Engines - long

[Jerry Budd]

>Jerry, we have some pretty good carbs so the idle and mid range 
>shouldn't be too much of a problem, as long the timing is 
>appropriate. I was even thinking of something along the Koger belt 
>drive reduction unit powered by something like a 120 or 145.

Hi Matt,

IIRC, Dean Koger flew a YS120 powered belt drive biplane at the 93 
Team Trials called a Dazzle-U-2.  It didn't have any advantage over 
the COTS motors of the day due to the weight of the flywheel needed 
to keep from stripping the teeth off the belt.  It wasn't the 
eye-opener that his Webra 61 powered belt drive Vortex was.  Dean 
didn't use it for very long.

>If Nat can turn a 17x10 in his OS 90 straight out at 7.5K, then it 
>should be possible to reduce the output of a 145 down to about 6K on 
>a 22-24" prop and keep the engine happy. It's times like this that I 
>wish I had a real machine shop around. I can only do so much with 
>hand tools.

Unless you can shift the middle of the torque curve to the left by 
about 3000 rpm while simultaneously  increasing its torque level by 
30% you're going to be way down on power (remember power = torque x 
rpm).  Prop efficiency will go up with the reduction in rpm but not 
enough to make up the difference.

>The webra 160 is a nice rig but it will not turn the large dia I 
>want unless it is reduced.

Agreed.  I've heard of some folks turning some pretty big props at 
surprisingly high rpms with their Webra 160's but trying to match the 
electric's output profile would likely be futile - with any glow 
motor.

>BTW did you put the electric on the back burner?

Only until I get time to start on the two ePartner kits sitting in my 
garage/workshop.  I learned a few interesting things at the Nats this 
year flying Frackowiak's ePartner that keep me headed in that 
direction.

1.  Electric has a distinct advantage over glow (and it doesn't 
matter whose/what glow motor we're talking about either).  If you 
tend to fly fast with minimal speed control the advantage is minimal. 
If you strive to  fly at a very constant pace the advantage is huge 
(even in Masters).  If you've seen the plane fly you probably know 
what I mean.

2.  Electric still has a ways to go wrt battery longevity and system 
reliability (cost issues aside - weight is no longer a problem with 
the new Generation II Lite LiPoly packs).  But overall, we're just 
not there - yet.

Nonetheless, I plan on flying electrics at the Nats next year (see #1 above).

Thx, Jerry
-- 
___________
Jerry Budd
mailto:jbudd at qnet.com
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