Chevy LS2 and Trans??? any real issues besides weight

Hey guys i'm a new pilot that really wants to build his own craft. help
me with this one issue.

I want to use a chevy ls2 or ls7 as the power plant in my craft.
now looking at everything including the hp/torque curves i've decided
running the engine around 3100 rpm should give me around 250 hp with
good torque now getting that power to a propeller seems to be an issue.
I'm wondering besides weight would there be any real issue using the
associated transmission locked in gear maybe 3rd/4th/5th gear whichever
is just under 1:1.

it would seem the car tranny has been engineered to convert the engine
motion into the spinning i would need to propel the propeller. plus
running the engine at 3100 rpm it would prob last longer than i will.

the aircraft i want to design is a very cab foward design with a
pusher prop and the engine would be mounted approx mid craft.

i'm new at this and besides having an engineering background i really
have no exp building an aircraft so any opinions would be helpful

thanx

Mrv

A car transmission is not a suitable propeller redrive, neither for a
car or a boat. Study marine practice carefully: it is the same duty
cycle, and after all, no one puts a Lycoming in a boat even though they
could afford to.

No sensible propeller for 250 hp is going to want to turn 3100 rpm.
The diameter of the prop sets its maximum RPM as the tips must be kept
below Mach 1. Probably, you are going to want about a 2:1 reduction.
With a Gilmer belt drive you need to be at exactly 2:1 or fairly far,
say 1.6:1 or 2.4:1, or it will hunt and skip teeth. With gears you will
want them ideally at prime number tooth counts, such as individual
teeth see each other only rarely, and very definitely not 2:1. This is
what caused the catastrophe known as the Continental Tiara.

Driveshafts are very problematic in aircraft drive applications, plus
which there are substantial negatives to pusher propellers.

You do not want to design a engine package _and_ an airframe. There
are more good airframes than engines, although admittedly many are
better built by factories (one wood design hawked by an arrogant son of
a bitch in Virginia who has never built an airplane himself comes first
and foremost to mind.) Most homebuilts are just not designed for 600+
pound power packages. Most people want smaller airframes, I think, for
lower materials cost and easier garage building, even if they are not
afflicted with the common brain disease pervading experimental
aviation, WSE. (Williamsport Spongiform Encephalitis-a disease where
the brain has cooling fins eroded in its surface, causing the victim to
think that 1939 lawn tractor technology is essential to flight.)

Thanx for the reply, i actually messed up in my previous post. the
intended numbers are 3200 to 3500 rpm and the propeller spinning approx
2500 to 2700 rpm.


why isn't a car tranny good ? it seems to do just what i want for
years in millions of cars reliably? Isn't the mated transmission made
to convert the slightly oval engine rotation into the circular motion
nec. for the prop? and also damp vib?


now the belt drive u mention seems reasonable but i really really don't
want my engine spinning faster than 3500 rpm:

thanx again

mrv

"MrV" wrote in message
ups.com...
Thanx for the reply, i actually messed up in my previous post. the
intended numbers are 3200 to 3500 rpm and the propeller spinning approx
2500 to 2700 rpm.


why isn't a car tranny good ? it seems to do just what i want for
years in millions of cars reliably? Isn't the mated transmission made
to convert the slightly oval engine rotation into the circular motion
nec. for the prop? and also damp vib?


now the belt drive u mention seems reasonable but i really really don't
want my engine spinning faster than 3500 rpm:

thanx again

mrv


The car transmission is not designed to run for hundreds of hours at high
loads in a lower gear. Lower gears in a car only accumulate tens of hours
over the life of the car. Plus you will be hauling a lot of excess iron
/aluminum around - excess weight is just about the last thing one needs in
an aircraft unless the intent is to minimize performance...

Slightly oval motion ot circular motion??????? It's just gears.

Damp vibrations? Not from a prop...

--
Geoff
the sea hawk at wow way d0t com
remove spaces and make the obvious substitutions to reply by mail
Spell checking is left as an excercise for the reader.

truthfully the idea is to make an OKAY craft. i'm thinking 150 to
160kts with okay fuel burn.
now if i'm right i'd be running the tranny in like 4th gear. isn't
this where its designed to spend a good deal of its time ?

if i remember right, a car engine's output is not perfectly circular
its kinda eccentric. and something is neccessary to convert the
irregular motion into the circular motion for the prop

"MrV" wrote in message
oups.com...
truthfully the idea is to make an OKAY craft. i'm thinking 150 to
160kts with okay fuel burn.
now if i'm right i'd be running the tranny in like 4th gear. isn't
this where its designed to spend a good deal of its time ?

if i remember right, a car engine's output is not perfectly circular
its kinda eccentric. and something is neccessary to convert the
irregular motion into the circular motion for the prop


If you are thinking of the top gear in a trans with overdrive, the overdrive
isn't designed for high torques (read the owners manual - "do not tow
trailers in overdrive"). Plus it will speed the prop, not slow it down. If
you are thinking 4th out of 5 gears in the typical trans with overdrive,
then you have direct drive - not much pont in bolting on a trans just to get
out what you put in, eh?

The auto trans has everything you don't want and nothing you do. No gears
would be a better choice than the wrong gears.

The torque output is not exactly constant, but the flywheel damps most of
that out. A propeller, on the other hand generates torque pulses as it goes
by cowling and stuff - that can cause problems if you are trying to run a
drive shaft. Pusher aircraft are "worst case". Note that most piston engine
aircraft have the prop bolted right on the end of the crankshaft - nothing
required to account for the torque pulses from the engine (Ignoring the
cases where you excite the resonant frequencies of the prop).

--
Geoff
the sea hawk at wow way d0t com
remove spaces and make the obvious substitutions to reply by mail
Spell checking is left as an excercise for the reader.

After building and flying a few airplanes you'll learn that weight is
the
MOST CRITICAL property there is in aviation.

Next comes harmonic resonance (well, in most auto mods anyway).

Richard

"One test is worth a thousand expert opinions"
Tex Johnston

600 LBS,,,, Yea right........I fly a auto conversion several times a
week and it is doing fine. Don't get me wrong, it took ALOT of time to
think it through and several generations of cooling systems but,,,
boy is it a blast to fly now..

Ben
www.haaspowerair.com

"stol" wrote in message
oups.com...
600 LBS,,,, Yea right........I fly a auto conversion several times a
week and it is doing fine. Don't get me wrong, it took ALOT of time to
think it through and several generations of cooling systems but,,,
boy is it a blast to fly now..

Ben
www.haaspowerair.com

I can't tell for sure, since you didn't include some of the original post,
but I think the 600 pounds was a ballpark figure, if the OP had used a V-8,
the full auto transmission, and another drive unit to take the prop loads,
as he suggested he would.

Don't get me wrong; I am an auto drive fan. (or supporter, at least) g
--
Jim in NC

I can't tell for sure, since you didn't include some of the original
post,
but I think the 600 pounds was a ballpark figure, if the OP had used a
V-8,
the full auto transmission, and another drive unit to take the prop
loads,
as he suggested he would.

Don't get me wrong; I am an auto drive fan. (or supporter, at least)
g
--
Jim in NC



///////////////////////
Jim is correct there, It would weigh in at a ton....g