What is the biggest airliner that can be made unpaved field capable?

[mithril]

i'm writing an article for a post-apocalyptic roleplaying game setting, and one thing i haven't been able to easily find out is whether aircraft larger than a 737 could operate off of unpaved airstrips. i know that various militaries have operated things like C-17's off unpaved airstrips, but i'm pretty sure those were specifically designed to do so.
the main thing i've had trouble finding out is whether something like a 767 or similar can be fitted with an unpaved strip kit like the 737 can use, allowing it to be flown off dirt or grass airfields. and if such could be fitted, what other issues and limitations would such aircraft face trying to operate off of such rough fields? (for example, would they need modified landing gear to deal with ground pressure issues? modifications for better STOL performance? etc.)
the game setting is more of a 'post-post-apoc', where there are a multitude of developed city-states in a partly developed wilderness, and while it's set far enough in the future that there is some fairly impressive advanced tech around, the typical city-state is stuck with mid to late 20th century level tech for most things. so i'm intending to use real world aircraft to determine the general performance of the aircraft i'm writing. before i start adjusting the stats for the fictional stuff, i'd like to have a better understanding of the real world issues those aircraft would be facing.

 

[Bill Walker]

Here is a quick answer.

http://www.youtube.com/embed/Lkl3jGxCKUI

Like any good engineer, my long answer to this question starts with "It depends".

How much useful load and cruise performance are you willing to give up, in order to fit inlet screens and/or deflectors, low pressure tires, dirt deflectors, stronger landing gear, etc.?

How long a grass field is available? You may not need STOL performance. If you do, again you will have to trade off useful load and cruise performance. One quick way to improve the field performance of any aircraft is to reduce the operating weight. Your 200 seat, 5,000 nm airliner might become a 50 seat, 500 nm airplane.

How rough is the field? If you need greater ground clearance you will need longer gear to keep the dangly bits out of the weeds. Again, trade off useful load and maybe cruise performance. It is not unknown to ferry damaged airliners with "gear down and welded" - temporary external repairs to damaged landing gear and/or the surrounding structure will permit a ferry flight with the gear left extended. Your cruise speed goes way down, and your fuel consumption per mile goes way up. But it still flies. One can picture a quick and dirty gear extension, if you give up retraction.

I can foresee some Mad Max kinds of mods permitting just about anything, up to and including an A380, being flown from a long enough grass or dirt field.

Now, can somebody tell me how to embed Youtube videos?

 

[mithril]

ideally, sacrificing as little cargo capacity as possible. part of the reason i'm writing this is to help explain how these communities conduct the officially decribed trade when there are no roads and the wilderness between them is supposed to be really hazardous for travellers.

 

[Michel Van]

I heard that the Frenchs used unpaved airstrips treated with chemicals for the Dassault Étendard
I don't know if this supports heavy aircraft like 737

Here is a quick answer.

http://www.youtube.com/embed/Lkl3jGxCKUI
Now, can somebody tell me how to embed Youtube videos?

you used the "insert hyperlink" that give only URL
Just paste the link without "insert hyperlink" and make sure you take link from youtube not embedded from other webpage
the rest made the Forum automatically like this

http://www.youtube.com/watch?v=Lkl3jGxCKUI

 

[Bill Walker]

It's very funny on this forum how UK and US are properly refered to as countries, ...

You mean the Brits and the Yanks? That's what us Canucks call them...

Slightly back on topic, if I was attempting to reconstruct commercial air travel in a post-post-apocalypse situation, I think I would prefer to put seats in a C-130 than try to do major aerodynamic and structural mods to a 767. Especially if all the tooling I have is a hammer and a file. A sail boat would be even easier.

 

[aam641]

Modern airliners probably wouldn't last more than couple of flights without a well-equipped shop and excellent maintenance, even if you can provide the tons of high quality fuel required. I would also think that any town large enough to justify heavy aircraft flying in regularly would have no problem in preparing a runway.

If you are building aircraft in that sort of world, they will probably look like DC-3. Piston engines are easier to build and maintain when you do not have access to a factory producing thousands of spares. They are also more tolerant of poor quality fuel and should be able to run on something like locally made corn ethanol.

 

[Stargazer]

I guess the Fairchild/Dornier 228 would also fit the bill...

 

[mz]

Modern airliners probably wouldn't last more than couple of flights without a well-equipped shop and excellent maintenance, even if you can provide the tons of high quality fuel required. I would also think that any town large enough to justify heavy aircraft flying in regularly would have no problem in preparing a runway.

If you are building aircraft in that sort of world, they will probably look like DC-3. Piston engines are easier to build and maintain when you do not have access to a factory producing thousands of spares. They are also more tolerant of poor quality fuel and should be able to run on something like locally made corn ethanol.

Isn't actually the opposite true: you can run a jet engine with worse quality fuel than a piston...

