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Posted: 12/22/2013 5:38:54 AM EDT
I am wondering why they have similar functions of lifting maximum cargo for long distances and yet are fairly different in form? I would have guessed both civilian and military would both just use the most efficient form whether it was high or low wing in their designs. Why the divergence in aircraft weight bearing design? The only guess I have is maybe they are trying to get the engines higher off the runway in military aircraft.
In general, is high wing or low wing more efficient for the purpose , all other considerations aside? Big Commercial bird; 
Big Military Bird; 
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Posted: 12/22/2013 5:40:03 AM EDT
[#1]
unimproved airfields.
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Posted: 12/22/2013 5:40:48 AM EDT
[#2]
... military utilize unimproved runways and adverse landing condition, commercial no
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Posted: 12/22/2013 5:40:53 AM EDT
[#3]
Quote HistoryQuoted:
unimproved airfields. My first thought as well. FOD concerns. |
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Posted: 12/22/2013 5:41:09 AM EDT
[#4]
FPNI
At least that has always been my belief. |
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Posted: 12/22/2013 5:41:32 AM EDT
[#5]
FaSPNI
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Posted: 12/22/2013 5:41:35 AM EDT
[#6]
Engines need to be higher so you don't suck a goat with an afghan attached to its ass through it.
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Posted: 12/22/2013 5:42:14 AM EDT
[#7]
Two reasons I can think of:
1. Ground clearance. Useful on poor or unprepared surfaces. 2. Short take-off. With the flaps down and at take-off thrust the wing/ground effect can get you airborne witrh less distance. m |
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Posted: 12/22/2013 5:42:28 AM EDT
[#8]
Quote HistoryQuoted:
unimproved airfields. Yup. Look at how much higher the engines are on that C-17. The inboard engines on my commercial derivative jet are only 18" off the concrete. |
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Posted: 12/22/2013 5:43:07 AM EDT
[#9]
Different design for different needs. Yes they both move cargo but WHERE they move cargo to and fro is the key factor in design.
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Posted: 12/22/2013 5:43:43 AM EDT
[#10]
And I would assume to keep the jet engines below the passengers, for both noise reduction and for a view out of the passenger cabin?
Just a W.A.G |
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Posted: 12/22/2013 5:46:22 AM EDT
[#11]
Quote HistoryQuoted:
Engines need to be higher so you don't suck a goat with an afghan attached to its ass through it. 
Yes... *laughing*... that's kind of what I was getting at... |
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Posted: 12/22/2013 5:48:43 AM EDT
[#12]
You need to check the take off weights again. People weigh less than tanks.
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Posted: 12/22/2013 5:49:33 AM EDT
[#13]
Quote HistoryQuoted: And I would assume to keep the jet engines below the passengers, for both noise reduction and for a view out of the passenger cabin? Just a W.A.G I'm also wondering which is the more efficient design, and I would think commercial keeping the aircraft more streamline. We need some wind-tunnel results |
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Posted: 12/22/2013 5:50:22 AM EDT
[#14]
Quote HistoryQuoted: Engines need to be higher so you don't suck a goat with an afghan attached to its ass through it.  |
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Posted: 12/22/2013 5:51:41 AM EDT
[#15]
Quote HistoryQuoted:
And I would assume to keep the jet engines below the passengers, for both noise reduction and for a view out of the passenger cabin? Just a W.A.G The simplest answer is usually the correct one. In this case I'd go with: It's easier to work on stuff close to the ground. 
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Posted: 12/22/2013 5:52:50 AM EDT
[#16]
Quote HistoryQuoted:
Engines need to be higher so you don't suck a goat with an afghan attached to its ass through it. fucking god dammit you made me spit out my vodak |
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Posted: 12/22/2013 5:53:31 AM EDT
[#17]
There is an additional safety/prevention of airframe damage factor with a high wing:
Idiots have a much lower chance of crashing a delivery vehicle, forklift, or other machine into the engines or wings if they're high off the ground. |
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Posted: 12/22/2013 5:55:13 AM EDT
[#18]
Quote HistoryQuoted:
Engines need to be higher so you don't suck a goat with an afghan attached to its ass through it. Engines need to be lower so this happens more often. |
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Posted: 12/22/2013 5:55:57 AM EDT
[#19]
Dakota had low wings.
