Engine power question
 

I have a spacewalker II powered by a thunder tiger .46 pro. Last year when I assembled, I followed the directions and mounted the engine canted to one side. Its between sideways and fully upside down. The muffler I have for the tt is stock. When I built it, I had to carve a bit of wood out since the front of the plane from bottom to top is on an angle in order for the muffler to fit. The end of the muffler's exit hole is roughly maybe 1/2 inch or maybe smaller away from the angled portion of wood so the exhaust hits the wood. This engine does not seem as powerful as my OS .46's. Today at the field, after 1 minute in the air at roughly 1/2 throttle, the engine was losing power and just died. I dead sticked into some high weed flipping it over. Damage was broken main gear. A club member told me that maybe since the exhaust was so close to the wood that it was maybe robbing some power from engine. This engine has had this problem before but this was the first time it ever quit in the air. Would having the exhaust so close have this effect of dropped power? When I started the engine, it throttled up from low to full without any hiccups. I just may yank the engine out, leave the spacewalker for awhile and throw the tt .46 on a Kaos.

Dave...

RE: Engine power question
 

I don't think the problem is with the exhaust flow being restricted. I suspect perhaps there is another problem such as air leak in the tubing, needle valve set too lean, etc. The TT Pro .46 engine should run very close to the OS .46 in terms of power. I have one of each also.

RE: Engine power question
 

I agree with DMcQuinn exhaust should not be a problem and the TT46 should be comparable to the OS46.

If you have removed the baffle in the muffler put it back in, it makes a big difference in the midrange and idle performance, the engine being reliable is more important than a few extra RPM at full throttle.
Since the engine is semi inverted try to make sure the fuel tank is not mounted to high in the plane.
Most will tell you the centerline of the tank should match the spray bar in the carb, I have found that the tank needs to be lower than that in relation to the spraybar or the engine will flood until the fuel level in the tank drops below the spraybar. This is particularly a problem at idle. Flooding at low throttle settings causes a lot of problems, the low end needle is set to lean to try to compensate for the flooding and this can result in virtually no range on the high speed needle since the high end is restricted by the low end.
The exhaust pressure to the tank varies with throttle setting so when the tank is full you set the needle valves so the engine runs semi correctly, as the fuel level drops below the spray bar level the engine will be to lean at less than full throttle because the exhaust pressure is low and gravity no longer siphons the fuel to the spraybar.
I don't know if what I have described fits your problem or not, but if your engine does not have at least one full turn of adjustability on the high speed needle where you can you adjust it from blubbering rich (and it will run for a prolonged period of time rich at full throttle) to peaked I would suspect that the low speed needle is to lean.
If fuel drips out of the carburator with a full tank of fuel when the plane is held horizontal then I think the tank is to high.
Good luck to you.

RE: Engine power question
 

Two things..........

An exhaust extension does wonders. There are ready made ones at the LHS or you can fashion your own. They'll show you where you should whack out some more wood. And it'd be very sensible to whack out that wood. It's dead simple and easy to do (if you have a few tools) and there are no rules that say you shouldn't. Matter of fact, I'm positive there is at least one rule that says you ought to. And any exhaust obstruction that's not plugging the exhaust is not really going to have much effect on the engine. Muffler pressure that's tapped out of the highest pressure area in a muffler isn't usually more than about 1psi, so anything thats outside the exhaust and is farther away than the diameter of the exhaust opening is going to have little effect.

And the other thing........ All the advice you've been given is good but....... What you described could also be a simple case of too lean. They'll shut off at half throttle when they're too lean just like they'll do when flatout. Did you see any exhaust trail? And when an engine is running on half-throttle, the lowspeed needle has some say in how it runs. Tuning the highspeed to lowspeed on some motors is not easy.

RE: Engine power question
 

Low end is too lean. Richen it up. YOu'll get better transitions as a bonus!

RE: Engine power question
 

What little experience at engine tuning I have has been learned right here in RCU from these guys and have gotten to the point where I can tune my engines to run well, fast & reliable with good transition from idle to full throttle. I don't believe however that the riding to close to the wood has anything to do with your problem. I took the stock muffler off of my OS .46 FXI in my NexStar & mounted a tuned pipe that came with a TS .56 that I had with a pitts style muffler on it. Britbrat had told me the FXI really liked this type of tuned pipe so I had this new one just sitting there and luckily the bolt pattern is the same from the .56 to the .46. However it doesn't stick as far out as the stock muffler did. It rides right along the side of the wood fuse, where as the stock muffler had at least 3/8 in clearance between the muffler & the fuse and it made know difference at all except a huge increase in power from the .46FXI, just as Britbrat had told me it would. It has been mounted this way for a few months now & is more powerfull & reliable than ever. Without a single dead-stick to it's name. I believe your answer was stated above in either DMcQinn, chashint, or darock's post. but I wouldn't get to carving on the fuse just yet. I think it's just a matter of one or more of the above listed scenarios. Either tank too high, or engine tuned too lean, or leak somewhere in fuel lines or a combination of the three.

