Almost there LOP, well maybe / update & report!

[RocketAviator]

Well after much ado and more $ than I want to disclose I was able to fly somewhat LOP reasonably smoothly with highest CHT at below 370 and my TIT at 1600!  Had a brutal head wind so I flew really low at 10.  Achieved 15.9 GPH @ 36 MP @ 2300, 180 TAS, not quite as smooth as I had hoped but barely acceptable at this point.

 

Goal is 14.7 - 15.5 GPH at relatively same TAS as with ROP, which for my ol bucket of bolts is 200 TAS, @ 12.

 

Spoke to a Rocket owner that Don Maxwell put me on to and this was the general performance he achieved.  Both Don(s) told me It took him and Don Maxwell a very long time to dial in on their accomplishment!

His performance was 14.7 - 15.5 @ 2400 @ 32 - 33" @ 192 @ 10

 

Each change that was made we flew and recorded the impact to the best of our ability and here are the results thus far:

 

Temperatures:

#1 single biggest impact for #1 CHT, GAMI / Bonanza / Pixie hole whopping 45 deg cooler!

#2 slight deflection of a baffle on the right side of cowl, just under 30 deg cooler

#3 Slower RPM

#3 changed method of ROP to LOP transition (now using relatively swift Big Pull)

#4 Removed a partial baffle suggestion that was posted on MS and opened up the clearance between cylinder 6 and the rear metal baffle. 

 

Smoothness:

#1 GAMI injectors (we are still working on this one, there may be some additional opportunity in this area, now that we have some of these other improvements, hope to know more on this soon.

#2 Spark Plug change from Champion Fine wire to Tempest Fine wire (slight lowering of TIT but noticeably smoother at LOP)

 

Things that we did that did not have a significant nor measurable impact on an individual basis were:

Turbo Induction system leaks (8 found)

New baffle seals all around, sealed every crack and seam with RTV

Critical Timing set to as close to factory perfect as we could using digital inclinometer. (we just made some changes to the timing last night and I hope to test fly this today or tomorrow)

 

This is not to say that collectively that some of the above were not a factor just not measurable in our test flights.

 

Onward we go.....

 

Rocket on, Fly safe,

Lacee

 

 

 

 

[N33GG]

Sounds like a lot of work... Long live ROP!

Just kidding. Good luck.

[fantom]

Don't trust Maxwell.....he's a ROP guy!

 

Seriously, glad it's finally working out for you.

[Shadrach]

#4 Removed a partial baffle suggestion that was posted on MS and opened up the clearance between cylinder 6 and the rear metal baffle. 

Lacee,

 

Can you expound on the above? Did you remove the wedge made of baffle material?  If so, was it because it increased CHTs?  how did you "open up" the clearance without using some sort of spacer?

 

Thanks,

[RocketAviator]

Lacee,

 

Can you expound on the above? Did you remove the wedge made of baffle material?  If so, was it because it increased CHTs?  how did you "open up" the clearance without using some sort of spacer?

 

Thanks,

Sure first based on a post here on MS, I inspected the metal baffling behind the #6 cylinder head.  According to what everyone said was SEAL UP EVERYTHING, every little leak could add up... so I did I folded a piece of silicone baffle material and RTV'ed it to the metal baffling, in doing this I had to pry back the metal baffling a bit to get the silicone in between the cylinder head and the metal baffling.   Flew a few flights and noted no better NO lower #6CHT temp, maybe even slightly higher by 5 deg or so.  Then looking at another post here on MS where someone took a small strip and placed it between only one or two of the fins and the metal baffling thereby increasing the space between the cylinder fins and the baffling, I decided to try that but while doing so found that I could fairly easily form the metal baffling with my metal working tools fo remain offset from the #6 CHT by about 5/16" without the need for the silicone strip.  So in simple terms I removed the silicone that I had previously installed and created additional clearance and therefore believe I allow sufficient or at least more air flow between the cylinder head fins and the baffling.  I am thinking it caused the overall airflow increase to the back of the engine by lowering the back pressure from the air being able to escape from between the cylinder and baffle.  In any case it worked dropped the #6 temp by 30 deg in flight.  Did not seem to affect the other cylinders.  I surmised it was a relatively easy project and can be replaced to normal by reforming the baffle or placing some silicone back in the space if need be, so I gave it a try! 

