Saturday, October 13, 2018

THE F-4 INBOARD PYLONS

Recently a discussion on The F-4 Phantom II Group on Facebook caught my attention and I thought I would take the opportunity to outline the differences between the Navy and Air Force inboard pylons on the F-4.

First, we need to understand that the pylons used were originally designed for different purposes.

THE NAVY PYLON

The Navy versions of the F-4, as well as both Navy and Air Force RF-4s, utilize the LAU-17/A as their inboard pylon.  As the nomenclature suggests, its primary purpose is as a launcher not as a weapons pylon

LAU-17/A pylon

The LAU-17/A was designed to carry and launch an AIM-7 Sparrow III missile so that the F-4 could carry a total of 6 (4 on fuselage semi-submerged stations and one on each inboard pylons).

LAU-17A pylon with an AIM-7 Sparrow III Missile

When the AIM-7 wasn't carried, the inboard pylon could also be fitted with a launcher rail on each side to carry and launch the AIM-9 Sidewinder missile. The AERO-3/A/B allowed the LAU-17/A pylon to carry an AIM-9B missile only.  The LAU-7/A launcher rail allowed the LAU-17/A pylon to carry either the AIM-9B, AIM-9D, and subsequent Sidewinder missile. The launcher rail consists of a power supply for the electrical requirements of the missile, a mechanism which retains the missile during flight and releases the missile when fired, a nitrogen receiver assembly to provide coolant for the missile seeker head, and safety elements to keep the missile from accidentally firing during loading/unloading and during catapult launch and arrestment. (Note: Don't confuse the LAU-7/A launcher rail with the AERO-7A which was the launcher for the AIM-7 on the semi-recessed fuselage stations).

LAU-17/A pylon with the AERO 3/A/B or LAU-7/A launcher rail installed
AIM-9B Sidewinder on the AERO-3/A/B launcher rail
AIM-9D used the LAU-7/A launcher rail
As the F-4 began to perform air-to-ground missions an adapter was fitted to the inboard LAU-17/A pylons to allow the carriage of air-to-ground weapons.
LAU-17/A pylon with an adapter fitted
From this adapter, a wide variety of single weapons could be hung.  To carry more than one weapon on each pylon a TER (Triple Ejector Rack) which had multiple ejector racks for additional weapons could be installed so that three weapons could be attached up to 750lb. each. Someone asked if the F-4 could carry a MER (Multiple Ejector Rack) on the inboard pylons. The answer is "No," MERs could only be carried on the centerline or outboard stations.

LAU-17/A pylon with adapter and TER fitted
When the adapter was fitted, the pylon cold also carry sidewinder rails as well.

THE AIR FORCE PYLON

The Air Force inboard pylon was sometimes called the MAU-12 pylon which refers to the Ejector Rack which was in the pylon.
MAU-12 pylon
Pylon with MAU-12 ejector rack removed for illustration
The ejector rack allowed the carriage of a single bomb, missile launcher or other weapons on the pylon. This pylon does not support the AIM-7 Sparrow III missile. But much like the Navy's LAU-17/A it could be fitted with a pair of AERO-3/B missile rails for the AIM-9 Sidewinder.  The AIM-4D was used in combat in South-East Asia by some F-4D Phantoms, which were equipped with special LAU-42/A launchers for this purpose. However, it became soon apparent that the AIM-4D was ill-suited for the close-range dogfights encountered over Vietnam, and only 5 kills were achieved with the Falcon. The main problem of the missile was seeker cooling. The limited amount of onboard nitrogen coolant meant that the seeker could not be pre-cooled for any length of time, which in turn meant that it had to be cooled more or less shortly before firing, i.e. when close-range combat had already started. This cooling, however, took up to 5 seconds which is like an eternity in a dogfight, so that most targets were out of reach again when the missile was finally ready. Moreover, when the coolant was exhausted after several aborted launches, the Falcon was just useless dead weight, which had to be brought back to base for servicing. Another problem of the Falcon was the lack of a proximity fuze, which made it effectively a hit-to-kill missile. The AIM-4D was gradually withdrawn from use beginning in 1969, and by 1973, the AIM-4D was no longer operational with the USAF.
Pylon with AERO-3/B or LAU-7/A missile rail installed

AIM-9 Sidewinder installed on AERO-3/B

To carry more than one weapon on this inboard station a TER could be installed which increased the load to 3 weapons.  Several other adapter rails could be installed for different missiles as well.
Inboard pylon with single Mk82 practice bomb
Inboard pylon with TER for carrying three weapons
AGM-45 Shrike on LAU-34 launcher adapter
AGM-65 Maverick on a LAU-88 triple rail launcher (although the Phantom only carried two on each launcher - inboard and lower stations)
As with the Navy's LAU-17/A, the Air Force could also install AERO-3/B Sidewinder rails on the pylon with some of the air-to-ground weapons installed.  Unlike the LAU-17/A the Air Force inner pylon could not be jettisoned.

