Aircraft: use of piston engine, small report

[Other]

Hello

The efficiency of the propeller 70 to 85% on small planes, reached 98% in the best of cases ... counter-rotating propellers.

I don't know what you are basing on to say 85% return
In practice I speak more of sliding
I'm not talking about counter-rotating propellers (it's extremely rare on airplanes that a small variable Hartzel or a MacCauley already costs the price of a car!
When an airplane in cruise it advances close to the speed of the theoretical step in blade tip it's already a good return
A small diameter propeller with a narrow blade can do no more than slide. (It's like putting small wheels on an agricultural tractor)

In static aircraft attach to earth at full throttle, the output is zero it is a simple fan, when going up there is a significant slip which can be 40%, in level depending on the smoothness the slip can be very reduced close to 5 % and full throttle the slip increases the drag of the plane is felt

A plane is like a car without a gearbox, you have to start, climb sides and drive on a cruise, so the adaptation must be well taken care of.

My values ​​are the result of practical experience and tests done on many planes.
Currently there are few studies on propellers for small aviation, it has two large propellers, and the others of small production of wood propeller or composite.
Andre
An almost unknown propeller in Europe, but the most used by bush pilots, it was specially designed at the request of Alaskan pilots
It has a diameter of 2,14m, it is rotated at 2500rpm continuously.

[Chatham]

The disadvantage in auto diesel is heavy, slowed down, needs a fairly consistent steering wheel, it will seek its maximum power at speeds of 4000 rpm, which requires the manufacturer to install a reducer, which has the disadvantage of limiting the choice in the propellers.
Metal propellers with a gear reducer pose a problem on gears
A reducer is also mechanical losses, the weight gain on the motor is lost in the reducer.

A variable pitch propeller is only useful for a fast plane, installing a variable pitch propeller on a Piper J3 or an ULM which has a speed of 120 km / h uphill and a speed of 160 km / h cruising is ridiculous, a propeller with fixed pitch well proportioning is also efficient.

In Russia it's big propellers, pale drop, square tip
In America it is large minimum propeller 1,80m to 2,15m with medium tip, square or rounded blades. Duralumin and composite
In France it is small propellers, with narrow ends, pointed or slightly rounded generally in wood or composite.

There is a Diesel level solution, it is the supercharged 2-stroke diesel which has none of the disadvantages mentioned and has a power-to-weight ratio equivalent to that of a gasoline aircraft engine: see Wilksch engines ...
Metal propellers are unknown in Europe on small aircraft of amateur construction because of a huge cost and inducing torsional mechanical fatigue not only on the reducers, but on the crankshaft (there have been cases of crankshaft failure). In Europe only uses glued laminated wood or carbon / fiberglass propellers
A reduction gear is not necessarily a disadvantage because it allows the use of a silent propeller of good performance which largely compensates for mechanical losses: large American propellers are impossible to use in Europe because of noise regulations: a thresher 2.15m in diameter which turns at 2800tr makes an abominable noise (I know a private plane of American origin which used one: he had to change it under threat of expulsion from the aerodrome because the neighbors complained ... )
When it comes to weight: a slow engine is necessarily heavy because of large displacement, an engine reduced by half or even less displacement will not be heavier and just as durable as modern technology (notably nicasil cylinders) and sometimes supercharged ...

I know an ULM which is equipped with a variable pitch propeller, on a Jabiru engine which as you know turns quickly (3300tr at maximum power), which requires a small propeller otherwise it sounds like a warbird, well the difference of acceleration and climb performance compared to a fixed is quite breathtaking, but the cruising speed is identical ... on the other hand, indeed with a 912, with reduction therefore, an HPV is only valid on a fast ulm kind MCR (with a propeller MT propeller of 87% maximum efficiency: 270km / h when cruising at 75% and FL80 ...): those who can afford this kind of toy do not care to pay a little more ...

On the Bear, the counter rotating propellers are huge (7m in diameter if I remember correctly) with a very low wing loading and a low rotation speed, this is among other things what explains their extraordinary performance ... and their very very special noise ...

[Christophe]

Updated link: https://www.econologie.com/telechargeme ... onautique/