Tailhook Topics

by Tommy H. Thomason

Friday, November 18, 2016

F9F Armament Installation - A Cautionary Tale

A new model kit of an aircraft is invariably found to have at least a few errors if not downright fatal ones. I don't wonder as much about how they could get it wrong as how they could possibly avoid error. The F9F armament installation is an example. This is an excellent picture of it, taken in 1949, showing the four cannon, the feed chute to the inboard ones, the avionics shelf, the black boxes above the cannon, etc.

The ammo boxes were located behind the nose wheel well, easily accessible from within it.

The only problem from a modeling standpoint is that this installation was only applicable to a total of 10 of the very first F9F-2s and -3s. For some reason, the installation was almost immediately changed to one with only two of the ammo boxes located behind the nose wheel well with the other two mounted above the cannon on the equipment shelf.
My guess is that the original location of the ammo boxes was predicated on center of gravity considerations. The change might have had something to do with problems with jamming in the feed chutes that went to either the inboard or outboard cannons. Or weight reduction. And perhaps locating avionics above cannons was a bad idea.

The F9F-6 Cougar used the same armament installation as the Panther. Note that the feed chutes from the aft-mounted ammo boxes are not shown.

Naturally, you would assume that the F9F-8 Cougar would have the same armament installation as the -6. You would be wrong.
According to the flight manual, all four ammo boxes were located above the cannon.

For other differences between -6 and -8 Cougars, see http://tailspintopics.blogspot.com/2010/11/f9f-6-vs-f9f-8-cougars.html

For details on the nose cones of the Panther and Cougar, see http://tailspintopics.blogspot.com/2016/02/grumman-f9f-nose-cone-variations.html 

Tuesday, November 1, 2016

McDonnell XF2H-1 Banshee BuNo 99860

Ron Downey is a retired McAir engineer who has an excellent blog, Aviation Archives, here: http://aviationarchives.blogspot.com/

He frequently posts high-resolution pictures, drawings, and illustrations, most but not all of McAir aircraft. I look at it about once a week and frequently see something that is new to me. In this case, it was a repost of an XF2H-1 drawing that I hadn't taken a close look at the first time: http://aviationarchives.blogspot.com/2015/07/xf2h-1-aerodynamic-three-view.html

There were three XF2H-1 (né XF2D-1) prototypes. This is the first one, BuNo 99858:
 Note the "thick" engine nacelle and the significant dihedral on the horizontal tail.

Several changes were required to solve aerodynamic problems. (see http://tailspintopics.blogspot.com/2009/12/f2h-banshee-modeling-notes.html). This is the second prototype after wing, nacelle, and empennage changes and the addition of the tip tanks similar to the ones that would be incorporated on the production F2H-2:

The production F2H-1 design was also lengthened a foot forward of the engine intakes to increase the amount of internal fuel. As it turns out the XF2H-1 drawing shows that the third prototype, BuNo 99860, incorporated this change. I hadn't noticed that until now because it retained the distinctive short XF2H canopy.
Note that it still has the handholds and steps on the right side of the forward fuselage and does not have an ejection seat.

Friday, October 28, 2016

North American FJ-4/4B Fury Notes

 28 October 2016: Updated to revise the horizontal tail discussion and correct other details.

In the process of preparing an information package requested by a kit maker, I revisited a question raised several years ago, the size and shape of the horizontal stabilizer. The problem is a fundamental inconsistency among the drawings and data available to me, which include the excellent North American FJ-4 four-view drawings, the FJ-4/4B Standard Aircraft Characteristics (SAC) charts, two NACA spin tunnel test reports, and a couple of measurements of an actual FJ-4B stabilizer by Jim Robbins. Thanks to FJ-4 maintenance manual data provided by Frank Truchi, a volunteer at the National Naval Aviation Museum, I can confirm that the NAA drawing of the horizontal tail is correct except for the span and the location of the elevator.


