Can't get full manifold pressure on my Rocket

[GIVCAPT]

Hello All,

 

I was wondering if anyone has an idea as to why I can't get full rated manifold pressure of 38 inches on takeoff. My mechanic has ran out of ideas, so I thought I would ask anyone here that may have had this problem in the past and how it was corrected. The engine has 350 hours TT since new.

 

Thank you all in advance.

[jrwilson]

Steam gauge manifold pressure or some kind of EDM? The JPI series has a way to adjust MP.

[orionflt]

It could be something as simple as an inaccurate gauge but if your actually not making the proper power then look at the turbo system. Turbo could have missing or broken blades, waste gate could be mis adjusted and dumping prior to 38in. Since you mechanic has looked at it I am assuming that it is not an exhaust leak, that would be easily seen.

[carusoam]

One of the newer ways to measure power is an app called CloudAhoy...

It measures your Take-off distance, climb rates and speeds. Compare to book or historical values and you can see how close you are to full power.

I used this app to measure performance of a newly installed STC.

If you match all the book values, look closer at your instrumentation.

I would expect that the next step is to open the turbo for inspection, the blades erode at high EGTs. There is a name for the hot side temp of the TC that doesn't come to mind...

How long have you owned it?

Good luck.

Welcome aboard,

-a-

[PaulB]

What does the gauge read when the engine is off?  Should be the same as the altimeter setting minus an inch for every 1000 ft of elevation above sea level. 

[GIVCAPT]

Steam gauge manifold pressure or some kind of EDM? The JPI series has a way to adjust MP.

It is a steam gauge type

[GIVCAPT]

It could be something as simple as an inaccurate gauge but if your actually not making the proper power then look at the turbo system. Turbo could have missing or broken blades, waste gate could be mis adjusted and dumping prior to 38in. Since you mechanic has looked at it I am assuming that it is not an exhaust leak, that would be easily seen.

Thank you for the information. I will pass it along to my mechanic tomorrow.

[GIVCAPT]

One of the newer ways to measure power is an app called CloudAhoy...

It measures your Take-off distance, climb rates and speeds. Compare to book or historical values and you can see how close you are to full power.

I used this app to measure performance of a newly installed STC.

If you match all the book values, look closer at your instrumentation.

I would expect that the next step is to open the turbo for inspection, the blades erode at high EGTs. There is a name for the hot side temp of the TC that doesn't come to mind...

How long have you owned it?

Good luck.

Welcome aboard,

-a-

Thanks, I will check out that app tonight when I get home. I just bought the plane two weeks ago and just love it's performance compared to my Piper Lance. I would guess the performance would even be better once i can get the MP problem figures out.

[chrisk]

I wish I knew enough about a rocket to give good advice.  In general though, I would look at:

• Leaks on the compressor output side.  This assumes leaks would be obvious on exhaust side.
• A possible obstruction in the inner cooler (not that I can imagine how that would happen)
• The waste gate and wast gate controller. 
• The turbo lacks sufficient output.

 

Unfortunately, all of this stuff is in a giant feedback loop.  I would expect debug probably involves removing one part of the loop to test the proper function on the other parts.  i.e. fix the waste gate like a 231 and see if you can get full manifold pressure.  Just don't over boost.  I would expect you (or your mechanic) could do this with a high speed taxi test.

 

But first, check the accuracy of the steam gauge.

[GIVCAPT]

I also wanted to mention that a local engine guy who has a repair station at KVNY took a look at my plane today and suggested that I change all the gaskets/O rings on the upper deck lines to the cylinders. He says it common for them to erode or just dry out from heat or just sitting. He says he has seen where they can leak and could lose pressure from them that could effect the MP. The airplane has not flown much in the past several years for what it's worth.

 

Thanks again everyone

 

Jack

[GIVCAPT]

I wish I knew enough about a rocket to give good advice.  In general though, I would look at:

• Leaks on the compressor output side.  This assumes leaks would be obvious on exhaust side.
• A possible obstruction in the inner cooler (not that I can imagine how that would happen)
• The waste gate and wast gate controller. 
• The turbo lacks sufficient output.

 

Unfortunately, all of this stuff is in a giant feedback loop.  I would expect debug probably involves removing one part of the loop to test the proper function on the other parts.  i.e. fix the waste gate like a 231 and see if you can get full manifold pressure.  Just don't over boost.  I would expect you (or your mechanic) could do this with a high speed taxi test.

