Featherbed frame design went against all engineering princip

Re: Featherbed frame design went against all engineering pri

With all of this interest in featherbeds, I wonder why very few people build featherbed singles anymore. Regardless of the critisisms of the frame's design, they all decrease quite a bit when you drop the weight of the bike a good 50-100 lbs (the weight difference between an atlas and a manx would be less than that for just the motor). Would make sense these days with something like an RE single if looking to stay british. Can get nearly 45 rwhp with one of the few kits available that does a big bore converison, motor is nice and light, and they make an absolutely steller racing 5 speed gearbox for it.

Re: Featherbed frame design went against all engineering pri

I realize I'm probably going against the community religion here, but from an engineers point of view (mine), featherbed frame design ignores every lesson learned in structural mechanicss 101, and would get any engineer working for me fired immediately.
With 40 rwhp and slippery tires the "rubber band" frame didn't matter much, but try such a design with modern power and grip and you'll see right away just how wonderful it isn't.

Re: Featherbed frame design went against all engineering pri

midnightlamp said:

With all of this interest in featherbeds, I wonder why very few people build featherbed singles anymore. Regardless of the critisisms of the frame's design, they all decrease quite a bit when you drop the weight of the bike a good 50-100 lbs (the weight difference between an atlas and a manx would be less than that for just the motor). Would make sense these days with something like an RE single if looking to stay british. Can get nearly 45 rwhp with one of the few kits available that does a big bore converison, motor is nice and light, and they make an absolutely steller racing 5 speed gearbox for it.

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Not sure I understand, but where would the 50-100 pound weight saving be in swapping out a twin for a single?

One of the advantages of the dommie twin engine was it's lightness. Doug Hele on the aluminium twin Dommie engine used in the Domiracer vs the magnesium Manx engines of the early sixties-

"Even with the engine in its present semi-standard form we start with an advantage, for it is already 28lb lighter than a Manx engine, without having to resort to Elektron crankcase castings. Moreover, it is smoother, so we can get away with a much lighter frame. Finally, it has a lower centre of gravity ,which should ease handling problems"

A 650SS or Atlas egine is going to be slightly heavier than the 500 was, but not 28 lbs. The weight and COG advantage is with the Dommie twin, and that is vs a fully developed racing Magnesium single, not just a common Al. lump of some sort.

Probably the best thing to do with a Norton Featherbed twin is to leave the existing engine in it, but also to do as much possible to increase smoothness for the 650 and 750 sizes, ie dynamic balancing etc.

Glen

Re: Featherbed frame design went against all engineering pri

LUCKY DAVE said:

I realize I'm probably going against the community religion here, but from an engineers point of view (mine), featherbed frame design ignores every lesson learned in structural mechanicss 101, and would get any engineer working for me fired immediately.
With 40 rwhp and slippery tires the "rubber band" frame didn't matter much, but try such a design with modern power and grip and you'll see right away just how wonderful it isn't.

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That may be, but get on one and ride it, you will be astonished at the precise handling and excellent steering. They just work.
I did some reading on an SV650 racing site recently. These are modified SV650s pushing 80 HP and capable of 140 MPH. The track they race at also has a class for 1950s and 1960s British singles. One weekend it was decided to run the six Manx Nortons present with the SV650s. The track was described as "very technical"
The SV650 riders complained that all they saw for the entire weekend was the back end of Manx Nortons and all they heard were the "bloody booming" Manx exhausts.
If you think the Featherbed frame isn't a good design, just go watch them race!:mrgreen:

Glen

Re: Featherbed frame design went against all engineering pri

Glen, my SuVee 120 mph 70 hp upgrade suspension on non DOT race tire$ can out hook/handle ordinary iso Commandos but I consider it a corner cripple at heart so share the glee know other skinny tire Featherbed weaklings can rub it in. The real rigids are great until powering near tire edge then everything so tense it reverbs forks to tire patches and can lose control by resisting pitch downs or back ups in time, the more force it takes pilot to do this or resist upsets, the less traction is left in the tires to stick on around. What motorcycles need to move beyond mere independent wheel suspension is an anti sway bar or two built in like maybe the Featherbed or added on to isolastics.

Re: Featherbed frame design went against all engineering pri

Lucky Dave, I'm an industrial chemist, so I know the limitations of engineers. You should not believe your own bullshit. If you believe you can design a better frame than a featherbed or a Seeley to house a 500cc fourstroke single cylinder motor - let's be having you.

