Classroom Discussion

[Tchkinjiu]

We had a brief discussion that I didn't really know. We were wondering why they dont have the wheels start spinning before the planes touches down. It would burn less rubber and make them last longer.

But then some counter-examples were that, that the friction between the gound and the wheel helps lower the speed of the plane once it hits. Also, it might cause it to become unbalanced.

So, if anyone has a real reason for this, please say so

[Hagar]

Hi Tchkinjiu. Very interesting. I'm surprised that nobody has brought this up before. I remember experiments being done on this back in the 1950s. It's expensive, adds weight & was found to have no real benefit. Unless a way could be found to spin the wheels to match the exact speed of the aircraft when it touches the runway it would probably cause more tyre wear, not less.

But then some counter-examples were that, that the friction between the gound and the wheel helps lower the speed of the plane once it hits.

I don't think there would be any noticeable slowing effect with conventional wheels/brakes on a modern jet airliner. If the parking brakes were left On by mistake it would simply skid along the runway & the friction would quickly burn though the tyres.

PS. If you have the opportunity, jack up a car so one of the front wheels is clear of the ground. Now try rotating the wheel by hand. That's with an ordinary single caliper disc brake. Imagine the size of the wheel multiplied several times over compounded by the multiple-disc brakes used on an airliner like the 737 & the power that would be required to spin just one wheel. It's impossible for one man to lift a typical brake unit fitted to a modern airliner.

[Fozzer]

In a similar vein...!

On small GA tricycle aircraft I always thought it a good idea to have a small electric motor driving the nose-wheel for taxying purposes...saving all the puffing with the propeller to get the aircraft moving...LOL... ...!

Imaging trying to navigate your car into the garage using the radiator cooling fan....LOL...LOL...LOL... ...!
...I don't think so... ..... ....!

Cheers all... ...!

Paul. On a cold, wet day.... ...!

[Politically Incorrect]

I would think if the wheels were spinning slower than the aircraft at touchdown there is not only the possibility of more wear on the tires but ripping off the plane. As soon as the spinning wheels touch the surface if not spinning the same speed as the aircraft they would immediatly stop resulting in severe damage such as ripping off the plane, extreme instant heat build up causing the tire to explode, loss of control etc.

You can easily test my theory with a common model, be it a airplane or car. Hold it off the ground spin a wheel and procede to land, you'll notice as soon as the wheel touches the surface it will stop, I tried this over and over and no matter how hard I try I can't get my "landing" speed the same as the spinning wheel.
Although I'm certain with technology today they can come up with something that could make the wheels speed the same as the speed of the plane.

Very interesting subject to ponder on though.

[FLYING_TRUCKER]

Over the years I have only had gear problems once.

I had one main refuse to come down and had to be pumped down by crew.

The problem I think with rotating wheels prior to landing is that if one unit could not be lowered it would cause a control problem for the A/C.  

The less an A/C has to worry about during an emergency landing the better.

I watched an RCAF Boeing 707 land with the one main stuck up, the crew tried everything.
After enough fuel was burned off the aircraft landed on the runway and gently settled on the one side, only damage was some scrapes to the engines.  The aircraft was lifted up and gear pulled down, pinned and towed away.

Cheers...Happy Landings...Doug

[Hagar]

On small GA tricycle aircraft I always thought it a good idea to have a small electric motor driving the nose-wheel for taxying purposes...saving all the puffing with the propeller to get the aircraft moving...LOL... ...!

A brilliant idea Paul. We could go into business & make our fortunes.

The Grumpy design department is already working on it. What I have in mind is self-propelled update kits for all popular light aircraft types. The "De Luxe" version will involve a series of chains & sprockets attached to the rudder pedals. No need to start the engine or run down the battery. Simply get in & pedal it into or out of the hangar. The Economy or "Flintstone" model will be a lot cheaper, consisting of 2 carefully positioned holes cut in the floor.

[Fozzer]

A brilliant idea Paul. We could go into business & make our fortunes.

The Grumpy design department is already working on it. What I have in mind is self-propelled update kits for all popular light aircraft types. The "De Luxe" version will involve a series of chains & sprockets attached to the rudder pedals. No need to start the engine or run down the battery. Simply get in & pedal it into or out of the hangar. The Economy or "Flintstone" model will be a lot cheaper, consisting of 2 carefully positioned holes cut in the floor.

Hi Doug...!
...love it...
Got my draughtsmans pencil and drawing board out for the first design prototype.
Holes in the floor seem to be the cheaper version at the moment...
...working on it at the mo'...

Cheers Doug...!

Paul....a member of the Gerrard Hoffnung/Roland Emmet appreciation society... .... ....!

...ya gotta larf... ...!

[FLYING_TRUCKER]

Hi Doug...Hi Paul

Can I be a silent investor....Please

If this takes off we can get Bjorn to invest half his allowance as well

Man I think I am going to be rich.

Cheers...Happy Landings...Doug

[Scottler]

I've always thought motorized gear for taxying would be a great idea...

As for spinning tires prior to landing...they wouldn't have to spin long.  But if weight and accuracy of matching speed are an issue, why couldn't one design some sort of "windmill" type device that would mount on the sides of the tires?  The passing air would automatically spin the tires at the speed air passes over it.

[Hagar]

[quote]As for spinning tires prior to landing...they wouldn't have to spin long.

[Jared]

In the end it's probably easier & cheaper to replace the tyres.

I second that motion, and suggest we end debate?  ;D

[Hagar]

[quote]I second that motion, and suggest we end debate?

[Jared]

Oh dear. I was just getting started. I thought you would be the ideal person to contribute to the discussion as I believe you're studying aircraft engineering & more up to date on this stuff than me.

If this doesn't excite you how about helping out with our other project, the FozGar patent self-propelled taxying unit (SPTU for short). We could all end up rich.

lol, it's just that I found your point was very clear, and true from what I have learned thus far... ;-)

I'll always sit back and learn a thing or two from the elders of the community...

As for the SPTU I would love to help out! :-) you guys send me a design concept drawing and whatever information you deem neccessary and I will begin to work on the physics, as well as physical design of this system...

[Woodlouse2002]

On the SPTU concept may I suggest a little electronic castor that extends hydrolically from the bottom of the plane onto the tarmac where it then scoots you along in a nice zig-zag.

[Jared]

lol, we can take that option into consideration for our basic prototype design, however there must be some stipulations to this design...

1.) This caster must be squeaky!

2.) This aformentioned caster must also be broken in half and if possible rusty.

3.) And as always this caster must annoy the user so much that he/she will gladly upgrade to our professional option for a modest fee to cover expenses...