Featherbed frame design went against all engineering princip

Rohan · Oct 10, 2014

Re: Featherbed frame design went against all engineering pri

engineering principles.

Folks here are still overlooking the bleedin obvious ?

You will not find any curved tubing or bent tubing incorporated into bridge designs, buildings etc. Or shouldn't.
Strength and/or stiffness, compressibility etc is compromised when the tubing has curves or bends in it.
When stressed or strained, it won't generally be as strong/unyielding as if it were straight tubing.
(some specific examples excepted !)

Thats where these 'engineering principles' come into this discussion...

Hobot · Oct 10, 2014

Re: Featherbed frame design went against all engineering pri

Ugh Rohan, there are great examples of strength of arched supports in bridges and other vital stuff when used right.

Featherbed frame design went against all engineering princip

Rohan · Oct 10, 2014

Re: Featherbed frame design went against all engineering pri

Arches are a completely different subject.
The forces are passed from one stone block to another.
More or less along straight pathways. (although with a bit of sideways vector)

A curved bit of pipe, in compression OR tension, is not as viable as a straight bit of tubing.
Try it on your spaghetti...

Hobot · Oct 10, 2014

Re: Featherbed frame design went against all engineering pri

Ok Rohan just some exceptions using bends we still see in many modern frames though not the most efficient when push comes to shove as you state. Still over rigid-strong has its handling issues too so I still like the funny isolastic frame best with 3 helpers. Some day they'll print out various configurations using a range of structures. Meantime best wishes on obsolete frames.

lcrken · Oct 10, 2014

Re: Featherbed frame design went against all engineering pri

acotrel said:
The featherbed frame came out of an era when tyres did not have much grip. If you ride the bike hard for a long time and climb off it regularly to get around corners, even with the old low grip tyres the frame will often crack because of the flexing caused by the cross loads from the swing arm, even though the manx frame was made out of chrome-moly tube. A Seeley frame is a much better option. Also the geometry and motor position are often better with the Seeley. The one thing that interests me is the crack which sometimes appears just below the front engine mount on the featherbed frame. I believe that many of us underestimate the forces involved when the bike is used in anger. There are plenty of replica featherbed frames around which have been made out of mild steel.

Just so nobody gets confused here, Manx frames, which are 531 manganese moly tubing, will eventually crack when raced extensively. Roadgoing featherbed frames, which are made out of mild steel tubing, will eventually crack when raced extensively. Seeley frames, which are also 531 tubing will eventually crack when raced extensively. Seeley replica frames, which are not all made from 531 tubing, will eventually crack when raced extensively. Rickman frames, which were orginally made with 531 tubing, will eventually crack when raced extensively. Later Rickman frames, which may have been made from 531, or from some other steel alloy, will eventually crack when raced extensively. I've personally had, or watched friends have all the above frames develop cracks from racing use. I've also personally had Commando frames and several Japanese bike frames (Including alloy TZ frames) develop cracks from racing. See the pattern here? What I conclude from this is that almost any bike frame will eventually develop cracks when raced extensively.

Also in the interest of clarity, I'm talking about serious, aggressive racing, with high horsepower and sticky tires, over several seasons, not gentlemen racers or canyon racing or casual track day use. I'm not knocking those pursuits, but they don't stress the frame nearly as much as real racing.

Ken

Rohan · Oct 10, 2014

Re: Featherbed frame design went against all engineering pri

Thanks Ken, good to keep things in perspective here.

The same could also be said for many of the racing cars of the era (all of them ?).
Some old footage the other day showed an AM being sidelined in the pits at LM,
with some cracking that meant the steering/wheels were no longer really connected to the steering wheel.
Yikes....

Not too many owners would have given them a flogging that would have shown that up as a potential long term problem even ?

wakeup · Oct 10, 2014

Re: Featherbed frame design went against all engineering pri

I've always believed that the frame is there primarily to keep the steering axis in it's designed relationship with the swinging arm spindle, and then hold all the other stuff, engine, gearbox, petrol tank etc.
The featherbed took the approach that "more material will be stiffer" approach. The Commando took a more engineering approach. Which when you consider the 20 year space between the design of the Featherbed and the design of the Commando is understandable.
Frank was quite right about the production Stormer frame, it did indeed include his triangular inserts to turn the round top tube into a tapering oval. At the time, as a junior draftsman I asked why not use a similar approach on the Commando frame and was told "....COST...."
cheers
wakeup

Fast Eddie · Oct 11, 2014

Re: Featherbed frame design went against all engineering pri

This is a great discussion!

I think it I s important to remember just when the featherbed was designed, the 1940s, and by a couple if independent Irish engineers, not one of the big companies. Considering that motorcycles didn't develop much in WW2, its competitors of the day were basically pre war affairs. In terms of a road bike chassis, it was a revolution in thinking.

Just that fact we are even comparing it with chassis made decades later is praise for it.

