EXTENDED SPEED RANGE (ESR) EFFECT
We are using the term ESR effect (Extended Speed Range effect) to define a fixed pitch propeller (or ground adjustable pitch one) which behaviour is near from the behaviour of a variable pitch propeller.
This ESR effect has the following characteristics : it causes very small gap between the static RPM and the flight RPM, and this allows to keep a strong power at take-off.
It seems that the max throttle RPM stays nearly constant.
For example :
- take-off : engine full throttle 5400 RPM
- max speed 200 km/h : engine full throttle 5500 RPM
The gap between 0 km/h and 200 km/h is in this case only 100 RPM. For comparison purposes, a standard propeller (not ESR) can have a gap up to 1000 RPM between take-off and max cruise speed.
very speed aircraft : MCR UL 912 S (see here comparative with Woodcomp propeller)
Example for a ROTAX 912 engine, for 5.800 RPM at 120 km/h :
- a propeller not ESR will have between 600 and 1000 RPM less at take-off, and its thrust will be lower than 185 kg
- a propeller with ESR effect will allow to have only 200 RPM less at take-off (5600 RPM), it means a static thrust of 210 kg (10 % more!)
The ESR effect can improve the performances at take-off, because then the engine is running very near of its max RPM, and provide all its power during take-off.
Some E-Props models allow to have more RPM at take-off than in flight...
From technical point of view, there are different solutions to obtain this ESR effect :
- narrow chord with classic profiles
- pitch reduction at low speed by blades deformation (difficult to obtain)
- narrow chord with special profiles, in order to avoid the stall of the blades => it is the case of E-Props propellers
a ground adjustable pitch E-Props propeller better than an inflight variable pitch propeller
COMPARATIVE CURVES (THRUST and RPM)
between an E-PROPS ESR effect propeller and a standard propeller
in thrust % (100% = an optimal variable pitch propeller)
the thrust of the E-PROPS propeller with ESR effect is always above the thrust of a standard propeller
indicated RPM in % of the maximum engine RPM
during take-off, the RPM of the E-PROPS propeller with ESR effect is always above a standard propeller
please note : what makes aircraft taking-off, it is not engine RPM but propeller thrust
Thanks to their geometries anf their profiles, the E-Props propellers have a very strong ESR effect,
which allows to improve the performances of the aircraft at take-off and in cruise,
in comparison with a standard fixed pitch propeller.