A tale of 2 Rockets, can you figure it out?

[Austintatious]

This may get a bit long, but Ill do my best to keep it short.

So I have these 2 rockets, both M20K.  One is a '79 and one is an '84.  The 79 has a JPI 900 and the 84 has an insight g2.  The engines have about the same amount of time on them... The 79 however has a brand new turbo and an E mag, neither of which had any effect on what I am about to describe.

Here is the observation that we cannot reconcile.  In a nutshell, both aircraft essentially get limited to a min fuel flow for various power settings.  That is to say that if we fly either of them at say 30/22 ,  we have to flow about 18 GPH in both of them.

Here is the curious part: 

The 79 is limited by the TIT.  Any less FF and the TIT is too high.  But the #5 cylinder (the hottest) temps are fantastic though.  

The 84 However is limited by the number 5 cylinder.  But the TIT is much lower, by about 100-130 degrees.

So I end up limited in ability to further lean at the same flow for any given power setting, but for different reasons and it strikes me as odd.  In the 84 if the number 5 cyl wasn't so hot, I could lean a lot more before the TIT got to hot.  And in the 79 if the TIT wasn't so high, I could lean a bit more before the #5 cylinder got above 370.  So It feels like some extra economy is being left on the table in each aircraft for different reasons.

 

Here are some more observations :

The EGT's on the 79 are higher, but the CYL head temps are lower ( TIT is higher)

Both have the "pixie hole" for the #5 cylinder

 

Example comparison              '79                                 '84

cruise@30/22      FF              18gph                          18gph

                            TIT              1600                           1480-1500 (according to 2 different gauges)

                          #5 cyl            360                               low 380's

 

Now, I know 20 degrees does not seem like a massive difference in CYL head temp, but I am in the yellow at 390 on the insight gauge, and according to Savvy aviation, I should be taking action at 380 to try to stay below that.

To put it simply, if these 2 TSIO520NBs  were actually on a twin, we would really be scratching our heads about why these two engines, which are identical have differing indications in these parameters.  The thing is, as I think about this there cannot be something "wrong" on just one of the aircraft if there is indeed something off... If it was only 1 aircraft, and the "issue" was fixed, that would allow more leaning on that aircraft and then we would be noting a difference in fuel flow between the two.

So, the Possible causes I can think of:  

1.  We are being too pedantic about the numbers.   If we did not have the two to compare to one another, we would have no complaints. However consider if they were on a twin.

2.  The TIT probes are not identically located and thus giving different readings and the 79 is reading hotter than actual  and the 84 reading cooler than actual.

3.  There is a slight difference in timing between the two aircraft.  the 84 having slightly more advanced timing, resulting in lower EGT's but higher CHT's and the 84 having slightly retarded timing resulting in higher EGTs and lower CHT's. 

4.  A combination of the above including the possibility that on the 84 the number 5 cylinder is running leaner than the others.

 

Anyhow, any ideas?  Any of you rocket owners care to share some of your engine parameters?

 

 

 

 

 

Edited August 29, 2022 by Austintatious

[KSMooniac]

You're on the right track.  You should measure the distance to each of the EGT and TIT probes from a solid reference point for both planes.  Do all of the probes read the same temps before you start?  Have they been inspected for wear/erosion?    Then you should measure the timing for each mag on both engines.  I assume the E mag does not advance it?

Have you done the GAMI lean test for both engines?  Verified there are no induction leaks?  Verified the fuel flow K-factors for both?  

[Steve Dawson]

Are the TIT probes the same type? J or K's? If they are try switching them from one aircraft to the other and see if the results are the same as before. Secondly, as for the cylinder cooling, are the baffles equal? Any leaks or areas not covered or are they different types of baffle material? 

[M20F]

1 hour ago, KSMooniac said:

Have you done the GAMI lean test for both engines?  Verified there are no induction leaks?  Verified the fuel flow K-factors for both?  

Probably where I would start.  18GPH does not mean each cylinder is getting 3GPH. 

[PeteMc]

One other thought on the difference in temps....  From the front, look at both #5 cylinders and see if the '79 has some holes in the panel that is in front of the lower portion of the cylinder.  A common issue with the K's is a hot #5 and a common fix I've heard various mechanics talk about is to drill some holes into that panel to get some more airflow on the lower portion of the cylinder.

NOTE:  If you're going to try it and your mechanic is going to give it a shot but hasn't heard about this or has never done it....  MAKE SURE they know to put a piece of steel between the plate and the cylinder to keep from drilling into the cylinder itself!!!!

