Today's Message Index:
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1. 10:21 AM - Re: Rotax 914 Dyno Test (rparigoris)
2. 05:51 PM - Re: Rotax 914 Dyno Test (Area-51)
3. 07:29 PM - Re: Rotax 914 Dyno Test (rparigoris)
4. 10:09 PM - Re: Rotax 914 Dyno Test (Area-51)
Message 1
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| Subject: | Re: Rotax 914 Dyno Test |
Hi Group
What I find interesting on the 914 is with the throttle about 1/2" or less, the
airbox pressure is greater than 44"! When setting up 914 with TCU software, I
found that 1/2" or less the wastegate is closed. Then remains opened from about
1" to 3" (this is with the engine not running:
https://www.cps-parts.com/cps/pdf/d05240.pdf
See page 7-10 for airbox pressure graph.
Boy, if the airbox is going to blow off, who would have thunk that it just may
have a better chance of doing so near idle with over 44" and probably more vibration
than at war emergency power (115% power, 100% throttle) which only has
a tad bit more than 40" or at 100% continuous power that has only a tad bit more
than 36".
See page 5-4 for MP from 55% to 115% power.
Ron P.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=511029#511029
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| Subject: | Re: Rotax 914 Dyno Test |
It's highly probable the manifold graph referred to in fig 6, p76, is referencing
the max MAP baseline which drops dramatically at engine startup.
The wastgate rests at full open position when the engine is not operating and/or
the wasgate switch on the instrument panel is switched off.
Turbo timing occurs at 46% throttle, with boosting available upward of 3000rpm.
Apart from Line Maintenance lubrication, unless you really have a total understanding
of what you are doing I wouldn't recommend fiddling with any of the turbo
controlling components.
Unlike a Supercharger a Turbo can runaway and bust the engine in a split second.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=511030#511030
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| Subject: | Re: Rotax 914 Dyno Test |
Hi Area 51
Graph 6 on page 7-10 is in fact airbox pressure, not manifold pressure. That would
be the pressure before it gets to the carbs. The wastegate is in fact fully
closed at idle position and up to about up to 1/2" advanced. There is turbo
pressure even at idle and because the butterfly is mostly closed and whatever
pressure there is can't escape thus airbox pressure increases, it increases the
airbox pressure to 44" as per graph. When the engine is off and you move throttle
to idle, the wastegate closes. Then you advance it to about 1/2" it opens.
Net increase of power over straight 912 doesn't start to occur till about half
throttle.
The old TCU had a airbox temperature intervention temperature of 160F, the newer
style TCU 190F. Even with new style TCU, if for whatever reason you are going
to trust that your 914 is going to be making boost HP and not 912 normally aspirated
HP, and your life is going to depend on that, Rotax suggests a DO 178
B take off. See page 3-11 in Operators manual. In other words, move the wastegate
to the closed position (which you can do by placing the throttle lever to
less than 1/2" advancement) then turnoff your TCU. Now you have a closed wastegate.
One needs to be extremely careful doing this, you can easily exceed maximum
boost. That said, if you advance slowly and select maximum boost using the
throttle, you can limit boost pressure. Just like at idle where airbox pressure
is way up and manifold pressure is way down, doing a DO 178B take off airbox
pressure will be way up and you are limiting manifold pressure with throttle.
At high power settings this is not something you want to do for a very long
time as it's hard on the turbo. But to clear those 50 foot trees taking off
downwind from a short field (which you should probably not be doing in the first
place) but if you ever do that or something where you don't the turbo to
quit when you can't abort, best eliminate uncommanded removal of turbo boost.
Ron P.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=511031#511031
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| Subject: | Re: Rotax 914 Dyno Test |
In that case the Wastegate switch referred to above is the TCU switch component,
and the Nominal Airbox pressure (2atm) would be residual from the compressor
function at 1600rpm-2000rpm. As soon as the throttle is cracked this pressure
drops suddenly as the compressor has no capacity yet to supply enough volume
to maintain boost pressure.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=511033#511033
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