Engine monitoring systems for towplanes

[[email protected]]

Hey, gang,

Soon we will be putting an overhauled engine on our Pawnee, and I am wondering if anyone has had experience with or has comments on engine monitoring systems on towplanes.

I am thinking a basic system with all 6 cylinders CHT (and EGT?) monitored, a shock cooling warning system, and data logging. Would monitoring other parameters be useful, also? If so, what parameters (adding sensors adds up $$$)?

Is such a system useful and helpful for our type of flight duty cycle (e.g., towing)? Do the shock cooling warning systems work for our very unique type of operations (I guess they are just an alarm if the rate of CHT drop exceeds a set value?)? Is the data logging useful for monitoring/predicting engine health and life? Am I overthinking/overkilling this issue?????

Thanks,
Jim

[Dan Marotta]

A graphic engine monitor will show CHT and EGT for each cylinder and
you'll spend more time looking at it than looking out the window. Please
read this article
<https://www.avweb.com/news/features/Shock-Cooling-Time-to-Kill-the-Myth-230134-1.html>.

On 9/6/2018 4:03 PM, wrote:
> Hey, gang,
>
> Soon we will be putting an overhauled engine on our Pawnee, and I am wondering if anyone has had experience with or has comments on engine monitoring systems on towplanes.
>
> I am thinking a basic system with all 6 cylinders CHT (and EGT?) monitored, a shock cooling warning system, and data logging. Would monitoring other parameters be useful, also? If so, what parameters (adding sensors adds up $$$)?
>
> Is such a system useful and helpful for our type of flight duty cycle (e.g., towing)? Do the shock cooling warning systems work for our very unique type of operations (I guess they are just an alarm if the rate of CHT drop exceeds a set value?)? Is the data logging useful for monitoring/predicting engine health and life? Am I overthinking/overkilling this issue?????
>
> Thanks,
> Jim
>

--
Dan, 5J

[Brian[_1_]]

A Recording engine monitor might be best. As noted engine monitors do tend to increase the heads down time. And looking at the data after the flights might actually be much more useful.

They are quite good at identifying baffling that isn't installed or working right.

They are also very good at helping keep the engine cool, as most experts agree that keeping the CHT's under 400F will extend the life of the engine.

Brian

[[email protected]]

On Friday, September 7, 2018 at 9:56:38 AM UTC-7, Brian wrote:
> A Recording engine monitor might be best. As noted engine monitors do tend to increase the heads down time. And looking at the data after the flights might actually be much more useful.
>
> They are quite good at identifying baffling that isn't installed or working right.
>
> They are also very good at helping keep the engine cool, as most experts agree that keeping the CHT's under 400F will extend the life of the engine.
>
> Brian

CHT is the critical measurement, with cooling rate a close second. It's good to give towpilots clear guidelines, and inform towpilots that engine monitor readings will be downloaded and checked, even if they are not....it will make them pay better attention to the engine parameters.

[[email protected]]

My experience bringing power back to idle after glider release in less than 30 seconds and then not adding power all the way to landing has not been a problem. Our previous engine was well over TBO when replaced, with no issues.
Having more sophisticated engine monitoring might help to run lean of peak to save gas.
Keeping your head outside the cockpit may save you more than gas.

[[email protected]]

We went with 6 cyl CHT only.

What I will say is that after the first year.. we don't really stare at it.

BUT.. it exposed some horrible standardization (our own fault) among the tow pilots.

I believe it was worth it's money from that standpoint alone. We didn't discover the operational error until we got comparing notes of temps amongst a few of the pilots.

JP

[[email protected]]

On Friday, September 7, 2018 at 11:10:08 PM UTC-4, wrote:
> My experience bringing power back to idle after glider release in less than 30 seconds and then not adding power all the way to landing has not been a problem. Our previous engine was well over TBO when replaced, with no issues.
> Having more sophisticated engine monitoring might help to run lean of peak to save gas.
> Keeping your head outside the cockpit may save you more than gas.

What kind of airplane?
Your experience certainly differs from my 40 years of running towplanes.
UH

[[email protected]]

On Saturday, September 8, 2018 at 5:32:18 AM UTC-5, wrote:
> We went with 6 cyl CHT only.
>
> What I will say is that after the first year.. we don't really stare at it.

[[email protected]]

On Saturday, September 8, 2018 at 2:42:00 PM UTC-5, wrote:
> On Friday, September 7, 2018 at 11:10:08 PM UTC-4, wrote:
> > My experience bringing power back to idle after glider release in less than 30 seconds and then not adding power all the way to landing has not been a problem. Our previous engine was well over TBO when replaced, with no issues.
> > Having more sophisticated engine monitoring might help to run lean of peak to save gas.
> > Keeping your head outside the cockpit may save you more than gas.
>
> What kind of airplane?
> Your experience certainly differs from my 40 years of running towplanes.
> UH

UH, do you think recording engine parameters and analyzing them post flight might be worth the effort?