But yes, like mentioned earlier, boats and ships would again become the best way to travel. If rivers are not full of collapsed bridges that make sailing impossible, they become very important for commerce again. When Sweden invaded what is now Northern Germany in the seventeenth century, the tolls collected from the rivers formed a large portion of the crown's income.

 

[Michel Van]

sorry about typing "The Frenchs", me german, my english writhing not good :-[
Nein nein nicht gut...

 

[mithril]

ok, i think there is a bit of confusion as to the state of the world. this isn't really a mad max type setting, it's more like Appleseed in that you have some fairly advanced tech nation-states surrounded by a wilderness. the wilderness has a bit of a Postman/Fallout type thing going on, but in most of the setting getting fuel and maintence isn't hard, just pricey. and there are some sizeable 'younger' nation states without access to much advanced tech that are like 3rd world countries. (think Whedon's Firefly.. mostly low tech living, but the people have access more advanced guns, communications, etc. through trade.) some of those lower tech groups have enough trade to need access to larger cargo transport, but wouldn't have the ability to make what we would consider a proper prepared airfield.
ocean travel, both brownwater and deep water, has become a major trade route for those with access to water, but not all the nation-states in the setting have access. some could, but have enemies that control the main water routes, others are land locked. the land locked ones can't really rely on trains due to issues with bandits and the enviroment.

 

[Bill Walker]

"fairly advanced tech nation-states" would build paved runways, and communicate with each other in the best of the old world airliners. High mileage types, maybe flying wings and/or propfans.

To visit their less advanced neighbours they will use old rugged turboprops. C-130s, A400Ms, Twin Otters. Painted to look like dragons, maybe with augmented sound, flame throwers, etc.

 

[Grey Havoc]

For certain applications/routes, they could use air cushion landing systems, although they would likely be something of a pain to maintain.

 

[RanulfC]

Your "criteria" is going to be centered on engine fan height above the surface for Foreign Object Damage (FOD) reasons. "Technically" in that case there would be few issues of the more "tech" nations doing some "upgrades" to existing airframes such as maybe re-mounting the tubrofans above the wings rather than below them to allow a wider range of access. (VFW-Fokker 614 or the HondaJet specifically comes to mind)

http://en.wikipedia.org/wiki/Podded_engine
http://hondajet.honda.com/designinnovations/enginemountdesign.aspx?bhcp=1

(I'm probably having a "senior-moment" but I seem to recall seeing some illustrations at one point for mounting engines to the aft section of the 747. Not the "5-engine" configuration stuff but two or more engines mounted on the aft fuselage side-by/or/over-under similar to the MD mid-jets)

One thing to note is that the 737 has LOW-BYPASS turbofans which are both technically in MORE danger from FOD than a high-bybass engine would be. Hence the "votex" suppressors on the 737 where as a 747 would not necessarily need them because the "fan" would not be as much in danger of generating such vortex's and have less "damage" done. (Another thing to keep in mind in this setting is that there would be some major "de-tunning" to engines and equipment to meet new demands. Efficency would "suffer" in order to up-grade mechanical reliabilty and maintenance. For example the multiple layers of "stators" for a high-bypass turbofan would probably be removed as they would be the most likely thing damaged during a "FOD" incident. While this reduces the engines overall fuel efficency rateing it makes "rough-surface" landings and take off much less hazerdous from a FOD viewpoint and makes oveall engine inspection and maintenance much less time consuming.)

Other possible "fixes" that can be included are things like over-filling the landing gear Oleo's with oil which allows higher "clearance" on take off and landing even with full loads. (This is used for the current "tanker" aircraft configurations of the 747, L1011, and DC-10 aircraft to accomadate the extensions needed for the tankage and discharge gear) and there are probably a few other things that could be done.

Don't forget you can simply "replace" the turbofan engines with geared-turbofan or even turboprop power plants too which reduces the FOD issues. Even more so if the engines go from "podded" to in-wing installations. For that matter a simple "fix" is to replace the duct and "fan" assemblies for simpler and more robust "prop-fan" or Un-Ducted Fan installations.

Attempting to stick to as much "air" access over surface routes is probably a really, really "good" idea as having that "3D-dimension" to work with has numerous tactical and logistics advantages that no one WITH the capability will want to give up. And I'm pretty sure there would be some serious "motivation" for the "higher-tech" city-states to ensure that the "less-fortunate" areas pretty much stayed ground-bound as much as possible.

BTW, can we get a hint as to where this is going to be avialable at? (RPG-er here thanks )

Randy

 

[aam641]

there are some sizeable 'younger' nation states without access to much advanced tech that are like 3rd world countries. (think Whedon's Firefly.. mostly low tech living, but the people have access more advanced guns, communications, etc. through trade.) some of those lower tech groups have enough trade to need access to larger cargo transport, but wouldn't have the ability to make what we would consider a proper prepared airfield.

In that case, UN has had a lot of good experience with Il-76 delivering aid to many "low-tech" places in Africa.