The throttle linkage parted company from the throttle arm on my Thunder Tiger .46 Pro yesterday. The engine was on a SIG Ultimate Fun Fly, and was sporting a Tower Hobbies muffler and Master Airscrew 11x5 prop.

The engine was at full throttle and stayed there until it ran out of fuel.

I didn't notice any obvious damage to the engine, but didn't run it again because I didn't have the hardware with me necessary to repair the throttle linkage.

When I got home, I fixed the linkage. I also swapped the MA 11x5 for an APC 11x5. The APC wouldn't fit in the small plastic spinner I had on the airplane, so I put on a 2 1/2" aluminum spinner.

I brought the airplane to the field this afternoon and flew it. I was not getting the usual RPM from the engine. When I tried tuning it, the engine hardly responded to the adjustment of the high speed needle; I was turning it a half turn or more in either direction with no apparent change in the engine RPM.

I took out the needle valve and flushed the seat with fuel. I also cleaned the in-line fuel filter in the fuel line. It still seemed to be unresponsive to needle adjustments and was not performing at its usual level.

After a few flights and some more adjusting, it started to act more like it used to. Maybe there WAS some dirt in the carb?

But now, I'm wondering if the WOT lean run damaged the engine. I'm also considering that the APC prop and big aluminum spinner are much heavier than the MA prop and little plastic spinner. Will that have a noticable effect on peak RPM?

I have lots of other engines, but this little TT .46 Pro is a favorite of mine. I hope I didn't kill it.... :cry:

Your thoughts?

Good flying,
Bob Scott

I doubt if you actually did any serious damage to the engine. Just be good too it and run it a little richer from now on. One of the reasons that it most likely didn't do any harm is that it is an ABC engine.

Good luck

Jim

Bob,

Have you change the glow plug yet?

Most lean runs will distort the glow plug and causes the problems you've mentioned above. Although the plug might looks good to the naked eyes, but in most cases it's not. Try changing the plug and let me know what happen. Hope this help.

Sam

Assuming it ran out the tank at a normal slightly rich setting then it won't have done any harm at all. Does it still feel the same when you turn it over? Changing to a different brand of prop can give completely different revs to what you're used to although the weight of prop and spinner won't affect revs.

I would bet that if you reinstall the MA prop it will run the same as before. This is not to say one prop is better than another, it is what suits your engine & plane that counts.
Ray

Running at full throttle for a full tank of fuel shouldn't hurt anything, many of my first R/C models didn't have throttle and we ran them at full all the time , several hours a day sometimes. A lean run does not have to be a full throttle to do damage. I would say that if it ran out the complete tank it probibly wasn't very overlean if at all. So was it overlean before you lost throttle ? if not no problem without throttle control.

Even the best spinners made will rob your engine of 500 rpm. Switch to an AMA safety nut and reap the benefits of your engine.

By way of comparison, a Royal .46 was running a MA 11X6 prop and revving up quite a bit with healthy speed and acceleration. The prop was switched to an APC 11X6 and the engine ran much differently. Low speed acceleration improved but top end speed and RPMs suffered.

Regarding your engine; I doubt any damage occurred.
I don't trust the needle O-rings - even when brand new. The chances of someone finding one of my engines without a piece of fuel tubing over the needle sealing it against the throttle barrel are very slim.

Try an APC 11X4 or 12X4 on your TT. You may be surprised.

Jeff

PLease explain how this can possibly happen. Always willing to learn

The carb was set properly. I was thinking people were missing my point about the lean run. The engine was running WOT and then ran out of fuel; you can't get much leaner.... But as Dave mentioned, non-throttled engines run WOT 'till out of fuel every time. Geesh! I guess I was worried about nothing.

As an experiment, I'll try:

a) going back to the original prop/spinner combination
b) a new glowplug

Thanks for the responses.

I understand , There are times when the tank may be situated to low and cause a overlean run for an extended amount of time as the fuel line lowers, it may cause some damge depending on the fuel used.

Jazzy,

The fact that the Top End RPM suffered is due to load and increase pitch from the APC prop. The MA maybe rated at 11x6, but in reality it's probably not. On the other hand, APC are pretty accurate when in come to pitch and that's why you noticed the engine suffered from it. Put a pitch gage to it and you'll know that the MA 11x6 in not what is all up to be.

An 11x6 prop on a .46 is Too Much prop for the engine. A good prop would be 11x5 or 10x6. Hope this clarify the misconception with engine suffering from APC 11x6 prop.

Sam

I flew it again today. I tried an APC 10x6 prop with the same aluminum spinner. Pretty good performance, but not the out-of-sight vertical I had with either the MA or APC 11x5 (which was expected).

Then, I put the MA 11x5 back on. Performance was back to it's original, satisfying level. I was really surprised at the big change in the way it runs with just a change in brand of props.

As Sam mentioned, the MA is probably not a true 5" pitch or maybe as I'm also guessing, is flexible enough to flatten out a bit at high RPM. In any case, the MA 11x5 allows the engine to rev high enough to hit the "sweet spot" for performance with the Tower Hobbies muffler. It would never seem to hit its stride with the APC 11x5 on it.

So... I'm back to the black paint-stirrer prop. (And darn happy with it, I might add!)

TT engines are ABN not true ABC.

Secondly they are the most sensitive engines available in the market. If you change spinner/prop or any load on crank shat the performance will vary much. These engines are also very sensitive to dust and moisture, and if there is a dust layer in the air you will definitely lose some compression with these engines.

