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#1
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Why are (some) delta wings stable without a horizontal tail?
I remember coming across the answer somewhere, but I've lost it.
Anyone know? TIA |
#2
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Why are (some) delta wings stable without a horizontal tail?
"xerj" wrote in message ... I remember coming across the answer somewhere, but I've lost it. Anyone know? TIA The aerodynamic factors inherent in a tailless delta wing planform are complex, but basically the trailing edge of the wing has designed upsweep to compensate for any longitudinal negative pitch moment produced by the difference between the cg and the aerodynamic center of lift normally handled by the horizontal tail downforce. Dudley Henriques |
#3
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Why are (some) delta wings stable without a horizontal tail?
The aft edge of a delta wing is further aft than ailerons would be on a
conventional aircraft. The elevons on the trailing edge both work in the same direction for elevator action and in opposite directions for roll. The two inputs are combined when executing a bank entry with a pitch change at the same time. All successful delta winged aircraft are basically stable if handled with care. Many have pitch dampers to assist in stability. The B-58 delta I flew had roll, pitch, and triple-redundant yaw dampers. When things went right it was an extremely stable platform. In flight refueling was a piece of cake. But when things went wrong it could eat your lunch. One issue that might confirm your suspicions that a delta is not always stable is "elevon coupling" during a landing attempt. If you're sinking towards the runway too fast and try to correct too quickly you find one area of instability. To raise your nose quickly you must move the stick back quite a bit. That raises both elevons. Elevons are part of the delta wing. Raising them temporarily loses lift. So, by moving the stick aft quickly the aircraft descends due to loss of lift until the nose raises enough to stop the increased descent. When you have the desired pitch attitude and move the stick back towards neutral the elevons come down to a relatively streamlined position further increasing lift. Whoops, ballooning above the runway. Try to correct by pushing the stick forward to lower the nose causes the elevons to come down (like adding flaps). So while your nose is coming down the elevons have increased the lift adding to the balloon. I've seen guys going down the runway like a jackrabbit due to elevon coupling. I had it happen to me on the checkout ride in a TB-58 and thought I wouldn't be cleared to go "solo" (pilot) in the B model which doesn't have an instructor pilot position. But my following landings were OK and the instructor (in debriefing) asked me if I had previously thought "elevon coupling" was an old wives tale. I had to admit he was right. He asked what I'd learned. I said I learned if I can't control the flare without making rapid large pitch inputs it's time to go around. He said "Go forth and fly, Grasshopper, because you have learned a valuable lesson". (a little poetic input) -- Darrell R. Schmidt B-58 Hustler History: http://members.cox.net/dschmidt1/ - "xerj" wrote in message ... I remember coming across the answer somewhere, but I've lost it. Anyone know? TIA |
#4
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Why are (some) delta wings stable without a horizontal tail?
Wow, Darrell I can just picture that elevon coupling with the way you've
explained it. Tricky stuff. The plane would be thinking "what the hell do you want me to do? Make up your mind!" as you oscillate down the glidepath. Incredible looking plane that you flew! |
#5
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Why are (some) delta wings stable without a horizontal tail?
Thanks Dudley.
Make sense now. |
#6
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Why are (some) delta wings stable without a horizontal tail?
"xerj" wrote in message ... Thanks Dudley. Make sense now. No sweat. Darrell hit on some of the operational issues for you. Also in fighters like the 106 and the Mirage, you could grab a yard of stick above corner, rotate the lift vector, and bleed the Ps down with the drag curve so fast that overshoot became a real issue for a shooter sitting on a tracking solution. It was Lippitsch I think who pioneered the delta without a tail. The idea was popular for a while, but the extremely high landing speeds made handling the airplane a real challenge. The whole deal centered around the trailing edge design. Putting the horizontal stab back on the airplane (Mig 21/blown flaps etc) helped the low speed/angle of attack situation on landings, but the delta remains even today as a huge induced drag machine into the left side of the envelope. Power control and front side/back side power curve issues on final are still major areas of concern for the deltas. Darrell knows......that arrowhead of an airplane he flew was one hell of a piece of equipment :-)) Dudley Henriques |
#7
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Why are (some) delta wings stable without a horizontal tail?
