Jet undercarriage…

VEGA ECM And of course, in the case of the JP1 the Ministry was just too “skinflint” to redesign the Pericival Piston Provost Landing Gear, until it was proven that it absolutely necessary!
No, Hunting Percival designed the Jet Provost. The use of Provost legs was to use a high commonality with the earlier aircraft ( about 80% by memory) in order for the company to gain the contract. By the time they had got to the JP4 I think it was down to about 20%. I’ll leave it to others to comment on the rest of your dissertation 🙂

I’m sorry, but I don’t believe FOD has anything to do with it at all;- just look at the minimal ground clearance between a 737-400/500etc engine intake and the ground.

The main design driver for the Landing Gear length is the tail clearance against a given take off angle at rotation . The aircraft’s take off rotation angle itself is a function of the type of high lift system fitted;- double slotted flap needs only a low angle, where as single stage flap have higher angles and delta’s need very high AOA. Also, where the landing gear is mounted within the airframe and where with respect to the wings, has a pretty significant effect on their length, I.e mounting the engine under the wing as opposed to in the wing tends to lengthen the gear and locating the engines at the rear tends to push the cg back and hence the wing aftwards…. in general the more aftwards the wing the shorter the gear (Delta’s are an exception to this because of the higher AOA).

Size for size Jet aircraft tend to be much heavier than prop aircraft, so they generally have more kinetic energy to dissipate during touch down. This kinetic energy has to be converted to potential energy over a longer shock absorber closing stroke by means of the damping. Hence the jet landing gear shock absorber strokes tend to be significantly longer for a telescopic type oleo. For aircraft where the retracted stowage length is limited a “trailing link” type Landing Gear may be used (Meteor, Buc, Jag) which gives the longer stroke in a shorter overall Landing Gear length. There are a very large number of variation on these basic two themes resulting a vast number of design all customised to meet the aircrafts particular configuration.

Other factors connected to Landing Gear lenght are carrier operations, VSTOL, and rough field operations.

And of course, in the case of the JP1 the Ministry was just too “skinflint” to redesign the Pericival Piston Provost Landing Gear, until it was proven that it absolutely necessary!

Foreign material ingestion is the main reason (other than necessary clearance on rotation and landing – given the oleos will compress quite a lot, esp. if its a hard landing).

If you could visualise the airflow into the intakes in a high rpm, low forward speed (i.e. takeoff) condition, then you would see that air is drawn in from many angles and consequently the possibilty for ingesting rubbish is quite high. Add to that the fact that the nose gear may also throw up quite a lot of material and you’ve got a real potential problem.

Hawker Siddeley did some tests on an HS125 (G-ASEC) in the 1960s with bags fitted inside wooden frames mounted on the wing leading edges to ascertain how real the problem was for their forthcoming HS136 design and found that it was very serious indeed so the engines were moved back to the fuselage for the next study, the HS144.

Can confirm that the J.P. 1 undercarriage did use “Piston” Provost legs in order to claim high commonality to help justify the contract – also note the canopy framing. When taxying on grass at Luton the JP1 used to noticeably “walk” with its undercarriage legs, leading to the shortening on the JP2.

Possibly the longer U/C was to make servicing the A/C easier i.e removal of gun packs ,attachment of missiles, fuel aux fuel tanks; many military Jets were designed with the Navy in mind as well as Airforce , they have longer travel oleos for obvious reasons. I read somewhere (doesn’t everybody) that the Vampire suffered from ground effect with the aux fuel tanks fitted, and the U/c needed to be retracted almost imediately to stop the vortices (?) adversly affecting the handling.

Reasons that come to mind without in-depth research . . .

Rotation
FOD
Ground clearance for weapons fits

This last doesn’t always hold true though. Look at, eg, the Nimrod with its bomb doors open. Or the Canberra. That had to be jacked-up on the mains to enable nuke fit! (Canberras were fitted with an independently selectable nose u/c hyd valve that that could be used to ‘kneel’ the aircraft. But hardly anybody used this as it was a pain to set up.)

Regarding the JP.1, I understand the stalky u/c was because they utilised Piston Povost legs to keep costs down. The later JP’s however were ground huggers.

Anyway, I don’t really think later jets have really noticeable stalkiness. Maybe in the early days they could be said to have had but this, in my opinion, was due to ‘older’ oleo and u/c designs rolling over from the piston era.

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I’d have thought “room to rotate” would be the most likely explanation. The Vampire could get away with a stumpy little undercarriage because the booms were angled upwards slightly. Something like a Hunter would need more room and so is fairly tall – still has a substantial tail bumber though because there still wasn’t enough room for some pilots! 😀