Bodge

Guys,

I have equipped my 91 with a 16 x 4 wideblade and mounted it in an Ultra-Stick 60. The engine has been carefully run for 2-3 hours on full 20% castor (with a 14 x 6) and is now showing 8,200 on the big prop. My question is: are those revs in the ball-park for that prop or should I go for something a bit smaller?

Also; do you recommend sticking with the 20% castor, or can I start introducing 50-50 synth?

The reason I am asking these kind of obvious questions is that I have run an MVVS 91 on a 13 x 6 before and it performed well. However, everything I've heard about the 91s tells me to load them up a bit. It seems, however, that 8,200 rpm might be a bit low...

DarZeelon

Mick,


From own experience, this engine will run better, the more Castor oil you put in the fuel.
Using 20% Castor is not likely to be a warranty voiding issue, but I do recommend to all my customers no less tha half Castor.
On straight Model Technics Duraglow, FE, this engine will disappoint you...

What type of silencer are you using?

The largest recommended prop for this engine is a 15x10.
While the 16x4 does offer a lower load, it does have significantly more inertia than a smaller diameter prop. If only for this reason, I would recommend going smaller for a 3-D plane.

Your Ultra Stick isn't one and you should use a 6" pitch prop.

Bodge

Dar,

I am using a Weston throttle pipe - see piccie - which does let the engine develop some grunt. This is an older shot with another engine (you remember - the one with the leaking shaft) and plane, but identical configuration except for the 14 x 6 shown. The plane flew well like this, however, I was intending to experiment with the 16 x 4 - as yet I've only run the engine in the back garden with the big prop. The weather has been too rubbish to fly.

You are correct: there is a definite "wind-up" time as the engine is struggling with the inertia of the big prop. I have tried it with a 15 x 4 wideblade, which hovers well and hauls the plane vertical with some acceleration.

I will take your advice and use full castor: I also take your point regarding the apparent "lower load". I think that while the aerodynamic load might be low, the mechanical load may be slightly too much for the motor.

So, I think I'll take your advice and go back to the 14 x 6.

Thanks for the opinion.

Bodge

Dar,

What revs should I be aiming for with this motor on the ground?

pe reivers

For better acceleration, you could use a wooden prop. These Plastic APC contraptions are way too heavy for proper throttle response.

DarZeelon

Mick,


Most of my customers use this engine on Tai-Ji 60 and similar F3A planes.

They use the #3250 pipe and a much extended header, with an APC 14x8 pattern prop and see 9,800+ RPM on the ground.

Seeing 8,200 RPM could mean your Weston Throttle Pipe is below its effective boost range.
If in unloaded conditions, full throttle level flight, the engine gets 'on the pipe', it could cause a lean condition...

For 'scale' speed, I would use a 16x5 wood prop. Good luck finding one...

Bodge

Pe, Dar,

Thanks for your response: I agree - the bigger APCs, especially the wideblades are heavy and take some winding up. I wanted to steer clear of a full on pipe because of the engine response, but I guess the flat plate pipes are fairly "soft". I have never seen 9,800 revs on this engine, but I have never used a full-length pipe.

Taking account of your comments, it would seem that a 15 x 6 Zinger would be in the ball park. I'll give it a try.

Cheers.

DarZeelon

Mick,


You're welcome.

If you select Zinger, go only for the Pro series only. Otherwise go for Bolly, Bambula, Menz.

The older design Zingers aren't as effective.

Bodge

The better wooden props are not so easily available over here (or I've not been looking in the right places), But I think I can get Bolly.

Thanks: I'll give it a try and let you know.

dinorc

Hi everybody, I have just purchased a new MVVS 91 and is now ready for break-in...The Dutch MVVS site suggests some large props from 14/7 to 15/10 ! The italian supplier suggests smaller ones and a chart on the Dutch site goes as far as 16/6... javascript:void(AddText('[]'))

Well ,I think I'll start the break-in with the 16/6 APC and then experiment with the other sizes on the Phoenix Extra 330S . Shall report on findings.
Any suggestions, comments, etc. are welcome in the meantime.
Good "motoring" to all.
Dino

DarZeelon

Dino,


This prop is very heavy and will only allow the engine to spin around 8,500 RPM.
It will not even come close to any RPM that the tuned exhausts are capable of supporting.

So, you would be using a normal silencer; #3255, #3255A, #3267, or #3298/10 (a lesser choice).


For break-in you want better cooling through high airflow (higher pitch), while at the same time, not over-loading the engine.
So the 16x6 prop is a very poor choice for this purpose.

A good selection of props for break-in is; 12.5x8, 12x9, 12x10, 13x8, or 13.5x8.

Follow [link=http://www.rcuniverse.com/forum/m_1850473/tm.htm]this RCU thread[/link] for best results.

pe reivers

I agree with Dar, and would add a 14x7 or 14x8 to the list for running in.
Use the prop that allows the engine to run about 9400 - 10500 rpm, and you will do fine.

dinorc

Thank you for the advice. Next week I will give some feedback.