I hope all this rambling helps, feel free to PM me and I will give you my phone # to discuss if that would be of any help.

Fly safe,

Lacee

[Shadrach]

I was the guy that posted the "thin strip" solution years ago. It works fairly well for me. The "folded wedge" version is too high profile and likely interrupts airflow in the area rather than allowing more to get through. I was just curious if it made a difference.

[RocketAviator]

I was the guy that posted the "thin strip" solution years ago. It works fairly well for me. The "folded wedge" version is too high profile and likely interrupts airflow in the area rather than allowing more to get through. I was just curious if it made a difference.

Ah so it was a trick question then...LOL  

I tried to test at least to the best of my ability with the limited resources I had available, each of the actions taken to see if I could see a notable change and not make more than one change at a time, mainly for my own satisfaction and confirmation.  

I know this if had not been able to form the baffle as easily as I was I would have most likely inserted some silicone baffle material to enforce or assist  the space I was attempting.  One issue I have with forcing especially aluminum is I have seen it induce fatigue points especially with heat cycles and vibration that can incur in an engine compartment.

Thanks for the feedback, if you come up with anymore good tips please share!

Fly safe

[aviatoreb]

Well after much ado and more $ than I want to disclose I was able to fly somewhat LOP reasonably smoothly with highest CHT at below 370 and my TIT at 1600!  Had a brutal head wind so I flew really low at 10.  Achieved 15.9 GPH @ 36 MP @ 2300, 180 TAS, not quite as smooth as I had hoped but barely acceptable at this point.

 

Goal is 14.7 - 15.5 GPH at relatively same TAS as with ROP, which for my ol bucket of bolts is 200 TAS, @ 12.

 

Spoke to a Rocket owner that Don Maxwell put me on to and this was the general performance he achieved.  Both Don(s) told me It took him and Don Maxwell a very long time to dial in on their accomplishment!

His performance was 14.7 - 15.5 @ 2400 @ 32 - 33" @ 192 @ 10

 

 

Hi RocketAviator - still enjoying your new avatar.

 

Great project - thanks for sharing.  I never dared to run such a high MP as 36'' when LOP.  I am too chicken to try - I know quite well the theory that peak pressures are much lower LOP and that is what counts.  The most I have run is 31'' and 2300rpm I think it was.  I have generally been chicken to run very high power LOP, and I have usually only gone to ~13gph....I am forgetting all the numbers but I was seeing ~175TAS at ~12k and 1570 TiT and very cool Cht like 310.  

 

I am curious to try 15gph, 32''.  Do you happen to know any of the rest of the numbers that your Don #2 was getting.  TiT and Cht.

[DaV8or]

Sounds like a lot of work... Long live ROP!

Just kidding. Good luck.

You know, there is some truth in your statement. I have spent some time and thought trying to get my plane to run smooth LOP and unless you have loads of time yourself, like you're retired or something, or you're willing to burn whatever money it takes to have someone else tweak your plane to run smooth LOP, running ROP isn't such a bad option. My plane runs like a Swiss watch ROP, but LOP it's more like a Russian tractor made in a labor camp. Guess which one provides a more enjoyable flight experience and gives more confidence flying over hostile terrain?

 

There seems to be an obsession about running LOP, so much so that we forget that there is nothing wrong with running ROP. Just use your engine monitor in same way and make sure your CHTs are under control and perhaps make sure you're not in the "red box" if you want. I personally run at 65% power, so I put it close to peak and don't worry about the red box too much. If I were to run a higher power setting, I'd go 125 ROP.

 

I guess the point of my thread is, if the quest for perfect LOP ops is costing loads of money, too much down time and taking the shine off of flying for fun because you're constantly worrying about what could be wrong with your engine, I say screw LOP. It's OK to run ROP. Fly to have fun folks!

[jetdriven]

Hi RocketAviator - still enjoying your new avatar.

