Is it possible to burn an engine with the wrong size prop?
 

I have a Thunder Tiger .46.. From what I understand, you should use a 11x5 or 11x6 prop on it.. Right now, Im using a 10x4 and I really like how it performs (and sounds too). It SCREAMS on flyby.

My problem is, I like to keep the throttle on.. Alot of guys have been asking me how old the engine is (8 flights old) and if its ball bearing because with that prop and full throttle, I may burn the engine up.

How much would a prop effect this??

Also, Im running 10%.. Someone suggested running 30%... True??

RE: Is it possible to burn an engine with the wrong size prop?
 

The recommended props you mention sound about right for that engine on 10%.
I run an MDS40 on 10% and an 11x6 and it is very happy to fly my Gangster on half throttle. I have trihe a 10x6 but it HOWLS with that and gets quite hot, so you may seize / wear out your engine sooner. As for 30%, the highest I've seen used is 20% and that was in a DF model with a high performance engine. I would stick to 10%, any more is useless unless you really need that little extra power.
Sergeant.

RE: Is it possible to burn an engine with the wrong size prop?
 

The important thing is not to go over the RPM limit on the engine. Not only will you shorten the life but will be on the back side of the horse pwer curve and not get the power you paid for. Dennis. PS any LHS will be glad to sell you another one and soon. Dennis

RE: Is it possible to burn an engine with the wrong size prop?
 

YES, but I doubt that you have hurt it much unless you have been running it too leaned out.

Too little load, resulting in excessive rpm (your example), or too much load, resulting in too much heat -- can both damage an engine.

I have several TT.46 Pros & haven't cooked one yet, despite some pretty high rpm operation (the engine reaches its peak HP @ ~15,000 rpm). I have heard of these engines surviving >20,000 rpm, although how long they will live is an interesting question.

Depending upon the specific model type (airspeed achieved), & assuming good lubrication, the usefull range of propellers for that engine is:

9-8
10-6
10-7
10-8
11-4
11-5
11-6
11-7
12-4
12-5
12.25-3.75

You have to match the prop to the flight application & some of the props noted above will be incorrect for particular flight applications. An 11-6 is a good "all around" choice, but not necessarily optimized.

RE: Is it possible to burn an engine with the wrong size prop?
 

Of course anything that runs harder will wear out faster. I used to run my TT46 and SC46 on Tornado fuel 30% for gas powered cars. I can turn a 11x6 at about 13,500 RPM w/o a tuned pipe (I live at the Equator so thats pretty decent as it gets really hot and humid here). Now with a tuned pipe and 15% its turning easily 14K rpm (I have not shortened the header by that much yet) on an 11x6.

a 10x4 is not a good choice, you end up with so much RPM that the prop is no longer efficient, so called RPM to Thrust ratio is no longer practical. For me its a 10.5 x 7 and I find that a great prop for speed and yet retain some decent torque. Of course your 11x6 is just a safe bet.

RE: Is it possible to burn an engine with the wrong size prop?
 

Yes a 10-4 is small for this engine. An 11-6 would be a good place to start. If you under prop an engine you certainly can tear it up. I would look for a bigger prop. I like APC's myself. Try one in 11-6 and see how it flies. It will have a lot more power and less speed.

Mark Shuman

RE: Is it possible to burn an engine with the wrong size prop?
 

I was using an APC 11x6, but for some reason it was vibrating the plane way too much and I was getting bad foaming (yes, it was a balanced propr).. So we put a master airscrew 10x4 prop on it and I liked how it performed. And soundwise, the 10x4 SCREAMED.. I loved how it sounds.

RE: Is it possible to burn an engine with the wrong size prop?
 

Peak HP is an absolutely useless number. The number that matters is peak Torque, which manufacturers rarely specify; and peak Torque is almost always at considerably less than peak HP.

bobby,
If you like the way the engine sounds, screaming along at RPM's way over what the engine was designed to run at, and you don't mind replacing your engines every 20 or 30 hours of running, keep using the 10 X 4. :eek:

(Would you drive a five speed car in 3rd gear at 70 mph because you liked to hear the engine scream?)
Dennis-

RE: Is it possible to burn an engine with the wrong size prop?
 

