Any tips out there for tuning a glow engine for sustained hovering? I recently built a spa3d after having spent several years sport flying. I have no experience on setting up a glow powered 3D plane. The engine seems to tune really well at level orientation and have a great transition. I set the HSN about 1/4 turn richer than normal flying and it seems to be alright at WOT pointed straight up, but will not keep running more than 15-20 seconds at mid range when pointed straight up. What does everyone else do when setting up for 3D?

yes HSN richer for sure, to compensate for the carb working harder to draw fuel while hovering

os #3 plug, 20% nitro would be my go to's.. (for the 46 range)

also a prop that will give you the thrust, but not bog down the engine in a hover... big fan of APC 12.25x3.75 over here

where did you find plans for your spa3d??

20% nitro is not needed at all, i hover on 0% nitro all the time (it works just as well if not better than 15%)
i wouldnt tune it any different than you would your normal sports plane, the key for 3D is getting a good transition because most of the time you are not hovering at full throttle, so if you richen the high end too much it will affect your transition/ mid range which is where you hover.
after a flight or two you should be able to tell if you need to richen or lean your high end, just listen to the plane when it is in the air, it will tell you what it wants

Thanks for the comments so far.  I realized I left the specifics out of my original post.  It is a GMS 47 using powermaster 15%.  I bought the engine new around 2001 and put a couple of good years on it in an extra.  It's been sitting for about 6 years.  I completely disassembled the engine yesterday and all internal parts appear immaculate and good compression. On the ground and test stand, it turns an APC 11x6 and 12x4 (over 12000 rpm at an off peak setting) just fine.  It has great mid range performance and smooth, quick transition at from any throttle position.  The issue comes up when I simulate hovering by holding the plane pointed up.  I've tried adjusting the HSN to avoid overlean at WOT.  When I begin playing with the throttle, it begins to bog down and die at around half to full throttle.  If I quickly level the plane, it smooths out immediately.  I followed the SPA3dT plans from the spadtothebone website.<div>
</div><div>Metallica: Donna huh?  I grew up in Brownsville.</div>

The GMS engines use a muffler that is not very restrictive. Makes for good HP numbers BUT a glow engine uses muffler pressure to help push the fuel to the carb. By reducing the muffler pressure for more performance the pressure to the tank is also reduced making it difficult to get an adequate supply to the carb when the tank is many inches below the carb in a hover. Some engines have better fuel draw and therefore are more forgiving when held in a vertical attitude.

While I do NOT own the GMS 47 I do have the GMS 40 and it can be tuned to sustain a hover but is somewhat sensitive on the needle setting for hovering. There is a sweet spot and it takes some effort to find it. It is very close to what you would use for normal sport tune (ie 300 to 400 rich of peak). Mine is on a Tribute 36 right now and I normally set it just where it turns max rpm when held vertical and then ONE click rich of that setting. Your 47 may require something different, don't give up.

Good propeller choice can help too. I used an APC 12.25x3.75 with good thrust, but switching to a Xoar 12x4 wood did wonders for throttle response on my OS50FSR!

The tanks on my 3D profiles are mounted very close to the engine and at the same level as the carb. No special tuning is required. Try to stay with high quality engines. Some of the 'bargain' brands don't throttle well, and that is a major issue for 3D.

It isn't the cost of the engine that determines how well it will serve as a 3D two-stroke engine, but I understand what the poster is saying. It is important to find an engine that transitions well to begin with, period.

Truthfully, IMHO, were I to become enamored with the idea of small glow engine 3D flying, and I have, I would try to buy a Saito .82 four-stroke, even if I had to buy used.

On the other hand, I did buy a Rossi .45 3D engine a few years back, but haven't gotten to try it out as yet. We shall see how it stacks up against my Saito .82A on the same model (Harrier 46) after surgery this December 2nd. After chasing my health problems around for years, my pulmonologist accidently stumbled upon a giant goiter in my neck that was choking off my air supply and reducing my ability to swallow. What this could mean is that I might be back in the flying saddle again and with some extra energy to boot. Hurray!!!


Ed Cregger

i have a gms .47 on a mojo 40.....i would trust the engine with my life in a hover...the thing never dies
i also run 0% nitro and 50/50 castor synthetic mix...but it was just as reliable on wildcat 10% nitro
try leaning out the low end slightly (but to me it sounds like your setting the high end too rich.. being cautious... which is messing up your mid range...but i dont know for sure since im not their)
set your engine correctly, like you would for any other plane, do not richen the high end because it is a 3d plane...