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Posted: 12/22/2013 5:55:58 AM EDT
[#20]
Quote HistoryQuoted:
You need to check the take off weights again. People weigh less than tanks. Doesn't explain the 747 freighter.
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Posted: 12/22/2013 5:56:29 AM EDT
[#21]
Quote HistoryQuoted:
Engines need to be lower so this happens more often. Quote HistoryQuoted:
Quoted:
Engines need to be higher so you don't suck a goat with an afghan attached to its ass through it. Engines need to be lower so this happens more often. Why do you hate crew chiefs and engine troops? 
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Posted: 12/22/2013 5:59:58 AM EDT
[#22]
Additionally, roll on, roll off capability. There are few cargo handling facilities at unimproved strips, so the cargo is closer to the ground.
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Posted: 12/22/2013 6:03:21 AM EDT
[#23]
Anyone remember this demonstrator?
I always wanted to see this Rutan design developed, but it's dead as a doornail. Twin engines, unrestricted rear access, fuel outside the fuselage, opposing dihedral dual wings for lift, stability, broad CG, almost stall proof, etc, etc. Scaled Composites Model 33 Advanced Technology Tactical Transport (ATTT)     |
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Posted: 12/22/2013 6:04:22 AM EDT
[#24]
Quote HistoryQuoted:
Additionally, roll on, roll off capability. There are few cargo handling facilities at unimproved strips, so the cargo is closer to the ground. A low wing rear opening box seems doable to me. |
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Posted: 12/22/2013 6:06:47 AM EDT
[#25]
Quote HistoryQuoted:
The simplest answer is usually the correct one. In this case I'd go with: It's easier to work on stuff close to the ground. Quote HistoryQuoted:
Quoted:
And I would assume to keep the jet engines below the passengers, for both noise reduction and for a view out of the passenger cabin? Just a W.A.G The simplest answer is usually the correct one. In this case I'd go with: It's easier to work on stuff close to the ground. Waaaaaaaaaay back when I was studying for my PPL (private pilots' license), we talked briefly about hi vs. lo wing. Liftwise, flyingwise, all that jazz, doesn't make a rat's rear end. Wing works just as well lo as hi, the air moving over the wing don't care. Only issue was obstruction of view, lo you couldn't see below you, hi you can't see above you. As others have said, it's so they can land on shitty airfields. |
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Posted: 12/22/2013 6:06:50 AM EDT
[#26]
Tag for AeroE response.
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Posted: 12/22/2013 6:07:22 AM EDT
[#27]
Quote HistoryQuoted:
Engines need to be lower so this happens more often. Quote HistoryQuoted:
Quoted:
Engines need to be higher so you don't suck a goat with an afghan attached to its ass through it. Engines need to be lower so this happens more often. There's more effective, less-expensive ways to do this.
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Posted: 12/22/2013 6:07:54 AM EDT
[#28]
Quote HistoryQuoted: A low wing rear opening box seems doable to me. Quote HistoryQuoted: Quoted: Additionally, roll on, roll off capability. There are few cargo handling facilities at unimproved strips, so the cargo is closer to the ground. A low wing rear opening box seems doable to me. Doable, yes, but more expensive. And the cargo would still be higher off the ground. And before someone mentions the 747 freighter, please keep in mind it delivers cargo to airports that have cargo handling capabilities. |
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Posted: 12/22/2013 6:07:57 AM EDT
[#29]
We don't want to put the spar carry through in the passenger cabin, so the lighter solution is to carry through below the cabin floor. An overhead carry through complicates the mold line shape and structure, adding weight for the structure and the fairings. The carry through could be kept inside the cabin, but don't expect many sales. (The Boeing Model 247 had the spar carry through above the cabin floor, hence the hammering it received by the DC-1, DC-2, and DC-3 in the market, besides the superior performance of the DC airplanes.)