Re: Featherbed frame design went against all engineering pri

hobot said:

Glen, my SuVee 120 mph 70 hp upgrade suspension on non DOT race tire$ can out hook/handle ordinary iso Commandos but I consider it a corner cripple at heart so share the glee know other skinny tire Featherbed weaklings can rub it in. The real rigids are great until powering near tire edge then everything so tense it reverbs forks to tire patches and can lose control by resisting pitch downs or back ups in time, the more force it takes pilot to do this or resist upsets, the less traction is left in the tires to stick on around. What motorcycles need to move beyond mere independent wheel suspension is an anti sway bar or two built in like maybe the Featherbed or added on to isolastics.

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What is sorely needed is a race class for 500cc fourstroke single cylinder engined bikes with no other rules. Then we would see the truth. Unrestricted development would make for very interesting racing when the big money guys come up against the law of diminishing returns.

Re: Featherbed frame design went against all engineering pri

seems a bit mean to restrict it to 500 c.c. , gags technological development . WHY NOT " Single Cylinder " and no other regs. ? :twisted:
or we'll all end up with whiney sniveling turbo rice burner buzz box stuff , like F! GP derived engine development . Without this we could
all drive 20 litre 200 mph 100 mpg relaxed cars that CAN pull out Tree Stumps , before breakfast . :lol: **



this ones only Two Litre , But a Bristol Centaurus Cylinder would give a bit more , and have lower top weight .



http://thekneeslider.com/nsu-2000cc-sin ... otorcycle/



must be the comercialiseation emasculation and lack of imagination in these modern consumer society times . :wink:

THERE ALL IN A RUSH , These Days .



SUCH is PROGRESS ! .

http://trove.nla.gov.au/ndp/del/article/21764395 ( 100 mph @ 100 mpg - 1931 )

Re: Featherbed frame design went against all engineering pri

One the most informative things I saw at Barbars vintage races with the 750 Indians out with the 125's. I saw those Indians bobbing up and down and twisting so thought at first how stupid in corning they must be till I saw an Indian and 125 exactly powered fight it out though a S turn with the 125 a bike length ahead entering it - tried to cut off the Indian by sharper farther lean through 2nd apex but the dang hippityhoppity Indian out leaned & out sharped it to gain a couple bike lenghts in a flash then they were stuck with exactly matched power so stayed same distance down the straight. This cut off contest happened as fast as a 125 can flip one way to the other so there's magic lurking in tamed flexing.

Re: Featherbed frame design went against all engineering pri

acotrel said:

Lucky Dave, I'm an industrial chemist, so I know the limitations of engineers. You should not believe your own bullshit. If you believe you can design a better frame than a featherbed or a Seeley to house a 500cc fourstroke single cylinder motor - let's be having you.

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I could do it easily. All I have to do is copy a modern design. Do you really think nothing has been learned in the last 40 years?

That may be, but get on one and ride it, you will be astonished at the precise handling and excellent steering. They just work.

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I've ridden one. With the (vintage) power level and tire grip, it worked OK.

Seeley (and Rob North) made some nice chassis with straight tubes between the steering head and swingarm pivot which is proper use of tubing's properties (tension, compression and torsion). Tubing is essentially useless as a beam, which is what you see in a featherbed design.
Both builders used 4130 material in their frames. Rob austenized and tempered his weldments after fabrication in a frame jig and machined the bearing surfaces post heat treat. This is correct use of chrome molybdenum steel.
Seeley employed silver braze fabrication. While pretty, this makes post weld heat treatment impossible (the brazing material melts a lower temperatures than the austenizing temperature), so the condition A 4130 is no better than water pipe. Early airframes followed this fallacy too, oxy-acetylene welding with no post weld heat treatment beyond manual annealing to prevent high localized carbide precipitation in the heat affected zone. It was a waste of expensive material.

Featherbed frames use mild steel (lots of it!) in heavy-ish wall tubes, most of which are bent. It's a miserable use of round tubing, but it's true they handled far better than anything else in the day. That may have more to do with mass placement and suspension action being better, than the actual frame construction being better. Saying one bike handled better than another solely because of frame design is ignoring all the other variables.

The SV650 riders complained that all they saw for the entire weekend was the back end of Manx Nortons and all they heard were the "bloody booming" Manx exhausts.

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The rider is always the most important thing.

