Springfield Flyer.

[tauruck]

Guys, there is absolutely no suspension on the rear end apart from the vibration dampers which offer almost no deflection. I said 5mm for a worst case scenario. There is no need for an anti roll bar because the components are bolted to the chassis. The Heim joints are there for set up. Sid (Kiwi Belly Tank) has advised against any form of shock absorber and the only suspension is the air in the tires. The surface I'll run on is very smooth but dusty. It doesn't see anywhere near the traffic Elmo does.

I'll finish what I think is OK and post pics. I've had to redo lots of stuff already on the liner so if I have to take a few steps back and start over it's no biggie.
Thanks to all of you for showing interest and wanting to help. It means a lot.

[Interested Observer]

What are the two black vertical tubular things behind the axle?
Another consideration is reacting the probably large driveline torque and associated impulse loadings.
Rubber springs, not dampers, are probably a lot less stiff than the wishbones.  Try shop testing with and without the wishbones.
Might consider removing the brake lines from the vicinity of the propeller shaft.

There is no need for an anti roll bar because the components are bolted to the chassis. The Heim joints are there for set up.

What components?   So, you’re going to run without the Heims and wishbones?

[ggl205]

What was the argument against using dampers? If suspension is air in tires only, you have un dampened oscillations akin to a bouncing basketball. Even on a smooth track surface, you will have some need for oscillation control be it high or low megahertz. I used a suspensionless lakester years ago because I didn't have the money to install suspension. The end result was suspension tuning via tire air pressure and constantly hearing the car unload at the rear with corresponding increase and decrease in engine rpm every time I hit an imperfection on the track.

John

[jl222]

What was the argument against using dampers? If suspension is air in tires only, you have un dampened oscillations akin to a bouncing basketball. Even on a smooth track surface, you will have some need for oscillation control be it high or low megahertz. I used a suspensionless lakester years ago because I didn't have the money to install suspension. The end result was suspension tuning via tire air pressure and constantly hearing the car unload at the rear with corresponding increase and decrease in engine rpm every time I hit an imperfection on the track.

John

    Yea jackhammering. Loading and unloading of tires, more so on unsuspended cars with a wheel rate of infinity.

    JL222

[tauruck]

What are the two black vertical tubular things behind the axle?
Another consideration is reacting the probably large driveline torque and associated impulse loadings.
Rubber springs, not dampers, are probably a lot less stiff than the wishbones.  Try shop testing with and without the wishbones.
Might consider removing the brake lines from the vicinity of the propeller shaft.

There is no need for an anti roll bar because the components are bolted to the chassis. The Heim joints are there for set up.

What components?   So, you’re going to run without the Heims and wishbones?

"Set up", sorry I meant adjustment.

[rgdavid]

Allthough your not running suspension, would it be a good idea to design a suspension system that could be added later if needed,  weld the brackets in place now for later use.  Could save a lot of hassle later.
Just an idea.
David.

[kiwi belly tank]

Allthough your not running suspension, would it be a good idea to design a suspension system that could be added later if needed,  weld the brackets in place now for later use.  Could save a lot of hassle later.
Just an idea.
David.

Yep, you got it David! That was my original suggestion. If you're going to run a narrow liner with suspension you must completely eliminate body roll or you will be dealing with a variable yaw situation & that will be an even bigger problem with a three point liner (tandem front end). Or you can run solid rear how I prefer, just like Betsy 76.
That rear setup picture Mike posted back there that everybody is commenting on is actually is actually the previous Speed Demon, the one that crashed.
  Sid.

[tauruck]

Thanks David.
Hey Sid, remember you said I'd be chasing the thing all over the track if I had suspension?.
If Betsy ran OK without it must be good enough for me and the Speed Demon did more runs
than most liners and the crash was attributed to a hole or dip in the poor salt. I've got three sets of very, very good
shocks here all with different rates and the director of Bilstein SA has been good to me since my MX days so I could
make provision for a sprung set up. The roll bar is what worries me. How many will I have to make and what choice in the stiffness,
size etc??.

I'm no engineer but I'm pretty good at building stuff if I get shown where to mount and what material to use.
This is my first liner and I'm basically shooting in the dark.

I can say that anti roll bars and tyres were a big problem for me when I raced F2.

Just one further question. What coil over shock can react to a small surface imperfection at 300MPH?.

[ggl205]

Thanks David.
Hey Sid, remember you said I'd be chasing the thing all over the track if I had suspension?.
If Betsy ran OK without it must be good enough for me and the Speed Demon did more runs
than most liners and the crash was attributed to a hole or dip in the poor salt. I've got three sets of very, very good
shocks here all with different rates and the director of Bilstein SA has been good to me since my MX days so I could
make provision for a sprung set up. The roll bar is what worries me. How many will I have to make and what choice in the stiffness,
size etc??.

I'm no engineer but I'm pretty good at building stuff if I get shown where to mount and what material to use.
This is my first liner and I'm basically shooting in the dark.

I can say that anti roll bars and tyres were a big problem for me when I raced F2.

Just one further question. What coil over shock can react to a small surface imperfection at 300MPH?.

I know these questions were for Sid but if it is OK, I would like to take a stab at them.

Anti roll bars primary duty is fine tuning your spring rates. Get your spring rates right and you may not need anti roll bars. Get spring rates wrong and no anti roll bar will work. So, begin by establishing correct spring rates.

