<<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>>

          <<  Lancair Builders' Mail List  >>

          <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>>

>>

>6-cylinder engines, both in-lines and horizontally opposed versions are

>balanced

>inherently both in first and second order frequencies.  This is why

>straight six

>cars are so smooth.

>V-6s and V-8s both have a 'rotating couple' (can't remember if it's first

or

>second order) that means that to smooth it out would require an additional

>counterrotating balance shaft.  These engines can sometimes feel 'lumpy'

as a

>result.





While it is true that theoretically a 6-cylinder opposed engine creates less

vibration than a V-8, the end result in a comparison between the TSIO-550

and the EngineAir V-8 is different. The difference between these two engines

is that they are running at different speeds

and their reciprocating masses are different.



The TSIO-550 has 550 cu in displacement and turns at 2500 rpm in cruise. The

EngineAir V-8 has 375 cu in displacement and turns at 3900 rpm in cruise (as

you might have guessed, it is geared). Because of the smaller displacement

of the whole engine and by it being divided by 8 instead of 6 to come up

with the displacement of each individual cylinder, the weight of each piston

and connecting rod in the V-8 is less than the weight of those parts in the

TSIO-550. This smaller mass results in vibrations of smaller amplitude which

is partially offset again by the fact that those masses move at a higher

speed.



I'm not an expert in vibration, but I think that the reason for the

EngineAir V-8 being smoother than the Continental is that you have lots of

smaller pulses rather than fewer large pulses and that higher frequencies

are perhaps easier to dampen. If it's the case that a lot of vibration on

the TSIO-550 is coming from the propeller, it sure helps that this V-8's

prop is turning around 1900 rpm in cruise





>Along with others, I've raised my eyebrows at the thought of someone trying

to

>develop an alternative powerplant without the backing of NASA or other well

>heeled organization.  I worked in the transmission department at Chrysler

>for a

>few years down the hall from engine design and recall that a lot of people

>took

>at least three years to develop a scratch engine (GM took about 8 with

>Northstar) with a lot of dynamometer and proving grounds time.





The EngineAir V-8 is in my opinion not a scratch engine. It is basically a

small block Chevy V-8 and is being built out of high quality and proven

components. The only "scratch" component is the gearbox.