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#1
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Air restart in PA30
Dennis O'Connor wrote:
The tip is to never shut down a good engine in flight... You can test the feathering on the ground - that is how the mechanic / prop shop does it... If the engine actually fails in flight there won't be a restart anyway so there is no defensible reason to put the plane at such risk, for no reason... Testing it on the ground won't really 'prove' that the props will feather when you need them to. You need to put them up in about a one-hundred mile per hour slipstream to do that. Anyway, there are good reasons. After my newly overhauled engines (and one new prop) had about two hundred hours on them, I felt it was time to verify that the props would feather as advertised. On a nice VFR day, with plenty of alittude to work with and near an airport, there is nothing wrong with doing this. Leave the family on the ground, though. The engine SHOULD restart successfully, but don't count on it until you've proven them out. Engines are also routinely shut down and secured in multi-engine training. -Ryan CFII-A/MEI/CFI-H |
#2
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Of all the PA30's I have flown, not one of them would come out of
feather until the engine was running and developing enough oil pressure to twist the blades back into high RPM. The starter alone is not enough to make this happen Most, if not all, of the start procedure is completed while the blades are still feathered, making for a whole lot of shakin' till it gets running again. On Thu, 31 Jul 2003 17:57:38 GMT, Chris Kennedy wrote: Julian Scarfe wrote: [snip] Unfortunately, it didn't restart fine. I was very close to a "uh, we've painted ourselves into a corner, here" call to ATC and a real engine-out arrival, when at the 6th attempt in a 1000 fpm dive at 130 KIAS it finally came back to life. Fortunately we'd been careful to get ourselves plenty of altitude before the shutdown. Any tips on air restarts from the other PA30 drivers out there? I think we followed the POH to the letter, in particular, mixture RICH for the start. Is that really best? Why does it differ from the ground start procedure? I'm going to assume from your description that the prop promptly unfeathered and windmilled when you cranked it -- the starter should certainly be able to spin things fast enough to get enough oil pressure to take the prop out of feather -- and that what you're describing is a situation where you're looking at the left window at a windmilling prop while trying to avoid conducting a what-not-to-do Vmc demo. A secured engine gets seriously cold in flight -- and in a hurry. An [I}O-360 can be surprisingly difficult to start after being shut down for just a few minutes (enough so that I don't think I'd even consider doing something like this on, say, an Aztec with 540s). Cowl flaps closed, max RPM, mixture full rich, mags in start configuration, maybe a shot of prime if the CHTs have fallen through the floor, crank until you come out of feather, then add a bit of throttle until you have signs of life -- all while remembering to fly the airplane. Mags to run configuration, adjust the mixture and unless you need the engine back _right now_, when it does come to live nurse it along at a low power setting until the temps start to look normal, then reset power on both engines. Don't forget to close the cowl flaps on the engine you left running when it settles back down... IMHO everyone should have to experience an actual shutdown and air start as part of their ME training. There's something seriously disconcerting about looking out the window at a prop that's not turning and air starts always seem to require both coaxing and pleading in equal measure -- as well as three hands (one each for yoke, throttle and starter). |
#3
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Julian,
