Multi-engine planes ? 1

[rb1957]

Can someone help me with a project ...

looking at a multi-engine plane, but I want to change out two (the outer pair) engines. The two new engines will have a different drive speed than the original. I have a propeller for the new engine (to suit it's speed) but the question is synchro-phasing. I know only enough to know what I don't know ... This is a real project and would probably engage professionally off line if there's a solution.

A thought I had was to manually adjust throttles ??

The current project is not for certification ... a proof of concept vehicle only. The final project would probably have all of the new engines. Would that be the easier way to go ??

another day in paradise, or is paradise one day closer ?

 

[GregLocock]

That's the easiest way, I don't see any particular virtue in trying to synch between the pairs. Incidentally you'll need a much better audio setup than I have here to really hear the fundamentals, 85 Hz is well into the roll-off of my decent speakers, and I ain't playing crude electronic crap through them. I'll dig a gaming subwoofer out of the pile of discarded toys and see if it makes more sense.

Cheers

Greg Locock


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[3DDave]

Spend some money on a real sub-woofer, one which approximates the circumstance:

https://www.soundandvision.com/content/eminent-technology-trw-17-rotary-subwoofer

. Pricey? Sure. Once in a lifetime spend. You may need to dedicate a room as the speaker enclosure.

 

[rb1957]

what I meant was synch-ing 1 and 4 ... right now there's none (2 and 3 would be synch-ed by a kludge of the OEM system) ... not much thought has gone into this detail (yet) ...

another day in paradise, or is paradise one day closer ?

 

[3DDave]

I would look to see if one engine is the master. Considering 1&4 are more influential it may be one of them.

 

[GregLocock]

Please ignore all the audio above. I have been finding out some undocumented assumptions that the wav writer makes.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[GregLocock]

Here you are in glorious 32 bit floating point at 44.1 kHz (undocumented feature being you can write wav files in all sorts of formats, but only that or 48 kHz is actually recognized by the player. Harrumph).

so the 4 numbers in the title are the rpm errors, you have a baseline, then engine 3 out by 5, then engine 4 out by 7 , then both out. I have reduced the amplitude of the outer engines as they will be attenuated by up to 6 db compared with the inners.

Here's what i used

%User input
N_blades=[3,4,4,3];
nominal_rpm=[1900,1200,1200,1900];
disp(N_blades.*nominal_rpm/60)
harmonic_structure=[1,0,.3,0,.1,0];%integer multiples of BPF, use complex for phasing
rpm_error=[0,0,5,7]; %usually LHS will be 0
wingpos=[-7.2,-3.6,3.6,7.2];%location in m. + and - don't matter. Not used
amplitude=[1,2,2,1];%arbitrary
duration=10;%seconds
dt=1/44100.;%seconds
wavfileout='waaWaa_sin_0_0_5_7.wav';



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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