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Engine Advantage

Sun Mar 28, 1999 7:41 am

Is there an advantage to putting the engines on the rear of the fuselage instead of the wings. It seems the engines on the MD-80 (on the rear of the fuselage) seem to be much smaller than the engines of the 737-300 trought 900 (on the wing). Does the putting the engines back there produce more lift, create less drag, improve climbing capabillities, etc.
 
dash8
Posts: 389
Joined: Sat Aug 27, 2005 8:23 am

RE: Engine Advantage

Sun Mar 28, 1999 8:15 am

There are several advantages when using rear mounted engines:

1:Less yaw moment at engine failure
2:More passenger comfort
3:No wing mounted engines allow for a cleaner wing design.
4:Less susceptible to FOD
5:An odd number of engines can be accomodated
6:The clean wing can be optimised in it's lift to drag qualitues through the whole
flight envelope.

The disadvantages:

1:Reduced pax accomodation for a given aircraft length (due to rear mounted engines)
2:Engine malfunctions can occur due to disturbed airflow from the wings.
3:Fuel line protection from tank to engines is absolutely necessary.
4:The engines produce a very aft CG which has to be compensated by a more aft wing and a larger tail.(MD80) Larger tail, because the CG is closer to the tail, making it less effective.
5:A higher structural weight due to wing and tail strengthening.
6:High set tail makes the aircraft susceptible to "deep stal"l tendencies.
7:3 engine layouts suffer from airflow and reverser design problems, and make engine failure of the third engine barely noticable to the crew.

If you have any of question regarding any of the above don't hesitate to ask.

Sincerely,
Dash8
 
L-188
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Joined: Wed Jul 07, 1999 11:27 am

RE: Engine Advantage

Sun Mar 28, 1999 8:42 am

I'll add another disadvantage.

You run the risk of ice forming on the upper surfaces of the wing and getting sucked into the engine. This is what brought down that SAS MD-80. There is quite a bit of diligance taken in dispatching that bird in winter. Where the wing root meets the fuselage is nicknamed the "Coffin Corner"
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dash8
Posts: 389
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RE: Engine Advantage

Sun Mar 28, 1999 9:02 am

It's interseting to point out that the term "Coffin Corner" is also used to define the altitude at which the Vs meets the Vmo/Mmo.
L-188 is right although with the proper deicing techniques an MD-80 should operate fine in icing conditions. They have for the past 30 years.
 
Guest

RE: Engine Advantage

Sun Mar 28, 1999 9:06 am

Thanks, that was what I wanted to know.
 
L-188
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Joined: Wed Jul 07, 1999 11:27 am

Coffin Corner And MD-80 Iceing

Sun Mar 28, 1999 2:11 pm

Yup it is used to descibe that too.

I get the feeling it is one of those terms that means different things to different people. It is the term I used to describe the same point of the wing of a 727-100 to our new guys when I was a Reeve.

The MD-80 is not an airplane that you can get complacet with in winter. If you watch one on the ground sometimes you will see a ramper or mechanice walk up to the trailing edge with a four foot long rod and a stepladder. What he is checking is these three wicks that are on the top of the wing right against the fuselage. He taps each of them with the rod to see if ice comes off. The MD-80 has pretty thin wing skins compared to other airliners. So what happens the airplane goes up to altitude during a flight the fuel in the wing cools off to the temperture up there. Very Cold. The plane lands and what happens it that the mositure in the air condenses and freezes against the wing which is chilled by the fuel inside. Since the de-iceing equiptment only covers the leading edge it is in effective agaist this ice formation. Also this actually isn't as big as a problem when the temperture is very cold as opposed to around the freezing point. This is because the colder the air get the less mositure it can hold. Still when I was working for Alaska they tried to keep from sending MD-80's north of Seattle during winter. This is probably the big reason why they want to go to an all-737 fleet, they go through a lot of glycol on the MD-80's.

I probably told this story before but it is a good one.

Up untill last December Alaska Airlines flew flights from Alaska to the Russian Far East. They used the MD-80's for these flights because of their longer range. They landed one at Magadan(Or Vladivostok, I forget) and after they had landed they found out they where out of de-icing fluid. Since they needed to de-ice the plane, the airport personell came up with a novel solution. They drove the truck down to the local distillery and filled it up with Vodka. I understand the FAA had a feild day with them using an unapproved de-icing fluid.
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dash8
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RE: Coffin Corner And MD-80 Iceing

Sun Mar 28, 1999 4:11 pm

Hehe......that's a good one !!!!!
 
L-188
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Vodka Story Is True

Tue Mar 30, 1999 4:18 am

The vodka story is absolutly true. This is why I belive it happened in Magadan. They make a really good brand of Vodka there. I understand it was Stalins favorite. I don't remember the brand name but the laber is a really ugly olive-green thing.
OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.