Rear folding undercarriage on single engined aircraft

Rearward folding undercarriage was used or proposed on a few single-engined fighters, bombers and trainers. Was there any design or production advantages?

Gloster F.5/34



Curtiss P-36



Curtiss P-40



Ilyushin IL-2



Miles Master



Douglas TBD.

The only advantage I think might appertain would be simplicity of design, but then the rotation involved in many examples removes even that. Maybe there's some CoG factors coming into play as well?

I remember reading somewhere that for the TBD that the wheels were left unrotated and exposed as a matter of providing some protection for wheels-up landing. I can't see much advantage to rear-folding as opposed to lateral-folding otherwise. I think the inward-folding wide-gear layout became standard for reasons of both mechanical simplicity as well as structural strength.

Thumpalumpacus said:

I remember reading somewhere that for the TBD that the wheels were left unrotated and exposed as a matted of providing some protection for wheels-up landing.

Click to expand...

I'd have to think that's the same intended feature for the Gloster F5/34. Its designers must have had some notion in mind when they left half of each wheel out in the slipstream.

Admiral Beez said:

I'd have to think that's the same intended feature for the Gloster F5/34. Its designers must have had some notion in mind when they left half of each wheel out in the slipstream.

View attachment 654219

Click to expand...

I've been unaware of the airplane until this post of yours but it looks like at the least a case of convergent evolution, and perhaps as you imply a matter of convergent design.

Surprised you didnt include the Hellcat and Corsair. Lots of advantages if you can get it to work. Much easier to put weapons and fuel in the wings.

Absolutely until the drag becomes a major issue.

The main offset was drag but a more rigid and therefore structurally superior wing leading edge or torsion box would have cancelled that at ww2 speeds

There will be a bigger change in CoG with rear folding wheels, dunno whether that is an advantage or disadvantage.

The Gloster F.5/34 was to all intents and purposes a modern aeroplane for the mid 1930s with all-metal structure, variable pitch prop, which even the Hurricane and Spitfire didn't have at the time they first flew, hydraulically actuated split flaps etc and the wheels were designed to take the weight of the aircraft during a belly landing, which was a bonus. It took awhile to be finished, Gloster was busy building Gladiators and all-metal aeroplanes were new to the firm so the first one didn't fly until December 1937. Its Mercury produced 840 hp, so its performance wasn't sparkling, but it was about the same as the Hurricane with a maximum speed of 316 mph at 16,000 ft, with a climb of 11 to 20,000 ft.

Nevertheless, the idea of the wheels being exposed was a common feature of the period and extended to aircraft such as the Blenheim and Wellington, the latter of which was more of maintaining the line of the lower cowl, as the fuselage line was lower than the nacelles. This view of the Wellington's undercarriage doors show the cutout for the wheel.

Stbd nacelle

In this Bolingbroke the cutout for the wheel is obvious.

MoF 132

Just to mention it; the Fairey Battle qualifies.

P-35

Northrop BT-1


Boeing XF8B


Skyraider


reasons are varied.
On the old airplanes it was a way save airplanes from pilots that forgot to retract the landing gear.
On the later war planes it was a way maximize underwing area for bombs, drop tanks and other "stuff".

On some of the in-between planes it can really vary. The P-36 and P-40 were not going to get as much protection from the flush wheels (although they had a vertical keel area) but keeping the wheels away from the real estate along the center of the wing may have been in the designers mind. Where are the fuel tanks located in the wing? were are the axillary bomb racks?

Nice picture of the P-35.

initially, it was just too easy to rotate the gear backwards, especially if strong gear is required, ala C-47. Additionally, it was easy to leave the gear partially down in case of a gear up landing, again, ala C-47, which I suspect happened a lot back then when no one had experience with retractable gear. It still can happen, as I can attest trying to land a C-141 gear up on a local test flight. Even rotating the gear as it retracted was not a complex engineering or manufacturing feat. Some aircraft, like the F4U, really had no where else to go, couldn't go inboard, it would have to go up the gull wing, certainly complex, and couldn't go outboard due to guns, fuel, etc. The A-1 goes backwards but I don't really know why, looks like inboard retraction should be easy, perhaps some thing internal was a problem, fuel? In general, there seemed to be a mishmash of designs, the AAF had the P-51, P-47, and early jets retracting inward and P-40 backwards (an older design). The Navy had the F4U and F6F retracting backwards and the F8F, and early jets all retracted inward. Thin wings may have been a factor.