And although I agree with those who say later designs (Seeley, Egli, Dresda, etc) were all better in some ways, one only has to watch a good rider on a good new Manx, with modern rubber and suspension on a track today to realise how good they can still be when built, set up and ridden correctly.

acotrel · Oct 11, 2014

Re: Featherbed frame design went against all engineering pri

That Egli frame of which I posted the photo was a spare for a TZ750 Yamaha which won a round of our Swann series in 1980 (?) it handled noticeably better than many others.
Goose Muir is the rider :

https://www.youtube.com/watch?v=VxzOmI2zat0

Fast Eddie · Oct 11, 2014

Re: Featherbed frame design went against all engineering pri

acotrel said:
That Egli frame of which I posted the photo was a spare for a TZ750 Yamaha which won a round of our Swann series in 1980 (?) it handled noticeably better than many others.
Goose Muir is the rider :

https://www.youtube.com/watch?v=VxzOmI2zat0

I'm sure it did! I had an Egli and it handled wonderfully and that one you showed was clearly in a other league!

I also think we should remember that the actual frame itself is only one part of the (rather complex) handling equation.

Tyres, forks, yokes, shocks, engine weight, engine power characteristics, engine location in the frame, rider weight and location are all huge factors in themselves and become a huge matrix of influencing combinations together.

Rohan · Oct 11, 2014

Re: Featherbed frame design went against all engineering pri

Fast Eddie said:
I think it I s important to remember just when the featherbed was designed, the 1940s, and by a couple if independent Irish engineers, not one of the big companies. Considering that motorcycles didn't develop much in WW2, its competitors of the day were basically pre war affairs. In terms of a road bike chassis, it was a revolution in thinking.

It is perhaps worth noting though that swingarm frames had been developed pre WW2, by folks such as HRD and Velocette,
in different guises. And that tele forks also were a pre WW2 invention. As were twin cradle frames - Indian for example.

Its just that the McCandless Bros threw off conventional (fuddy duddy) thinking, and combined these elements
with a curved tubes twin cradle frame. With, initially, a monocoque rear end of sorts. But that was soon discarded...

Fast Eddie said:
And although I agree with those who say later designs (Seeley, Egli, Dresda, etc) were all better in some ways, one only has to watch a good rider on a good new Manx, with modern rubber and suspension on a track today to realise how good they can still be when built, set up and ridden correctly.

True indeed - a good manx is a joy to behold in action.

It must be noted here though that John Tickle thought that the curved tubes of the featherbed could be improved.
Voila - his frame with more straight tubes, the Tickle T5. (note there are still some curves there though).

Easier to make - as was the fuel tank.
This was past the era of the big thumper road racer though, so had less sales, less exposure and less success ??
In theory they were better, but there are not too many back-to-back tests to compare ??
They are also different eras, so don't compete much ?

Rohan · Oct 11, 2014

Re: Featherbed frame design went against all engineering pri

Rohan said:
We have all heard that, in theory, bumblebees should not be able to fly....
.

pommie john said:
Interesting analogy.

The idea that bumblebee couldn't fly "in theory" was put forward by a physicist who had no knowledge of bee anatomy so didn't know that a bee flies by flexing keratin and releasing it to make the wings rather than by pulling it's wings downwards with the muscles. That meant his calculations were meaningless.... he was applying the wrong principles to a subject he knew nothing about.

We are getting a shade off topic here,
apart from examples of things that should not work but do.

It was the simple physics of bumblebee flight that was deemed impossible, not the anatomy ?
Small wings and a large weight do not add up to the ability to fly.
It wasn't until the invention of the high-speed camera that revealed that the wings flap slightly forward
that aerodynamic theory was satisfied - the extra lift and control meant that theory and practice matched.
Bumble bees never doubted that they could fly however.
And manx pilots likewise knew that curved tubes worked pretty good....

Matt Spencer · Oct 11, 2014

Re: Featherbed frame design went against all engineering pri

Featherbed frame design went against all engineering princip

They said that about Velo's too .

Hobot · Oct 11, 2014

Re: Featherbed frame design went against all engineering pri

74ok · Oct 11, 2014

Re: Featherbed frame design went against all engineering pri

ended up googling 'backbone dunstall racer'

took me here
http://en.wikipedia.org/wiki/Norton_Dunstall

and info about drainpipes!!

For the 1969 season, Dunstall created a new machine with a lower frontal area, the inclined engine being 'underslung' from a large-diameter steel tubing spine frame (nicknamed The Drainpipe) designed by Eddie Robinson. The main frame component ran front to back with a second large-diameter vertical tube at rear of the power plant carrying the engine oil,[1] avoiding the need for the traditional separate oil tank. The filler was conventionally placed ahead of the seat nose[8]

Although Dunstall's open-class racers (non production-race category) were equipped with lowboy frames[1] based on the works design which Dunstall had acquired during the Norton factory race-shop closure,[8] this re-design was based on an established concept not yet applied to the Norton twin for road racing. With no front downtube(s) hence no conventional engine mountings, the spine frame needed substantial cantilever bracing from the central-point of the frame forwards under the gearbox and engine to control the torque reaction

The original 'drainpipe' configuration included aluminium dual 'pannier' fuel tanks inside the top-half fairing sides to lower the centre of gravity and improve handling but following fuel starvation problems a conventional fuel tank was fitted.[1]