This is the type of pipe I changed the .46FXI too. While it is not the .46 AX it has been pointed out to me that the same updates that were done to make the .46 AX have also been done to the .46 FXI resulting in the same type of power out put. I've seen it for myself in performance as my flying partner gets mad as &*$% when we break out the Trainers & My NeXstar laps his Sky Raider with the .46 AX with the stock pipe on it.[sm=lol.gif] Especially since the price for the .46AX is quite a bit more. The pipe is very similar to the one that comes stock on my Tower .46 PRO, which by the way will also outrun his AX.


http://www2.towerhobbies.com/cgi-bin...?&I=LXJB16&P=0


That pipe made all the difference in the world for my OS .46 FXI and as I said it literally rides right along side the fuse no moe than 1/32 clearance between the two if that, as in I might be able to slide a few sheets of paper between them but that's about it and it doesn't burn the covering on the fuse & it certainly doesn't effect the performance of the eninge except in a 100% positive way. IMO you should just break out the manual from your TT .46 PRO & re-read their tuning procedure as well as looking at some previous engine tuning threads here on RCU & you will get it dialed in without having to hack away at your fuse. I had a recent problem trying to get my TS .56 running right, dead-sticking an such eventually while the experienced person at the club who was trying to help me did find a fuel line leak (sucking air) he got the thing so out of whack tuning wise after we re-placed all the fuel lines to new, that it wouldn't even start anymore. He was so frustrated with it at that time he stated I'm done with it there is something seriously wrong with that engine!! As he walked away back to his planes I got out the manual set both high & low end needles to the original factory settings. It fired right up, he turned around & gave me this look [&:] then I started tuning per tuning techniques learned in here, & in just a few minutes had the high end adjusted for peak performace then backed it off about 1/4 turn for a thin stream of blue smoke. Then adjusted & leaned the low end till I had a perfect smoothe transition. By this time he was just standing there with his arms crossed and giving me that same look again. So I asked him if he would pick the plane up for me so I could re-check the high end after setting the low end. I had him point it straight up while at full throttle after a few seconds it sputtered & died, still a little too lean, I fattened it up another 1/4 turn & tried it again. It just kept on screaming at full throttle pointed staright up, had him put it back on the ground & let it idle then stabbed the throttle. Still had perfect transition wa-lah! Houston we have ignition.;) He then asked where I learned to do that & stated "see if I ever try to help you anymore, you don't need me" ( in a friendly way though). So I told him I learned that from an engine tuning thread on that website called RCU that you guys allways roll your eyes & scoff at everytime I mention it. LOL:D:)[sm=lol.gif]

RE: Engine power question
 

If the engine continues to give you problems, the glow plug maybe starting to go bad. It won't hurt any thing to try a new one but keep the old one just in case that the new plug doesn't make any difference. Means the original plug is still ok. :D

RE: Engine power question
 

How quickly I forget past lessons learned ....
I had not thought about the plug being a potential problem until Fastsky mentioned it.
But this story comes immediately to mind now that my memory has been jogged....
Back in my first year in RC after running perfectly for 3 months my engine started giving me trouble. It would fly for a while then die, and I thought that it was a tuning / overheating issue. So I fiddled with it for a few hours and then one of the knowledgable guys at the field offered to help me. After a little while of fidding with the engine he asked about the glow plug and after my reply he said OS#8 ... I argued and from that point on all he would say was OS#8 ... well I didn't have any OS#8 plugs and besides that I was stubborn since the cheap plug I was using had been flawless .... I tried a new plug of my own with the same results and asked him if he had any more ideas ... OS#8 was the reply and he held out a bubble pak with a new plug in it .... he said if it didn't fix it to give it back to him and if it did fix it and I wanted to keep it it was $5 .... I had no hopes of it working but once I installed it I flew for the rest of the day without another deadstick .... when I handed him the $5 he just smiled that I told you so smile.

Since then I have not tried to be cheap on the glow plugs and have had very few problems, I have worn out my fair share of plugs though and if a previously working engine starts to misbehave that is the second place I look after fuel line inspection.

RE: Engine power question
 

Gents, thanx for all the replies!!! Going to check the fuel lines for cracks/holes. I do have new OS #8's. Will check the needles.
This is after of course I re-do the mounting block for the main gear.
Matter of fact, can't remember what glow plug is in there now. Don't think its an OS #8 but maybe an A5. I'm running 15% nitro.


Dave...

RE: Engine power question
 

The lack of a muffler baffle makes zero difference to the TT 46 Pro -- it has a excellent carb & it can even pull fuel a reasonable distance without any muffler pressure at all. The piece of wood isn't going to cause a problem unless it is right up close to the muffler outlet & largely covers the outlet. The fact that you think that the power is low compared to your OS suggests a tuning problem -- the TT Pro should be indistinguishable from either an FX or AX in power.

As suggested, check the plumbing, the plug, & the mixture (both high speed & low speed).

Additionally, is the cowl open enough for adequate cooling? You may be overheating.