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 post29 Dec 2015, 19:00

tincansailor wrote:
Remember the Soviets designed the MIG-15 has an interceptor to take down the high flying B-36. That's why the armament on the MIG-15 was so heavy. Two 23mm, and one 37mm cannon. The 37mm was devastating when it hit, but it's slow rate of fire made it less likely to score a hit on a fighter. That was the same reason the Germans put four 30mm cannon on the ME-262. It was meant to kill B-17's & B-24's not P-51's.

In Korea a Chinese tactic was to form up a large group of MIG-15's at over 45,000 ft. where the F-86's couldn't reach and then dive down in mass on a formation of Saber jets. They'd make one pass and head back up stairs avoiding a furball. It was a late WWII tactic used by ME-262's. Our pilots called them "Roller Coasters". Late Korean War Sabers could climb higher and surprised the Chinese who thought they were safe at 45k.


i know Mig-15 work better than F-86 at high altitude , iam still very surprised that it can cruise at 45- 50K feet since mig-15 have really bad T/W and top speed performance compared to modern fighter , and VK-1 engine doesnt even have afterburner mode
an F-16 with drag index of 100 cannot even reach 50K feet at full mil power
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basher54321

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Unread post29 Dec 2015, 19:42

eloise wrote:i know Mig-15 work better than F-86 at high altitude , iam still very surprised that it can cruise at 45- 50K feet since mig-15 have really bad T/W and top speed performance compared to modern fighter , and VK-1 engine doesnt even have afterburner mode
an F-16 with drag index of 100 cannot even reach 50K feet at full mil power


Does it have a bad TW ratio at 50,000ft? - If the MiG-15 turbojet could allow it to maintain level flight at max power (clean?) then it is clearly pretty good if it is similar to a clean F-16 in MIL with a turbofan.

You could take from that high altitude cruise has been less of a priority since as you can see an F-16 can cruise with load but has to be done with an afterburner setting.

btw DI 100 would be near 2 x 370 drop tanks + ECM Pod + 4 missiles - Pretty sure the MiG-15 never came close to that loadout.


To add - in Yefim Gordons MiG-15 book there are several accounts from a 1953 exploitation of the MiG-15bis by the USAF, and they seem to settle on a ceiling of ~51,000ft. (Loadout not mentioned)
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tincansailor

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Unread post29 Dec 2015, 21:58

basher54321 wrote:
eloise wrote:i know Mig-15 work better than F-86 at high altitude , iam still very surprised that it can cruise at 45- 50K feet since mig-15 have really bad T/W and top speed performance compared to modern fighter , and VK-1 engine doesnt even have afterburner mode
an F-16 with drag index of 100 cannot even reach 50K feet at full mil power


Does it have a bad TW ratio at 50,000ft? - If the MiG-15 turbojet could allow it to maintain level flight at max power (clean?) then it is clearly pretty good if it is similar to a clean F-16 in MIL with a turbofan.

You could take from that high altitude cruise has been less of a priority since as you can see an F-16 can cruise with load but has to be done with an afterburner setting.

btw DI 100 would be near 2 x 370 drop tanks + ECM Pod + 4 missiles - Pretty sure the MiG-15 never came close to that loadout.


To add - in Yefim Gordons MiG-15 book there are several accounts from a 1953 exploitation of the MiG-15bis by the USAF, and they seem to settle on a ceiling of ~51,000ft. (Loadout not mentioned)


Interesting analyzes comparing a MIG-15 with an F-16. As far as I know a MIG-15 load out was just fuel, and ammo. I don't even think they carried drop tanks, the Sabers did. Your point about high altitude cruise is very relevant to the strategic conditions of the Korean War. The UN Air Forces had destroyed all the Communist Air Field in N Korea. The Sabers flew right up to the Chinese Border to keep them from extending their air cover south. If they allowed them to do that they could have rebuilt their air bases, and used tactical aircraft to attack our ground troops. So the air war in MIG ally developed as a pure fighter battle with both sides going for an altitude advantage.

