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Dirt tire pressures


damnpoor
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It says in the GE and in the -6 to set tires to a slightly lower pressure for substandard fields, as I\'m sure you all know. It also says to set pressures for the highest takeoff weight of the day. So if you\'re taking off from a concrete runway, then landing on dirt, then coming back to concrete, do you set the tire pressures to the max gross weight for standard fields or for the dirt fields?

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If I were king, it\'d be for the substandard field. I\'d rather have decreased performance, increased tire wear on concrete than get stuck in the dirt!

I\'ve been stuck in the mud carrying an APC into Rattlesnake LZ precisely because they set tire pressure for the max T/O weight on a concrete runway...we got out, but it wasn\'t pretty!

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Hey

looking at the tyre presure chart in the -1 it shows (39%) as a limit. Where is it written that it is a deflation limit. The wheels tyres and brakes book, just said for under \"inflated tyres if not towed or taxied just pump them back up.. It does not mention 39% as anything??

even the -1 now does not have what 39% even is???

Chris..

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Puredrenalin wrote:

For a combo of both, run them at 93+/- 5 psi...thats what weve been runnin in the Herks that we fly for the last 14 yrs, that along with soft struts, works like a charm!

I run \'em in the middle as well (about 85psi), but I want something more clearly established than \"that\'s how we\'ve always done it.\" It must not be too important if there\'s no good guidance on it.

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Chris Down Under wrote:

Hey

looking at the tyre presure chart in the -1 it shows (39%) as a limit. Where is it written that it is a deflation limit. The wheels tyres and brakes book, just said for under \"inflated tyres if not towed or taxied just pump them back up.. It does not mention 39% as anything??

even the -1 now does not have what 39% even is???

Chris..

I\'m not sure where you got 39% from...

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Well, there is such a thing as a \"substandard field\" and then there is dirt that we shouldn\'t be landing on. If we have to drop tire pressures so low that we chance tire failure on a real runway, perhsps we should not be landing on the dirt that requires such a low pressure to keep from getting stuck.

We do have tire pressure limits for a reason. Personally, I don\'t care to have runway tire blow outs, so my pressure has to stay high enough to prevent that. If that causes the plane to get stuck in the dirt, shame on the pilot for landing there.

;)

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I blew a tirein the middle of the nite at Da Nang that was not a good nite. Stopped on runway had to get out and open wheel well doors in the dark and walk along while he got the plane of the runway. I had just put the tire on at Clark that morning

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Perhaps some pilots don\'t pay any attention to where they land. In the civilian world, the pilots are responsible for all those decisions, and the discussion frequently takes place among the crew about those \"unimproved airfields\" before any decision to land.

Really none of that has anything to do with tire pressures. The requirements for pressures are given in the maintenance manuals. If you get stuck because a field was too soft, then you really should not have landed there.

And, yes, I have seen fields that were about as firm as bread dough that we were told was OK to land. Not every pilot is actually able to figure that out. A King Air or Twin Otter pilot looks at runways a little differently than Herk pilots.

If you have to run under-inflated, you will do damage to your tires. Someone will end up paying for it. The question is where and when would you like to have your blowout? I\'ve never been allowed to pick the time or place, but I did get to change the tires.

;)

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In my 10 years on herks it was very rare to have a tyre blow out due to dirt ops, one that i do remember was when the center tread seperated on a recapped tyre, it ended up with about 3 feet flailing around before getting caught under the aft wheel assy causing this one to fail as well. i seem to remember having more issues with tyres deflating in flight and when the anti-skid system was selected off.

kevin

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Steve1300 wrote:

Perhaps some pilots don\'t pay any attention to where they land. In the civilian world, the pilots are responsible for all those decisions, and the discussion frequently takes place among the crew about those \"unimproved airfields\" before any decision to land.

Well, we\'re not in the civilian world - it\'s not a question of \"paying attention\" to where we land, it\'s a question of being tasked into someplace and accomplishing the mission.

When tasked with this, a crew will do everything they can to mitigate risk going into an unimproved field.

Steve1300 wrote:Really none of that has anything to do with tire pressures. The requirements for pressures are given in the maintenance manuals. If you get stuck because a field was too soft, then you really should not have landed there.

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I had 23 years in the military before the last seventeen in civilian herks. I am somewhat familiar, but the \"modern day\" military is a bit unknown to me.

If I had to choose between under-inflated and over-inflated for the day\'s weight and conditions, I\'d go with over-inflated. It does much less damage to the tire sidewalls. I tend to cheat my pressures up rather than down.