I do wonder if our standard procedure is deficient, maybe analyzing engine parameters would reveal a bad procedure (or a tow pilot that doesn't follow a good procedure). And it would gather hard data that might show, as Dan suggests, that shock cooling is a myth....

Our procedure is to speed up to 100-110 mph put a notch of flaps down and throttle back to 2200 RPM immediately after release, descend/spiral down while reducing RPM by 100 every 10 seconds, until we get to 1500, then we are free to go to any speed/RPM. Sometimes we sideslip, but not always. Please critique!

Maybe we ought to start a new thread on cooldown techniques....

Cheers,
Jim

[[email protected]]

On Saturday, September 8, 2018 at 5:53:12 PM UTC-4, wrote:
> On Saturday, September 8, 2018 at 2:42:00 PM UTC-5, wrote:
> > On Friday, September 7, 2018 at 11:10:08 PM UTC-4, wrote:
> > > My experience bringing power back to idle after glider release in less than 30 seconds and then not adding power all the way to landing has not been a problem. Our previous engine was well over TBO when replaced, with no issues.
> > > Having more sophisticated engine monitoring might help to run lean of peak to save gas.
> > > Keeping your head outside the cockpit may save you more than gas.
> >
> > What kind of airplane?
> > Your experience certainly differs from my 40 years of running towplanes..
> > UH
>
> UH, do you think recording engine parameters and analyzing them post flight might be worth the effort?
>
> I do wonder if our standard procedure is deficient, maybe analyzing engine parameters would reveal a bad procedure (or a tow pilot that doesn't follow a good procedure). And it would gather hard data that might show, as Dan suggests, that shock cooling is a myth....
>
> Our procedure is to speed up to 100-110 mph put a notch of flaps down and throttle back to 2200 RPM immediately after release, descend/spiral down while reducing RPM by 100 every 10 seconds, until we get to 1500, then we are free to go to any speed/RPM. Sometimes we sideslip, but not always. Please critique!
>
> Maybe we ought to start a new thread on cooldown techniques....
>
> Cheers,
> Jim

This has been studied and findings published in the past. I think it was in Soaring and was quite some time ago. It may also have been in Free Flight.
Our procedure, used in Super Cub and Pawnee, is to smoothly reduce throttle to 2300 rpm while accelerating to 110 mph. We carry this through the descent, including some of the downwind, followed by gradual reduction as speed is reduced to approach speed. We try to not be less than 2 minutes from release/throttle reduction to throttle closed. We discourage slips because this can make the flow through the cowl unbalanced which can lead to less even cooling.
I know Lycoming does not believe shock cooling is a myth. They have a recommended cooling rate, but I can't quote it from memory.
We have CHT on all 4 cylinders to watch for one getting unusually hot. This tends to be due to a damaged baffle though one time we did find signs of an intake leak that can make a cylinder go lean.
If you want to do the study, go for it and then compare with what your engine manufacturer recommends.
FWIW
UH

[[email protected]]

On Saturday, September 8, 2018 at 6:06:39 PM UTC-5, wrote:
> On Saturday, September 8, 2018 at 5:53:12 PM UTC-4, wrote:
> > On Saturday, September 8, 2018 at 2:42:00 PM UTC-5, wrote:
> > > On Friday, September 7, 2018 at 11:10:08 PM UTC-4, wrote:
> > > > My experience bringing power back to idle after glider release in less than 30 seconds and then not adding power all the way to landing has not been a problem. Our previous engine was well over TBO when replaced, with no issues.
> > > > Having more sophisticated engine monitoring might help to run lean of peak to save gas.
> > > > Keeping your head outside the cockpit may save you more than gas.
> > >
> > > What kind of airplane?
> > > Your experience certainly differs from my 40 years of running towplanes.
> > > UH
> >
> > UH, do you think recording engine parameters and analyzing them post flight might be worth the effort?
> >
> > I do wonder if our standard procedure is deficient, maybe analyzing engine parameters would reveal a bad procedure (or a tow pilot that doesn't follow a good procedure). And it would gather hard data that might show, as Dan suggests, that shock cooling is a myth....
> >
> > Our procedure is to speed up to 100-110 mph put a notch of flaps down and throttle back to 2200 RPM immediately after release, descend/spiral down while reducing RPM by 100 every 10 seconds, until we get to 1500, then we are free to go to any speed/RPM. Sometimes we sideslip, but not always. Please critique!
> >
> > Maybe we ought to start a new thread on cooldown techniques....
> >
> > Cheers,
> > Jim
>
> This has been studied and findings published in the past. I think it was in Soaring and was quite some time ago. It may also have been in Free Flight.

