Those things you just forget, or aren't competent with.

[Tomo]

best glide will vary.

Yes it will, but as Darky is a Student and learning to fly, I'd highly reccomend she do as she is told, and what the POH states.

 

Don't want to start an argument, but until you know your aircraft back to front (like Bob Hoover did) stick to the book. Yes it mayen't be exact, but it is there to get you out of trouble.

 

 

[DarkSarcasm]

I'd highly reccomend she do as she is told, and what the POH states.

Thank you for the kind recommendation but it is unncessary, I'm not going to disregard my training simply based on a forum discussion

 

 

[Thx1137]

Thank you for the kind recommendation but it is unncessary, I'm not going to disregard my training simply based on a forum discussion

hehe, yeah, weigh up the arguments but err on the side of the designers is how I look at it.

 

The only time I will consider changing my best glide speed is as FH said, based on wind, even then it is only if I really had to. At the altitudes I fly at I don't want to get creative with speeds, I think I would have have other things I need to ponder! The point is to get down safely not set glide distance records!

 

I think the idea of having one speed is partially so we can concentrate on the problem at hand while flying at a fairly efficient speed.

 

 

[Tomo]

TOMO.. The glider will not go Further , It will go as far, but FASTER because it is the best L/D for the new weight. Nev

Ah, thanks Nev, that was what I was going to say, but got the two words back to front! Faster, further... Can't blame old age either can I?

 

 

[Mazda]

I did a long reply and the internet dropped out, I can't do it all again.

 

There are misconceptions on here. Do read the manual and ask your instructor.

 

A few quick points, I won't launch into the long post I had.

 

Best glide is for range. It varies with weight but this is insignificant over small weight ranges. If your aircraft has one speed published, use that. If it has speeds for different weights, use the speed for the weight you are at.

 

If flying into a headwind you may need to increase glide speed. (If you glide at 65 knots and are gliding into a 65 knot headwind, you won't make your field).

 

Maydays and pax briefs are if you have time only. Aviate first. Your pax will know what is going on. Groundloop rather than hitting anything.

 

Engines DO stop without catastrophic failure, eg doing aeros. You can't use the starter if the prop is windmilling. Set it up and it should start. If that doesn't work and there is time you can stop the prop by hauling the nose up, then try the starter, but if that doesn't work the option is an air start (dive) which requires a lot of height, speed, and pulling out of a dive.

 

Prec searches take a lot of time, probably 20 mins after you've found your field, so don't leave things until the last minute. You might not have time to do all the passes you would like, maybe just one or 2 passes. Doing a pass at 20 feet has dangers as there could be a single wire down there. Better to stay above wire height, and if you see a wire when landing you can duck under it.

 

I won't go into the length I'd written previously!

 

 

[Guest MackAgri Aviation]

An interesting discussion

 

I think facthunter and Mazda are pretty much on track.

 

Most of my flying experience has been in GA aircraft so my comments have that bias, however my current aircraft is a J120.

 

Here are a couple of thoughts to keep things ticking along....:stirring pot:

 

Most POH quote speeds in KIAS (which is sensible as you don't want to have to be converting from/to KCAS while conducting an approach or forced landing, etc) and at MTOW. Therefore most quoted best glide speeds are at MTOW. Best glide speed reduces as actual weight reduces below MTOW (not by much in our aircraft, I admit).

 

Most of the time we are flying at less than MTOW (I hope). In that situation then your best glide speed will be less than that quoted in the manual. So, Thomo, when you add a bit of airspeed for Mum you are actually getting even further away from the ideal than you seem to think.

 

Most pilots I see doing a glide approach and/or PFL (in flying comps or BFRs) fly too fast, often by 10 kts or more, initially and then closer to the ground try to stretch the glide by pulling back and getting the airspeed too low. So, for a forced landing:

 

* Use the recommended glide speed

 

* Do your trouble checks. >90% of engine failures are due to fuel or ice problems.

 

* Initially aim to land 1/3 of the way into the selected landing area

 

* Keep the selected area in sight at all times

 

* Try to fly a relatively long base and short final

 

* DO NOT use flap until you are sure you will make it to the selected area

 

* If you are too high you can lose height by selecting (full) flap, sideslipping and/or making S turns

 

* Use the short field landing technique for the touchdown and stop asap.

 

Mazda, why would you want to go to all the trouble of stopping a windmilling prop just to use the starter to try to get it going again? Seems like a lot of effort for very unlikely reward to say nothing of wasting time and altitude.

