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Some reasonable suggestions, Bob
The modifications that are
offered by the Aussies for the stock turbo should result in less
rotating speed for a give mass flow (which will not appreciably change).
This will tend to minimize the over-boost problem at higher rpms common to the
stock turbo. To compensate for the lower rotation speed, they are
installing a bigger compressor wheel which will be more efficient that the
smaller stock wheel. So for the same boost should produce a cooler air
charge. It will take a bit more engine rpm to get the same boost, will
reduce exhaust back pressure and should in generally made the turbo better
suited for aircraft use.
I think the modifications you suggested point
toward controlling the exhaust gas better which would certainly help
things. I think the modifications that John is having made will do that
and improve the intake (compressor) side as well.
I believe that Todd's modifications of enlarging
the integral waste gate port and drilling through the scroll divider will also
improve control of boost levels at higher rpms.
I guess we will have to wait and see how this all
turns out.
Ed
Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
----- Original Message -----
Sent: Monday, July 12, 2004 3:42 PM
Subject: [FlyRotary] Re: Three candidates
for Turbo Failure
Ed and John,
So this brings us to what do we do
now?
Test 1: install new modified turbo! Check MAP to see if he
is still producing to much boost.
I believe he should get some ramp-up of
boost and it appears he is making to much.
Test 2: put a spacer in
between the back cover of the turbo and the turbo, where the wastegate is
located.
this will allow the wastegate to open farther.
Test 3:
Remove the wastegate all together.
Test 4: Find a more suitable turbine
wheel.
Bob
On Jul 12, 2004, at 12:45 PM, Ed Anderson
wrote:
1. we could have a condition whereby the turbine was not in
the "overspeed"
territory but operating at a lower (safer speed) and a
condition existed
that build up a deposit on the turbine wheel until its
out of balance state
caused it to touch the housing and fail.
2. A
worn bearing ultimately resulted in failure due to wobbly and
wheel
contact (Possibly acerbated by periods of long boost at high speeds
- but,
not a true overspeed condition)
3. Overspeed of the
rotating assembly resulted in failure (due to operating
too far to the
right on the compressor map possibly acerbated by the leak in
John's
intercooler and/or BOV valve).
4. Defective weld of wheel to shaft
(Pretty remote chance - I believe -
especially with two turbos)
5.
Some combination of the above. But, I believe that in all cases
higher
turbine speed would acerbate the condition and lead to quicker
failure -
whether true overspeed or not.
Good addition to the
theory stack, Bulent.
Ed
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