Tailhook Topics

by Tommy H. Thomason

Monday, August 22, 2016

A4D Skyhawk, One More Time

Questions have arisen about the size of the A4D stabilizer and width of the fuselage in various kits. This is a top view that I created from pretty good Douglas drawings and dimensional aero data for the wing and horizontal tail (root chord, tip chord, and span). Note that the interface of the horizontal stabilizer with the vertical fin is notional.

Some of the questions stem from comparison of kits with the Dana Bell's A-4E multi-view drawing in Detail & Scale Volume 32. It would appear that his fuselage is too wide and the horizontal tail slightly too large, among other errors. I asked Dana about that and he wrote back: "My job (on those drawings) was to take drawings and notes provided by the author, re-ink them onto mylar, and add the author's details."

For a lot of other A-4 stuff, see https://tailspintopics.blogspot.com/2013/03/a4d-4-skyhawk-collector.html

Friday, July 22, 2016

Grumman F8F Gunsight

According to the F8F Pilots Handbook for all Bearcat types, "Early model day fighters were equipped with a Mk 8 Mod 6 (gunsight), while later models are equipped with a computing sight unit Mk 8 Mod 0".

The Mod 6 was a simple fixed reticle sight that projected deflection rings and cross hairs on the windscreen.  The Mod 0 was a gyroscopically controlled range-finding sight that provided lead; it projected cross hairs and ranging images on a reflector glass mounted on the gunsight itself.

I don't know that the change in the gunsight had anything to do with the change in the windscreen angle of the -2 (see http://tailspintopics.blogspot.com/2016/07/grumman-f8f-bearcat-windscreen.html) but it's possible that it was necessary to provide clearance between the Mod 0 sight and the center panel of the windscreen.

Dave Collier adds the following background:  Most of the F4U-4s that I worked on had Mk 8 Mod 6 Sight Heads. Unfortunately we had two aircraft which were equipped with the Gun Sight Mk 18 Mod 6 System which used a Sight Unit Mk 8 Mod 0 that was part of the Aircraft Fire Control system (AFCS) Mk 6 Mod 0. Because this system was still classified “Top Secret” in 1954-55 we had to post an armed guard on the planes whenever the flight line was not in operation. I did not enjoy the winter nights carrying a shotgun to protect the planes. In 1956 we received AD-5Ns which had Mk 20 Mod 4 sights. He also referred me to this interesting website: http://www.aircraft-gunsights.com/usn-sights/

Grumman F8F Bearcat Vertical Tail

Although there are numerous detail differences between the -1 and -2 (see http://tailspintopics.blogspot.com/2010/12/f8f-bearcat-1-vs-2.html), the tail (and now the windscreen, see prior post) is the most obvious.

Note that the -1 is an early-production F8F provided to NACA for flight test and does not have the turnover structure behind the pilot's headrest; the -2 is the -2P photo reconnaissance variant.

For years I've used this Grumman drawing from the F8F SAC to illustrate the difference between the -1 and -2 vertical tail.
Upon closer examination recently, I was chagrined to discover that the difference in height depicted (as opposed to dimensioned) was incorrect. Instead of the -2 tail being 12 inches taller, it scaled to be only about eight inches taller. (As a result, the 1/72 Monogram kit's tail is not quite halfway in height between the -1 and -2 but a little less that halfway.) There was also no difference between the trailing edge of the rudder and the trim tab of the -2 versus the -1, which is now obvious to me in pictures.

The larger tail was not just the result of the -2 having a somewhat higher horsepower R-2800. The -1 Bearcat was in need of more directional stability at small side-slip angles and had marginal directional control during a waveoff. BuAer therefore requested NACA to do an evaluation of vertical tail modifications. These are sketches of the original vertical tail and two variations that were flight tested.

This is the test F8F-1 with the configuration 2 vertical tail:
Note the kludge to increase the chord of the rudder and the lack of the dorsal-fin fairing.

NACA recommended configuration 3 (larger rudder and trim tab) with the addition of a small dorsal-fin fairing like the F8F-1's.

I had assumed that Grumman just added 12 inches to the bottom of the existing F8F-1 vertical fin to save engineering and tooling cost and retained the -1 aft-spar attach structure. However, doing that made the leading-edge angle wrong compared to pretty good pictures taken from the side. It then occurred to me that Grumman probably wouldn't want to change or kludge the location of the attachment of the vertical fin's front spar, which meant that the -2's leading edge had to come down at a steeper angle.

