Merlyn Waste Gate for 231

[chrisk]

I'm just curious how many of you have installed a Merlyn Waste Gate controller on your 231.  Do you feel it was money well spent?  I've talked with a few mechanics, and most say it just reduces pilot work load.   On the other hand, the product literature seems to indicate a higher critical altitude and better efficiency at lower altitudes.

[N201MKTurbo]

I installed one on a 231 once. It only took about two hours. It did make the MP more stable.

I didn't think there were any 231 left without it.....

[FAST FLIGHT OPTIONS LLC]

I still don't have one on my 231. Might get one at some point in the future. Should increase critical altitude and extend turbo life as it allows/causes the turbo to spin less at lower altitudes.

[RJBrown]

This type of device is part of what made the 252 so much better. There are few left without a wastegate and an intercooler. From a buyers standpoint I consider these to be normally installed parts and would deduct for their omission. A plane without them reflects poorly on the owners attitude about properly caring for his plane. A glaring omission by the factory and even a more glaring omission 30 years later. No turbocharged airplane should fly without both the automatic wastegate or an intercooler.

[FBCK]

Just dealt with the Merlyn people last month and have to say they are a great group of people to deal with.  If you dont have one you should consider it, as said above its a must  in my book for a 231.

[jlunseth]

The crit. altitude on a factory 231 is about 15k (its in the POH but I am too lazy to look it up again).  The critical altitude in my Merlyn equipped 231 is 22,500, which I determined from actual testing with my plane.  It varies a little with ambient conditions of course. 

 

To my mind, however, the better addition to a 231 is the intercooler.  That is if you have any intention of flying above roughly 17 k.  On a factory 231 the CDT redline is 280.  Because of the thin air at altitude cooling is poor and the turbo is having to do more work.  In combination, you will see CDT's at or over redline under nearly all conditions in the Flight Levels.  The redline is there to protect the cylinders from detonation because of high IAT's, so you will be flirting with or in detonation at high altitudes.  Moreover, the usual things that bring temps down, such as enrichening the mixture, only make the issue worse at high altitude.  The only thing to do is get out of there.  With the intercooler, the IAT will drop by as much as 100 dF or more, which is healthier for the engine obviously, and allows flight all the way to the service ceiling of 24k without the CDT redline issue.  The CDT will exceed 280, but that is no longer relevant because the IAT will be low and safe.  Of course, your climb rate without a Merlyn will be anemic getting up there.  The best deal is the combination of the two of them.  The increase in the critical altitude with the Merlyn alone will be of little help without the intercooler, it might enable you to get from 14k to 17 or 18k, but not much higher. 

[panther1400]

This type of device is part of what made the 252 so much better. There are few left without a wastegate and an intercooler. From a buyers standpoint I consider these to be normally installed parts and would deduct for their omission. A plane without them reflects poorly on the owners attitude about properly caring for his plane. A glaring omission by the factory and even a more glaring omission 30 years later. No turbocharged airplane should fly without both the automatic wastegate or an intercooler.

I bought my K only about 3 years ago and right away I put in a MVP50 engine monitor so I can watch everything as close as possible, which is very important to me, and now I find out that I totally screwed up and don't properly take care of my plane, guess I will have to start saving my pennies for a wastegate and intercooler so I won't wreck my plane.  Just my thoughts?

[chrisk]

On a factory 231 the CDT redline is 280.  Because of the thin air at altitude cooling is poor and the turbo is having to do more work.  In combination, you will see CDT's at or over redline under nearly all conditions in the Flight Levels.  The redline is there to protect the cylinders from detonation because of high IAT's, so you will be flirting with or in detonation at high altitudes. 

 

This is by far the best explanation I have heard for the usefulness of an intercooler.  i.e. to prevent detonation due to a hot intake air. 

[panther1400]

I think an intercooler and wastegate make it easier on the engine up high if you run it hard, I run real easy and the temps look fine to me.

[jlunseth]

This is by far the best explanation I have heard for the usefulness of an intercooler.  i.e. to prevent detonation due to a hot intake air. 

Well, I didn't know initially what that redline was for, whether to protect the cylinders or protect the turbo.  Turbo did not make alot of sense because it is capable of 1650, and briefly to 1725, and has its own redline(s).  So I asked the question at an APS seminar a few years ago, and then went directly to Mooney on it, and the answer was the same in both cases. 

 

The problem with high altitude flying is that the CDT starts to creep up and the usual solutions such as enriching the mixture or opening cowl flaps, either don't make any difference or actually make the problem worse.  The only thing you can do is reduce power, and when you are at 20,000 and trying to climb, a power reduction is not very helpful.  Over 22,500 you are going to get an automatic power reduction just like an NA engine, the climb rate goes down immediatly to around 300 fpm max.  So the last 1,500 feet from 22,500 to the service ceiling of 24,000 takes at least five minutes and if you had no intercooler the CDT would be 290 - 300 (over the redline).

 

I don't go up there unless really necessary.  FL210 or 220 work just fine and the time of useful consciousness starts to drop precipitously after that, but I have tried it and that is what happened.

 

It will happen to a nonintercooled engine and without exceeding the redline you are going to be blocked from going higher than somewhere around 18 - 20,000.  Doesn't matter that the temp. up there is -50, you just won't get enough cooling from the air.

