Predicting airplane performance

[Barb-SAN]

Capt. Hutch, We've been posting about the Madrid crash over in the general discussion forum http://www.takingflight.us/forums/showthread.php?t=8453 and http://www.takingflight.us/forums/showthread.php?t=8454 .

There's been a lot of speculation in the mainstream media about the possible causes. WE know that it's best to wait for the official investigation before jumping to conclusions. :D

However, I was wondering if you would tell us a bit about the aircraft performance calculations that you do before every flight, related to the weather conditions (temperature, humidity, wind direction), altitude, fuel load, passenger load, etc. (Or do you just review the numbers given to you by dispatch?).

Are there certain guidelines the baggage handlers have to follow as far as where they put heavy cargo (freight, other than normal passenger suitcases)?

Do you expect to be taking off by a certain point down the runway, and if you aren't able to become airborne at that point, would you assume a problem and abort the take-off? Would you notice anything different about how the plane was handling before take-off if the slats and flaps were not extended?

I have a friend who was a Navy fighter pilot. He said that any time he flies commercially, he sits where he can see a wing, and checks himself that the slats and flaps are extended before takeoff. He said if they weren't, he'd jump up and yell to stop the plane before take-off!

Note to fellow TF'ers... one way to reassure yourself on take-off...look at that wing...and know what to look for. This take-off video by St.Pete Mark http://www.youtube.com/watch?v=di0J2oCNXak shows the flaps extended, and at the very end of the video they are retracted.)

[Captain Hutch]

All good questions, Barb-SAN. I'm on my way out the door to fly right now but I will try to give you a good answer tomorrow!

Hutch

[Barb-SAN]

Thanks, Capt. Hutch. I have another question to add to the previous ones. I was just reading this article on the Madrid crash http://www.forbes.com/afxnewslimited/feeds/afx/2008/08/26/afx5358727.html


One of the single-aisle plane's two engines was found to be in reverse, which is usually used to help it slow down when landing, El Pais and its rival El Mundo reported earlier Tuesday.
The pilot may have put the engine in reverse in an effort to abort the take-off because he noticed the plane lacked the strength needed to take off, El Pais said.
An airport video recording of the doomed take-off shows the plane lifting itself off the ground about 500 metres (1,650 feet) later than it should have, the newspaper reported Monday.

Question: Is putting one engine in reverse an accepted way of aborting a take-off? Trying to visualize this, it seems to me that if one engine was going forward, and one in reverse, that would make the plane turn in the direction of the engine in reverse, no? Would it make a difference where the engines were mounted (in back (MD-82) vs. on the wings (B-737))? This is probably more technical than we really need to know...but then again...we are trying to evaluate the information presented in the mainstream media for accuracy.

Awaiting an opinion from the expert...:)

[tusphotog]

Would it make a difference where the engines were mounted (in back (MD-82) vs. on the wings (B-737))?

It doesn't make a difference where the engines are stuck for aborted takeoffs. All of that is factored in to the performance data.

For weight and balance calculations, tail mounted engines do affect the aircraft's center of gravity and it has to be loaded and balanced accordingly. This is due to the tail section being much heavier (obviously) on a MD-80 than a 737. Again though, this is all factored in to the performance data of the plane.

By the way, I don't know about Hutch's airline, but Southwest has this nifty little laptop computer, dubbed the magic box, that calculates everything the pilots need to know about the flight. This is in addition to the on board computers they have. It spits out runway distance required for takeoff relative to the weight, weather, power settings etc. I think I was told it could also calculate the power setting required for takeoff in a certain distance, like at Orange County where there's only 5,700 feet of runway to play with. The magic box's numbers are double checked by the crew, but from what I've heard, the magic box is always correct.

[MathFox]

One of the single-aisle plane's two engines was found to be in reverse,The investigators will look at this... one possibility is that the reverser was activated by the crash, when the plane broke up. On the other hand it could be a clue for the malfunction that caused the accident. Let's wait on what is found in analysis of the black boxes.

Trying to visualize this, it seems to me that if one engine was going forward, and one in reverse, that would make the plane turn in the direction of the engine in reverse, no? Would it make a difference where the engines were mounted (in back (MD-82) vs. on the wings (B-737))?Asymmetric trust can be used to turn a plane, but the effects will be more pronounced with wing mounted engines: they are further away from the centreline of the plane, create a larger turning momentum with the same difference in force.

[Barb-SAN]

Asymmetric trust can be used to turn a plane, but the effects will be more pronounced with wing mounted engines: they are further away from the centreline of the plane, create a larger turning momentum with the same difference in force.
Thanks...that's what I was thinking about, and remembered the Madrid plane was an MD-82, so maybe having one engine in reverse and one going forward wouldn't have as much turning
effect since the two engines are closer together in back than if they were mounted on the wings. (Things to think about when photographing planes...;))