This is the resulting pretty-good approximation of the difference between the -1 and -2 vertical tails (the dorsal fairing is a not so pretty approximation). Note that the angle of the -2's trailing edge changed below the trim tab to be steeper so that it terminated in the same place as the -1's.

Wednesday, July 20, 2016

Grumman F8F Bearcat Windscreen

One more time - all these years looking at something and I didn't notice the obvious. The F8F-1 and F8F-2 had slightly different windscreens...
(Ignore the fact that the F8F-1 does not have the turnover structure behind the headrest; the windscreen is still representative.)

My guess is that the change was an attempt to help increase the Bearcat's top speed when the change to a more powerful R-2800 was made or perhaps offset the drag of the taller fin (more on that later) and carrying approximately 600 lb more weight. However, it might have been necessary because of the change in gunsight on the -2 (see http://tailspintopics.blogspot.com/2016/07/grumman-f8f-gunsight.html).

Because of incidences of cracking, some Bearcat canopies subsequently received an additional frame a little more than halfway back on the sliding section. This reportedly began after 1949 and included both -1s and -2s.

Thursday, July 14, 2016

Detail & Scale F2H-1/2 eBook

Bert and Rock's latest eBook is now available and a must-have for the serious modeler looking forward to the forthcoming Kitty Hawk 48th F2H-2/2P kit. Visit the Detail & Scale website at www.detailandscale.com to download it for only $9.99. And it's not just for Kindles and Kindle-compatible devices: Bert also created a Mac version that can be downloaded via iBooks, which is what I do.

What you get in this instance is almost 300 pages of text, photos (many in color and some not previously published), and detailed illustrations covering the five variants of the early Banshees: the F2H-1/F2H-2/F2H-2B/F2H-2N/F2H-2P, and a review of available kits, detailed and illustrated, and aftermarket items that matches the best that I have ever seen. (The Kitty Hawk kit will be added in due course, one of the advantages of an eBook; Part 2 will cover the -3 and -4.)

Fully covered and well illustrated are configuration differences including the various cockpit layouts, paint and markings,  operational use summary, and squadron assignments. Attention to detail is paramount, as in noting (which I did not know) that the tip tanks were interchangeable from left to right, not an obvious conclusion since they hang off the wingtip at an angle rather than extending straight out or being hung directly underneath. Also little known is that the F2H-2 Banshee's wings could not be folded or unfolded with fuel in the tip tanks since the F2H-1 did not have them and the wing-fold structure and actuator were not redesigned to accommodate a tip tank loaded with fuel.

One telling example of the research involved is this book is that it does not make the oft-repeated error of stating that the production F2H-1 was shorter than the F2H-2 but correctly identifies the XF2H-1 as having the shorter fuselage but not the production F2H-1.

 If you are reluctant to make the move to eBooks as I was, you need to reconsider and try one, certainly one as user-friendly as those from Detail & Scale. For a synopsis of what you'll get and the benefits, go to http://www.detailandscale.com/detailandscale_digital_publicationss.html.

Sunday, July 10, 2016

F-111A/B Ejection Seats

The first F-111s, both As and Bs, were completed before the McDonnell-furnished escape module was qualified. The escape modules for these airplanes were therefore equipped with ejection seats. In order that the pilot be properly positioned with respect to the controls, the seat's rails were actually aft of the rear frame of the side hatch.

A panel, identified as the "overhead structure", therefore had to be added to the top of the fuselage to allow the ejection seat a clear pathway out. The edge of this panel is apparent in the picture above and in the following picture of an escape module which is to be completed with ejection seats.

The emergency canopy-removal sequence was complicated.
It was used both for jettisoning the canopy and as the initial step in the ejection process, which was automatically initiated by either crew member pulling the seat's face curtain or alternate ejection handles and had to be completed before seat ejection could occur.

The canopy removal and ejection seat operation were qualified in a sled test conducted by McDonnell. (See https://www.youtube.com/watch?v=9gyIhOGyGA8)

The following still from the sled-test cockpit camera shows the canopy as it is being jettisoned prior to the seats going out.

Grumman F8F Bearcat Redux

Someone drew my attention to this analysis by a Japanese master modeler. http://www.geocities.jp/yoyuso/f8f/f8fe.html. I have a few doubts about the information (I'll have to take a closer look at the reported windscreen difference and adding detail by reference to photos is an unreliable technique). However, it is well worth a look and includes photos of a stunning modification of the Monogram 1/72 F8F kit.

My prior posts: