using model aircraft digital optical tach on full sized aircraft

[Al Skierkiewicz]

Frank,
Lot's of airplanes use speed reduction on the prop. The Cessna 400 series and Beech Bonanza have them. Many experimentals that use automotive engines use them to keep the engine RPMs up in the power range. Lycoming engines with the "O" prefix are all reduction engines.

[FrankJ]

My point was that even with speed reduction, it is a constant. So if you know one RPM you know the other.

Fixed reductions are pretty common. CVTs (constantly variable transmission) is the red herring since I do think they get used on planes. I should watch putting too many thoughts in one paragraph.

Lycoming IO series engines are direct direct drive though

[IndySam]

Only on CD can you learn about aircraft engines in a discussion probably started by a spam bot

I love this place!

[orvie6]

Thanks guys for the responses..
To help clarify the issue.. I have an experimental aircraft that uses a full VW engine in direct drive.. I have a shielded ignition system using a Magneto..so the 'wire to distributer' wont work, nor will my Tiny Tach that has the wire that wraps around a spark plug wire..Since it is direct drive, I thought that using the 'model airplane tac' with extended photocell would be the best way to monitor rpm..and as usual...that would only be a reference..Im sure that I could tell if there was a problem with the engine by listening to the noise..and since I dont plan on flying this is any kind of bad weather, nor is there room for two people..it is all relative!!
Thanks again for the replys

[Garrett.d.w]

If you are using a VW engine, couldn't you just use the tachometer that was sold with the vehicle for which the engine is designed?

[orvie6]

I do not have one available...actually, I was mistaken...it is a 1/2 VW..and most of the unwanted holes have been welded shut!! So to use the mechinal tach wont work..besides...too heavy and cable too long!! and no connection for an electrical tach.

[Nate Laverdure]

How about a hall effect sensor instead? You could set it up to sense the passing of gear teeth, or bolt heads...

[DonRotolo]

Originally Posted by orvie6

..and since I dont plan on flying this is any kind of bad weather,

Aye, but weather has a way of sneaking up on you.

I agree, your ears will give you a good indication, using this as a secondary reference may be acceptable. Again: Tape it to the cowling and see what happens!