What Would the F-108 Have Flown Like

[KJ_Lesnick]

I'm wondering if anybody has any idea how the F-108 would have behaved from a maneuverability standpoint?

 

[Orionblamblam]

Real fast in a straight line. It was not designed to be a dogfighter.

 

[Lampshade111]

Couldn't have been worst than a Mig-25 I would imagine.

I understand a version of the F-14 (when it was still the VFX) was offered to the USAF as an interceptor at one point. Although details are rather rare, in fact I only have one photo of it. When exactly did the USAF decide they didn't need a true interceptor?

 

[KJ_Lesnick]

Lampshade,

I understand a version of the F-14 (when it was still the VFX) was offered to the USAF as an interceptor at one point. Although details are rather rare, in fact I only have one photo of it. When exactly did the USAF decide they didn't need a true interceptor?

That is a good question...

Anybody here know when did the USAF decided it didn't want or need the F-14 ADF?


KJ

 

[SOC]

I think the USAF decided it didn't need (or maybe didn't want to pay for) the AWG-9/AIM-54 combination. The F-14 proposed to the USAF would've retained both. It wasn't a direct F-15 competitor if I remember right, but maybe an F-106 replacement? Then again they could've both been competing with each other to a small degree, F-14s and F-15s in various guises were offered to both services.

 

[KJ_Lesnick]

What was the thickness/chord ratio of the F-108's wings assuming it's not classified or anything?

 

[F-14D]

I think the USAF decided it didn't need (or maybe didn't want to pay for) the AWG-9/AIM-54 combination. The F-14 proposed to the USAF would've retained both. It wasn't a direct F-15 competitor if I remember right, but maybe an F-106 replacement? Then again they could've both been competing with each other to a small degree, F-14s and F-15s in various guises were offered to both services.

Hey! It was a Navy plane! AF didn't want to buy those (F-4 was forced on them, A-3 had to be turned into B-66 to be acceptable, and although A-7 was really perfected by AF in the A-7D version, they had an unseemly haste to get rid of it). Besides, there was the perception that if any version of F-14 was used by AF, it would threaten funding for F-15. Given the climate of the times, this was probably correct.

 

[Rosdivan]

I think the USAF decided it didn't need (or maybe didn't want to pay for) the AWG-9/AIM-54 combination. The F-14 proposed to the USAF would've retained both. It wasn't a direct F-15 competitor if I remember right, but maybe an F-106 replacement? Then again they could've both been competing with each other to a small degree, F-14s and F-15s in various guises were offered to both services.

Hey! It was a Navy plane! AF didn't want to buy those (F-4 was forced on them, A-3 had to be turned into B-66 to be acceptable, and although A-7 was really perfected by AF in the A-7D version, they had an unseemly haste to get rid of it). Besides, there was the perception that if any version of F-14 was used by AF, it would threaten funding for F-15. Given the climate of the times, this was probably correct.

I believe I've also seen it mentioned before that the F-15 option was cheaper, while their was a spirit of "Ignorance is bliss" when presenting that fact without mentioning that F-14 with AIM-54 was far more effective.

Speaking of A-7s though, what happened to the A-7F info you kept promising?

 

[F-14D]

I think the USAF decided it didn't need (or maybe didn't want to pay for) the AWG-9/AIM-54 combination. The F-14 proposed to the USAF would've retained both. It wasn't a direct F-15 competitor if I remember right, but maybe an F-106 replacement? Then again they could've both been competing with each other to a small degree, F-14s and F-15s in various guises were offered to both services.

Hey! It was a Navy plane! AF didn't want to buy those (F-4 was forced on them, A-3 had to be turned into B-66 to be acceptable, and although A-7 was really perfected by AF in the A-7D version, they had an unseemly haste to get rid of it). Besides, there was the perception that if any version of F-14 was used by AF, it would threaten funding for F-15. Given the climate of the times, this was probably correct.