[carusoam]

Holy Cow!

We have gone a long way to prove…..

A man with two watches doesn’t know what time it is…. 

 

Like any other engine challenge… start with proving each thermocouple/temperature sensor is reading correctly…

Ancient EGT sensors are known to go bad over the years…

TIT sensors are mounted in the worst/harshest environment, and are known to fail most often….

 

With one engine, we swap neighbors, to see if a temp issue follows the sensor….

With two engines, swapping a TIT sensor should be easy…

 

One thing we don’t know anything about… how do we know if the two turbos are behaving similarly?

Does the ‘newer’ turbo’s efficiency differ from the older one?   Would it matter…

 

If you were flying a twin… I bet you would have the same concerns… and find a way to not let it bother you…

 

Let’s invite @kortopates join the fun… he knows engine instrumentation and flys an M20K…

Invite @aviatoreb as well… he is the sharpest Rocket pilot we have…

Don’t forget to invite… @jlunseth he has written plenty of good stuff about operating his M20K…

I bet @Parker_Woodruff has the sharpest memories regarding M20K operations…

The list of Rocket pilots is long and distinguished….  
 

Best regards,

-a-

[N201MKTurbo]

I would start by checking the timing, and maybe trying to lean them on individual mags and see what happens. It would give you some more data points.

[carusoam]

Bust out some data…!

See if you can collect some really good run up data…

Allow the EGTs to peak each time the switch gets changed….

This may take about 20 seconds or so on each switch location including ‘both’….

Mag timing differences on one engine are really stand out kind of events…

Trying to minimize all the variables as much as possible… select one MP, and do it for both….

 

Send the data to Savvy… press the share button… copy the link here….

We might learn something about the Savvy collection of services while we are at it…

We may also learn about the differences in Engine monitors….  We have a really good EI guy around here…  we can always invite him…  

Best regards,

-a-

[Will.iam]

7 hours ago, Austintatious said:

This may get a bit long, but Ill do my best to keep it short.

So I have these 2 rockets, both M20K.  One is a '79 and one is an '84.  The 79 has a JPI 900 and the 84 has an insight g2.  The engines have about the same amount of time on them... The 79 however has a brand new turbo and an E mag, neither of which had any effect on what I am about to describe.

Here is the observation that we cannot reconcile.  In a nutshell, both aircraft essentially get limited to a min fuel flow for various power settings.  That is to say that if we fly either of them at say 30/22 ,  we have to flow about 18 GPH in both of them.

Here is the curious part: 

The 79 is limited by the TIT.  Any less FF and the TIT is too high.  But the #5 cylinder (the hottest) temps are fantastic though.  

The 84 However is limited by the number 5 cylinder.  But the TIT is much lower, by about 100-130 degrees.

So I end up limited in ability to further lean at the same flow for any given power setting, but for different reasons and it strikes me as odd.  In the 84 if the number 5 cyl wasn't so hot, I could lean a lot more before the TIT got to hot.  And in the 79 if the TIT wasn't so high, I could lean a bit more before the #5 cylinder got above 370.  So It feels like some extra economy is being left on the table in each aircraft for different reasons.

 

Here are some more observations :

The EGT's on the 79 are higher, but the CYL head temps are lower ( TIT is higher)

Both have the "pixie hole" for the #5 cylinder

 

Example comparison              '79                                 '84

cruise@30/22      FF              18gph                          18gph

                            TIT              1600                           1480-1500 (according to 2 different gauges)

                          #5 cyl            360                               low 380's

 

Now, I know 20 degrees does not seem like a massive difference in CYL head temp, but I am in the yellow at 390 on the insight gauge, and according to Savvy aviation, I should be taking action at 380 to try to stay below that.

To put it simply, if these 2 TSIO520NBs  were actually on a twin, we would really be scratching our heads about why these two engines, which are identical have differing indications in these parameters.  The thing is, as I think about this there cannot be something "wrong" on just one of the aircraft if there is indeed something off... If it was only 1 aircraft, and the "issue" was fixed, that would allow more leaning on that aircraft and then we would be noting a difference in fuel flow between the two.

So, the Possible causes I can think of:  

1.  We are being too pedantic about the numbers.   If we did not have the two to compare to one another, we would have no complaints. However consider if they were on a twin.

2.  The TIT probes are not identically located and thus giving different readings and the 79 is reading hotter than actual  and the 84 reading cooler than actual.