Note that the FJ-4 empennage was subjected to development changes.

The original FJ-4 horizontal tail was swept at 35° at the 25% chord. At some point in flight test, the sweep was changed to 35° at the leading edge, probably to reduce the overall length of the airplane, an important consideration from the standpoint of compact parking on aircraft carrier flight and hangar decks. The span was subsequently reduced by 18 inches on each side for production due to structural problems found in flight test.

In the process of reviewing the documentation I have, I discovered a detail that I wasn't aware of before. The major change between the FJ-3 and the FJ-4 was the wing. The new one provided more area to lift more weight, much of which was fuel. The knock on the FJ-3 was that performance suffered when it was carrying external tanks and endurance suffered when it was not. As a result, the FJ-4 was to have the same internal fuel capacity when clean (no external tanks) as the FJ-3 configured with external tanks. The ailerons were also to be moved inboard to avoid weight that would otherwise have been needed to stiffen the wing torsionally, which didn't leave much trailing edge available for flaps. As a result, the FJ-4 had narrow-chord leading edge flaps to further increase camber and a panel hinged to the bottom of the flap to scoop air into the slot between the leading edge of the flap and the aft spar of the wing.

This panel isn't shown on the NAA drawing bottom view.

One tidbit about the FJ-3 versus the FJ-4 that I'd forgotten was the increase in tread. This didn't result from the main landing gear struts being relocated more outboard: the wheels were simply located on the outboard side of the strut rather than the inboard side.

The FJ-4 had excellent handling qualities, eliminated the FJ-2/3's gunnery inaccuracy that resulted from the excessive downward angle of their cannon, and was almost certainly one of the best jet fighters from a performance and maneuverability standpoint that didn't have an afterburner.  Unfortunately, fighters with afterburners had an innate interception and air-to-air combat advantage so the Navy gave all the FJ-4s to the Marine Corps, which was happy to have them until Vought produced more F8U Crusaders than the Navy needed.

However, that wasn't the end of the FJ-4. The Bureau of Aeronautics decided that Douglas' Ed Heinemann wasn't paying proper attention to its concerns about the A4D Skyhawk program so it contracted with North American for an attack variant of the FJ-4.
Note the spoilers added to the upper surface of the wing for increased roll-control power required for the asymmetric loading of the heavy nuclear weapon that was the raison d'etre for the A4D/FJ-4B. Most descriptions of the FJ-4B state that these were located forward of the flaps, which I had presumed to be correct since that is where they would normally be.

It turns out that they were on the upper surface of the flaps as shown in the SAC drawing above. Note the open spoiler on this FJ-4B's damaged flap.
They are also evident in this FJ-4B walkaround photo taken by Fotios Rouch (for the complete set, see http://www.aircraftresourcecenter.com/awa01/401-500/awa463-FJ-4-Rouch/00.shtm).

For an FJ-4B configuration with the left-hand cannon removed, see: http://tailspintopics.blogspot.com/2012/03/modelers-guide-to-sabre-fury.html

For some detail under the canopy see http://tailhooktopics.blogspot.com/2012/12/fj-4-detail-under-canopy.html. Note that the FJ-4B was in service long enough to be retrofitted with the Martin-Baker ejection seat.

For an excellent set of annotated photos with configuration and other information, see this Phil Friddell post: http://tailhooktopics.blogspot.com/2012/12/fj-4-detail-under-canopy.html

And, of course, there's great information and drawings in Steve Ginter's FJ-4/4B monograph, Naval Fighters Number Twenty Five, which is regrettably out of print.

Tuesday, October 18, 2016

Grumman AF-2W Guardian Redux

In a 25 May 2015 post to a Special Hobby 1/48 AF Guardian thread on Britmodeler (HERE), "Homebee" noted that there appeared to be two different radomes for the AF-2W. To my chagrin, I must report that I hadn't notice the difference before I tripped over his unanswered post yesterday.