What impresses me most about the Saber was it's ability to fight on long past it's time. It fought over the Taiwan Straights in 1958 with brand new sidewinders against MIG-17's and came out on top. In the 60s Pakistani Sabers successfully fought Indian MIG-21s. The Saber was doing to the supersonic radar, and missile equipped MIG-21 over South Asia what the MIG-17 did to the F-100 over North Vietnam.

I can only imagine what Israeli pilots would have done with Sabers in the 50s. The Saber was IMHO superior to the British and French Fighters Israel was using at the time. Of course the air combat in the Middle East was at much lower altitudes then over Korea. Both sides fighters spent most of their time intercepting low level attacks on their ground troops. Totally different conditions then at 40,000ft in MIG Ally. Well that never was, and the USAF had retired the Saber by Vietnam so we'll never know how it would have faired in that environment, (probably not to well). at any rate it was just an amazing aircraft.
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basher54321

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Unread post29 Dec 2015, 22:35

On the drop tanks Yefim does mention they were sparse at the start of the war and this guy has his take on it


— How often did you use drop tanks?
We used them on every mission we flew. And we always dropped them, regardless of if there was a fight or not. There was no problem with quantity of drop tanks, but their quality was horrific. Kerosene simply leaked in streams. Sometimes these tanks would snap due to the air pressure in midflight.


— But if you dropped tanks before they were fully expended, you might not have enough fuel to return.
You are right. We often landed with a zero fuel left. I once landed, taxied to the taxiway, and my engine stalled. It was not due to the bad tank quality, but due to the overall situation.

http://www.airforce.ru/history/cold_war ... er5_en.htm


I would say earlier MiG-15s are about 3,000ft lower on max ceiling - tanks might reduce that further.

The Mystere IV / Hunter F.6 might be considered comparable to some variants I guess - although personally give me the F-104 any day for the late 50s fights with the Vulcan (where it was still fitted) - you can keep the Super Sabre :)
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eloise

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Unread post30 Dec 2015, 00:40

basher54321 wrote:
Does it have a bad TW ratio at 50,000ft? - If the MiG-15 turbojet could allow it to maintain level flight at max power (clean?) then it is clearly pretty good if it is similar to a clean F-16 in MIL with a turbofan.

both mig-15 and f-16 have fixed intake so their pressure recovery at high speed should be similar ( similar thrust lost rate )
and turbofan engine still have the jet engine core inside so it not like they lose all the thrust at altitude
Mig-15 engine push out 26.5 kN of thrust
While F-16 engine can generate 76.3 kN of thrust in Military setting
that is almost 3 times more thrust

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basher54321

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Unread post30 Dec 2015, 01:04

eloise wrote:
Mig-15 engine push out 26.5 kN of thrust
While F-16 engine can generate 76.3 kN of thrust in Military setting
that is almost 3 times more thrust



Those thrust ratings only apply at sea level if anywhere - especially when comparing turbojet and turbofan. The actual difference varies greatly with thrust curves I have seen.

This is an estimation of thrust output for the PW-229 that might help you.

Thrust.JPG
PW-229 MIL
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eloise

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Unread post30 Dec 2015, 14:28

basher54321 wrote:Those thrust ratings only apply at sea level if anywhere - especially when comparing turbojet and turbofan. The actual difference varies greatly with thrust curves I have seen.

This is an estimation of thrust output for the PW-229 that might help you.

Thrust.JPG

do you have similar graph for tuborjet engine ?
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basher54321

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Unread post30 Dec 2015, 16:35

eloise wrote:do you have similar graph for tuborjet engine ?



Ha - currently nothing as good or as relevant to the above unfortunately - someone has to reverse engineer them. Eagle Dynamics did a HD MiG-15bis recently but not sure if they go to that level of fidelity without asking.

