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9 hours ago, old man emu said:

That's why I suggested pulling the throttle back to idle revs. Keep the engine firing, but not doing much else.

In that case....Yes we do it frequently.

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The true glide performance at mtow in my SP 500 is 65kts. By true I mean the prop is not providing any thrust or breaking force. At 1200rpm (settles at this rpm at 65-70 kts in the landing circuit) th

If you really want to know how your aircraft glides, turn the engine off. Forced landing practice with engine at idle is not the same as gliding with the engine off. Even at idle some thrust is being

I think you are tempting fate by intentionally stopping the motor and I think it's illegal without an instructor. We used to do it way back for in flight engine starts  (without a starter motor) which

If you fly at best gliding speed the aircraft will fly the furthest distance. 

 

If you fly faster or slower than best gliding speed, the aircraft will always undershoot

 

The same applies when the engine is idling or switched off. The key is to know your best gliding speed.

 

Simulating engine failure by switching the engine off whilst in flight is beyond my comprehension..

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"The same applies when the engine is idling or switched off."

- as long as the prop thrust, possibly net negative at some airspeed, is taken into account.

I've realised that most of my EPs to date have been at engine  idle, which has been 'negative thrust', compared to engine stopped.

So, I would go a bit further in a real engine stopped scenario.  I might find myself high and have to put it into a steep forward slip.

 

Someone else mentioned about there can be a big difference when prop stopped and engine running at  idle as far as the tail authority. Be ready for that . Forced cross wind landing  on engine fail might get rather ugly if you cannot get it straight...  My guess is that the reduction in tail authority might become  detectable in the glide if the air  speed gets low enough. 

 

 

 

 

 

 

 

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They don't make gliders with the poor performance of most U/L's. It's all over too quickly. I believe it's illegal to intentionally shut down an engine in flight unless with an instructor. We did it in the olden days to do inflight engine starts without the starter motor. Often  a fairly extreme manuever that went over Vne unless you were very careful. 

 Note this post is over a day old.  Nev

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Talking of best glide speed, IF you are gliding into wind your TAS must be faster to "range" furthest. ALL the TIME you are in the air the wind is blowing you somewhere. IF the windspeed equalled your airspeed you'd be stationary.  Nev

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42 minutes ago, RFguy said:

My guess is that the reduction in tail authority might become  detectable in the glide if the air  speed gets low enough. 

 

You will usually find that out when trying to hold off (or flare depending on what you call it) and the elevator has insufficient authority to keep/bring the nose up.

 

1 hour ago, Bosi72 said:

f you fly at best gliding speed the aircraft will fly the furthest distance. 

 

If you fly faster or slower than best gliding speed, the aircraft will always undershoot

 

The same applies when the engine is idling or switched off. The key is to know your best gliding speed.

 

Simulating engine failure by switching the engine off whilst in flight is beyond my comprehension..

 

 

Best glide speed is all well and good, but if you are at the point where whether or not you make a landing spot depends on a perfect glide, you've probably made serious errors already.

For those that accept the risk of flying over the tiger country, that's fine, I have no beef with that, but, then that also comes with accepting that one day you will probably get bent if you do it for long enough.

 

With the engine off, some aircraft will go further, some will not. Do you know that your aircraft does?

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I agree with the idea of flying with a gliding instructor in a real glider to test this stuff out. There have been some awful crashes into flat paddocks following engine failures, and it is possible that the hitherto unknown sound of silence causes some pilots to panic. So, because Kensla is correct about some engine rpm causing more drag than a stopped prop, and Facthunter is correct about the risk of a restart failure,  there is no other safe way to experience a real engine failure.

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5 hours ago, M61A1 said:

You will usually find that out when trying to hold off (or flare depending on what you call it) and the elevator has insufficient authority to keep/bring the nose up.

 

 

 

Best glide speed is all well and good, but if you are at the point where whether or not you make a landing spot depends on a perfect glide, you've probably made serious errors already.

For those that accept the risk of flying over the tiger country, that's fine, I have no beef with that, but, then that also comes with accepting that one day you will probably get bent if you do it for long enough.

 

With the engine off, some aircraft will go further, some will not. Do you know that your aircraft does?

