Friday, September 30, 2011
F-111B Aft Main Landing Gear Door
It turns out that there's an F-111 main landing gear maintenance trainer at the Chanute Air Museum in Rantoul, Illinois with the original aft main landing gear door and the Curator there, Mark Hanson, was kind enough to take pictures of it. I've posted a couple of them, one heavily annotated, HERE. (Note: I subsequently revised the annotated picture because I had incorrectly guessed what the hidden portion of the aft main landing gear door leading edge idler looked like.) I'm still working on a more accurate illustration of the mechanism than this one, which turned out to be a pretty good guess as to the moving parts:
Since then, I've renamed Link A as the aft main landing gear door bellcrank and Link B as the aft main landing gear door leading edge idler.
TF-1/WF-1 Forward Fuselage Change from S2F-1
Click HERE for my guess at the differences between the forward fuselage of the S2F-1 and the TF-1/WF-1.
Saturday, September 10, 2011
F-4 Flap/Stabilizer Change
Because the original design was intended for a somewhat lighter aircraft, the F4H (F-4) Phantom II wing underwent some subtle changes in development to provide more lift to go with the increase in gross weight. The first of these were the addition of the inboard leading edge flap and boundary layer control to the sixth F4H. (See HERE and HERE.) Note that I've added information from Craig Kaston about the earliest changes to the stabilator. Also see: http://tailhooktopics.blogspot.com/2012/11/f-4-stabilator.html
As on all airplanes that don't have the highest level of pitch stability augmentation, the F4H stabilator created down load in most flight conditions. The original stabilator had a symmetrical airfoil.
Because the F4H was short coupled, as carrier-based airplanes tended to be for compact parking on deck, an early modification of the original stabilator added notable negative camber to increase the download available. (Note the zig-zag line at about 20% chord where the cambered leading edge was added on this interim stabilator.)
This was the sixth Phantom aboard during early at-sea trials. Note the cutout in the bottom of the rudder due to the stabilator trailing-edge-up travel being provided at the time.
The Phantom's gross weight continued to increase over time with upgrades, fixes, additional equipment, etc. It was clear that with the next round of improvements planned for the F-4J, another lift increase would be required. Step one was obvious, drooping the ailerons when the flaps were lowered: 16.5 degrees was determined to be adequate from wind tunnel test.
As expected, the droop resulted in more nose-down moment with the flaps extended, too much as it turned out. The problem was most obvious with the increase in nose wheel liftoff speed and the inadequate pitch control power after catapult launch and during bolters. Additional wind tunnel tests established that elimination of the inboard leading edge flap (added during development as noted above for increased lift) reduced the nose-down moment at nose-wheel liftoff speeds and turned out not to affect lift at approach speeds.
Although eliminating the inboard leading edge flap was beneficial, it was inadequate. Further wind tunnel tests indicated that the stabilator was stalled at nose wheel liftoff speed. As McDonnell engineer Bill Weber remembers it, "We tried a matrix of planform and area changes to correct the problem and finally determined that adding a fixed leading slat would delay the stall and could fix the problem. (Note: These wind tunnel tests were conducted without a simulated jet exhaust - later tests with jet effects indicated that the slat did not delay the stall and the improved stabilator power was probably due to an increase in effective area.)"
Even before the wind tunnel tests of the slotted stabilizer were accomplished, McDonnell program management decided to fabricate a slotted stabilator by adding a fixed slat to the leading edge of the existing one and flight test it. Bill Weber again: "As a consequence flight tests of the slotted stabilator took place very shortly after we had wind tunnel results. In any event the flight tests demonstrated that the problem had been fixed. We used the same configuration changes to fix a similar problem on the F- 4E which didn't have aileron droop but had a more forward C.G. due to the installation of the gun."
Although created for the F-4J, which first flew in June 1966, the drooped aileron and associated changes (the slotted stabilator and the elimination of the inboard leading edge flap) were of benefit to the F-4B as well. The package of changes was incorporated with Block 26 production, the first of which was BuNo 152995 that first flew in March 1966, and retrofitted to most of the surviving earlier F-4Bs over time.
