Date:         Mon, 24 Jun 1996 21:07:28 -0700
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         Arnold Schultz <aschultz@smartt.com>
Subject:      RE:Re: Well oh ya?


> << In all oppsed engines, exceeding 4000 rpm for any lenghth of time will
>heat up the oil and
>>>pound out the main bearings.  This pounding even happens to Waterboxers.
>>>
>>>Dennis H.
>
>Why then do so many aircraft engines have horizontaly opposed engines? They
>run at that rpm for long periods. 


        Aircraft have horizontally opposed engines so the can fit it in the
space allotted for aerodynamic reasons and maintain visibility. The flat
radial engines were an attempt to maximize the cooling and a disaster for
visibility.
        Rumor has it that the VW engine was originally designed as a
compromise. It was  to be able to fit in to a car or used in an aircraft.
That way they could make lots of the same engines for different markets.
That is why the VW engine has a lower than normal RPM than the engines found
in other cars. And was the engine of choice with home built aircraft for
some time, it required minimum modifications. 
        As for the RPM... generally most if not all general aviation engines
red line at 2750 RPM. Takeoff power at max would give about 2500 to 2700
RPM, cruise power is about 1500 RPM to 2200 RPM, idle is 6-800 RPM but set
at 1000 RPM for cooling. This is not for the engine but to keep the
propeller tips from exceeding the speed of sound. Some higher turning
engines are use to get the power from smaller engines, just go to your local
altralight field and you will see most if not all having a gear or belt
reduction system. 

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