Cold Weather Spin Training - Engine shock cooling?

Discussion in 'Aerobatics' started by MattC, Oct 22, 2019.

  1. MattC

    MattC Filing Flight Plan

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    Hello All,

    I'd like to know if there is any greater risk of engine shock cooling while practicing spins in Winter vs Summer.

    The obvious answer is: "Hell yes! The air is colder (and thicker) so - sure - you are at greater risk shock cooling"
    The counter argument is: "The engine will be operating cooler in Winter so, although in Winter it will cool to a lower temperature than in Summer, since it started off from a lower temperature, it is at no greater risk of shock cooling than in Summer".

    I have heard flight schools ban spin training when the temps went below 40F, I've heard 32F, but haven't really read any consensus on the cutoff temperature, nor any credible explanation for the decision to even have a cutoff temperature in the first place.

    Anybody have any insights they'd like to share?

    Thanks

    Matt
     
  2. Dana

    Dana Line Up and Wait

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    :popcorn:
     
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  3. RoscoeT

    RoscoeT Cleared for Takeoff

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    Don't worry about it. Think about AOA and airspeed during spins. You're pumping a lot more cold air through the cylinders doing a regular power off landing approach than you are doing a spin.

    Oh, and also because shock cooling damage is BS.
     
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  4. James331

    James331 Touchdown! Greaser!

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    You shouldn’t be super nose down except for a sec in the recovery, infact if you want a nice tight spin keeping power in helps till recovery.

    That said when it’s COLD, like say sub 30 its kinda hard on the plane, below 0f it’s just not worth it for fun anymore IMO

    I’d also consider could you last 24hrs if the plane went down in those conditions?
     
  5. Clip4

    Clip4 En-Route

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    A spin is a low airspeed maneuver. There is probably less shock cooling potential as a simulated power out emergency approach.
     
  6. Dan Thomas

    Dan Thomas Final Approach

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    It's the spin recovery that can get close to Vne in some airplanes and with some students. That's a lot of cold air.

    Simulated forced approaches in winter bring another problem: a cold engine will often stumble and maybe not recover power soon enough to abort a touchdown. We had one of our Citabrias end up in a snowy field due to that. One has to go to low cruise power for ten seconds or so every 1000 feet in the descent to keep that engine ready to roar, and that messes up the whole exercise. Better to do it in warmer weather.
     
  7. Clip4

    Clip4 En-Route

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    I agree with the Vne, but the duration of a spin maneuver < a minute vs minute or two with simulated engine out emergency.
     
  8. MattC

    MattC Filing Flight Plan

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    Thanks all. Good points made, and I agree that the low power dive is the key issue that might drive any potential shock cooling.

    So where I'm coming from is that most of my business, these days, is spin training. And, since I teach in the North East, I would pretty much be out of work from December through March, if I am limited to 40F or higher. So I need some good arguments to convince the "higher ups" that 40F is unnecessarily restrictive. Previous employer was OK with me teaching acro all the way down to 20F. I seem to recall 32F might have been his cutoff for teaching spins, again, due to a concern for shock cooling.

    Simulated emergency descents are authorized in Winter, so one could argue they have a similar effect on the engine.

    I might email Rich Stowell.

    Matt
     
  9. EdFred

    EdFred Touchdown! Greaser! PoA Supporter

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    No one ever worries about shock heating in a NA.
     
  10. champ driver

    champ driver Line Up and Wait

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    Winter in Florida or winter in Minnesota? There is a difference.
     
  11. Tantalum

    Tantalum En-Route

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    Has anyone ever had a power failure or engine issue attributed to shock cooling? I've read some articles that this is a myth.. and the (at most) 200* CHT swing is honestly inconsequential compared to the massively high tolerances inside these piston engines. When you start the plane and power up for takeoff, isn't it heating up just as fast?

    I'm gentle on the throttle because turbo.. but I don't believe in shock cooling
     
  12. ahypnoz

    ahypnoz Pre-takeoff checklist

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    I would think flying under a rain cloud would shock cool an engine more than just powered down flight.
     
  13. sarangan

    sarangan Line Up and Wait

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  14. James331

    James331 Touchdown! Greaser!

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    Not sure about a full on failure, but going through jugs.

    Go ask on the drop zone forums/groups.

    There is a reason JPI does this

    Shock Cooling: The JPI scans all cylinders in a rotation and the text "CLD" (see photo) indicates the rate at which cylinders are cooling. Pulling back on the RPM (ie going from cruise power to idle) will cool the engine too quickly. Try to keep the rate of cooling less than 60 degrees CHT per minute. Easy to remember - there's 60 seconds in a minute right? See attached photo "Cold". To demonstrate this, I had to chop the power so please don't do this unless it is necessary for a maneuver or emergency.
     