First of all, I'm not stupid enough to run the engine until it burns up just because of how the prop sounds.. I was just saying, it sounds great and I liked its performance. Who knows if its revving TOO HIGH or not?? It may just be the pitch of the prop that is making it sound like that.. So until I put a RPM meter on it, its stupid to assume that Im over revving it.

Who doesnt like the sound of their engine when its tuned good at full throttle??

Having said that, I was simply asking is a 10x4 prop too small, which many have answered yes. I'm trying to find a happy medium.. I'm having foaming problems with an 11x6 (which I dont know why. It may simply me I bought a couple props out of a bad batch). So I guess that means trying a 10x6 or 11x5.

For those willing to give advice, is there a website that has prop tutorials?? Like which prop is recommended for what size motor and what are the advantages and disadvantages to each size??

RE: Is it possible to burn an engine with the wrong size prop?
 

I think the point that DBCherry was trying to make is that it's best to tach the engine with any prop change to determine if the engine is running within specs. Keep in mind that any prop will unload once it is flying, so the readings you get on the ground are gonna be higher in the air. The term "screams" would surely suggest that the engine is probably over- revving.

RE: Is it possible to burn an engine with the wrong size prop?
 

That was my fault.. Maybe Im wrong, but I think the change in the prop pitch gave it a different sound.

Will a 10x6 give a decent speed and climb?? I guess its ignorance, but I dont know what the difference would be in the performance of a 10x6 or 11x6... I know the lower pitch = more torque/less speed.. But I dont know what performance a higher diameter would yield.

RE: Is it possible to burn an engine with the wrong size prop?
 

Oh the prop pitch was definitely the factor in changing the sound, but the sound change was most likely a by-product of the RPM's going ballistic. Prop selection is based mainly on whether you are looking for top speed or pulling power (torque). If you want all out speed you would choose a prop with smaller diameter and larger pitch. If you want torque, choose a prop with larger diameter and less pitch. Whatever prop is chosen needs to be within range for the specific engine so the RPM's at wide open throttle (needle adjusted correctly) are within specs. I would say that a 10x4 is probably too small for your specific engine, 6" pitch would most likely be the limit for a 10" diameter.

RE: Is it possible to burn an engine with the wrong size prop?
 

You know what guys, I apologize.. I thought I was running a 10x4.. Im actually running an 11x4..

Ill just play around and see what I come up with.. Recommened in the book for the engine is 10x7 after break in, so I might as well pick one up and see what happens.. Now, a 10x7 would probably be noticably faster than the 11x4, right?? Since Im new with the plane, should I go with maybe a 10x6 so the speed difference wont make me pinch a loaf in my pants when I come in for a landing?? Or, with landing, prop size really doesnt matter because Im almost to idle anyways??

RE: Is it possible to burn an engine with the wrong size prop?
 

11x4 could still be under-propped, you really need to check it with a tach. If you want to stay with an 11" prop, 5" pitch would probably be the lower limit. Unless you're looking for more speed, I wouldn't go with the 10x7. The pitch of the prop will usually make a difference in the landing speed. In most cases, the larger the diameter of the prop, the slower you can get the engine to idle due to the flywheel effect. A smaller diameter prop with more pitch is gonna fly the plane faster at any given throttle setting, including idle.

RE: Is it possible to burn an engine with the wrong size prop?
 

[:@] ARRGGHH Too many prop decision!! :) Forget it, I'll just buy one of each and try them all out!!

Thanks for the help!!!

RE: Is it possible to burn an engine with the wrong size prop?
 

It's really not that difficult. If you're not looking for all out speed, just go with an 11x6 and you'll be fine. When you get a little more experience you can play around with different combinations using a good tach and go from there. ;)

RE: Is it possible to burn an engine with the wrong size prop?
 

bobby,
I may have been a little snide in my comment, and I apologize for that, but it seemed that everyone was saying the prop wasn't enough load for the engine, and all your replies only said, I like the sound.

