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convair880mfan
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Posts: 156
Joined: Fri Jun 25, 2021 12:33 am

DC-10 Horizontal Stabilizer Size

Sun Jul 25, 2021 10:44 pm

When looking at plan view drawings of various jetliners in the evolution of the industry, I was surprised at the seeming size of the DC-10 Horizontal Stabilizer in comparison to that of other aircraft.

I'm sure it is the result of balancing the various performance objectives of that aircraft but wonder why, at a more specific level, that is was so big.

It also seems to have a lot of dihedral in comparison to the DC-10 wing. The Lockheed L-1011 Tristar also seems to have a large Horizontal Stabilizer.

Is it because of the relative shortness of the fuselage? The Boeing 747SP, which is also seems relatively short has a seemingly large horizontal stabilizer.

The later iterations of the Boeing 747 do not seem to have such proportionally large horizontal stabilizers as the DC-10.

Anyone know why? Thanks in advance for all information and opinions!
 
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CostaDelSol90
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Re: DC-10 Horizontal Stabilizer Size

Sun Jul 25, 2021 11:29 pm

Not and engineer but a pilot (737, not DC10) so I might hazard a guess for you.

The force required from the horizontal stabiliser depends on the arm length. This arm length is the distance from the centre of balance (near the wing) to the horizontal stabiliser. When this distance is short, more energy needs to be applied to get it to move, imagine a short see saw verse a long see saw - or a short lever vs a long lever.

Because the tri-star and DC10 both have a big, heavy engine mounted in the tail, there will be less fuselage behind the centre of balance (wing) then in front. As a consequence the arm (lever length) that the elevator is working over is shorter, so it need to be more forceful and thus, bigger.

Hope this helped.
 
convair880mfan
Topic Author
Posts: 156
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Re: DC-10 Horizontal Stabilizer Size

Mon Jul 26, 2021 12:15 am

That makes sense to me. Thanks. That would explain the relatively small horizontal stabilizer atop the vertical stabilizer on the Boeing 727

I wonder why the MD-11 has a much smaller horizontal stabilizer? Of course it is different plane with a longer fuselage. I read somewhere that the MD-11 horizontal stabilizer was designed in part to reduce cruise drag. Having flown a lot on DC-10's and MD-11's, I always thought the DC-10 had a more solid feel to it. Perhaps that is just an illusion.

I do thank you for taking the time to respond. Your see saw image is a good illustration. Thanks again.
 
69bug
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Re: DC-10 Horizontal Stabilizer Size

Mon Jul 26, 2021 12:25 am

The MD-11 had smaller stabilizers as the arm (CostaDelSol90) is longer. The see-saw analogy is a good one .. basically the whole tail is a lever.. the longer the lever the less force required.

Wrt to cruise drag. The stabs also had trim-tanks...this meant you could use fuel to get the aircraft in trim instead of using the stabs (like on other aircraft before), this will reduce drag and increase fuel economy.

rgds
bug
 
9QCLI
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Re: DC-10 Horizontal Stabilizer Size

Mon Jul 26, 2021 8:39 am

My vague recollection is that the dihedral was due to the small rudder of the DC-10 (vs the L-1011). The smaller and lighter stabilizer of the MD-11 was due to the LSAS (a form of FBW for the stabilizer) allowing relaxed stability to decrease fuel burn. The resulting MD-11 behavior on landing was and still is a hot topic.
 
CosmicCruiser
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Re: DC-10 Horizontal Stabilizer Size

Mon Jul 26, 2021 5:57 pm

The landing issues were corrected with a LSAS software update.
 
DeltaMD95
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Re: DC-10 Horizontal Stabilizer Size

Mon Jul 26, 2021 9:32 pm

CosmicCruiser wrote:
The landing issues were corrected with a LSAS software update.


