Comments by "Alan hat" (@alanhat5252) on "Engineering Explained" channel.

  1.  @ifixit775  they do have to be in sync
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  2.  @ifixit775  double-helix gears are cut from 1 blank. They're less common nowadays because they're a pain to mass-produce & bearings have improved so the side-load is less relevant. The Victorians loved them though.
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  3. The blower on the Commer was noisy because it had straight-tipped vanes & I think a straight-walled port -- it made an almost-perfect siren. Careful adjustment of the geometry would drastically reduce the noise without affecting efficacy. As others have stated they were made in an era when noise wasn't an issue so nothing was done about it.
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  4.  @chicken29843  traditionally opposed-piston engines are large
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  5.  @marshalberthier2402  the Rolls-Royce Merlin only revs to 2,200rpm, there were several geared propeller drives in the era, I believe there still are.
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  6.  @chicken29843  they're taller than an OHC engine but tipping it over would probably fit it under modern low bonnets
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