Zpat

My Feedback: (2)

I have a MVVS .15 mounted on a 32 oz, 44" span, profile w/404 sq. in wing.

The manufacturer claims 26000 rpm for this engine. I've run 7x6, 8x3, 8x4, 8x6, 9x4, and 9x5 propellers.
It's now running an APC 9x3 N spinning @ 17,000 rpm and it seems to work best.
The model flies excellent at low speeds.

Is it possible to get strong verticle performance with this combo?
It barely pulls itself out of a hover. What kind of rpm can I expect from this engine?
I run Wildcat premium 5% fuel.


Thanks for the info.

eroc144

My Feedback: (1)

17k with a 9x3 is pretty good! Try smaller props with more pitch like 7x5 or even a 7x4. My Magnum .15 tears up the sky with a 7x5.

EG

Toad

The 7x5 is my favorite .15 prop. My next choice next would be the 8x4.. I have never ran a .15 on low nitro.
I use 15% - 30% nitro fuels in 'em
Sounds like you have a very fun plane there.
Is'nt that MVVS suposed to be a high power .15 that rivals the older big dogs like the Conquest and the Rossi?

fizzwater2

My Feedback: (61)

to get those kinds of RPM on quarter midget engines (15 - Nelson, Conquest, etc) we used to use props about 6" diameter, 4 1/2 to 5" pitch or so. Carbon fiber props with thin blades

combatpigg

My Feedback: (3)

32 ozs is too much for a .15 sized 3D model to weigh.
28 ozs is more like it, not that hard to accomplish.
This will make your engine much happier. I think the best all around prop for throttle response and thrust combined is the 8x3. The 9x3 might make more thrust, but the throttle response is not as good for hover control. It also is harder on the engine.

To run the bigger props it's sometimes a good idea to lower the compression by adding a head shim. Not always a rule, but keep the idea in the back of your head if tuning gets difficult.

Zpat

My Feedback: (2)

I already removed the landing gear to save weight. The only other weight savings would be the removal of the mini pipe but I wouldn't know what to use for exhaust.
I'll go back to the smaller props and see what develops.

MJD

My Feedback: (1)

26,000 maybe on a 6-4, 5.5x5 prop or thereabouts, but not on any props you've mentioned. It is a high timed engine and will be totally out of its element on large prop loads. 8-4 is the largest load I would ever put on a sport .15, let alone this guy. CP nailed it, 8-3 prop - let the engine spin, to pull out of a hover you need power, and you need to harness it efficiently. For this engine the power is all up high, 17/18k minimum and up, and peak power is likely up in the low-mid 20's. I doubt the blade area will work out for this kind of flying and aircraft, but you could try a 7-3 and get the engine rpm up there to test those waters. You have a 2 pound airplane on a .15 for 3D - you need more displacement turning more blade area or less weight.

Don't lose the mini-pipe unless the power loss is made up for by removal of weight - doubtful.

MJD

DeviousDave

This engine is timed like a .15 QM engine and will need a 6-6ish to be used as designed.

Zpat

My Feedback: (2)

Thanks for the replys.
I'll be testing and tuning.

DeviousDave

Just understand that peak power has nothing to do with what prop will work best for your airframe. Prop efficiencies are so horrible in the 6" range that a larger slower turning prop may likely be better for a draggy airplane used a as a sport flyer. The high top speeds seeen in QM15 are after having a lap and a half to accelerate to top speed so keep in mind that making lots of HP is great if you have the luxury of being able to fly straight for a football field at a time.