I believe I've also seen it mentioned before that the F-15 option was cheaper, while their was a spirit of "Ignorance is bliss" when presenting that fact without mentioning that F-14 with AIM-54 was far more effective.

Speaking of A-7s though, what happened to the A-7F info you kept promising?

The F-15 would have been cheaper to be a regular F-15, but to do the interceptor mission the F-14 would have actually been cheaper. What actually happened was that they gave the mission to the F-16 in a move to insure that the F-20 would never enter production, and then quickly retired the F-16 interceptors.

Regarding the A-7F, some might note that I've been absent from 6 months or so, so everything's gotten pushed back, although I still intend to post it (it's about 2/3 done since I returned). Just call me the 787 of posters.

 

[KJ_Lesnick]

Orionblamblam,

Real fast in a straight line. It was not designed to be a dogfighter.

Instinctively, I would normally be inclined to agree with you, but when you consider that

- Interceptors, such as the F-102A and F-106A, which despite being exceptionally fast, were actually quite agile -- and from what it would seem had a number of the dedicated air superiority fighters of the century-series beat in terms of maneuverability.

- The XF-108, like the F-102A and F-106A, had delta wings, with very large wing-areas (650-700 square feet, IIRC for the F-102A and F-106A, and like 1800 or 1900 square feet for the F-108)


KJ Lesnick

 

[Orionblamblam]

Orionblamblam,

Real fast in a straight line. It was not designed to be a dogfighter.

Instinctively, I would normally be inclined to agree with you, but when you consider that

- Interceptors, such as the F-102A and F-106A, which despite being exceptionally fast, were actually quite agile -- and from what it would seem had a number of the dedicated air superiority fighters of the century-series beat in terms of maneuverability.

They were also *relatively* small.

The XF-108, like the F-102A and F-106A, had delta wings, with very large wing-areas (650-700 square feet, IIRC for the F-102A and F-106A, and like 1800 or 1900 square feet for the F-108)

The F-108 was much more like the B-70, which coudl hardly be described as nimble... especially at Mach 3. As they say in Starfleet, "Faster than light, no left or right." Maneuvering at such high speeds is not advisable.

 

[Sundog]

Orionblamblam,

Real fast in a straight line. It was not designed to be a dogfighter.

Instinctively, I would normally be inclined to agree with you, but when you consider that

- Interceptors, such as the F-102A and F-106A, which despite being exceptionally fast, were actually quite agile -- and from what it would seem had a number of the dedicated air superiority fighters of the century-series beat in terms of maneuverability.

- The XF-108, like the F-102A and F-106A, had delta wings, with very large wing-areas (650-700 square feet, IIRC for the F-102A and F-106A, and like 1800 or 1900 square feet for the F-108)


KJ Lesnick

That's true, in the sense that a delta wing usually has a higher instantaneous turn rate than a conventional winged aircraft, but they suffer in sustained turn rate due to the large drag created by the vortices shed over the leading edge which give them good high alpha capability, in a similar sense as strakes induce over the wing of modern fighters. But, unlike modern fighters with strakes, the older delta's were limited by lack of control power and a limited T/W ratio. Of course, in terms of control power, one exceptiion was the MiG-21, since it had a conventional tail. The F-106 was a better dogfighter than the F-4 above approximately 32k ft., mainly due to it's large wing area. However, below 32k ft., the F-4 had the advantage.

 

[KJ_Lesnick]

Orionblamblam,

They were also *relatively* small.

I suppose, but the F-108 from what I remember despite it's substantially heavier weight, had substantially bigger wings and bigger control-surfaces. From what I remembered it was rated for a g-load that met ADC's requirements as well.

The F-108 was much more like the B-70, which coudl hardly be described as nimble... especially at Mach 3.

Actually, from what I remember hearing, the B-70 handled surprisingly well for an aircraft of it's size (regardless, it's no fighter) and I've been told it's maneuverability at Mach 3 was not entirely unimpressive...

