The aft stairs were required on the ground as a tail stand, so they stayed open.
GF
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- DocLightning
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Re: Possibility of the 797 having a T-Tail?
VirginFlyer wrote:Veigar wrote:Hm. All of the points posed here bring up the question as to why Boeing even did the design they did when developing the 727. If anything, the rear end of the 727's area (everything where the tail is) would be even HEAVIER with the middle engine that has the S-duct inlet. Also, do low bypass engines only work on this type of aircraft? (If it's as big as the 727 or 757 obviously) I know for a fact no manufacturer will make a plane nowadays with low bypass engines, so it'd make sense as to why it could've worked back then and not now.
When the 727 was designed, there weren't high bypass turbofans; the JT8D was basically it. They needed three engines for performance. I am under the impression podded engines under the wing were discounted in favour of getting a cleaner wing to enable better field performance. The rest of the design would have flowed on from that.
The "clean wing" is a bit overrated from an aerodynamic point of view. On a clean wing, there is a very abrupt increase in total airframe cross-section at the wing root. This causes a larger diversion away from the ideal Sears-Haack body. In fact, the MD-80 and 90 have upgraded flap track fairings to try to soften the decrease in cross-section at the trailing edge.
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https://s30.postimg.org/ldn46b0vl/IMG_2412.jpgThe engine pods mounted forward of the wing serve, among other things, to "soften" the sudden increase in cross-section at the leading edge. In addition, they help to reduce the bending moment on the wing root.
There are two main advantages to tail-mounted engines. First of all, they allow the fuselage to sit lower to the ground. When the 727 was introduced, that was important as many airports had to use airstairs and belt loaders. Second, when the 727 was introduced, there were still some semi-prepared airfields and moving the engines up high reduced the risk of FOD ingestion.
For the MoM, it would likely be serving at least medium-sized airports that will have a jetway and baggage loading equipment that can reach a fuselage. It certainly won't be operating out of any gravel runways. So the advantages of tail-mounted engines are moot.
A T-tail is not only heavier, but it also increases overall length. There is that stall risk, although this is an uncommon occurrence. I think the days of the T-tail for commercial airliners are over.
Re: Possibility of the 797 having a T-Tail?
One of the reasons that the C-5 and C-17 et al have T-tails is to provide clearance for paratroopers who jump from a rear side door. (That information was provided by flight crew on a tour of the ANG at Stewart Airport).
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- GalaxyFlyer
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Re: Possibility of the 797 having a T-Tail?
Well, there wasn’t a problem using the C-130 troop doors with a fuselage mounted horizontal tailplane. I never heard that in 18 years in the C-5. The troops would have to fall up about 22’ for them to hit a horizontal tail. Neither my unit nor Stewart had an airdrop mission. The C-17 had a very difficult time with troop drops because of vortices; finally fixed it, mostly.
Can’t say for -17; but the T-tail on the C-5 has had fatigue issues remlated to being the wake of the tanker during AAR and gets stress cracking. The tie-boxes have been replaced, the torque deck at the base of the rear fuselage has been replaced or repaired on a pretty high priority basis. Remember, all the control forces applied on the tail are transmitted to the fuselage thru the vertical stabilizer thru the torque deck to the plane to maneuver.
GF
Can’t say for -17; but the T-tail on the C-5 has had fatigue issues remlated to being the wake of the tanker during AAR and gets stress cracking. The tie-boxes have been replaced, the torque deck at the base of the rear fuselage has been replaced or repaired on a pretty high priority basis. Remember, all the control forces applied on the tail are transmitted to the fuselage thru the vertical stabilizer thru the torque deck to the plane to maneuver.
GF
Re: Possibility of the 797 having a T-Tail?
Another thing to consider is how monstrously large the T-tail on the C-5 is, I doubt any commercial airliner would ever have one that big.
Re: Possibility of the 797 having a T-Tail
TWA772LR wrote:Veigar wrote:jubguy3 wrote:Yes, because Boeing's primary concern is to make a throwback aircraft.
