using model aircraft digital optical tach on full sized aircraft

[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!