While the F-108 was like the XB-70's in a number of ways, same engines, same honeycomb steel skin, same ejection capsules, it did have a number of differences. It had a different radar and fire-control system, different weapons, it probably had a different auto-pilot system, it could probably self-start it's engines like the F-102A and F-106's could (ADC requirements specified an aircraft when standing on alert had to be able to be started up, taxied to the runway and be ready to takeoff within two minutes)

Regardless, in terms of the F-108's maneuverability, I'm generally talking in terms of subsonic agility and dog-fighting performance -- I realize it would never engage in such a role, but I still would be interested to know how it would do (as, I said, the F-102A and F-106A weren't really meant for dog-fighting either but they handled surprisingly well, probably better than most of the dedicated fighters of the century-series fighters!)

At Mach 3, I assume it would fair similar to the MiG-25 as they had similar roles, but I'm not 100% sure 'bout that.

As they say in Starfleet, "Faster than light, no left or right." Maneuvering at such high speeds is not advisable.

Have you ever watched Star Trek? They did a lot of maneuvers at warp -- Still, that is an entirely different issue...


Sundog,

That's true, in the sense that a delta wing usually has a higher instantaneous turn rate than a conventional winged aircraft, but they suffer in sustained turn rate due to the large drag created by the vortices shed over the leading edge which give them good high alpha capability, in a similar sense as strakes induce over the wing of modern fighters.

I would have thought the opposite. The huge area of those wings, you'd think would offer excellent sustained turning rates, especially if you were between 300-400 kts.

Regardless, the outboard portion of the F-108's wing was lower in sweep at 45-degrees.

But, unlike modern fighters with strakes, the older delta's were limited by lack of control power and a limited T/W ratio.

I'm surprised there would be any control-power issues with the F-108 because of it's long-range supersonic performance -- you'd want low trim-drag for that (I don't recall seeing trim-tanks in that aircraft) which would in turn mean a lot of control power for a relatively low control-surface deflection...

The F-106 was a better dogfighter than the F-4 above approximately 32k ft., mainly due to it's large wing area.

That's what I was thinking, the large wing would give better sustained turning. It strikes me as a great surprise that a delta would work poorly in that area (unless it was flying at a high alpha)

However, below 32k ft., the F-4 had the advantage.

I thought the F-4's advantage died off in the low 20,000 foot range (as it didn't turn too well at lower speeds, and the larger wing of the F-106 worked against it at higher airspeeds)


KJ Lesnick

 

[cosmicpop]

Aerodynamically stable tail-less deltas always bleed loads of speed while turning. The wing effectively turns into a big speedbrake as the aircraft has to pull a higher than normal alpha to achieve the same turning performance as a tailed plane. The fact that the elevons have to deflect upwards to force the rear-end down and subtracting from the overall lift of the wing doesn't help.

Unless the trail-less delta is unstable and has the use of artificial stability (and maybe leading-edge lift devices) then I don't think it's a very manoeuvrable plane. This is why the Mirage 2000 overcomes a lot of the deficiencies of a tail-less delta, though even then I notice that video footage of a Mirage 2000 still shows the nose of the aircraft passing through high positive and negative alpha while performing an airshow routine - more than the average 4th-gen fighter anyway.

The F108 looks like is had a very thin wing - like a knife. That can't have been good for manoeuvrability either, but probably excellent for speed.

James

 

[Abraham Gubler]

Almost a whole page of posts about the F-108 Rapier flight performance and no one's mentioned wing loading? Sure at Mach 3.0 the F-108 would turn like other Mach 3.0 aircraft, even at 4-5 Gs it would take >25 NM to turn 180 degrees...

