Lucky13
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Shouldn't they be compressed and not extended?
Landing gear....
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mikewint
Captain
Jan, yes and no. If you are doing a FLYING model with the doors closed then yes but if you are doing a static display standing on the tarmac then no. Since most? modelers do the latter the parts are cast in their extended form
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Lucky13
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I thought that they'd be in the extended position, when there's no weight on them....
Airframes
Benevolens Magister
I'm not sure that those brass landing, taking-off, taxiing and standing still gear legs (much easier to call them 'undercart' !) are extended. The torque links look about right, and would be closed further if the oleos were compressed, and open further if extended.
However, they might have been patterned from a museum aircraft, which might have been on axle stands or otherwise 'lifted', to relieve the pressure on the oleos and tyres, in which case they could (on the real aircraft) have been extended further than if under load, but not fully extended.
Note that the '109 usually had canvas or rubber 'boots' over the oleos, although these were sometimes removed in severe snow, ice or muddy conditions, as they froze or got 'clogged' and stiff, and could impede the operation of the oleo.
However, they might have been patterned from a museum aircraft, which might have been on axle stands or otherwise 'lifted', to relieve the pressure on the oleos and tyres, in which case they could (on the real aircraft) have been extended further than if under load, but not fully extended.
Note that the '109 usually had canvas or rubber 'boots' over the oleos, although these were sometimes removed in severe snow, ice or muddy conditions, as they froze or got 'clogged' and stiff, and could impede the operation of the oleo.
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Lucky13
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mikewint
Captain
Sorry Jan I should check my sources FIRST. The lower cylinder is a shock absorber just like in a car. It fully extends with no weight and collapses with shock and weight, again, just like an automotive shock absorber. With the gear DOWN and the planes weight on it the cylinder partially collapses compressing the gas in the cylinder. When the aircraft leaves the ground the weight is removed and the cylinder fully extends, again just like jacking up a car extends the shocks.
The LONG upper cylinder is a hydraulic cylinder that extends and/or retracts as fluid is pumped into the top or bottom while the opposite end has fluid removed. Thus the gear is either extended or retracted by the fluid pressure
The LONG upper cylinder is a hydraulic cylinder that extends and/or retracts as fluid is pumped into the top or bottom while the opposite end has fluid removed. Thus the gear is either extended or retracted by the fluid pressure
Crimea_River
Marshal
The portion of the leg spanned by the torque links would be compressed when the aircraft is on the ground but only partly as you would would not want to have the piston bottomed out under normal conditions.
turbo
Staff Sergeant
Agree with Terry and Andy, the part looks about right when compared to reference pics of aircraft on the ground. The piston would only become more fully compressed at moments of high pressure like when the aircraft impacts the ground on landing.
Crimea_River
Marshal
Cutaway of landing gear leg, Bf 109 E, which will show how the assembly worked.
This system (and some other German ones) seemed to leave quite a long length of the piston (kolben) visible at the bottom between the arms of the 'Lenkhebel' even when the aircraft was loaded on the ground. There are many English words for 'Lenkhebel', scissor, torsion link, torque arm are probably most common.
For an example of how little piston might be visible find a photograph of a heavily loaded P-47 !
Cheers
Steve
This system (and some other German ones) seemed to leave quite a long length of the piston (kolben) visible at the bottom between the arms of the 'Lenkhebel' even when the aircraft was loaded on the ground. There are many English words for 'Lenkhebel', scissor, torsion link, torque arm are probably most common.
For an example of how little piston might be visible find a photograph of a heavily loaded P-47 !
Cheers
Steve
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Lucky13
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Suspension systems are complicated, ideally under maximum load they should not bottom out and become rigid/locked but also under neutral loading some travel should be used up otherwise the slightest bump or undulation means you lose contact with the ground. I would imagine planes had progressive springing so an increased load doesnt bottom out the suspension just reduces it. In cases of serious overload as mentioned by Stona I suspect there must have been stipulations as to the condition of the runway.
Crimea_River
Marshal
Adjustments were made by increasing air pressure via the nozzle at the top of the strut labeled "Einfullventil".
I have just read that the left strut on the Bf109 had 100 PSI more thn the right to compensate for the torque.
Crimea_River
Marshal
Yeah, interesting. I read that somewhere as well.
Even at the heaviest operational weight the oleo struts shouldn't compress more than 1/3 of their travel at rest on the ground as a rule of thumb. The rest is needed for landing impact and taxiing on uneven surfaces. Imagine a "Jug", fueled and armed for an attack mission over the continent, that experiences an emergency after takeoff and comes back to land . Even with external fuel and ordnance jettisoned, there's no fuel dump so the landing will be heavy, and the pilot's pucker factor may not make for the smoothest landing. Bad time for a strut to bottom out.
Cheers
Wes
Cheers
Wes