Why the dive? Does the airplane have unfeathering accumulators (I've instructed in Twinkies but don't recall ever being in one with accumulators)? With or without them, you should not have had to dive the airplane. (That part of your post bothers me in that I can't think of what would make it necessary.) Have a long chat with your mechanic. I've never had problems with airplanes with accumulators. Without them, there have been a few times where it took as many as ten or fifteen brief sessions with the starter to get the prop to windmill and the engine to start, but I'm usually just patient and careful not to overwork the starter. (All of that assumes warm weather. On cold weather shutdown and feather exercises I start the engine again immediately otherwise it can cool down very fast and I've been told it may or may not restart.) I also do the exercise up high and very near an airport that is adequate for a landing if I can't get the offending engine to snort and bellow again, although in over 25 years of giving multi-engine instruction I haven't had that happen yet. All the best, Rick "Julian Scarfe" wrote in message ... As part of a "debugging" process yesterday, chasing a collection of minor issues, we tested the feathering of the left engine of our Twin Comanche, which had appeared significantly slower than the right one. It seemed to feather fine, with the prop stopping in about 10 seconds. Unfortunately, it didn't restart fine. I was very close to a "uh, we've painted ourselves into a corner, here" call to ATC and a real engine-out arrival, when at the 6th attempt in a 1000 fpm dive at 130 KIAS it finally came back to life. Fortunately we'd been careful to get ourselves plenty of altitude before the shutdown. Any tips on air restarts from the other PA30 drivers out there? I think we followed the POH to the letter, in particular, mixture RICH for the start. Is that really best? Why does it differ from the ground start procedure? Julian Scarfe |
#4
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Bill Zaleski wrote:
Of all the PA30's I have flown, not one of them would come out of feather until the engine was running and developing enough oil pressure to twist the blades back into high RPM. Hmm. Semantics maybe. I don't consider "out of feather" to be the same as "high RPM" -- only that the blades have moved off the stops and are presenting increased drag. The starter alone is not enough to make this happen It certainly isn't going to take it to high RPM pitch. No argument there. Most, if not all, of the start procedure is completed while the blades are still feathered, making for a whole lot of shakin' till it gets running again. I've always associated that shake-n'-rattle with the period between when the engine gasps to life and the prop starts to govern again. It's been a while since I played this game (it was one thing to do it over the flatlands, but it's not my idea of fun since moving to the mountains) so my recollection may be suspect. -- Chris Kennedy http://www.mainecoon.com PGP fingerprint: 4E99 10B6 7253 B048 6685 6CBC 55E1 20A3 108D AB97 |
#5
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"Julian Scarfe" wrote
As part of a "debugging" process yesterday, chasing a collection of minor issues, we tested the feathering of the left engine of our Twin Comanche, which had appeared significantly slower than the right one. It seemed to feather fine, with the prop stopping in about 10 seconds. That doesn't sound fine to me. Actually, it sounds quite slow. Mine feather in less than half that time, worst case. Unfortunately, it didn't restart fine. I was very close to a "uh, we've painted ourselves into a corner, here" call to ATC and a real engine-out arrival, when at the 6th attempt in a 1000 fpm dive at 130 KIAS it finally came back to life. Fortunately we'd been careful to get ourselves plenty of altitude before the shutdown. 1000 fpm dive? 130 KIAS? I must be missing something - were you using the starter? Was the starter not able to crank the engine? Any tips on air restarts from the other PA30 drivers out there? I think we followed the POH to the letter, in particular, mixture RICH for the start. Is that really best? Why does it differ from the ground start procedure? No clue. Unless I've had the engine shut down long enough for the CHT's to drop to ambient, I use the hot start procedure. Prop full forward Throttle full open Mixture full rich Boost pump on for 3 seconds Mixture to idle cut-off With one hand, crank starter Once engine catches, advance mixture with second hand while pulling back on throttle with third hand. Millions of Martians can't be wrong No, seriously - once the engine catches, it will idle and you have time to set the throttle and mixture as necessary. I usually set it for 11 inches manifold to warm up, since that gives approximately zero thrust. It should never be necessary to dive for airspeed - if the starter can't crank the engine then something is seriously wrong. If the engine was warm and flooded, then starting with mixture rich can take a long, long time. Michael |
#6
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Thanks to all for the comments.
