A Question About Drag

[Whiskey226]

Back in the good 'ol days of ppl training, I seem to recall an instructor saying that in an engine failure situation, the glide can be extended by gaining as much height as possible straight after the failure. i.e. convert speed into height until best glide speed is achieved, then glide as normal.
My question is, would the extra induced drag caused by such a manouvre put you in a worse situation than by slowing to glide speed in a level attitude?
Cheers in advance,

Whiskey:=

[troppo]

i was always under the impression that speed to height thing was a marginal call in a light training aircraft.
it's origins come from the military when speed could be converted to height when you're in sumthing like a spitfire or a p51 with a rolls royce merlin and over a 1000 hp up the front.
however in a low powered training aircraft with a very little difference between climb, cruise and stall speeds any abrupt control input that could potentially result in a stall close to the ground just aint kosher in my book.
Fine if you have the experience and performance to actually fly the aircraft and make it do what you want, but for the ppl syllabus flying the aircraft to a safe landing area and walking away from it takes priority over trying to squeeze an extra few feet in height.

my two cents...be good to see what others think

[currawong]

I'm with troppo.

In a high speed/low altitude situation it may serve to improve your view of spots to land.

If cruising at altitude, why bother?

If low and slow and it really fails, you may be faced with poling FORWARD to keep it flying.

Even if the way ahead does not look so good, it is better than the way straight down if it is not kept flying.

As to how drag is affected by all this...:O

[Arm out the window]

There must be a tradeoff.
You've got a combination of potential and kinetic energy. The drag varies with the square of the speed, so if you're a fair bit faster than best glide speed you are burning energy quickly; it makes sense to get to best speed reasonably smartly and then stay at it.
However as has been mentioned already, if there's not much of a margin between the speed you're at and where you want to get to, it doesn't make sense to pull the nose up high and then have to shove it straight down again.
You'd have to compare the height gained for a given excess of speed for various pitch up rates to see how much difference it made; test pilot territory; but my gut feeling is that if you have more than 20 kt or so excess speed, a 'smooth and positive' pitch up until 10 kt above best glide speed and then selection of the glide attitude would have to be a fairly energy efficient method of converting speed to height.
Anything less than 20 kt excess, don't bother, just maintain attitude until it bleeds back to about 5 kt above best glide speed.
Sound fair?

[R2000]

Gentlemen,

Another option which is perhaps more in vogue amongst lower performing military aircraft ie light aircraft equivalent, is to extend the old mantra "speed to height" to "speed to manoeuvre".

This is a recognition that there is little height gained in these types due to their low momentum, as discussed above. You also risk overdoing it and ending up nose high with no engine and speed decreasing below the best glide speed where you are going to have to trade a lot of height to regain glide speed, if indeed you do not mishandle the aircraft and stall etc (the traditional saying "stall spin crash burn die" comes to mind).

Where you will not have height (as well as training, practice and skill) to recover from any mishandling it might be better to use your excess speed (from cruise speed for instance) to make a level turn onto a more desirable heading, lowering the nose at the right time to commence the glide profile. These turns could have a higher angle of bank at the higher speed with more sensible angles of bank as the speed washes off. You finish the turn established in the glide with the direction you want, perhaps towards a better terrain area or if you are at low level over a bad area you might just use the turn to head into wind and reduce your impact speed.

Please talk to your chief instructors and get some dual practice in advance if you think it is a reasonable idea for your aircraft type.

Regards,

[Ultralights]

interesting read. Just try any of those manuvers in a very high drag aircraft, like a good ol'e drifter, in the event of total engine failure, you have approx 3 seconds to get the nose down to maintain speed!

I also remeber an intructor a long time ago saying that in the event of a Partial engine failure, (such as a dead cylender or 2) or a failure that reduces engine power to idle, then it would be better to shut the engine down as a windmilling or slow turning prop (idle) will produce more drag than a stationary unfeathered prop!

[flying ginge]

we teach speed to height as most training estabs probably do. If they're low and slow then concentrate on staying above the stall and getting the a/c on the ground. I think speed to height is good in that it gets the a/c closer to the best glide speed sooner so once it's trimmed that's one less thing to worry about.

[Lodown]

This argument has been going on for probably 100 years now. It has a cousin in the argument about climbout after takeoff in a twin - build up speed or climb for height.

What does your POH say?

[Whiskey226]

Thanks for the thoughts guys, much appreciated.
The question started burning in my mind when I was ferrying a 182 with a poxy engine back for maintenance. Funny how on these flights you start to remember all the stupid questions you never asked in training but wished you did... Especially when the thing starts running on 4 and a half cylinders over water at 1000ft!

[The Messiah]

The only reason for converting speed to height is for a better view of a place to put it down.

Whether you bleed the speed off level or zoom climb, your glide range will not change a scrap, and your point about induced drag increasing is just complicating the issue unnecessarily. Glide speed is best L/D ratio end of story.

[ovum]

a windmilling or slow turning prop (idle) will produce more drag than a stationary unfeathered prop!

True, a windmilling prop will generate the same amount of drag as a disc of the same radius.

[The Messiah]

ULTRALIGHTS you must be talking about flying an ultralight because in any lighty the prop would still be turning (provided no major internal damage), hence the term 'windmilling'.

Yes I know you can get it to stop if you go slow enough but that's a whole new thread.