How flat is a tyre?

Ross_Moorhouse · 13 December 2002, 11:10 AM

Knowing that most WWI plane tyres are not very wide I was wondering what the effect of the weight on the plane would have in producing a bulge on the bottom of the tyre when the plane is at rest on the ground.

TIA

PeterL · 13 December 2002, 11:53 AM

Ross: "...what the effect of the weight on the plane would have in producing a bulge on the bottom of the tyre...?"

Tyres on contemporary photographs or *museum survivors like this Thomas pusher don't appear to bulge at all. For modeling purposes I usually sand a very slight flat on each wheel to give the impression that it does actually wiegh something even if it's not very much.

13 December 2002, 02:55 PM

Some tyre technician could probably tell you more, but as I recall from reading the history of Firestone, the Balloon tyre came into use in the early '30's.
Prior to that, tyres were inflated very hard, to keep the sidewalls apart and vertical. Weight was carried on the (thick)sidewalls in a vertical plane in high-profile tyres. Common motor cars had about 60-80 lbs sq/in or so.
Balloon tyres carried the weight on the column of air within the tyre, i:e, the imaginary column of air between the axle and the ground contact point.
Consider the bicycle wheel. Is the axle held up by the bottom spoke, or held up by the top spoke?
Dig out a Palmer Cord if you can. There might be words like, " inflate hard," or " Min pressure X lbs.", allsame bike tyres today.
In WW2 the Dauntless had high pressure tyres to absorb deck landing stresses. But DON'T QUOTE ME!

Ross_Moorhouse · 13 December 2002, 05:17 PM

I went through all the photos etc I have and also looked on the net and you are both right. So I have just taken Peter's advise and flattened the bottom of the tyre.

In fact they seemed to be inflated so hard that I saw pics of the plane sitting on a mud/grass strip with mud up to its rim. Also considering there isnt much surface area of these tyres would also explain the amount they sink into the ground.

Cheers.

Barker · 13 December 2002, 06:48 PM

Ross, I laid off this one to see.
These tyres seem more like bicycle tyres than WW2 tyres, to me. I'm with all of y'all. Flatten the bottom, pretty much as you would see a bicycle tyre look. and not just because they're spoked...

Rickenbacker's Spad appears to be on somewhat of a grassy field (not too unusual when you think about it) and it's more difficult to infer.

When I saw your post I could not remember a photo where they *did bulge* such as WW2 aircraft, fwiw.

-Barker