Saturday, December 8, 2018

Republic F-84 Thunderjet Fuselage Length

I can't remember why I did this illustration of the fuselage difference between the F-84A/B/C/D and the F-84E/F or who I did it for, but it was a typical update to early jets to provide better range and/or endurance, although in this case, given the relatively small increase in fuselage fuel capacity (36 gallons), it might have been a center of gravity adjustment:


Note that the fuselage change also involved different fairings at the wing root, access panels, etc.
The differences among the F-84s over time was extensive. The ejector around the engine tailpipe changed along with changes in the tail-light installation and the ventral-fin fairing. The pitot tube was in difference places, the landing gear doors were redesigned for the D and its landing gear compression mechanism changed from hydraulic to mechanical, etc.

The go-to guy for the F-84 was Bruce Craig but his web site appears to have gone walkabout.

Monday, November 12, 2018

Thursday, September 20, 2018

Bell P-39 Wing Planform

In my post on the Bell XFL-1 (see https://tailspintopics.blogspot.com/2015/09/modeling-bell-xfl-1-airabonita.html), I included a sketch to show the difference between the P-39 and XFL-1 wings. It was created before I had become proficient with Illustrator and regretably, I wasn't very rigorous about the shape of the P-39 wing (the XFL-1's is pretty good but I'll redo that illustration in the near future).

It turns out that some modelers gave me more credit for the drawing's accuracy that it deserves and lacking a better one of the P-39, have used it to evaluate the wings in various Airacobra kits. As a result, I have created a pretty accurate drawing of the planform using Bell data and a piece of a Bell P-39 drawing in my collection.

Wing planforms are generally defined by span, root and tip chords, and the location of the root and tip chords along a span-wise line. Usually the root chord is located at the aircraft centerline for the benefit of the aerodynamicists but not in the case of the P-39. It was located at the side of body, which is where non-aeronautical engineers would think the root chord would be. The span-wise line in the case of the P-39 is perpendicular to the centerline and at 30% chord. That data establishes the location of the leading and trailing edges. The tip can be defined in different ways; based on an XFL-1 wind-tunnel model drawing, it was probably a portion of a pair of circles that were faired into the leading and trailing edges. Unfortunately, I did not have a drawing with that data but I did have a Bell drawing of the Model 4A wing tip that is probably close to right. On the other hand, the shape of the aileron is iffy; I don't have a Bell drawing for it and the ones on the internet differ.
Note that I didn't correct for dihedral or incidence but those would be very small differences. 100" is given as the root chord for the Model 4 proposal (and a wing span of 35'), the P-39E and the XFL-1. In the case of the latter, however, it is located at 17" from the centerline and might therefore be consistent with the P-39D root chord value.


Monday, May 14, 2018

EKA-3B Aft Fuselage

Yet another question about the accuracy of the Trumpeter 1/48 A-3 Skywarrior kit has been brought to my attention, in this case the location of the main landing gear wheel well, which is reportedly a bit too far aft. Leaving it where it is creates a problem with national insignia placement. Moving it forward 4-5 mm means the big antenna fairing on the aft fuselage now appears to be too short.

One problem with addressing the accuracy of the kit is establishing a baseline from which to determine the proper placement of major details. In this instance, I've shown the location of the trailing edge of the wing on the fuselage, the vertical fin fold joint, the interface of the rudder with the fin, and a few fuselage station locations (in inches from just forward of the tip of the nose).
The outline of the fuselage and the location of the wheel well and the speed brake are from
pretty good Douglas drawings. The location of the antenna pod is from a sketch of unknown provenance. This is from a set of Luc Colin walkaround pictures:

For many more, see http://www.primeportal.net/hangar/luc_colin3/eka-3b_skywarrior_142251/

Sunday, April 8, 2018

NAEL F9F-2KD

By coincidence, I received questions last month from two different modelers about this particular airplane that was a profile in Scale Aircraft Modeler Vol 7 No 5. It was also a subject on Blackbird Models decal sheet BMD 72013.

Unfortunately, some critical information was missing. This was a former F9F-2KD (no BuNo) that had been stricken (no national insignia) but instead of being scrapped, it was transferred to the Navy test facility for Ship Installations, e.g. development of aircraft carrier catapult and arresting systems. Here is a picture of it in a display of a barricade at an open house.
If you look closely at the nose landing gear, it clearly isn't stock. That's because it was used in the development and evaluation of the nose-tow launch system (see http://thanlont.blogspot.com/2011/01/catapult-innovations.html)


Note that it didn't fly away after the catapult stroke since it was no longer airworthy.

Other configuration details: the tip tanks had been removed but they weren't replaced by the wing tip fairings; the fence outboard of the engine inlet is present; and the antenna fairing under the nose cone has either been added or the nose cone from another Panther/Cougar has been substituted.

Paul Bless reminded me that this particular F9F-2 (or a stablemate at NAEL or its nose gear) survived and may still be displayed in a bogus paint scheme at Aviation Heritage Park at NAS Oceana. See http://warbirdsnews.com/warbirds-news/fun-facts/this-day-in-history/happy-birthday-grumman-f9f-panther.html


Thursday, March 1, 2018

FJ-1 Tip Tanks - 1948 Bendix "Race"

Once upon a time, there were big-deal airshows with military participation, including "races". At some point the services were prohibited from competing with each other directly so they took turns year-by-year for the major events. The 1948 Bendix race was to be a Navy year, showcasing the new North American FJ-1 Fury assigned to VF-51. Takeoff was from Long Beach, California with the finish line at Cleveland, Ohio about 2,040 statute miles away.

