Western727
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Positive Rate Of Climb Or Run Out Of Runway

Mon Aug 27, 2001 12:11 am



Which is the correct practice? To retract the landing gear when the VSI shows a positive rate of climb? Or to wait to retract the gear when the airplane has overflown all the runway that could be used in the event of an engine failure?

Specifically reffering to piston aircraft, I've seen both done. And most things I've read on the subject advise the pilot to wait, though in practice I've seen quite a different technique - Yanking the wheels up when the airplane is barely 10 ft above the ground.
Jack @ AUS
 
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RE: Positive Rate Of Climb Or Run Out Of Runway

Mon Aug 27, 2001 12:42 am

It is safer to reatract them when you have used up all the runway. Also another thing to consider is do you have enough time to get them down, even if it is not on the runway if you started to have problems.
Iain
 
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RE: Positive Rate Of Climb Or Run Out Of Runway

Mon Aug 27, 2001 1:25 am

By the way, welcome back. For what it's worth, here is my humble (but absolutely correct) opinion on your question...

It's not a matter of "piston" or "turbine", but rather does the airplane have one or more engines. If you're in a single and you loose the engine the laws of physics dictate what will happen next. Leaving the gear down until you have no more "usable" runway left only makes sense. It will leave the airplane in much better condition should the engine decide to pack it on while you're still over the runway. (By the way, I've had it happen to me once.) I've seen some "hotdoggers" rotate and immediately suck the gear up. A while back I even heard of a guy who would place the landing gear in the up position as he took the runway. His thinking was that the squat switch would keep the gear from coming up while the airplane was on its takeoff roll and immediately start the retraction process as soon as he broke ground. What a weenie - his practice came to light one morning when he rotated a bit too early and the airplane settled back onto the runway. You don't need a PhD in Physics and Aeronautical Engineering to figure out what happened next.

(By the way, these are usually the same guys who immediately pull the throttle back to climb power as soon as the gear is in the wells. Statistically, that's the time when your most likely to have an engine - piston or turbine - come apart.)

Multiengine aircraft are an entirely different matter - you want to get the airplane cleaned up as soon as possible. In the case of most propellor twins - rather piston or turboprop - their ability to maintain controlled flight depends upon the pilot getting the gear up, the propellor feathered, and the flaps up. Failure to this often results in the airplane being turned into a lawn dart.

In the case of the larger turboprop and turbojet aircraft they operate under a different set of rules. They have what they call a V1 or Takeoff safety speed. Engine failures before reaching V1 would result in aborting the takeoff. With engine failures after V1 the crew would continue with the takeoff and, upon reaching Vr, rotate and take the airplane into the air. For many reasons, it is safer taking the airplane into the air with the failure rather than trying to abort after passing V1. While the need to immediately clean up the airplane isn't normally as pressing it is still something that the crew needs to get around to doing at some point in working the problem. (This is a very simple explination of a very complex subject - there have been many EXCELLENT threads on this subject.)

There you have it - if you're flying a single engine aircraft you should leave the gear down until the last inch of usable runway passes under the nose. If you're in a propellor-driven twin get the gear up ASAP and hold up reducing to climb power until you're in a position to handle an engine failure. If you're flying a turbojet, get the gear up ASAP and you can mess with the rest when you get around to it.

 
Western727
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Jetguy

Mon Aug 27, 2001 2:16 am


Wow! Thanks for the great answer. That clears up a lot of confusion for me.

And thanks for the welcome back...
Jack @ AUS
 
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RE: Positive Rate Of Climb Or Run Out Of Runway

Sat Sep 01, 2001 6:12 pm

i would say after positive rate of climb as a landing is impossible as the aircraft would have already passed V1
desicion speed.
 
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RE: Positive Rate Of Climb Or Run Out Of Runway

Sat Sep 01, 2001 11:45 pm

Mike,
I found a mistake upon rereading my earlier post. V1 is not the takeoff "safety" speed - V2 is Takeoff Safety Speed. V1 is Takeoff Decision Speed. Gee, it wasn't even late when I typed the reply either. Oh well, I guess I'll just have to fall back to my "all purpose" flight instructor defense of, "Do what I mean, not what I said."  Nuts

Jason,
Nice catch. You do have your facts on aviation straight. However, a twin-engine turbojet aircraft, operating on one engine, will always be capable of a positive rate of climb after rotation - it is designed into the performance charts and is a requirement. Likewise, upon landing, a twin-engine turbojet aircraft, operating on one engine, will be capable of a positive rate of climb in the event of a missed approach. Pilots are required to refer to a maximum landing weight chart whch provides us with the maximum weight we can be at landing which will allow us to be able to meet the appropriate obstacle clearance requirements. (Again, this is a very simple explanation of a very complex subject.)
Later,

Jetguy
 
Buff
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RE: Positive Rate Of Climb Or Run Out Of Runway

Sun Sep 02, 2001 12:59 am

Jetguy: Very nice answer. I'd like to add an opinion though with regards light twins (Commanche, Seneca, Baron, Cessna 402 type aircraft). It has been measured that with the loss of one engine, these and similar airplanes lose up to 90% of their ability to climb. I clearly remember those days from my background and decided way back then that gear retraction would be initiated once there was insufficient runway left to land straight ahead. Many times these light twins are operated at very close to or exactly at (catch my drift?) their max certified takeoff weight.

Prudency in those situations was to close the other throttle and land straight ahead. I know of many accidents from those days that would have been "incidents" otherwise.

Just another way of looking at it!