A lesson to all you pilots and wantabe. Breaking a memorized series of events can be conducive to leaving out steps or forgetting steps. My experience mention above provides a good example. I was on a annual pattern (flying skills) check flight. My specific task was to fly a holding pattern depart on a specified heading when cleared intercept an ILS inbound course, fly the ILS and do a touch in go. Straight forward. The procedures were, when cleared from holding, fly a heading and maintain altitude, when intercepting the inbound localizer descend to and maintain approach altitude until glideslope intercept. In holding I had set up my outbound heading bug and my inbound localizer course on my horizontal situation indicator HSI. When cleared for approach, I departed on prescribed heading, and since we were not far from the runway, began configuring for landing. The memorized steps were, Flaps landing, wait until down (flaps used a lot of hydraulic fluid), gear down, before landing checklist. Just as I had place my flaps down and was waiting to put the gear down, the Iocalizer course indicator came off of its stop. Now I had to turn to intercept course and descend to approach altitude, and of course, maintain airspeed. This I accomplished with my usual excellent flying skills, and as I was approaching glide slope a horn was going off in my ear! I thought, it's usually quiet at this point in time (all the crew members were usually busy holding their breath, praying and crossing themselves). I glanced over the cockpit and saw it! THE GEAR HANDLE WAS UP AND LIGHTED RED. I quickly called out "gear down, before landing checklist". The flight examiner threw the gear lever down and quickly ran down the check list. Just as I flared he said checklist complete, and I touched down. He asked me what I would have done had he not completed the check list? "I would have gone around", I said. Right answer. I passed the flight test. So, beware broken memory patterns.

According to something I read the Landing gear setup that Curtiss used was actually a Boeing patent so we can get rid of most of the conspiracy theories
I would also note that on the P-36 and the P-40 the landing gear struts went underneath the wing with no cutouts or notches in wing structure except for the holes for the wheels/tires. The under wing fairings held the struts.

I am guessing that the A-1 Skyraider just used the same landing landing gear for all versions (aside from beefing up)


Just leaving a large space under the fuselage/wing roots just made it easy to fit different radars and/or sensors under the airframe.


The F8F used an articulated strut. the lower leg actually folds back nearly 180 degrees over the upper leg in order to get the necessary landing gear strut length inside the space available for it.

My guess on the Spad's rearward retracting gear was twofold. First, an attack plane will get shot up and resulting in greater odds of landing gear up (same logic used on A-10). Second, gear that lay aft under the wing increase wing area for weapons stations.

Complete with battle patina. It appears there are 7 stations on each wing, and one on the centerline. The station nearest the gear hangs down further but would still appear to be limited in size of weapon / fuel tank by the gear doors. The plane was a weapons truck.

During design, consideration would have to be given towards weight, bomb load, and wing design. Also consider that there are manufacturers who specialized in the manufacture of landing gear (Cleveland Pneumatic, Manasco and Dowty to name a few) If a component can be purchased "off the shelf" and made to work in a given design, production costs can be kept down. IIRC the F-117A had the same landing gear as the A-10.

I have no idea what they were planning do with the Plane during initial design and testing.
A competitor, the Martin Mauler had 3 torpedoes under the wing . It also used rearward retraction.

The Navy (and the air force) were putting Tiny Tims under all kinds of things.



Maybe they decided to leave out everything the landing gear and the under fuselage station?

It has been alluded to by some here already but one of the most obvious reasons would be to help ease and increase the wing folding capability of carrier based aircraft.

Shortround6 said:

View attachment 654735

I have no idea what they were planning do with the Plane during initial design and testing.
A competitor, the Martin Mauler had 3 torpedoes under the wing . It also used rearward retraction.

The Navy (and the air force) were putting Tiny Tims under all kinds of things.

View attachment 654736

Maybe they decided to leave out everything the landing gear and the under fuselage station?

Click to expand...

They have a Mauler at the Naval Air Museum in Pensacola. It is a huge aircraft with huge engine. Very impressive. It out performed the A-1 but Martin couldn't produce it acceptably.

Shortround6 said:

According to something I read the Landing gear setup that Curtiss used was actually a Boeing patent so we can get rid of most of the conspiracy theories
I would also note that on the P-36 and the P-40 the landing gear struts went underneath the wing with no cutouts or notches in wing structure except for the holes for the wheels/tires. The under wing fairings held the struts.

I am guessing that the A-1 Skyraider just used the same landing landing gear for all versions (aside from beefing up)

View attachment 654727
Just leaving a large space under the fuselage/wing roots just made it easy to fit different radars and/or sensors under the airframe.


The F8F used an articulated strut. the lower leg actually folds back nearly 180 degrees over the upper leg in order to get the necessary landing gear strut length inside the space available for it.

Click to expand...

Shortround6 said:

According to something I read the Landing gear setup that Curtiss used was actually a Boeing patent so we can get rid of most of the conspiracy theories
I would also note that on the P-36 and the P-40 the landing gear struts went underneath the wing with no cutouts or notches in wing structure except for the holes for the wheels/tires. The under wing fairings held the struts.

I am guessing that the A-1 Skyraider just used the same landing landing gear for all versions (aside from beefing up)

View attachment 654727
Just leaving a large space under the fuselage/wing roots just made it easy to fit different radars and/or sensors under the airframe.


The F8F used an articulated strut. the lower leg actually folds back nearly 180 degrees over the upper leg in order to get the necessary landing gear strut length inside the space available for it.

Click to expand...

The P-47 used a telescoping gear for the same reason.

There is a distinct advantage to having the main gear exposed when retracted.

The A-10 has that purpose-built feature, so that if it's tricycle gear fails to extend, it still has conventional gear to land on.

This series of photos was one such instance, that happened at Edwards AFB.