3.  There is a slight difference in timing between the two aircraft.  the 84 having slightly more advanced timing, resulting in lower EGT's but higher CHT's and the 84 having slightly retarded timing resulting in higher EGTs and lower CHT's. 

4.  A combination of the above including the possibility that on the 84 the number 5 cylinder is running leaner than the others.

 

Anyhow, any ideas?  Any of you rocket owners care to share some of your engine parameters?

 

 

 

 

 

One thing you didn’t clarify is this ROP or LOP operation?

 

[Will.iam]

If running ROP then i would do the vacuum pressure test with a soapy solution in a spray bottle and spray it around cylinder #5 intake manifold to check for leaks. 

[Pinecone]

Agreed with trying swapping TIT probes.

When they start to fail, the tend to read low.

[Austintatious]

Thank you everyone for the input. 

To clarify a few things....

1- This is ROP operation... these aircraft only like to run LOP when at very low power settings (55%)  Especially up high... the TIT prevents it.. IE: the TIT is too high and does not come down before the onset of rough running.

2- Both aircraft have GAMIs.  Though the Gamis are relatively new on the 79 and we have not gone through the gami process.  I have been through that process on the 84 with the hot number 5.  We even put a new injector into the number 5 cylinder to increase its fuel flow a bit trying to cool it off.  It did help a bit.

3- The single TIT probe in the 79 is brand new...  The probes on the 84 are not new, however as per the rocket TIT test they are both accurate

4- The E mag does not advance/retard timing

5- The baffling is all in very good condition on both and all appears in order.

6- Both aircraft have the "pixie hole" in front of the number 5 cylinder.  Though they look identical and like they are "stock" ... If anyone has a picture of theirs I would love to compare.

 

I will concoct a plan to gather some data with the engine monitors.   I'll incorporate the single mag run up data, lean find data and TIT Test and get that posted.  It may be a bit before I can get both.

 

Thanks everyone!

 

[N201MKTurbo]

Cylinders misfire from a weak spark or lean mixture. If your engine is running rough when going LOP, one of those things are happening. Your engine monitor should tell the tale of which cylinder is misfiring first.

[Will.iam]

I think your 79 is later timing than your 84. Because you are turning 2200rpm and rop your flame front is faster than it would be LOP. If the timing is later then it gives the piston more time to get over TBC before the fuel ignites but doesn’t burn completely before exhaust starts to open dumping hotter exhaust gases to the turbo showing up as higher tit. Also doesn’t give cylinder as much time to extract the power before the exhaust valve opens thus lower cht’s. If everything else is truly the same between the 2. 
as i lean LOP my exhaust gets cooler but then it starts to rise as i go deep lop as i have leaned the mixture so much the flame front slows down to the point some of it is still burning when the exhaust valve opens and dumps the the last part of the flame to the turbo and registers on the tit as an increase in temp. 

[carusoam]

Let’s invite Ross… he may be interested in the conversation… @Shadrach…

Best regards,

-a-

[Austintatious]

22 hours ago, N201MKTurbo said:

Cylinders misfire from a weak spark or lean mixture. If your engine is running rough when going LOP, one of those things are happening. Your engine monitor should tell the tale of which cylinder is misfiring first.

Neither engine runs rough when we go LOP... Until we go TOO LOP.  The issue is that we get to the temp limit of the TIT if we are at any power setting over 55%.  It would be nice to run 70% power and LOP.... but we simply cannot as the TIT will be too high.  When we have tried, we keep leaning until the TIT starts to dropto safe levels, but by the time it does, we get an onset of rough running.

[A64Pilot]

I think a large amount of what your getting is that while we like to think engines are identical, they aren’t. For example take an engine with a perfect “Gami spread” EGT’s should be identical, but are they?

To really try to eliminate timing, or to get timing close to exact you need to ignore the timing marks and break out the degree wheel and the dial indicator, because the marks are as precise as they need to be, but there are manufacturing tolerances. To be precise you have to eliminate variables. 

I know nothing about Rockets, but an engine is an engine.

Enjoy the airplanes and keep the temps down, most of us can’t have one, you have two, enjoy and quit worrying about it.

Remember these engines were built to be run with instrumentation that often didn’t even have numbers on them, just one or two numbers and colored arcs, we now are looking at them with instruments that read down to a single degree, how accurate are they? I don’t know, it would take a multi point calibration to know.

