Why am I talking about friction? See my previous post. 🙂

And you explained it better than I could – ta. 🙂

ok, with the aircraft sitting stationary on the belt thrust is applied by the engine, this would normally be imparted through the wheels in order to create ground speed.

The problem – or rather the clever bit of the question – is that from an early age riding bicycles, being driven round in cars and buses, we understand that the driving force goes through the wheel. We rely on “intuition” that we learn early in life but the question catches us because an aircraft applies the force to the air. The wheels are passive.

Try thinking about an aircraft on skis, or, and this one I like, a floatplane.
If we are allowed to write our own question then how about an aircraft floating on a fast flowing river going in the opposite direction to the aircraft – how does it get airborne? At least it won’t have overheated wheel bearings but then there is the issue of surface tension creating water drag. :diablo:

I would have thought in the case under consideration the wheel bearing friction was minimal and could even be considered zero.

The aircraft is on the conveyor.

Consider the conveyor accelerates from zero up to the point where the velocity of the conveyor relative to ground exceeds the lift off speed of the aerofoil.

If the brakes are not applied the, due to inertia, the aircraft will remain stationary and the wheels will spin in reverse.

There is no reason why that should not be. You are assuming that the conveyor belt is the main driving force in this scenario.

If the brakes are applied, there will be zero friction in the bearing, the aircraft will accelerate relative to the ground and the air, remain stationary relative to the conveyor and at the critical speed will lift off, stall and return to the conveyor. If engine power is applied at the point of lift off it will fly.

Again based on your assumptions, this should happen.

But taking the question literally, “the belt . . rotates . .at the exact same speed as the wheels” then when the wheels slow under braking the conveyor slows and stops. We’re all making our own assumptions based on a question which did not define all the parameters. Which means the question has no right answer – help 😮

You assume the conveyor belt drives the scenario, CD assumes the aircraft engine drives his scenario and I assume the conveyor is computer controlled to match the speed of the wheels exactly and got positive feedback. Now I really do have a headache.

I’m going home. :p

The type of aircraft is irrelevant; it wouldn’t matter if it was a microlight or a Boeing 747, the result would be the same. 🙂

A colleague at work has just asked what happens if the aircraft is a Harrier. :diablo:

Why are we talking about friction? I think we should be talking about positive feedback loops.

The question is phrased is a vague way so we have to make a number of assumptions, eg zero wind speed, which is fine. But lets work through what happens. Consider the aircraft engine is off and the the wheels are not moving. The question states:

If an aircraft is sitting on a conveyor belt.. that rotates in the opposite direction to the wheels, at the exact same speed as the wheels, will the plane take off?

So, the conveyor belt is not moving. Everything is stationary. OK

Now, start the engine and, as stated very well above:

The aircraft propeller pushes against the air, the stationary air, above the belt to generate the thrust…and the only part of the aircraft touching the belt are the wheels that are free to spin.

So the aircraft moves forward at, say 1 metre per second (relative to the air and a fixed point on the ground – remember the air is not moving, no wind)
The wheels rotate at this speed – 1m/s
The conveyor belt accelerates to this speed (acceleration is an issue but lets assume it is very impressive)
Do the wheels stop moving? No, and because the aircraft is still moving at 1m/s relative to the ground and the conveyor is going 1m/s in the opposite direction relative to the ground, the wheels are accelerated to 2m/s and the belt accelerates to keep up (the question states clearly, that the belt goes at the exact same speed as the wheels) and the wheels go faster and faster and faster – positive feedback loop.
The aircraft may well reach take off speed but with melted wheel bearings.

Or have I completely missed something important because, to be honest, I’m starting with a headache now :confused: :confused:

Excellent news. There seem to be quite a few plans coming together to mark the centenary of flight in the UK but marking Cody’s flight with a replica will be very special. I wish it well – and welcome to the forum.
So, have the original plans for the aircraft survived or have they had to be recreated?

Many thanks for that one,I am chuffed to see there is still some more surviving documents.would the owner be able to get/allow a copy for Aeroventure?

I’m sure he would be happy to let me send you what I have. He is very old and frail so borrowing the original might be problematic. Check you PMs.

I’ve done a brief search and there are others in collections which might be in better condition. Sheffield Archives has one and the Bodleian Library at Oxford has another. The East Ridings Archive also has a programme and some postcards/photos. Doncaster Archives has a supplement to the Doncaster Gazette.
If you try http://www.a2a.org.uk you can search several of these repositories at once. You can also get to this search through the National Archives site: http://www.nationalarchives.gov.uk
And to add to your evening of fun, I’ve had a quick look on The Guardian’s new digital archive and they’ve got lots of press reports, giving background to the event. They have a “free for 24 hours” offer on just now.

looking at the list of participants I don’t recall seeing a large green ogre with a scottish accent in any photo’s of the event:D

I don’t suppose the accent and colour would show in a B&W photo 😀 Actually, it’s a 100-year-old typo – should be Schercke

Just spotted this on the Guardian’s website:

http://archive.guardian.co.uk/Repository/ml.asp?Ref=R1VBLzE5MzIvMDUvMjMjQXIwMDgwMQ==&Mode=Gif&Locale=english-skin-custom

The Guardian was using the article as one of several to highlight their new digital archive – so they must still recognise Earhart’s importance.

Being the original article it is a fascinating insight into how Earhart was viewed at that time. I was particularly touched by the paper warning her of the dangers of trans-oceanic flight. But it was only a few years later that the first transatlantic airlines were starting.

I wonder if TIGHAR will ever get proof of what happened to her?