I have seen several big ships with reduction, not all of the big diesel/HFO are (that) slow speedTommy Cookers wrote:backlash is often seen as the cause of the problem when it is just the symptom (removing backlash doesn't cure inadequate design)langwadt wrote:I can see why it might be problem for an engine driving a propeller where the propeller might have bigger inertiaautogyro wrote:'Gyro' (hmm) backlash does occur .......
It is why Ken Wallis always uses a direct drive prop on the Wallis autogyro designs. (no problem with electric drive of course)
A high reving engine that needs a reduction gearbox to slow the prop always gives excess wear due to backlash vibration, it can be very bad and even lead to breakage.
Weslake designed a one off prototype engine for Ken that suffered from this problem as did the Norton Wankel prototype they gave him but to a lesser extent. The engine designed and built for Ken by Hewland was not as bad and had a damper fitted.
On light aircraft it is useful to use 'boxer' and long stroke engines to keep rpm to 4000 or lower with a direct drive.
It may be why there have been almost no real development in light aviation engines since the 1930s.
However, F1 engines dont usualy run at very low rpm.
It might also be a reason for 'blipping' the throttle at idle to keep the revs up and the gears driving.
than the engine itself
eg propellor inertia depresses the natural frequencies of the whole system
major and ill-defined torque vibration (aerodynamic ripple and plane of rotation blade flexing) is always a design problem
BTW the 'real developments' in light aviation engines have been numerous and have all failed to be good enough
(Detroit V8s from Buick/Rover to bigblock, Renault, Porsche, Honda etc and diesels)
part of the long life (2800 hr TBO) of the 'old-fashioned' engines is due to their pushrod seperate-cylinder air-cooled design
(only one ever cylinder fails a compression check and is easily sorted in situ and without dismantling the whole engine)
reduction gearing is both pointless and worse than useless below 300 hp
(variable propellor pitch though is usual above 120 hp, and is very compact, very light and very reliable)
real diesels are always found in big ships and have never had reduction gears (that's a big selling point)
they are the most efficient piston engines (cruise BTE 50-55%)
don't many aircraft and F1 engines have resonance rpm (to be avoided) below their normal running rpm ?
eg Peugeot F1 engines had ring flutter resonance around 11000 rpm and blew up after a few seconds at that (ask Mr Brundle !)
isn't that type of thing part of the throttle blipping culture ?
apart from the complexity wouldn't modern tdi etc. be a good fit for aircrafts? power at lower rpms and they could probably be made to run on jet-a
Blipping makes sense, in neutral all the pressures and forces are "wrong" and there is very little load to dissipate any resonances