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#11
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Engine out practice
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#12
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Engine out practice
Matt: At least in my experience shock cooling did exist. I flew sky divers
in a Skylane and had taken over after another pilot who would climb hard and chop the throttle and descend to the ground. There were frequent low hour Top Over hauls, and cracked cylinders. When I began flying the bird the owner asked me to be aware of cooling it down to fast. My method was to climb to the drop and then close the cowl flaps, carry 15" MP and spiral tightly down. It stopped the low hour top overhauls. My descent rate could be pretty high and the engine was kept relatively warm. Stu Fields Experimental Helo Magazine. "Matt Whiting" wrote in message ... Bertie the Bunyip wrote: Matt Whiting wrote in It is the same if the same delta T is present, but my point is that it is easier to heat something quickly than cool it quickly. Even at 250 C, you are only 523 degrees above absolute zero. So, this the absolute largest delta T you can induce for cooling, and it is very hard to get absolute zero, so you are more likely to have a cool temp closer to 0 C yielding a delta T of only 250 degrees. On the hot side things are more open-ended. It isn't too hard to get 450 C exhaust gas temperatures. For an engine that is started at say 20 C ambient temperature, you now have a delta T of 430 degrees which is much greater than the 250 likely on the cooling side of the cycle. That is one reason why I suspect that "shock heating" is more likely to be an issue than "shock cooling." I suspect you can induce a higher delta T during a full-throttle initial climb than you can during an idle descent from a cruise power setting. Right, I'm with you now. yeah, I can buy that. Froma strictly clinical viewpoint it absolutely makes sense. My experience with damage says otherwise, though I can offer no explanation why that should be the case. Years ago I towed gliders with Bird-dogs and we cracked a lot of cylinders when we just closed the throttle after release. When we moved to gradual reduction to ultimately 1500 RPM the problem disappeared completely. Later, when I flew big pistons,the procedures for cooling down the cylinders on the way down. You were almost gaurunteed a crack if you yanked the taps closed. Can't see how we went from cold to hot any more than you would just starting up and taking off. I've just bought an aerobatic airplane with a Lycoming. We're not expecing to get to TBO with the engine because we'll be doing aerobaics with it, but of course we're prepared to live with that. I suppose the point I'm making is that even if shick cooling is over- rated, it certainly does no harm to observe trad practices as if it did. I suspect, as with most "real world" problems, that there is more in play than delta T induced stress. Probably geometry and other factors. Maybe having the thin fins on the outside vs. thick metal on the inside is making a big difference in the stress profile. I've not had experience with the larger engines or with radials. However, my experience with O-470 and smaller engines is that shock cooling just isn't an issue and many folks are paranoid for nothing. Operating the engine as if shock cooling was an issue is probably not a problem in most cases, but if it causes you, as it has with Jay, to not practice essential emergency procedures, then I disagree that it causes no harm. This may be very harmful should Jay experience an engine failure for real. Matt |
#13
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Engine out practice
On Oct 15, 8:49 am, Bertie the Bunyip wrote:
The examiner wouldn't allow him to slip because he reckons they are dangerous with the flaps out and that he should wiggle the ailerons back and forth to lose height. He didn't even want him to slip clean. Jesus wept. This examiner had had a fright in a 172 (this was an archer anyway) and did not alow anyone to slip with flaps out. While I am firmly in the camp that says some cessnas can get a litle fuzzy in pitch with full flaps, this is just stupidity incarnate. Shoot. We do slips with full flaps all the time in 172s, have done so for years, and never had a scare. I wonder if that "Avoid Slips With Flaps Extended" applied to some earlier models? I'll have to check the TCDS sometime. Dan |
#14
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Engine out practice
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#15
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Engine out practice
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#16
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Engine out practice
Ernest Christley wrote in news:47142123$0$32479
