Pro's and Con's for a T-Tail
Looking at the historical use of T-tails, it seems that the primary advantage was to make room for tail-mounted engines. Which doesn't say much about the tail itself, other than - it had to be someplace the engines weren't.
(And even then, there were the L-1011 and DC/MD-10/11)
A lesser advantage - to make c. 1970-designed bug-smashers look "F-104 supersonic cool" even sitting still on the ramp. Generally, the lower the power, the more prominent the T-tail.
Kind of the aviation equivalent of 1950s car tailfins.
The F-104 itself is worth some research - it was given a T-tail to counteract the likelihood of inertia coupling (wild gyrations on all three axes with control input) due to the long thin fuselage and stubby wings. In the event, it may have created as many problems as the one(s) it solved.
(And even then, there were the L-1011 and DC/MD-10/11)
A lesser advantage - to make c. 1970-designed bug-smashers look "F-104 supersonic cool" even sitting still on the ramp. Generally, the lower the power, the more prominent the T-tail.
Kind of the aviation equivalent of 1950s car tailfins.The F-104 itself is worth some research - it was given a T-tail to counteract the likelihood of inertia coupling (wild gyrations on all three axes with control input) due to the long thin fuselage and stubby wings. In the event, it may have created as many problems as the one(s) it solved.
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T Tail on Ground Effect Craft / ekranoplan
Alexander Lippisch (designer of Me163 rocket fighter and many sailplanes) used T Tails so that pitch control could be applied to prevent nose up pitch as the mainplane left ground effect. Note in GE the trailing vortices are cancelled out by the ground and therefore cause a low mounted tail to be even less effective.
Rostislav Alexeev helped develop the ekranoplan from hydrofoil boats and used T and high set V tails on the huge Caspian Sea machines:
Ekranoplan - MoscowTopNews.com
The advantages of GE are more to do with Drag reduction than any gains in lift.
The recent Gulfstream flight test crash report noted a reduction in stalling AoA for the main wing due to a reduction in the maximum Lift Coefficent in GE.
www.ntsb.gov/doclib/reports/2012/AAR1202.pdf
Rostislav Alexeev helped develop the ekranoplan from hydrofoil boats and used T and high set V tails on the huge Caspian Sea machines:
Ekranoplan - MoscowTopNews.com
The advantages of GE are more to do with Drag reduction than any gains in lift.
The recent Gulfstream flight test crash report noted a reduction in stalling AoA for the main wing due to a reduction in the maximum Lift Coefficent in GE.
www.ntsb.gov/doclib/reports/2012/AAR1202.pdf
Both the HS125* and BAe146/RJ have ‘T’ tails, but apparently for different reasons. *(125 original design)
The 125 design followed on from the Trident where a ‘T’ tail enabled rear mounted engines.
The BAe 146 used the ‘T’ tail to enhance the fin effectiveness in the four engine design. It may also have required the advantages of a high tailplane/elevator with a high lift wing (as #14, also cf YC14/YC15, C17).
Both the 125 and 146 were predicted to have deep stall characteristics, but none were found in flight test.
Both aircraft could establish an angle of attack greater than the stall angle with a dynamic entry and to a lesser degree by continued elevator input; however, no significant (unexpected) loss of elevator effectiveness was seen nor any tail blanking leading to a locked in condition. Both aircraft were test flown with stall/spin recovery parachutes.
Both aircraft had stick push systems which reduced the development and certification risk. This also enabled the basic stall speed to be established relatively quickly, and thence all of the certified performance speeds.
Also note the Vampire/Venom’s apparent low set ‘T’ tail (??!) vs the high set Sea Vixen. The latter stalled relatively normally without wing/fuselage blanking, and it was above the jet wash. Then cf Sea Vixen vs Javelin; I don’t know the reasons why the choice of tail position or any advantages other than for transonic performance.
Much of the early research into jet / swept wing tailplane position was flown by the Shorts SB5 which could be configured with either a low set or high ‘T’ tail.
