Gordonsmall From UK - Scotland, joined Jun 2001, 1995 posts, RR: 29 Posted (8 years 6 months 1 week 4 hours ago) and read 4464 times:
Hi All,
I know this topic has been discussed to death dozens of times this year already but I thought it was about time we forgot about the "Will it?" or "Why can't it?" type discussions an concentrate on the "How to do it!" side of things.
Obviously each aircraft (or any object for that matter) has it's own "best glide speed" where the least height is lost for the maximum forward travel but what is the technique for getting to that speed? Would the pilot maintain altitude until the aircraft decelerates to best glide speed and then descend to maintain the speed, or would he/she begin a shallow descent to decelerate at (for instance) half a knot per second until best glide speed and then maintain the speed?
Does the best glide speed and/or maximum glide distance vary with weight? I know that drag aside, two objects of unequal mass dropped from the same height should hit the ground at the same time but how does this theory translate to a lift producing wing? Would the pilots dump fuel while gliding to reduce the weight (assuming the engines hadn't quit because the tanks were dry) ?
Is the best glide speed published in the operating manuals? If not is there a rule of thumb for estimating/calculating it? I think I read that the pilots of the AC 767 that landed "dead-stick" had to guess the glide speed because they had no references for it.
Any other pertinent factors/techniques I've missed?
Regards,
Gordon.
Statistically, people who have had the most birthdays tend to live the longest.
FlightSimFreak From United States of America, joined Oct 2000, 720 posts, RR: 0 Reply 2, posted (8 years 6 months 1 week 3 hours ago) and read 4506 times:
The best glide speed is usually slower than the cruise speed, so the pilot can pitch up to slow to best glide speed. Most of the time, however, the pilot does not think quick enough to do so. The FAA estimates that it takes 3 seconds for a pilot to recognize that there is an engine failure, and to initiate the appropriate procedures. For a Cessna pilot, that means that if an engine fails in cruise, that he is left sitting there for three seconds slowing down. That doesn't leave much speed for a 'zoom climb' with airspeed.
Here is the procedure I use in the 172 I fly: first pitch for best glide. Just get it close, it doesn't have to be exact. The numbers published are for a given weight, and I almost never am at that exact weight, so that speed isn't exact. Often times, I will estimate the weight, and interpolate the speed. After I get in the ballpark of best glide, I will trim for it. The position of the trim wheel is usually about 1 to 1.5 turns nose up from cruise flight, so after I pitch up to the right visual "picture", I reach down and turn the trim wheel. This is all done in about 2 seconds. While the plane is slowing down, I reach down and grab the "emergencies" checklist and attach it to my kneeboard. Then I look back up and ensure that I am close to the best glide speed as shown on the checklist. So far, about 5 seconds have elapsed. Now I begin to chose a landing site, looking for fields that are of short grass or concrete, long enough with no obstructions to the approach or landing, are facing in to the wind, if available, and that are near some civilization (a farmhouse, a boat, a road) so if I am incapacitated, someone will know I have gone down. This takes about 10 seconds, perhaps making S-turns in the plane to check for landing sites below or behind me. Next, I look down and go through the checklist, verifying that I am on the best glide speed that I determined earlier, and trimming for the exact speed, calling ATC if time permits, and attempting restart if time permits. (I don't know the exact order of the checklist items, just the memory items I've already gone through). The last thing I do before the forced landing is brief the passengers, if any, secure the aircraft, then open the doors and lock them so the locking mechanisms ensures that they stay open. I fly the approach as if it were a normal power off landing, flare, hold the nose off as long as possible so it doesn't dig in, gently put the nose down, then evacuate the aircraft. On the ground, I verify that the aircraft is secured, and that there is no smoke or fire, and that the passengers are all evacuated, then I check to see if the ELT is operating. If there is no smoke or fire, the passengers are all safe, and I was gentle enough that the ELT did not go off, I would go back inside, turn on the master and avionics master and try to contact ATC or anyone on the frequency I was on last, and on 121.5. If that doesn't work, and I am near civilization, I will meet my passengers, then flag down a car or go to a house and call 911. If I am far from civilization, I will turn on the ELT and then go to my passengers and wait it out.
