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Early F-111 undercarriage doors


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Thanks Guys,

As usual, Tommy's stuff is inspirational! I am building '972 and I hope that your drawings and images will help. Even with these it still hard to visualise where the linkages attach to the airframe and main gear but I will look a bit harder. Sadly I passed on my Revell TFX without taking enough notice of the gear door attachment but I built it back in the 70's and I know that the whole thing folded up pretty well - until plastic fatigue set in!

Thanks Andre, I'd looked at Jim's site last week but the one thing it doesn't show is the early gear mechanism. Rats!

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Simon,

You may also search for pics of the A model 'Vark, at least one of the B's was modified from an A airframe and I cannot find any empirical evidence that the gear doors (particularly the hinges) were substantially different from model to model. However, having said that, I'm sure someone will point out that I am incorrect!

There are some really detailed pics in the Squadron Walk Around title on the 'Vark and those may help you! They are of other models, but again I am not sure that there was substantial difference.

Rick

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Thanks Guys,

As usual, Tommy's stuff is inspirational! I am building '972 and I hope that your drawings and images will help. Even with these it still hard to visualise where the linkages attach to the airframe and main gear but I will look a bit harder. Sadly I passed on my Revell TFX without taking enough notice of the gear door attachment but I built it back in the 70's and I know that the whole thing folded up pretty well - until plastic fatigue set in!

Thanks Andre, I'd looked at Jim's site last week but the one thing it doesn't show is the early gear mechanism. Rats!

This is one way to do it...

F-111BAftMainGearDoorActuation.jpg

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Thanks Tommy,

I can sort of see the retraction sequence but I'm having problems with linkage B. The point where B revolves must move forward and up into the gear bay as the u/c retracts? Link A appears to attach to and to pivot at the rear end of the gear bay? Wouldn't it be great to have photos of the two linkages as B seems to be a real strange shape - straight in your drawing but bent (hinged?) in the Grumman illustration? Maybe the easy answer is to just make two open triangles and attach the top to the rear edge of the bay?!!

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Thanks Tommy,

I can sort of see the retraction sequence but I'm having problems with linkage B. The point where B revolves must move forward and up into the gear bay as the u/c retracts? Link A appears to attach to and to pivot at the rear end of the gear bay? Wouldn't it be great to have photos of the two linkages as B seems to be a real strange shape - straight in your drawing but bent (hinged?) in the Grumman illustration? Maybe the easy answer is to just make two open triangles and attach the top to the rear edge of the bay?!!

Note: This is just a guess at the kinematics (I'm still thinking about it) and the diagram is a stick figure, not a accurate representation of the shape of the parts. The good news is that you just have to attach the door with some bits of plastic and not have it retract. Revell did but cheated by mounting the door on a slider.

However, I'm pretty sure that the mechanism is similar in function to a parallelogram linkage. I think the upper end of link B pivots off a fitting attached to the canted bulkhead that is the aft end of the main landing gear well and that the maintenance manual illustration does not represent it in the gear-up position like it does link A (I have another illustration that shows link B angled aft although not as much as I depict it). Link A appears to be attached to a pivot point on the vertical beam on the landing gear (the V shape in the following picture), perhaps slightly lower than the pivot point of the beam. From the pictures and the illustration, link A looks like a fairly beefy part and link B looks like a control tube.

This picture is looking forward from behind the airplane. The aft main landing gear door is edge on so it's hard to see. Note that link B is located just outboard of link A.

Aftmainlandinggeardoorlookingforward.jpg

My current theory is that the door is pulled forward by link A which is pivoting on the V-shaped beam as the gear retracts. (There may be some sort of cam or idler involved at the attachment point on the beam.) All link B does is keep the door more or less level as it moves toward the retracted position. I assume that the bend shown in link B provides clearance with something at some point in the retraction process.

It's easy to understand why GD discarded this arrangement and simply hinged the door at its aft edge.

