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MLD-28 gasoline engine

Old 01-21-2012, 11:30 AM
  #1301  
flyracer
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Default RE: MLD-28 gasoline engine

Alright... I got the maiden flight done Friday afternoon on the Extra260/MLD28 setup.... I tried for over an hour out at the airpark to "tune" the low to mid throttle response to no success.. I put three flights on the Extra flying at mid to full throttle the whole time.

Engine cracks to life pretty easy... once she gets to mid throttle.. she roars all the way to full throttle. However, without the low to mid range throttle there's no way you can do any 3D stuff.

Wondering if a velocity stack is in order here? Thoughts or inputs?


Flyracer
Old 01-21-2012, 05:44 PM
  #1302  
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Default RE: MLD-28 gasoline engine

For most gassers, most of the power range is in the first 3rd to half of the butterfly movement on the carb. Consequently the throttle is not very linear. It helps a great deal to use the transmitter features to compensate. Some transmitters are capable of throttle curves. Mine isn't but there is a fairly effective work around. I've a JR 7202 so can't say about Futaba or others but on the JR, the travel settings control their half of the stick. That means that a servo will be linear to the stick if the up/down travels are the same percentage.

What is wanted however is servo travel that is not linear, ie the low expanded greatly forcing more travel to the high side of the stick. To do that, find how much up and down travel are needed. Lets say the number is 75% for each or 150% adding the two together. Generally, what can be done now is to change the high to 100% and the low to 50% to still equal 150%. The effect is to move the power range up the stick making it easier because of less sensitivity at lower throttle settings to jockey the throttle to produce the proper approach to landing speed. It simply makes throttle power more linear.

Hope this helps.
Old 01-21-2012, 06:42 PM
  #1303  
Jimeni
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Default RE: MLD-28 gasoline engine

Can you give a description of what its doing, and what you tried to fix it?
Old 01-21-2012, 07:11 PM
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Default RE: MLD-28 gasoline engine

Jimeni

The engine stumbles and threatens to die right past idle up to mid throttle.... if I apply the throttle to fast the engine acts likes its running lean and dies immediately.

The manual that came with my engine recommends starting at 2-1/2 turns out on both the low and high needles.... the engine runs way to lean on the low end and dies immediately past idle.. I have the low needle out to 3 turns and the high needle about 2-2/3 out.

I've tried richening the low needle to try and resolve the stumble and tendency to die... no dice! any quick movement of the throttle and the engine dies. Once I'm at middle thottle... the engine responds beautifully all the way to full throttle.

Flyracer
Old 01-21-2012, 07:42 PM
  #1305  
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Default RE: MLD-28 gasoline engine

If you have those needle settings you are running extremely rich. On both.

Fortunately, these engines are very easy to tune. But, contrary to the manual, the only way to properly tune, is with the engine running.

Start the engine and let it warm up for a few minutes. You can start with your needle valves where they are. Go to full throttle, and adjust your high needle to peak rpm. You do not need a tachometer, just listen. Once you get it to peak rpm you can richen it a little if you like, but it is not needed. That is only on glow engines.

Once high is set, bring your throttle down slowly. At about half throttle, or a little less, it will start to burble, or sputter, stop throttle movement as soon as It does, and lean the low needle until it is running smooth. Then continue bringing throttle down slowly until it starts to burble again, then lean low needle again. Continue until throttle is all the way down.

The go to full throttle again, and come back slowly just to check low needle, adjust if needed. Then take throttle rapidly from low to full. If it hesitates, richen the low needle just enough for good transition.

That's it. This is the best way I have found to tune. From what you stated, if this does not completely fix your problem, it will get you 98% of the way there.
Old 01-22-2012, 06:33 AM
  #1306  
flyracer
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Default RE: MLD-28 gasoline engine



Jimeni

I'll give it try.... stay tuned.


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Old 01-22-2012, 06:54 AM
  #1307  
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Default RE: MLD-28 gasoline engine

LOL stay tuned!!!!!!!!
Old 01-22-2012, 09:19 AM
  #1308  
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Default RE: MLD-28 gasoline engine

a  little fruedian slip there on my part! i crack myself up sometimes.

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Old 01-22-2012, 09:26 AM
  #1309  
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Default RE: MLD-28 gasoline engine

If you look back in this thread, I did a quick little mod that allows you to tune with the cowling on, and holds long screwdriver in place while the engine is running. It helps alot since cowling on and off settings will likely be different. Plus saves alot of time.
Old 01-23-2012, 07:47 AM
  #1310  
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Default RE: MLD-28 gasoline engine

I have the carb mounted so the low/high needle adjustment screws are pointing down and toward the front toward the prop! it scares the hell out of me to try and adjust those when the prop is spinning

Flyracer
Old 01-23-2012, 12:50 PM
  #1311  
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Default RE: MLD-28 gasoline engine

Have not taken a carb off to see but is it possible that by turning the carb you have cut off the crankcase pulse to the carb? It looks to me like the carb is only intended to be mounted one way.
Old 01-23-2012, 02:50 PM
  #1312  
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Default RE: MLD-28 gasoline engine

Lol Flyracer, you'll be fine Have a buddy hold your plane or tie it down real good while you're working on the needles.
Jimeni's idea that allows you to tune with the cowling on, and holds long screwdriver in place while the engine is running is the way to go.
Old 01-23-2012, 04:09 PM
  #1313  
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Default RE: MLD-28 gasoline engine

You need to mount the Carb the way it came. The pulse port only lines up that way. Make sure the hole in the gasket is lined up as well. I'm surprised you weren't having alot more trouble. That port operates your pump diaphragm.
Old 01-23-2012, 06:24 PM
  #1314  
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Default RE: MLD-28 gasoline engine

I checked the pulse ports on the carb before flipping it over... the intake manifold has slots that allow the carb to mount both ways. I flipped the carb for better servo, control arm and thottle arm alignment. The pulse port works... gas gets pulled into the carb no problem.




