503 Static Thrust?

[Scot White]

Anyone measured the static thrust of a Rotax 503? If so I would be
interested in hearing from you.

Scot White

[Bob Anderson]

Scot White wrote:

Scot, "thrust" is produced by the propeller, not the engine. For
instance, if the 503 is running at 6,200 rpm it may be producing 50 hp,
but the speed and diameter of the propeller at that engine rpm will
determine the static thrust. Basically, a large diameter prop with low
pitch (helicopter rotor) turning at a few hundred rpm produces a lot of
static thrust but little top speed, while a small propeller turning at
high speed produces little static thrust but high speed. This is why
there is a variety of "reduction ratios" available for engines such as
the Rotax 503. A 2:1 ratio will have the prop turning at half the
engine speed. E.g., the engine running at 6,200 rpm will be turning the
prop at 3,100 rpm which requires a small diameter prop. This is very
inefficient in converting hp to "thrust". What you can do (NOT
RECOMMENDED) is use a ground adjustable prop. Simply keep increasing
the pitch until the engine runs about 6,000 rpm at WOT (wide open
throttle). This is all the engine can do. The problem is there is no
simple way to know how fast the aircraft will be traveling at this RPM.
If you buy a fixed pitch prop it will have the pitch and diameter
stamped on it, e.g., a 24 X 60 prop has a pitch (blade angle) that will
move it 24 inches (2 feet) forward in one revolution, and the prop
diameter (length) is 60 inches (5 feet). It takes a little math to
extract mph from the prop pitch and rpm. Every design becomes a
compromise. If you are modifying or designing an airplane you should
already know all about this, otherwise I would suggest you simply trust
a reputable propeller manufacturer! He has probably seen about
everything tried for your application, and he knows what will work best
for you. Be sure to talk to more than one propeller manufacturer. They
ALL would like to sell you a prop.

[Bill Baker]

You also have to remember that the pitch on the prop is called the
Geometric pitch which you are right that in theory for every revolution
the prop moves forward 24". But there is a certain amount of slip so
the Effective pitch is less than 24". I think how much less depends on
how much drag the aircraft has. If the prop has to work hard to keep the
aircraft flying then the effective pitch is less. With a Sleek airplane
the prop does not have to work as hard so the effective pitch will be
closer to the geometric pitch.
I feel that the ground adjustable is the way to go as you can "tune" the
prop and engine configuration to the optimum for what you need. i.e.
Fine pitch for short takeoffs and fast climb rates or a coarse pitch for
cruising.
Just my opinion though.

[Ronald Kline]

Hi Scott

We have measured static thrust on several UL's , the best I have ever
seen was 350 lbs.
, with about 250 sa normal and down to 180 lbs.

Ron

[Watch FLTV]

I've measured 400# with my "tuned exhaust" on a stock Rotax 582 with stock
jetting.

We now have three tuned systems for the 503 and 582. (You pick the max rpm)

Will be doing static thrust tests on the 503 soon. I'm flying the tuned 503
and all I can say is WOW!

FACTS to follow.

Hank Austin

[Rainier Lamers]

Watch FLTV wrote in message
<19990512175516...@ng-cb1.aol.com>...

Very interested.
Hope you will post the details soon.

Rainier