 11-10 is extra insurance that doesn't cost much.

can't find the recommended 11x10 break in prop anywhere
 

I think understand the importance of the 11x10. I ordered one from quantum yesterday. I guess I just need to have patience and wait for it. This is my first glow powered plane/engine and now thinking going with a 4 stroker is getting a little above my head. I've been flying epower for over two years now. There's just a lot to learn and I'm eager to get her built and in the air. Sport pilot,,thanks for your help. Please keep on sending advice.

can't find the recommended 11x10 break in prop anywhere
 

Maybe I'm a moron but I think you guys are over-thinking your break-ins.

can't find the recommended 11x10 break in prop anywhere
 

Maybe so, not sure which of your comment is correct either.:confused:

can't find the recommended 11x10 break in prop anywhere
 

Garcia,,,

Please tell me your method. I'm open to all suggestions.

can't find the recommended 11x10 break in prop anywhere
 

Typically I run 1-2 tanks through on the groud with the engine needle set really rich and I follow the instructions somewhat close. I use whatever prop I plan on flying with. Then I simply complete the break-in process in the air, again with rich settings. And if I get a stubborn engine that doesn't want to stay running while in the air I'll run a couple more tanks through on the ground. All my engines run great (including my MDS) and require nearly no tuning from week to week. That's what I do.

can't find the recommended 11x10 break in prop anywhere
 

Yeah, you can get away with that on ABC engines, even many ringed engines. But with THIS engine you may be lucky to get it to idle. And if you do you may be lucky to have your airplane back in one piece!

As someone just reminded me. Breakin is very important. It will determine how reliable and how well your engine runs.

can't find the recommended 11x10 break in prop anywhere
 

Guys, guys, me being new to this I want to do the right thing, especially with my first glow engine. Plus, I don't wanna hurt it, being that they're so expensive.

can't find the recommended 11x10 break in prop anywhere
 

cruz, I forgot to mention the prop I used for break in. I couldn't find an 11x10 either so I picked up a 12x8 at the LHS.
I'm amending my rather long previous post about the break in procedure. After remembering more of my break ins I agree that WOT is NOT a good idea. Running the first couple tanks slobbering rich and at relatively low RPMs however is.
(I'm not sure what I was thinking...)
After the first couple tanks running slobbering rich then gradually lean the high speed needle during the next few tanks.
If the engine starts holding steady RPMs at various throttle settings it's successfully getting broken in and its time to see where the idle is.
I think the manual does a pretty good job of describing the idle needle adjustment process.