Retrofit involved the development, qualification, and approval of a different package of drawings and other documents for use by the Naval Air Rework Facilities before crash-damaged and overhaul-due F-4Bs would get these changes. I've read that "by late 1971 or early 1972 it would have been rare to see a F-4B without these modifications, except perhaps in RAGs or Marine reserve units." For sure the slotted stabilator was present on F-4Ns coming off the Bee Line at North Island. The first F-4N flew in June 1972.
This is an F-4N, which is an upgraded F-4B. Note the drooped ailerons and fixed inboard leading edge along with other detail changes to the original B configuration.
As on all airplanes that don't have the highest level of pitch stability augmentation, the F4H stabilator created down load in most flight conditions. The original stabilator had a symmetrical airfoil.
The Phantom's gross weight continued to increase over time with upgrades, fixes, additional equipment, etc. It was clear that with the next round of improvements planned for the F-4J, another lift increase would be required. Step one was obvious, drooping the ailerons when the flaps were lowered: 16.5 degrees was determined to be adequate from wind tunnel test.
As expected, the droop resulted in more nose-down moment with the flaps extended, too much as it turned out. The problem was most obvious with the increase in nose wheel liftoff speed and the inadequate pitch control power after catapult launch and during bolters. Additional wind tunnel tests established that elimination of the inboard leading edge flap (added during development as noted above for increased lift) reduced the nose-down moment at nose-wheel liftoff speeds and turned out not to affect lift at approach speeds.
Although eliminating the inboard leading edge flap was beneficial, it was inadequate. Further wind tunnel tests indicated that the stabilator was stalled at nose wheel liftoff speed. As McDonnell engineer Bill Weber remembers it, "We tried a matrix of planform and area changes to correct the problem and finally determined that adding a fixed leading slat would delay the stall and could fix the problem. (Note: These wind tunnel tests were conducted without a simulated jet exhaust - later tests with jet effects indicated that the slat did not delay the stall and the improved stabilator power was probably due to an increase in effective area.)"
Even before the wind tunnel tests of the slotted stabilizer were accomplished, McDonnell program management decided to fabricate a slotted stabilator by adding a fixed slat to the leading edge of the existing one and flight test it. Bill Weber again: "As a consequence flight tests of the slotted stabilator took place very shortly after we had wind tunnel results. In any event the flight tests demonstrated that the problem had been fixed. We used the same configuration changes to fix a similar problem on the F- 4E which didn't have aileron droop but had a more forward C.G. due to the installation of the gun."
Although created for the F-4J, which first flew in June 1966, the drooped aileron and associated changes (the slotted stabilator and the elimination of the inboard leading edge flap) were of benefit to the F-4B as well. The package of changes was incorporated with Block 26 production, the first of which was BuNo 152995 that first flew in March 1966, and retrofitted to most of the surviving earlier F-4Bs over time.
Retrofit involved the development, qualification, and approval of a different package of drawings and other documents for use by the Naval Air Rework Facilities before crash-damaged and overhaul-due F-4Bs would get these changes. I've read that "by late 1971 or early 1972 it would have been rare to see a F-4B without these modifications, except perhaps in RAGs or Marine reserve units." For sure the slotted stabilator was present on F-4Ns coming off the Bee Line at North Island. The first F-4N flew in June 1972.
This is an F-4N, which is an upgraded F-4B. Note the drooped ailerons and fixed inboard leading edge along with other detail changes to the original B configuration.
Thursday, September 8, 2011
World War II ASW Schemes versus the Norfolk Scheme
In January 1943, the U.S. Navy directed that its combat airplanes be painted in a new, complex camouflage scheme that utilized counter-shading and counter-shadowing. (Sometimes referred to as the tri-color scheme, it actually involved more than three shades.) It took some time for the Navy airplane manufacturers to switch over to the new requirement, no doubt in part because they had to figure out exactly how to implement it and then get Navy approval for their design.
