Re: Engine selection

[Jerry Davis <lts@avnet.co.uk>]

I am not sure why people think three blades are less efficient. Like
everything in aircraft design propeller selection is a compromise. The most
important feature is probably that the propeller is well matched. The blade
size needs to be matched to the engine hp. Large diameter props are more
noisy and having a large diameter prop may limit the tops speed of the
aircraft. In my experience a 64" three blade wide chord (130 mm) is a good
choice on aircraft with the 912S at speeds up or near 160 kts. If you think
your A/C can go faster it might be advantageous to have a smaller prop but
at the loss of take off and climb performance.

Jerry

                                                LTS@avnet.co.uk
                                http://www.avnet.co.uk/touchdown
----- Original Message -----
From: Nigel Charles <72016.3721@compuserve.com>
Subject: Engine selection


> Message text written by INTERNET:clevelee@cswebmail.com
> >
> In addition to wondering why Europas use 3 blade less efficient (than two
> blade wood) carbon fibre props, he offered the best advice yet (which has
> been rattling in the back of my mind) on engine selection:  The Europa is
> an expensive aircraft (from his VW aircraft perspective) and installing
> anything other than the factory recommended engine will severely
> deteriorate the resale value of the aircraft.
> <
>
> The loss of efficiency for the 3 bladed prop doesn't seem to be as much as
> the theory would predict. The main reason for the 3 bladed version is to
> improve ground clearance - very relevant for the mono wheel. The necessary
> increase in diameter for a 2 bladed prop would increase the risk of prop
> strike. It may be practical to look at  2 bladed props with the tri-gear.
>
> Nigel Charles