XF8U-3 Performance Comparison with F4H-1/F-4B

[Zipper730]

FLYBOYJ ,

Understood, I'll sift through the documents as a precautionary

BTW: The preliminary document lists takeoff speed as being 90% CLMax. I'm curious how one would calculate for 100%? Is this a linear relationship or some kind of exponential curve?

 

[FLYBOYJ]

FLYBOYJ ,

Understood, I'll sift through the documents as a precautionary

BTW: The preliminary document lists takeoff speed as being 90% CLMax. I'm curious how one would calculate for 100%? Is this a linear relationship or some kind of exponential curve?

This should be linear at takeoff and at sea level. When you're taking off in an F-4 (for example) you're at full power on AB. Once the gear is up and you're at a given climb angle (probably Vy) is when you'll reach 100% CLMax. The flights I had in my company's F-4s, we normally took off and climbed rapidly towards a MOA north of Edwards AFB. I could remember seeing 20,000 feet in about 30 seconds or so. Because of the power of the F-4s engines I would guess we were at 100% CLMax or very close to it (we normally flew with a center line tank).

 

[Zipper730]

FLYBOYJ

So, if takeoff speed was 146 @ 90% CLMax, the relationship from 100% CLMax would be direct (i.e. 146*0.9)?

 

[FLYBOYJ]

FLYBOYJ

So, if takeoff speed was 146 @ 90% CLMax, the relationship from 100% CLMax would be direct (i.e. 146*0.9)?

I would think so but this might be indicated in the flight manual shown as Vy at a given speed

 

[XBe02Drvr]

Ref: complexity of pilot transition, the differences are far greater than 2 engines vs 1 and the size and weight discrepancy. The radar was far more capable and complex and the dynamic of crew coordination and the division of functions added another whole dimension. Single seater fighter pilots have always had trouble ceding any of the tactical and situational awareness responsibility to "a damn navbag backseater", "a damn loser flight school washout!".
I was in the Navy during the waning days of the F8, when many pilots were getting "retreaded" in the F4, and these "single seater ego trips" were a common problem. Especially, since they generally were senior to, and way more experienced than their fellow nuggets.
I think you guys are barking up the wrong tree regarding CLMax. According to Aerodynamics for Naval Aviators, CLMax occurs at the wing's highest angle of atttack before the onset of stall, whether in slow flight or a high G maneuver. Vy is not a direct function of CLMax, but is at or very close to the point of max L/D for the airframe, with some slight modification for powerplant effects. This is nowhere near max AoA. In the case of a rocket powered brick like the F4, the powerplant effects are massive. A J model advertises 17,900 pounds of thrust per engine in full AB, giving it (lightly loaded) a fairly close approach to a 1:1 thrust to weight ratio. I'm betting your climb to 20K, Joe, was not in burner all the way, otherwise you wouldn't have much flight endurance at altitude. We did a burner climb (slick airframe) to 12K from an unrestricted takeoff, and I was looking at the 80° circle on the Attitude Indicator "globe" as we showed 285>300 KIAS on the dial. Nothing to see from the "pit" but blue and the rapidly shrinking island of Boca Chica in the canopy mirrors. Once we dodged the errant Bonanza and got sorted out we were down to 25 minutes "play time" remaining. What a rush!

 

[FLYBOYJ]

I think you guys are barking up the wrong tree regarding CLMax. According to Aerodynamics for Naval Aviators, CLMax occurs at the wing's highest angle of atttack before the onset of stall, whether in slow flight or a high G maneuver. Vy is not a direct function of CLMax, but is at or very close to the point of max L/D for the airframe, with some slight modification for powerplant effects.

I believe this is what out friend is chasing based on his questions. I'm trying to relate this to what would be found in the -1 (or NATOPS) manual,

This is nowhere near max AoA. In the case of a rocket powered brick like the F4, the powerplant effects are massive. A J model advertises 17,900 pounds of thrust per engine in full AB, giving it (lightly loaded) a fairly close approach to a 1:1 thrust to weight ratio.

OK

I'm betting your climb to 20K, Joe, was not in burner all the way, otherwise you wouldn't have much flight endurance at altitude. We did a burner climb (slick airframe) to 12K from an unrestricted takeoff, and I was looking at the 80° circle on the Attitude Indicator "globe" as we showed 285>300 KIAS on the dial. Nothing to see from the "pit" but blue and the rapidly shrinking island of Boca Chica in the canopy mirrors. Once we dodged the errant Bonanza and got sorted out we were down to 25 minutes "play time" remaining. What a rush!