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Hi Tommy,

The geometry of this gear door is more complex than that of the wings! These exchanges have brought home to me just how low the door sits. In my mind it was quite close to the underside but in reality its about 1/3rd or so of the distance between the underside and the ground.I know that there's a working u/c unit in one of your museums which is used to demonstrate how the gear folds away but that's probably from a later unit with the vertical fixed door. I don't suppose there are many 'A' models left with the early door? I notice that the TACT airframe was one though but, no doubt it has been scrapped a long time ago?

Turning back to your drawing, I thought that the length of the linkages changed between gear up and gear down but I help up a piece of paper to the screen and I can see that they are the same! You realise that the next thing will be to knock up something out of cardboard and pins to see it work in profile?!!

Thanks again Tommy - and for clarifying that Revell's method was non-scale!

Simon

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After looking at what is available to me and doing some more work on the kinetics, it looks like link A is a bell crank rather than the simple link that I described earlier. Its upper end is attached to a pivot point on the bulkhead and lower end on a pivot point forward on the door. It's also attached to and pivots on the V-shaped landing gear beam near its pivot point for swinging the wheels up and into the wheel well. The rotation of this beam results in the door first swinging down and forward and then up into place. Link B is what's called an idler. Its upper end appears to be attached just outboard of the pivot point of the upper end of the shock strut although I can't be sure yet. (I haven't found a picture or illustration to confirm it; at one point I thought it might be attached to the upper part of the shock strut itself.) The idler restrains the door in pitch and the geometry is such that the door is level when the gear is locked up or down; the door goes leading edge up as it swings forward toward its up and locked position as demonstrated by a video of the NASA TACT F-111 gear retraction, consistent with the kinematics on my notional layout. See

I'm working on an updated illustration of the aft main landing gear door actuation mechanism. When I'm satisfied with it, I'll update http://tailspintopics.blogspot.com/2009/10/grumman-f-111b.html

In other news, Peter Russell of Pete's Hangar has added the early F-111B knife-edge boat tail and speed bumps to his F-111B conversion kit in both 1/72 and 1/48 scale. (There may also be another kit with the early Phoenix and the F-111B Phoenix pylons.) At the moment, these kits are only available through Victorian Hobby Centre in Melbourne, Australia. However, I have dealt with them from the U.S. and the service is good. Their web site is being reconstructed but it provides contact information. See http://www.vichobbycentre.com.au/page19279/HoldingPage.aspx. Pictures and a description of what's in the conversion kit are at http://tailspintopics.blogspot.com/2009/10/grumman-f-111b.html

Oh - and the later door isn't hinged on its aft edge. It is simply hard mounted to that vertical beam. So simply that when the gear is retracted, there is a sizable gap between the aft end of the door and the aft end of the wheel well. See http://www.clubhyper.com/reference/f111indetailjr_4.htm

Edited by Tailspin Turtle
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Hi Tommy,

Thank you for going to all this trouble to research the retraction sequence! I will have a look at the YouTube video to see if it helps!

I'm part way through my build of 972 - photo's below - and maybe you can clarify another point? I think that the splitter plates were painted light gull gray? I know that the first two airframes were white and I think that the imagery that I have suggest LGG as being most likely for my airframe but it would be good if you could confirm!

F-111photos005.jpg[/img]

F-111photos006.jpg[/img]

Best regards

Simon

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Hi Tommy,

Thank you for going to all this trouble to research the retraction sequence! I will have a look at the YouTube video to see if it helps!

I'm part way through my build of 972 - photo's below - and maybe you can clarify another point? I think that the splitter plates were painted light gull gray? I know that the first two airframes were white and I think that the imagery that I have suggest LGG as being most likely for my airframe but it would be good if you could confirm!

Best regards

Simon

Actually, I'm pretty sure that only the first F-111B (970) and the fifth (974) had white splitters. (974 originally had a gray early splitter but it was replaced with the Triple Plow I inlet and splitter, which was painted white.)

The following pictures of 972 in flight test at Hughes provided to me by Craig Kaston should be of interest. Note that the bottom of the 972 splitter is deeper at its aft edge than its forward one. 972 also had the ducts over the underwing vents. Some of the antennas and the bump on the top of the fairing on the vertical fin were added by Hughes.

