Engine out, use 10 degree flaps???

[jollyroger]

I was told by my instructior that using 10 degrees of flaps increases your lift more than it increases drag. So using that same logic I would assume that if you had an engine out emergency, you would want to

1) Adjust for best glide speed
2) Lower flaps to 10 degrees to increase lift more than you increase drag

However the POH does not say keep flaps up or use flaps to increase glide distance. Does anyone have some insight into this?

 

[Dave Krall CFII]

I was told by my instructior that using 10 degrees of flaps increases your lift more than it increases drag. So using that same logic I would assume that if you had an engine out emergency, you would want to

1) Adjust for best glide speed
2) Lower flaps to 10 degrees to increase lift more than you increase drag

However the POH does not say keep flaps up or use flaps to increase glide distance. Does anyone have some insight into this?

It depends mostly on the individual aircraft's airfoil, so use its POH proceedures.
It's not typically going to make a lot of difference one way or the other anyway compared to all the other tasks that will need doing.

 

[Greebo]

I was told by my instructior that using 10 degrees of flaps increases your lift more than it increases drag. So using that same logic I would assume that if you had an engine out emergency, you would want to

1) Adjust for best glide speed
2) Lower flaps to 10 degrees to increase lift more than you increase drag

However the POH does not say keep flaps up or use flaps to increase glide distance. Does anyone have some insight into this?

Yea, unless your instructor is an Aerodynamics engineer who's run hours of model testing on the particular bird being flown, follow the POH.

It sounds to me like your instructor is making the far too common mistake of taking a rule of thumb that may apply for one bird, and trying to apply it unilaterally. Bad idea, and it could cost you more glideslope than you can afford in a real engine out situation.

 

[cwyckham]

I was told by my instructior that using 10 degrees of flaps increases your lift more than it increases drag. So using that same logic I would assume that if you had an engine out emergency, you would want to

1) Adjust for best glide speed
2) Lower flaps to 10 degrees to increase lift more than you increase drag

However the POH does not say keep flaps up or use flaps to increase glide distance. Does anyone have some insight into this?

This is true of the DA20-A1 Katana (and I assume with other DA20s), and so the POH says so. It isn't true of most other aircraft. Your instructor is just trying to impress upon you how much drag change you should expect with different flap settings and is not making a statement about the lift to drag ratio. Lowering one notch of flaps will generally give you a worse lift to drag ratio than with no flaps.

Chris

 

[Richard]

What Chuck said. Also, you should decide do you want to go far or get down now? EX: no sense maintaining Vglide to increase loiter time over an airport, so just get down. I say that to point out that even once established in best glide you should ask yourself if it's still a good idea to remain at best glide.

 

[cwyckham]

What Chuck said. Also, you should decide do you want to go far or get down now? EX: no sense maintaining Vglide to increase loiter time over an airport, so just get down. I say that to point out that even once established in best glide you should ask yourself if it's still a good idea to remain at best glide.

That's a good point. Best glide will increase your choice of landing fields because it gets you the furthest. Once you're at a good field, you have to choose to either get down right now if the problem is something like carbon monoxide poisoning or structural failure, or hang out for a bit at altitude so that you have more time to do your checks and get a radio message out.

If the latter is the right choice, you want to be flying at minimum sink, not best glide once you're at your landing area. This will give you less range (which you don't care about since you're already there) and more time (which is a good thing). Minimum sink is slower than best glide, and is usually not too far above stall. If you were to add a comfortable margin like 10 knots above the bottom of the green arc so you don't stall while you're distracted with checklists or radios, that would probably be a good approximation of minimum sink.

Chris

 

[tonycondon]

Chris is right on. I was trying to stop the CFI-Glider from coming out in me cause it seems like this subject has been beaten to death lately. In almost any case bar fire and the ones Chris mentioned, time is your friend in an off field landing. Time to scope out wind, terrain, obstacles, access. Time to adjust your glide path to compensate for these. Time to give yourself an out until the last possible moment. It really is all about time.


-7 off field landings. Hope to at least double that this summer

 

[gismo]

Yea, unless your instructor is an Aerodynamics engineer who's run hours of model testing on the particular bird being flown, follow the POH.

It sounds to me like your instructor is making the far too common mistake of taking a rule of thumb that may apply for one bird, and trying to apply it unilaterally. Bad idea, and it could cost you more glideslope than you can afford in a real engine out situation.

I can't think of one single that has a better L/D with any flaps than without. Some of the fancier gliders even have a negative (reflex) flap setting that increases the glide ratio. Seems to me the CFI is just plain wrong.

 

[cwyckham]

I can't think of one single that has a better L/D with any flaps than without. Some of the fancier gliders even have a negative (reflex) flap setting that increases the glide ratio. Seems to me the CFI is just plain wrong.

Diamond DA20-A1 Katana POH says to use one notch of flaps for an engine failure (I'll look it up tonight when I get home from work to make sure). Seems odd to me, but that's what it says. I'd like to understand why this is the case with this aircraft.

