another poor man's car engine conversion

bildan wrote:
You might like this.http://ibis.experimentals.de/downloa...lvibration.pdf

I've read this several times in the past. What strikes me is the
absence of test equipment like wireless load cell torque sensors on
the shafts. If used, any torsion oscillations could be seen on an
oscilloscope long before they became destructive.

You must have missed the fact that this all took place in the early
sixties and seventies. Even if they had practical wireless sensors for
this, they didn't have the compute power available economically to
process it. Having said that, you still have to account for the effects
of the sensor. For that matter I think that wireless sensors and
attendant equipment are still not practical for the average modern
homebuilder.

High speed shafting is as old as the industrial revolution. Solutions
to torsion oscillations are just as old. Yes, there are potential
problems but there are also well tested solutions. The trick is
knowing what they are and how to use test instrumentation.

The other thing that jumps out about the Bede saga is that fact that
they were trying to put an experimental engine/prop drive into an
experimental airplane before it was de-bugged and they were doing it
under a deadline.

That's snakebite country. Even things that work everywhere else are
almost certainly going to bite you under those conditions.

It's vital to work one problem at a time. If it's an experimental
engine and prop drive, work on that until it's been running sweetly
for a long time. Then, maybe, think about designing an airframe
around it.

Sometimes an experimental airframe demands an experimental engine.
Engineering is seldom one dimensional, which is why I was poking at the
use of a long flexible shaft as a guaranteed solution. As far as
deadlines go, thats may not be a factor for a homebuilder, as many
projects get completed post mortem, but it is a factor form commercial
endeavors (Moller notwithstanding)

Charles

On Feb 15, 11:43*am, Charles Vincent wrote:
bildan wrote:
You might like this.http://ibis.experimentals.de/downloa...lvibration.pdf

I've read this several times in the past. *What strikes me is the
absence of test equipment like wireless load cell torque sensors on
the shafts. *If used, any torsion oscillations could be seen on an
oscilloscope long before they became destructive.

You must have missed the fact that this all took place in the early
sixties and seventies. * Even if they had practical wireless sensors for
this, they didn't have the compute power available economically to
process it. *Having said that, you still have to account for the effects
of the sensor. *For that matter I think that wireless sensors and
attendant equipment are still not practical for the average modern
homebuilder.

I didn't miss it. I did tests like this in the early 1960's. Load
cells are just Wheatstone Bridges and the wireless tech WAS available
then - it just used discrete components instead of IC's. It needs no
computer power whatsoever since it's an analog signal. If you don't
like wireless tech, slip rings are available.

The sensors are very light and have little or no effect on the shaft
under test - if they did, no one would use them. In any event, you
can put an accelerometer on a shaft bearing housing and see if it's
output changes when you remove the torque sensor.

The only reason they didn't use instrumentation must have been that
Bede was cheap and in a hurry. It was definitely available and not
expensive.

Torsional resonance instrumentation is absolutely practical for home
builders and it doesn't cost all that much. The oscilloscope is
probably the most expensive thing and you could probably borrow one.

If I were going to do the auto engine shaft drive thing, I'd buy a
cheap running engine from a junk yard. If it ran rough, so much the
better. I'd build up the firewall forward drive system on a trailer
with a club prop. Then I'd run it to find and eliminate resonances.
Only then would I build an exact replica of the flight article using
new components and run that on the test stand.

"bildan" wrote in message
...
I didn't miss it. I did tests like this in the early 1960's. Load
cells are just Wheatstone Bridges and the wireless tech WAS available
then - it just used discrete components instead of IC's. It needs no
computer power whatsoever since it's an analog signal. If you don't
like wireless tech, slip rings are available.

The sensors are very light and have little or no effect on the shaft
under test - if they did, no one would use them. In any event, you
can put an accelerometer on a shaft bearing housing and see if it's
output changes when you remove the torque sensor.

The only reason they didn't use instrumentation must have been that
Bede was cheap and in a hurry. It was definitely available and not
expensive.

Torsional resonance instrumentation is absolutely practical for home
builders and it doesn't cost all that much. The oscilloscope is
probably the most expensive thing and you could probably borrow one.

If I were going to do the auto engine shaft drive thing, I'd buy a
cheap running engine from a junk yard. If it ran rough, so much the
better. I'd build up the firewall forward drive system on a trailer
with a club prop. Then I'd run it to find and eliminate resonances.
Only then would I build an exact replica of the flight article using
new components and run that on the test stand.


While it is very likely that Jim Bede was cheap, or broke, and in a hurry; I
have also heard that they, meaning the senior staff on the project, simply
did not believe it--and also had great difficulty accepting the idea that a
softer, and intuitively a weaker, drive system could solve a torsional
resonance problem.

Also, my persoanl recollection is that there was once additional information
posted somewhere regarding the BD-5 development project--but I have no idea
where to find it on the free Internet. A very similar, if not the same,
article is also available in a back issue of Contact! and used to be readily
available--possibly on PrimeMover--and I could swear that there were more
pictures and possibly longer text.

In any case, you are absolutely correct that all sorts of strain guages, and
connections for them, were readily available and inexpensive by the middle
sixties and the frequency range was perfect for the cheapest oscilloscopes
commonly used in high school electronics classes at that time.