Re: Featherbed frame design went against all engineering pri

worntorn said:

Not sure I understand, but where would the 50-100 pound weight saving be in swapping out a twin for a single?
One of the advantages of the dommie twin engine was it's lightness. Doug Hele on the aluminium twin Dommie engine used in the Domiracer vs the magnesium Manx engines of the early sixties-

Click to expand...

I'm not sure I phrased my original thought well at all, now that I'm re-reading it. I could see a modern single being able to drop the weight of the bike by a bit. After doing some digging, looks like you are right (and I was wrong) about the domiracer being disgustingly lightweight and the manx engine not being all that light. In a modern view, a not that far from stock Enfield powerplant I have kicking around is 100lbs (with trans and primary drive, but no alternator) and that's with a 22lb crank. Now obviously this is a very poor comparison, but my commando mill weighs in @ around 95lbs with rotor and carbs but no primary cases and no gearbox. Turns out that http://www.enfieldmotorcycles.com/forum ... c=17556.30 has already done this actually! I do not see any weight figures there on on their website, but I imagine it's not that much.

As for the comments regarding the featherbed frame from a modern perspective, one would not be wise to compare the performance of a half century old frame design to anything relatively modern. A honda RS125R weighs about what a bag of chips does (or 70kg/154lb if not being facetious) and makes about 42hp. If one were to analyze the featherbed, it would not be all that difficult to see that a large chunk of the frames stiffness in at least one direction comes from the motor and the headsteady (that bears down on the motor). While it may have worked...that is not an exceptionally efficient arrangement, or are the pre-bent tubes doing the frame any favours in terms of stiffness or load path.

Re: Featherbed frame design went against all engineering pri

LUCKY DAVE said:

Tubing is essentially useless as a beam, which is what you see in a featherbed design

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not sure what you mean?

Re: Featherbed frame design went against all engineering pri

I expect some sort of engineers had a hand in all the awful designs of plunger rear ends, the sprung hub and the Triumph swing arm bracket brazed to the saddle tube.

I think we can pooh-pooh those, without looking self-aggrandising.

Re: Featherbed frame design went against all engineering pri

It's OK fellas, I know some engineer stuff.

Re: Featherbed frame design went against all engineering pri

84ok said:

LUCKY DAVE said:

Tubing is essentially useless as a beam, which is what you see in a featherbed design

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not sure what you mean?

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If I'm right (and I've been wrong before), LD may mean that tubes bend when a perpendicular load is applied. The swing arm pivot on a Featherbed puts perpendicular force onto the rear vertical sections of the main loop, when cornering and/or acceleration tries to pull the swing arm to the side.

The frame tubes are reinforced by gusset plates and (maybe a bit) by the cross tube and engine plates. That appears to be good enough for the bikes which used the Featherbed frame. People here tell us it's OK with a Commando engine too. More powerful engines and super tyres might overcome the frame's capabilities. That may be what 1960/70s Japanese factories and race teams came up against when they made similar frames and put better engines in. Their bikes handled a bit screwy.

Seeley had the right idea: brace the swing arm pivot ends directly, with straight members, under end loads, to the item you want it to be aligned with. That item is the steering head, on a bike with forks.

Almost nothing in this World goes against "all engineering principles." It's the sort of thing a smart-arse says. Designers may weld two straight pipes together at an angle, or they may bend a pipe. Widelines have straight pipes welded, to hold the shock tops, Slimlines and BSAs have a bent tube. Production engineering is still engineering.

Re: Featherbed frame design went against all engineering pri

Steve , you want to salute a guy who produced the worlds weakest frame, that snapped by sneezing on it?..then a motorcyclest showed him how to do it....properly!

hobot said:

Can't beat large dia thin wall hollow triangulated steel for wt to strength but I salute Dr. Stefan Bauer and side kick Hopper for the ingenious Isolastic Commando spinal column and over lapped re-enforcement that driven my nutz to find its pecking order. Do keep in mind Norton bean counters likely stiffed its full development so un-tammed its too dangerous to test much for me. Sanely operated I love it most too.

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Re: Featherbed frame design went against all engineering pri

LUCKY DAVE said:

acotrel said:

If you believe you can design a better frame than a featherbed or a Seeley to house a 500cc fourstroke single cylinder motor - let's be having you.

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LUCKY DAVE wrote:
"I could do it easily. All I have to do is copy a modern design. Do you really think nothing has been learned in the last 40 years?"