 

Great project - thanks for sharing.  I never dared to run such a high MP as 36'' when LOP.  I am too chicken to try - I know quite well the theory that peak pressures are much lower LOP and that is what counts.  The most I have run is 31'' and 2300rpm I think it was.  I have generally been chicken to run very high power LOP, and I have usually only gone to ~13gph....I am forgetting all the numbers but I was seeing ~175TAS at ~12k and 1570 TiT and very cool Cht like 310.  

 

I am curious to try 15gph, 32''.  Do you happen to know any of the rest of the numbers that your Don #2 was getting.  TiT and Cht.

 

If you limit power with FF, manifold pressure above what is required cools the engine. Think of it this way, more MP is further from peak EGT with the same fuel flow.  You can use MP to set the EGT to your desired value.  Of course CDT will go up as the turbo spins faster, so at some point that becomes limiting.

[RocketAviator]

Hi RocketAviator - still enjoying your new avatar.

 

Great project - thanks for sharing.  I never dared to run such a high MP as 36'' when LOP.  I am too chicken to try - I know quite well the theory that peak pressures are much lower LOP and that is what counts.  The most I have run is 31'' and 2300rpm I think it was.  I have generally been chicken to run very high power LOP, and I have usually only gone to ~13gph....I am forgetting all the numbers but I was seeing ~175TAS at ~12k and 1570 TiT and very cool Cht like 310.  

 

I am curious to try 15gph, 32''.  Do you happen to know any of the rest of the numbers that your Don #2 was getting.  TiT and Cht.

Avitoreb,  Don #2 reported to me the following LOP settings he used in his rocket and the results he achieved.

31 - 32"MP, 2400 RPM, 14.7 - 15.5 GPH at 190kts TAS @ FL10, 200kts TAS @ FL12, 212kts TAS @ FL15

He also mentioned one other item he apparently did not know about until after he sold his Rocket to the new owner who reported an advance timing of 3 degrees.  He did not know if the new owner had the timing set back to factory specifications or not!

 

I was running at 2300 and will now try the range between 2200 & 2450 as flight time permits.   Also I intend to try several lower MP settings as flight time permits.  Then possibly some combinations of MP / RPM as well.  

 

Let me know what you come up with,

Lacee

[RocketAviator]

DaV8or%

[RocketAviator]

You know, there is some truth in your statement. I have spent some time and thought trying to get my plane to run smooth LOP and unless you have loads of time yourself, like you're retired or something, or you're willing to burn whatever money it takes to have someone else tweak your plane to run smooth LOP, running ROP isn't such a bad option. My plane runs like a Swiss watch ROP, but LOP it's more like a Russian tractor made in a labor camp. Guess which one provides a more enjoyable flight experience and gives more confidence flying over hostile terrain?

 

There seems to be an obsession about running LOP, so much so that we forget that there is nothing wrong with running ROP. Just use your engine monitor in same way and make sure your CHTs are under control and perhaps make sure you're not in the "red box" if you want. I personally run at 65% power, so I put it close to peak and don't worry about the red box too much. If I were to run a higher power setting, I'd go 125 ROP.

 

I guess the point of my thread is, if the quest for perfect LOP ops is costing loads of money, too much down time and taking the shine off of flying for fun because you're constantly worrying about what could be wrong with your engine, I say screw LOP. It's OK to run ROP. Fly to have fun folks!

Dave, I could not agree more, this is simply a personal goal of mine in addition to attempting to curb the cost of operating my aircraft not only in fuel but the long term benefit I expect to gain from LOP operations.  We now have a place that is 600 km away which we fly to frequently so 25% fuel cost savings can add up quickly in considering my ROI.  And that is NOT to say that appropriate ROP operations would not also significantly contribute to long lower cost life.  I am doing almost all the work myself.  The biggest single expense has been the Tempest Fine Wire Plugs.  I am not absolutely convinced that the massive tip Tempest Plugs would not work well either, but I am not going to by a set just to test my theory!  In any case I appreciate the feedback and understand your position.

Lacee 

[RocketAviator]

If you limit power with FF, manifold pressure above what is required cools the engine. Think of it this way, more MP is further from peak EGT with the same fuel flow.  You can use MP to set the EGT to your desired value.  Of course CDT will go up as the turbo spins faster, so at some point that becomes limiting.

ok Byron I just have to ask what is CDT? 