Here is an early AF-2W in Grumman flight test (it is configured with an ejection seat):

Here is a Navy Reserve AF-2W:

My post on the AF Guardian (HERE) failed to note that. I overlooked the obvious yet again.
The interface of the radome with the fuselage on the early version is smoothly faired between the bomb bay opening and the radome. The later interface (possibly an added sheet-metal fairing) is flat sided and appears to terminate abruptly. Unfortunately, I don't have a good picture of the aft end of the later radome.



I have no idea when or why the change occurred. It appears to have been a production change as evidenced by this picture of BuNo 124783 on the Grumman flight line.

Wednesday, September 21, 2016

Kitty Hawk 1/48 F2H-2/2P Banshee

3 November 2016: I just noticed in the ongoing Aeroscale build (see link below) that Kitty Hawk misinterpreted a photo of the ammo bay and added a "block" on the gun-bay aft bulkhead that shouldn't be there:

17 October 2016: I'm periodically adding information and links to build articles as I come across them. These will be identified from now on by being in bold.

Kitty Hawk sent me a kit for review but all I've been able to do so far is compare the big pieces to McAir drawings and dry fit the inboard wing and the fuselage. There's a good summary of what the kit includes here: http://www.cybermodeler.com/hobby/kits/kh/kit_kh_80131.shtml

For a very detailed and helpful build article, see http://modelingmadness.com/scott/korean/us/usn/f2h.htm. (One nit is that the positionable surface on the outboard wing panel is a flap, not an additional speed brake.)

This Cybermodeler build article provides detailed insight into assembly glitches: http://www.cybermodeler.com/hobby/builds/kh/build_kh_80131.shtml

Another illustrated build is in progress at Aeroscale: http://www.aeroscale.co.uk/modules.php?op=modload&name=SquawkBox&file=index&req=viewtopic&topic_id=252094

My first impression was very, very favorable. There are many detail features like a complete gun bay for the F2H-2 and a camera bay for the F2H-2P, the seldom-seen speed brakes, and options for extended flaps and folded wings. Assembly and fit are facilitated by the presence of small tabs and posts and corresponding slots/ledges and holes. For example, if you choose to close the gun bay doors, which have a neat representation of the piano hinge at the top edge, there is a lip on the other three sides that sits on a ledge in the opening of the nose to minimize fit problems.
I held back initially on some of my observations about the assembled kit that I saw at the IPMS Nationals this summer and photographs of sprues when they fell into one of three categories: 1) the problem would be fixed before production, 2) distortion due to lens effects, and 3) the builder was working without instructions or familiarity with the subject and therefore had to guess where some parts went. (In the latter category, for example, the assembled F2H-2 had the right-hand ammo cans on the left side of the nose).

Some of the problems noted on modeling websites early on were exaggerated by camera effects. Yes, the model is a little sway backed but not as bad as photos would have it and it can be reduced by some shimming between the aft side of the inboard wing assembly and the lower side of the fuselage. The overall fuselage height and length are to scale: the model is not tubby. The canopy ledge is not too steep; it is as close to the right angle as I can measure. The engine inlet looks a lot better than it does in the picture although it is a bit too deep.

There are some things that could be fixed or not. Few will notice that the nose landing gear yoke is too long or the vertical tail is a little oversized in height and chord. However, there is that excessive upward bulge in the engine nacelle. It is by no means eggplane-like in appearance, but if you think of the Banshee as being sleek as I do, it is distracting. I haven't been able to come up with a reasonably easy fix to minimize it.

Some have speculated as to the usability of the ancient Hawk F2H  center wing section that appears to have a more accurate upper contour. For one discussion and comparison photos, see this thread on Hyperscale: http://www.network54.com/Forum/149674/message/1476637062/1-48+scale+Kittyhawk+vs.+Hawk+inner+upper+wings-

Another comment elsewhere cited the box art as an accurate depiction of the nacelle:
Note that the box art is based on this picture of the XF2H-1 prototype BuNo 199859:
As a result, it depicts the prototype's short forward fuselage, short canopy sliding section, the windscreen with the straight-sided center panel, and the prototype tip tanks. However, the engine nacelle is the same as the production F2H-1 and -2.