In his 2012 article Powered by Dunstall,[8] Nolan Woodbury states there were four Drainpipes made, whereas Drainpipe owner Jamie Waters suggests only three,[9] his own bike having been originally sold by Dunstall to a Swiss Norton dealer and raced in Europe. Jamie also owns a 500cc Domiracer which he built from a NOS (New Old Stock) Dunstall lowboy kit[9]

pommie john · Oct 12, 2014

Re: Featherbed frame design went against all engineering pri

Rohan said:
It must be noted here though that John Tickle thought that the curved tubes of the featherbed could be improved.
Voila - his frame with more straight tubes, the Tickle T5. (note there are still some curves there though).

Easier to make - as was the fuel tank.

Easier to make would IMHO be the main factor here. The Featherbed had one tube that went down from the steering head, curved under the engine, curved back up to the SA mount, then curved again to turn into the top tube that went back to the steering head.

That's a long tube with reasonably complicated bending to get it right. The Tickle frame is much simpler to make.

Fast Eddie · Oct 12, 2014

Re: Featherbed frame design went against all engineering pri

pommie john said:
Rohan said:

It must be noted here though that John Tickle thought that the curved tubes of the featherbed could be improved.
Voila - his frame with more straight tubes, the Tickle T5. (note there are still some curves there though).

Easier to make - as was the fuel tank.

Click to expand...

Easier to make would IMHO be the main factor here. The Featherbed had one tube that went down from the steering head, curved under the engine, curved back up to the SA mount, then curved again to turn into the top tube that went back to the steering head.

That's a long tube with reasonably complicated bending to get it right. The Tickle frame is much simpler to make.

+1 on that, the Tickle frame has a similar overall appearance to a Dresda frame (but the dimensions are different) and when I asked Degens why he didn't replicate the top bend his response was that it basically didn't add any benefit and dispensing with it made it easier to make. His early frames had a vertical rear frame section, he changed this to be angled forwards purely on aesthetic grounds.

For those who don't know, the brief history of the Dresda frame is thus: Degens found he could lap Brands quicker on a 350 Aermacchi than a 650 Bonnie, and he attributed this to the Aermacchi chassis. So, he copied the topography of the Aermacchi chassis to house a 500cc Triumph Daytona engine. This was a very successful chassis. It was later tweaked to take the unit 650 engines (he won his second Barcelona 24hr race on one of these). I raced a Dresda Daytona and was so impressed that I inserted a 906cc Weslake modified unit engine, and that was an excellent tool!

I like your description of the featherbed as having "one tube that went down from the steering head, curved under the engine, curved back up to the SA mount, then curved again to turn into the top tube that went back to the steering head" and can't help but notice that is exactly how one would also describe a full cradle Seeley frame as well!

pommie john · Oct 12, 2014

Re: Featherbed frame design went against all engineering pri

Fast Eddie said:
when I asked Degens why he didn't replicate the top bend his response was that it basically didn't add any benefit and dispensing with it made it easier to make. His early frames had a vertical rear frame section, he changed this to be angled forwards purely on aesthetic grounds.

Aesthetic? Is that what he said?

I'll simply tell you a story about a friend of mine who had a Dresda chassis:

It had the early frame with the vertical rear tube. It cracked several times where the vertical tube met the horizontal one and Degens told him it had never happened to any other frame and blamed his balance factor, refusing to accept any responsibility.

I was in the Dresda workshop one day and Dave was working on his own race bike... which had cracked in exactly the same place.

pommie john · Oct 12, 2014

Re: Featherbed frame design went against all engineering pri

Rohan said:
We are getting a shade off topic here,
apart from examples of things that should not work but do.

It's not getting off topic, I'm simply pointing out that you have to apply the right principles to the problem you're working on. Not everyone who understands structural engineering understands motorcycle chassis design. Flex is as important as stiffness and simply making a frame strong and stiff does not mean it will be a successful motorcycle chassis.

Fast Eddie · Oct 12, 2014

Re: Featherbed frame design went against all engineering pri

pommie john said:
Fast Eddie said:

when I asked Degens why he didn't replicate the top bend his response was that it basically didn't add any benefit and dispensing with it made it easier to make. His early frames had a vertical rear frame section, he changed this to be angled forwards purely on aesthetic grounds.

Click to expand...

Aesthetic? Is that what he said?

I'll simply tell you a story about a friend of mine who had a Dresda chassis:

It had the early frame with the vertical rear tube. It cracked several times where the vertical tube met the horizontal one and Degens told him it had never happened to any other frame and blamed his balance factor, refusing to accept any responsibility.

I was in the Dresda workshop one day and Dave was working on his own race bike... which had cracked in exactly the same place.

Ha! Well it just goes to show there are always two sides to a story eh?

I know he had a problem once with his big racing Honda frames. They'd crack where the short, triangulated brace from the top tube met the front down tube. He solved this by changing to a curved brace tube...

Perhaps that long radius top bend on the featherbed was not so naive after all!