[jetdriven]

CDT is the compressor discharge temp. As you increase MP, the temperature coming out of the turbo is higher, and as you approach the edge of the compressor map, gets very hot. This problem gets worse the higher you go, as the turbo must compress air from a lower ambient pressure to the set MP.  Intercoolers reduce the temp, but density still decreases.  There is a limit to cooling with MP when running LOP. At a certain point, the high incoming air temp works against you for cooling.  I understand this is a real problem with 231s that don't have intercoolers.

[carusoam]

Dp...

[aviatoreb]

If you limit power with FF, manifold pressure above what is required cools the engine. Think of it this way, more MP is further from peak EGT with the same fuel flow.  You can use MP to set the EGT to your desired value.  Of course CDT will go up as the turbo spins faster, so at some point that becomes limiting.

 

Hi Byron, That makes a lot of sense.  I never thought of using the black knob that way - increasing pressure to effectively push the burner further into LOP.  brilliant.  

 

But then you point out also my ignorance of how to use CDT vs TiT. Generally I have been looking at TiT and worrying about my turbo on that inlet temp number, but I also have a CDT guage and I confess that I have so far gained no further useful knowledge from this gauge.  Can one tell me one story but the other another story?  Can discharge temps and inlet temps be telling a different story?

 

And for my own engine, it seems to be worrying about TiT that wants to climb high when I go LOP is the limiting factor instead of smoothness - so I have only been running lop at very low power settings, which is boring to go at 45-50% so I have only done it a few times to extend range.   I am curious to try some of the settings I have read in this thread since I know I can do better.

[jetdriven]

CDT can be used to evaluate the efficiency of the turbo. As you reach the edge of the compressor map, the CDT increase for the increase of MP becomes nonlinear. To get another 2" of MP may raise the CDT to an unacceptable value.  At some point, the increase in the CDT, (and corresponding decrease of air density), outweighs the increased manifold pressure. Its higher pressure air, but hotter as well and density doesnt increase much at all. But you still lose because really hot air fed into the engine lowers the detonation margin and makes the engine run hotter.  This becomes a hard limit at higher altitudes, the turbocharger simply cannot take 12" or lower ambient air and compress it to 36". These turbos spin at 150K + RPM and at some point they hit a wall. They can only process so much air.   An IAT gauge, showing the air temp at the fuel servo inlet will tell you what your intercooler's doing for you.  Intercoolers lower intake air temperature but cannot add mass to the intake charge, only a turbocharger can do that, they simply cool it to an acceptable temperature for the engine.  When the turbo "temps out" that's your critical altitude. I suspect this is very high altitude on a TSIO-520. CDT measures turbo efficiency, and IAT measures real air temp ingested into the engine.

 

Someone with a Rocket try running LOP at a fixed fuel flow. Lacee, you'd make a good candidate. Then add or subtract MP 2" at a time, and readjust FF to the same value.  More MP equals further from peak EGT for a given fuel flow.  The highest efficiency can be had at the highest TAS for that fuel flow.  It may require extra MP to push the EGT down to a lean enough value to keep TITs in line.  This is all speculation, I have lots of time in turbocharged piston twins, but I didnt know about LOP then.

 

I do know that Beech TNIO-550 turbonormalized Bonanza pilots run as much as 95% power LOP and get away with it with cool CHTs.  They run it at the full 30" MP and limit power with fuel flow. An A-36 at 17,000' running this kind of power can hit 200 KTAS at something like 16-17 GPH. 

[carusoam]

To make it short and to the point...

Watching TIT keeps from melting the turbo...

Watching CDT (no heat exchanger) keeps from sending too hot air down stream to the engine...

Watching AIT (post heat exchanger) keeps from sending too hot air down stream to the engine...

Watching the economics and hardware cost of two snails on the TNIO550s keeps me from being too jealous...

I would still prefer the Acclaim over our friend's machines @ BT.

Thanks for the details, Byron,

-a-

[aviatoreb]

Both your posts above are really helpful to me Byron.  Thank you.

