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

[Zipper730]

Oh, I thought the G-load change was due to the fact that they simply listed the maximum g-load as lower for some kind of secrecy reason. However if they did beef up the plane here and there, that would explain the discrepancy. It also would almost certainly encroach on fuel-space.

BTW: I know about the designation change. From what I recall the F4H-1F became the F-4A (not sure why it didn't become YF-4A) but the F4H-1 became F-4B.

 

[FLYBOYJ]

Oh, I thought the G-load change was due to the fact that they simply listed the maximum g-load as lower for some kind of secrecy reason. However if they did beef up the plane here and there, that would explain the discrepancy. It also would almost certainly encroach on fuel-space.

BTW: I know about the designation change. From what I recall the F4H-1F became the F-4A (not sure why it didn't become YF-4A) but the F4H-1 became F-4B.

That was a time when the Pentagon was trying to consolidate things, the USAF F-4C designation was originally the F-110 for example. The navy's designation system was a bit confusing.

List of McDonnell Douglas F-4 Phantom II variants - Wikipedia

en.wikipedia.org

 

[Zipper730]

That was a time when the Pentagon was trying to consolidate things

From what I remember, the designation scheme (this could be wrong) started when McNamara got got confused over the designation scheme (he apparently mixed up two aircraft, maybe the F4D-1 and F4H-1).

The USN's system isn't that hard to grasp, but you're limited to 26 letters.

 

[SaparotRob]

Could I buy a vowel?

 

[FLYBOYJ]

From what I remember, the designation scheme (this could be wrong) started when McNamara got got confused over the designation scheme (he apparently mixed up two aircraft, maybe the F4D-1 and F4H-1).

The USN's system isn't that hard to grasp, but you're limited to 26 letters.

It was if you were in the air force!

 

[Zipper730]

It was if you were in the air force!

It was if you were Robert McNamara too!

 

[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

That nine gallon difference wouldn't quite cover your taxi from the de-arming pad back to the flight line. Arriving back at the flight line under tug power is guaranteed to earn you a new callsign.

 

[XBe02Drvr]

That was a time when the Pentagon was trying to consolidate things, the USAF F-4C designation was originally the F-110 for example. The navy's designation system was a bit confusing.

From what I remember, the designation scheme (this could be wrong) started when McNamara got got confused over the designation scheme (he apparently mixed up two aircraft, maybe the F4D-1 and F4H-1).

The USN's system isn't that hard to grasp, but you're limited to 26 letters.

It was if you were in the air force!

And so in mid-changeover when the head shed at DOD asked for a batch of F4B flight manuals, some wag at BuAer sent over Xeroxes of the 1929 Boeing F4B biplane fighter's flight manual. The head of the shed was not amused.

 

[Zipper730]

And so in mid-changeover when the head shed at DOD asked for a batch of F4B flight manuals, some wag at BuAer sent over Xeroxes of the 1929 Boeing F4B biplane fighter's flight manual. The head of the shed was not amused.

Honestly, I would have thought he'd have gotten the F4D and F4H mixed up.

While this is something that is totally outside my scope, but well within yours (as well as FLYBOYJ ): I've more or less found information from Mr. Thomason's book that indicates what the stall speed would have been at 29000 lb. (BuNo 146340: 123; BuNo 146341: 125 kn.: The two aircraft had slight differences to the flap-setting), and the variations of stall-speed with the BLC On/Off came from Chance Vought's preliminary flight-manual I got off Avialogs.

Of course, when it comes to calculating the flaps-up speed for the F8U-3, I don't really have much to work with, but I did find something: Apparently, with a 33000 lb. aircraft in the clean configuration, you'd touchdown at 185 kn. While I don't know how you would calculate engine-out speed for even a Cessna (let alone a supersonic fighter prototype from the late 1950's), but I assume the speed you'd touch down would have some correlation to stall speed (since at that point landing is basically assured), correct?

This is the page

 

[FLYBOYJ]

While this is something that is totally outside my scope, but well within yours (as well as FLYBOYJ ): I've more or less found information from Mr. Thomason's book that indicates what the stall speed would have been at 29000 lb. (BuNo 146340: 123; BuNo 146341: 125 kn.: The two aircraft had slight differences to the flap-setting), and the variations of stall-speed with the BLC On/Off came from Chance Vought's preliminary flight-manual I got off Avialogs.