 

A metal prop is hard to stop. I know, I have done it in a C150 - you just about have to stall it. Even the J120 Flight Manual says you will probably have to slow to <50Kts to do it with its wooden prop. The only benefit I can see of stopping the prop is to reduce drag - a windmilling prop has considerably more drag than a stopped one.

 

In an engine failure situation, if you have the skill and quick reaction, the theoretically best procedure is to convert airspeed to height until you get to the appropriate glide speed then set attitude and trim for that speed. In some aircraft you can gain quite a bit of height with this procedure. I do not teach it to my students as by the time they have recognised and reacted to the situation the opportunity has passed.

 

The J120 Flight Manual does not state a "Best Glide" speed it only recommends a speed (65kts) to use during a forced landing. [A picky point, I know.] It is close enough to the best glide speed for practical purposes but it also happens to be 1.3 times Vs which is the usually recommended minimum approach speed for any aircraft. Could this have some bearing on the use of 65Kts for the J120?

 

Preparing for incoming.

 

David

 

 

[Spin]

Preparing for incoming.

David

I wouldn't worry about that, all sounds pretty sensible. About the only thing I will gently disagree on is the issue of "converting speed to altitude", I reckon that is only valid at high speed and low altitude combined and you're in a world of trouble then anyway. Otherwise I'd rather see a pilot maintain level flight as the speed bleeds away and then lower the nose to maintain the required speed, trimming to maintain that. KISS has a lot to recommend it in what is a high stress situation anyway. And definitely try and restart or even several if at all possible, ask the bloke who bumped the mag switch off (single ignition) and glided down to a landing in the trees how much that hurts:black_eye:

 

 

[Tomo]

You can't use the starter if the prop is windmilling. Set it up and it should start. If that doesn't work and there is time you can stop the prop by hauling the nose up, then try the starter, but if that doesn't work the option is an air start (dive) which requires a lot of height, speed, and pulling out of a dive.Prec searches take a lot of time, probably 20 mins after you've found your field, so don't leave things until the last minute. You might not have time to do all the passes you would like, maybe just one or 2 passes. Doing a pass at 20 feet has dangers as there could be a single wire down there. Better to stay above wire height, and if you see a wire when landing you can duck under it.

 

I won't go into the length I'd written previously!

From a Mechanical point of view, the only reason you can't push the starter while the prop is spinning, is because the starter will not engage onto the ring gear - like hitting the starter when your car engine is already going. It will just grind away at the gears.

 

Another thing if the prop is spinning, it's already doing what needs to be done without using the starter motor. That is all the starter does, it spins the engine over.

 

Good advice there Mazda re the wire thing. Pity about your big post getting lost, would loved to have read it.

 

Ps. Guys this is really good, keep it up.

 

 

[REastwood]

Restarting the engine...

 

I thought the reason (in Jabiru's) you have to either slow down enough to get the prop to stop windmilling, or go fast enough that you are close the Vne was because of the electronic ignition. In other words a Jabiru engine will not auto restart when the prop is windmilling anywhere between 60 and 120 knots because it is not windmilling fast enough for the ignition to work, is this true?

 

Has anybody had the experience in a Jabiru where the engine has quit (fuel, ice, mags), and once the problem fixed the engine has restarted?

 

Cheers,

 

Rick.

 

 

[Tomo]

I thought the reason (in Jabiru's) you have to either slow down enough to get the prop to stop windmilling, or go fast enough that you are close the Vne was because of the electronic ignition. In other words a Jabiru engine will not auto restart when the prop is windmilling anywhere between 60 and 120 knots because it is not windmilling fast enough for the ignition to work, is this true? Has anybody had the experience in a Jabiru where the engine has quit (fuel, ice, mags), and once the problem fixed the engine has restarted?

Cheers,

 

Rick.

A good point Rick, as Jabiru's do need to be spinning at 300rpm to produce spark, and you are probably right, it mightn't be doing that if windmilling. Have to try it one day.

 

 

[Spin]

I think, from the POH, Jab are suggesting that even at Vne you'd have no certainty of getting the prop turning fast enough for a re-start.

Not the way I read it at all and I think we are guilty of taking Mazda's comment out of context too.

 

I would be very interested to hear whether a Jab does restart with a windmilling prop at normal speeds - I very much suspect that it will and that David is on the money, the prop will windmill at substantially more than 300rpm at normal gliding speeds. One thing though, don't lets have every student rushing out to try this in the school's aircraft, for one thing there is a fair chance of a backfire when reintroducing a spark, potentially damaging mufflers or worse!:ah_oh:

 

 

[Tomo]

Tomo, come on mate you know a windmilling prop is spinning way more than 300 rpm and way faster than the starter can spin it. The prop is spinning at the forward speed displacement rate related to the pitch of a the prop...