IIRC he did use burner into most of the climb. The flight(s) I took were post maintenance flights and were about 30 minutes in duration. We had the luxury of a MOA right next door to out airport so we were able to burn the gas and b close to home

 

[Barrett]

I was compiling some data on performance figures for the F-4 & the XF8U-3 to see how they compare. I should have most of it up in the next few days.

X XBe02Drvr , since you worked on F-4's, I figure you might have some useful data on this.

Excellent thread, gents. I can only add one item: I talked to the Vought chief engineer and a senior test pilot. They said the limiting factor on the Threesader was the canopy melting point...

 

[Zipper730]

Ref: complexity of pilot transition, the differences are far greater than 2 engines vs 1 and the size and weight discrepancy. The radar was far more capable and complex and the dynamic of crew coordination and the division of functions added another whole dimension.

When I was talking about pilot-transitioning, I was referring to handling characteristics and figured the CG positions would probably be similar since some who evaluated it said it behaved like a big F8U-2 with more docile performance in terms of carrier landing (from what I recall, about half the F-8's were lost in carrier-accidents), but the CG thing was kind of a guess.

The radar complexity was greatly different between the F8U-3 and the F8U-1/-1E/-2. The radar system was equal to or superior to the F-4B, using the AWG-7 system and the AN/APQ-74 radar with a 34" radome (the nosecone didn't require any significant shape change owing to the fact that the radar was repositioned further aft in the nose with some equipment displaced into the fuselage), and had a cockpit display that included either a heads-down display (the traditional scope) or a head-up display. Regardless, workload would've been higher than the F-4B because it had only one crew versus two.

Single seater fighter pilots have always had trouble ceding any of the tactical and situational awareness responsibility to "a damn navbag backseater", "a damn loser flight school washout!".

Ironically, the USN seemed to still have better crew-coordination than the USAF with their F-4C's.

I think you guys are barking up the wrong tree regarding CLMax. According to Aerodynamics for Naval Aviators, CLMax occurs at the wing's highest angle of atttack before the onset of stall, whether in slow flight or a high G maneuver.

No, that's exactly what I meant: The ratio of lift to dynamic pressure which tends to peak around the stall.

Excellent thread, gents. I can only add one item: I talked to the Vought chief engineer and a senior test pilot. They said the limiting factor on the Threesader was the canopy melting point...

Oh yeah, that was really a serious problem. While they were working on it, I'm not sure if they'd fully sorted it out at the time of cancellation.

 

[XBe02Drvr]

I believe this is what out friend is chasing based on his questions. I'm trying to relate this to what would be found in the -1 (or NATOPS) manual,

OK

IIRC he did use burner into most of the climb. The flight(s) I took were post maintenance flights and were about 30 minutes in duration. We had the luxury of a MOA right next door to out airport so we were able to burn the gas and b close to home

Just out of curiosity, what do you think your endurance would have been without the C/L tank? Don't have my NATOPS any more, or I'd look it up. I did once calculate a buster scramble to 20K and 50NM, on internal fuel only, with four AIM9s, two MERs, and four pylons. One firing pass and a max conserve profile back to homeplate had the engines flaming out on the taxi back to the flightline. The hotpad birds always carried at least two drop tanks, and often came back min fuel. In my part time fueler job, I occasionally got a "buster" refueling call on the primary hotpad birds after a min fuel landing, if they had already scrambled the secondaries and Fidel's boys were feeling frisky.

 

[FLYBOYJ]

Just out of curiosity, what do you think your endurance would have been without the C/L tank?

We were flying F-4Ds and the way my pilot was flying (I was the crash dummy in the back seat) I'd guess 20 minutes...

 

[XBe02Drvr]

I'm curious how one would calculate for 100%?

FLYBOYJ

So, if takeoff speed was 146 @ 90% CLMax, the relationship from 100% CLMax would be direct (i.e. 146*0.9)?

What's this fascination with 100% CLMax? It's the ragged edge of a stall, and not a place you want to be when anywhere near terra firma. Ever see the famous video of "the Sabre dance"? 100% CLMax + backside of the power curve = guaranteed disaster.

When I was talking about pilot-transitioning, I was referring to handling characteristics and figured the CG positions would probably be similar

CG positions will always be similar, but not in the sense of a fixed position on the airframe. CG varies through a range relative to the center of pressure (lift) according to the loading of the aircraft. This is true of any aircraft. The range is limited by elevator authority on one end and unacceptably sensitive control response on the other.