  15. Tantalum

    Tantalum En-Route

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    Thanks, I'm aware of the 60* per CHT per minute, and I honestly baby the engines I fly on, because.. why not? Plus I think it makes you seem like a more "pro" pilot with smooth power changes, etc. But I always felt like CFIs put an unusually high emphasis on "don't shock cool" the engine

    Drop zone planes live a hard life.. there could be co-variable factors there too

    Out of curiosity, with the tight tolerances of a turbine engine, and the temps they face.. is there such a phenomenon with shock cooling a turbine? Does pulling a CF6 in flight from 80% N1 to 20% N1 cause potential issues?
     
  16. Dr. O

    Dr. O Pattern Altitude

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    Much ado about almost nothing. In working up to the stall the power has been reduced in stages (usually - and if not you CAN make it that way) so that is the huge difference from a jump plane that is flogged to within 10 degrees of melting the cylinders- then the throttle jerked back for the descent. And I do not believe it is shock cooling the kills the jump planes, it is being pushed until metal starts to warp in the climb.
     
  17. MuseChaser

    MuseChaser Line Up and Wait

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    Sub 30 is Tshirt weather around here if the sun is out, and below 0 can be great fun for far more than 24 hours if equipped. It got down to 28 below on one of my winter backpacking trips... loved it. When I woke up in the morning, my breath had frozen into a stalactite (stalagmite? Can't ever remember which is which) onto the roof of my tent above my face and was flaking off and falling back onto me. We practice building snow shelters in my backyard. Lasting 24 hours should be a nonevent for anyone equipped properly... and you shouldn't be flying in that kind of climate if you are NOT equipped properly. If I only flew when it stayed above 30F, especially at admittedly low PA28-140 altitudes, I'd probably be limited to about four months a year.

    As far as the original question re/ shock cooling and spins.. I don't really know. My CFI doesn't seem to worry about it when practicing emergency power-off descents, but I haven't done any spin training with him. My former partner in the plane, who is a fantastic mechanic, DID take it into consideration and did not like doing power-off descents and cautioned me against them due to shock-cooling concerns.
     
  18. brcase

    brcase Pattern Altitude

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    What makes the most sense to me is that Shock Cooling is only an issue if the engine is excessively hot to begin with.
    The generally accepted number seems to be if the CHT is less than 400F you probably aren't going to hurt the engine. Use a lower number if you want to baby the engine even more.

    Drop zone planes and even most training airplanes seldom have much issue because they usually run at medium power for a minute or two before beginning their descent, cooling the engine below that 400F mark, if they even do get that hot to begin with.
    I have heard of the glider towing planes having issues with cracked cylinders until their let down procedures were modified to reduce shock cooling.
    I briefly flew a jump plane where the operator wanted it leaned until it was 500F CHT during the climb, it gave them best power for the climb. I haven't heard of them having any particular issues with cylinders (C-182, not sure which engine), But that was hotter than I liked.
    I also suspect that small engines are less susceptible than bigger engines, they just generate less overall heat and have have smaller bores so the expansion/contraction of the cylinders is less.

    I would be concerned a bit about prolonged low power in cold temps due to carb icing concerns, as it might not be generating enough heat to prevent carb ice. I have had a couple engines die on final when doing power off approaches in cold weather, I always already had the runway made so not really an issue and they started right up after a sitting for a minute or less on the ground.

    Brian
    CFIIG/ASEL
     
  19. James331

    James331 Touchdown! Greaser!

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    Turbines don’t care.

    But go to a good DZ and there is a VERY specific procedure for the piston drop planes, there are often large differences between little weekend DZs and multi plane 7 day a week drop zones, the decent and climb profile is normally OJT with another pilot or DZO riding along for a bit and it’s enforced because DZO doesn’t want to be buying new juggs, unless they are for his girlfriend.
     
    Last edited: Oct 29, 2019
  20. dell30rb

    dell30rb Final Approach PoA Supporter

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    Makes sense to me. 500F.. yikes!
     
  21. Dan Thomas

    Dan Thomas Final Approach

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    Nope. We had a discussion here a while back about that. Someone had hosed down a hot engine while washing the airplane right after it landed, and someone else said that was no different than flying through heavy rain. But even in heavy rain it's still mostly air coming into the cowl, certainly not five or ten gallons of water per minute, and the engine is still making plenty of heat to limit any cooldown. The airplane wouldn't even fly in any medium consisting of so much water.