TUSDawg23
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Jets Nay Be Able To Taxi Using Just APU By 2016

Wed Jun 22, 2011 5:51 pm

I came across this article recently that by 2016 airliners can taxi using just the APU without any use of the engines. http://www.aopa.org/aircraft/article...2011/110620taxi_green_in_2016.html

What do you think? Is it feasible. Sounds like electric motors would be attached to the gear and it can operate just as an airliner is normally taxied today. It sounds like a great concept that could save airlines millions in fuel costs over tima and I think the timing is right with fuel prices going as high as they are.
 
mmedford
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RE: Jets Nay Be Able To Taxi Using Just APU By 2016

Wed Jun 22, 2011 6:04 pm

Fuel savings would be neglected by the weight of the motors needed to move a fully loaded aircraft any reasonable distance and speed.

Plus Engines do need to warm up and stablize before being firewalled for takeoff.
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thegeek
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RE: Jets Nay Be Able To Taxi Using Just APU By 2016

Wed Jun 22, 2011 11:29 pm

You'd also eliminate the need for tugs to do push backs. 4% saving? Pretty hard to believe. You'd also wonder about the structural strength of the gear, and the electrical output of the APU. UA tried tugging planes forward to achieve the same savings and was given a "cease and desist" notice, although perhaps if done on the main gear it would likely be OK.
 
Horstroad
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RE: Jets Nay Be Able To Taxi Using Just APU By 2016

Fri Jun 24, 2011 12:13 am

i guess the Taxibot is a better solution than adding electric motors to the landing gear as aircraft don´t need to be modified.
http://www.youtube.com/watch?v=Kbq2pVfss9o
 
thegeek
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RE: Jets Nay Be Able To Taxi Using Just APU By 2016

Fri Jun 24, 2011 4:01 am

Quoting horstroad (Reply 3):
i guess the Taxibot is a better solution than adding electric motors to the landing gear as aircraft don´t need to be modified.

Is it better than the MLG attaching remote controlled tow vehicles?
 
LMP737
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RE: Jets Nay Be Able To Taxi Using Just APU By 2016

Sat Jun 25, 2011 4:09 pm

The question I have is how much will this system wiegh and what will be the costs to maintian it. As meddford pointed out you cannot just go tot he end of the runway, start the engines and hit the TOGA button. Once those aircraft got to the runway they would have to warm up their motors for takeoff. This would obviously cause conjestion.

Quoting horstroad (Reply 3):
i guess the Taxibot is a better solution than adding electric motors to the landing gear as aircraft don´t need to be modified.

You still have some of the same issues with Taxibot as you would with motors on the landing gear. Mainly engines needing to warm up before takeoff. There is also the issue of reliability. A lot of airlines use Goldhofers to move planes between the terminal and hangars. However they do break. Moving aircraft between gates or from the terminal to the hangar is one thing. Moving them to or from the runway is another.
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DocLightning
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RE: Jets Nay Be Able To Taxi Using Just APU By 2016

Sun Jun 26, 2011 12:58 am

Quoting LMP737 (Reply 5):

You still have some of the same issues with Taxibot as you would with motors on the landing gear. Mainly engines needing to warm up before takeoff. There is also the issue of reliability. A lot of airlines use Goldhofers to move planes between the terminal and hangars. However they do break. Moving aircraft between gates or from the terminal to the hangar is one thing. Moving them to or from the runway is another.

Depends. If it's a short taxi, then using engines probably makes sense. But consider the case of AMS's 36L, or an aircraft going from SFO's T3 going to the 28's. These represent very long taxi distances. These sorts of situations aren't rare at major airports, either. There is also the case of congestion ("We're number 23 in line for takeoff"). In all of these situations, the engines must be left running for far longer than is necessary to allow for temperature equilibration. Often, both (or all four) engines are idling for over 15 minutes.

Engines need only a few minutes to warm up. At SFO, WN often pushes back, starts engines, and then taxis the ~200m to 1R and departs less than 5 minutes after both engines are powered up.

In cases where a taxi time longer than a few minutes is expected, a system like this makes sense. In the case of "taxibot," the only modification to the aircraft seems to be a tiny transmitter, which adds negligible weight. But even with electric motors, they need not weigh more than a few kg. Modern electric engines can pack quite a lot of power in a very small package. They also pack a lot of torque. Given that a few men can push a fully-loaded aircraft, the total required torque and HP is not as high as you might think, especially with the low speeds and accelerations required.
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LMP737
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RE: Jets Nay Be Able To Taxi Using Just APU By 2016

Fri Jul 08, 2011 4:49 pm

Quoting DocLightning (Reply 6):
Engines need only a few minutes to warm up. At SFO, WN often pushes back, starts engines, and then taxis the ~200m to 1R and departs less than 5 minutes after both engines are powered up.

