F-104 Supersonic T-Tail Trim Drag & AOA

Cold war, Korea, Vietnam, and Desert Storm - up to and including for example the A-10, F-15, Mirage 200, MiG-29, and F-18.
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kdub104

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Unread post01 Feb 2019, 20:00

Is there an advantage of the F-104's T-Tail regarding supersonic trim drag?

The design point of the 104 is for supersonic flight. But what if the elevator was positioned lower on the fuselage like most other jets? Would there be less trim drag at supersonic speeds?

Does the trapezoidal design already minimize the drag or does the T-Tail take this into consideration?

Gums as T-Tail experience on the Voodoo... what say you?
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sprstdlyscottsmn

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Unread post01 Feb 2019, 20:35

The only way a T-Tail improves trim drag is by allowing it to be mounted further aft than it would be on the fuselage.
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Unread post02 Feb 2019, 01:01

Salute!

Actually, the T-tail is a bit "cleaner" than the low, traditional slab/stab WRT drag. It also has a more "robust" effect upon longitudinal aircraft pitch moments.

I have to ask my test pilot buddies about the trapezoidal surfaces. Ihave a feeling it is more bout transonic and supersonic and RCS than other aspects. To be honest, about the zipper, I just wnted to fly the damned thing!!!

The Voodoo pitchup had to do with the distance between the t-tail and main wing and such. So at certain AoA the downwash from the main wing reversed the air flow over the T-tail. So the sucker would "dig in", and the elevator was eliminated from the equation. For those who never flew it, I can tell ya that subsonic the plane gave plenty of warning. Burble was there at slow speeds most time we were at endurance speeds, and it got pronounced if we pulled back. At higher speeds we would get buffetand wing rock. If you kept pulling you departed! Most guys prolly departed due to rate. The limiter and physical warnings could not help. So we had a "rate" pusher that likely helped many pilots.

Gotta go.

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kdub104

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Unread post02 Feb 2019, 18:52

sprstdlyscottsmn wrote:The only way a T-Tail improves trim drag is by allowing it to be mounted further aft than it would be on the fuselage.


What is the advantage moving it further aft of the fuselage?
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kdub104

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Unread post02 Feb 2019, 18:53

What effect does thrust vectoring have regarding trim drag? Is there a significant reduction?
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sferrin

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Unread post02 Feb 2019, 18:53

kdub104 wrote:
sprstdlyscottsmn wrote:The only way a T-Tail improves trim drag is by allowing it to be mounted further aft than it would be on the fuselage.


What is the advantage moving it further aft of the fuselage?


It can be smaller. And maybe there's no room for it on the fuselage (see F-35 for example).
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kdub104

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Unread post03 Feb 2019, 00:36

High Alt AOA

I PM'ed Walt BJ... waiting for him to show up.

70,000ft and M2.0

KIAS was 310-315

Trying to understand how the 104 flew with such "little" airspeed or flow over the wings. We see the 104 flying at airshows with takeoff flap even well above 450kts. Takeoff flaps were good for 550/M1.8.

What am I missing here?
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alfakilo

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Unread post03 Feb 2019, 05:35

310-315 KIAS is pretty slow. The only time I ever saw that speed was accelerating on takeoff and slowing down in the break for landing.
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kdub104

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Unread post06 Feb 2019, 22:57

alfakilo wrote:310-315 KIAS is pretty slow. The only time I ever saw that speed was accelerating on takeoff and slowing down in the break for landing.



What model did you fly? G model?

At FL730 in the light "A" with probably 3000lbs gas saw a KIAS of 310. Walt BJ isn't here to comment but he stated it was a head of the L/D curve. Yet he didn't use any flap and had a comfortable cruise way up there.

How is this possible?

From your experience alfakilo, how does the 104 fly "clean" with very light fuel load at 310 KIAS? How much AOA is there?
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alfakilo

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Unread post07 Feb 2019, 14:51

I flew the G at Luke.

I don't understand the question about something being "possible".

At 310KIAS and flaps up, the airplane will maintain level flight but will not have an abundance of available g! At Luke, we flew initial at 350KIAS with the takeoff flaps out. The jet will fly quite nicely at that speed with the flaps up but things tend to get interesting in this situation when the pilot begins the pitchout. It was not unusual to get a pitch up due to the added g for the level steep banked turn. Not particularly dangerous but definitely is something the guy won't likely do again.

Since the G was primarily a fighter-bomber, we didn't do much work at altitude. Consequently, we tended to think IAS rather than mach when it came to speed issues.
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sprstdlyscottsmn

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Unread post07 Feb 2019, 15:55

Well that seems to clear it up. The 310 KIAS statement was about flying in transit at FL730. Not much G happening up there anyway.
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alfakilo

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Unread post07 Feb 2019, 17:07

kdub104 wrote: We see the 104 flying at airshows with takeoff flap even well above 450kts. Takeoff flaps were good for 550/M1.8.


Minor point, but the takeoff flap limit for the G is 450KIAS, and that is the model most likely seen at airshows. As for mach, the F limit was .85 and the TF was .8.
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Unread post07 Feb 2019, 21:33

Thanks alfakilo.

The jet was rated at 7.33G. Could you put higher G on the jet?

I read the S version had a higher G limit about 8.

I don't suppose Mach 2 G limits were that high. I understand the F-14 could pull 9G at Mach 2.

G limitations were caused by low AOA or C/G limits?


My father was the first in his class to go Mach 2 (CF-104 out of CFB Cold Lake Class of 69'). Was this also a part of the training at Luke?
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Unread post07 Feb 2019, 21:47

kdub104 wrote:I understand the F-14 could pull 9G at Mach 2.

The F-14 was never RATED for more than 7.5G at any speed, and the A-model with glove vanes was noted for the ability to pull 7.5G at Mach 2 and hold 7.5G all the way down to corner velocity.

The F-14 was KNOWN to pull as many as 12G, speed/Alt unknown.

The F-14 COULD pull any G the pilot asked for so long at there was enough airflow over the wings. It had no computer controlled limiters in any way shape or form for G. If a pilot flying 2.3M at 36,000 braced himself and put the stick in his lap he could rip the plane apart.
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alfakilo

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Unread post07 Feb 2019, 22:11

kdub104 wrote:The jet was rated at 7.33G. Could you put higher G on the jet?

My father was the first in his class to go Mach 2 (CF-104 out of CFB Cold Lake Class of 69'). Was this also a part of the training at Luke?


It wasn't hard to exceed the g limit. Those who flew the jet aggressively probably had an over-g every now and then, unintentional but it happened.

Mach 2 limit was 4.5g max.

The Mach 2 demonstration was part of the initial checkout as I recall. For our low level missions, there wasn't much point to it other than a gee-whiz moment. Fast as far as I was concerned was IAS, not mach. Warp 9 at low altitude was exhilarating, back then few jets could sustain speeds in excess of 700KIAS. Our Gs could do that easily as long as we weren't loaded down with external stores.
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