UAV landing load factor 3

[MichaelkSA]

I have to design a forward looking camera gimbal to be mounted on the nose of a UAV. How would I go about calculating the load factor experienced by the vehicle during landing?

I am sure the landing load factor would be much higher than any loads experienced during manouvres, is this a valid assumption?

I have heard load factors up to 16 g's are possible, does this sound exessive or plausable?

The vehicle is to have skid landing gear which will be built as to absorb some of the landing shock, the gimbal will also be mounted on rubber grommets or something similar to absorb shocks, but I am looking for a worst case scenario.

Thank you in advance.

------------------------------------------
Here's looking at you, looking at me, looking at you

 

[IRstuff]

Typical design values for hard landings are around 16 g, and crash landing, anywhere from 20g to 40g. In the latter case, your mount needs to be designed so that it does not break and cause the gimbal to break loose and hit someone. It does not have to operate after a crash, but does have to operate after a hard landing. Typically, MEs will design for a 1.5x to 2x safety factor. Your requirements document should have clearly delineated these requirements

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529

 

[rb1957]

it depends on the distance for the MLG contact. It can be "outrageously" large ! I'd use as big a number as you think you can get away with, 16g sounds large enough to me. if you have to you can derive a number based on an assumed ground contact ...
assume a static attitude,
assume a sink rate (10 fps is a common assumption, for limit load)
this leads to a ground contact force (or assume a reaction factor, =2?)
this gives you the pitch moment of the landing
with the pitch mass moment of inertia you can get the aircraft's rotational inertial reaction, "alpha ddot"
and this leads to the linear accelration at the station in question, z ddot = alpha ddot*distance
and divide by 384 (assuming inches for distance) for g's

Quando Omni Flunkus Moritati

 

[3DDave]

Gimabals I worked on used 30gs. I mentioned that if the gimbal got smashed there would not be much of a plane left anyway, but was told it didn't matter as fatigue life was the driving limitation. Not so sure about the rubber - properties change a lot with temperature. Equipment inside a plane with people is different. It's bad if people might survive a crash and get killed by a box that breaks loose.

 

[tbuelna]

The worst case load for most aircraft structures is a ground impact, and this usually requires a 20g factor. But it also is usually acceptable for the structure to yield, but not fracture, at this impact case. However, I would not imagine that the camera and gimbal system you are using are capable of anywhere close to 20g loading, unless it is a system designed specifically for military applications. A commercial system is probably qualified for something like 3g-4g in service.

It is quite difficult to predict the loading from a skid landing. The X-15 suffered a structural failure during its first landing using a skid. The same thing happened with the Boeing Phantom Eye UAV.

 

[Sparweb]

That's why it is more easily modeled as a kinetic energy / energy absorption problem, rather than a static force problem.
Asking for the g-load factor is asking the wrong question in landing gear design.


STF

 

[KENAT]

Although the OP isn't designing landing gear.

MichaelkSA, depending on market customer is there a relevant Mil Std or similar to look at?

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[KENAT]

Sorry, or does the contract if applicable say anything.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[WKTaylor]

ASTM F2910 Standard Specification for Design and Construction of a Small Unmanned Aircraft System (sUAS) ? or similar ASTM?

There is a significant difference between landing and crash loads. UAVs rarely worry about manned crash loads... no one to protect. Maybe OEM/customer requirements for damage limits [rapid repair/return to service] will define strength for crash-worthy UAV structures and systems.... or element replacability.

Landing loads are usually defined by weight/CG/max sink-rate/assymetry... then these CG centric force-generating elements are translated to the XYZ off-set location of the component.

CAUTION. Sometimes landing/takeoff/taxi loads on rough/harmonic surfaces can create peculiar loads with forcing functions that drive internal structures and systems loads sky-high.I have personally dealt with a scarry C-130 incident: acft flew with internal damage to both outer wings, discovered on post-flight. Cause? rough taxiiway, perfect [worst] taxi-speed, and max fuel load W/O cargo. Double outer wing change was mandatory before next flight. I understand that certain Cirius [single engine composite aircraft] have actually buckled the aft fuselage due to Taxi conditions.

Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

Unfortunately, in science what You 'believe' is irrelevant – "Orion"

 

[tbuelna]

The OP was asking about safe operational load limits on a nose mounted camera gimbal system. I would imagine that camera and gimbal mount load limits are less than what airframe and skid landing gear are good for. A three point UAV skid landing gear configuration likely means that the two main skids will contact first, and then the nose skid will be quickly slammed down due to the friction from the main skid contacts. So the question the OP should be asking is what can I do to make sure the camera & gimbal mount are not subjected to excessive dynamic loads during landing? The answer would be to use some device like an accelerometer located close to the camera to record the dynamic forces during landing. If the dynamic forces exceed what the camera and gimbal mount are designed for, then they should be replaced.

 

[IRstuff]

"camera and gimbal mount load limits are less than what airframe and skid landing gear are good for"

Not by spec, typically. The assumption is that the body is a rigid structure, so loads are directly carried to the payloads. Only on rare instances do we get any indicating that the loads are attenuated by the structure, and that's usually only because the payload is heavier than what was used in the data collections.

Of course, this is caveated by the useful life of the aircraft in some cases. We have a UAV gimbal that's designed specifically for bout 1000 hrs of operating life, because the platform will either be shot down or crash, on average, in that time frame.

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529