OK - you're talking abut 2 specific aircraft that were not "normal" production units so you're going to get variations on stall speeds depending how they were configured during fight testing

Of course, when it comes to calculating the flaps-up speed for the F8U-3, I don't really have much to work with, but I did find something: Apparently, with a 33000 lb. aircraft in the clean configuration, you'd touchdown at 185 kn. While I don't know how you would calculate engine-out speed for even a Cessna (let alone a supersonic fighter prototype from the late 1950's), but I assume the speed you'd touch down would have some correlation to stall speed (since at that point landing is basically assured), correct?

When you say "engine out" I'm assuming you're talking about best glide after losing an engine. For an aircraft like a Cessna 172 it's clearly in the POH (65 KIAS depending on model). IIRC stall speed is usually .3 X touchdown speed and subtract that amount from touchdown speed as a general wag but this would vary with aircraft weight. Using that 185 knot touchdown speed, I would guesstimate stall speed would be close to 130 knots 185 x .3 = 55. 185-55=129.5

This is the page

View attachment 686474

Now something to keep in mind - if this data is from any "XF-8U" flight manual or report, it's going to be specific to the units being tested and generally not relevant to the rest of the F-8 production run.

Wes - what's your thoughts?

 

[XBe02Drvr]

Honestly, I would have thought he'd have gotten the F4D and F4H mixed up.

I believe that also happened, and was part of the motive for reclassification. The biplane caper was later, during the implementation process.

Of course, when it comes to calculating the flaps-up speed for the F8U-3, I don't really have much to work with, but I did find something: Apparently, with a 33000 lb. aircraft in the clean configuration, you'd touchdown at 185 kn. While I don't know how you would calculate engine-out speed for even a Cessna (let alone a supersonic fighter prototype from the late 1950's), but I assume the speed you'd touch down would have some correlation to stall speed (since at that point landing is basically assured), correct?

In a normal power on approach in a Cessna, you'd be touching down at or near stall speed. In a normal Navy tactical jet operation, 1.2x Vstall. The profile you provided is a whole different case, as the speeds in a dead stick or flameout approach will be much higher to improve controllability and keep sink rate under control. Remember, in a heavy, high speed aircraft best L/D (glide ratio) occurs at much higher speeds than with light aircraft, and you'll want to have energy stored up to flare away most of your sink rate prior to impact. Given that you'll be touching down on F8 family landing gear, you want to get rid of as much sink rate as possible. Forget the greaser landing; you just want to walk away from the mishap afterwards.
Oh, and one more thing. You want to touch down prior to the emergency arresting gear, as your brakes will be useless.

 

[Zipper730]

OK - you're talking abut 2 specific aircraft that were not "normal" production units so you're going to get variations on stall speeds depending how they were configured during fight testing

From what it appears, this was based with the aircraft in the landing configuration (flaps down, BLC on): 146341 had a lower flap-deflection angle, and 146340 had a higher one. That probably accounted for the speed difference.

When you say "engine out" I'm assuming you're talking about best glide after losing an engine.

Correct.

For an aircraft like a Cessna 172 it's clearly in the POH (65 KIAS depending on model). IIRC stall speed is usually .3 X touchdown speed and subtract that amount from touchdown speed as a general wag but this would vary with aircraft weight. Using that 185 knot touchdown speed, I would guesstimate stall speed would be close to 130 knots 185 x .3 = 55. 185-55=129.5

Firstly, when did 1.3 Vs become the norm in civilian and military aviation? Secondly, this produces an unusual discrepancy based on flight-test data.

I did some calculations for the stall speed based on the plane at 29000 lb. and stalling at 123 kn. This was found during flight-test by a NASA test-pilot. The 185 kn. final approach speed (I'm curious if the speed was based upon the premise that touchdown was all but assured) for the aircraft at 33000 lb. came from the preliminary flight-manual (I screen-capped some pages here) which showed differences in stall-speeds based on the CG range with the flaps/droops down and BLC on/off. I basically took the chart, transcribed all the numbers and, provided everything's right, I put down everything here.