The 125 design followed on from the Trident where a ‘T’ tail enabled rear mounted engines.
The BAe 146 used the ‘T’ tail to enhance the fin effectiveness in the four engine design. It may also have required the advantages of a high tailplane/elevator with a high lift wing (as #14, also cf YC14/YC15, C17).
Both the 125 and 146 were predicted to have deep stall characteristics, but none were found in flight test.
Both aircraft could establish an angle of attack greater than the stall angle with a dynamic entry and to a lesser degree by continued elevator input; however, no significant (unexpected) loss of elevator effectiveness was seen nor any tail blanking leading to a locked in condition. Both aircraft were test flown with stall/spin recovery parachutes.
Both aircraft had stick push systems which reduced the development and certification risk. This also enabled the basic stall speed to be established relatively quickly, and thence all of the certified performance speeds.
Also note the Vampire/Venom’s apparent low set ‘T’ tail (??!) vs the high set Sea Vixen. The latter stalled relatively normally without wing/fuselage blanking, and it was above the jet wash. Then cf Sea Vixen vs Javelin; I don’t know the reasons why the choice of tail position or any advantages other than for transonic performance.
Much of the early research into jet / swept wing tailplane position was flown by the Shorts SB5 which could be configured with either a low set or high ‘T’ tail.
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And the only real large turboprop options are T-tail such as the ATR and DHC-8.
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With over 1000 hrs on the Dominie (HS 125) I can state with certainty that it did NOT have a stick-push system.
We regularly stalled the aircraft clean but only went to the calculated stick shaker speed / actual stick shaker (whichever was the higher) in the Approach Configuration - Gear and Approach Flap.
There was some discussion from Multi Engined Standards Sqn that a fully developed approach stall would be quite nasty.
We regularly stalled the aircraft clean but only went to the calculated stick shaker speed / actual stick shaker (whichever was the higher) in the Approach Configuration - Gear and Approach Flap.
There was some discussion from Multi Engined Standards Sqn that a fully developed approach stall would be quite nasty.
Thanks Ascoteer, memory fades; the stick push on the 125 came in with the longer fuselages - 800 onwards?
Thence is fuselage length (wing-tailplane distance) a factor in the choice of a ‘T’ tail?
Thence is fuselage length (wing-tailplane distance) a factor in the choice of a ‘T’ tail?
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PEI,
The reason for the T-tail in the 146 has more to do with the fact that it was based on the HS681, which was a VSTOL military freighter originally designed to support the Harrier II (P1154) fleet. The T-tail came with the usual military aft cargo ramp. 146 also needed 4 engines as the 681 was powered by twin Pegasus and thus four jet effluxes to effectively cover the flaps.
The reason for the T-tail in the 146 has more to do with the fact that it was based on the HS681, which was a VSTOL military freighter originally designed to support the Harrier II (P1154) fleet. The T-tail came with the usual military aft cargo ramp. 146 also needed 4 engines as the 681 was powered by twin Pegasus and thus four jet effluxes to effectively cover the flaps.
''One advantage in a glider (sailplane) of having a T tail is that when doing an out-field landing it helps keep the elevators and horizontal stabilisor out of a tall standing crop.''
True, but the main reason why gliders have T tails is that there are only two right angle jucntions instead of four. It reduces interference drag.
True, but the main reason why gliders have T tails is that there are only two right angle jucntions instead of four. It reduces interference drag.
The VC10 had a T tail so that the engines could be mounted at the back. The main reason was that it was designed for the British ''Empire Routes'' which had short and high runways. Having the engines at the back meant the whole length of the wing could be used for high lift devices. Consequently had much slower take off and landing speeds that it's competitor, the B707. IIRC, the approach speed was some 20 to 25 konts slower for similar weights.
However, the extra structure of the suppot for the engines being away from the lift generators (the wings) added some seven tonnes to the structure and the VC10 was quite a bit heavier and more expensive to build than the B707 - one of the reasons it wasn't a huge commercial success and why only about 60 were built.