Regardless, workload would've been higher than the F-4B because it had only one crew versus two.

Task saturation loses battles and kills pilots.

Ironically, the USN seemed to still have better crew-coordination than the USAF with their F-4C's.

"Too many cooks spoil the stew". That's what you get when you put two pilots in a fighter that really wants a pilot and a WSO. USAF insisted on flight controls in the back seat, against the recommendations of McDonnell, so deserved what resulted.

They said the limiting factor on the Threesader was the canopy melting point...

As it is on most Mach 2+ tactical jets.

 

[FLYBOYJ]

What's this fascination with 100% CLMax? It's the ragged edge of a stall, and not a place you want to be when anywhere near terra firma. Ever see the famous video of "the Sabre dance"? 100% CLMax + backside of the power curve = guaranteed disaster.

Yep - My thoughts as well

I was trying to relate this at takeoff when the aircraft (in out case a pretty robust and powerful fighter) was producing most lift base on excess thrust. I remember some of the pilots at my former employer talk about "powering" out of the incipient stall (full power, nose up and at CLMax?)

When I flew L29s and L39s, the engines took a bit to spool up but once they did you really got going, so when you rotated you didn't lift the nose up right away, you let the aircraft fly itself into the air.

CG positions will always be similar, but not in the sense of a fixed position on the airframe. CG varies through a range relative to the center of pressure (lift) according to the loading of the aircraft. This is true of any aircraft. The range is limited by elevator authority on one end and unacceptably sensitive control response on the other.

100% and since we're talking F-8s and F-4s, as long as you're in the C/G envelope, it's now a matter of how the specific aircraft behaves under a given flight parameter.

 

[Zipper730]

What's this fascination with 100% CLMax?

I'm trying to compare the airplanes from the standpoint of T/W ratio and stall-speeds. The stall-speed dictates the turn-capability and the T/W affects climb and stuff.

Ever see the famous video of "the Sabre dance"?

Yeah, it had a bad pitch-up combined with yaw/roll oscillations. The airflow also appeared to get disrupted in the inlet duct as the afterburner seemed to be going on and off rapidly.

CG positions will always be similar, but not in the sense of a fixed position on the airframe.

Of course, I just figured it was probably closer to the F8U-2 than, say, the F-4B (the %MAC seemed a bit different).

Task saturation loses battles and kills pilots.

And losing a battle could get the CVBG toasted. Regardless, the F4D & F3H had a single crew, and the F-106 also did and the USAF entrusted the whole CONUS and Alaska to it.

"Too many cooks spoil the stew". That's what you get when you put two pilots in a fighter that really wants a pilot and a WSO. USAF insisted on flight controls in the back seat, against the recommendations of McDonnell, so deserved what resulted.

That was remarkably dumb. I don't know why the hell they did that.

 

[XBe02Drvr]

Of course, I just figured it was probably closer to the F8U-2 than, say, the F-4B (the %MAC seemed a bit different).

Of course %MAC will be different; wing planform is different, so will center of pressure, and hence CG range, be different.

the F4D & F3H had a single crew, and the F-106 also did and the USAF entrusted the whole CONUS and Alaska to it.

In the days of primitive low thrust jet engines, likely interception targets were going to be lumbering unescorted bombers (think TU4) in a GCI supported environment (DEW Line, SAGE), a relatively simple problem for a single pilot all weather interceptor.
Make your target smaller, faster, and more maneuverable with standoff weapons and effective ECM in mid-ocean (think Backfire) with limited GCI or AEW support (think E1, "the Stoof with a roof"), and you've got a much more challenging problem.
If you haven't read Tom Clancy's Red Storm Rising, you should. While a fanciful action novel of mid 1980s vintage, it does describe a number of tactical and strategic scenarios that can give a perspective on the problems involved from an operational, rather than theoretical POV. The man did his homework.

That was remarkably dumb. I don't know why the hell they did that.

Despite all the hype, Steve Canyon was never Superman. Ego and testosterone out-wheighed brains, and officer career expectations often distorted intelligent analysis.

 

[Zipper730]

since we're talking F-8s and F-4s, as long as you're in the C/G envelope, it's now a matter of how the specific aircraft behaves under a given flight parameter.

Would it be fair to just assume the middle CG position listed on the chart?

Of course %MAC will be different; wing planform is different, so will center of pressure, and hence CG range, be different.

