Engineer Ted's How to Make Your Engine Last (while running)

Discussion in 'Maintenance Bay' started by Ted DuPuis, Jan 27, 2013.

  1. GLMS_NC

    GLMS_NC Pre-takeoff checklist

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    Ted

    Shock cooling - Do you have science behind this? When I shut the motor off temps drop quicker than what I could do flying and the motor does just fine with this.

    Have you read this?
    http://www.avweb.com/news/maint/182883-1.html
     
  2. Maciej

    Maciej Line Up and Wait

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    Have you factored in the air flowing over the engine as your flying opposed to you being at a standstill?
     
  3. GLMS_NC

    GLMS_NC Pre-takeoff checklist

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  4. mondtster

    mondtster Pattern Altitude

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    Considering that one of the things I do in the engine test lab I work in is head crack testing, I do believe that there is a potential for problems and/or damage when there are rapid temperature changes. Do I go out of my way to insure that temperatures don't change too rapidly? No, but I also don't go out of my way to create large, rapid temperature changes either.

    One of the harshest piston aircraft engine operating environments I've personally been around is in skydive operations, and I haven't seen an excessive amount of damaged or cracked cylinders on those engines. If anything, I'd say they enjoy a longer than normal cylinder and engine lifespan due to actually being used, at least compared to the typical low use privately owned aircraft.
     
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  5. Checkout_my_Six

    Checkout_my_Six Final Approach

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    but....I'm told the skydiving guys have a few tricks up their sleeve to prevent over temping CHTs.....and it's not so much the cooling that they're worried with.
     
  6. mondtster

    mondtster Pattern Altitude

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    The drop zone I occasionally fly at has no climb rate or cylinder head temperature restrictions, time and temperature delta restrictions, or obsessive engine operating regimens. They also often employ ink wet commercial pilots, so you know most of those guys have survival on their mind, not engine management best practices. I'm not aware that they go through any more cylinders than anyone else does, for the amount of hours flown. :)

    Obviously I do what I can when I fly their planes but I am definitely not the only one operating them.
     
  7. Checkout_my_Six

    Checkout_my_Six Final Approach

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    Ted may know of the operation that did the engine study....but, my other Lycoming bud Tim knows of it and it related more to control of heat vs. cooling.
     
  8. Fearless Tower

    Fearless Tower Touchdown! Greaser!

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    I have no direct experience with piston skydive operators, but I have made an observation:

    Every time the subject comes up, it seems that some people who have worked for skydive outfits report frequent cylinder problems/changes while others swear that they're changing cylinders no more frequently than a typical GA operator.

    IOW, there doesn't seem to be a consensus.
     
  9. mondtster

    mondtster Pattern Altitude

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    All I can relate is personal experience and observation, which is that this specific drop zone has no ridiculous "procedures" to try and keep cylinders alive. In the time I've been around there, the only time those planes have been down is for 100 hour inspections, and no cylinders have ever been replaced. I'm not sure how many hours are being flown annually, but I'd expect 500ish per plane, maybe more.

    One must remember that DZ planes are getting flown a lot more than privately owned planes so someone may perceive that there are frequent cylinder changes calendar time wise, but when hours flown is factored in it isn't excessive.

    I'd also want to see some information on those excessive cylinder replacements. Since the topic I was replying to was about shock cooling, how many of those cylinders were replaced for cracking? I'd probably discard data on any cylinder that was replaced due to poor ring seal or valve leakage for this purpose.
     
  10. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

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    First off, I assume that you read my first post in detail where I explained my views on shock cooling. It is summarized as below:

    The articles you listed look at single point CHTs on each cylinder, and don't look at the thermal map of what's going on inside the cylinder. Keep in mind that CHT numbers we see are from a single point. During certification, cylinders had CHT probes all over the cylinder to get a full mapping of temperature, and those numbers do vary quite a bit. Of course, these were still outside temperatures. The change in temperature when you shut down and everything is stationary isn't going to be as hard on an engine as when it's running simply because you don't have the temperatures and pressure changes/forces occurring every cycle.

    Also, as I've stated, there's a difference between an O-360 and a TSIO-520. O-360s don't make much power and their internal pressures and temperatures are low. A TSIO-520 makes a lot of power (other than the Crusader's TSIO-520 that he specifically points out in the article you linked - that was derated to 250 HP) and is typically in an engine with poor baffling, thus resulting in running at higher temperatures.

    The example of removing fins from the Crusader and running too cool is also not a particularly good one. There was more going on. First off, like I said the Crusader is a derated engine (250 HP vs. 285-335 HP for other TSIO-520s). Second off, it was the most modern baffling design that Cessna had ever created. It was really very good. The baffle designs used by Cessna in the previous TSIO-520 aircraft varied from marginal to horrendous. Baffling makes a huge difference in CHTs and oil temperatures, and anyone who has spent any time improving an engine with truly poor baffling knows this.