If you have dampers that control bounce and jounce (rebound), they can be valved to dampen small surface imperfections. Get with your Bilstein guy for this. Bilstein is a very good, moderately priced damper with a ton of racing experience behind them. Spax is another good damper company but not sure if they are still around. At the high end, Penske and Ohlines but both are almost prohibitively expensive. Keep in mind that at 300 mph, even the best damper will have trouble keeping up with dampening events. But the point of all this is to control spring and tire occillations and keep that tire contact patch on the surface as long as is possible. The closer you get to this, the more power you can put down and for a longer period of time.

John

[wobblywalrus]

Mike, talk to Bilstein about the latest electro-pneumatic damping systems.  Some high end street bikes are starting to use them.  They are more likely to give you the reaction times you need for high speeds.

[tauruck]

Thanks John, your explanation of what goes on makes sense. I get it now. 
I'll chat to Ted at Bilstein. He's been at it for about 35 years and owns the agency.
We go way back and he won't let me down. Maybe I can get him to calibrate what I
have to suit the conditions. I have three sets of new shocks and if they aren't suitable
I know he'll come on board in some way. One set has Magnesium bodies and are worth
big bucks and Ted has wanted to buy them back from me for a while.

 Maybe Bo???.
I'll ask about those electro pneumatic units. Thanks brother.

The anti roll bar material and size is still a mystery though?.

[Interested Observer]

High speed LSR tires are generally run with rather high pressures in order to deal with what are generally heavy cars and to minimize standing waves in the tire carcass.  This results in a pretty stiff vertical spring rate of the tire, so it is debatable as to how much “suspension” is provided by tire deflection.
When a stiff tire is bolted to the chassis, uneven surface features then are largely transferred to the whole chassis which can set that large mass in motion resulting in degraded contact with the ground (wheelspin) and an unsettled (scary) ride.  Hence the advent of “suspension” and the conundrum of whether to have any.  The answer is really a function of the surface upon which the vehicle is operating.  Bonneville racers probably don’t need much, while Baja racers can’t get enough.  Short of exhaustive analysis the decision is a judgement call based on intuition or learned experience. 

Dampers - In normal circumstances dampers do not so much keep the tires on the ground as they keep the sprung mass from getting out of control, dampening its motion relative to the tires and smoothing the vertical load variations.  It is doubtful that a damper will react to a pothole at 300 mph.  Ask the Bilstein guy for a frequency response curve for the units.  They will probably become very stiff at high frequencies, in effect making the “suspension” take on the behavior of being solid mounted.

Anti roll bars primary duty is fine tuning your spring rates. Get your spring rates right and you may not need anti roll bars. Get spring rates wrong and no anti roll bar will work. So, begin by establishing correct spring rates.

This is simplistic confusion.  It is often the case that the desired spring rates and the desired roll rates and F/R roll distribution are different.  Anti-roll bars allow the roll rate and roll distribution to be adjusted, or modified from the roll rates resulting from the suspension springs alone.

you must completely eliminate body roll or you will be dealing with a variable yaw situation

It is not clear how a “variable yaw” situation would necessarily arise as a result of body roll, but clearly, minimizing rear axle roll-steer would be a priority.

Betsy - If I recall correctly, Betsy sprouted a rear wing in the later runs, which helped keep the (solid?) rear axle on the salt.

Speed Demon - As far as I know, no definitive cause for the crash has been identified, or at least spread beyond the team.  However, aero instability in conjunction with wheelspin was being discussed at the time and Demon II took steps to improve that aspect.

[ggl205]

"This is simplistic confusion.  It is often the case that the desired spring rates and the desired roll rates and F/R roll distribution are different.  Anti-roll bars allow the roll rate and roll distribution to be adjusted, or modified from the roll rates resulting from the suspension springs alone."

I think this more true in a road racing car but far less needed in an LSR car. If differences in front and rear roll rates were that important to an LSR car, we would greatly benefit from driver adjustable front and rear links like those found in Formula cars.

You correctly state the need for all of this when you say it is largely based on ones experience. Mine was road racing so I see value in chassis tuning and especially for track surfaces that can change hour to hour.

[ggl205]

"It is doubtful that a damper will react to a pothole at 300 mph."

It very well will react but maybe not as fast as you would like. Still, some control is better than none.

[kiwi belly tank]

Mike, what I said was "if you run rear suspension" you will need to eliminate body roll or you will be chasing it all over the place. I prefer a solid rear i a liner.
A narrow track liner "that can lean" will go in the direction of the lean & that will vary with engine torque/throttle loads, now you have a variable yaw problem you are trying to correct with the steering. A 3 point liner as in a tandem front end is even more susceptible to this condition.
Go back & look at the in car footage of George's crash in Speed Demon. The car is leaning to the right with engine torque, trying to go right & he has a bunch of left steering input in it to keep it straight, then the front wheels found some more bite or it grabbed enough air on the right side & the front end came out from under him.

The wing on Betsy was I think in 89 & 90, it made no difference & we took it off & by the way, I was never in favor of it. More drag was not helping the top speed plus it gave us a chute issue.

The higher tire pressure is more to do with keeping the tire seated on the bead at speed due to the excessive growth wanting to pull them in. This is why you see them on such a narrow rim, 9 1/2" tire on a 5 1/2" for the 30" Mickey.
  Sid.