Weren't they aiming to do something similar with the 7J7? I believe it looked identical to a 727 minus the s-duct engine
A 3-engine, UDF, T-tail, MoM plane would be the coolest airliner to grace the skies since Concorde. Would have to have a super tall landing gear so the fans don't hit the runway upon take off, but who cares? That would be one sexy machine! Like the love child of a 727 and Q400!
I can tell that you'll never have to maintain that "T" tail arrangement. The MD80 that went down off of Santa Barbra prety much ended the need for the "T" tail.
getting to that jackscrew is hard enough without it being 33 feet in the air as it is it's a 22 hour job to replace it on a Non-T tailed airplane. Why make it harder for non- operational reasons??
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- GalaxyFlyer
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Re: Possibility of the 797 having a T-Tail?
Not to mention de-icing the damned thing.
GF
GF
Re: Possibility of the 797 having a T-Tail?
That would be awesome! I don't know if there is any real efficiency difference between a standard shark fin tail and a T-Tail, but I know T-Tails are a little old. I think it will be a shark fin tail with blended wing all of that other new stuff etc. But if they did make it a T-Tail, picture this: an MD-80 body, with a 787 cockpit, and smaller 787 engines. Who knows. We all know that Boeing does get creative sometimes.
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- GalaxyFlyer
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Re: Possibility of the 797 having a T-Tail?
an MD-80 body, with a 787 cockpit, and smaller 787 engines. Who knows. We all know that Boeing does get creative sometimes.
No, please I cannot imagine.
GF
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- VirginFlyer
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Re: Possibility of the 797 having a T-Tail?
GalaxyFlyer wrote:an MD-80 body, with a 787 cockpit, and smaller 787 engines. Who knows. We all know that Boeing does get creative sometimes.
No, please I cannot imagine.
GF
Imagine if it had the MD-80s let's-install-one-of-everything approach to types of switches!
V/F
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- kitplane01
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Re: Possibility of the 797 having a T-Tail
Veigar wrote:SWALUV wrote:Correct me if I'm wrong, but I believe the main reason T-Tail aircraft aren't designed more often is simply because of the added weight needed for structural purposes.
I would love to see another modern T-Tail though. That'd be gorgeous!
Yeah, I had thought this to be the case, but on the flip side, aren't T-Tail airplanes more aerodynamic?
Typically not so much.
The reason to have a T-Tail is to either ...
1) Get the tail out of the blanking effect of the wing for stall recovery.
2) Get the tail out of the way in order to place the engines on the tail (DC-9).
Piper had a bunch of aircraft that they converted from normal tails to T-Tails for looks and marketing.
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- Starlionblue
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Re: Possibility of the 797 having a T-Tail
kitplane01 wrote:Veigar wrote:SWALUV wrote:Correct me if I'm wrong, but I believe the main reason T-Tail aircraft aren't designed more often is simply because of the added weight needed for structural purposes.
I would love to see another modern T-Tail though. That'd be gorgeous!
Yeah, I had thought this to be the case, but on the flip side, aren't T-Tail airplanes more aerodynamic?
Typically not so much.
The reason to have a T-Tail is to either ...
1) Get the tail out of the blanking effect of the wing for stall recovery.
2) Get the tail out of the way in order to place the engines on the tail (DC-9).
Piper had a bunch of aircraft that they converted from normal tails to T-Tails for looks and marketing.
3) Increase the stabiliser moment arm without extending the fuselage. Admittedly it is probably easier to increase the size of the stabiliser or cantilever it further back.
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- Apprentice
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Re: Possibility of the 797 having a T-Tail?
2. Placing Eng on the Tail, in the case of a T- plane, it’s not a +, it’s a ——.
It add several structural desventages:
a) Wing Heavier
b) Tail Heavier
c) Engines’ fuel feed system, also heaviy and more complicate.
Rgds
It add several structural desventages:
a) Wing Heavier
b) Tail Heavier
c) Engines’ fuel feed system, also heaviy and more complicate.
Rgds
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