For an interesting take on a modification of the Air Force inboard pylon found on Israeli and Turkish F-4s for carrying the Popeye missile see this post:  https://phantomphacts.blogspot.com/2013/10/israeli-mods-to-f-4-pylons.html


References:

  1. Drawings (c) by Kim Simmelink


Sunday, June 10, 2018

F4H-1 WINGTIPS

Ok, I have been working on my new (version 15) master drawings for the F-4 Phantom.  I have chosen to start from the beginning with the F4H-1. When I do master drawings, I do a lot of research, looking at pictures, and so forth. I lay out a grid with the Fuselage Stations, the Butt lines, and the Water lines.  I begin by gathering all the measurements I can, station number references, and any other information that will put a particular part at a particular location.  I then start by laying out the "skeleton" of the aircraft, locating as many ribs and spars as I can (this usually gives a good reference to where panels and joints occur.  In fact, I probably spend just as much (or even more) time researching and looking for answers as physically drawing.  I try to make everything as accurate as possible.

This week I have been working on a new bottom view, and so far I have been working on the wings.  One thing I have noticed is the different wingtip variations.  According to NAVWEPS 01-245FDA-3-1, there appear to be two different options here (in reality three).



1. The first is found on 142259 through 148374 unless they were modified with ASC (Aircraft Service Change) 40 and 41. Here is my illustration of this variation:


You can see in this drawing that first of all, it has an inset leading edge light. Next, the trailing edge light is smaller and recessed.  Information in NAVWEPS 01-245FDA-3-1 seems to support this.  Finding photographic evidence is much harder.  I think I see it, but most pictures are taken from so far away that when you blow it up to get better detail, well, you just can't be sure.


Here is a picture of 145313 (the 14th airframe) with the original wingtip.  See how clean and devoid of bumps, humps, and lumps.  This is actually a fairly good picture of the original wingtip.


Here is a picture of 148254 (the 26th airframe) still sporting the old wingtip. Not as nice a picture, but it clearly shows a very clean wingtip.


This is a picture of 148261 (the 33rd airframe) with what seems to be the original wingtip.



2. The second variation was installed on 148375 through 15102 and any aircraft that had ASC 40 and 41 take place. Here is my illustration of this variation:


This version has the more traditional trailing edge light.  NAVWEPS 01-245FDA-3-1 indicates that these aircraft still had the early leading edge light.


This is a picture of 146820 (22nd airframe) with what seems to be the mod with still the old style leading edge light.  See what I mean by pictures not showing very much detail?

One of the things that make this change odd, is that it took place mid-block, rather than starting a whole new block with the change.  148375 was the 13th aircraft in block 6, there were 9 more to be constructed in that block.



3. The third variation is what eventually became the production version. OK, now the 1 million dollar question.  When was the "bug eye" leading edge light introduced?  I don't have the foggiest.  I see pictures of the F4H-1 airframes later in life with the "whole package" of newer wingtip lights.


The "bug eye" leading edge nav light clearly would have better side visibility.  Don't know if this was the only reason for the change.  But you can see pictures of it scattered throughout the F4H-1s, most often later in their careers.



This picture of 145307 (first Block 2 aircraft, the 8th airframe) shows later in life it had the production wingtip retrofit.



Here is a picture of 148265 (the 37th airframe) with the "full monty."

Of course, this post probably brings up more questions than it answers.  If you have any answers, I would love to hear from you so this change can be fully documented.