Incidently, Boeing got round the problem of the 707's inferior performance by getting the US Government to fund longer runways at all of it's destinations!
However, the extra structure of the suppot for the engines being away from the lift generators (the wings) added some seven tonnes to the structure and the VC10 was quite a bit heavier and more expensive to build than the B707 - one of the reasons it wasn't a huge commercial success and why only about 60 were built.
Incidently, Boeing got round the problem of the 707's inferior performance by getting the US Government to fund longer runways at all of it's destinations!
One interesting and unplanned benefit of the T tail on the Handley Page Victor when it was in it's testing phase was that on landing, the low set anhedral wings would be subject to ground effect whereas the tail would not. The resulting pitch would flare the aircraft almost perfectly for a very smooth landing and it prompted Handley Page to bill the Victor as "The aircraft which lands iteslf".
Unfortunately, the tail came off one of the prototypes during testing during a high speed low level position error test at Cranfield and the resultant re-design shortened the fin and the "autoland" effect was lost. It certainly didn't do that when I flew it, as anyone who suffered any of my Victor landings would attest!
Unfortunately, the tail came off one of the prototypes during testing during a high speed low level position error test at Cranfield and the resultant re-design shortened the fin and the "autoland" effect was lost. It certainly didn't do that when I flew it, as anyone who suffered any of my Victor landings would attest!
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the stick push on the 125 came in with the longer fuselages - 800 onwards?
Thence is fuselage length (wing-tailplane distance) a factor in the choice of a ‘T’ tail?
Thence is fuselage length (wing-tailplane distance) a factor in the choice of a ‘T’ tail?
The long fuselage came into service with the 600 series 125, the 700 series being essentially a cleaned up 600 but with the Garrett fan engines. These 'stretched' variants had the fuselage length increased forward of the wing root leading edge (ie the wing - tailplane distance was the same as the earlier variants).
AIRC neither were fitted with a stick push system.
The 800 series and later (800XP, 1000), of course, have a very different (totally redesigned) wing to the earlier aircraft, extended in span by some 4' 4.5" (as well as further fuselage extensions). I would guess that this new wing fundamentally altered the stalling characteristics, hence the stick push system?
Last edited by ExAscoteer; 21st Jan 2013 at 23:13.
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Never posted on this forum before bur, here goes. I have always understood, like Dan Winterland, that a major disadvantage of tail mounted engines was the extra weight to compensate for so much concentrated on the (almost) centre line. An additional disadvantage is that, to keep the cg where it should be, the wings had to be a long way back thus reducing the tail moment. This requires a larger stabiliser to maintain its required power. Thus more drag. You have to admit the VC10 tailplane is a bit big. The BAC111 accident taught us that T tails are prone to locked-in stalls. There is always that danger despite some getting away with it. Hence the requirement to have a recovery parachute during trials of such configurations.
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Pontifex et al,
No, I remember seeing the structural drawing for the 1-11's tailplane and being surprised to see that it was originally called out for the VC-10. Must have been for the inner member only as the 1-11's tail span is given here as 29 ft 6 inches, while the VC-10's is given as 43 ft 10 inches.
No, I remember seeing the structural drawing for the 1-11's tailplane and being surprised to see that it was originally called out for the VC-10. Must have been for the inner member only as the 1-11's tail span is given here as 29 ft 6 inches, while the VC-10's is given as 43 ft 10 inches.
Last edited by ICT_SLB; 31st Jan 2013 at 02:08.
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high tail is best....
Here's a summary of why the high tail on the C-141 (It saved 7800 lb TO weight)
Google this AIAA paper:
Effect of horizontal stabilizer vertical location on the design of large transport aircraft Byrnes, Hensleigh, Tolve
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Google this AIAA paper:
Effect of horizontal stabilizer vertical location on the design of large transport aircraft Byrnes, Hensleigh, Tolve
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Last edited by peter kent; 8th Sep 2013 at 01:26. Reason: clarification