But at lower speeds with a combat weight of around 75,000 lbs (50% fuel) it would have a wing loading of 40 lb/sqf and a thrust to weight ratio of 0.78 which is much better than a Miro (Mirage IIIE) at combat weight (~19,000 lbs) with 50 lb/sqf wing loading and TW of 0.68. So the F-108 could potentially outfly circa 1960 no. 1 hotrod. Of course the F-108 can also cruise at 80,000 feet which is 5 NM *ABOVE* just about anyone else...

While the Proto-Phoneix missile system would not give a dogfight capability the F-108 would more than old its own with other 1960s fighters. With a Project Sixshooter like the F-106 it could deign to descend from the mid stratosphere and mix it up with lesser mortals.

 

[KJ_Lesnick]

Abraham Gubler,

Almost a whole page of posts about the F-108 Rapier flight performance and no one's mentioned wing loading?

That's actually the primary reason I asked the question. It wasn't just because "other interceptors ADC at the time were agile so this one must be", but because of why the other interceptors in ADC's inventory were agile. Both the F-102A and F-106's had good T/W ratios for the time and had large-wings.

In posts #5, #9, and #12, my statements and questions were partially based on wing-loading or L/D related figures...

But at lower speeds with a combat weight of around 75,000 lbs (50% fuel) it would have a wing loading of 40 lb/sqf and a thrust to weight ratio of 0.78 which is much better than a Miro (Mirage IIIE) at combat weight (~19,000 lbs) with 50 lb/sqf wing loading and TW of 0.68.

Well, I'm guessing you're just taking the wing-area figures and dividing that by the weight of the aircraft -- that isn't actually the only factor that determines wing-loading. Lift-to-Drag vs Thrust to Weight is the best way to go about it. I would not be surprised if the Mirage-3's wings were thicker than the F-108's (Mirage III's wing T/C ratio = 4.5%)

I wouldn't be surprised if the J-93 were a bit more powerful than advertised. I remember reading in at least one of the many books I have on the Blackbird, it stated that the original J-58, prior to it being developed into the engine used on the A-12/YF-12A/SR-71A/M-21 was supposed to have a maximum afterburning thrust in the ballpark of 45,000 lbs.

Another source, which I believe was mentioned on this site stated that P&W wanted it's new engine to be 50% more powerful than it's previous biggest jet, which was the J-75 and produced 17,500 lbf dry, a dry thrust of 26,250+ lbf (1.5 x 17,500 lbf) could yield that kind of power with a large afterburner (which the J-58 had). Since the J-93 was considered at least as powerful as the J-58, it would be logical to conclude that it could produce similar thrust figures with full A/B lit...

So the F-108 could potentially outfly circa 1960 no. 1 hotrod.

The Mirage IIIE was the most maneuverable fighter in the world?


KJ Lesnick

 

[Abraham Gubler]

Well, I'm guessing you're just taking the wing-area figures and dividing that by the weight of the aircraft -- that isn't actually the only factor that determines wing-loading.

Ahh actually it is. The only other variable in wing loading other than wing area and weight is gravity and since we aren't flying on Mars its pretty much a given... Wing loading is however not lift or drag or the overall aerodynamic performance of an aircraft.

Since the other major factor (on top of wing loading) for lift is speed (in level flight) the F-108 with its low drag and oddles of thrust (what it needs to get to Mach 3) can produce enough lift to be in the top of the class of 1960s fighters. Lots of lift means high rates of climb and high sustained rate of turn.

The Mirage IIIE was the most maneuverable fighter in the world?

Probably not, but it was the best selling fighter jet of the early 1960s. This was because of its superlative performance in air combat manoeuvres.

A more similar aircraft to the F-108 that actually flew was the Avro Arrow. It was capable of a sustained 2G turn at Mach 1.5 and 50,000 feet without loss of speed and altitude. The F-108 would have a similar sustained rate of turn thanks to its wing loading (better) and TW (lower).

 

[KJ_Lesnick]

Abraham Gubler,

Ahh actually it is. The only other variable in wing loading other than wing area and weight is gravity and since we aren't flying on Mars its pretty much a given... Wing loading is however not lift or drag or the overall aerodynamic performance of an aircraft.