[Pinecone]

GAMI spread and EGT numbers have nothing to do with each other.  And unlikely to be the same EGTs for many reasons.  Starting with your comment that each engine is different.

My car engine, for factory specs has a HP rating.  But the factory produces engines that vary HP in a range of 10%.  So my engine may put out 10% more HP than your engine in the same make, model, year car.

 

[A64Pilot]

2 hours ago, Pinecone said:

 

My car engine, for factory specs has a HP rating.  But the factory produces engines that vary HP in a range of 10%.  So my engine may put out 10% more HP than your engine in the same make, model, year car.

 

The difference with aircraft engines is that the spec is a min spec, the new engine will produce at least rated power, easiest way to ensure that is the average engine exceeds the min, some 200 HP engines produce quite a bit more than 200, some not. One reason why different engines with the same rating are faster or climb better etc than others rated the same

I had two Sister aircraft in my first unit, 84-24201 and 84-24209. For some reason they were significantly faster than all the others and I dug as deep into it as I could to find out why, rigging, weight, CG, engine performance everything. Reason was if I could find out what made them so fast I might could make the others that fast too. I could hang 1600 lbs of missiles on them and they would still slowly pull away from the rest that only had empty rocket pods and a couple of missiles.

I never did find anything, they were just FAST, but everything was in the middle of spec, engines were torque limited so it couldn’t be engines, if you made 100%, that’s all you could use.

Some airplanes are just faster than others, some just simply fly better than others. I don’t think it’s one thing but a combination of several things. The Monday morning airplane is not a myth.

I have done the Production test flight of a couple hundred brand new zero time identical airplanes, with brand new zero time turbines. There is a considerable spread in engine power, and some airplanes do in fact just fly better, lighter on the controls and better behaved in a stall etc.

Funny thing is the FAA does not allow an aggregate of aircraft for Certification testing, for us the whole thing was based on one aircraft.

General Electric knew this too it seems, the engine sent for flight testing carried sea level power to 12,000 ft which was as high as we Certified, average production engine hit ITT limit at 10,000 or so. Sometimes but rarely an engine would hit Ng speed limit before ITT. But they all made spec power.

Oh, and I’m about 90% sure EGT difference in flow matched cylinders is due to compression being different, no one that I know of CC’s aircraft heads to take out production tolerances, but I bet if they did the EGT’s would be very close

[Fly Boomer]

5 minutes ago, A64Pilot said:

Funny thing is the FAA does not allow an aggregate of aircraft for Certification testing, for us the whole thing was based on one aircraft

That’s how Mooney got the 231 and 252.  Marketing told the test pilot “we are going to call it the 252” and he had to go up to 28,000 to get it done.  He said he would never do it again.

[A64Pilot]

Why would he do it again? I wasn’t comfortable in a crop duster at FL 250, but I think I would have been OK in a Mooney

[Fly Boomer]

7 minutes ago, A64Pilot said:

Why would he do it again? I wasn’t comfortable in a crop duster at FL 250, but I think I would have been OK in a Mooney

He would not do it again because if something goes TU safety is far, far away.

[Pinecone]

3 hours ago, A64Pilot said:

The difference with aircraft engines is that the spec is a min spec, the new engine will produce at least rated power, easiest way to ensure that is the average engine exceeds the min, some 200 HP engines produce quite a bit more than 200, some not. One reason why different engines with the same rating are faster or climb better etc than others rated the same

Variation is variation.

My car happens to be a min spec also.  All of that model make at least the published HP, could be as much as 10% more.

MOST car companies publish the highest that any engine every made.  So all the ones sold have less than the published HP.  

But in both cases, there is a range that all the engines built fall within some range

 

[A64Pilot]

17 minutes ago, Fly Boomer said:

He would not do it again because if something goes TU safety is far, far away.

You can glide for a long ways at that altitude but if you mean flight control issue, you would be just as dead from 5,000

Just curious, I didn’t like it in a crop duster largely because I had zero instruments and the windows were icing over pretty bad, and it just felt odd up there in a crop duster, it wasn’t just one flight, but a series of flights

[Fly Boomer]

20 minutes ago, A64Pilot said:

You can glide for a long ways at that altitude but if you mean flight control issue, you would be just as dead from 5,000

Just curious, I didn’t like it in a crop duster largely because I had zero instruments and the windows were icing over pretty bad, and it just felt odd up there in a crop duster, it wasn’t just one flight, but a series of flights

Oxygen?  Long glide not helpful.