Engine doesn't know if it's flying over populated city or over the mountains. 

 

Best gliding speed (and minimum sink speed) are approximately half way between Vx and Vy (e.g. 55 and 65kts) and beside aircraft aerodynamics, it depends on weather (eg. wind) and weight. However, you need to fly in some serious weather (or weight) to be outside 55-65kt range.

 

To me, it is sufficient to know Best gliding speed from POH, and to fly around it depending on situation. 

 

The fact there are number of accidents related to >simulated< engine failure tells me enough this is not a joke.

 

A good outcome may be once you master engine off landings, you could do every landing with engine off and save some $ from fuel or Hobbs meter..

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7 hours ago, RFguy said:

.  My guess is that the reduction in tail authority might become  detectable in the glide if the air  speed gets low enough. 

 

 

 

Best glide speed is not a slow speed. 

You will have authority over aircraft when flying Best glide speed.

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Geez! This is getting all technical and stuff. All I was saying that an area of powered aircraft performance is gliding, and can you catch a thermal in a powered aircraft with the no help from the engine. I specified a situation where the engine was running at idle revs, simply to eliminate the danger of not being able to restart it.

 

I was looking for responses simply about going out and committing aviation for fun.

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59 minutes ago, Bosi72 said:

Engine doesn't know if it's flying over populated city or over the mountains.

You are correct, but I'm not sure what your point is. 

All I was getting at is that is that it's the pilot's responsibility to make sure you have somewhere to land when the engine stops unless you are happy to accept the consequences. ( No point flying over tiger country then blaming the engine if it goes to pus)There is no infallible engine, but some are more reliable than others, so it ends up a numbers game...The more you do it, the more likely it is that something will eventually go wrong. You might get away with it your whole life, or you might not.

 

A sign over a certain military flightline desk used to say: (words to that effect)

"If you fly a single engine aircraft over water often enough for long enough, sooner or later you are going to get wet"

 

1 hour ago, Bosi72 said:

The fact there are number of accidents related to >simulated< engine failure tells me enough this is not a joke.

There have been more actual engine failures that have ended badly because they were handled poorly. Perhaps they would have been handled less poorly if they had actually flown the aircraft beforehand with a stopped engine.

 

 

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7 hours ago, M61A1 said:

You are correct, but I'm not sure what your point is. 

 

My point are your paragraphs of "subliminal messages" such as "you are going to kill yourself",  or to crash water/land, or whatever. What can happen to me in the mountains, the same can happen to you in the city, or in a "perfect flat" rural farm when at the very last moment realising there is a powerline in front of you...

 

My apology for returning those messages back to you, but we all know what can happen when the engine stops for real.

 

Stopping engine for real, and on purpose, to establish a speed which varies +/-5 kts from POH depending on circumstances, is again beyond my comprehension.

 

 

 

 

 

 

 

 

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Regarding "negative thrust" from a rotating prop at low rpm, while I understand the theory, in practice I find this hard to see in the air or even with a model plane. It seems to me that any rpm helps a bit, and though I know this can't be so, it is what I think I observe.

For some years, I crewed for my son in model-plane aerobatics competitions, and the guys there said that an idling prop was more drag than a stopped one, and they were better pilots than me.

Even knowing all this, I still can't see it with the Jabiru.

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1 hour ago, Bosi72 said:

My apology for returning those messages back to you, but we all know what can happen when the engine stops for real.

 

Stopping engine for real, and on purpose, to establish a speed which varies +/-5 kts from POH depending on circumstances, is again beyond my comprehension.

 

No need to apologise.

Yes things can go badly very quickly, but you make your own luck to a large degree. What a lot of people call "bad luck" is often nothing more than poor airmanship, but sometimes it really is down to luck as to how it all goes.

There were no subliminal messages.

I really don't care how others fly, as long as they accept that the consequences of their actions were entirely theirs also.

 

I'm not suggesting that anyone go breaking the law and stop their engine in flight, but it has nothing to do with establishing best glide speed and everything to do with not being surprised by the change in glide performance and aircraft handling qualities at a time when it really matters.

We have had a few crashes where an engine failure has  resulted in more damage than necessary because the aircraft was handled poorly after the engine stopped.