You're right, but I wouldn't know unless someone has done it. I reckon at 65kts, it wouldn't be spinning all that fast, but I'm just speculating now, so wouldn't know for sure.

 

I've had a EFATO in a Jab a yr or so ago, and it dropped revs faster than you could say boo! Engine still was running, but it just dropped to idle. But I guess that's a different kettle of fish altogether.

 

 

[Spin]

Not sure how else you could read: "when the propeller has stopped rotating"

 

I think the part in blue is the bit you're overlooking, it doesn't necessarily follow that the propellor will stop if the engine fails, in fact the advice we have received is that you're going to have to make a determined effort to get the plane slow enough for the stop to occur.

 

So yes I suspect we are largely in agreement; - if the noise stops, keep flying and see whether you can reintroduce the necessities of life ie. spark and fuel in between finding somewhere to park the contraption should you fail.

 

 

[facthunter]

Air restarts after prop has ceased to rotate.(fixed pitch props)

 

How many of the commentators have done this procedure? Till it has been done whether it will work is speculation.'

 

It used to be part of normal training as many aircraft didn't have a starter.' I can make a few GENERAL statements.

 

It is hard to get an engine to stop in flight. Even with the ignition off and/or the fuel in cut-off. You often have to fly below stall speed or enter an incipient spin in ONE direction (depends on engine rotation direction).

 

Restarting usually requires that the plane be put into a vertical dive and with the positive lift aspects of a normal wing, this means that the plane is actually beyond vertical. With a clean plane you reach VNE in no time flat. This was from memory 162 Kts in the Chipmunk. With a good compression engine the prop is most reluctant to turn, and you cannot guarantee a start. The prop is well and truly stalled in this situatuon and does not apply a lot of torque to the engine shaft. You need lots of height and at height your AIS is not indicating TRUE airspeed so that introduces another hazard.

 

I have little doubt that the Jabiru 230 would be much the same as the Chippie as the prop is a bit of a toothpick and the plane is very clean. I STRONGLY suggest that this procedure be NOT ATTEMPTED, in any circumstances, as it is bloody dangerous. Nev

 

 

[Spin]

Nev aren't we talking about two different scenarios here? 1) engine fails and prop continues windmilling because you keep her flying at best glide or better. Restore spark and/or fuel and away she goes. 2) Engine fails and for whatever reason you slow to stall or thereabouts and the fan stops dead. You then decide it needs restarting and have to dive to plus minus VNE and hopefully get her turning again.

 

I haven't tried this in a Jab, but an O-200 started quite cheerfully when fuel was reintroduced, after being cut off in a glide. To support your earlier point, even a Rotax 912, a geared powerplant, required that the aircraft be slowed to well below best glide before the prop stopped dead.

 

 

[Yenn]

My Jab engine with prop designed for a Jab stopped dead turning base at 80kts. The cause was idle speed set too low on a very cold morning. No problem to restart with the starter. I very much doubt that I could have restarted it with a dive for speed in under about 3000'

 

 

[Tomo]

My Jab engine with prop designed for a Jab stopped dead turning base at 80kts.

Thanks Yenn, that answers my speculation about the Jab engine windmilling. I did have the suspicion that with a Small prop, and the high compression it would steady up pretty quick.

 

I've done engine off in a Rotax on the Drifters, you switch off, and it takes a while for it to stop turning, I generally raise the nose to help stop it to give a bit better glide, also getting ready incase you need to start again for some reason - without a pot full of fuel.

 

 

[facthunter]

Engine stopped.

 

Spin, quick response. Just hit the starter. This diving to get it to windmill is a bad idea. Nev

 

 

[facthunter]

restart engine in flight.

 

If the prop stops HIT the starter. as yenn states mostly this occurs because the idle is set too low. This might appear to be in conflict with the difficulty of getting an engine to stop windmilling. There is no reason to ever stop the motor turning unless you are trying to demonstrate a "Prop stopped" situation. When the prop is stopped there is potentially LESS drag than when it is windmilling, because it is not aerodynamic . In fact a turbo prop situation where a turbine is geared to a propeller can generate at least twice the drag as it can deliver in forward thrust. Therefore the need to have auto-feather on most of these engines, because of the enormous amount of drag that they can generate, in a power loss situaton. Nev