The kit does not include the fighter's gunsight, only the -2P view port. The gun sight was a Mk 8 Mod 0 that set in a trough in the glare shield similar to the photo view port's.
This is one of several pictures of this gunsight on the web site, http://www.aircraft-gunsights.com/usn-collection/

 Another omission is some of the detail stuff behind the headrest.

I'm not sure about the size and angle of the armor plate behind the ejection seat. It's present in the illustration above but doesn't seem very prominent in pictures, if there at all.

Note the fixed links on each side of the forward lower edge of the canopy. They have rollers on the bottom that slid back in a trough that angled upward as it went aft so the canopy bow rose to clear the pilot's head.

Nose landing gear improvements/corrections:

The wing flaps need some work to be accurate. The two inboard flaps should not have mostly parallel leading and trailing edges; the trailing edge tapers forward toward the fuselage center line so that the flaps are parallel to the ground when extended. The assembly instructions for the outboard flap are incorrect. The narrow chord section (A15 and 16) should be glued to the upper wing half. The wider chord section (A14 and A18) is the flap; its trailing edge includes a small portion of the upper wing surface.
Although the two inboard flaps (shown in the color inset above) are separate structures, they are actually bolted together to form one surface and are roughly parallel to the ground when extended.


Another view of the wing upper surface included on the outboard flap trailing edge. Note the corresponding "cutout" in the upper wing trailing edge.

The top of the engine "nacelles" are incorrectly bulged upward and the intakes, not raked enough when viewed from the side.
Note also the position of the nose wheel relative to the wheel well on the assembled kit.

The kit has the two most inboard pylons staggered longitudinally. It would appear that they were in fact not staggered. They may also be slightly too close together. Unfortunately, I don't have station data for them.

Only the two inner-most pylons could be loaded with 500-lb bombs and if they were, the adjacent pylons could not be used. All four of the most inboard pylons could be loaded with 250-lb bombs; the pylons on the outboard wing panels could only be loaded with 100-lb bombs. All eight pylons could be loaded with rockets. (The kit includes two 250-lb bombs and four rockets.)
Note that the tip tank is not mounted square to the wing tip but is notably angled downward. (The kit parts provide a lot of latitude with respect to the mounting angle.)

The following illustration (note the correction to the size of the box from the original post) provides the lines-drawing information to check the engine nacelle size and shape if you are so inclined. (FYI, the top of the nacelle is about 1/8" too high; the top of the engine inlet is a bit too high, making the inlet too deep, but the width looks about right.) Note that the cut of the nacelle is slightly outboard of the fuselage and therefore does not include all of the interface of the nacelle with the fuselage going aft:
Compared to this McDonnell lines drawing, the leading edge of the vertical fin is almost 1/8" too far forward and it is about 1/8" too tall. The horizontal stabilizer is positioned about 1/16" too high. The most notable problem to my eye though is that the tip of the horizontal stabilizer is not raked slightly outboard as it should be and the aerodynamic balance (the tip of the elevator that extends forward to the leading edge) is not clearly demarcated relative to the panel lines.

An F2H-modeling post from several years ago: http://tailspintopics.blogspot.com/2009/12/f2h-banshee-modeling-notes.html

Two recommended references:
http://www.ginterbooks.com/NAVAL/NF73.htm


















http://www.milavnarc.com/f2h_banshee_in_detail_scale_part_1_digital_book.html


















Monday, September 12, 2016

Things Under Wings - Post-War External Tanks

Early on, AD-5s were seen with external tanks that were clearly not the so-called high-speed ones developed by Douglas in conjunction with the Mk 8X bomb shapes*. This is an example.