[Skypilot]

The Airforce Cadets Pawnee in Warwick Queensland Australia has just had a new engine and new engine monitoring system installed. If you pm me or email me I can get you in contact with the pilot who organised and is flying it.

Justin


Hey, gang,

Soon we will be putting an overhauled engine on our Pawnee, and I am wondering if anyone has had experience with or has comments on engine monitoring systems on towplanes.

I am thinking a basic system with all 6 cylinders CHT (and EGT?) monitored, a shock cooling warning system, and data logging. Would monitoring other parameters be useful, also? If so, what parameters (adding sensors adds up $$$)?

Is such a system useful and helpful for our type of flight duty cycle (e.g., towing)? Do the shock cooling warning systems work for our very unique type of operations (I guess they are just an alarm if the rate of CHT drop exceeds a set value?)? Is the data logging useful for monitoring/predicting engine health and life? Am I overthinking/overkilling this issue?????

Thanks,
Jim

[[email protected]]

On Sunday, September 9, 2018 at 8:02:30 AM UTC-7, wrote:
> On Saturday, September 8, 2018 at 6:06:39 PM UTC-5, wrote:
> > On Saturday, September 8, 2018 at 5:53:12 PM UTC-4, wrote:
> > > On Saturday, September 8, 2018 at 2:42:00 PM UTC-5, wrote:
> > > > On Friday, September 7, 2018 at 11:10:08 PM UTC-4, wrote:
> > > > > My experience bringing power back to idle after glider release in less than 30 seconds and then not adding power all the way to landing has not been a problem. Our previous engine was well over TBO when replaced, with no issues.
> > > > > Having more sophisticated engine monitoring might help to run lean of peak to save gas.
> > > > > Keeping your head outside the cockpit may save you more than gas.
> > > >
> > > > What kind of airplane?
> > > > Your experience certainly differs from my 40 years of running towplanes.
> > > > UH
> > >
> > > UH, do you think recording engine parameters and analyzing them post flight might be worth the effort?
> > >
> > > I do wonder if our standard procedure is deficient, maybe analyzing engine parameters would reveal a bad procedure (or a tow pilot that doesn't follow a good procedure). And it would gather hard data that might show, as Dan suggests, that shock cooling is a myth....
> > >
> > > Our procedure is to speed up to 100-110 mph put a notch of flaps down and throttle back to 2200 RPM immediately after release, descend/spiral down while reducing RPM by 100 every 10 seconds, until we get to 1500, then we are free to go to any speed/RPM. Sometimes we sideslip, but not always. Please critique!
> > >
> > > Maybe we ought to start a new thread on cooldown techniques....
> > >
> > > Cheers,
> > > Jim
> >
> > This has been studied and findings published in the past. I think it was in Soaring and was quite some time ago. It may also have been in Free Flight.
> > Our procedure, used in Super Cub and Pawnee, is to smoothly reduce throttle to 2300 rpm while accelerating to 110 mph. We carry this through the descent, including some of the downwind, followed by gradual reduction as speed is reduced to approach speed. We try to not be less than 2 minutes from release/throttle reduction to throttle closed. We discourage slips because this can make the flow through the cowl unbalanced which can lead to less even cooling.
> > I know Lycoming does not believe shock cooling is a myth. They have a recommended cooling rate, but I can't quote it from memory.
> > We have CHT on all 4 cylinders to watch for one getting unusually hot. This tends to be due to a damaged baffle though one time we did find signs of an intake leak that can make a cylinder go lean.
> > If you want to do the study, go for it and then compare with what your engine manufacturer recommends.
> > FWIW
> > UH
>
> Thanks, Hank, good stuff.
>
> I checked out the Lycoming website linked out of the shock cooling myth article posted by Dan:
>
> https://www.lycoming.com/content/how-avoid-sudden-cooling-your-engine
>
> It says keep the rate of cooling under 50 deg F (28 deg C) per minute. Burt Compton says keep it below 30 def F per minute (Soaring Magazine October 2012 Page 14, and I think also in his "Tow Pilot Manual").
>
> Also, I found those articles you referred to, Hank, in the Soaring Magazine archives. Done by some glider and tow pilots with advanced engineering degrees in Canada. December 1992 (for a 150HP Citabria) and April 1993 (for a Pawnee). Briefing looking them over, I am impressed that these tests were done competently, looks like good science (I used to flight test military jets for a major aerospace company, so I have some qualifications to make that judgement).
>
> VERY interesting that the results show a much different letdown procedure is needed for the Citabria than the Pawnee. The Citabria is much more sensitive to letdown procedure, and their original procedure did exceed the Lycoming recommended cooling rate, by up to 200%. And that was the airplane that they had cracking cylinders on, prompting the study. Strong indication that shock cooling is NOT a myth, I would say. They significantly changed their letdown procedure for their Citabria, needless to say.
>
> Their Pawnee did not have cylinder cracking problems, and the data on it showed it to be much more robust to letdown procedure, and that their original procedure (quite similar to yours, Hank) did not exceed the Lycoming cooling rate limits. Hence they ended up sticking with their original procedure for the Pawnee.
>
> They theorized that the differences were due to the Citabria being more tightly cowled than the relatively-wide-open Pawnee cowling. Makes sense to me.
>
> I did find one other reference to letdown procedure mentioned in Soaring Magazine, February 2015, used by Cypress Soaring in Southern California on their Pawnee. "I was advised to keep an eye on the oil temperature gauge and to take the reading (190 degrees (for that particular tow being described - JH)) and multiply it by 10. That would be the rpm that I should use during the descent." Somewhat similar to the procedure determined by the folk in Canada.
>
> I may still proceed with a DIY system for recording data on our towplane, just for fun. And, as raxy noted, when the tow pilots are aware that their letdown procedures are (or can be) checked, they might be more careful to stick to them! Haha!
>
> Keep the comments and information coming, thanks again.
>
> Cheers,
> Jim J6