: Bertie the Bunyip wrote: It's the same either way. Cooling and heating are two sides of th esame coin. It takes time to disapate heat and it's not so much the passage of heat from one area to another (or the disappation, it's irrelevant) but the speed at which the cooling or heating is taking place and thus the gradient across the material. In short, you take a frozen lump of metal and apply a torch to one side you have a problem. Take a cherry red pice of metal and put some ice on side and you have the same problem (more or less, and disregading crystalisation) It is the same if the same delta T is present, but my point is that it is easier to heat something quickly than cool it quickly. Even at 250 C, you are only 523 degrees above absolute zero. So, this the absolute largest delta T you can induce for cooling, and it is very hard to get absolute zero, so you are more likely to have a cool temp closer to 0 C yielding a delta T of only 250 degrees. On the hot side things are more open-ended. It isn't too hard to get 450 C exhaust gas temperatures. For an engine that is started at say 20 C ambient temperature, you now have a delta T of 430 degrees which is much greater than the 250 likely on the cooling side of the cycle. With the heating, you only have the few hundred CFM of air passing through the engine to heat it. With the cooling, you have all of the great outdoors to do the trick. To tie it into your anology, you have a butane lighter to heat the metal, and the Atlantic Ocean to cool it. Kind of besides th point. you coudl say the same thing about an oxy acetylene setup and we all know what that will do to a bit of metal. Bertie |
#17
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Engine out practice
On Oct 16, 12:43 am, Bertie the Bunyip wrote:
wrote in news:1192492570.300275.289550 @i38g2000prf.googlegroups.com: On Oct 15, 8:49 am, Bertie the Bunyip wrote: The examiner wouldn't allow him to slip because he reckons they are dangerous with the flaps out and that he should wiggle the ailerons back and forth to lose height. He didn't even want him to slip clean. Jesus wept. This examiner had had a fright in a 172 (this was an archer anyway) and did not alow anyone to slip with flaps out. While I am firmly in the camp that says some cessnas can get a litle fuzzy in pitch with full flaps, this is just stupidity incarnate. Shoot. We do slips with full flaps all the time in 172s, have done so for years, and never had a scare. I wonder if that "Avoid Slips With Flaps Extended" applied to some earlier models? I'll have to check the TCDS sometime. Dan Dunno. the manual in a 172 makes reference to a possibility of degraded elevator control, but I think it's only a bit of a nod, really. The Bird dog suffers from this ailment big time, though. it has, essentially, the 172's wing, but the flaps go to 60 degrees. I can tell you first hand that blanking of both the rudder and elevator are a very real characteristic of that airplane if you slip it ith full flaps. I did it once close to the ground and never even thought about it again.. Here's what the Type Certificate Data Sheet says: .................................................. ................................... D. On flap handle, Models 172 through 172E (1) "Flaps - Pull to extend Takeoff Retract 0° 1st notch 10° Landing 0° - 40° (2) "Avoid slips with flaps down." E. Near flap indicator Models 172F (electric flaps) through 17271034, excluding 17270050) "Avoid slips with flaps extended." .................................................. ......................................... The applicable models, 172 through 172F, were built between 1956 and 1964 ('65 model?). There's no mention of the slip with flaps thing for later models. I wonder if the addition of the back window changed the airflow enough to keep the elevator flying? Dan |
#18
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Slips with Flaps, was: Engine out practice
Souns about right. The Bird dog's reaction was anything but mild, but with
60 degrees of flap it's not surprising really. Teh 172 this DE claims to have had problems with was a relatively late one, but I could have been anything that caused it. Some turbulence or maybe his mimagination coupled with the horrow stories about it. |
#19
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Slips with Flaps, was: Engine out practice
Seems if one must use full flaps AND slip in landing, I would say the
approach was an abortion that lived. I prefer slips to flaps as you can instantly remove a slip but the same can't be said for flaps... Just MY personal opinion...not trying to slam anybody. Scott Bob Moore wrote: Bertie the Bunyip wrote This examiner had had a fright in a 172 and did not alow anyone to slip with flaps out. While I am firmly in the camp that says some cessnas can get a litle fuzzy in pitch with full flaps, this is just stupidity incarnate. About once-a-year I post the following excerpt from "Cessna, Wings for the World", a book by William D. Thompson. Bill Thompson is an Aeronautical engineer from Purdue University and worked for Cessna Aircraft Company for 28 years as an engineering test pilot and later as the Manager of Flight Test & Aerodynamics. ------------------------------------------------------------------- "With the advent of the large slotted flaps in the C-170, C-180, and C- 