Using the mid CG range I compared the difference in effect on stall speed (Power & BLC being on/off)

This is an abbreviated version which displays the differences in speed as a result.

With actual flight testing data included which indicated a Vs of 123 kn. @ 29000 lb., here's the compiled data.

The 26000, 30000, and 34000 lb. figures are based on the effects of CG on stall-speed with flaps down (with variations for power & BLC). The 26156 lb. figure was based on a Standard Aircraft Characteristics sheet which was in Mr. Thomason's book (the preliminary flight manual lists 26160 lb. which is functionally the same), the 29000 lb. weight-figure was the speed at which a stall would occur at 123 kn., 33000 kn. was a listed speed for a flame-out landing, 40000 lb. was the maximum listed weight for takeoff in the preliminary flight-manual, 40086 lb. was the highest weight the plane reached during development (they appeared to have reduced it to 39551 lb., which is why that is also listed). 37701 lb. was an earlier weight figure with 3 x AIM-7C, 38236 lb. was 3 x AIM-7C + 2 x AIM-9B.

I believe that also happened, and was part of the motive for reclassification.

Understood

In a normal power on approach in a Cessna, you'd be touching down at or near stall speed. In a normal Navy tactical jet operation, 1.2x Vstall. The profile you provided is a whole different case, as the speeds in a dead stick or flameout approach will be much higher to improve controllability and keep sink rate under control. Remember, in a heavy, high speed aircraft best L/D (glide ratio) occurs at much higher speeds than with light aircraft, and you'll want to have energy stored up to flare away most of your sink rate prior to impact.

Of course, I just didn't know if there was some kind of formula to compute that.

Looking at the image from the preliminary flight-manual (page #3, post #49): It appears that the landing-speed being the same as the "final approach" speed is probably the speed you'd do when touchdown is all but assured, correct?

 

[FLYBOYJ]

Firstly, when did 1.3 Vs become the norm in civilian and military aviation? Secondly, this produces an unusual discrepancy based on flight-test data.

It's not - just a wag I've learned over the years and it's not far off, this from civilian AND military pilots

I did some calculations for the stall speed based on the plane at 29000 lb. and stalling at 123 kn. This was found during flight-test by a NASA test-pilot. The 185 kn. final approach speed (I'm curious if the speed was based upon the premise that touchdown was all but assured) for the aircraft at 33000 lb. came from the preliminary flight-manual (I screen-capped some pages here) which showed differences in stall-speeds based on the CG range with the flaps/droops down and BLC on/off. I basically took the chart, transcribed all the numbers and, provided everything's right, I put down everything here.

And my "wag" came out to almost 130 knts so there's a safety margin there. If I was flying the aircraft I wouldn't let the airspeed drop below 140 until I was over the numbers

 

[XBe02Drvr]

It appears that the landing-speed being the same as the "final approach" speed is probably the speed you'd do when touchdown is all but assured, correct?

For a normal tactical jet arrival, that's right. Fly the ball at optimum AoA, on speed, on glideslope, straight to intersection with TD zone. No flare. Flameout approach is a different case as explained upthread. There you will flare and bleed off your excess speed.

 

[SaparotRob]

I love that kind of talk.

 

[Zipper730]

And my "wag" came out to almost 130 knts so there's a safety margin there. If I was flying the aircraft I wouldn't let the airspeed drop below 140 until I was over the numbers

Yeah, but that's kind of the problem: Flaps were up for the engine-out approach. The figures I have were flaps down (full-down). The variations in speed were CG, whether the power was on/off and BLC on/off...

 

[FLYBOYJ]

Yeah, but that's kind of the problem: Flaps were up for the engine-out approach. The figures I have were flaps down (full-down). The variations in speed were CG, whether the power was on/off and BLC on/off...

A few knots on the higher (and safer) end are not going to make a difference provided you're in the C/G envelope

 

[XBe02Drvr]

Yeah, but that's kind of the problem: Flaps were up for the engine-out approach. The figures I have were flaps down (full-down). The variations in speed were CG, whether the power was on/off and BLC on/off...