From a general Carnot cycle perspective, everything you say makes complete sense to me.  I have always been a little undereducated on how to use both my TiT and CDT appropriately in deciding how to manage my engine, and I admit that I mostly have been monitoring my TiT alone as the controlling factor and just peeking at CDT to make sure nothing is too large.  Luckily as you said, in my particular engine, the TSIO520 and the particular install, it runs cool every which way you measure it as long as you run it reasonably, even at high altitude - the certified altitude of FL24 of my airplane seems to be well below whatever altitude significantly stresses my engine.  I have read it was tested up to FL35 with the initial intention of extending certification to that height and it ran well enough.

 

In my experience, smoothness or EGTs or not the limiting factor in LOP, but watching TiT as I have (but not closely enough CDT as you are instructing), I will quickly start pushing the TiT up higher than I would like.  With a TiT redline of 1650 (for ops greater than a minute), I have decided to try and keep that parameter below 1600, which ends up limiting how much fuel I can push through the engine on the LOP side, as it forces me further lean of peak than I wish I could, even at lower power settings.  So I will end up at say 2300, 25'' maybe up to 27'' but maybe 12.5gph.

 

So am I understanding you correctly that I can do the following?  Suppose I find a lower power LOP setting as follows, 2200, 26'' at 15gph is the official book setting for 55% ROP, but according the AD saying we should no longer run <2300rpm in large bore continentals, I would run 2300 26'' and 15.5-16gph to keep sufficiently ROP.  Then from there, I can big pull to say 13.0gph or whatever is slightly LOP that day, like 10df LOP.  Now if I increase MP from there, say womewhere from say 30'', or 31'' or 32'' - that effectively pushes quite a bit deeper LOP and it will be outside of the red box.  So TiT may go down a bit, but CDT may go up a bit?  And not yet having touched the red knob, will fuel flow go up slightly but only slightly due to greater MP?  Then from there I may choose to control power by increasing or decreasing fuel flow with the red knob adjusting for roughness, and temps on EGT, TiT, CDT, and CHT.  Though I seriously doubt that CHT will ever be a problem in this airplane since it seems to stay quite low esp LOP.

 

Hopefully this would yield an acceptable setting within temp parameters with fuel flow as high as 14 or 15gph.  So far I have not really found any LOP settings I was happy with much greater than 13gph.

 

If this is a good idea to try this order of adjustments, then it would be quite different in details from what I was previously trying, which would be to choose the ROP setting that has the rpm and mp as I wish.  Say for example 2300 and 31'' - POH calls for 20gph for that 72% ROP setting, and I have tended to run 20.5gph there since I do believe the book was written in an era when closer to peak temps was more in vogue that the 125ROP that is currently more currently taught.  Anyway, from there, I would try to big pull to a guessed fuel flow of 15 or 15.5gph directly.  But I end up unhappy with TIT and end up pulling further to say 13gph and there it is so far LOP that she runs a bit rough.  So instead I setup at 55% ROP as I said, 2200 (but 2300), 26'' 15gph and big pull to 12.5 or 13gph.  

 

What's your thought?  I read on the other thread you posted yesterday that you run 83% power LOP in your IO360, and I have read also that some Bonanza guys run as high as 95% LOP.  Wow, if I could somehow push 18gph LOP through my engine, that's 81%, boy would I go like a bat out of hell.  I rarely go >72% and even more rarely >75% ROP as those already call for 20 and 21gph respectively (and a tad more for modern 125df ROP setting) - but I can say she is one very fast airplane at 75%.  At 81% wow would that be fast - and clean and less fuel...rocket Nirvana.  But can it be done within TiT/CDT temps?  What's your guess?

 

Holy Moly a rocket would be fast if we could shove 20gph LOP through the engine - that would be 95% power.  If only....

[carusoam]

Somebody posted a paper on balanced intakes the other day.... They had a statement regarding tube length and rpm.

EB,

When you get roughness while trying different LOP settings, have you tried higher rpm settings as well?

It would be interesting to see if the balance of intakes improves with higher rpm.

Best regards,

-a-

[aviatoreb]

Somebody posted a paper on balanced intakes the other day.... They had a statement regarding tube length and rpm.

EB,

When you get roughness while trying different LOP settings, have you tried higher rpm settings as well?