I bet the low end needle is just a tad to lean. APC 12-4 or a wooden 12-4 will give you alot better response than the heavy mass APC 12.25-3.75

I'm trying to put all these ideas together.  My GMS came with a standard baffled muffler and not the "tower" muffler.  It appears that exhaust pressure is good in the tank based on what I can see in the tank and that I don't have to excessively richen it on the ground.  I can see the point of putting the tank as close as possible to the engine, but don't see an issue with tank height because the plane will be high alpha flight most of the time anyway.  I'm definitely not one to brag about making cheap equipment work fine; I've learned as with most things it's either buy right the first time or end up buying twice.  I built this plane as an experiment because I had the equipment laying around in storage.  If this were a well built 3D plane, I would probably rather put a 4 stroke on it.  I like the instant torque rather than waiting on the 2 stroke to wind up.  I've seen enough videos of this plane to realize people are making it work fine.  This engine actually has much better transition and mid range (when level) than my just broken in os 46fx.  It doesn't seem to matter whether it is an APC 11x6 or 12x4, they both spin and transition well.  I already broke the 12.25x3.75 that I had used on this engine a few years ago when on the extra.<div>
</div><div>The next 2 things I will try:</div><div>
</div><div>1. LSN tweaking.  It seems at WOT to be leaning to peak when pointed vertical and maintains well without sagging.  The issue comes up at mid range.  I found when playing with the finicky OS the other day that the LSN adjustment had a huge effect on mid range.  If it was even the slightest bit rich, the mid range would load up.  Therefore, if this one is dying at mid range without warning, it leads me to think that it may be lean on the LSN setting.</div><div>
</div><div>2. Glow plug.  When playing with this engine on the ground a couple of days ago, it would seem to tune great at low and high speed and then randomly quit when the throttle was advanced.  After about 15 minutes of back and forth with the LSN, I changed to a "newer" OS 8 glow plug and got much better results.  Maybe I will try an OS #6 (A3) glow plug if I can find one locally.</div><div>
</div><div>Thanks again for the comments.  If I was setting up for an everyday flyer, I would have set up my equipment for success, including a well built plane that I can fly rather than constantly tweaking.  Even though this one is fun, it still flies like a chunk of plastic.  This one is for an experiment and so I can get my tinkering "fix" when needed.  </div>

Hi!
Tank set up is as always important!
For a .45-.47 engine use a 8-10oz tank! Not bigger! Prefearably set up with uni-flow system (Two clunks) and at correct height!
Nitro in fuel is important but 15 or 20% is just overkill on mot engines. 20% nitro could even be too much for some.5% is just fine!
Prop: 12x4 APC or RAM. 13,25x3,75 APC could also work.
Glow plug : OS 8 or Enya 3...but there are lot's of others that also work good. Avoid old-style plugs with idle bar!

If your spad is rather stiff you might be getting some tank foaming..... so point her up and look for that while on the ground. Make darn sure the pressure nipple is not plugged with a booger. Also, run it up to midrange on the ground and pinch the fuel line. It should speed up slightly, if not, it is running lean in the midrange for some reason still. Check everything for a possible air leak too.

Keep us posted, interesting, hope you don't have one of those GMS, 99 page threads.....

Ernie

Ernie knows of what he speaks.

If all else fails, a spritz or two of Armor All spray on treatment liquid into a gallon of model fuel will tame the beast enough to usually fly without much of a problem. The downside of using this technique is that it does cut the life of the glow plug by about one half, so don't be using expensive glow plugs. Besides, house brand plugs have been working flawlessly in my models for years. A friend and I were the first in our area to fly 3D and that was with cheap plugs. That was back in 84 or so.


Ed Cregger

For most reliable hovering tune on the rich side and use some nitro. 15-20% nitro will reduce the mixture change noticeably over 0-5%. The best hover needle setting will usually be much too rich in level flight. Also keep the tank small and close to the engine.

Well....  I never start a sentence with well, but it works here.  Anyone want to buy a used GMS 47?  Just joking.  I greatly appreciate all the comments, but I've all but given up on this engine.  I hate to admit defeat on it; it served me well when I bought it while on a limited budget in grad school.  I really can't tell what could have changed.  It shouldn't have enough time to be worn out.?    Yesterday afternoon I spent over 45 minutes and probably over a quart of fuel playing with that engine.  I think there is either an air leak, or it needs a hotter glow plug.  The day before, it ran great when level, so I thought it would be some simple LSN adjustment.  When I started it, it began surging constantly and would hardly advance past half throttle unless the glow starter was attached; even after warmed up.  I played with the LSN for about half an hour and finally got it running good while level.  Then I had the same issues when pointed up.  The high end would lean quite a bit and when slowed to half throttle, it would die as if too lean. I continued to play with the LSN and became more frustrated.  By now, the low voltage alarm on my transmitter  was beeping away annoyingly making things worse.  I then pulled the engine and replaced it with the os 46fx I have on my extra. As a side note,  I bought this engine from an RCU member a couple of months ago as "NIB" and fought the mid range on it for a few days and realized it was just very picky about the LSN; could not take even slightly rich setting.  It started immediately.  About 5 seconds to adjust the HSN a little rich and pointed to the sky.  It leaned to approx peak with no sagging and stayed that way no matter how long I held it up, and excellent response throughout the throttle range.  I slowed it to a smooth, slow, reliable idle and literally threw the plane into the air.  I flew three short flights with excellent engine performance at any attitude.  Being new at glow powered 3D, I found that with the 46. the 12x4 APC prop has much better throttle response and instant torque than the MS 11x6.  Let the chinese engine bashing  begin, I might even join in.  I had almost forgotten how nice it is to start an engine and fly without worry.

