Impact forces of vertical landing
Impact forces of vertical landing
(OP)
How to calculate the impact force when an lighter-than-air vehicle performs Vertical Landing? Actually, the vehicle lands vertically on the ground using air cushions. I tried to establish a speed corresponding to the impact forces. The impact forces are obtained from max ground reaction force the vehicle structure can withstand.
Besdies the simple energy equation: 1/2MV^2=Fd, are there other ways of calculating the speed?
Thanks!
Lin
Besdies the simple energy equation: 1/2MV^2=Fd, are there other ways of calculating the speed?
Thanks!
Lin





RE: Impact forces of vertical landing
getting the "landing" sink rate is easy, determining the impact force requires assuming the time interval of the impact.
Quando Omni Flunkus Moritati
RE: Impact forces of vertical landing
RE: Impact forces of vertical landing
one thing (other than drag) is the stiffness of the air cushion (ie the air cushion will absorb some of the KE.
i guess your initial conditions are just before the cushion starts to deflect (ie close to the ground).
Quando Omni Flunkus Moritati
RE: Impact forces of vertical landing
Cheers
Greg Locock
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RE: Impact forces of vertical landing
My question is how accurate if I use acceleration and cushion deflection to calculate vehicle speed 1/2MV^2=Fd=M*a*d? I have asssumed that the acceleration is constant though it is not. The time used for landing might be just around one second. The vehicle landing speed is around 0.5~2mph.
RE: Impact forces of vertical landing
You have another element to consider: unless this is a rigid/semi-rigid airship, a blimp-like lifting bag [or cells] will have some flexibility. This means the entire airship envelope will be elastic, so total deceleration forces thru the cabin to the bag may occur over several seconds as everything smushes, then rebounds. Perhaps.
Might try making a 1/5--1/10th scale flying model: could answer some of these questions. Perhaps.
Suggest You search Google for "lighter than air vehicle design"... lots of interesting hits.
Regards, Wil Taylor
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RE: Impact forces of vertical landing
The bad news is that your problem is best stated and solved with a differential equation. The good news is that DE's are fun to learn!
If you're willing to give it a go, you will find that the solution to the impact-absorption problem is a classic example of a DE. In my textbook it was in chapter 2.
STF
RE: Impact forces of vertical landing
my answer ... not very (IMHO) ... but if v is 2mph, and t = 1sec then maybe it acceptable for your purposes. but i have to ask why an FEA of the cushion ? why build a sophisticated analysis (a palace) on such rough assumptions (in a swamp) ?
Quando Omni Flunkus Moritati
RE: Impact forces of vertical landing
I would think that any forces would be less than that of a 5-ft drop
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RE: Impact forces of vertical landing
RE: Impact forces of vertical landing
Yes, you are. Try re-reading the first two sentences of the OP, and go from there. Nothing wrong with anything else you wrote.
STF
RE: Impact forces of vertical landing
RE: Impact forces of vertical landing
Regards, Wil Taylor
Trust - But Verify!
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RE: Impact forces of vertical landing
If so then the 'suction' force from the 'air cushion' may need to be taken into account.
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RE: Impact forces of vertical landing
The vehicle is different than a conventional non-rigid airship. The vehicle is equipped with air landing cushions for vertical landing. Suction force can not be applied before the vehicle fully lands on ground. The cushion pressure can be controlled to avoid "bouncing".
rb1957, I thought about building a FE model for cushion, but I don't have the software for this kind of nonlinear analysis/large deforamtion analysis/transient analysis. Try to figure out a test plan to obtain this acceleration and deflection.