All of the other reasons have been covered in the thread. What is really important to understand is that an unusual configuration has to (or should) earn its way onto the airplane; installing the wing at the fuselage mid line, or on top of the fuselage, or on struts completely off the airframe for a ridiculous example, has to be done for real and solid engineering reasons, not because a manager thinks it looks cool or a bean counter believes it has to be cheaper to manufacture. Anything else should be viewed with great skepticism until proof is offered. |
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Posted: 12/22/2013 6:09:28 AM EDT
[#30]
Quote HistoryQuoted:
Doesn't explain the 747 freighter. Quote HistoryQuoted:
Quoted:
You need to check the take off weights again. People weigh less than tanks. Doesn't explain the 747 freighter. That's a conversion. 
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Posted: 12/22/2013 6:13:14 AM EDT
[#31]
Quote HistoryQuoted:
Dakota had low wings. Piston engined |
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Posted: 12/22/2013 6:16:38 AM EDT
[#32]
It would be hard to stick howitzers and multi barreled cannons out the side of a low winged aircraft.
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Posted: 12/22/2013 6:21:01 AM EDT
[#33]
If the benefits are negligible to either design it would seem like the high wing design would win out to me. It would be a cost savings to have one simple design for the companies manufacturing these to not have separate lines if that makes sense.
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Posted: 12/22/2013 6:22:55 AM EDT
[#34]
Quote HistoryQuoted: fucking god dammit you made me spit out my vodak Quote HistoryQuoted: Quoted: Engines need to be higher so you don't suck a goat with an afghan attached to its ass through it. fucking god dammit you made me spit out my vodak Needs more vodak. It is, after all, only 10:22am |
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Posted: 12/22/2013 6:34:10 AM EDT
[#35]
They have to hide the engine exaust from civ aircraft so passangers can't see chemtrail dispersing ops.
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Posted: 12/22/2013 6:38:19 AM EDT
[#36]
Quoted:
Big Military Bird; http://www.tampabay.com/resources/images/dti/rendered/2012/07/b2s_plane072112_A_231709a_8col.jpg Sure is a lot of tall stuff in that photo. Must be an obstacle course. |
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Posted: 12/22/2013 6:44:42 AM EDT
[#37]
Quote HistoryQuoted: Sure is a lot of tall stuff in that photo. Must be an obstacle course. Quote HistoryQuoted: Quoted: Big Military Bird; http://www.tampabay.com/resources/images/dti/rendered/2012/07/b2s_plane072112_A_231709a_8col.jpg Sure is a lot of tall stuff in that photo. Must be an obstacle course. Funny you should say that. The C17 landed on a small (3500 feet) airfield in the middle of Tampa Bay by mistake. The runway has the same heading as the military field (12000 ft, MacDill) a few miles away. Most of what you see in the background is Port Tampa. |
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Posted: 12/22/2013 6:46:07 AM EDT
[#38]
FPNI
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Posted: 12/22/2013 6:49:25 AM EDT
[#39]
Quote HistoryQuoted:
That's a conversion. Quote HistoryQuoted:
Quoted:
Quoted:
You need to check the take off weights again. People weigh less than tanks. Doesn't explain the 747 freighter. That's a conversion. There are freighters, and then there are military freighters. Civil freighters are designed around standard containers that don't require loading off the ends of the airplane. The special cases are moving vehicles and manufacturing equipment, hence civil use of AN-124's and AN-224's, Guppies, or 'Lifters. End loading is really not suitable for the tempo or space available during passenger operations, especially when the airplane has to be supported on jacks or a special loading fixture/floor is required, along with all the special equipment required to support the operation. |
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Posted: 12/22/2013 6:53:46 AM EDT
[#40]
In part, the high wing design puts the engines higher for unimproved airfields. Also beneficial for wing wobble on hard landings.
