using model aircraft digital optical tach on full sized aircraft

[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!