My bad... I think what my intentions would best be illustrated by this statement: "Well, I'm guessing you're just taking the wing-area figures and dividing that by the weight of the aircraft -- that isn't actually the only factor that determines energy maneuverability performance. Lift-to-Drag vs Thrust-to-Weight is the best way to go about it."

Probably not, but it was the best selling fighter jet of the early 1960s. This was because of its superlative performance in air combat manoeuvres.

Understood...

A more similar aircraft to the F-108 that actually flew was the Avro Arrow. It was capable of a sustained 2G turn at Mach 1.5 and 50,000 feet without loss of speed and altitude.

What airspeed would Mach 1.5 at 50,000 feet amount to, roughly?

The F-108 would have a similar sustained rate of turn thanks to its wing loading (better) and TW (lower).

At least if you just measure out the wing-loading figures, the CF-105 has a lighter wing-loading than the F-108

 

[Abraham Gubler]

What airspeed would Mach 1.5 at 50,000 feet amount to, roughly?

Using the US Standard Atmosphere 1976 it would be 860.3540095850143 knots (TAS) which is 1,593.375 6257 kph. It would probably be a bit slower over Canada as its a bit colder.

So; "Nighthawk Six, Centre, we have you at 860 on the ground."

At least if you just measure out the wing-loading figures, the CF-105 has a lighter wing-loading than the F-108

Don’t know about that. The F-108 had a wing area of 1,865 ft² and an ACM weight (~50% fuel, no big AIM-47s) of ~75,000 lbs for a WL of 41 lbs per ft². The Arrow had a wing area of 1,225 ft² and an ACM weight of ~55,000 lbs for a WL of 45 lbs per ft². Weight at takeoff with full fuel for a long range CAP mission does not determine WL for ACM.

 

[KJ_Lesnick]

Abraham Gubler,

Using the US Standard Atmosphere 1976 it would be 860.3540095850143 knots (TAS) which is 1,593.375 6257 kph.

When I said airspeed, I meant like equivalent airspeed.

 

[Abraham Gubler]

When I said airspeed, I meant like equivalent airspeed.

Mach 1.5 at 50,000 feet IS 860.3540095850143 knots true airspeed (TAS) using the standard accepted atmosphere model. Of course not every bit of the world's atmosphere at 50,000 feet throughout the year has the same air density so the speed of sound will change. But the standard atmosphere average (US 1976) is used if you want to do a non-specific and quick calculation.

Who knows what you mean by "equivalent airspeed" because its plain to see you don't have much of a knowledge base in aviation. If you want to keep playing here and at "What If" at this level you should try and at least get the basics right. Any half decent local library should have a basics guide to aerodynamics...

 

[KJ_Lesnick]

Abraham Gubler,

Are you kidding me?

At altitude, the air gets thinner so the airspeed levels read lower, not to mention there's less airflow over the wing. Indicated Airspeed is commonly used but to my knowledge Equivalent Airspeed better factors in compressability effects...

 

[Antonio]

Abraham Gubler and KJ_Lesnick,

please don't go personal

 

[KJ_Lesnick]

Pometablava,

Abraham Gubler and KJ_Lesnick,

please don't go personal

Sorry 'bout that...


KJ Lesnick

 

[Abraham Gubler]

At altitude, the air gets thinner so the airspeed levels read lower, not to mention there's less airflow over the wing. Indicated Airspeed is commonly used but to my knowledge Equivalent Airspeed better factors in compressability effects...

Of course... but what's your problem? I've given you the Mach number and the altitude? After further sponging I've given you the TAS... Why can't you work out the EAS? Its just a formulaic relationship... I'm sure there would be an online calculator anyway! I didn't exactly pull out a slide rule to work out the TAS!

please don't go personal

I'm not personal I'm just dismayed at KJL's conduct. Apart from the constant sponging - made worse by him taking answers and then posting them on another forum (What If) - he is making demands of me to work out the particular airspeed he wants...