It is not as simple as just copying anything modern.
Sometimes frame design goes backwards for a decade or three. The idea that anything modern is automatically superior doesn't always hold.
If you used that thinking in the 1970s and copied just about any common road going frame, it would have produced a bike with handling far inferior to that 1951 Featherbed. If you happened to choose a popular bike like the Kawi triple, for example, you would be copying one of the worst handling death traps ever produced! Suzuki's Titan was another very scary handler and even the highly regarded BMW produced some seriously poor handling and dangerous machines well into the 80s.

Glen

Re: Featherbed frame design went against all engineering pri

The frame tubes are reinforced by gusset plates and (maybe a bit) by the cross tube and engine plates. That appears to be good enough for the bikes which used the Featherbed frame. People here tell us it's OK with a Commando engine too. More powerful engines and super tyres might overcome the frame's capabilities. That may be what 1960/70s Japanese factories and race teams came up against when they made similar frames and put better engines in. Their bikes handled a bit screwy.

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You sir have hit the nail right on the head!
Featherbed frames worked because of all the bracing around the tubes. My point is only that it was an inefficient use of material.
The Japanese developed some great engines but didn't bother understanding chassis dynamics and simply copied the featherbed design that worked so well on 40 hp bikes.
I raced AMA Superbike in the 70's and 80's and I can tell you first hand just how scary those featherbed copies were with 150+ hp and slicks. We welded extra gussets and tubes everywhere and they were still terrible! If I look at the frames of the bikes in my garage (Aprilia Tuono, KTM 1290 Superduke, Redline framed street tracker with Sportster engine, 2014 R200RT, and Honda dirt bikes, they all have one thing in common. Tubes that go straight from the steering head to the swing arm pivot.
Everyone in the industry understands chassis dynamics now, it wasn't always so.

Re: Featherbed frame design went against all engineering pri

JRB and crew I'm totally flabbergasted in a FABULOUS way on how much power and G forces I could apply to Peel in rough windy surfaces rather faster-harsher-sharper leans out accelerating any modern I pressed to loss of traction or tires thrown out of surface contact by almost crashing from low or hi sides after horrific bar slapping &or frame whipping. My goal is to see if next Peel can out handle way more advanced and powerful new cycles even those run by digial controls and robo pilots and pretty sure I can as past Peel was able to put down-hook up more power on leaned than I ever thought possible after corner school on tract and Ozarks Mt's hwys that make Barbers seem like a freeway route. My next biggest surprise shocker was the wild raw off road security which after the clam collected pavement even snatching down with over powered leans till fork snapped wrong way and frame twisted up an inch between bars and pegs then released like a sling shot in direction I wanted/needed, fast as a bink breath taking. Someday may try to do a frame based on isolastics but using different construction materials and configurations.

Re: Featherbed frame design went against all engineering pri

Here's what I ran into with corner cripples everyone else but me looks up to ...

http://www.motorcycledaily.com/2012/03/ ... -team-lcr/

in moto-GP racing, the importance of HOW does an engine
release the its max.output (versus HOW MUCH this output is
in net-terms and HOW SOON it occurs in the rev range) is
much bigger compared to 4-wheeled racing.

this is mostly due to the fact that a motorcycle rear tyre,
being a VERY elastic dynamic model (flexing under load,
contact patch variations linked to lean angle and MOST OF ALL
power “pulses” influencing the shape of the actual contact patch
at any moment of time), is much more dependant on the engine’s
torsional-vibration-characteristics and the frequency/mode of
the power delivery pulses. The latter is MOSTLY influenced by
the engine firing order / crankpin angling, which is one of the
key reasons why top-notch racing bikes are going in the direction
of V-engines and I-3, as opposed to flat-plane I-4 etc..

Of course, there are other reasons linked to packaging, aero, mass
centralisation, reliability, and (last but definitely NOT least),
engine structural rigidity at high-RPM (as engine blocks are getting
more and more used as stressed parts of the “frame”, or what’s left of it..
(not unlike F-1 singleseaters).

As soon as an engine becomes a VITAL part of the chassis/frame load-bearing
structure (and this goes BOTH for cars and bikes..), you’d be surprised to see
how suddenly some ‘packaging’ and design issues become of FAR greater importance than (comparatively) V.E. or friction related advantages that the “other” solution has…

Bottomline: the Inline-4 (at least when mounted in a conventional position in a bike’s frame) is VERY disadvantageous for the requirements of a top-level racing bike design.
Just try to imagine how edgy it must be to control 250-ish HP at the rear tyre under extreme lean angles, and you’ll anticipate how every single aspect of the way HOW is the power delivered suddenly becomes extremely important.