I totally agree that an aerotow engine monitor is money well spent. And I think that data downloads should be done to pillory offending tow pilots, and 'to encourage the others'. In the midwest (airport elevations about 1000msl) aerotow climbs are always (in my experience) best done full rich. If CHTs get too high (which I take as above 400) then the only remedy is to increase speed, reduce throttle a bit, or wave off the glider. Out west (ie above 5000msl airport elevation), and where tows are often much higher, Pawnee engines seem to run rough on the climb at full rich, but leaning must be done VERY carefully, or CHT will soar. A very small decrease in throttle (a movement of the throttle, but hardly enough to reduce rpm at all) seems to help CHT a lot. The hottest cylinders are usually the ones at the rear: baffling is a black art.

[Boom Powell]

TSS has a EDMI in our 235 Pawnee for over a year and think it was a good investment, although, at times I wonder if it tells us more than we want to know. We had both CHT and EGT at higher limits on tows. EGT unexplainable after several inspections. Having cowling louvers installed to get the CHTs lower. The cooling monitor is most useful to avoid shock. Keep below 30deg change while reducing power. The power decrease to stay less than 30 keeps the Pawnee level after release, but as temps stabilize and power keeps coming back, you're soon doing 110mph and 1800rpm. Total tow time is about the same as with previous 2000rpm/100mph technique.

[danlj]

On Thursday, September 6, 2018 at 5:03:42 PM UTC-5, wrote:
> Hey, gang,
>
> Soon we will be putting an overhauled engine on our Pawnee, and I am wondering if anyone has had experience with or has comments on engine monitoring systems on towplanes.
>
> I am thinking a basic system with all 6 cylinders CHT (and EGT?) monitored, a shock cooling warning system, and data logging. Would monitoring other parameters be useful, also? If so, what parameters (adding sensors adds up $$$)?
>
> Is such a system useful and helpful for our type of flight duty cycle (e.g., towing)? Do the shock cooling warning systems work for our very unique type of operations (I guess they are just an alarm if the rate of CHT drop exceeds a set value?)? Is the data logging useful for monitoring/predicting engine health and life? Am I overthinking/overkilling this issue?????
>
> Thanks,
> Jim

I've been using a recording engine monitor for the dozen years that I've owned an airplane -- it's invaluable in understanding how to operate the engine safely and in looking back on flights where one suspects that "something" may have happened.

Some tips I got from Ed Kollin...
- "Shock cooling" does not happen. "Shock heating" happens often (when pilots take off at full power without taking a few minutes to at least get the oil temperature above 100 degrees (an engine monitor will tell you exactly where itis)
- CHT are optimally between about 380 and 320 dF. Aluminum begins to deform above about 400 dF; in my own experience, rings can lose their temper and become brittle and later break above about 430 df.

My own experience is that CHT is extremely helpful in operating an engine for maximum longevity. I have mine alarmed at 400dF.

Oil temperature is important to understand whether the engine is adequately warmed up before takeoff.

Carb temp is useful in understanding risk of carb ice.

I like to run LOP in cruise for economy at low power (<65%) but high-power, ROP operation only makes the oil dirty. It's good for the engine.