 

But first, check the accuracy of the steam gauge.

Thanks I will also pass that along to my mechanic tomorrow.

[chrisk]

Thanks I will also pass that along to my mechanic tomorrow.

Before you pass that along, read: http://www.avweb.com/news/maint/182847-1.html?redirected=1. It should answer some of your questions, or at least make you feel like you are not the only one.

My guesses in order are:

1) Gauge

2) Induction leak. I hear a shop vac and soap is how you find these.

3) waste gate controller/pressure sensor

[mike_elliott]

I don't know how far you are from Fairhope, Al., but if close, take your Rocket to Roger Gradle at Continental and he will make it right in no time.

[Awful_Charlie]

I don't know the Rocket setup, but on a Lycoming/Bravo install, there is a section in the maintenance manual about the MP to be expected at various induction temperatures. Although the POH maximum is 38", it goes down with decreasing IAT such that on a 'normal' day the maximum is between 35-36"

The maximum MP is set on the absolute controller (which is a b*tch of a job to adjust - it is lockwired, and only needs moving 1/32 of a turn at a time).

There is also the issue that getting the full 38" of MP at a low IAT is technically an overboost situation, which if done significantly then means you are due an overhaul!

[Mike A]

What kind of MP are you getting?  I had the turbo stop spinning on my 231 early on and was only able to produce about 25" full throttle.  Like yours, it had sat for a while and the turbo had to be replaced.

[John Pleisse]

I say induction leak...check the O rings on the tubes. If they are fuel soaked, they need to be changed.

[GIVCAPT]

I want to thank each and everyone of you for your valuable input. I'm heading down to the airport with a list of all your input and ideas and will be spending the day with the mechanic trouble shooting. I will report back what was found.

 

Thanks again everyone

[carusoam]

Were you able to perform a Pre-Purchase Inspection?

From a similar safety point of view...

Also have them look for exhaust leaks while you are in there.

In the worst case, these can grow into little torches under the cowling. A known source of challenge for Bravo owners is the re-use of exhaust system clamps.

If you find the cold side leaking, it bears looking into the hot side as well.

Keep in mind, I am only a private pilot, not a mechanic...

Best regards,

-a-

[chrisk]

What kind of MP are you getting?  I had the turbo stop spinning on my 231 early on and was only able to produce about 25" full throttle.  Like yours, it had sat for a while and the turbo had to be replaced.

I bet that required an underwear change!  As I recall this was on a test flight and the owner blamed you?

 

Anyway, this sort of mystery always peaks my curiosity.  And as an owner, its always satisfying when the real problem has been found.

[GIVCAPT]

Well we changed all the upper deck O rings and then went and flew the plane. Takeoff MP was again 35 inches with no change,this time I flew it to 10,500 feet and once level and everything stabilized I ran the everything firewall forward and still got 35 inches of MP,so I ruled out i'm pretty sure a leak of some kind. Once I landed and secured the plane I checked the altimeter setting against the MP gage and noticed about a three plus inch difference from the local altimeter setting of 29.85 and the MP which was reading 26.50. I have taken out the MP gage and will be sending it in for overhaul tomorrow.

 

Thanks again for all the help everyone,

 

Jack

[GIVCAPT]

One more question,

 

Does anyone have a recommendation on a shop that can overhaul my MP gage or should I just buy a new one and if anyone sells them still new or overhauled?

 

Thank you in advance

[carusoam]

Sounds like good news!

Did you get book speed values at those altitudes as well?

Or do they not exist from the STC?

Any dough left in the kitty for a digital engine monitor?

Always looking for engineering level solutions, in an attempt to avoid an accidental misstep...not trying to wish ills upon the new Mooney guy...

Best regards,

-a-

[orionflt]

Keystone in pa has always done well by me

Brian

[GIVCAPT]

Sounds like good news!

Did you get book speed values at those altitudes as well?

Or do they not exist from the STC?

Any dough left in the kitty for a digital engine monitor?

Always looking for engineering level solutions, in an attempt to avoid an accidental misstep...not trying to wish ills upon the new Mooney guy...

Best regards,

-a

To be honest I have not checked book value as of yet but will see what I have in the paperwork later tonight if there is anything.  I have a JPI 700 in it now.

 

Reagards,

 

JW

[GIVCAPT]

Keystone in pa has always done well by me

Brian

Thanks Brian, I'll check them out