I haven't been able to find any data of these tanks other than examples, no two of which agreed in dimensions, of 150-gallon tank drawings on Standard Aircraft Characteristics for some airplanes. I was also initially confused by conflicting results from scaling photographs until I realized that there were probably two different but similarly shaped variants, a 150-gallon tank and one with a 300-gallon capacity. The result:
 I'd appreciate it if anyone can provide any information for these tanks, even just dimensions.

 *http://tailspintopics.blogspot.com/2011/07/douglas-low-drag-external-fuel-tanks.html

Thursday, September 8, 2016

Skale Wings 1/72 Douglas AD-5W Skyraider

11 September 2016 Update: I've been adding to this post over the past few days but I am pretty close to declaring victory. Note that this is not a build review; all I've done so far is dry fit the radome and the fuselage halves. There is a build review started HERE. It is in Russian but there are lots of pictures and Google Translate deciphers most of it.

The kit that Skale Wings graciously sent me well over a month ago finally arrived from Ukraine today (I had despaired and finally ordered one from Hannants last week, which should also be here soon).

The excellent news is that the kit is injection molded, not resin, and also not simply a mashup of the undersized Monogram AD-5 fuselage and the Hasegawa wing/cowling, although it is clearly based on (but not simply copies of, e.g. the main landing gear is a bit more detailed than Hasegawa's) those kits. The fuselage size is in the ball park and the kit includes a better-than-average instruction sheet, what looks like a good decal sheet with four option, vinyl masks for the canopy, and engraved panel lines on well-molded parts (there is some flash and cleanup of mating surfaces is required but the sprues and runners are petite) : a very good first effort from Skale Wings.

There are some hiccups, like the shape of the upper part of the front of the radome (the radome is a very, very difficult shape to define: I've tried to do it a few times without becoming satisfied although I think I'm close now), the erroneous presence of the narrow-body's catapult hooks located in the wings (and the wrong forward-facing landing gear doors), a not quite right aft canopy, two seats in the aft cabin rather than one, the external tanks mounted too far aft—but all-in-all, a far better starting point than trying to enlarge the Monogram fuselage and come up with a radome, not to mention that everything I've noted above, and detailed below, is either fixable without undue effort or can be ignored.

The Cockpit

Beginning with the instrument panel, the right side was basically a duplicate of the APS-20B Indicator in the cabin as shown in this sketch, only with a hood added for viewing the radar screen.

This is the pilot's instrument panel. Note the curved protuberance at the bottom and the center pedestal under that.

The AD-5 seat was an elegantly shaped aluminum shell.

The headrest and back were covered with a cloth-covered cushion. A parachute and seat cushion were located in the bucket.
The kit provides control sticks for both the left and right side of the cockpit but Navy AD-5s only had a stick on the left side.
The stick was on a pedestal that moved back and forth for pitch control. The kit stick (D2) might need more of pedestal.

None of the cabin detail provided will be seen since the opening between the cockpit and the cabin was closed off with a light-proof curtain. However, for completeness, there was only one crew seat back there, rather than the two provided in the kit, with the rest of the cabin filled with electronic gear.

The kit's radar operator's instrument panel resembles an AD-5N's rather than the AD-5W's shown here:
The Canopy

However, unless you go to the trouble of opening at least one of the aft hatches, any detail in the cabin will go unseen:
The canopy provided in the kit is pretty much a copy of the Monogram AD-5's "blue-room" version. The AD-5W aft canopy hatch and the section between the hatch and the sliding canopy were redesigned early on to be all metal, except for a small window (which could be blanked from the inside by a cover), to allow the radar operator to better view the radar scope. In the process, the hatch was reshaped to have a bulge over the operators head, with the fore-and-aft center section being unchanged.
One option to view the rear cabin is Falcon's vacuform canopy (Clear-Vax) set number 4. It includes an A-1E canopy that should fit this kit. You'd have to cut out the rear hatches and vacuform bulged ones, but that's no hill for a stepper...

