mick15

I am flying a Scalewings La7 and a Bates Quarter scale Sea Fury, they are both equiped with 250's both running 32x12 three blade Biela props. Both engines have been tachoed at 4k on the ground. This setup I think is ideal for these large warbirds, my view is people tend to fly this type of model much too fast.

The other thing much overlooked is throttle expo I run -65 (Futaba) with a linear throttle the last 30% does absolutely nothing so over-reving is a danger because at 3/4 the engine is actually flat out!

m

reyn3545

I'd say my 150 is about the same on the throttle curve... probably in the -65% range (Futaba), and I have the last 15% or so of carb throttle arm movement limited out of the travel range.... the motor actually decreases RPM a little at "full" throttle on hte throttle arm.

DrScoles

My Feedback: (18)

I made a feeble attempt at reading this whole thread. Too many tangents... Would it be possible for someone, preferably the OP, to make a 1-2 page caring and feeding tips sheet and post it to the first post? Maybe it could get stickied in the engine forum? I have a 250 on the way, like to know what to look for and the best way to maintain, can't read through this many pages. Maybe its already been done?

wingstrut

Thank you for the reply Detlef, I will be using a 32x18 sep prop on my 215, also a turbulator and an E-pump.
I agree, about the 12 pitch props, They are not enough, I have a 34x12 zoar if anyone is interested in it, it was used for bench running only, about ten minutes worth.

I don't think I will have too much of a problem with this as I will be flying an AMR 1/3 Waco.
A little more drag than a Corsair or Focke-wulf 190.
Also looking at a 34x16, I will test out the 32x18 first.

Ron

wingstrut

So Mick and Reyn, you are not opening the throttle all the way, because it doesn't run any faster the last quarter throttle, Did I get this correct?

Straightleg

Wingstrut, there is no increase in rpm from 3/4 to full. If you mechanichly adjust your servo arm to do this, you will also get a better resolution on the same travel...

/Straightleg

mick15

On the contrary Ron I would suggest a 12 prop is ideal for a slow draggy aeroplane such as the Waco. I fly my 3W 130" Yak54 (Moki215) on a Mentz 34x12 two blade wood, I can post a video link if you're interested. Your question regarding throttle expo is it makes the top end throttle "do something" linear throttle has no effect from 2/3 to full open, it has no relationship to whether you have the stick forward or not.

m

reyn3545

That's the way my motor runs the best... your mileage may vary! I actually see mine drop a few hundred RPM if I advance the throttle arm to full.

mick15

This high end throttle condition is not peculiar to Mokis, most piston engines exhibit this phenomenon.

m

samparfitt

My Feedback: (43)

Interesting as I have the low end of my throttle doing very little as I was finding the low end too sensitive so, as you can see in the picture (graph on right side), the curve starts out flat and then goes into a parabolic shape.
I just adjusted the curve until I was comfortable with the throttle curve.
I keep my throttle away from the full throttle most of time, anyway.
My PM test last week is 800/3660 on the ground turning a solo 32" 3-blade paddle style prop at around a 15-16 pitch and this is way more power than I need for this size plane (comparf F4U); ie, why I rarely need full throttle.
I find the plane flies very scale at about 60-75% throttle.
The last picture shows the pitch I'm using:

mick15

Yeah Sam, that's not that desimilar to the -65 Futaba curve, almost flat until 50% travel.

m

oy4310

Do any of you guys use expo on the throttle to keep rpm down in the middle gas.

mick15

No, the idea of expo is to achieve a linear response ie, 1/4 throttle 1/4 revs 1/2 throttle 50% revs and so on.

m

RichardGee

My Feedback: (156)

Here is CARF-Models P-47D Razorback, 'prototype #2' - I built the second available kit and wrote the builder's manual in the process.
In discussions with Andreas Gietz, we set up the 30" 4 blade prop with an indicated 14" pitch on the Solo adjustable hub. This resulted in 3900 rpm, full throttle, on the ground.
Performance in the air was awesome!
Other than needing frequent maintenance (and a $380 fuel pump for the ultimate in reliability), the Moki 250-5 is one hell of an engine!!
http://www.youtube.com/watch?v=8i9pTrbO67E

wingstrut

Thank you guys, I finally get it, I put some fruit in my cheerios this morning to help my brain start working.
I won't give the 34x12 away yet until I try it, thanks Mick, the way this thing turns up on the bench with the 34x12, I believe it may be too small of a pitch.
Here at sea level it swings it at 4800
Thank you everyone for the info, I'm sure I would have ruined my engine if this forum wasn't here.
Now I know how to set up the engine, prop, oil mixture and definitely keeping an ear out for the engine speed.
Richardgee, that is one heck of a good running Moki, and the plane is no slouch either.
Sam, I love that Corsair.