Another factor is the typical airliner design allows for loading passengers at one level, cargo at another. Military jobs don't need to segregate the two types of cargo, so there's just a bog box with a ramp on it. The wing can't go through jetways or buildings. The high wing on military cargo designs also puts the wing spar up high so it doesn't pass through the fudelage, therefore allowing large stuff to be loaded. The split deck design on airliners, it doesn't matter so much. |
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Posted: 12/22/2013 6:53:57 AM EDT
[#41]
Asked my BIL at Boeing he said its because military ones are designed for non paved runways while commercial are designed for paved runways.
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Posted: 12/22/2013 7:12:12 AM EDT
[#42]
In addition to some things mentioned already, the private sector cares about efficiency.
A high wing heavy lift v say a 747 will be less efficient Example the need for high heavier reinforced tail sections to keep the stabilizer clear. Landing gear is in the belly instead of the wing requiring more weight and loss of some aerodynamics to reinforce. Also, think from a physics standpoint of siting the weight of the airplane on the wings and puts the load through the floor of the aircraft v being transmitted through the fuselage. These are the highlights from a friend of mine who is a retired aircraft designer. |
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Posted: 12/22/2013 7:54:59 AM EDT
[#43]
Quote HistoryQuoted:
Anyone remember this demonstrator? Quote HistoryQuoted:
Anyone remember this demonstrator? I always wanted to see this Rutan design developed, but it's dead as a doornail. Twin engines, unrestricted rear access, fuel outside the fuselage, opposing dihedral dual wings for lift, stability, broad CG, almost stall proof, etc, etc.
Scaled Composites Model 33 Advanced Technology Tactical Transport (ATTT) http://www.aerofiles.com/scaled-attt.jpghttp://www.air-and-space.com/19891030%20Mojave/893444%20Advanced%20Technology%20Transport%20ATTT%20N1335SC%20left%20side%20l.jpghttp://www.air-and-space.com/20031025%20Edwards/PICT0037%20Scaled%20Composites%20Model%2033%20ATTT%20N133SC%20left%20front%20l.jpg http://cdn-www.airliners.net/aviation-photos/photos/9/4/2/1247249.jpg I've never seen it, but the fact that it wasn't developed gives me a sad. 
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Posted: 12/22/2013 8:30:17 AM EDT
[#44]
Quote HistoryQuoted:
Additionally, roll on, roll off capability. There are few cargo handling facilities at unimproved strips, so the cargo is closer to the ground. Putting the wing spar above the cargo makes RORO easier (in addition to the other considerations discussed above). |
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Posted: 12/22/2013 8:31:41 AM EDT
[#45]
Quote HistoryQuoted:
My first thought as well. FOD concerns. Quote HistoryQuoted:
Quoted:
unimproved airfields. My first thought as well. FOD concerns. Yep, lots of FOD hazard in a war zone, even on an improved airfield. |
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Posted: 12/22/2013 8:34:14 AM EDT
[#46]
Ease of loading.
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Posted: 12/22/2013 8:34:17 AM EDT
[#47]
Quote HistoryQuoted:
It would be hard to stick howitzers and multi barreled cannons out the side of a low winged aircraft. Hard? They were one of the first ones. http://en.wikipedia.org/wiki/Douglas_AC-47_Spooky |
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Posted: 12/22/2013 8:34:19 AM EDT
[#48]
Military aircraft require the ability to take-off from a treadmill if necessary.
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Posted: 12/22/2013 8:34:22 AM EDT
[#49]
Quote HistoryQuoted:
Engines need to be higher so you don't suck a goat with an afghan attached to its ass through it. Ok, that even woke up my dog.
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Posted: 12/22/2013 8:36:36 AM EDT
[#50]
I will have to ask my BIL this question since he works on the C130 line and see if he can get an answer about this.
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