"Chris Kennedy" wrote in message ... I'm going to assume from your description that the prop promptly unfeathered and windmilled when you cranked it -- the starter should certainly be able to spin things fast enough to get enough oil pressure to take the prop out of feather -- and that what you're describing is a situation where you're looking at the left window at a windmilling prop while trying to avoid conducting a what-not-to-do Vmc demo. My recollection is that it didn't come out of feather, or at least not much. So my experience was closer to what Bill describes. But it's tricky to see if the blades are fully feathered or "moved off the stops". It didn't seem significantly more draggy. Rick wrote: Why the dive? Does the airplane have unfeathering accumulators (I've instructed in Twinkies but don't recall ever being in one with accumulators)? With or without them, you should not have had to dive the airplane. (That part of your post bothers me in that I can't think of what would make it necessary.) No, no accumulators. The dive was an attempt to get more airflow through the prop and therefore more lift on the blades helping them to turn as they unfeathered slightly (or is it less drag as they start to turn?). I don't have any conclusive evidence that the speed and the restart success were related, but it "worked". (FWIW we performed the exercise at altitude and within a few miles of home base with a nice long runway.) Julian |
#7
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Hmmmmmmmmmm
Denny "Paul" wrote in message |
#8
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Julian Scarfe wrote in message ... No, no accumulators. The dive was an attempt to get more airflow through the prop and therefore more lift on the blades helping them to turn as they unfeathered slightly (or is it less drag as they start to turn?). I don't have any conclusive evidence that the speed and the restart success were related, but it "worked". :-) From my experience with the Twin Comanche, the feathered position is a you-beaut, fair-dinkum FEATHERED position and no way known to man would diving the a/c to Mach 4 to Mach 6 have any effect on the prop/engine. BUT, because the feathered position did/does require a lot of travel and wasn't often used, the effect of sludge in the prop cylinder was very marked.... (I know the PA30 has always had a lot of bad press, but I consider it to be a very nice little a/c - albeit requiring a considerable amount of respect............) |
#9
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RT wrote:
From my experience with the Twin Comanche, the feathered position is a you-beaut, fair-dinkum FEATHERED position and no way known to man would diving the a/c to Mach 4 to Mach 6 have any effect on the prop/engine. BUT, because the feathered position did/does require a lot of travel and wasn't often used, the effect of sludge in the prop cylinder was very marked.... Thanks, RT, I was wondering if someone might bring this topic up. In the Comanche owner's forum I was surprised when a very senior and respected flight instructor made a comment which I had never considered before. The subject of discussion was air-restarts and the effect, either beneficial or detrimental, that an increased airspeed would have on the restart process. In his opinion, additional airspeed would actually inhibit the restart process (during that period before the engine had started and the prop started coming out of feather) because "the prop would have to 'displace' a greater amount of air" or words to that effect, which was opposite of what I would have thought. My initial opinion was that since no prop is truly completely feathered - i.e. 82 degrees is a typical 'feathered' position, and some surface of the propeller airfoil will always be presented at some angle to the relative wind, more wind would be better to restart the prop. After all, props want to windmill. The conversation continued and it was specified that we were talking quite specifically about the portion of the restart process in which the prop was feathered, NOT as it started coming out of feather. It was agreed upon by all that increased airspeed would assist in bringing up the RPM as the prop came out of feather, but not before (i.e. the initial cranking period prior to engine start.) This distinction was important in understanding this person's point. The conversation meandered from that point but I've always wondered since if diving to increase airspeed would in any way assist in getting the engine started, assuming of course the prop was fully feathered. -Ryan CFII-A/MEI/CFI-H |
#10
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On Fri, 01 Aug 2003 20:23:49 GMT, Ryan Ferguson
wrote: snip The conversation meandered from that point but I've always wondered since if diving to increase airspeed would in any way assist in getting the engine started, assuming of course the prop was fully feathered. snip Hmmm. If the prop ain't turning, but is aerodynamically (?) on the verge of turning, a little more airspeed probably wouldn't hurt. Never really figured how close the angles work out to zero rotational force, I figured if the force generated wasn't enuff to overide the cylinder compression, the prop wouldn't turn. Never shutdown a PT6A in flight, but feathered 'em for fun, in every case the propeller windmilled, but at a slow rate. Do know, from experience with un-feathering accumulators (Baron & Colemill Navajo's) and un-feathering pumps (Beech 18's) that the visible angle on the propeller blade doesn't change very much before the engine starts turning over at a fairly rapid rate. Have air-started a Twin Co and an Aztec (for the heckofit) and it seemed really, really similiar to the engines I've started with feathered props on the ground. A lot of shuddering and shaking at low rpm until the oil pressure in the gov builds enuff to start driving the prop back to "flat". Actually, they shudder a lot more on the ground (no "airspeed" to help accel the engine) but my rectal condition was nowhere near as critical with the tires sitting on the tarmac. TC |
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