 

 

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A stopped prop is just like a couple of flat planks in the airstream. Rotating ones have extra ability to be more aerodynamic and can produce (or absorb) a lot of force. This effect is most marked at higher speeds where prop safety speed count and on turboprops where the DRAG can be multiples of the thrust when the fire goes out in the turbine. . At "Some" rpm the prop will create no thrust or drag that's certainly true  and that's about what you will have if the prop falls off the plane. . Unless the figures have been done by test or accurate calculations then you will ONLY know when it happens. There are instances where some damage will happen to cowls etc that also affect DRAG and therefore glide performance. You need your safety speed whatever the configuration. Most bad accidents are where CONTROL is lost so maintaining control is most important especially IF you are trying to change direction with NO power and extra  drag. Most rapid directional changes are made with quite a bit of bank and if you are a bit slow, definately keep the ball in the middle. Gliding practice in draggy powered planes should be about manouvering and not losing control. . Watch RoD near the ground and adjust speed to allow a more forceful flare. You may need it. On your approach be HIGH  till you are sure of making it with certainty. Plan to land into the field by some margin. Hitting the downwind fence at above flying speed is far worse than hitting the far fence at a low speed. Nev

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I have well over 1000 landings in my Corby and amongst them I have I think 3 deadstick landings. The last one being on my most recent flight, notice I didn't say last flight.

I nearly always cut the throttle as I turn onto base leg, or sooner and then attempt to land without having to apply power.

On those deadstick landings I could not detect any difference from when I had the motor on minimum rpm. There is a theory that a stopped prop has less drag, but it was not apparent to me.

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That's the issue Yenn. It varies. It you have an in Flight controllable prop there's more likelihood of it being able to have a lot of drag, if it's still rotating and ends up in fine pitch.. Thin chord blades would have a smaller effect stopped than wide cord ones. Nev

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4 hours ago, Yenn said:

I have well over 1000 landings in my Corby and amongst them I have I think 3 deadstick landings. The last one being on my most recent flight, notice I didn't say last flight.

I nearly always cut the throttle as I turn onto base leg, or sooner and then attempt to land without having to apply power.

On those deadstick landings I could not detect any difference from when I had the motor on minimum rpm. There is a theory that a stopped prop has less drag, but it was not apparent to me.

I think Nev is correct when he says it varies between aircraft. I couldn't pick the difference with a 582 powered Drifter. A Verner powered Drifter with a 70" prop definitely glides further with the engine stopped. A 95:10 I had wouldn't glide as far without engine, even just at idle.

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What I have noticed is that when I cut power to idle and set up best glide the tacho rpm is about 1000 -1100 rpm. On the ground not moving idle rpm is 800 or thereabouts. The air pressure at 65 knots means that the idling prop isn't doing any work and is allowing the idle speed to increase by helping the blades to turn. When backtracking  even if there is no wind, once I get the aircraft rolling on the bitumen to 15-20 knots or so if I pull the throttle it will keep going all the way to the end of the 1000 metre runway losing hardly any momentum.

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Here's my figures...  my new prop has a 44" pitch so it would have a no-thrust forward speed of 44/(12times 6076) n-m/rev.

So at 3000 rpm, the no thrust speed would be this times 3000 times 60 or 108knots.

This is smaller than I expected. It means my plane can never get to 108 knots at 3000 rpm.

Slowing to idle of 1000 rpm, the no-thrust speed is now 36.2 knots so a glide of faster than 36.2 knots will produce negative thrust from the prop. But the idle speed is higher when you have the windmilling effect helping the engine turn over.

At 1700 rpm, the no-thrust speed is just over 60 knots.

I have never done this calculation before, and I think that my idle speed on the glide has been too high for me to notice the drag from the prop.

 

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Pitch and RPM move the air at a certain speed..  IF you are going faster than that speed the prop will be absorbing  energy, and the reverse applies also.. If the propwash is faster than your TAS you are getting thrust.. . A stopped prop only creates drag but not a large airmass is involved especially if it's feathered.  A prop blade has twist so even when feathered it's not perfect . Some feathered turboprop blades turn slowly Nev

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