Did the GMS run in a dusty environment or digest any crud? It is possible to "wear one out" in short order. You get an A+ for effort!

Ernie ..... and thanks Ed....

What you are describing is perfectly normal behavior for a glow two-stroke engine. Sorry.

The lack of hesitation during throttle up is the number one reason for folks using mostly four-stroke glow engines over two-stroke glow engines.

Have you ever watched someone using a two-stroke gas engine while hovering and noticed how their throttle thumb doesn't stop moving? The engine is constantly being revved up and down. Same thing. Two-stroke engines are poor candidates for 3D flying. Four-strokes aren't perfect, but they are the closest thing we have to perfect except for electric power.

The GMS .47 was designed to be flown mostly at WOT. In that flight regime, it serves its purpose well.


Ed Cregger

It's possible that some crud may have gotten into the engine.  I have not run it in a dusty environment until the past few weeks in the field behind my house.  I just don't understand because it still feels like a good pop in compression when cold and the cylinder and piston appear very smooth from the naked eye.  I was certain to line up the ports correctly when reinstalling.  It is very possible that I changed the direction of the piston.  Would that make a difference in GMS engines?  This one did not have any markings on the piston such as an arrow pointing towards the exhaust port.<div>
</div><div>Before I completely give up on it, I will extensively check for air leaks and try a fresh glow plug.  </div><div>
</div><div>By the way, as far as my original question of how to tune for 3d; I tuned the OS 46fx (os 8 plug; 15% powermaster) as I would for normal sport flying, maybe a click or two richer on the high speed than I would normally.  It ran flawlessly</div>

I appreciate your comments. I definitely realized this while learning this plane. While sport flying, I never noticed the 2 stroke time lag to wind up to power. I've gotten used to the little electric 3D foam plane and instant power when needed. I am considering this a great learning experience in engine work and flying. When I move to a "real" 3D plane, I will most probably use a 4 stroke. Granted, I'm not used to the plane yet, but this SPAD is not nearly as much fun as the videos and others' comments made it seem. It just takes too much work to keep the sheet of plastic pointing the engine in the right direction. I won't even attempt to call it flying.

If by chance you did get the piston in backwards that would make all the difference in the world. The engine would need to be ran and rebroke in but not a good idea, if indeed the rod is in backwards.
If you didn't remove the piston from the rod, it should be easy to tell which way it went in. Most engine rods have a larger chamfer on the pin hole which faces forward to clear the radius on the crankpin.

IF the piston is in backwards it could have really screwed up the delicate piston/liner fit in an ABC type engine. Cyberwolf is so right. I doubt if it would ever actually break in properly again. Do look for that chamfer on the big end of the rod just for kicks.

Thanks,

Ernie

I took the engine apart last night to take a look.  I never have removed the piston from the rod, so they are still matched at least.  Both sides of the rod had a chamfer, but one side appeared to be ever so slightly more than the other and that side was facing towards the back.  I reversed it and put it back together.  Everything feels smooth.  I will try to put it on a stand sometime today or tomorrow and come back and report my results.

I know I've gone way off original topic here, but just thought I would post an update.  I ran it on a stand yesterday and as usual ran great level.  When pointed vertical, the high speed did great with very little leaning.  At 1/2 to 3/4 throttle, it would make it about 10 seconds or so and then immediately lose power.  If I leveled it quickly enough, it would regain rpm.  I'm now thinking further LSN adjustment, or air leak.  I want to connect it back to a throttle servo to have a good solid endpoint to listen to idle and response before adjusting.  I then had an issue with the muffler that I will bring up in a new thread.  I submerged the engine with a fuel line attached to the carb to check for air leaks.  I noticed a very little bubbling around the throttle arm (not through the LSN, but on the outside of the barrel), but quite a bit of leaking around the front bearings.  I know some leaking around the bearings is normal, but not sure at what point it becomes excessive.  Would a new aftermarket front bearing help?