When I wrote about this event in U.S. Naval Air Superiority, the range and speed numbers originally didn't add up. The FJ-1 cruising at 40,000 feet had a range of about 2,300 miles but almost certainly at a long-range cruise speed of only 350 mph versus the winning speed of 490 mph. However, looking at pictures of the airplanes involved, they clearly had different tip tanks than standard.


They were longer relative to their diameter, didn't have the position light in the tip and also had a rounded aft end and a fore-and-aft horizontal flange. The nose and tail resembled those on a 150-gallon external tank of the time with a longer, bulged center section and the FJ-1 tip tank fins added.

According to a Naval Aviation News article, these bespoke tanks could carry 290 gallons of fuel each versus the standard FJ-1 tip tank capacity of 170 gallons. These enabled the Bendix racers to fly much faster and still get to Cleveland. Just barely. One pilot flamed out 50 miles away from Cleveland at something over 40,000 feet and glided there for a dead-stick landing. The winner flamed out while taxiing in. Another climbed to 50,000 to stretch his fuel (the FJ-1 cockpit was not pressurized), became hypoxic and lost, finally crash landing in a field.

Now misreported most places on the internet, a California Air National Guard pilot, Major Robert De Haven, not officially competing but just going to Cleveland in a F-80C nonstop on the day of the race, also with nonstandard tip tanks, unofficially beat the Navy's best time by a few minutes. Actor Jimmy Stewart happened to be on hand with a checkered flag for its start from Long Beach. Note that the fuel in the tip tanks have been chilled to increase their capacity from an energy standpoint. Two F-80Cs took off but as with the FJs, fuel was critical and the other Shooting Star pilot, short of fuel, elected to land in Chicago, short of Cleveland.
A.U. Schmidt via Tailhook collection

The question has come up as to the size of the non-standard FJ-1 tanks. It can't be directly scaled from the picture above because of the camera lenses distortion of length versus diameter. Knowing the volume proved to be less useful than I hoped. It turns out that the standard 150-gallon tank must have fore and aft voids. Stretching it to add a 140-gallon cylinder results in a tank that looks too long relative to the diameter. I also tried to correct the picture of the tank using the fore and aft sections of the 150-gallon tank, which looks better with respect to length but means the voids had to be eliminated; if retained, the addition only came to about 48 gallons.

The new tank center section did have to accommodate the tip mounting of the FJ-1's as opposed to being slung under a wing on a pylon so it may be that the fore and aft sections were modified to eliminate voids as part of this reconfiguration. This is my best guess at the size and shape:

Tuesday, February 27, 2018

FJ-1 Fury Canopy

Initial open/close mechanism:




Later open/close mechanism:



Wednesday, January 10, 2018

The Grumman XF9F-9, Too Little, Too Soon

After the debacle of the XF10F Jaguar and the hasty conversion of the straight-wing F9F Panther to the swept-wing F9F Cougar, Grumman elected to propose the jet-powered equivalent of their F8F Bearcat to the Navy, encouraged to do so by BuAer's Fighter Class Desk. It was to be light, simple, inexpensive, maneuverable, and capable of near sonic speed in level flight without an afterburner. The engine selected was the Wright J65, a license-built British Armstrong Siddeley Sapphire that had also been selected to power the Navy's FJ-3 Fury and A4D Skyhawk. At the last moment, BuAer decided to add an afterburner in this instance.

Wright experienced difficulty in qualifying the afterburner so the first XF9F-9 made its first flight without one (it was subsequently redesignated F11F Tiger, since it bore no resemblance to its F9F Cougar forebear even in a dim light).

Like the Bearcat, it was relatively small and would have been wrapped snugly around its engine except that it was snugly wrapped with fuel tanks, not enough as it turned out.




Unfortunately, the F11F not only proved to be too small, lacking endurance, it was too soon, since the General Electric J79 then in development subsequently exceeded expectations as the afterburning Wright J65 was falling short of them. When evaluated with the J79, the F11F not only had terrific performance, it had somewhat better endurance. By then however, the Vought F8U Crusader had enough of a head start that the little Tiger became an also-ran.

A model of the first-flight prototype would be a relatively straight-forward conversion of a production F11F since most of the airframe was unchanged.
Note that the nose is even shorter than the original production F11F's but the wings, horizontal tail, and much of the fuselage is the same (the extreme aft fuselage has to be reshaped and shortened). Deletions include the wing fillet on the second production lot airplanes and the splitter plate ahead of the inlet (the inlet was offset from the fuselage, however). The vertical tail is smaller. Some other notable differences are the large pitot on the right side of the forward fuselage (it was subsequently moved to the vertical fin), the nose-landing-gear doors, the size of the wing fence, and the leading edge slat arrangement.



Another option, in 1/48, is the old Lindberg kit: https://www.britmodeller.com/forums/index.php?/topic/235037783-f11-f-tiger-ever-build-one-of-these/