Best Regards,

Buff
 
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RE: Positive Rate Of Climb Or Run Out Of Runway

Sun Sep 02, 2001 1:34 am

Buff,
You're exactly right. That's why they pay us the big bucks - to know when to and when not to. There will always be exceptions to the general rules. Here's amother example - you don't want to get into too big a hurry with Cessna Skymasters. There is a tremendous amount of drag created when their gear doors open up. Immediately after takeoff - near to the ground with an engine out - is not exactly the time to be opening all of those gear doors. By the way, do you mean to say that people in your country actually fly their light twins overweight? The audacity of you Canadians! (wink, wink)
 Innocent
 
Buff
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RE: Positive Rate Of Climb Or Run Out Of Runway

Sun Sep 02, 2001 3:03 am

Did I say that? I must have been mistaken.

Shamefully,

Buff
 
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RE: Positive Rate Of Climb Or Run Out Of Runway

Sun Sep 02, 2001 4:08 am

The Beechcraft i got my MEI in we sucked the gear up on postive rate.. the gear operation time is in between 3-4 seconds.. fastest landing gear ive ever seen.

If you do lose an engine though and your gear is up in that plane with remaining runway, youd actualy have enough time to drop the gear before you touched down.

Chicks dig winglets.
 
Buff
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RE: Positive Rate Of Climb Or Run Out Of Runway

Sun Sep 02, 2001 6:04 am

Yeah, but...

Oh well.


Buff
 
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RE: Positive Rate Of Climb Or Run Out Of Runway

Sun Sep 02, 2001 7:20 pm

Interesting ideas.

The way i was taught and i completely agree with it for amny reasons is to take the gear up when "a landing ahead is no good". This means that if we are out of remaining runway, and a landing ahead looks bad, the gear can come up to reduce drag, accelerate the aircraft (less drag) and aim at gaining the desired climb out speed.

I disagree with pulling the gear up seconds after lift off as drag is greatest from the landing gear during retraction and this is why on small aircraft, the landing gear isn't retracted at all during precautionary search and landing practices (along with the low flying danger). I know of flying schools that adopt this kind of teaching(pulling the gear up immediately) and i think it is silly and dangerous.

On the subject of decreasing power early after the gear is up, i think this is silly too. The power is reduced when the pilot judges that the aircraft is at a safe height to do this. The most likely point of engine failure is at the first power change which would add to the stupidity of decreasing power 20 ft off the ground.

these are my thoughts and any constructive criticism is welcomed.

Regards
Geebar
 
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RE: Positive Rate Of Climb Or Run Out Of Runway

Sun Sep 02, 2001 9:08 pm

Well said Geebar. Couldn't agree more.

Welcome to Airliners.net!

Best Regards,

Buff
 
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RE: Positive Rate Of Climb Or Run Out Of Runway

Mon Sep 03, 2001 1:52 am

Welcome Geebar...

I don't want anyone misunderstanding my comments on the need to get gear up on light-twins ASAP. I'm not implying that you need to get the gear cycling the moment the aircraft breaks ground. You don't need to be cocked and on a hair trigger - just get to it as soon as you can get around to it. Sure, there will be situations where you can delay it - here in Klamath Falls, Oregon we have a 10,300 foot runway and there is no need to be in a rush with the gear. You could takeoff and land most twins 3 times on this runway. But I believe that on a more typical runway once the airplane's up and climbing having the gear out becomes more of a liability than an asset if and when an engine decided to "go south" on you. We tend to take engine reliability for granted, but I believe that this is a very dangerous thing to do. Many propellor driven twin-engine aircraft simply won't maintain altitude with a wind-milling propellor and/or the gear down. The old Metroliners had a rocket bottle in the tail to buy the flight crew enough time to get the gear in the wells. Auto-feather systems are on most, if not all, turboprop twins. The manufacturers wouldn't put up with the increased costs and complexity of doing this if there wasn't a true need for it. They put this stuff on the turboprops that have significantly better single-engine performance than piston-twins. It really ought to be on the "little" twins, but no one is willing to pay for it. As Buff said, propellor driven light twins will lose up to 90% of their climb capability. The figure is probably even higher than that - I've seen several non-turbo'd twins that wouldn't climb out of ground effect and several turbocharged twins that could barely achieve climb rates of 100 fpm or so. But never the less, the point is that twin engine aircraft have two engines because they need two engines and under certain conditions they can maintain controlled flight on one engine IF THE PILOT DOES EVERYTHING RIGHT. You don't have time to dawdle, it has to be done right and right now.

Oops, I've gotten on my soapbox again. Sorry, I'll get off of it now.
 
Buff
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RE: Positive Rate Of Climb Or Run Out Of Runway

Mon Sep 03, 2001 2:10 am

My 90% number came from an old article long since lost from Aviation Week back in the mid-80's. It gave a list of types and percentages. The Seneca I had the worst reputation with about a 92% loss.

One other thing that should be considered is operation off contaminated runways, especially in winter time. Muddy strips can be just as bad. Failure to let the wheels spin off slush/mud prior to retracting the gear may cause you grief down the line. Especially slush as it can re-freeze in the very tightly enclosed gear bays light twins have. This could ultimately prevent you from extending the gear for your next landing. Otherwise, damage is possible which while not a safety issue, is certainly a financial one.

Best Regards,

Buff
 
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RE: Positive Rate Of Climb Or Run Out Of Runway

Mon Sep 03, 2001 2:20 am

Buff,
Also, brake cooling considerations - I can remember having to occassionally delay put the gear up on the 727s to give the brakes a chance to cool off a bit. I can give you a 1,001 exceptions to the general rules and that's a good thing - it's why I doubt if we'll ever see a pilotless passenger airplane. There are just too many exceptions to the rules. By the way, the next time I get to Ottowa I'll look you up. I'll show you mine if you show me yours! I'll even buy lunch.  Big grin
Ward

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