Flyracer
Old 01-23-2012, 06:33 PM
  #1315  
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Default RE: MLD-28 gasoline engine

Mine doesn't, but I have an early version, so maybe that's different. I would think it wouldnt run otherwise. Thats what i meant by more trouble. Will suck to tune that way, but while running is the only sure way to tune, unless you feel lucky Good luck.
Old 01-24-2012, 05:13 AM
  #1316  
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Default RE: MLD-28 gasoline engine

Tuning while running is the far easier way... but most of us have been forced to use configurations that don't allow it and they can be tuned but it does take a tach, patience and close observation.

The HS needle is done by tach... start rich and keep leaning in 1/16" increments taching each. When no more gain is reached, go back to last setting. The LS is easier but finer in adjustment... keep leaning until it stumbles on spool up and back out until stumbling is gone.

It can't be emphasized enough that unless there is twice as much air exit on a cowled gas engine, a nipple should be soldered to the atmospheric hole on the carb and a line run inside the plane to seek neutral pressure. Can't tune a gas engine if the pressure within the cowl is varying with engine RPMS. This is the most often problem encountered when tuning a gas engine within a cowl.

The better way of course is to damper or baffle the cowl to meet the 1:2 ratio of inflow/outflow area as engine rpms won't change the atmospheric pressure in the cowl.
Old 01-24-2012, 06:59 AM
  #1317  
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Default RE: MLD-28 gasoline engine

AA5BY

I think I need to do alittle more cutting on the cowl to improve the in/out airflow ratio.... the cowling is currently too tightly cut around the engine... interesting too is the article in the latest  AMA magazine... it talks about using a tach to properly tune the carb. I have the kind that you plug into the ignition line but it's almost impossible to use this with the cowling on... I'll need to get the kind you can just point at the prop.


Flyracer

Old 01-24-2012, 01:25 PM
  #1318  
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Default RE: MLD-28 gasoline engine

Want to hear something funny? I was reading the manual last night for my 3W 55 US Competition Version. It states that the cooling air inlet to outlet ratio should be 4 to 1 (outlet to inlet). I can't imagine having that much outlet area. My MLD-28 engines sure don't need that much. I do agree that round cowl planes probably need to have most of the intake blanked off though. My 3W 55 is in a YAK55 . We had to block off most of the intake area with carbon fiber sheet. That made a big difference.
Old 01-26-2012, 12:55 PM
  #1319  
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Default RE: MLD-28 gasoline engine

I made some space between the cowling and engine on the Extra 260 last night... but even still, I don't think I'm getting a 2:1 ratio. I'm thinking about baffling the front inlet on the cowling just a bit.

I ordered a hand held tach to help with the carb tuning. I'm hoping it comes in by tomorrow so I can work on the tuning Saturday.


Flyracer
Old 02-04-2012, 10:49 AM
  #1320  
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Default RE: MLD-28 gasoline engine

On my Slick and Extra I blocked off both of the full scale inlets on both sides of the prop forcing all the air to come in around the cylinder.
Old 02-04-2012, 04:42 PM
  #1321  
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Default RE: MLD-28 gasoline engine

ENGINE AIR-COOLING MADE EASIER
http://www.troybuiltmodels.com/ns/le...g-easy-how-to/

Engine baffling for best cooling. How is it done?
http://prme.nl/forum/viewtopic.php?t...33de23e8221518
Old 02-10-2012, 02:08 PM
  #1322  
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Default RE: MLD-28 gasoline engine

Rex and Airborne... thanks for posting airflow info... I took the Extra260 out yesterday afternoon. I tuned her on the ground to a solid 7700 rpm. However, once in the air she coughs and sputters. I'm going to block the main intake ports on the nose cowling this weekend and try it that way.

Flyracer
Old 02-10-2012, 04:46 PM
  #1323  
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Default RE: MLD-28 gasoline engine

I was having mixture issues on mine. Would adjust great on the ground with no cowl. Put on the cowl and she would go rich when in the air. If I leaned it our enough to run well at speed it was hard to start and ran lean on the ground. I believe I had the cowl pressurizing at speed throwing off the mixture. I soldered shut the hole in the regulator cover and added a fitting. Mine have a velocity stack so I added a fitting to that like 3W uses. Connected a hose between the two and viola! constant mixture.
Old 02-10-2012, 04:49 PM
  #1324  
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Default RE: MLD-28 gasoline engine

If the engine is tuned without pressure influence on the carb... then put in a cowling where pressure increases for lack of outflow, the mixture will go rich at high rpm as the pressure inside the cowl anvils the metering needle more open. If the engine is tuned for running inside such a restricted cowl, it will get leaned to counter that richening tendency but then as the rpms fall back, the high needle will be too lean and it will stumble on transition. That then gets countered with too rich of a LS needle to avoid the spooling up problem and then the idle is too rich. Neither needle ends up being set where it ought.

Old 02-10-2012, 04:49 PM
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Default RE: MLD-28 gasoline engine

I still have the stock intakes blocked so all the air has to go around the cylinder.

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