A Trent or GE-90 at ORD in Febuary is going to take more than a few minutes.
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boeing767mech
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RE: Jets Nay Be Able To Taxi Using Just APU By 2016

Sat Jul 09, 2011 5:26 am

Quoting LMP737 (Reply 7):
A Trent or GE-90 at ORD in Febuary is going to take more than a few minutes.

Typical for a Trent to take 5 plus minutes to warm up before we can even push the throttles forward on a cold day in Boston. The AMM states NOT to apply thrust to the engine until the engine oil temp is over 50 degree C. I have seen the remains of engines after the pilot lights it off and pours the coals to it. used to do it to #2 on the DC-10's. Light it off turning to line up with the runway. Makes for nice overtime doing engine changes because the enigne corn cobed itself.

Also would love to see how this TowBot is going to work in the snow or ice.

David
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SchorschNG
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RE: Jets Nay Be Able To Taxi Using Just APU By 2016

Sat Jul 09, 2011 3:08 pm

Some facts as I happened to work on this topic lately:

- The engine warm-up is pretty much no issue. If it isn't the first leg or very cold, 3 to 5 minutes are perfectly OK. Engine run-down is another issue, CFM recommends up to 10 minutes. But this again depends on the usage of the engine before shut down. If the aircraft landing using just IDLE REVERSE the run-down period can be reduced.

- The weight is critical, but current single aisles react very slowly to increased weight. Airbus gives 48kg/1000nm additional fuel burn for 730kg additional weight. So, if the system comes out a 400kg additional weight, the additional fuel burn will be 20-25kg per 1000nm.

- Coming to the savings: CFM56 burn about 300-400kg/hr in IDLE (each!). That is 10kg per minute for the aircraft. The APU at full power burns about 120kg/hour. Or 2kg/minute. Easily spotted: 3 minutes saved engine IDLE and you have "earned" the additional fuel a 1000nm trip.

- There are other advantages: a big issue is the taxi fuel allowance. The pilot has to anticipate the required taxi fuel. If he guesses low, he needs to return for refueling (or land below reserves). So he will always guess high and on average the aircraft tankers fuel it actually doesn't need. I would assume this additional fuel as 100-200kg, and this weight can be deducted from the system weight.

- One issue is rarely mentioned: taxi speed. Aircraft usually go 20-30kts, especially when taxiing a longer distance. This is 56km/h! Now, it requires some power to move a 70-75t aircraft at 60km/h. I would assume 100kW (136 PS) are the required. Now, the APU only provides half of that. Therefore, I doubt the taxi speeds we know are achievable using such device.

- The system would be very interesting for North American mainline carriers. Many airports have average taxi times of 45 minutes (taxi in and taxi out combined). My calculation resulted in the finding, that a trip distance of 1000nm the system generates fuel saving when added taxi time exceeds ~22 min (The Assumptions are not too optimistic: assumed 400kg system weight, full APU fuel burn, no consideration of taxi fuel allowance, 5 minutes run-up and run-down time for the engine). Basis is the A320 with current engine technology.
From a structural standpoint, passengers are the worst possible payload. [Michael Chun-Yung Niu]
 
jwenting
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RE: Jets Nay Be Able To Taxi Using Just APU By 2016

Mon Jul 11, 2011 5:44 am

Quoting SchorschNG (Reply 9):
Aircraft usually go 20-30kts, especially when taxiing a longer distance. This is 56km/h!

I've paced aircraft on the taxiway to AMS 36L doing almost twice that!
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SchorschNG
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RE: Jets Nay Be Able To Taxi Using Just APU By 2016

Mon Jul 11, 2011 8:54 am

Quoting jwenting (Reply 10):
I've paced aircraft on the taxiway to AMS 36L doing almost twice that!

Sure, but usually outside Standard Operating Procedure. Officially, no airline allows that. And the manufacturer wouldn't recommend at, either. Technically, it is no problem.
From a structural standpoint, passengers are the worst possible payload. [Michael Chun-Yung Niu]
 
SchorschNG
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RE: Jets Nay Be Able To Taxi Using Just APU By 2016

Mon Jul 11, 2011 9:08 pm

Quoting boeing767mech (Reply 8):
Also would love to see how this TowBot is going to work in the snow or ice.