It would be interesting to see if the balance of intakes improves with higher rpm.

Best regards,

-a-

 

I need to get more systematic with the whole LOP thing.  I have not typically run LOP since I have not been enough comfortable with the whole thing.  I have run it more as an experimental thing to do on a few flights when I am going no place in particular, other than a few occasions when I wanted to extend range.

 

So just by memory, I cannot remember specifically a trend as you are suggesting.  I think sometimes at some altitudes I increase rpms and it improves roughness, and other times, it does not.

 

Just thinking it through - someone correct me if I am wrong - if I am at a specific rpm/mp/fuel flow setting and I am too far LOP and so I try to fix it by increasing rpms, that would effectively push me further LOP for that new setting, so I would expect even more roughness?

 

Generally, my particular engine setup runs pretty smoothly pretty far LOP, and the limiting factor is just the temps at the turbo getting higher than I like.

 

How would I balance intake?  Wouldn't that require new equipment and some kind of STC?

[pinerunner]

Dave, I could not agree more, this is simply a personal goal of mine in addition to attempting to curb the cost of operating my aircraft not only in fuel but the long term benefit I expect to gain from LOP operations.  We now have a place that is 600 km away which we fly to frequently so 25% fuel cost savings can add up quickly in considering my ROI.  And that is NOT to say that appropriate ROP operations would not also significantly contribute to long lower cost life.  I am doing almost all the work myself.  The biggest single expense has been the Tempest Fine Wire Plugs.  I am not absolutely convinced that the massive tip Tempest Plugs would not work well either, but I am not going to by a set just to test my theory!  In any case I appreciate the feedback and understand your position.

Lacee 

I think the trouble you're going through will be worth it even if you decide to run mostly ROP when you're done. Even though an engine with a terrible GAMI spread will run pretty smooth ROP, the different cylinders will be experiencing very different conditions, from in the red box to so filthy rich that plugs are fouled and exhaust valves stick (I'm imagining extreme case here). With an engine that that's able to run well LOP you'll also have an engine that'll get the best possible results run under ROP conditions.  

[carusoam]

EB,

A change in intake hardware would probably be required....

Long curvy intake pipes on the IO550 allow for smooth LOP ops until it just shuts off after 100f LOP.

Bravo owners report mixed results on wether they can operate LOP.

I would expect to get reliable LOP with a turbo system, good cooling from an intercooler then splitting the airflow through long curvy pipes. Nice control of air flow and pressure waves in the intake is required.

Using an acclaim as a model... Adapt the hardware ideas there to your system... Of course, the Acclaim uses a twin turbo normalized system. Expect some surmountable differences.

Price probably becomes out of hand to improve in this manner...

Best regards,

-a-

[aviatoreb]

EB,

A change in intake hardware would probably be required....

Long curvy intake pipes on the IO550 allow for smooth LOP ops until it just shuts off after 100f LOP.

Bravo owners report mixed results on wether they can operate LOP.

I would expect to get reliable LOP with a turbo system, good cooling from an intercooler then splitting the airflow through long curvy pipes. Nice control of air flow and pressure waves in the intake is required.

Using an acclaim as a model... Adapt the hardware ideas there to your system... Of course, the Acclaim uses a twin turbo normalized system. Expect some surmountable differences.

Price probably becomes out of hand to improve in this manner...

Best regards,

-a-

 

That sounds quite doable from an engineering perspective, but impossible from an FAA perspective.  Changing around intake pipes surely would require some STC to approve it, and for the cost of that it would be cheaper to buy an acclaim.  A shame.

 

My specific difficulty of running LOP is not being able run deeper LOP but as I said, I can run smoothly reasonably deep into LOP but then to run at a less lean setting to allow to recoup a reasonable amount of power for speed (to push through more fuel when LOP) makes the turbo get hotter and eventually hotter than I would like.  So I only run relatively deep into lean side to keep the turbo cool enough, which makes yes for very low fuel burn but also very non-rocket slower speeds.

 

My general impression though is that anything that is done to improve the system, yes perhaps balancing air to fuel ratio, would make the whole thing run better and perhaps allow a better LOP at higher settings.