In the meantime, the Navy had to repaint airplanes that had already been delivered and for a time, those being delivered. It appears that a goodly number of these repaints were done at Norfolk, Virginia to a standardized and somewhat different scheme than the ones that the manufacturers would come up with. It is characterized by the Sea Blue upper surface color extending almost straight down on the side of the fuselage to the leading and trailing edges of the wing and relatively less Sea Blue on the side of the fuselage than the eventual production schemes. In this example, the TBM? on the left has the factory paint scheme and the TBF? on the right is the Norfolk scheme.
Click HERE for my prior discussion of it and more examples.
ASW Schemes I and II were implemented by the Commander Aircraft, Atlantic in July 1943 but not covered by a Navy specification until June 1944. In a recent discussion on one of the modeling websites of these schemes, I began to wonder if I hadn't mistaken at least one picture of an aircraft with an ASW scheme for an example of what I term the Norfolk scheme.
ASW Scheme I: For use in areas where the prevailing weather was clear or clear with broken clouds (the southern United States seaboard, Gulf of Mexico, Caribbean, and South America). This was a topside of nonspecular Dark Gull Gray, sides of nonspecular Light Gull Gray, and bottom of Gloss White. The side surfaces in the shadow of the wings and horizontal tail were to be painted nonspecular Insignia White. In a gray-scale picture, it looks very much like the blue tri-color scheme.
ASW Scheme II: For use in areas where the prevailing weather was overcast of heavily clouded (the middle and northern United States seaboard and the North Atlantic). This was a topside of nonspecular Dark Gull Gray, sides of nonspecular Insignia White, and bottom of Gloss White. The difference between it and Scheme I was the use of White rather than Light Gull Gray on the sides.
In both Scheme I and II, the leading edge and inside of the cowlings, propeller domes, and propeller blades (out to the inner edge of the cowling opening) were to be painted nonspecular Insignia White.
However, the examples are somewhat confusing. This is a picture of SBDs from VMS-3, which was based in the Virgin Islands (rough duty).
It would seem that these airplanes should be in Scheme I (Light Gull Gray on the sides) since they're based in the South Atlantic. Instead, the sides appear to be white, which is Scheme II. One theory for this discrepancy is that the anticipated basing of the airplanes was not the same as their actual assignment. Note that the extension of the top color directly down to the wings is very similar to the Norfolk scheme in this example as well as the two that follow.
This is an example of Scheme II provided by Steven (Modeldad) Eisenman:
The white sides are pretty unmistakeable.
This is an example of Scheme I (Light Gull Gray sides) provided by Steven:
Note the white propeller dome in both cases as well as the early rocket launchers; a hole made by a rocket was an effective way to keep a surfaced submarine from submerging to the relative safety of the depths.
The picture that got my attention was this one:
It was also cited as an example of the ASW Scheme I. However, based on the fact that it has a circle and star national insignia, (and does not have the white-painted propeller dome and inner blades) my guess is that it's an example of the Norfolk tri-color scheme, since the start of the transition to the star and bar insignia predated the multi-color ASW schemes:
n.b. A two-tone white ASW Scheme was reportedly used on the TBFs, if not the F4Fs, of VC-9 when it deployed aboard Bogue in early 1943 to the North Atlantic. However, I haven't found a picture that clearly shows no grey on the Avengers. This one, provided by Steven Eisenman, of TBFs on Card that was possibly taken in July 1943 is the best evidence of that scheme on TBF that I've seen so far.
In the meantime, the Navy had to repaint airplanes that had already been delivered and for a time, those being delivered. It appears that a goodly number of these repaints were done at Norfolk, Virginia to a standardized and somewhat different scheme than the ones that the manufacturers would come up with. It is characterized by the Sea Blue upper surface color extending almost straight down on the side of the fuselage to the leading and trailing edges of the wing and relatively less Sea Blue on the side of the fuselage than the eventual production schemes. In this example, the TBM? on the left has the factory paint scheme and the TBF? on the right is the Norfolk scheme.
Click HERE for my prior discussion of it and more examples.
ASW Schemes I and II were implemented by the Commander Aircraft, Atlantic in July 1943 but not covered by a Navy specification until June 1944. In a recent discussion on one of the modeling websites of these schemes, I began to wonder if I hadn't mistaken at least one picture of an aircraft with an ASW scheme for an example of what I term the Norfolk scheme.