............Ron

mick15

Here's the video of my Yak54, I think it clearly shows how the 34x12 works on my 215.

http://youtu.be/nzyQJfkOKtY

m

samparfitt

My Feedback: (43)

FYI on RPM's:
My buddy Scott has a solo 3 blade on his 110" wildcat with a moki 250 and it's turning around 3200 on the ground and it goes like a 'bat out of hell' at full throttle. My F4U is heavier so I'm comfortable with my 3660 on the ground. The moki 250 is made for high torque and low rpm's. A friend of mine could measure his rpm's while flying and it was about 1000 more in the air (granted, his was a gas, single piston) but as far as I'm concern, 4200-4660 is more than enough rpm's in the air, especially when plane performance is excellent.
To me, RPM wise, going from a single piston gas engine to a 5 cylinder moki 250 is like going from a glow engine to a gas engine.

wingstrut

Thanks for the video Mick, your engine is clearly not over-revving, actually it sounds great.
It has that deep throaty roar and not the high pitch screaming you usually hear from the warbirds, it really loads up when you go vertical.
Your aircraft is not what I consider a high drag aircraft either, I will definitely try the 34x12 on my Waco and set the throttle curve as you suggested, if it over-revs then I will try a 34x16.
I assume you are still using the 80 weight gear oil in the front gear case, are you still having good luck with that?
I'm going with an electric fuel pump so I think I will add some to my engine also.

Thanks for your time, Ron

PS: I'm using a zoar 34x12 and you are using a Mentz 34x12, your prop could be more efficient explaining the lower rpm's...........Just guessing.

reyn3545

That reminds me... how often should you check/change the gear oil in the front case? Do you have to remove the case to check it? How do you refill it? I've pulled the cylinder off of the fuel pressure pump to add some grease, but I assume the front case should also be checked and filled once in a while?

I've only had mine off the ground 3 or 4 times, so it's probably fine for now..just checking.

Maxam

My Feedback: (62)

In studying aerodynamic efficiency curves of propellors the efficiency nosedives when the pitch to diameter ratio is below 1/2. A low pitch for a lets say "draggy" airplane such as a WACO is not necessarily best. A higher pitch such as a 32x18 is still excellent. The prop will pull the airplane as well as a lesser pitch but only if the engine is running at a wasteful high RPM. Full size warbirds even from WWI ran high pitches. Ultra low pitch to diameter props have high thrust if not moving or are moving at very low speeds such as the 3D crowd. When the speed of the aircraft reaches any significant speed, the efficiency drops dramatically. -Tom

mogman

To fill the front case on my 400, I remove a pushrod and lifter that is just below the centre of the crankshaft( #4 intake). Remove a pushrod and lifter from the top of the case and add oil 'till it runs out the lower lifter hole.
Can't overfill it that way. I use 40 weight engine oil with a bit of STP to "sticky" things up a bit. Before I started using oil in the front case, I pulled a few lifters and the contact face with the cam was DRY!!! After using oil, the faces have noticeable lube on them. I suppose gear oil (80/90) could be used, but some gear oil has detrimental effects on some brass components....not sure if Moki still uses any brass pieces in the front of the engine.

Cheers,
Dave.

oy4310

Okay I understand thats. I just need the power for take of, but have more than need in the air. I just think to expand the area at the sender for the 1500 to 3500 rpm

wingstrut

Tom,

I think I understand what Mick was saying, that most people fly their airplanes too fast to look scale, by reducing the pitch you can maintain a slower flying aircraft.
On the other side of the coin a higher pitch prop on a higher drag aircraft will give you better performance if you have the power to pull it, and I think we do!
The higher drag aircraft along with throttle management will help keep the speed down.
I think after it's all said and done, the left stick needs to be operated more.
We have one fellow in our club, he doesn't need a throttle just a toggle switch.

Ron

reyn3545

I took the Pilot Yak with the Moki 150 to the field today... for the first time, the motor ran perffect, got in 3 good flights and it's decent enough on the trimming that I had a little fun with it. I have a 26x16 prop on it now, but I think a plane this light would benefit from a 26x18 or so... at only 32 pounds, there's plenty of motor to handle the extra bite in the prop.

Quick question... I did get just a little oil coming out of the front seal, behind the prop backplate... is that normal for these motors?

Also, should what type of oil should I use in the front gear case?

Moebius44

My Feedback: (1)

On page 20(!) now, still no mention of 3-bladed composite props that work well on a 215 in a SU-31....anyone???