The good thing: if for any reasons it doesn't work, you just do it the old way. OK, you lifted the system for no reason then, but more important for airlines are operational robustness. And that's given.
From a structural standpoint, passengers are the worst possible payload. [Michael Chun-Yung Niu]
 
dkswim
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RE: Jets Nay Be Able To Taxi Using Just APU By 2016

Tue Jul 12, 2011 3:53 am

I like the idea in concept. I dont think its a viable solution just yet.

Q how much bigger APU is needed to supply the added load of taxiing the aircraft?

If using APU only APU needs to supply Air for cooling cabin and avionics, need to supply electricity for avionics and lights, needs to supply hydraulic power for brakes and steering, and need to produce enough electricity to propell fully loaded plane, possibility of crossing active runways?

Q so bigger APU how much of Fuel burn penelty?

Q why not strength nose gear and tractor them to and from?

this APU taxi would work at hubs and bussy airports where long taxies of more then 10-15 min expected, but what about out at satalite and smaller where no wait?
 
bonusonus
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RE: Jets Nay Be Able To Taxi Using Just APU By 2016

Tue Jul 12, 2011 7:08 pm

I think the APU system is pretty interesting, but the size of the electric motor required to provide enough torque would be significant. This would inevitably add more weight to the landing gear trucks (even if the motor is mounted inside the fuselage and is attached through some sort of gearing system) which would in turn require a larger motor for retracting the LG, also adding more weight.

As for the Taxibot, it looks like a very innovative system. However, I'm not sure it would reduce costs, because as opposed to tugs only being needed to push planes back from the gate, now you need a tug for every plane that is taxiing. You also need a 'safety driver' for each of those tugs to return to the gate. Assuming this vehicle costs as much, if not more than a standard tug, I think it would be difficult to realize the cost savings.
 
rcair1
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RE: Jets Nay Be Able To Taxi Using Just APU By 2016

Tue Jul 12, 2011 9:13 pm

Quoting SchorschNG (Reply 9):
- The weight is critical, but current single aisles react very slowly to increased weight. Airbus gives 48kg/1000nm additional fuel burn for 730kg additional weight. So, if the system comes out a 400kg additional weight, the additional fuel burn will be 20-25kg per 1000nm.

Looks like the Taxibot add's no weight at all.

Quoting SchorschNG (Reply 9):
- The system would be very interesting for North American mainline carriers. Many airports have average taxi times of 45 minutes (taxi in and taxi out combined). My calculation resulted in the finding, that a trip distance of 1000nm the system generates fuel saving when added taxi time exceeds ~22 min
Quoting bonusonus (Reply 14):
As for the Taxibot, it looks like a very innovative system. However, I'm not sure it would reduce costs,

Who pays for the Taxibot and sleeping driver? I could see some interesting battles here - presumably the Taxibot is owned/operated by the airport, not the airline. The airline is saving the bucks - so the airport will want at least some of that money. The savings will be related to aircraft size, weight, efficiency - i.e., it is not the same for every aircraft every time.

BTW - Being the driver in the Taxibot has to be one of the more boring positions I've ever seen. Sit all the time, ride out under a jet - then drive back. Is there a buzzer to wake them up when they get out to the runway. I can just see the pilot leaning out of the window going - HEY YOU - WAKE UP AND MOVE THAT THING....

Even in the video - the driver looked incredibly bored - and that was marketing so they would coach him.
rcair1
 
SchorschNG
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RE: Jets Nay Be Able To Taxi Using Just APU By 2016

Wed Jul 13, 2011 6:50 am

Quoting rcair1 (Reply 15):
Who pays for the Taxibot and sleeping driver? I could see some interesting battles here - presumably the Taxibot is owned/operated by the airport, not the airline. The airline is saving the bucks - so the airport will want at least some of that money. The savings will be related to aircraft size, weight, efficiency - i.e., it is not the same for every aircraft every time.

BTW - Being the driver in the Taxibot has to be one of the more boring positions I've ever seen. Sit all the time, ride out under a jet - then drive back. Is there a buzzer to wake them up when they get out to the runway. I can just see the pilot leaning out of the window going - HEY YOU - WAKE UP AND MOVE THAT THING....