[panther1400]

Yes if going to the vertical limit it does make a lot of difference to have an intercooler and merlin.

[RJBrown]

My first plane was a stock 1980 231. I bought it with 1100 hours in 1994. I thought I had done the research and was flying it properly. At 1200 hours the engine needed major work. I was in Spokane when it gave up. Long story but I ended up with a Rocket conversion. The Rocket has an automatic wastegate and 2 intercoolers. The Rocket mod included a fuel flow meter. Shortly thereafter I had a EDM 700 and speed brakes added. Any turbo installation should include these items. A Rocket also needs the long range tanks I added at same time. 

 It took Mooney until the 252 to get the basics right. The 262 conversion on a 231 brought it up to 252 specs but was expensive and the improvement was incremental. It cost very little more for the Rocket conversion at the time. In Mooney speak a Rocket would be a least a "275" 

 Engine management on the 231 was troublesome. If you flew it VERY conservatively it could last but would not achieve much more than 201 performance. If you flew it "as Advertised" it was a 1200 hour engine. With a wastegate, an intercooler, fuel flow and an engine monitor both longer life and reasonable performance can  be attained. Without these additions it is impractical to fly to the altitudes Mooney implied were normal. The higher you fly the more important the additions become. If you never fly that high there really is no need for the additional cost over a 201.

 All that you get after adding a wastegate, an intercooler and proper instrumentation is what Mooney promised from the beginning. Without them performance and durability  are compromised.

[M20Kid]

I fly a 231 with a Merlyn Waste Gate buy no intercooler.  I bought the airplane about a year ago and planned on adding the intercooler.  The problem is that when I tried to buy an intercooler I couldn't find anyone still selling one.  I checked with salvage yards and still no intercooler.

 

Does anyone have a lead on where to get an intercooler for the 231?

[RJBrown]

http://www.airflow-systems.com/intrcimp.html for airflow systems. the other STC is from Turboplus, I have no contact info for them.

[chrisk]

I ended up adding the Merlyn waste gate to my new to me M20K 231.  I wish I could describe the performance difference before and after the waste gate, but I didn't fly the plane before adding the waste gate.  --I knew if I didn't add the waste gate now, I would probably never get around to it.

[M20Kid]

http://www.airflow-systems.com/intrcimp.html for airflow systems. the other STC is from Turboplus, I have no contact info for them.

I called Airflow Systems and they are no longer making the intercooler.  Apparently the salvage yards are cleaned out, as well.

 

I did have an interesting conversation with this company, though.  Bill at Airflow Systems told me that they stopped making these units because they couldn't sell enough to make them commecially viable.  They only need to sell 10 per year but they weren't even at that low number.  He did tell me that if we could get 10 people to commit to buying an intercooler that they may be able to make a limited production run and get us these intercoolers!  Any takers?  If you're interested call Bill directly at 949-218-9701.

 

I'm going to start a new thread with this information, as well, since I would like to buy one and I need 9 of my Mooney brothers and sisters to jump on this bandwagon to possibly make it happen.

[jlunseth]

The problem is that most 231's have long since had one installed, back around 2000 or earlier.

[M20Kid]

Right.  Most, but not all.  I'm hoping to catch a few that are in the camp that is still missing this important component and want to remedy that situation.

[skeptic]

If you look at the 231's currently listed for sale, there are plenty that do NOT have a Merlyn or an intercooler.  An intercooler in particular does not seem to be that common on the planes that I have seen advertised.

 

That said, I would personally prefer to have both devices if I owned a 231.

[manu damaschin]

Is the climb performance so much different with/without Merly wastegate?

[jlunseth]

Yes it is different.  It is different because the factory set up is a fixed wastegate that cannot fully close as altitude increases.  This means that critical altitude (the point at which the engine can no longer make 100% power) is reached much lower than with the Merlyn.  The fixed wastegate is still spilling exhaust gases (power for the turbine) at that point, where the Merlyn has the ability to continue to close and use those gases to turn the turbine.  The fixed wastegate aircraft turns into a normally aspirated aircraft at 15k, and climb performance drops sharply.  Below 15k, climb performance should be about the same.   

 

Keep in mind that the Merlyn is "semi-automatic" not fully automatic.  You still need to manually adjust the throttle from time to time as altitude increases (or decreases) in order to maintain a given MP.  You keep adjusting until the throttle will not go in anymore.  At that point you are at critical altitude.

[manu damaschin]

thanks for the input jlunseth...!

[rainman]

When I bought my 231 two years ago, it had an intercooler but no automatic wastegate. Based on Mr Lunseth's comments and some research, I added the automatic wastegate this week at the annual. Previously, I found myself constantly having to make adjustments which made already busy flying that much less fun. I have several long/high trips planned soon and will let you know about the difference. Ray

[manu damaschin]

...Ray, do not forget us with the feedback regarding the wastegate...

[Crawfish]

Reviving an old thread for a quick question!

I was told that just the Merlyn UDC will help lower CDT due to more efficient Turbo operations, has anyone seen this in real world operations? (obviously an intercooler is the best way to lower CDT) 

 

Thank you! 

Austin