172 we encountered a nose down pitch in forward slips with the wing flaps deflected. In some cases it was severe enough to lift the pilot against his seat belt if he was slow in checking the motion. For this reason a caution note was placed in most of the owner's manuals under "Landings" reading "Slips should be avoided with flap settings greater than 30° due to a downward pitch encountered under certain combinations of airspeed, side-slip angle, and center of gravity loadings". Since wing-low drift correction in cross-wind landings is normally performed with a minimum flap setting (for better rudder control) this limitation did not apply to that maneuver. The cause of the pitching motion is the transition of a strong wing downwash over the tail in straight flight to a lessened downwash angle over part of the horizontal tail caused by the influence of a relative "upwash increment" from the upturned aileron in slipping flight. Although not stated in the owner's manuals, we privately encouraged flight instructors to explore these effects at high altitude, and to pass on the information to their students. This phenomenon was elusive and sometimes hard to duplicate, but it was thought that a pilot should be aware of its existence and know how to counter-act it if it occurs close to the ground. When the larger dorsal fin was adopted in the 1972 C-172L, this side- slip pitch phenomenon was eliminated, but the cautionary placard was retained. In the higher-powered C-172P and C-R172 the placard was applicable to a mild pitch "pumping" motion resulting from flap outboard-end vortex impingement on the horizontal tail at some combinations of side-slip angle, power, and airspeed." -------------------------------------------------------------------- 1959 C-172 Notice that this prohibition appears in Section III, Operating Details of the C-172Owner's Manual and NOT in Section IV, Operating Limitations. It is NOT an FAA limitation. Sounds more like "Lawyer" talk to me. "LANDING Normal landings are made power off with any flap setting. Slips are prohibited in full flap approaches because of a downward pitch encountered under certain combinations of airspeed and sideslip angle." --------------------------------------------------------------------- I wear my "Slips with Flaps" T-Shirt proudly! Bob Moore 12 years instructing in Skyhawks -- Scott http://corbenflyer.tripod.com/ Gotta Fly or Gonna Die Building RV-4 (Super Slow Build Version) |
#20
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Engine out practice
On Oct 16, 7:52 am, wrote:
On Oct 16, 12:43 am, Bertie the Bunyip wrote: wrote in news:1192492570.300275.289550 @i38g2000prf.googlegroups.com: On Oct 15, 8:49 am, Bertie the Bunyip wrote: The examiner wouldn't allow him to slip because he reckons they are dangerous with the flaps out and that he should wiggle the ailerons back and forth to lose height. He didn't even want him to slip clean. Jesus wept. This examiner had had a fright in a 172 (this was an archer anyway) and did not alow anyone to slip with flaps out. While I am firmly in the camp that says some cessnas can get a litle fuzzy in pitch with full flaps, this is just stupidity incarnate. Shoot. We do slips with full flaps all the time in 172s, have done so for years, and never had a scare. I wonder if that "Avoid Slips With Flaps Extended" applied to some earlier models? I'll have to check the TCDS sometime. Dan Dunno. the manual in a 172 makes reference to a possibility of degraded elevator control, but I think it's only a bit of a nod, really. The Bird dog suffers from this ailment big time, though. it has, essentially, the 172's wing, but the flaps go to 60 degrees. I can tell you first hand that blanking of both the rudder and elevator are a very real characteristic of that airplane if you slip it ith full flaps. I did it once close to the ground and never even thought about it again.. Here's what the Type Certificate Data Sheet says: .................................................. .................................. D. On flap handle, Models 172 through 172E (1) "Flaps - Pull to extend Takeoff Retract 0° 1st notch 10° Landing 0° - 40° (2) "Avoid slips with flaps down." E. Near flap indicator Models 172F (electric flaps) through 17271034, excluding 17270050) "Avoid slips with flaps extended." .................................................. ........................................ The applicable models, 172 through 172F, were built between 1956 and 1964 ('65 model?). There's no mention of the slip with flaps thing for later models. I wonder if the addition of the back window changed the airflow enough to keep the elevator flying? Dan Wait a minute. I just noticed something, and it's not clear from the way Cessna put it on the TCDS. It says under "E" that the avoid slips thing applies to the 172F through 17271034. That serial number is the end of the 1978 172 N production, so the warning applies to a lot more that I though it did. I hope nobody's gone out and hurt themselves, now. But we still slip with full flaps. Dan |
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