F-104 with FBW

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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eloise

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Unread post31 Dec 2015, 15:09

basher54321 wrote:I would expect that to be a static thrust Sea Level figure - so in flight at speed the actual Max thrust at sea level would probably be higher.

i wonder at speed what would be the max thrust at sea level of F-100
seem like with that sort of performance, F-16/79 acceleration at high mach, cruise altitude and top speed would be alot better than F-16 equipped with F-100/F-110 engine series
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basher54321

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Unread post31 Dec 2015, 15:15

One book I have states the T tail was chosen for best control & stability and low drag for it intended flight envelope

Apparently the pitch up is caused by turbulent air from the wing & Fuselage that causes the T Tail to lose control authority at a certain AOA. (>15 degrees?)
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basher54321

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Unread post31 Dec 2015, 15:27

eloise wrote:i wonder at speed what would be the max thrust at sea level of F-100
seem like with that sort of performance, F-16/79 acceleration at high mach, cruise altitude and top speed would be alot better than F-16 equipped with F-100/F-110 engine series



Yes potentially it could have had some high altitude benefits - note the only F-104A type that could cruise at 70,000ft (in pilot accounts) was powered by a similar J79-GE-19.

The PW-200 on the other hand was lighter more efficient and better in the intended flight envelope - if this is anything to go by put out ~29,000 lbs of thrust at Sea Level.

pw-200.JPG
PW-200 Max
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eloise

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Unread post31 Dec 2015, 15:40

this bring up another question, why did all modern fighter change from turbojet to turbofan engine and from variable intake to fixed intake ? :?
and what is the actual factor that limit top speed of F-35? the engine or intake? do you think ADVENT will change it significantly?
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vilters

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Unread post31 Dec 2015, 16:19

Weight. The F-16 is build as a dog-fighter. less weight was a critical factor for turning performance.
The fixed inlet is simple and the weight for a variable intake was not worth it.

Top speed of an F-16 is limited by canopy plexi heating anyway so no need to try and go beyond.

Why Turbofan? For fuel consumption and range/pound of fuel.

Turbojet has its advantages at high speeds and flight levels.
But when you hang a democratic amount of weight and/or stores on the jet, your speed and altitudes are limited, and you are left with an uneconomical engine.

Fully armed jets cruise at combat speeds and flight levels, and turbofans are the way to go for fuel consumption.
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johnwill

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Unread post31 Dec 2015, 17:36

eloise wrote:
basher54321 wrote:
J79-GE-17X
SL Max AB Rating = 17,900 lbs
Max AB thrust @ M2, 35,000ft = 20,840 lbs


:shock: so J79 have more thrust at high altitude and speed than at sea level? what the hell? :?


That explains why a J-79 powered F-16 test airplane had a higher top speed than the normal F-16A with the F100 engine.
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eloise

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Unread post31 Dec 2015, 18:24

johnwill wrote:That explains why a J-79 powered F-16 test airplane had a higher top speed than the normal F-16A with the F100 engine.

what is the top speed of F-16/79?
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johnwill

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Unread post31 Dec 2015, 20:27

To my knowledge, the F-16/79 was never taken to max speed, stopping at 2.05 mach, which it attained rather easily. The F100 powered F-16A struggled to reach 2.0.

Why stop at 2.05? There was no clearance for flutter, stability & control, structural loads, propulsion, or any other discipline. To obtain those clearances would have been very expensive and time consuming. In those days, canopy heating was not a concern.

The installation of the J-79 included a new inlet, optimized for J-79 airflow requirements. It could have also been optimized for higher mach, but I don't know if it was. That inlet could have made a big difference in high mach performance, as the normal F-16 inlet is optimized for 0.8 to 1.2 mach, where it flies 99% of the time.
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eloise

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Unread post31 Dec 2015, 20:34

johnwill wrote:To my knowledge, the F-16/79 was never taken to max speed, stopping at 2.05 mach, which it attained rather easily. The F100 powered F-16A struggled to reach 2.0.

The installation of the J-79 included a new inlet, optimized for J-79 airflow requirements. It could have also been optimized for higher mach, but I don't know if it was. That inlet could have made a big difference in high mach performance, as the normal F-16 inlet is optimized for 0.8 to 1.2 mach, where it flies 99% of the time.

I see, seem like F-16/79 can make better interceptor than F-16 ( higher altitude, speed)
would F-16/79 cruise at higher altitude than normal F-16? ( since the engine is more optimize for high altitude, and lower air density reduce fuel consumption)
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vilters

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Unread post31 Dec 2015, 22:53

eloise wrote:
johnwill wrote:To my knowledge, the F-16/79 was never taken to max speed, stopping at 2.05 mach, which it attained rather easily. The F100 powered F-16A struggled to reach 2.0.

The installation of the J-79 included a new inlet, optimized for J-79 airflow requirements. It could have also been optimized for higher mach, but I don't know if it was. That inlet could have made a big difference in high mach performance, as the normal F-16 inlet is optimized for 0.8 to 1.2 mach, where it flies 99% of the time.