These all factors are due to internal metallurgy of the piston, sleeve and crankshaft material.

It sounds like your engine simply ran at full throttle until the fuel was expired. Providing the engne was properly tuned when you left for the sky a LEAN run did not occur. Running the fuel tank dry prior to the engine completley running out of fuel for this very short period of time would not hurt your engine....

As you now realize allprops are not created equal....

i dont know if this would help much, but i will offer what ive learned.

in my short time in the hobby ive used grish, MA (regular), Zinger (maple), and APC. ive found that there are a few things that tend to be the same no matter what engine you install them on:

Zinger: my FAVORITE prop. ive found these to have the most thrust of all i have tried combined with a light weight. my engines constantly turn a high rpm with these. but they are easily broken. one grass strike and its toast.

APC: my most used prop. good balance of thrust and durability. they stand up to ground strikes and tend to last a really long time. i have found that i can get my engines to tick over easily at a really low idle with these props.. but they are heavy and arent as resistant to unloading as the maple zingers are.. but are more resistand than;

MA: good prop. good vertical, performance, and idle on any engine i install them on.. but less raw thrust than an APC or Zinger.. and seem to be more fragile than APC.

Grish Tornado: this is the black composite prop they offer, nice and light. ive noticed that my engines with these props perform well, but they dont idle very low.. (probably from reduced rotating mass?) and the vertical performance isnt "awesome".. good middle of the road prop. tend to work best on my plain busing engines (because of the light weight?) along with;

Grish Nylon: these work GREAT on K&B sportsters.. for some reason the sportsters absolutely love these. they unload a pretty good bit at speed, but you never have to worry about breaking a prop. =)


of course this is only from my experience. so others might have different results.

Interesting analogy, however all engines, any engine will suffer from a moisture and dust rich environment... All engines will loose compression due to the accelerated wear associated with dust particles. Moisture is an unwanted byproduct and is prone to be prevalent in our fuel as well. Moisture will cause premature bearing failure, little if any culpability is allowed for accelerating engine wear, under normal circumstances.

The effect metallurgy will have on any model engine is the ability to with stand abuse from the continuous heat cycles and or extended use. The science of metallurgy in our world has more to do with the ability of these dissimilar metals to grow and shrink proportionately for the desired effects of the given component use. Given the piston; a high silicone content aluminum, the cylinder of brass or aluminum, plated with chrome or nickel are dissimilar materials. An engine with this metallurgy technology relies on the expansion and contraction of these dissimilar metals to achieve a compression seal, with the relationship of when and how these particular metals react under use [heat] it's a wonder they function for any length of time at all.

Sam,
As I said, "By way of comparison,..." don't you think I already knew what you said about the MA prop?
I didn't think it was necessary to spell out the obvious but, in retrospect maybe I should have.

Being that the engine in question is on a funfly and I happen to own four of said engines I have a pretty good idea what runs best on it.

If hover-batics are what he is after a 12X4 would be an excellent choice. An APC 11X6 just happens to be a perfect match for the TT Pro .46 in just about any sport flying application. A 10X6 is not nearly enough prop for the muscle this engine has. The engine will easily whirl a 10X6 reaching maximun eficiency of the combination while not expressing the engine's true potential.
The APC may have been too much prop for the Royal but it is definately not too much for the TT Pro .46. Trust me on this one.

Bob S,
Try an APC 12X4 if you want to hover and have instant acceleration. Top end speed will suffer from such a low pitch prop but vertical and hover-batics are superb. Then again, if your happy with the MA 11X5 stick with it!

Sincerely,
Jeff

hmm.. a little snippy there.. alot of that goin around here lately.. maybe somethin in the water. hehehe

judging by the context of Sam's post i believe he may have stated that more for bobs benefit than yours.

-Joe-

Rather than try to explain the obvious, tach an engine with and without. You'll see what I'm talking about.

Jeff,

Thanks for the recommendation. I already did it! After yesterday's experience at the field, I ordered a variety of lower-pitch props when I got home. I'm anxious to see it perform with a 12x4....

Michael Glavin

Interesting comments...

For ABC (aluminum/brass/chrome) the chromeium plating is better suited with aluminium and have almost same expansion coefficient as aluminum. But sad that most manufacturers have given up this to cut the price of their engines.

Some of the engines like Irvine and top end OS are still true ABC and run very well and are reliable. Any more thoughts of yours...

I believe the brass liner is chrome plated. Are you saying the plating expansion rate is helpful with the aluminum piston expansion rate ???

Using Tachs to compare power of a prop on a Specific engine usually has little value other than to compare to previouse readings on the same prop and engine, What is the Ideal prop for one Aircraft is is differant for another, if you going for speed a small high rpm run is needed , TT46 a 10X6 or 10X7 or about is a good choice provided your aircraft is designed to go fast. Slow aircraft that hover alot use flat props for continious static running and load, Sport Flying has a wide range depending on the pilots and aircraft. Even the brand can be better for a size than another for some aircraft. If you want your planes to slow for landing use a flat prop. So far I have not found any prop size or brand that works 100% for every application and aircraft for a .46 size engine. I can't count the number of times people thought something was wrong with thier Aircraft and how it was flying and how the engine was running simply because they had the wrong size and type prop.

A heavier rotating mass definitely takes longer to accelerate to top RPM. It is even more noticeable when throttling down, taking longer to get to idle speed. It will not affect the top speed, but the flywheel effect may help to maintain a lower idle speed.