All of this assumes that I am the only pilot on board. If there was another pilot, the pilot flying continues flying while the pilot not flying handles checklists and radio calls, as well as passenger briefs, and all other non-flight duties.
Jhooper From United States of America, joined Dec 2001, 6193 posts, RR: 16 Reply 3, posted (8 years 6 months 1 week 2 hours ago) and read 4350 times:
That's really good FlightSimFreak . The only thing might mention is that some recommend you stick a pillow or something in the door so that it doesn't jam shut on you. As I'm sure you've practiced this several times, it's never the same as if it were to happen for real. The key is to be proficient enough so that the outcome is as close to what you've trained for as possible.
Last year 1,944 New Yorkers saw something and said something.
Dufo From Slovenia, joined May 1999, 713 posts, RR: 6 Reply 4, posted (8 years 6 months 1 week 1 hour ago) and read 4299 times:
Interesting question at interesting time..
after three years of flying this is exactly what I have done today - climbed 2000ft above the runway threshold, pulled the mixture and turned off the magnetos (C172N).. the engine barely stopped until the speed was just above stalling..just a reminder that non-feathering props have a lot of drag. It is quite thrilling to fly with the propeller in fixed position everything else except very quiet glide towards the runway is the same as the 'usual' engine failure imitation that I've done many times during my initial training. In other words.. try this with your instructior just for the feeling that the real engine shutdown is not much different than the idle-powered descent.
Regards,
Jernej
I seriously think I just creamed my pants without any influence from any outside variables.
Flyf15 From , joined Dec 1969, posts, RR: Reply 5, posted (8 years 6 months 1 week 1 hour ago) and read 4295 times:
I'm going to have to disagree with Dufo and say please don't try this in a single. If you really want to shut down an engine inflight, at least do it in a twin, with a proficient multiengine pilot onboard.
XFSUgimpLB41X From United States of America, joined Aug 2000, 3664 posts, RR: 36 Reply 6, posted (8 years 6 months 1 week 1 hour ago) and read 4313 times:
You should be shot for shutting down your only engine in flight in a non-emergency situation.... I'll never ever ever do that with one of my students... its stupid to get slow enough to where you stop the prop anyways.
Dufo From Slovenia, joined May 1999, 713 posts, RR: 6 Reply 7, posted (8 years 6 months 1 week 1 hour ago) and read 4288 times:
I don't find this more dangerous than spin training or engine shutdown in a light, underpowered twin. In any case you should know what follows (normal landing, engine restart or .. oh well!).
Regards,
Jernej
I seriously think I just creamed my pants without any influence from any outside variables.
Bellerophon From United Kingdom, joined May 2002, 556 posts, RR: 62 Reply 8, posted (8 years 6 months 6 days 23 hours ago) and read 4236 times:
Gordonsmall
Does the best glide speed and/or maximum glide distance vary with weight?
This question, in all its various forms, is an old favourite at all sorts of aviation interviews, so it might just pay to know the correct answers!
Does Best Glide Speed vary with weight: YES
Does Maximum Glide Distance vary with weight: NO
An aircraft’s best glide angle (and therefore its best glide distance) is found at max L/D, which does not vary with weight but is purely a function of the design and aerodynamic efficiency of the aircraft.
A variation in weight however does affect the speed at which the max L/D occurs, and the best glide speed will increase as aircraft weight increases.
Consider two aircraft, both identical apart from their weights, and both trying to achieve the best glide distance possible from the same altitude. Let’s take the still air case, to keep life simple, and assume there is no wind.
Both aircraft can achieve exactly the same maximum glide distance (as both have the same max L/D) but the heavier aircraft will have a faster best glide speed (Vmax L/D) than the lighter aircraft, and so will have to fly a bit faster than the lighter aircraft to achieve maximum glide distance.
The heavier aircraft will fly faster, descend faster, and land first, but it will not glide further than the lighter aircraft, which should eventually land beside it!
Would the pilots dump fuel while gliding to reduce the weight
I hope I’ve convinced you it will make no difference to how far they could glide.
An interesting example of the practical use of this principle - that you can vary the speed at which max L/D occurs by varying aircraft weight, without affecting max L/D itself - can be seen by watching competition glider pilots, who, on good soaring days, will often load up to 500 lbs of water into their gliders.