"Dudley Henriques" wrote in message k.net... "xerj" wrote in message ... Thanks Dudley. Make sense now. No sweat. Darrell hit on some of the operational issues for you. Also in fighters like the 106 and the Mirage, you could grab a yard of stick above corner, rotate the lift vector, and bleed the Ps down with the drag curve so fast that overshoot became a real issue for a shooter sitting on a tracking solution. It was Lippitsch I think who pioneered the delta without a tail. The idea was popular for a while, but the extremely high landing speeds made handling the airplane a real challenge. The whole deal centered around the trailing edge design. Putting the horizontal stab back on the airplane (Mig 21/blown flaps etc) helped the low speed/angle of attack situation on landings, but the delta remains even today as a huge induced drag machine into the left side of the envelope. Power control and front side/back side power curve issues on final are still major areas of concern for the deltas. Darrell knows......that arrowhead of an airplane he flew was one hell of a piece of equipment :-)) Dudley Henriques Yeah, Dudley, I was an instructor in the TB-58 towards the end and we demonstrated high sink to the new pilots. We'd slow well below approach speed in level flight and raise the nose to stay level. We'd slowly add power up to 100% but stay out of afterburners. Pretty soon we'd hit high drag/high sink and I'd have the student note his vertical speed. We "looked" level but were descending at nearly 4,000 FPM. He could still change the pitch and roll with apparently normal response but he couldn't stop sinking until he could increase the speed. We practiced at medium altitudes where you could lower the nose, accelerate and fly out of the danger area. The main point of the exercise was to show how important it was during approach to landing to keep the speed within normal boundaries. On final approach there's not enough altitude to lower the nose and fly out of it. If you ever got into high sink on final you'd have to light all four afterburners and hope they all lit off. If one didn't light at that very low speed you'd not have enough control to handle it. Especially if it was an outboard engine that didn't light off. |
#8
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Why are (some) delta wings stable without a horizontal tail?
Hi Darrell;
Don't know if you got to the T38 or went through in the T-Bird, but what you are describing isn't all that far off from what can happen to you in the 38. Of course the Talon is a trapezoidal low aspect wing, but on final, if you weren't careful, you could set up a sink that was unrecoverable. I've seen 6000 FPM on the VSI in the 38. The Hustler must have come down like a brick with all that hardware hanging under the wing :-) Getting one of these high performance birds way back in the coffin corner killed many an otherwise descent pilot. I'm sure you remember that kid out at Edwards in the 100 who got into the backside so deep he ended up in the corner and couldn't power out without reducing the angle of attack and didn't have the room to generate any nose rate in pitch at all. I'll bet I've seen that film clip a thousand times. It's still the best lesson for keeping the final approach speed where it belongs that I've ever seen. I guess in the Hustler you went backside and into the left corner mighty fast :-)) Dudley "Darrell S" wrote in message news:Cqz_f.186$Oe2.34@fed1read07... "Dudley Henriques" wrote in message k.net... "xerj" wrote in message ... Thanks Dudley. Make sense now. No sweat. Darrell hit on some of the operational issues for you. Also in fighters like the 106 and the Mirage, you could grab a yard of stick above corner, rotate the lift vector, and bleed the Ps down with the drag curve so fast that overshoot became a real issue for a shooter sitting on a tracking solution. It was Lippitsch I think who pioneered the delta without a tail. The idea was popular for a while, but the extremely high landing speeds made handling the airplane a real challenge. The whole deal centered around the trailing edge design. Putting the horizontal stab back on the airplane (Mig 21/blown flaps etc) helped the low speed/angle of attack situation on landings, but the delta remains even today as a huge induced drag machine into the left side of the envelope. Power control and front side/back side power curve issues on final are still major areas of concern for the deltas. Darrell knows......that arrowhead of an airplane he flew was one hell of a piece of equipment :-)) Dudley Henriques Yeah, Dudley, I was an instructor in the TB-58 towards the end and we demonstrated high sink to the new pilots. We'd slow well below approach speed in level flight and raise the nose to stay level. We'd slowly add power up to 100% but stay out of afterburners. Pretty soon we'd hit high drag/high sink and I'd have the student note his vertical speed. We "looked" level but were descending at nearly 4,000 FPM. He could still change the pitch and roll with apparently normal response but he couldn't stop sinking until he could increase the speed. We practiced at medium altitudes where you could lower the nose, accelerate and fly out of the danger area. The main point of the exercise was to show how important it was during approach to landing to keep the speed within normal boundaries. On final approach there's not enough altitude to lower the nose and fly out of it. If you ever got into high sink on final you'd have to light all four afterburners and hope they all lit off. If one didn't light at that very low speed you'd not have enough control to handle it. Especially if it was an outboard engine that didn't light off. |
#9
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Why are (some) delta wings stable without a horizontal tail?
Getting one of these high performance birds way back in the coffin corner
killed many an otherwise descent pilot. Doesn't a high sink rate sort of =define= a descent pilot? Jose -- The price of freedom is... well... freedom. for Email, make the obvious change in the address. |
#10
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Why are (some) delta wings stable without a horizontal tail?
"Jose" wrote in message m... Getting one of these high performance birds way back in the coffin corner killed many an otherwise descent pilot. Doesn't a high sink rate sort of =define= a descent pilot? Jose You know Jose, when you make a post like this to someone, you can go one of two ways. You can stick a smilie on the end of it demonstrating the good nature intended and make a friend, or you can just be a pedantic bore and lose one. :-) Dudley Henriques |
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