ASW Scheme I: For use in areas where the prevailing weather was clear or clear with broken clouds (the southern United States seaboard, Gulf of Mexico, Caribbean, and South America). This was a topside of nonspecular Dark Gull Gray, sides of nonspecular Light Gull Gray, and bottom of Gloss White. The side surfaces in the shadow of the wings and horizontal tail were to be painted nonspecular Insignia White. In a gray-scale picture, it looks very much like the blue tri-color scheme.
ASW Scheme II: For use in areas where the prevailing weather was overcast of heavily clouded (the middle and northern United States seaboard and the North Atlantic). This was a topside of nonspecular Dark Gull Gray, sides of nonspecular Insignia White, and bottom of Gloss White. The difference between it and Scheme I was the use of White rather than Light Gull Gray on the sides.
In both Scheme I and II, the leading edge and inside of the cowlings, propeller domes, and propeller blades (out to the inner edge of the cowling opening) were to be painted nonspecular Insignia White.
However, the examples are somewhat confusing. This is a picture of SBDs from VMS-3, which was based in the Virgin Islands (rough duty).
This is an example of Scheme II provided by Steven (Modeldad) Eisenman:
This is an example of Scheme I (Light Gull Gray sides) provided by Steven:
The picture that got my attention was this one:
Tuesday, August 16, 2011
Early F4H Redux
It turns out that there was a change to the tailhook and the deletion of a fairing behind the tailhook that I hadn't noticed. There was also a change to the stabilator that was brought to my attention by Craig Kaston. I've updated the second early F4H entry, HERE, with a drawing and a couple of pictures that illustrate the changes to the tailhook and the deletion of the fairing. I've updated the first early F4H entry, HERE, to illustrate the stabilator change.
Thursday, August 11, 2011
F9F-6 vs. 8 Cougar Redux
I've updated this entry, HERE, in response to a question about the difference in the length between the F9F-6 and the -8 as provided on the interweb—and also in Steve Ginter's monograph Number 66, Grumman F9F-6/7/8 Cougar Part One—of 16 inches versus the eight inches that I show. I also updated the planform view of the F9F-5/6/8 to reflect the eight-inch increase in length of the -8 compared to the -6.
Sunday, July 31, 2011
Douglas Low-drag External Fuel Tanks
11 October 2017: A3J-1/RA-5C tank drawing and discussion updated.
13 September 2016: For the earlier 150 and 300-gallon tanks, see http://tailspintopics.blogspot.com/2016/09/things-under-wings-post-war-external.html
30 July 2016: I added some discussion about the 400-gallon tank.
27 July 2012: I added a few more example pictures of the different sizes of standard Douglas-design tanks and an evaluation of the accuracy of the tanks in some 1/72-scale kits here: http://tailspintopics.blogspot.com/2012/07/douglas-low-drag-external-fuel-tanks.html
7 August 2011 Update: Gerry Whiteside provided some first-hand information on the fin attachment arrangement, which I have incorporated.
3 August 2011 Update: I made some changes to the 150-gallon tank based on a drawing provided to me by Craig Kaston. It corrects the number and location of frames and the 14-inch lugs, as well as adding the 30-inch lugs. Note that on 2 August, I also added some Don Hinton pictures of the 300-gallon tank..
In the early 1950s, Douglas created a series of low-drag external fuel tanks and bombs. The latter became the Mk 8X series. The tanks came in three standard sizes: 150, 300, and 400-gallons. The number and orientation of the fins varied depending on the airplane and pylon station. The 150-gallon tanks, after appearing initially on the A4D-1 and early F4Ds, appear to have had limited operational use although the Douglas AD Skyraider and Grumman F9F-8 Cougar were qualified to carry them and the AD-5W often carried one of them. The 400-gallon tank was primarily carried by later models of the A4D Skyhawk and was also the basis for the Douglas D-704 in-flight fueling store, which was often referred to by the Douglas design number, and carried by the AD tankers for maximum giveaway.
