Ken,
I would double check the prop governor. Especially since you stated the
problem did not occur during the static run up. Not knowing what prop
you have, is it possible to set the pitch manually (not rpm)? If the pr
op is an electric controlled unit, while the engine is off adjust/set th
e pitch to approximately 22 deg and then pull the circuit breaker. Now
you have a fix pitch prop, effectively isolating the governor. Perform
a static ground run up and verify engine performance. With the prop iso
lated any surging noticed during the take-off roll can then be attribute
d to the engine.
If problem still persists, check throttle potentiometer for correct resi
stances. As you are aware the turbo will surge between 108-110% throttl
e position.
Also, you can always isolate the turbo. This is a little more difficult
since the default position of the waste gate is fully closed. In order
to bypass the turbo the waste gate must be manually set full open. Thi
s can be done one of two ways. The first and simplest, is to cycle the
TCU, and when the waste gate is fully open, electrically isolate the ser
vo motor (two pole switch installed per Rotax manual). This is a two pe
rson activity, as one will need to watch the waste gate cycle and call o
ut the moment it is fully open so that the person in the cockpit can iso
late the servo motor. The second method would require you to disconnect
the servo cable at the servo motor, fully opening the waste gate. Of c
ourse you will still need to electrically isolate the servo motor. Nex
t perform a ground run up and verify you do not exceed max RPM at full t
hrottle. If problem persists during take-off run abort take-off.
Other checks of the turbo system, ie pressure sensors, 3-way solenoid va
lve, etc. can also be made with relative ease.
Finally, you mentioned a drop in RPM from 5700 to 4800, do you recall wh
at the manifold pressure was at the time?
Good luck.
Erich Trombley
N28ET, Classic Mono 914
From: "ken carpenter" <kbcarpenter@comcast.net>
Subject: Europa-List: surging engine on take-off
Yesterday taking off, the engine surged as the turbo kicked in it went
up to 5700 RPM then dropped back into the 4800 range. I tried several
runs but aborted the take-off as it continues to surge. Checked the
prop governor and it checked out as functioning correctly.; Took the
cowl off and the turbo arm seems to cycle correctly when the master
turned on and the throttle cycled. Tied the plane down and ran it up to
5700 rpm. It did not surge at all.
Any idea? I have not tried to fly it again yet.
Ken Carpenter
N 9XS 914 Mono at 430 hours TT
<html><P>Ken,</P>
<P>I would double check the prop governor. Especially since you st
ated the problem did not occur during the static run up. Not knowi
ng what prop you have, is it possible to set the pitch manually (not rpm
)? If the prop is an electric controlled unit, while the engine is
off adjust/set the pitch to approximately 22 deg and then pull the
circuit breaker. Now you have a fix pitch prop, effectively isola
ting the governor. Perform a static ground run up and verify engin
e performance. With the prop isolated any surging noticed during&n
bsp;the take-off roll can then be attributed to the engine.</P>
<P>If problem still persists, check throttle potentiometer for correct r
esistances. As you are aware the turbo will surge between 108-110%
throttle position. </P>
<P>Also, you can always isolate the turbo. This is a little m
ore difficult since the default position of the waste gate is fully clos
ed. In order to bypass the turbo the waste gate must be manua
lly set full open. This can be done one of two ways. The fir
st and simplest, is to cycle the TCU, and when the waste gate is fully o
pen, electrically isolate the servo motor (two pole switch installed per
Rotax manual). This is a two person activity, as one will need to
watch the waste gate cycle and call out the moment it is fully open so
that the person in the cockpit can isolate the servo motor. The se
cond method would require you to disconnect the servo cable at the
servo motor, fully opening the waste gate. Of course you will
still need to electrically isolate the servo motor. Next pe
rform a ground run up and verify you do not exceed max RPM at full throt
tle. If problem persists during take-off run abort take-off.</P>
<P>Other checks of the turbo system, ie pressure sensors, 3-way solenoid
valve, etc. can also be made with relative ease.</P>
<P>Finally, you mentioned a drop in RPM from 5700 to 4800, do you recall
what the manifold pressure was at the time?</P>
<P>Good luck. </P>
<P>Erich Trombley<BR>N28ET, Classic Mono 914</P>
<P> </P>
<P><BR>Time: 06:02:04 PM PST US<BR>From: "ken&n
bsp;carpenter" <kbcarpenter@comcast.net><BR>Subject: Eur
opa-List: surging engine on take-off<BR><BR>Yesterda
y taking off, the engine surged as th
e turbo kicked in it went <BR>up to&n
bsp;5700 RPM then dropped back into the&nb
sp;4800 range. I tried several <BR>runs&n
bsp;but aborted the take-off as it continu
es to surge. Checked the <BR>prop go
vernor and it checked out as functioning&n
bsp;correctly.; Took the <BR>cowl off and
the turbo arm seems to cycle correct
ly when the master <BR>turned on and
the throttle cycled. Tied the plane
down and ran it up to <BR>5700 rpm.&n
bsp; It did not surge at all. <
BR>Any idea? I have not tried to&nbs
p;fly it again yet.<BR>Ken Carpenter<BR>N 9XS&n
bsp; 914 Mono at 430 hours TT<BR><BR
></P>
<pre><b><font size=2 color="#000000" face="courier new,courier">
</b></font></pre></body></html>
|