As I asked Joe, would just assuming a mid-CG range be adequate without further data?

If you haven't read Tom Clancy's Red Storm Rising, you should. While a fanciful action novel of mid 1980s vintage, it does describe a number of tactical and strategic scenarios that can give a perspective on the problems involved from an operational, rather than theoretical POV. The man did his homework.

That's the one where the Soviet's just launched a saturation attack on the carrier?

Ego and testosterone out-wheighed brains, and officer career expectations often distorted intelligent analysis.

Plus, I guess the whole SAC-umcising process might have played a role. "Uh, let's not go with that pilot/radar guy, that'll make the SAC guys think of fighters more like bombers".

 

[FLYBOYJ]

Would it be fair to just assume the middle CG position listed on the chart?

Yes, but I'm saying that without looking at the chart right now, I'm sending this on my cell phone as I wait for my daughter to get out of school. Sometimes the chart may depict an "envelope" and your best C/G position is in the middle of that envelope. Now with that said, for the most part, the aircraft should operate with no adverse effects as long as the center of gravity is maintained within that envelope. Wes, what's your thoughts?

 

[XBe02Drvr]

As I asked Joe, would just assuming a mid-CG range be adequate without further data?

Wes, what's your thoughts?

I THINK the mid-MAC assumption would work reasonably well with the F8U, with its conventionally shaped, symmetrically tapered wing, but the F4's cranked wing planform might throw us a curveball. The inboard wing section, with its significantly greater chord and thicker airfoil will produce a lot more lift than the thin passive panels outboard of the hinge line. I THINK this would shift the center of pressure (and hence, CG) forward of 50%MAC. That's my best guess without a NATOPS for reference.

 

[Zipper730]

I'd bet dollars to donuts there's little to no difference

You're correct.

1. RF-4B
   • OEW: 28981 lb.; MAC: 29.2%
   • Takeoff Weight: 43103 lb.: MAC: 33.7%
2. F-4C
   • CG Travel
     • OEW: 29.2%
     • Fuselage Tanks Full: 33.5%
   • Aft Limit: 36% (32% under some load-outs)
3. F-4D
   • CG Travel
     • OEW: 28.6%
     • Fuselage Tanks Full: 33.9%
   • Aft Limit 36% (32% under some load-outs)

A quote out of T.O. 1F-4C-1: "USAF SERIES F-4C, F-4D, AND F-4E AIRCRAFT", Section 5 reads

"The center of gravity (CG) position moves forward as
fuselage fuel is transferred and consumed. For a
clean configuration (no external stores), the approximate
CG travel is from 33.5% to 29.2% of the mean
aerodynamic chord (MAC) for the F-4C, from 33.9%
to 28.6% MAC for the F-4D, and from 32.7% to 26.1%
MAC for the F-4E. Therefore, fuselage fuel distribu-
tion becomes the primary control of CG position. A tape
indication of 5500 pounds (cells 5 and 6 nearly empty)
indicates mid-ranged CG. This mid-range CG condi-
tion can be attained earlier by using the tanks 5/6
locout feature (F-4C/D after T.O. 1F-4-773) from
the time of engine start. At 2500-3000 pounds on the
tape, the CG is forward. The maximum allowable aft
CG must be kept forward of 36% MAC, and with some
loadings as far forward as 32% MAC. This is nec-
essary to maintain minimum longitudinal stability."

I THINK the mid-MAC assumption would work reasonably well with the F8U

That seems like as good a guess as we'll probably get.

 

[Zipper730]

FLYBOYJ & X XBe02Drvr

It's amazing how many variations there are in the F4H-1/F-4B. The fuel capacity went from 2007 gallons to 1998 gallons at some-point

Data Sources
F-4B Standard Aircraft Characteristics Sheet, February 1, 1963
Avialogs: F-4 Plane Captain's Handbook

 

[FLYBOYJ]

FLYBOYJ & X XBe02Drvr

It's amazing how many variations there are in the F4H-1/F-4B. The fuel capacity went from 2007 gallons to 1998 gallons at some-point

View attachment 686306

Data Sources
F-4B Standard Aircraft Characteristics Sheet, February 1, 1963
Avialogs: F-4 Plane Captain's Handbook

Yes - this is pretty typical especially during the era when the F-4 (or similar fighters) were first being built and deployed, you'll see changes possibly based on structural modifications. BTW, the F4H-1 designation, although appearing in some of the early manuals was eventually deleted.