While the bombs became standard across the board, the 300-gallon fuel tanks were primarily utilized by Douglas aircraft: the AD Skyraider, A2D Skyshark, F3D Skyknight, F4D Skyray, and A4D Skyhawk. The other Navy aircraft that deployed in the 1950s like the F3H Demon, FJ-3/4 Furies, and F7U Cutlass carried custom low-drag tanks. Later fighters also had to be equipped with unique tanks to maximize the amount of fuel that they could carry: the F4H/F-4 wound up with two, a huge 600-gallon one on the center-line station and/or 370-gallon tanks on the outboard wing stations. However, the Douglas 300-gallon tank configuration did become standard on the Grumman A-6, Vought A-7, and Lockheed S-3.
The number and orientation of the fins could be easily changed to the configuration required for a particular airplane's requirements. I had guessed that the aft end of the tank would have to be rotated to mount fins at 45 degrees. Gerry Whiteside provided the following:
I was in A-7's (VA-82) and we used the same tanks. The longitudinal slots (at 0, 90, 180 and 270 degrees on the A-7 tanks) are the mounting points for the fins and the vertical slots (at 45, 135, 225 and 315 degrees) are for access to the mounting nuts for the bolts that attached the fins. For the A-7 there was a different fin configuration for the outboard stations (1 and 8) versus the inboard stations (3 and 6); (stations 2 and 7 were dry and for nukes).
Every once in a while, somebody asks about these or compares/contrasts the tanks available from different kit manufacturers. I don't have much but here is a comparison of the 150 and 300-gallon tanks. I drew the 150-gallon tank from a Douglas engineering reference drawing for the A4D; the 300-gallon one was done by a Vought predesign engineer once upon a time. The shapes can be considered to be close to the actual tanks. I was particularly surprised and pleased to see that the fin on the Douglas drawing was exactly the same as the one on the Vought drawing.
I did have Navy documentation for the 300 and 400-gallon tanks:
Unfortunately, the fin isn't shown for the 400-gallon tank but the span shown suggests that it used the same fin as the other two tanks.
30 July 2016 Update: I'm not convinced that the shape of the 400-gallon tank shown in the drawing above is exactly representative of the fielded tank. For sure, both the A4D and the A3J appear to have carried a tank with a less pointed nose, probably ending at the station 0 shown on the drawing.
The A4D tank (the aft end was also bobbed to allow access to the hell hole in the aft fuselage):
The A3J tank:
The A3J 400-gallon tank appears to taper more going aft than the standard tank drawing. The following is based on a pretty good North American general arrangement drawing.
Note that the nose of the tank in the drawing doesn't appear to bulge as much as the one in the picture above or taper as much. Here is another perspective:
However, the 400-gallon tank was rarely seen on the RA-5C since it had more internal fuel than the A3J-1.
2 August 2011 Update: Don Hinton photos of the 300-gallon tank on the F4D at the National Museum of Naval Aviation at Pensacola.
Note that because of parallax, etc. it wouldn't be wise to try to use this to establish the shape of the tank.
The tip of the tank is a little bulbous and definitely not pointed.
Note the 30-inch lugs, sway braces, and connections to the pylon.
Note the vertical and longitudinal slots on the aft end of the tank for installing different fin configurations as described by Gerry Whiteside above.
The silver rectangle on the top of the tank is a data plate.
When a tank required the "X" orientation of the fins, as on the S-3 shown here (from a crop of a Christopher Ishmael picture found HERE), the aft end of the tank was rotated 45 degrees.
As a bonus, here is the Navy documentation for the D-704 store:
For more on the inflight refueling store, see http://tailspintopics.blogspot.com/2015/06/things-under-wings-inflight-refueling.html
13 September 2016: For the earlier 150 and 300-gallon tanks, see http://tailspintopics.blogspot.com/2016/09/things-under-wings-post-war-external.html
30 July 2016: I added some discussion about the 400-gallon tank.
27 July 2012: I added a few more example pictures of the different sizes of standard Douglas-design tanks and an evaluation of the accuracy of the tanks in some 1/72-scale kits here: http://tailspintopics.blogspot.com/2012/07/douglas-low-drag-external-fuel-tanks.html
7 August 2011 Update: Gerry Whiteside provided some first-hand information on the fin attachment arrangement, which I have incorporated.