Even in the video - the driver looked incredibly bored - and that was marketing so they would coach him.

The "Bot" in "TaxiBot" implies, that the whole system relies on automated vehicles. These are controlled by the pilot when connected to the aircraft, and drive on their own when proceeding to their next job.
The TaxiBot would make sense for some applications, especially long range aircraft, especially when the TaxiBot would also feature some power generation. For short ranges, the carried wheel drive is much more interesting.
From a structural standpoint, passengers are the worst possible payload. [Michael Chun-Yung Niu]
 
yeelep
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RE: Jets Nay Be Able To Taxi Using Just APU By 2016

Thu Jul 14, 2011 1:08 am

Quoting SchorschNG (Reply 16):

The Taxibot in its current guise uses a operator to drive it when not connected to an airplane. I assume the operator also performs the lifting/lowering of the nose gear and the pushback.

I can see the day when all aircraft operations on the ground are controlled by a system of autonomous tugs. Which are directed by ground controllers, without aircrew or ground crew input. It seems the Autobot is a step in this direction as it appears the forward movement of the tug when connected to a plane is controlled by a central computer, not the crew or tug driver.
 
rcair1
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RE: Jets Nay Be Able To Taxi Using Just APU By 2016

Thu Jul 14, 2011 3:36 am

Quoting SchorschNG (Reply 16):
The "Bot" in "TaxiBot" implies, that the whole system relies on automated vehicles. These are controlled by the pilot when connected to the aircraft, and drive on their own when proceeding to their next job

That's what I would have thought based on the name, but if you watch the video you see that it is not quite that way.

- The steering of the taxibot is controlled by the pilot using the nose gear steering on the aircraft. It has a clever arraingement that senses when the NLG turns and steers the bot accordingly.
- Stopping the bot is done using the aircraft MLG brakes on the aircraft.
- I don't recall how the pilot tells the 'bot' to speed up - but if I recall it is also something require little if no change to the aircraft.

However, when the aircraft reaches the runway - the 'safety driver' in the cab of the bot drives it to it's next assignment. It is not autonomous.

If you watch the video through - it describes this.
rcair1
 
SchorschNG
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RE: Jets Nay Be Able To Taxi Using Just APU By 2016

Thu Jul 14, 2011 7:34 am

Quoting rcair1 (Reply 18):

That's what I would have thought based on the name, but if you watch the video you see that it is not quite that way.

- The steering of the taxibot is controlled by the pilot using the nose gear steering on the aircraft. It has a clever arraingement that senses when the NLG turns and steers the bot accordingly.
- Stopping the bot is done using the aircraft MLG brakes on the aircraft.
- I don't recall how the pilot tells the 'bot' to speed up - but if I recall it is also something require little if no change to the aircraft.

However, when the aircraft reaches the runway - the 'safety driver' in the cab of the bot drives it to it's next assignment. It is not autonomous.

If you watch the video through - it describes this.

OK, but the long term concept sees it without driver.
But the requirements are tough:
> some kind of standarized interface between aircraft and TaxiBOT, probably using some kind of wireless connection
> a robust solution so the vehicle doesn't damage the aircraft
> some sort of vehicle detection system
So, the entire system only works for some airports. Probably the bigger ones with lots of large aircraft, long taxi times and some cash.
From a structural standpoint, passengers are the worst possible payload. [Michael Chun-Yung Niu]
 
Spacepope
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RE: Jets Nay Be Able To Taxi Using Just APU By 2016

Thu Jul 14, 2011 3:45 pm

Quoting bonusonus (Reply 14):
I think the APU system is pretty interesting, but the size of the electric motor required to provide enough torque would be significant. This would inevitably add more weight to the landing gear trucks (even if the motor is mounted inside the fuselage and is attached through some sort of gearing system) which would in turn require a larger motor for retracting the LG, also adding more weight.

Could the weight be more palatable if the motors could also be used to spin up the wheels before landing to mitigate tire scrub? (just had to throw out that classic A.net issue).

Dual purpose could take some of the sting out of the pounds.
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thegeek
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RE: Jets Nay Be Able To Taxi Using Just APU By 2016

Fri Jul 15, 2011 4:37 am

Quoting Spacepope (Reply 20):
Could the weight be more palatable if the motors could also be used to spin up the wheels before landing to mitigate tire scrub? (just had to throw out that classic A.net issue).

That would make more sense on the MLG than on the NLG. Which would also mean more and smaller motors on bigger wheels which minimises unsprung weight issues.