From that the MiG-15 engine only needs to put out as a guess 1500 - 2000 lbs thrust for its weight @ m0.9 50,000 ft

The 229 might look lack lustre up high but the requirements probably centred on better fuel consumption and lower level performance than past engines.

Here is something interesting - taking figures from http://www.f-16.net/f-16_versions_article12.html

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

P100-PW-229
SL Max AB Rating = 29,100 lbs
Max AB thrust @ M2, 35,000ft = ~16,000 lbs


When I say differences in turbojet/turbofan I mean typically older Turbojets put out more thrust at high Alt/ Mach to give those interceptors the required performance. But that doesn't mean you cannot create a turbofan and optimise it to perform better at high Mach & altitude (MiG-31 perhaps). Overall the thrust output would be more engine specific than whether its a turbofan or turbojet.
Even the J-58s that powered the SR-71 were not pure turbojets and had a degree of bypass air (Leaky turbojet as TEG called it IIRC)
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alfakilo

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Unread post31 Dec 2015, 01:43

charlielima223 wrote:Unfortunately the F-104 isn't so much recognized for its service record but rather its checkered past with accidents and crashes. Its more known for its reputation for being difficult to fly.

I always wondered though. If all things being equal, an F-104 version with FBW. How would that aircraft fair?


My guess is that the date of that pic is fairly early in the GAF training program at Luke, give the C-124 in the background. We kept two jets in excellent condition for use in open house events at other bases (243 and 269). This was likely one such event.

Not every 104 user had a "checkered" history with the jet. By the time the G model came along (the a/c in the pic), a lot of the problems had been worked out.

I didn't consider the jet difficult to fly, no more so than the F-4, for example. Certainly, pilots had to pay attention, but that's the case with any high performance airplane.

One major aspect of F-104 flight characteristics that contributed to its reputation (the same is true of the F-101) was the pitch up issue at high angles of attack. I doubt that FBW would have had any effect on that. It had a very high roll rate, and the same comment about FBW goes here as well. My thought is that FBW may have contributed to a reduction in gross weight and thereby improved the thrust to weight numbers, but that's about it.
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johnwill

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Unread post31 Dec 2015, 04:27

Knowing nothing about F-104 flight characteristics, I can believe FBW could improve on them. High AoA pitch up has been mentioned, and an AoA limiter could go a long way toward eliminating that. AoA limiters are not fool-proof (can be defeated at very low airspeeds), but are fool-resistant. High roll rates have been mentioned. FBW can tailor the roll response to a more consistent level, so the airplane would roll about the same no matter the speed / altitude condition. FBW could easily have an aileron / rudder interconnect to reduce any yaw from rolling. With its very high speed range, I'm guessing the -104 stick force per g varies quite a bit. A FBW g-command system can smooth out the pitch axis so it feels the same just like the roll axis and include a g limiter. A g-roll limiter could reduce roll rates at high g to prevent structural overload. FBW allows a greater cg range, with reduced trim drag for longer range and reduced structural loads for lower weight (which alfakilo mentioned).
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madrat

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Unread post31 Dec 2015, 07:28

FBW on the F-104 using its T-tail would be boring. Be creative, think V.

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basher54321

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Unread post31 Dec 2015, 12:38

I'm sure I have read in the past the pitch up issue was related to the T Tail and wing position - cant find the quote though.

An AOA limiter had to be better than the stick shaker you would think - the manual does describe a few situations where the shaker doesn't even come on.
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eloise

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Unread post31 Dec 2015, 14:17

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? :?
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Unread post31 Dec 2015, 14:39

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


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.
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vilters

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Unread post31 Dec 2015, 14:43

Here is an example of a F-104 pitch-up crash.

https://www.youtube.com/watch?v=FJtTYzUIwBQ

If the video does not work search YouTube for " F-104 crash ". 41 seconds from 1983
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During the study phase a "V" tail version was being looked at but the "T" tail won.
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