I've never seen a picture of 972 with a nose boom. That doesn't mean that it never had one, but it was not used in Grumman flight test. 971 and 972 were assigned to Phoenix missile development at Hughes and flew only shakedown flights at Grumman.

F-111BBuNo151972HugheswfF-4.jpg

F-111B151972frombelow.jpg

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Geoff,

Many thanks for sorting out my photos!!

Tommy, what gorgeous photos! I'm not sure about that boom. F-111 in Action shows an illustration of the 3rd prototype with boom and also a photo purporting to be the 3rd prototype but with the fin code blanked by the taileron/elevon! To be honest I think it looks prettier without the boom!

Thanks for highlighting the bottom edge of the splitter - an easy fix but a fairly vital correction! This also clarifies the ducts over the under wing vents - I thought they were just flush openings but the ducts would obviously improve air extraction. Do you think the forward edge of the wing root/module is white or is the light making it look like that? Presumably a dielectric aerial fairing and normally black on air force 'vaarks. Also interesting to see that the natural metal finish on the slats extends all the way back on the underside and, I presume, an equal distance on the top surface?

The nose on my conversion is basically the Revell nose (I now have a mold!)but the upper view suggest that the upper line of the nose is almost a continuous line, including the windscreen line. Ah well, hopefully it will look something like! As it stands I'm using standard wheels on the basis that they were used from time to time on the 'B' but, no doubt, not on 972!!

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Tommy, what gorgeous photos! I'm not sure about that boom. F-111 in Action shows an illustration of the 3rd prototype with boom and also a photo purporting to be the 3rd prototype but with the fin code blanked by the taileron/elevon! To be honest I think it looks prettier without the boom!

Thanks for highlighting the bottom edge of the splitter - an easy fix but a fairly vital correction! This also clarifies the ducts over the under wing vents - I thought they were just flush openings but the ducts would obviously improve air extraction. Do you think the forward edge of the wing root/module is white or is the light making it look like that? Presumably a dielectric aerial fairing and normally black on air force 'vaarks. Also interesting to see that the natural metal finish on the slats extends all the way back on the underside and, I presume, an equal distance on the top surface?

The nose on my conversion is basically the Revell nose (I now have a mold!)but the upper view suggest that the upper line of the nose is almost a continuous line, including the windscreen line. Ah well, hopefully it will look something like! As it stands I'm using standard wheels on the basis that they were used from time to time on the 'B' but, no doubt, not on 972!!

With respect to the In Action illustration, I'm all but certain that 972 didn't have a nose boom when it was marked like that and carrying Phoenixes. All three of the pictures on pg 34 are of 970. The tell is the location of the demarcation line between grey and white on the forward fuselage. Only 970 had this scheme. One configuration oddity is that 970, in the picture that is purported to be of the third F-111B (and is on the cover of my F-111B monograph), has an F-111A wing with the ferry tips on it during this test phase.

The white or cream-colored triangular area at the forward edge of the wing root is an antenna cover.

As best I can tell, the "metal" finish on the upper leading edge goes back as far as it does on the lower leading edge. This is usually Corogard, but the Grumman external finish drawing is ambiguous about this.

There is in fact a slight difference in the slant of the windshield and the upper line of the nose. The Revell nose is a bit misshaped in cross section as mentioned on my F-111B web page:

F-111BRevellNose.jpg

Good news from a landing gear standpoint is that 972 had the F-111A landing gear, fat tires and all. After one of its accidents, the original nose gear was replaced with an F-111B's.

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Thanks for the additional clarification Tommy. The boom is definitely coming off the! A black and white barber pole had an appeal but the jet still looks better without it! I think thats pretty much clarified things for me. As I'm mating essentially a Revell radome onto an ESCI airframe there was a bit of filling required, but not a great deal. We'll have to see how the line of the nose/windscreen looks when the canopy is on - the cockpit is stuffed with tissue and masking tape right now but, hopefully, it will look something like when its finished. I notice from the photo that '972 has vane on the forward lower fuselage side and another one pointing upwards on the right hand side of the upper nose. Is the first an AOA sensor and the second a yaw vane, maybe in lieu of a nose probe? The lower vane is in the same position as the F-111A/E AOA sensor(?) and there is one on each side?

