The Murphy Builders Site

Boy, this Chevy V8 thing is creating all sorts of questions and reminding me
of how much I have forgotten since I went to school and got a degree in
Aeronautics. I was hooked on 2700 RPM purely because virtually all of the
planes I have flown from the SPAM CAN fleet seem to redline around that
figure. Bigger prop and spin it slower is sounding good. I have always
been more interested in takeoff and climb performance than cruise speed. I
like to fly. If it takes a little longer to get somewhere, that is usually
a good thing. (Unless I have to see a man about a horse.) I'm beginning to
think that I should begin my package at the prop instead of the engine,
which is what I have been doing. Get the biggest three blade prop I can and
still retain a comfortable distance from the ground in a level attitude.
Then, I think the next step might be to compute what RPM gives me mach speed
at the tip, and back off from there a bit to give me max prop RPM. Then
determine once and for all what engine RPM I should use as redline and find
a reduction unit based on those figures.

On another subject, I mentioned a while back that I replaced the front door
post channels with much beefier ones. Recently I noticed something pretty
disturbing. The square tube front wing spar carrythrough somehow became
angled back slightly towards the tail after the changeover. Even worse,
after I completed installation of the rear wing attach mounts, they appear
to be angled slightly forward! One builder who has completed his airplane
told me I should be able to deal with that during final fitting of the wing.
Might have to run a drill or ream through the holes with the wing somehow
held in place due to the misalignment. Is this common? There's room with
the front attach fitting to maneuver around a bit but the back fitting is
snug in between the mounts. Ideas?

Mike Kimball
SR#044

-----Original Message-----
From: murphy-rebel@dcsol.com [mailto:murphy-rebel@dcsol.com]On Behalf Of
Wayne G. O'Shea
Sent: Saturday, December 01, 2001 7:22 PM
To: murphy-rebel@dcsol.com
Subject: Re: Marcotte group purchase


Brian is spinning the original 2 blade Hartzel Seabee prop, still hooked up
to go Beta for backing away from the dock, if anyone knows what length they
came with you can go from there. He stayed with the original prop as he had
it already and for the fact that he couldn't go any longer on the Seabee
without putting a large slice in the fuselage boom on the first turn of the
engine! The only book I have says the Franklin spun it at 2500RPM.

Regards,
Wayne G. O'Shea
www.irishfield.on.ca

----- Original Message -----
From: "John Worden" <worden@owt.com>
To: <murphy-rebel@dcsol.com>
Sent: Saturday, December 01, 2001 11:10 PM
Subject: Re: Marcotte group purchase

I checked my Contact! issue #59 with the article by Brian Robinson.
He says he is using a 1.7:1 ratio and a 2 inch chain. He claims that Fred
Geschwender
convinced him to build his own redrive since Fred's unit was too short.
He does not say what diameter prop he is swinging but he does say that
it is a Hartzell with a max speed of 2600. It would still be good to talk
to Brian now that he has experience with this ratio.
Brian's phone number is 705-374-4347

I have to agree with Wayne about lower prop speed on the larger props.
Most props that are spinning at 2700 are not much bigger than 72 inches.
John



At 07:28 PM 12/1/01, you wrote:

I claim to know ABSOLUTELY NOTHING about torque curves, gearing and where
(what RPM) to make horsepower with your auto conversions (that's why I

take

the easy/proven way out and stick with WWII technology!), but I can offer
that the reason a geared Lycoming outperforms (STOL, not cruise) a direct
drive Lycoming rated at the exact same Horsepower is the fact that it

puts

out more torque at the propellor (were it matters) and can turn a larger
prop at a slower speed where it is more efficient, creating more THRUST.
This is also the secret to the radial engine plugging away at slow speed

and

spinning a large prop.

If I'm full of sh@# let me know, I've been told before! Just my view on

the

gearing issue!

For reference I provide the GSO 480 Lycoming. Take off power is 340 HP at
3400RPM. The prop is a 3 bladed Hartzell that is 96" (8 feet) in diameter
and is only turning 2182 RPM at full power due to the 77:120 gear ratio
(1:1.5584) and you want to see climb!!! Even in an aircraft that weighs
2875lbs empty I see close to 2000FPM, with 2 on board and 66 gallons of
fuel! Cruise is about 125 MPH at 60% (204 HP burning approx.17GPHUS).
Doesn't get much faster at 75%, with about 130 MPH, but really increases
the fuel burn on a supercharged engine.

This probably offers you nothing to go by with your 350 block, but you

need

someone (that has been there before NOT THEORY) to determine a gearing

that

lets you spin it to a reasonable engine speed (that will allow it to make
good power and remain dependable), while creating sufficient thrust at a

low

enough prop speed to remain efficient, without bogging the engine down.
Maybe since you are going auto engine you could throw in the transmission
and shift gears after take off!!!! ;>)

I think you have already done so, but I strongly suggest trying to get

Brian

Robinson to tell you the ratio on his drive in the LS1 Seabee. He derated
the Corvette engines HP, so it would last longer and turns it slower than

it

would in the car also. The climb of this (pusher) aircraft is nothing

short

of AMAZING!! Cruise is a lot better than the Franklin powered "bee also,

but

of course it should with an extra 100 HP under the cowl!

Regards,
Wayne G. O'Shea
www.irishfield.on.ca

----- Original Message -----
From: "Peter Cowan/Lexy Cameron" <cowcam@pipcom.com>
To: <murphy-rebel@dcsol.com>
Sent: Saturday, December 01, 2001 8:36 PM
Subject: Re: Marcotte group purchase

350-400HP.

housing

happen

to

speed

at

4500,

RPM

to

engine

2700

effect

use

of

Does

Mike all of Marcotte's larger drives have provision for a constant

speed

oil

supply.
Is there something magic about the 2700 rpm number? While you and I

are

into different engines (and planes) we both will want good take off
performance with relatively slow cruise. To me that says go for as big

a

prop as possible and if necessary run it slower. So what is wrong

with,

say,

a 2400 max rpm? There have been lots of aircraft that had max prop rpm

less

than that. No one has offered any data that says it is "bad" to design

for

lower prop rpm unless I've missed something.
Peter.


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Hi Mike,
I just talked to a new friend that is building a Velocity and I had heard that he is installing a V8. It's true. He's been through alot of the questions that you have been asking, and it sort of peaked my interest. Just a couple of things to begin with . Head choice. He has gone with the edlebrock heads but part of the determination was made by the use of headers. He had to send one set back. He also has gone with the edlebrock fuel injecton, and has had a great deal of help from the factory, with the m knowing what his application is. He also went with a Dart engine, but he has found that the timing chain cover is to close to the new 4 bolt bearing support and he had to drop the oil pan to make small grooves for the oil to drain back. This was all in abou t a half hr. Sooo the best part is he has no problem discussing the whole setup with anyone in aircraft. He is Bill Mulrooney, E-mail is majomlry@ aol.com. Give him a shout, I think he can help. Curt N97MR

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