Out of curiosity, do you recall what year the corrective software update was released?
Did you know that a Boeing 717-200 is really a McDonnell Douglas MD95-30? ;-)
 
Moosefire
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Re: DC-10 Horizontal Stabilizer Size

Mon Jul 26, 2021 10:55 pm

CosmicCruiser wrote:
The landing issues were corrected with a LSAS software update.


I think a lot of MD-11 pilots would disagree with you.
MD-11F/C-17A Pilot
 
CosmicCruiser
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Re: DC-10 Horizontal Stabilizer Size

Tue Jul 27, 2021 2:31 pm

DeltaMD95 wrote:
CosmicCruiser wrote:
The landing issues were corrected with a LSAS software update.


Out of curiosity, do you recall what year the corrective software update was released?


I went to the -11 in 2000 so it was done before that. I avoided bidding it for awhile after hearing the stories of landing issues. When I did go to it it had been updated and I never saw any real issues. Flew it for 12 years. I'm not saying it was easy as the 777 is, so I hear, but nothing outrageous.
 
CosmicCruiser
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Re: DC-10 Horizontal Stabilizer Size

Tue Jul 27, 2021 2:34 pm

Moosefire wrote:
CosmicCruiser wrote:
The landing issues were corrected with a LSAS software update.


I think a lot of MD-11 pilots would disagree with you.


Well, I was among them and don't remember too much being said after the update. Everyone will have some interesting moment as we all do but nothing habitual. I could say the same thing about the 727.
 
Moosefire
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Re: DC-10 Horizontal Stabilizer Size

Tue Jul 27, 2021 6:13 pm

CosmicCruiser wrote:
Moosefire wrote:
CosmicCruiser wrote:
The landing issues were corrected with a LSAS software update.


I think a lot of MD-11 pilots would disagree with you.


Well, I was among them and don't remember too much being said after the update. Everyone will have some interesting moment as we all do but nothing habitual. I could say the same thing about the 727.


Looks like we’re at the same company. Maybe you moved onto something else but I fly it every week.

Page 10, Sentence 1 of the company’s (61 page!) guide to landing the MD-11 sums it all up well. The same words are used in every MD-11 PMR sim.
MD-11F/C-17A Pilot
 
CosmicCruiser
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Re: DC-10 Horizontal Stabilizer Size

Tue Jul 27, 2021 8:23 pm

2000-2012 in the -11. I never saw the nose come up after touchdown or while in reverse or anything similar which is what I remember the problem being before I went over to it. I don't remember any surprises except my own screw up during landing with flaps 50, LOL. I guess the 777 is the way to go.
Fly Safe my friend.
 
chimborazo
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Re: DC-10 Horizontal Stabilizer Size

Wed Jul 28, 2021 9:00 pm

As noted shorter moment arm requires a bigger input to give the same relative effect of a longer moment arm for a given airspeed. This feeds into weight and balance- particularly on “small” aircraft where, if loaded outside of defined envelope, can quickly run out of margin and reduce elevator authority. Couple of heavy people in the back of a 172, bit of heavy baggage and light people up front, lots of nose-down trim needed. Exceed the limits (plus a safety margin because people do this) and once you rotate you just keep going into a stall, even with maximum nose-down input. Increasing speed will help as the elevator will offer more nose down force… but it’s probably too late at that point as the nose will be continuing skyward, further hampering ability to accelerate.
 
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rfresh737
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Re: DC-10 Horizontal Stabilizer Size

Thu Aug 05, 2021 12:50 pm

convair880mfan wrote:
I always thought the DC-10 had a more solid feel to it. Perhaps that is just an illusion.


I was a flight engineer on the L-1011. I rode many times in the jump seat on DC-10's and B-747's. The DC-10 had the quietest cockpit of all the wide bodies (built in the US anyway). From a noise perspective it was a pleasure to be in the cockpit. The 747 and Tristar cockpits were noisy. The Tristar has 3 air conditioning packs and I'd often run only 2 of them because with 3 running the air noise was high. The 747 cockpit noise came mostly from the outside air hitting the front of the cockpit but it too had pack air noise.

RalphF
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