LH707330
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Will We See Jet Donkeys Soon?

Thu Sep 06, 2012 3:26 am

I was reading this FG article and the picture of the aircraft taking off with the dolly caught my eye. The idea of propelling aircraft with a ground-based acceleration device is not new (aircraft carrier catapults), but what regulatory hurdles would need to be surmounted to enable this for commercial aircraft?

I see many benefits to jet donkey use, including reduced weight due to smaller engines, less flaps gear, shorter takeoff rolls, better climbout due to lower flap drag (smaller/no flaps), less jet noise, and the ability to use a rechargeable (with renewables) dolly to accelerate the aircraft. Downsides include infrastructure dependency (what if you divert to a field without them?). When I was in college I considered entering this as an Airbus fly your ideas challenge entry, but then figured that it seemed like such an obvious move that it would have been done already if there weren't a big log in the road. Thoughts?
 
rwessel
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RE: Will We See Jet Donkeys Soon?

Thu Sep 06, 2012 4:18 am

Quoting LH707330 (Thread starter):
Downsides include infrastructure dependency (what if you divert to a field without them?).

Emergency airfields could be equipped with an updated version of the USAF's HAVR Bounce or USN's Flexdeck systems (or perhaps the contemporary British system). Basically an arresting cable to stop the aircraft, and a bouncy mat for the now stopped aircraft to drop onto.   

Check out the article in:

http://www.public.navy.mil/airfor/centennial/Documents/vol3iss3.pdf
 
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TWA772LR
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RE: Will We See Jet Donkeys Soon?

Thu Sep 06, 2012 5:09 am

They do have arresting cables for military fighter planes, like the Israeli F15 that lost the wing and landed used an arresting cable. I guess it could be possible to launch a 747 or A380 with a catapult-like system, just the ammount of power and force behind it would be immense.
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flyingturtle
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RE: Will We See Jet Donkeys Soon?

Thu Sep 06, 2012 8:11 am

Hm, why not use the landscape - and build downhill sloped runways for take-off, like the one at CVF?


I've seen that in a magazine, back in the late 1980ies... I wonder how the V1 and required runway length calculations will be, though.



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Starlionblue
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RE: Will We See Jet Donkeys Soon?

Thu Sep 06, 2012 10:06 am

Quoting flyingturtle (Reply 3):

Hm, why not use the landscape - and build downhill sloped runways for take-off, like the one at CVF?


I've seen that in a magazine, back in the late 1980ies... I wonder how the V1 and required runway length calculations will be, though.

There was a post years ago about this I think. The Dash 7 is at V1 when it releases the brakes. 
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tdscanuck
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RE: Will We See Jet Donkeys Soon?

Thu Sep 06, 2012 2:55 pm

Quoting LH707330 (Thread starter):
what regulatory hurdles would need to be surmounted to enable this for commercial aircraft?

The "hurdle" is that no regulations exist right now; such a system would require a total re-write of the takeoff requirements regulations because the existing regulations just wouldn't work. The last time a regulatory re-write of that magnitude was required was probably the invention of the jet engine.

You also need to figure out a way to deal with single-engine go-around, where you can't get any help from the ground.

Tom.
 
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HAWK21M
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RE: Will We See Jet Donkeys Soon?

Thu Sep 06, 2012 7:23 pm

Quoting LH707330 (Thread starter):
jet donkey

Whats the history on this term usage.
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vikkyvik
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RE: Will We See Jet Donkeys Soon?

Thu Sep 06, 2012 7:55 pm

Quoting flyingturtle (Reply 3):
Hm, why not use the landscape - and build downhill sloped runways for take-off, like the one at CVF?

Some airports are exceptions due to terrain, like CVF, but in general, what do you do when the wind switches directions?
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flyingturtle
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RE: Will We See Jet Donkeys Soon?

Thu Sep 06, 2012 11:30 pm

Quoting vikkyvik (Reply 7):
Some airports are exceptions due to terrain, like CVF, but in general, what do you do when the wind switches directions?

Hoist sails and call it a sailplane.   


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AirframeAS
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RE: Will We See Jet Donkeys Soon?

Fri Sep 07, 2012 1:01 am

Quoting LH707330 (Thread starter):
The idea of propelling aircraft with a ground-based acceleration device is not new (aircraft carrier catapults), but what regulatory hurdles would need to be surmounted to enable this for commercial aircraft?

You couldn't do it with today's commercial airframes. The structure is not built for this kind of abuse. You'll rip that nose gear off like a toothpick!

Even if the technology was applied to commercial aircraft, it would be a very expensive venture. The costs outweigh the benefits. IMO, I don't ever see this coming.
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LH707330
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RE: Will We See Jet Donkeys Soon?

Fri Sep 07, 2012 5:12 am

Quoting HAWK21M (Reply 6):
Whats the history on this term usage.

Not precisely sure, but I think the USAF thought of it back in the 1950s sometime when they were looking at ways to get a/c off the ground from short strips.

Quoting AirframeAS (Reply 9):
You couldn't do it with today's commercial airframes. The structure is not built for this kind of abuse. You'll rip that nose gear off like a toothpick!

