Zpat

My Feedback: (2)

I 've read in some forums about propellers shattering due to excessive rpm. Where can I learn more about the durability of propellers in regards to rpm?

mpalermo

This something I have read, there is probally more out there.

http://www.apcprop.com/Safety/safety_concerns.html

Mike

Zpat

My Feedback: (2)

Mike,
Thanks for the information.

If I'm spinning a 7x4 Master Airscrew @ 19000 rpm static on the ground, what would you think it would unload to in the air?

ZAGNUT

My Feedback: (1)

for apc props divide 190,000 by the prop diameter in inches for the max rpm
for mas props do the same but use 160,000.

but then i've spun the mas 7x4 way past its "rated" 23k rpm and haven't killed myself...yet


dave

DarZeelon

Dave,


Change to an APC of the same size.
It will slow you down a bit, but that 'yet' bothers me.

I would not test it, if I were you.

...Unless you want to hear your MVVS at 40K for a second....

Nice to know you have already exceeded 23K.

Ed Smith

Zpat,

It depends what engine you are using.

Ed S

ZAGNUT

My Feedback: (1)

Dar, i'm still running the first cylinder but with a pipe, still haven't played with the head either. just did a quick run with the MAS to see if the 500 rpm gain meant anything in the air, the APC is still faster.

pretty sure i'm exceeding or very close to the 27K limit for the APC when unloaded in the air, need to start looking at some pylon props or maybe a cut down 7x5-7x6 before i go on to the next round of mods

Zpat, you're running the MVVS .15 with tuned silencer right? i doubt very much that it would get close enough to 23k unloaded to be a concern but if you switch to the APC you'll have a much larger safety margin and better speed. you will also get a lot more noise with the APC[>:]....


dave

TLH101

My Feedback: (90)

A friend was turning a M/A 8x9 or some wild size at about 18K+ on a MVVS Grrt .40 a few years ago. It was on a Diamond Dust, and when he made one of his "haul-ass" low passes, the motor just screamed and then stopped. We assummed he had lost a prop, but when we picked up the plane , the prop hub was still there! The plane was directly in front of the pits when it happened. Luckily we never knew where any blades landed. We did not know about reccomended prop rpms at the time.
Oh yeah, the bearings were "toast" .

DarZeelon

Terry,


Bearings are prone to go, when the prop blades are thrown.

That MVVS GRRT you are talking about, is the old #3065 model.
It was a converted standard 6.5 (.40) engine, that had rather ordinary bearings.

It is no longer in the MVVS catalog, but the US distributor still has them in his web site.

Even then, most standard bearings withstand 30,000 RPM, as do most bearings in model engines.
They are actually rated for this speed, open; in oil-mist lubrication, by their manufacturers.

MVVS use Swiss made WIB racing bearings in their 'real' racing engines, the #3070R GRRT and #3070F GRFT.
These bearings are rated to higher RPM and radial load levels and are less likely to fail.

These engines also sport a needle bearing con-rod.

TLH101

My Feedback: (90)

Dar,
Was definatley an older motor, it's been about 7 or 8 years ago. He sent the motor in to the distributor a couple of years ago, but it still did not feel right when it came back, so he has not run it since.