The Murphy Builders Site

Hi All,

We are trying to pin down the length of the MT 3 blade propeller (with
reverse) to install on the nose of our M-14PF 400HP Super Rebel on Areocet
amphibs.

Converting cm to feet we are trying to decide between the 8 ft. or 8.5 ft.
lengths.

The issues seem to be shorter will give a faster cruise. Longer better take
off and climb. The factory's initial recommendation was 8.5 ft. We have also
been told by the American dealer that with the 400HP the shorter prop will
give us ALL the take off performance we will need and will gain a few knots
in cruise.

We would appreciate any input to help us make a decision before ordering
this week.

Regards,
Don Boardman
& Partner
Randy Bowers
SR3500#130 "The Muskie" M-14PF Aerocet 3400 amphibs, Rome, NY




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Hi Don !

Can't help much, but I have heard that the Pitts guys are
using the longer props - not sure why....

Generally, a long, slow turning prop is more efficient than
a short faster turning one, but .... you might want to dig out
the calculator & see what the tip speed will be on that long prop
at the peak rpm - if it's getting up to more than 80% of supersonic,
efficiency will drop drastically. In that case, the shorter prop
would definitely be the better choice ...... (and your neighbours
will like you a LOT more ! :-) )

Dragging floats pretty much takes 'cruise' out of the
picture anyway - the dealer may have some other reasons, like:
is the shorter prop a bit stronger, therefor better for all
those ponies ?? Or maybe he has a bunch in stock - and the
longer ones are harder to get ??

Sorry - as usual - more questions than answers !! ;-)

.....bobp

-----------------------------------orig.--------------------------
At 11:03 AM 3/11/02 -0500, you wrote:

Hi All,

We are trying to pin down the length of the MT 3 blade propeller (with
reverse) to install on the nose of our M-14PF 400HP Super Rebel on Areocet
amphibs.

Converting cm to feet we are trying to decide between the 8 ft. or 8.5 ft.
lengths.

The issues seem to be shorter will give a faster cruise. Longer better take
off and climb. The factory's initial recommendation was 8.5 ft. We have also
been told by the American dealer that with the 400HP the shorter prop will
give us ALL the take off performance we will need and will gain a few knots
in cruise.

We would appreciate any input to help us make a decision before ordering
this week.

Regards,
Don Boardman
& Partner
Randy Bowers
SR3500#130 "The Muskie" M-14PF Aerocet 3400 amphibs, Rome, NY


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Hi Don !
Can't help much, but I have heard that the Pitts guys are
using the longer props - not sure why....

From what I have been told, for aerobatics they want max climb ... and
straight up performance. They are going 9' I think.

Generally, a long, slow turning prop is more efficient than
a short faster turning one, but .... you might want to dig out
the calculator & see what the tip speed will be on that long prop
at the peak rpm - if it's getting up to more than 80% of supersonic,
efficiency will drop drastically.

Tip speed is not a problem on the geared M-14

Dragging floats pretty much takes 'cruise' out of the
picture anyway -

A definite consideration. Maybe the biggest one... So I was leaning to the
longer 8.5' Might as well get max performance take off and climb if you
aren't going to go fast anyway. BUT then, if the floats are slowing you down
already do you want the prop to add to the problem?????

Bob, a crystal ball view of what you think the rig can cruise at ?

the dealer may have some other reasons, like:
is the shorter prop a bit stronger, therefor better for all
those ponies ??
Or maybe he has a bunch in stock

Strength should not be an issue. Each prop is built to order presently a 10
week wait

Sorry - as usual - more questions than answers !! ;-)

Bob, thanks for taking the time ALL input is helpful.

Regards,
Don Boardman
& Partner
Randy Bowers
SR3500#130 "The Muskie" M-14PF Aerocet 3400 amphibs, Rome, NY





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In a message dated 3/11/02 8:38:45 PM Central Standard Time, bob.patterson@canrem.com writes:

you might want to dig out
the calculator & see what the tip speed will be on that long prop
at the peak rpm -

Propeller Speed Calculator
Here's a site thats kind of fun to play with.
Phil&Lisa Smith

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