I see, seem like F-16/79 can make better interceptor than F-16 ( higher altitude, speed)
would F-16/79 cruise at higher altitude than normal F-16? ( since the engine is more optimize for high altitude, and lower air density reduce fuel consumption)



If both airframes are "clean" (no external stores), yes.

Hang stores on them and the turbofan wins again.
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eloise

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Unread post31 Dec 2015, 23:23

vilters wrote:

If both airframes are "clean" (no external stores), yes.

Hang stores on them and the turbofan wins again.

Not at high speed and high altitude since F100 ,F110 engine lose significant amount of thrust at high altitude, speed , up to a point then the thrust of turbofan engine is significant smaller than thrust of turbojet one
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alfakilo

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Unread post31 Dec 2015, 23:35

basher54321 wrote:One book I have states the T tail was chosen for best control & stability and low drag for it intended flight envelope

Apparently the pitch up is caused by turbulent air from the wing & Fuselage that causes the T Tail to lose control authority at a certain AOA. (>15 degrees?)


Or to say it a different way...above a certain AOA, the wing downwash and airflow vortices stream up and then down on to the top of the horizontal stabilizer, thereby pushing the tail down and the nose up.

The "shaker" and "kicker" systems did a pretty good job of giving an advance warning to the pilot that this AOA was being reached...however, both could be activated by the rate of AOA build up caused by a rapid application of back stick...the AOA in this case would increase so rapidly that the shaker would be followed quickly by the kicker, too fast for the pilot to react. The result was a "rate kicker". For example, coming in to the break for landing with the flaps up and a relatively slow speed (say, 300KIAS)...if the pilot rolled into the break and then pulled back on the pole aggressively, he was often in for an exciting ride as the kicker would repeatedly fire until the pilot unloaded the stick. For this reason, we used maneuver flaps and a faster speed when pitching out in the break.

We sometimes saw rate kickers on the pull out from a low angle strafe pass...this could get really exciting because of the descending flight path and low altitude.

Could a FBW mod have minimized this? I don't know.
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madrat

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Unread post01 Jan 2016, 01:49

The V tail would have extended control surfaces into smoother airflow. An all moving tail either side of the exhaust, like on F-16 would have been far superior. Adding FBW was already an expensive undertaking, probably more expensive than offering better control surfaces. By the time you changed anything, including the cramped internal space to add FBW, you essentially may be cheaper building new airframes. May as well eliminate the original sin at that point, too.

The F-20A was a good example that old designs could be tweaked to keep them relevant. F-4's owned by Israel almost went with a new engine. Imagine F-104 getting that engine, too. With Lavi cancelled no chance it would happen.
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basher54321

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Unread post01 Jan 2016, 13:40

eloise wrote: Not at high speed and high altitude since F100 ,F110 engine lose significant amount of thrust at high altitude, speed , up to a point then the thrust of turbofan engine is significant smaller than thrust of turbojet one


What you say is true - and you might be able to get away with 2-4 missiles - however was there any requirement for this in the 70s? - not really . Nuclear bombers had to go low level due to SAMs (bye bye XB-71) . Have a book of RAF F-4M Phantoms (Turbofan powered) doing nothing but low level interception practise over Germany in the 70s/80s.

The only potential high altitude intercept missions would be against the MiG-25R or SR-71 and even then getting up there to fire an AIM-9 seems pretty unlikely to me. The F-14A by accounts could lock up and fire on the MiG-25R due to its AWG-9/AIM-54 system even though it couldn't get as high - this was obviously seen as a better way of doing things.

The F-16 was put into service as a multirole aircraft with an A-G role as primary for the USAF (that is why there was no AIM-7 initially) - it would have gone in low level in a Cold War environment to penetrate radar. Also the majority of AG loadouts are limited to <M0.9 set by stores limits ( so Vilters would be correct in this context)
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Unread post01 Jan 2016, 15:32

alfakilo wrote:Or to say it a different way...above a certain AOA, the wing downwash and airflow vortices stream up and then down on to the top of the horizontal stabilizer, thereby pushing the tail down and the nose up.

The "shaker" and "kicker" systems did a pretty good job of giving an advance warning to the pilot that this AOA was being reached...however, both could be activated by the rate of AOA build up caused by a rapid application of back stick...the AOA in this case would increase so rapidly that the shaker would be followed quickly by the kicker, too fast for the pilot to react. The result was a "rate kicker". For example, coming in to the break for landing with the flaps up and a relatively slow speed (say, 300KIAS)...if the pilot rolled into the break and then pulled back on the pole aggressively, he was often in for an exciting ride as the kicker would repeatedly fire until the pilot unloaded the stick. For this reason, we used maneuver flaps and a faster speed when pitching out in the break.

We sometimes saw rate kickers on the pull out from a low angle strafe pass...this could get really exciting because of the descending flight path and low altitude.



Thanks for that write up and Happy New Year
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