Revision History:
  • 09 JUN 2018 - Original Post
Sources:
  • Artwork by Kim Simmelink
  • NAVWEPS 01-245FDA-3-1
  • Pictures from the internet

Monday, December 18, 2017

The Radome Road to a 32-inch Radome

HISTORICAL BACKGROUND:

During the design phase, just as the mission of the F4H-1 changed several times, so did the radar that was proposed to help the Phantom see its prey.  Early on, when the proposed aircraft mission was ambiguous, many proposals emerged. When it looked like the aircraft would be primarily an attack aircraft the choices were:
  • Westinghouse AN/APQ-56 (modified) with a Teledyne AN/APN-79 Doppler set for navigation
  • North American Aviation Autonetics Division’s NASARR (North American Search and Ranging Radar) which was being developed at the same time. This radar was optimized for the attack role and thus fit in nicely with the anticipated role of the AH-1 and the early F3H/F4H designs. The early F4H-1 models showed this pedigree with their 24-inch radome which had been designed around the NASARR radar requirements.
But in 1956, when BuAer changed the mission and dropped the cannons in favor of an all missile armament, the North American Design was dropped.  So, the scramble was on for a replacement radar that would fulfill the new mission requirements but still fit in the space carved out in the design for the NASARR. There were two immediate contenders. A modified Westinghouse AN/APQ-50 X-band fighter interceptor radar (similar to that flown in the McDonnell F2H-3 Big Banjo and Douglas F4D Skyray), and the Hughes AN/APG-51B (similar to that flown in the McDonnell F3H-2N Demon and Douglas F3D Skyknight).

Both were proven, although by no means state of the art designs, that used discrete components that were connected by long wiring harnesses. In an aircraft where real estate was at a premium, this was not ideal. Also, their design posed other problems. Long wiring runs connecting the components weakened the radar signals passing through them as well as made the introduction of noise into the system more probable.  And each time the signal strength was boosted, the amount of noise introduced into the system increased as well.

Westinghouse was the first to come up with a solution. The team at Westinghouse decided to combine the AN/APQ-50 modules into a cylinder shape that would fit into the aircraft nose right behind the radar antenna so that the signals did not have to travel through long wiring harnesses. McDonnell need only supply cooling air and electricity to a central inlet and Westinghouse distributed it. The entire radar was supported on an I-beam on which it could be extended out for easy maintenance. (This design feature was one of the improvements that helped the F4H-1 win the fly-off with the Vought F8U-3.)

But, during testing Westinghouse could not satisfy the most basic requirement of the radar and that was the range at which the APQ-50 detected a target aircraft. Westinghouse blamed the radar antenna. McDonnell's engineers had designed the F4H nose to hold the 24-inch diameter antenna of the NASARR radar they had intended to use. Westinghouse claimed that 24 inches was simply too small, as their calculations showed that the APQ-50 needed at least a 32-inch antenna to meet the required range. In testing they had confirmed the size at an outdoor radar range where they took a prototype of the 32-inch antenna and shot it at aircraft landing at Baltimore airport. The Navy approved the bigger antenna renaming the system the APQ-72, and gave Westinghouse a production contract.

By this time the prototype F4H aircraft (first 18 airframes) were in various stages of completion on the assembly line, all designed for a 24-inch antenna. The 32-inch antenna design changes wouldn't be implemented until the next series of aircraft (Block 3).

The 32-inch antenna would pose several engineering challenges. First came the fuselage redesign to widen the nose cylinder to allow for a 32-inch antenna. From FS 77.0 forward the fuselage was redesigned to deepen and widen the nose. (All future nose changes also took place from FS 77.0 forward like the RF-4, and F-4E)
Fuselage structure modifications forward of FS 77.0

Another technical challenge that they faced was building a radome for a high-speed aircraft that was 32-inches wide.  This had never been done before. Rain hitting a radome that large at Mach 2 could have some very serious consequences. The radome had to be structurally strong while being light-weight and aerodynamically correct. But most of all it needed to be transparent to the radar waves both outgoing and incoming. Radar manufacturers like Westinghouse worked with an exposed antenna in the lab and in the field trials, and then expected the radome manufacturers to provide a transparent dome that did not absorb or reflect the radar waves. Any imperfections in the radome, either in thickness or density, could distort the radar signal and give false information.

After extensive research into the state of radome technology, McDonnell chose the Brunswick Company in Virginia (maker of bowling balls and fiberglass boats) to construct the new radome. The Brunswick engineers came up with a way to wind fiberglass filaments around a conical form provided by McDonnell in the exact shape of the radome. The filaments are wound in alternate layers which are 90 degrees from each other. One layer of filaments, called circs, are wound around the form circumference and the other layer of filaments, called longos, are wound around the radome lengthwise. The layers of filaments are then saturated with resin, to seal it from absorbing moisture, and baked in an oven until it is cured into a strong yet flexible cone. The engineers at Brunswick then constructed a grinder connected to a special meter that measured the phase shift of an electromagnetic wave as it passed through a section of the radome. The grinder would grind the thick or dense areas of the radome until the whole radome registered identical readings. The bonded fiberglass shape is then covered in a layer of neoprene to act as a rain erosion barrier and a small metal nose cap is affixed to the radome to prevent rain and airflow from peeling back the neoprene shell. (I have seen a pin hole on the neoprene peel half the radome like a banana when it came back from a flight.)