Chris

 

[cwyckham]

Yup, one notch of flap (15 degrees) at 72 knots is best glide at maximum weight of 1609 lb for a DA20-A1. Interestingly, they also publish the speed at 1322 lb to be 66 lb for those of us who don't want to calculate the square root of the weight during an emergency.

Another interesting side note is that the DA20-A1 has a glide ratio of 14 compared to the Cessna 152's 9.4.

Chris

 

[KennyFlys]

<Snip> Seems to me the CFI is just plain wrong.

I'm pretty certain an administrative law judge would see it this same way.

He'll give a lot of weight to the hundreds of hours that engineers and test pilots put into that design and various configurations. Remember, this was also done in part to help their lawyers defend against the lawyer for the crackpot who did not follow the POH!

 

[jesse]

If you guys are talking about using flaps during your attempted glide to your field. I'm with you. Do what the POH says.

If we are talking about using flaps during the final stages of the landing..I'm not.

I can fly slower with a far shorter ground roll with full flaps in every airplane I have been PIC in so far. Thus in an engine out into a rough or short field I will be using flaps during the final stage when I am committed to landing. Flaps combined with slips also give me the ability to extend or reduce my glide.

This is like suggesting that you would go into a place like 6Y9 with no flaps, No thanks. I'd rather not die.

If the FAA has a problem with that--Well..I'd rather be alive and dealing with some idiot judge than dead.

 

[EdFred]

This is like suggesting that you would go into a place like 6Y9 with no flaps, No thanks. I'd rather not die.

Just wait till you see it this summer. You could no flap landing there with quite a few planes when the grass grows in, a runway lengthening of 30%+ will do that for ya.

 

[cwyckham]

If you guys are talking about using flaps during your attempted glide to your field. I'm with you. Do what the POH says.

If we are talking about using flaps during the final stages of the landing..I'm not.

We're talking about getting to the field in a glide only. I agree fully with your statements about full flaps and a minimum speed touchdown.

Chris

 

[bbchien]

Just wait till you see it this summer. You could no flap landing there with quite a few planes when the grass grows in, a runway lengthening of 30%+ will do that for ya.

Not in mine.

 

[EdFred]

Not in mine.

Your plane was not on my list of planes when I made that statement. Although, I am getting you an extra 32%, and possibly 50% over the current layout in '08.

 

[flyingcheesehead]

Just wait till you see it this summer. You could no flap landing there with quite a few planes when the grass grows in, a runway lengthening of 30%+ will do that for ya.

I will vouch for the fact that the extra couple hundred feet available on Labor Day weekend made a HUGE difference. Ya know, like actually being in the white arc before having to pull up over the trees!

 

[EdFred]

Um. It helps if you reduce drag by not carving a line in the soil with your tie down ring on takeoff.

And we tacked on ANOTHER 650 feet in addition to that.

 

[jollyroger]

Just to keep things in perspective, My CFI did not say to use 10 degree flaps during an engine failure, I was referring to the fact that one the C152 POH does not say either way, which may imply don't do it. What I was asking had more to do with using knowledge of your airplane (Which I don't claim to have absolute knowledge yet) to make a smart decision during flight or emergencies. One thing my CFI did say is do whatever you need to do to fly the plane in all situations. So if you could use the information that 10 degrees flaps increases lift more than drag maybe you could use the info in a pinch. However it sounds like it is more likely to work against me. This was the reason for asking the question. And thank you for the answers

 

[jesse]

Just to keep things in perspective, My CFI did not say to use 10 degree flaps during an engine failure, I was referring to the fact that one the C152 POH does not say either way, which may imply don't do it. What I was asking had more to do with using knowledge of your airplane (Which I don't claim to have absolute knowledge yet) to make a smart decision during flight or emergencies. One thing my CFI did say is do whatever you need to do to fly the plane in all situations. So if you could use the information that 10 degrees flaps increases lift more than drag maybe you could use the info in a pinch. However it sounds like it is more likely to work against me. This was the reason for asking the question. And thank you for the answers

Measure your glide ratio in the same conditions with and without 10 degrees. Also make sure to try this at different weights, etc. If 10 degrees gets you further after extensive testing. I'd use it in the same conditions you tested. If you don't go through all this effort to test it in a controlled intelligent manner. Do what the POH says. Because they did the testing.

There are one or two things I will do in conditions that I have tested even though the POH doesn't support it. But my tests did.

 

[Dave Krall CFII]

Measure your glide ratio in the same conditions with and without 10 degrees. Also make sure to try this at different weights, etc. If 10 degrees gets you further after extensive testing. I'd use it in the same conditions you tested. If you don't go through all this effort to test it in a controlled intelligent manner. Do what the POH says. Because they did the testing.

There are one or two things I will do in conditions that I have tested even though the POH doesn't support it. But my tests did.

The aerodynamic logic is sound however in light Cessnas and Pipers, I've found in multiple trials no advantage in either configuation of flaps (10 degrees or zero). I'll be paying attention to all the other needed tasks.