Deleting AD-6 Features

Skale Wings unfortunately did not delete some of the AD-6 specific features on the underside of the wing (the lower wing half also includes the hole for the cannon barrels).
The oil cooler air outlets (the top two Xs) can be left alone on an AD-5W build since they are covered by the radome.

The catapult hooks moved to the main landing gear struts of the AD-5. Note that the forward-facing gear door was notably different than the AD-6's included in the kit since the AD-5 did not have the doors covering the wheel wells.
The oil cooler outlet was moved to the side of the fuselage just above the wing leading edge.
This is very faintly represented on the kit fuselage. Note that the door, which was hinged on its forward edge and opened outward like a cowl flap, does not extend as far aft as the trough it closes off. The door doesn't open very far, at least not that I've seen in photos and is usually closed tight on the ground (you need the oil temperature to be above a minimum value for takeoff).

Dive Brake Well

The AD-5 had only a single dive brake, the one under the fuselage. I knew that it had been deleted from the AD-5W but I only very recently learned that its well was not closed off as it had been on the AD-4W (to the extent possible, the basic AD-5 airframes were identical when they left Douglas).


For a bit more on the dive brake well, see http://tailspintopics.blogspot.com/2016/04/ad-5w-belly-detail.html

Dorsal Fin

The Skale Wing's representation of the intersection of the dorsal fin with the fuselage is a bit crude. Monogram's is much better and looks much more like this:
On the other hand, the Skale Wings kit  depicts the air inlet on the leading edge of the vertical fin and Monogram's does not. (Both omitted the orange and white running lights on the sides of the fin.)

Radome

The shape of the APS-20 radome is very difficult to pin down, at least to my satisfaction. I've spent a several hours off and on over the past few years trying to do so.  The Skale Wings version looks pretty good to me except for the excessive recurve at its upper front. This is how it should look (and where it is located relative to the lower intake; also note the radome intersection with the wing root just aft of the leading edge):

This is the kit's radome and my suggested correction (the fit with the fuselage isn't all that good anyway):

Drop Tanks

The kit comes with two 300-gallon drop tanks that appear to be accurate in size and shape. However, they are located too far aft on the pylon. It appears that the location of the tip of the 150-gallon tank was used to incorrectly position the tip of the 300-gallon tank:

In any event, most AD-5Ws are pictured with only one drop tank, invariably in that case on the right-hand side, almost always the smaller 150-gallon one, and sometimes the 150-gallon tank that predated the Douglas high-speed shape. The reason is that the AD-5W could loiter for over four hours on internal fuel alone, about three carrier cycles. Two 300-gallon external tanks gave it an endurance of 11 hours, which probably exceeded the radar's mean time between failures. As it happens, the Monogram AD-5 comes with 150-gallon drop tanks that are just slightly undersized but acceptable representations.

Decals

Color profiles and decals are provided for four different AD-5W/EA-1Es. Note that the LSO sight lines for angle of attack indication should only be on the left side of the vertical fin. The name of the Kearsarge is misspelled, but it doesn't appear on the AD-5W in the profile and the name is misspelled that way on the accompanying text of a photograph of it that is available on line.

On many (most?) AD-5Ws the national insignia on the underside of the wing is located well outboard like those on the attack-mission ADs, which was done to avoid the stores pylons on the outboard wings.
 (Also note the presence of the dive brake well.)

Radio Antennas, etc.
 There is a stall strip on the leading edge of both wings just outboard of the wing pylon.


My go-to references for configuration detail are Steve Ginter's Douglas AD/A-1 Skyraider Part One (Navy Fighters Number Ninety-Eight) and squadron/signal publications A-1 Skyraider Walk Around Number 27 by Ed Barthelmes and Richard S. Dann.