A few knots on the higher (and safer) end are not going to make a difference provided you're in the C/G envelope

I've watched F4s and A4s doing flameout practice approaches. They appeared to be putting their flaps down on short final just as they started their flare. I don't think an F4 can make a survivable zero thrust touchdown with no flaps. If they lose all power and can't deploy the RAT it's Martin Baker time. A high sink, high speed belly flop is a terminal case.
The F4s especially are heart stoppers to watch, as they touch down at high speed and eat up a lot of runway as those J79s spool up enough to support an afterburner light for another go. On the go they rocket back up to high key position for another rep. Three reps will get you to bingo fuel on internal fuel only. Chug-a-lug!

 

[FLYBOYJ]

I've watched F4s and A4s doing flameout practice approaches. They appeared to be putting their flaps down on short final just as they started their flare. I don't think an F4 can make a survivable zero thrust touchdown with no flaps. If they lose all power and can't deploy the RAT it's Martin Baker time. A high sink, high speed belly flop is a terminal case.
The F4s especially are heart stoppers to watch, as they touch down at high speed and eat up a lot of runway as those J79s spool up enough to support an afterburner light for another go. On the go they rocket back up to high key position for another rep. Three reps will get you to bingo fuel on internal fuel only. Chug-a-lug!

Yep - my time around the F-4 heard the same thing. I think the only time I got nervous is when we were on final and observing the sink rate. I realized that if we lost an engine my spine might wind up coming through my nostrils!

My company also had a few F-100s, mainly Ds and Fs. We had a couple of Cs and got rid of them because they had no flaps!

 

[Zipper730]

A few knots on the higher (and safer) end are not going to make a difference provided you're in the C/G envelope

Of course. The thing that I was trying to get at was that the flying speeds flaps-up are higher than flaps-down. All the images I gave on Post #52 were based on flaps being down (the variations in speed were weight and whether the power and BLC was on/off).

With the XF8U-3, normal landings (carrier or field) were done with the wings up, flaps-down and BLC on. I doubt they would have attempted an engine out landing on a carrier-deck (I figure they'd have just ejected), but the diagram depicted a field-landing and was to be done flaps-up which would mean that, even if engine power and everything was present, you'd be going quite a bit faster. Looking at a NATOPS pilot's pocket checklist for the F-8D/E (which called for this to be done with the droops in the cruise position), it stands to reason that the XF8U-3, if it had become operational, would have probably done the same, but the figures calculated seemed to be with flaps-up.

I did some looking through several sources: One source was a NATOPS Pilot's Pocket Checklist (F-8D & E); the other was an F-8H&J Flight Manual. The former looks like a rickety piece of shit that has pages missing (This unfortunately excludes landing speeds , except for an engine-out landing, ironically), but the F-8H/J manual does have this data and it roughly reads as follows (some numbers are rounded up)

1. Carrier Landing Approach Speeds
   • F-8H Landing Speeds (Stall speeds are listed in the manual on the graph with landing-speeds being 1.15-1.16 Vs)
     • 133 kn. @ 20000 lb.
     • 138 kn. @ 21000 lb.
     • 140 kn. @ 22000 lb.
     • 144 kn. @ 23000 lb.
     • 147 kn. @ 24000 lb.
   • F-8J Landing Speeds (Stall speeds are listed on the graph and seem to indicate 1.18-1.19 Vs).
     • 118 kn. @ 20000 lb.
     • 120 kn. @ 21000 lb.
     • 123 kn. @ 22000 lb.
     • 127 kn. @ 23000 lb.
     • 129 kn. @ 24000 lb.
     • 131 kn. @ 25000 lb.
2. Engine Out Landing Speeds
   • F-8D: 140 kn. @ 23000 lb. (Vs is 115 kn. at 23000 lb. based on the F-8H manual with speed being apparently 1.22 Vs)
   • F-8E: 135 kn. @ 23000 lb. (1.17 Vs)
   • F-8H: 140 kn. @ Unspecified
   • F-8J: 140 kn. @ Unspecified

With all that, I figure you'd end up with the speed you'd come over the runway once landing is assured would probably be around 1.17 to 1.22 Vs for the XF8U-3 for an engine-out landing. This would yield a stall speed of around 152 - 158 kn. at that weight.