I was thinking you attach it to the mains and have a sort of backstay from the gear legs aft.
 
AirframeAS
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RE: Will We See Jet Donkeys Soon?

Fri Sep 07, 2012 12:24 pm

Quoting LH707330 (Reply 10):
I was thinking you attach it to the mains and have a sort of backstay from the gear legs aft.

With some aircraft, like the 738 and 739 which are tail heavy, that's not going to work.
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wingscrubber
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RE: Will We See Jet Donkeys Soon?

Fri Sep 07, 2012 6:47 pm

I don't think the term 'jet donkey' will catch on! How about 'runway shuttle', or 'aircraft acceleration carraige' ?  
I think usage of something along the lines of aircraft carrier-style catapults, winches or carriages (the wright brothers used this method) is overdue for modern airliners. The obvious benefits are noise reduction, increased take-off performance and increased fuel efficiency - but it's a cost prohibitive concept.

Here's another idea; what about a Maglev runway? That could drastically improve take-off efficiency if an air vehicle could be accelerated up to a safe climb speed and then released, and in addition if that same aircraft could land on a Maglev runway too then it would need no landing gear or brakes, which could result in a much lighter aircraft.  

But - I severely doubt it'll ever happen, even though there's the old adage, a mile of road will take you one mile, a mile of runway will take you anywhere, the seem could apply to a mile of maglev runway  
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bhill
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RE: Will We See Jet Donkeys Soon?

Fri Sep 07, 2012 6:52 pm

Conveyor belts anyone?.................................
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Fabo
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RE: Will We See Jet Donkeys Soon?

Fri Sep 07, 2012 11:38 pm

Quoting flyingturtle (Reply 3):
Hm, why not use the landscape - and build downhill sloped runways for take-off, like the one at CVF?
Quoting flyingturtle (Reply 3):
I wonder how the V1 and required runway length calculations will be, though.

I cant help, but post a meme:



(ASDR stands for Accelerate-Stop Distance Required, and stands for the distance that the aircraft need to accelerate to V1 and stop again, obviously must be less than runway available)

Anyway regarding smaller engines, the aircraft would still have to be able to drag itself into climb on MTOW with one engine out, so I am not sure that would be feasible,
less/simpler flaps, I am afraid you still have to land... but it might be possible to get away with less flaps actually used for T/O,
all in all too small a benefit to be viable IMHO.
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LH707330
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RE: Will We See Jet Donkeys Soon?

Sat Sep 08, 2012 1:55 am

Quoting Fabo (Reply 14):
less/simpler flaps, I am afraid you still have to land...

Couldn't you use a massive spoiler mounted directly over the gear leg that goes all the way back to the trailing edge to plant the gear and enable more aggressive braking? On a long haul a/c this might make more sense because your landing weight is a lot lower so you can lower your approach speed.
 
flyingturtle
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RE: Will We See Jet Donkeys Soon?

Sat Sep 08, 2012 9:21 am

Quoting Fabo (Reply 14):

Thank you, I've had a good laugh. 

I can't find that drawing that apeared in the 1980ies popular science magazine "P.M.", but it was even more dangerous - it was really a ski jump, and the airport was on top of a 30-story building. With a downward-sloped runway at least, you could offer a generous overrun area...



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HAWK21M
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RE: Will We See Jet Donkeys Soon?

Sat Sep 08, 2012 10:27 am

Quoting bhill (Reply 13):
Conveyor belts anyone?........

sure remember that debate...went on for a long time....
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AirframeAS
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RE: Will We See Jet Donkeys Soon?

Sat Sep 08, 2012 12:29 pm

Quoting HAWK21M (Reply 17):

Quoting bhill (Reply 13):
Conveyor belts anyone?........

sure remember that debate...went on for a long time....


With record replies and views! Good old days!
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Pihero
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RE: Will We See Jet Donkeys Soon?

Sat Sep 08, 2012 6:01 pm

As usual, many things have been invented already. Just need to come out with improvred design.
The Baroudeur was designed some sixty years ago.
Have a look at this

But trhere probably is a simpler solution : electric motors bto the main gears.
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LH707330
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RE: Will We See Jet Donkeys Soon?

Mon Sep 10, 2012 4:33 pm

Quoting Pihero (Reply 19):
The Baroudeur was designed some sixty years ago.

Which in turn took that idea from the Me-163 Komet, but I digress.

Quoting Pihero (Reply 19):
But trhere probably is a simpler solution : electric motors bto the main gears.

I'd imagine you'd have wheelspin issues with current aircraft tires....
 
OldAeroGuy
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RE: Will We See Jet Donkeys Soon?

Sat Sep 15, 2012 1:45 pm

Quoting HAWK21M (Reply 6):
Whats the history on this term usage.

The donkey part goes back to railroading where "helper" engines were kept at hilly portions of a route to assist in getting a train over the hills. The "helpers" were referred to as "donkeys".
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LH707330
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RE: Will We See Jet Donkeys Soon?

Mon Sep 17, 2012 6:00 pm

Here's another reference, this time referred to as "tractors." Looks like they may seem serious about finding a way to solve this issue.

http://www.flightglobal.com/news/art...ails-are-all-in-the-future-376312/

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