    Many have discussed shock heating as the real concern. A gradual power application for takeoff is also good. I will normally do a gradual power application over the course of ~3 seconds.

    My point regarding shock cooling has always been pretty simple: I can't say with certainty that shock cooling will hurt your engine, but I can say with certainty that reasonable practices to prevent shock cooling will not hurt your engine. I take a practical approach to this. When I can, I try to make gradual (~1"/minute) power reductions. My power reductions from takeoff to climb power and then climb to cruise power (I am now flying turbocharged engines) are done over the course of several seconds and not at the 1"/minute rate, that would be impractical. When operational considerations require me to take more significant power reductions out, I do so over the course of several seconds again, and I don't worry about it.

    If you plan your descents well from a cross country, gradual power reductions won't cause any of the nonsense like gliders beating a tow plane back to the ground. I would never advocate practices like that. That's just ridiculous.
     
  11. GLMS_NC

    GLMS_NC Pre-takeoff checklist

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  12. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

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    It may have been published recently, but it's the same argument that others have been pushing for a long time. Rick's a lawyer, not someone with a technical background. In fact, I think the common trait I've observed with those who push the "Shock cooling is a myth" way of thinking is that none of them have strong technical backgrounds, and are generally trained in non-technical careers.
     
  13. Checkout_my_Six

    Checkout_my_Six Final Approach

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    ya but....the author is a CFI....that should account for something. o_O
     
  14. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

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    Generally having a CFI means that someone is teaching incorrect engine procedures that were taught to him by a CFI who knew incorrect engine procedures that were taught to him by... you get where I'm going with this.
     
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  15. Checkout_my_Six

    Checkout_my_Six Final Approach

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    yup, where is that sarcasm smilie.....? o_O
     
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  16. Checkout_my_Six

    Checkout_my_Six Final Approach

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    and.....and.....make sure the timing is set correctly. ;)
     
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  17. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

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    :yes: :yes: :yes:
     
  18. MtnMarcus

    MtnMarcus Pre-takeoff checklist

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    read this a while ago and just re-read. One thing that jumped out at me was mention of continental recommending that they like to see CHT max temp at 380. makes sense and I will be paying more attention to this
     
  19. Fearless Tower

    Fearless Tower Touchdown! Greaser!

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    It is particularly important in Continentals. Continental cylinders just don’t handle heat as well. I’ve seen this from experience. Keeping them below 380F is important for longevity. Lyc cylinders can take a little more heat before failure. Same for P&W.
     
  20. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

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    It's worth noting that Lycoming sets its recommendation at 400F max continuous vs. the 380F for Continental, and also that the Lycoming CHT limits are 475-500 vs. typically 465 for Continental.

    On Lycomings I aim for 380F or below, on Continentals I aim for 360F or below. LOP with proper baffles that's usually doable, other than climb in the 414 where they'll tend to creep up.
     
  21. Mtns2Skies

    Mtns2Skies Super Moderator Management Council Member

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    @Ted DuPuis what are your thoughts on spin-on oil filter conversions? Worth it or is the screen enough?
     
  22. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

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    I personally did it on the 310. There's a reason why all the engines now have filters instead of screens - it's better. The filters do a better job of getting junk out of the oil, they're easier to inspect for debris when you do changes. Per the book you can extend your oil changes to 50 hour intervals with a filters (although there's still a 4 month calendar time component).

    So, I think it's worth doing. I went with AirWolf and did the remote mount, but there are lots of ways to go about it.
     
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  23. timwinters

    timwinters Touchdown! Greaser! PoA Supporter

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    Austin,

    I too have a straight tail with an 0470 and I went with the F&M "pistol grip" adapter simply because I didn't like the thought of adding hoses (another potential failure point) to my oil circuit but, to each his/her own. The pistol grip adapters aren't without their downfalls either...there are repeating torque check requirements (IIRC).

    There's one (C6LC-S) on ebay right now for about $50 cheaper than you can buy it for on Aircraft Spruce, etc.

    https://www.ebay.com/i/142685247988?chn=ps

    Whatever you decide, I agree with Ted that a filter is relatively cheap (in aviation terms) add'l protection. Not that my opinion means much! ;)
     
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  24. Gary Austin

    Gary Austin Pre-Flight

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    Doesn't the "pistol grip" adapter have an AD against it?, I just changed one in a repair station where I work
     
  25. timwinters

    timwinters Touchdown! Greaser! PoA Supporter

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    I believe that AD applies to Cessna oil filter adapaters only and not the F&M adapters. But, regardless, the AD (as I recall) basically requires inspection of the torque putty at every oil change, something I do anyway.
     
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  26. Checkout_my_Six

    Checkout_my_Six Final Approach

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    btw....I googled "torque putty"....and nuth'n turned up. o_O