Regards

Simon

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Thanks for the additional clarification Tommy. The boom is definitely coming off the! A black and white barber pole had an appeal but the jet still looks better without it! I think thats pretty much clarified things for me. As I'm mating essentially a Revell radome onto an ESCI airframe there was a bit of filling required, but not a great deal. We'll have to see how the line of the nose/windscreen looks when the canopy is on - the cockpit is stuffed with tissue and masking tape right now but, hopefully, it will look something like when its finished. I notice from the photo that '972 has vane on the forward lower fuselage side and another one pointing upwards on the right hand side of the upper nose. Is the first an AOA sensor and the second a yaw vane, maybe in lieu of a nose probe? The lower vane is in the same position as the F-111A/E AOA sensor(?) and there is one on each side?

Regards

Simon

The thing on the right forward side of the fuselage is a pitot. There's also one on the left side but further forward. The F-111B angle of attack sensor is on the left side, roughly in the same location as the pitot on the right side. Hughes added a blade antenna pointing upwards on the right side of the upper nose and another one pointing down on underside of the nose to the right of the nose landing gear well.

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The thing on the right forward side of the fuselage is a pitot. There's also one on the left side but further forward. The F-111B angle of attack sensor is on the left side, roughly in the same location as the pitot on the right side. Hughes added a blade antenna pointing upwards on the right side of the upper nose and another one pointing down on underside of the nose to the right of the nose landing gear well.

Okay, just a standard blade with a pitot on the right and then upper and lower blade aerials. Strange to put them off centreline and, now you mention it, I see the lower blade is alongside the TV pod, mabe 24" or so forward of the nose bay doors? I wouldn't have seen it if you hadn't said! Will also check for photos of the l/h pitot - its starting to look Russian!!

Edited by Simon Cornes
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It turns out that the Chanute Air Museum in Rantoul, Illinois not only has an F-111 main landing gear maintenance trainer, but it has the original aft main landing gear door and the Curator, Mark Hanson, was kind enough to take some detailed pictures of it. I am pleased to say that I pretty much guessed right. I've posted an annotated picture of the door mechanism on my F-111B post, here: http://tailspintopics.blogspot.com/2009/10/grumman-f-111b.html

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  • 2 weeks later...

Hi Tommy,

Well those photos certainly show how complicated undercarriage units and there associated doors are, even back in the early 60's! I will do my best to incorporate some of that mechanism!

One. hopefully easier question, you may be able to shed some light on. How big are the fuselage and wing stars and bars? The reason I ask is because the Microscale sheet I have for '972 has had the national markings removed so I will have to find replacements. Any suggestions as to the size - and what other aircraft may have used the same size - would be very useful. I have the Scale Model World show in a few weeks time and I can look for a set, if I know what size I need! (This is all 1/72nd by the way!)

Many thanks

Simon

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Hi Tommy,

Well those photos certainly show how complicated undercarriage units and there associated doors are, even back in the early 60's! I will do my best to incorporate some of that mechanism!

One. hopefully easier question, you may be able to shed some light on. How big are the fuselage and wing stars and bars? The reason I ask is because the Microscale sheet I have for '972 has had the national markings removed so I will have to find replacements. Any suggestions as to the size - and what other aircraft may have used the same size - would be very useful. I have the Scale Model World show in a few weeks time and I can look for a set, if I know what size I need! (This is all 1/72nd by the way!)

Many thanks

Simon

I've subsequently discovered, thanks to Craig Kaston, that the idler link that positioned the leading edge of the aft main landing gear door probably pivoted on a fitting mounted on the side of the wheel well basically outboard of the upper attach point of the main landing gear shock strut. I'll put a picture of that up on the web site in a few minutes.

As best I can tell from close examination of photographs against drawings, both the fuselage and wing national insignia have 30" stars, which is to say that the blue circle is 33.75" in diameter.

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