3 August 2011 Update: I made some changes to the 150-gallon tank based on a drawing provided to me by Craig Kaston. It corrects the number and location of frames and the 14-inch lugs, as well as adding the 30-inch lugs. Note that on 2 August, I also added some Don Hinton pictures of the 300-gallon tank..
In the early 1950s, Douglas created a series of low-drag external fuel tanks and bombs. The latter became the Mk 8X series. The tanks came in three standard sizes: 150, 300, and 400-gallons. The number and orientation of the fins varied depending on the airplane and pylon station. The 150-gallon tanks, after appearing initially on the A4D-1 and early F4Ds, appear to have had limited operational use although the Douglas AD Skyraider and Grumman F9F-8 Cougar were qualified to carry them and the AD-5W often carried one of them. The 400-gallon tank was primarily carried by later models of the A4D Skyhawk and was also the basis for the Douglas D-704 in-flight fueling store, which was often referred to by the Douglas design number, and carried by the AD tankers for maximum giveaway.
While the bombs became standard across the board, the 300-gallon fuel tanks were primarily utilized by Douglas aircraft: the AD Skyraider, A2D Skyshark, F3D Skyknight, F4D Skyray, and A4D Skyhawk. The other Navy aircraft that deployed in the 1950s like the F3H Demon, FJ-3/4 Furies, and F7U Cutlass carried custom low-drag tanks. Later fighters also had to be equipped with unique tanks to maximize the amount of fuel that they could carry: the F4H/F-4 wound up with two, a huge 600-gallon one on the center-line station and/or 370-gallon tanks on the outboard wing stations. However, the Douglas 300-gallon tank configuration did become standard on the Grumman A-6, Vought A-7, and Lockheed S-3.
The number and orientation of the fins could be easily changed to the configuration required for a particular airplane's requirements. I had guessed that the aft end of the tank would have to be rotated to mount fins at 45 degrees. Gerry Whiteside provided the following:
I was in A-7's (VA-82) and we used the same tanks. The longitudinal slots (at 0, 90, 180 and 270 degrees on the A-7 tanks) are the mounting points for the fins and the vertical slots (at 45, 135, 225 and 315 degrees) are for access to the mounting nuts for the bolts that attached the fins. For the A-7 there was a different fin configuration for the outboard stations (1 and 8) versus the inboard stations (3 and 6); (stations 2 and 7 were dry and for nukes).
Every once in a while, somebody asks about these or compares/contrasts the tanks available from different kit manufacturers. I don't have much but here is a comparison of the 150 and 300-gallon tanks. I drew the 150-gallon tank from a Douglas engineering reference drawing for the A4D; the 300-gallon one was done by a Vought predesign engineer once upon a time. The shapes can be considered to be close to the actual tanks. I was particularly surprised and pleased to see that the fin on the Douglas drawing was exactly the same as the one on the Vought drawing.
I did have Navy documentation for the 300 and 400-gallon tanks:
30 July 2016 Update: I'm not convinced that the shape of the 400-gallon tank shown in the drawing above is exactly representative of the fielded tank. For sure, both the A4D and the A3J appear to have carried a tank with a less pointed nose, probably ending at the station 0 shown on the drawing.
The A4D tank (the aft end was also bobbed to allow access to the hell hole in the aft fuselage):
The A3J 400-gallon tank appears to taper more going aft than the standard tank drawing. The following is based on a pretty good North American general arrangement drawing.
2 August 2011 Update: Don Hinton photos of the 300-gallon tank on the F4D at the National Museum of Naval Aviation at Pensacola.
The tip of the tank is a little bulbous and definitely not pointed.
Note the 30-inch lugs, sway braces, and connections to the pylon.
Note the vertical and longitudinal slots on the aft end of the tank for installing different fin configurations as described by Gerry Whiteside above.
The silver rectangle on the top of the tank is a data plate.
When a tank required the "X" orientation of the fins, as on the S-3 shown here (from a crop of a Christopher Ishmael picture found HERE), the aft end of the tank was rotated 45 degrees.
As a bonus, here is the Navy documentation for the D-704 store:
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