It doesn't affect their maximum glide distance, but it does allows them to fly a lot faster whilst doing it.
Skyguy11 From , joined Dec 1969, posts, RR: Reply 9, posted (8 years 6 months 6 days 23 hours ago) and read 4233 times:
See the thread 'Why Can't they Glide?'; it has almost the same info as discussed here.
As for whether to pitch up or hold your altitude until reaching best glide; after the engine quits #1 set the best glide pitch attitude, #2 turn toward your landing spot, #3 fine tune the airspeed and pitch and check the engine controls;
Reasons why it's unnecessary if not impossible to pitch up after engine loss:
-reaction times
-energy loss during the pitch up maneuver will equal or exceed any benefit to getting to your best glide speed sooner
-you should be looking for a place to land and or turning to that spot instead of worrying about pitching up
Ralgha From United States of America, joined Nov 1999, 1614 posts, RR: 6 Reply 10, posted (8 years 6 months 6 days 23 hours ago) and read 4389 times:
The difference between shutting down your only engine and doing spin training or shutting one down in a twin is that in the single, you have only one shot to get it right.
In a twin, you've got another engine if you can't get it started again, and underpowered or not, that will get you to a safe landing (assuming you're qualified to fly it, not all multi pilots are). In a spin, you can screw up the recovery and try again, barring extreme screw ups like overstressing. Spins are very predictable in most airplanes, and can be done safely.
Intentionally shutting down your only engine puts you in an extremely dangerous situation that you did not have to be in. I'm sure you're aware of how finicky airplane engines can be to start. Just how long are you going to wait until you try to restart it? What if you misjudge and are going to over or under shoot the runway? Will you realize it in time to get the engine started again? What if it doesn't start? What if you flood it in your excitement? What if your battery's dead and the prop is stopped? What if (granted it's a one in a billion chance) your starter decides to die when you need it most (if your prop has stopped)? Do you know that a C152 requires about 1500 vertical feet to start the engine if your prop is stopped and the starter doesn't work? It's more for bigger airplanes/engines, probably not possible for some very high compression engines.
What if someone taxis out onto the runway when you're nearly on the ground? What if a deer runs onto the runway? What if a sudden gust of wind shoves you over the edge of the runway in a 45 degree bank at 15 feet? Shall I go on?
I'd have to rank this activity up with doing spins at night over the ocean on my stupid meter.
Woodreau From United States of America, joined Sep 2001, 810 posts, RR: 8 Reply 11, posted (8 years 6 months 6 days 21 hours ago) and read 4182 times:
I guess I've always just followed the best glide speed published in the POH. I never really sat down and thought about the whole theory of it all.
A Cessna 172 published best glide speed is 75 kts. pitch for it then trim out the forces. My instructor would say - just put the trim wheel at full nose up. - sure enough at full nose up I was doing around 75kts.
In a Krosno KR-03 (a glider) published minimum sink is 42kts. You fly that speed when you're in lift to get best climb. And in a Dutchess it's 95kts with both engines feathered.
But the point is when you have an engine failure there's no time to figure out what the best glide is, just pitch for the best glide speed and move on. No interpolating or finetuning needed. Just fly the aircraft.
And I don't think purposely shutting down the only good engine on a single-engine aircraft is a good idea either.
Cheers
Woodreau
Good judgement comes from experience. Experience comes from surviving bad judgement.
Mirrodie From United States of America, joined Apr 2000, 7306 posts, RR: 70 Reply 12, posted (8 years 6 months 6 days 21 hours ago) and read 4186 times:
Gordon, I appreciate how you tried to make this thread different to the other one that, incidentally, I started, in this forum. However, most of the discussion is VERY similar in nature.
So instead of deleting this one, I will archive it and ask that you continue this conversation in that thread.
I hope you understand that this helps to preserve the flow of the forum.
Regards, mirrodie
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everything else except very quiet glide towards the runway is the same as the 'usual' engine failure imitation that I've done many times during my initial training. In other words.. try this with your instructior just for the feeling that the real engine shutdown is not much different than the idle-powered descent. 
From United Kingdom, joined May 2002, 556 posts, 
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