Interesting. I doubt that it makes it work though.
 
TheSonntag
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RE: Jets Nay Be Able To Taxi Using Just APU By 2016

Fri Jul 15, 2011 2:56 pm

Quoting SchorschNG (Reply 11):
Officially, no airline allows that

Ryanair?  
 
spudsmac
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RE: Jets Nay Be Able To Taxi Using Just APU By 2016

Fri Jul 15, 2011 6:48 pm

Quoting thegeek (Reply 2):
UA tried tugging planes forward to achieve the same savings and was given a "cease and desist" notice

Care to expand on that?
 
JoeCanuck
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RE: Jets Nay Be Able To Taxi Using Just APU By 2016

Sat Jul 16, 2011 6:24 am

Another thing to take into consideration is noise. Current engines can be quiet in a large part due to their high bypass configuration. A small jet can be very noisy and running it at full crank to taxi might make quite a racket.

An APU strong and quiet enough for taxi operations might be big enough to provide enough thrust for emergency flight operations...as was talked about on the 777.
What the...?
 
SchorschNG
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RE: Jets Nay Be Able To Taxi Using Just APU By 2016

Sat Jul 16, 2011 8:45 am

Quoting JoeCanuck (Reply 24):
Another thing to take into consideration is noise. Current engines can be quiet in a large part due to their high bypass configuration. A small jet can be very noisy and running it at full crank to taxi might make quite a racket.

An APU strong and quiet enough for taxi operations might be big enough to provide enough thrust for emergency flight operations...as was talked about on the 777.

And that was BS all along.
An APU delivering thrust is bad engineering.

The APU may be loud, but it still is far less noise than the big engines.
And honestly, who cares about noise on the airport?
One advantage is the lack of jet blast on the apron, making operations there safer.

In order to generate enough electricity for the drive motor the APU maybe needs to deliver more power, which means only new aircraft can use the system to full extent. But the power to weight ratio of an APU is rather good (usually about 2kg for every additional 1kW of generated power), so some additional power (we are talking about 30-60kW additional APU power) wouldn't hurt too bad.

Of course, all these taxi motor things shouldn't exist in the first place, they are a consequence of large and congested airports. In my hometown Hamburg the average taxi time is 3-7 minutes. Nobody would install a taxi motor in that scenario.
From a structural standpoint, passengers are the worst possible payload. [Michael Chun-Yung Niu]
 
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HAWK21M
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RE: Jets Nay Be Able To Taxi Using Just APU By 2016

Sat Jul 16, 2011 9:57 am

Quoting SchorschNG (Reply 25):

The APU may be loud, but it still is far less noise than the big engines.
And honestly, who cares about noise on the airport?

The V2500 powerplant is quieter than its related APU on ground.
Unfortunately folks purchase residences near Airports & then ask for silence at the cost of Airport operations.
I may not win often, but I damn well never lose!!! ;)
 
thegeek
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RE: Jets Nay Be Able To Taxi Using Just APU By 2016

Sat Jul 16, 2011 10:26 am

Quoting spudsmac (Reply 23):
Care to expand on that?

I should have prepended that with "I have read on a.net that ..." I think there was a link to an article though, so I never thought it was made up.

I understand that sustained towing of the plane in the forward direction was not designed for.
 
JoeCanuck
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RE: Jets Nay Be Able To Taxi Using Just APU By 2016

Mon Jul 18, 2011 11:09 pm

Quoting SchorschNG (Reply 25):

The APU may be loud, but it still is far less noise than the big engines.

An APU strong enough to move a fully loaded aircraft would be running at full power, which would probably be significantly noisier than a modern jet engine on a wing barely above idle.

Noise is the number one reason NIMBYs hate airports.
What the...?
 
MarkC
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RE: Jets Nay Be Able To Taxi Using Just APU By 2016

Mon Jul 18, 2011 11:54 pm

FYI, a big PW4000 does 2,200 pounds per hour. I would assume the GE and Rolls 777 engines are also similar. If this happens, it will be on large aircraft.
 
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HAWK21M
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RE: Jets Nay Be Able To Taxi Using Just APU By 2016

Wed Jul 20, 2011 11:15 am

Balance between added complications prone to snags,added weight against Costs.......

Quoting thegeek (Reply 27):

I understand that sustained towing of the plane in the forward direction was not designed for.

Pls elaborate......
I may not win often, but I damn well never lose!!! ;)

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