I do understand folks not wanting to get stuck where the ground is soft. I\'ll bet most folks understand not wanting to have a blowout at that \"unimproved airfield,\" too. Did you know that a heavy Herk will push a jack into the ground long before the jack will lift the aircraft?

It smashes half-inch plywood pretty well, too.

Been there, done that. Peace, \'migo.

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My two cents --

In my 7 years flying for Transafrik, I averaged changing at least one tire per month; usually on a dirt strip in the rain, and we didn\'t carry mechanics. Steve1300 is correct, the jack will usually go down before the airplane goes up. I have no idea what Transafrik used as tire pressures, but I\'d bet no one there even had an air pressure gauge.

Here\'s a photo of a rare one on a paved airport at Malange, Angola.

Don R. [img size=1200]http://herkybirds.com/images/fbfiles/images/Malange.JPG

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I get it, believe me, I understand how tires are made.

But if the choice is between almost certainly stuck or maybe blown tire, I\'ll go with almost certainly stuck & run lower pressures to mitigate...

Guess we\'ll agree to disagree. I\'ve been stuck before - not fun & kinda helpless feeling - fortunately, training vs combat. It\'s still a lot easier to change a tire - even in the dirt - than to recover a plane stuck in soft dirt.

Our experiences color our opinions - your experience seems to have been changing tires - mine has been being stuck in the mud! ;)

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Well I guess I have to chime in with my 2 cents, in my 16 years of maintenance experince and countless trips to a lot of unimproved landing surfaces, dirt, volcanic rock, rock and soft ground conditions. I have never had an FE or any other crew member for that matter come up to me and ask me to lower or raise the tire pressures. We would set them at 93 +/- 5 and call them good. I guess I just got lucky and never had to dig an acft out.

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FCCtoFE wrote:

Well I guess I have to chime in with my 2 cents, in my 16 years of maintenance experince and countless trips to a lot of unimproved landing surfaces, dirt, volcanic rock, rock and soft ground conditions. I have never had an FE or any other crew member for that matter come up to me and ask me to lower or raise the tire pressures. We would set them at 93 +/- 5 and call them good. I guess I just got lucky and never had to dig an acft out.

You have been lucky. Lucky that you didn\'t land on an airfield that was too soft for your aircraft\'s footprint and weight.

I did get stuck on a gravel runway, but not in mud. I was stuck on the runway with both right side tires blown. It takes a bit of inginuity to jack an aircraft when both tires are flat. I was fortunate enough that a Canadian Herk was preparing to take off and loaned me a spare tire. Otherwise, my goose was cooked.

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When you come back from running special forces training in the desert and have a 45 minute turnround time to prep the a/c for a scheduled passenger flight, there is no time for adjusting tyre pressures, so you have to compromise. With soft sruts and 80 psi in the mains, i never got stuck in the sand or on a rocky strip and never had a blowout in 15 years. As Steve1300 says\' maybe i got lucky, or maybe we found something that worked. Also, carry an iron plate with you for emergency jacking in soft conditions with your spare tyre. It dosn\'t look good when the jack goes down instead of the a/c going up. I learnt that one on Ascencion Island during the Falkland war. With an overloaded Herk and a soft surface it is time to throw away the book and make it work.

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  • 5 months later...

Hi Kev,

I remember numerous times at Richmond taking mains down to 55psi for soft dirt landings.

Also doing a pressure "adjustment" in flight when it was found we were 10 psi over our pavement concession going into Devonport with 15,000lbs of DC, full centre seating (rigged in-flight) plus 50+ grunts going to Hobart. Bennie Raffin was the captain too!

Bob M

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Now that we have pissed on every ones leg, and have "agreed to disagree", lets get back to the real question. Is it better to lower pressures or not. I have run with tires at the normal pressures and with under-inflated tires into/out of unimproved LZs. Luckily, I have never blown a tire or been stuck, but I think the best thing a crew can do is risk-mitigate all the situations/possibilities and what-ifs. If you are operating from a FOB that has a robust Mx package, then you might opt to run lower pressures. If you're at a location with very limited Mx and know you will be operating day in and day out (initial OEF) into areas that only SOF were allowed to land, then you might run with higher pressures. Getting an asset stuck at an LZ in a combat area is something that you do not want to do. Not just having an acft stuck, but having people there in a hostile environment might digging it out and running security may not be the best choice (MC-130E in eastern A-Stan Jan-Feb 2002). Flew overhead comm for that one. We just recently had one stuck in in a LZ (whitesands), luckly the crew was able to dig their way out.

G

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