(Note: the lone exception to this process was the RF-4s which had a painted radome (epoxy enamel finish) with a fabric/neoprene boot only covering the first 12-inches of the radome.)

F4H-1 RADOMES

Please understand that this isn't a definitive list. I am having a hard time finding pictures to validate each aircraft. I have included BuNos. of the ones that I have been able to verify and will keep it updated as I find more information. 

VARIATION 1 : All Metal 24-inch Nose with Metal Rib Structure (opens left)
Verified on BuNos: 142259a, 142260a, 143388a, 

This was an all metal nose with internal metal rib structure not intended to be compatible with radar, so these aircraft were not equipped with radar while equipped this radome. Many of these aircraft had an instrumentation pallet in the nose where the radar would have been.


Internal Structure of the 24-inch metal nose.



BuNo. 142259a with metal nose. Notice TAT probe installed later in test program.
BuNo. 143388a Showing to good effect the screw pattern on the metal nose.
BuNo. 143388a Showing screw pattern on metal nose.
BuNo. 143388a With radome open. Notice instrumentation pallet swings out to the right (just beyond the open radome).
VARIATION 2: Glass Fiber 24" Nose with Metal Rib Structure (opens left)
Verified on BuNos: 145307b,  



Again, aircraft fit with this radome would not have had radar installed because of the metal rib structure that underlies it.
BuNo. 145307b - The screw pattern can easily be seen showing the underlying structure.
VARIATION 3: Glass Fiber 24" Nose (opens upward)

Verified on BuNos: 145308b, 145315b, 145317b

For some reason three aircraft had a modified radome which opened upward instead of to the left like the others.  The radome was a new 24 inch glass fiber type, without internal structure other than the mounting ring so it would be compatible with a radar set. Externally I am not sure you would see any differences, just that internally it was hinged differently.



Structural Repair manual shows a glass fiber radome which opens upward.
VARIATION 4: Glass Fiber 24" Nose (opens left)
Verified on BuNos:  143389a, 143390a,

Aircraft equipped with this radome could have had AN/APQ-50 radars installed because of the lack of internal metal structure. 


BuNo. 143389a with 24-inch fiberglass nose.
VARIATION 5: Hybrid 32-inch Long Nose with Metal Rib Structure
Verified on BuNos: 143392a, 145311b 

These aircraft had a much longer radome which actually was built over a 24-inch radome structure. The nose appears to be much straighter on top as well as being more symmetrical in shape than the eventual production noses. This nose was used to test out the aerodynamic qualities of the proposed 32-inch radome. Since it had two layers of metal ribs (one on each radome) and a test instrument boom installed, these aircraft did not have a radar installed.
Illustration showing the outer structure built around the normal inner 24-inch structure. 



BuNo. 143392a showing its 32-inch nose

BuNo. 145311b showing its 32" nose
VARIATION 6: 32" Glass Fiber Nose
Verified on BuNos: 145313b, 146817c and subsequent aircraft.

This was to be the production standard for all future F-4(B,C,D,K,M,N,S) Phantoms starting with Block 3. The airframe forward of FS 77.0 was modified to accommodate the antenna of the APQ-72 radar and the larger radome it required. (FS 77.0 was the point where all future nose modifications started - RF-4s, F-4E,F, etc.)
The new 32" radome was laminated glass filaments bonded together and then covered with a neoprene exterior which was to keep rain from eroding the glass fibers. It had no internal metal structure other than the mounting ring and a small metal nose cap is affixed to the radome to prevent rain and airflow from peeling back the neoprene shell. The new radome opened to the right unlike its predecessors. This made a lot more sense as it wouldn't impede access to the cockpit when completely open.

32-inch production radome 






Revision History:


  •  18 Dec 2017 - Original Post


Sources:

  • Glenn E. Bugos, Engineering the F-4 Phantom II - Parts into Systems 
  • NAVWEPS 01-245FDA-3-1 - F-4A, F-4B & RF-4B-Structural Repair Manual 15 MAY 1965
  • Photos found on the Internet