Hi DarZeelon

I need your opinnion [8D]

I have bougt this large p-38 that weighs 5kg un-assembled. Im guessing with 12 servos and 2 motors and glue, it will be around 7 kg`s

Do you think the MVVS 49`s and standard silencers and 11/6 props will fly my plane ok ?

I was looking at the new os FL-70 four strokes, instead of the MVVS`s
do you think they would be better?

Or will the 70`s only be marginaly better than the mvvs 49`s ?

The reccomendatin on the box says 40-46 2 stroke........but Im a little concerned with that.


Thanks, Sonnich

Sonnich,


That is a big plane.

The MVVS .49 is at its best when equipped with the #3248 tuned silencer.

When using the #3245 silencer it is a standard .46-.50 sport engine, as far as power is concerned.
Its timing and compression are designed to utilize the most the tuned exhaust system can give it.

The experience I personally have with this engine with the normal silencer, is on a 67" (1.70 m) span, high wing aircraft.
With the tuned silencer, I had it on a 58" span low wing model.

Both weigh 2.5-2.7 kg.

Several other such engines, most with the tuned silencer, are flying on light, aerobatic and 3-D planes.

Your estimate of 7 kg seems scary.

I now have a 1.92 m plane, that I am powering with a 26 cc MVVS glow, with the MVVS tuned pipe. It only weighs about 4.5-5 kg.


If your intentions are to fly this P-38 in a scale manner, not expecting it to pull up too steeply, it would fly with the standard silencer and will need a considerable runway length to take-off. The tuned silencers will give it a respectable boost.

With the #3245A silencer, as we talked in previous threads (and see in one of the photos), it will suffer from a power shortage, with this much weight to haul; to the point of being under-powered.

Thanks Dar.

The tuned pipe sounds like a great option for te engine, but Im concerned by the noise level. I haven't run the engine with the tuned pipe yet, but just looking at it seems like it will be very noisy

You can see through the thing

If I use the tune pipe, then it will have to be inside the boom of the p-38.
will this overeat the engine somehow ? (no cool air around the pipe)

I will have to install a 45 degree silicone tube to the rear end of the pipe to lead the exhaust gasses out of the booms.
Will this extra length of silicone have any bad effect on the engine ?


Thanks for you expertise Dar :-)

how do you think the mvvs 50 will compare with the os fl-70 powerwise ?

looks noisy

Sonnich,


The tuned silencer is noisier than the regular silencer, but this is mainly because of the higher pitch sound.
If the tuned silencer is cowled, noise will be reduced somewhat.

With the tuned silencer, this engine is capable of spinning an 11.5x6 Bolly prop, at 13,600 RPM.
For this specific model, I would recommend switching to an APC 12x5 prop, which will be spun at nearly the same RPM, but the thrust will be about 15% greater.

From a power POV it will have more than a .70-.72 four-stroke engine.

Cooling is very important for the engine, but the tuned silencer will not be harmed by extra heat (within reason).
So as long some airflow is also available for the mini-pipe, it should be OK. You will have to replace the silicone coupling, every now and then, however.

But the engine, if cowled in, must have sufficient cooling, with a large enough exit behind it and possible with baffles that direct cooling air onto the cylinder and the head. There must be a sufficiently sized, direct flow path for cooling.

About the exhaust deflector; I have had bad experience with it and the normal muffler. It reduced the RPM by 1,000!.
I cannot know what effect it may have on the tuned silencer.

Thanks Dar.
Ill use the 49`s :-)


But I have run into a problem.
How do I reach the needle valve in this large cowl?
There is no hole for a wire, or even a slit so I could adjust it with a screwdriver.

any ideas ?

Sorry, Sonnich.


You will have to put your mind to it and improvise.

This is not specific to the MVVS .49, of-course, as you would have this problem with any engine.

all my other engines have a hole and a set screy to install a wire
except my webras....they can be adjusted with a screwdriver.

ill have to think of something....maybe dremel a slit in it so I could reach it with a flat head screw driver.

hmm....thanks anyway

Ill think of something

Bit of a late reaction but:

The tuned silencer IS loud...BUT! only on the ground. In the air it's hardly any louder than other engines.

1st hand experience from my .26 Combat which probably runs at a little higher RPM's (14500-15000 on the ground :P) than the .49 will do :P

Didn't i reply in this thread?

If memory serves me will i posted something like..

It IS loud...but only on the ground. In the air it's just as silent as any other glow engine?