I think in this forum one should be allowed to post an aircraft's mach at altitude number (as specified by the RCAF for the Arrow) and not have to explain yourself further.

 

[KJ_Lesnick]

Abraham Gubler,

Of course... but what's your problem? I've given you the Mach number and the altitude? After further sponging I've given you the TAS... Why can't you work out the EAS? Its just a formulaic relationship...

Pometablava has specifically instructed me not to say anything personal, so I will try to avoid that.

With that said, I do not know the formula to convert TAS to EAS, I only know of some basic rules of thumb... M=0.95 @ 25,000 is about 350 kts, and M=1.0 @ 60,000 feet is about 196-198 kts.

My skill with solving complex equations (especially anything physics related) has also declined immensely since I have been out of school, and I'm actually going to take a remedial math course at a community college (Even despite the fact that I actually attended and graduated a four-year college from 1997 to 2001) in September to help get back up to speed.

I didn't exactly pull out a slide rule to work out the TAS!

True airspeed is a far easier calculation to work out.

Mach 1 @ Sea Level is about 760 mph
Mach 1 @ ~35,000 feet is about 660 mph
1 Knot = 1.1505 mph

I'm not personal I'm just dismayed at KJL's conduct. Apart from the constant sponging - made worse by him taking answers and then posting them on another forum (What If) - he is making demands of me to work out the particular airspeed he wants...

I don't honestly understand why asking questions is such a big deal on this forum. There has never been any other forum I have been a member of in which I have gotten in trouble or banned for asking questions, and I've been a member of many online forums. Regardless, I have generally tried to keep my questions related only to questions that I cannot find on a google-search (such as the intentions of the F-104 design and the handling qualities of the F-108).


K.J.

 

[overscan (PaulMM)]

The issue for me i I can't actually recall KJ ever providing any information other than vague assertions ("I read in a book"), just questions. This forum isn't just a social club, its a forum for the exchange of information on esoteric subjects. Many (most?) of the questions KJ asked could be answered with 2 seconds search in Google or are essentially unanswerable due to lack of relevant information. Perhaps consider doing some research *before* posting; it just feels like you are wanting others to do basic research for you.

I'm normally happy to help out when people posts questions, but there comes a point where you just have to say JFGI (Just F**king Google It). There are hundreds, possibly thousands of webpages with online and downloadable calculators which will calculate TAS/IAS/EAS/Mach etc. No need to learn maths, just type in the values.

 

[Rosdivan]

Abraham Gubler,

Of course... but what's your problem? I've given you the Mach number and the altitude? After further sponging I've given you the TAS... Why can't you work out the EAS? Its just a formulaic relationship...

Pometablava has specifically instructed me not to say anything personal, so I will try to avoid that.

With that said, I do not know the formula to convert TAS to EAS, I only know of some basic rules of thumb... M=0.95 @ 25,000 is about 350 kts, and M=1.0 @ 60,000 feet is about 196-198 kts.

Here you go

 

[KJ_Lesnick]

Rosdivan,

According to Aerospaceweb.org Mach 1.5 @ 50,000 feet = ~ 336.65 KEAS


KJ Lesnick
BTW: Looking at a google-entry it says certain formulae are only accurate up to Mach 1.2, can be used under some circumstances up to 1.5, and should not be used above that. Is that the particular formula used in this application?

 

[KJ_Lesnick]

I obtained a wing-thickness figure from a member of A.net who knows a great deal about the XB-70 and the XF-108 Rapier program (If you really must know the member's screen-name, I will reveal it upon request).

According to his figures, the average T/C ratio was 3.5%


KJ Lesnick

 

[KJ_Lesnick]

I'm not trying to sponge here, but is there any way to factor wing-area with wing-thickness to try and figure out an L/D ratio?