An 11 X 4 is better than a 10 X 4, but still a bit small for the engine. The 10 x 7 will give you a considerable increase in speed over the 11 x 4, and will properly load the engine, which in turn will likely result in better overall performance because the engine will be operating closer to peak torque.

An 11 x 5 MIGHT be the optimal all around prop for your engine, but as you said, you need to buy a few within the operating range, try them, and determine which best meets your flying style.
Dennis-

RE: Is it possible to burn an engine with the wrong size prop?
 

Bobby ... 10x6 to 11x6? Heheheeee ... just keep the 11x6 if you want a bit more torque ... a Bolly 10.5x7 is nice. I have a Phoenix Scanner with a tuned pipe and a TT46 Pro, that throws an 11x6 as I want more torque to pull nice verticals. My Black Horse SU31 (SC46) is a little heavy so I prop it with a 10.5x7 for more speed ... all depends on what you want.

One way not to kill your engine is to check its temperature, when I played RC cars we kept it around 110C ... till today when I land the plane I will check on my engine temperature, of course I know what an over heated engine feels like so that helps. :)

RE: Is it possible to burn an engine with the wrong size prop?
 

I don't recall seeing what aircraft the "screaming TT" is in. If it is in a slow airframe, an 11-4 will not under-prop it. I use 11-4s on float planes with TT.46 Pros & they tach @~ 13,800 rpm static with the 11-4. This is just fine for the application, but it would be under-propped on an Ultra Sport 40, or something similar.

What are you flying?

RE: Is it possible to burn an engine with the wrong size prop?
 

Seagull PC9

RE: Is it possible to burn an engine with the wrong size prop?
 

A simple way to remember how to prop. Start with the reccomended prop in the manual. Diameter= power, Pitch=speed. If you need more verticle or pulling power. Drop 1 pitch and go up 1 diameter. To go faster drop 1 diameter and go up 1 pitch. Example 11-6 is the base reccomended. Power prop would be a 12-5, speed prop 10-7. And so on. You do have the right idea. Get a bunch of sizes and brands. Do a little experimenting. Find something you like and stick with it. Also remember the higher you are above sea level the bigger diameter you will need. Simply because of the thinner air. Good luck with your engine.

Mark Shuman

RE: Is it possible to burn an engine with the wrong size prop?
 

You are on the right track, but it is not quite that simple -- diametral increases raise power load faster than pitch increases.

A 12-5 would have a noticeably greater power load than an 11-6, whereas a 12-4 is somewhat closer in power load to an 11-6. You really need to have a tach for application-specific prop selection. What you try to do is prop your partricular application (climb, speed, areobatics etc. ) for the same static rpm as the "ideal" prop (whatever that is), then make an educated correction for airframe-driven effects (fat slow plane vs slim fast one, for example).

RE: Is it possible to burn an engine with the wrong size prop?
 

Just to answer the question about is it possible to actually damage the engine? Yes, but you usually have to work at it.

I've seen engines fail due to too high RPMs a few times. Usually the failure is either a broken con rod, exploded bearing, or broken crankshaft. In all of these cases, enough metal fragments go through the engine that it usually becomes a paperweight, though I do know of a Megatech .15 that blew a rear bearing and lived to tell about it. (It's still running, though the piston has some visible scoreing from the fragments).

I've also seen engines run for very short periods of time with NO prop, or a dramatically shortened prop with out damaging the engine. (after a mid-air that damaged the prop). Shaft runs are pretty distinctive sounding, that's for sure. On ABC engines, if it doesn't go on too long, the engine often lives to fight another day (or round).

However, extended running at too high an RPM will wear out the internal parts sooner than they should. Mostly, the conrod bushings and piston/liner.

If you're going to run it at high RPM, be sure to keep it on the rich side, the extra fuel and oil will really make a huge difference in the lifespan of your engine.

RE: Is it possible to burn an engine with the wrong size prop?
 

Bobby, I have run 10X6 props on 46 engines for as long as there have been .46 engines. You might step the pitch up a bit, but I wouldn't worry too much about running 11 inch on it. I also wouldn't run 30%. 15% maybe, but anything more than that and you are kind of wasting your time in my opinion. Run it rich if you step up or you will smoke plugs like crazy.