I found this picture from Guffey interesting. It has a single 1/4 elliptic spring in the middle of the axle. They even put a shock absorber on it. I was thinking of using this on an I-beam with hairpins to add a little roll control. Hopefully Guffey will chime in and let us know if it worked well or not. http://i281.photobucket.com/albums/kk225/wellohhhkthen/waterpipec.jpg
Well looking at the height of the spring attachment, and hence roll centre, that has too be low enough to defeat any arguements by Warpspeed with regard to roll couples. Certainly shows proof of concept, my guess would be that it was 'good enough for a few runs before the next game plan', sure is built light, way more fragile than the kind of thing I figure you have in mind using a beam axle and over sized hairpins. Actually I have to say that seeing that gives me a lot more confidance in my own home made tube axle design, Reversing the king pin set up allows the hub upright to carry a couple of cheap taper races, which are very easy to pop out and change track side, plus it meant the axle could be two fairly thin walled tubes rather than needing to go for much heavier walled or very large diameter for a single.
Thunderace, I'd like to see more pictures at different angles so I can understand it better. Also, how do you get ImageShack to display this and other pictures? I did a search on the HAMB and you have some pretty interesting pictures posted. They all came from ImageShack but I couldn't figure out how to see any of them.
Sure, It is all certainly built extremely low, but so is the ground clearance. Can you imagine the damage if the front of that chassis dips on it's spring a couple of inches, and the chassis then hits something solid ? Another problem I can see with this greatly extended front chassis, is lack of torsional rigidity at the very front. The chassis is going to flex long before the front antiroll bar does. My guess is, with a still reasonably high front roll centre, and a flexy chassis there is not going to be sufficient roll couple transferred to the front to eliminate the massive oversteer caused by the high rear weight bias. As mentioned earlier by Tunderace, Formula V's have this exact same problem, and they get around it by having very high roll resistance at the front and very low roll resistance at the rear. Rear engined Porsches have this high rear weight bias problem too. But that long extended chassis will prevent you from building in sufficient front roll stiffness, without making the chassis heavy and ugly. Your problem will be getting enough front roll resistance. Building a zero roll resistance front suspension is absolutely the wrong way to go with this design. I assumed this was going to be a conventional wheelbase hot rod chassis, not an ultra long wheelbase slingshot dragster. This design certainly has it's virtues, but good cornering ability, and neutral handling, are not going to be among them.
Suspension theory is all well and good, but it doesn't seem that's what the OP is looking for. All he needs is an innovative front end to hold up the front of his street digger. Like a regular spring perch, turned 90degrees and attached to the center of the front axle, to hold the front of his spring. The perch will pivot up-n-down and allow the axle to rotate (one wheel in a pothole, the other on the curb issue). Some radius rods/wishbones/hairpins/whatever to locate the axle. How about some rotary shocks from a motorcycle (like a Suzuki TL1000) for damping? A Watts linkage to keep the whole thang from getting overly wobbly. I'm thinking a ring or oval that the spring pokes through, with mounting studs mounted at 12:00, 3:00, 6:00 and 9:00 (or North, South, East, West if you want to think of it that way). The East-West are mounted to the axle (somehow, it's gotta be behind the yaw pivot point so that will still, well, yaw..."an exercise left to the reader") -- think of the center mounting of a traditional Watts linkage -- and the North-South points are the end-points for the rods that mount to the frame. Just some more non-educated wondering to further stir the pot...
O/k then, why not use only one front wheel ? I am serious. That has zero front roll stiffness. Build a trike. That would be both unique, simple, very light weight, and have the pointy front end "look" he is seeking.
I agree, but skinny front tires and fat rear ones will help a little. It will never corner like a Lotus. I'm just trying to optimize a dragster for street duty as best I can. Lots of good ideas there, Nitrobrother. Would it be too much trouble for you to draw this? I think I can see it in my mind's eye but not sure. I know the chassis' aren't very stiff on dragsters. I'll certainly have to stiffen it up for street duty. By design, a dragster is not optimal for cornering but I wouldn't mind a little cornering ability. I agree a trike would be light, but it wouldn't corner as well as a four-wheeler, especially when braking. Besides, they look a little too weird (IMHO). Check out this one:
Oh no don't start me on trikes, I have built a few dozen down the years. With the right weight split so the tyres have equal slip angles they can corner real fine. This is kind of the same problem, And hence why I think it has every chance of working. I think the rear bias = bad thinking is being over played, if the rear tyres are proportionaly larger so that the contact patch load per unit area is the same as the fronts then the whole thing will slide evenly front and rear. Rear biased cars dominate most areas of motorsport where the rules permit the configeration. I will grab some more pictures of the Thunderace tube axle, but for now here is a picture showing a bit more detail; The stub axles have two inches of lead ahead of the king pin axis, which reduces the rise and fall of the frame when steering with a high caster angle.
I'm trying to be objective because I see a lot of people get an idea and then they can't let it go, regardless of its shortcomings, because of ego. But I see what you're saying about the wheel size and it makes sense to me. I hope it's not just because I want it to! I understand your axle a lot better now. Thank You. Two light bars far apart would be stronger than a single heavy one. I like the simplicity. It's brilliant! If you want to complicate things up a bit and make a Thunderace Tube Axle with Independent Suspension, take a gander at this. It would adapt well to your design. (PovertyFlats found this at a swap meet. It's off a '34 or '35 Hudson.)
How did I miss this???!!! I just now saw this post. Thanks for showing this to me! I'll be following this build for sure!!!
I'm glad you brought that up. Mine will be a little higher than those pictures but it still has given me some cause for concern. Having a single spring support the entire front end leaves no fail-safe support, should something happen to it. I'm thinking the very front of the frame needs to be turned up a little, like a water ski. At least if the spring breaks or you hit a speed bump or curb at full force, you wouldn't pole vault. It would jar you pretty good, but you should ski right over it. Maybe with the extra wide rear tires and a ski-shaped front frame, I can skim over lakes and through the snow.
I was thinking along similar lines. Some sort of small turned up front skid pad or ski that will just raise some sparks, but have nothing up front that is going to easily dig into the road. How about a small concealed roller? (maybe a few ball bearings on a shaft or a water pump bearing) The guys with wheelie bars at the back use some pretty small wheels for that, and they work fine.
Unfortunately I suck when it comes to graphics...haven't done anything worthwhile since 2002 and my Paint Shop Pro days. All I have is GIMP on this laptop and I don't have the skills or patience to do anything of value. I can't get my head around how to give the "ring" the pivoting capabilities of a traditional Watts linkage. The other ideas was to have a spring perch that pivots to allow the axle to articulate, removing the twisting stress on the spring itself; basically the spring only does what a spring it 'posed to do: suspend the car. I don't know any theory or practical implementation of how a "hollow-center" Watts linkage would work with narrow front frame rails, but hopefully someone smarter than me (which wouldn't take much) can throw out some ideas to further refine this. IMHO, it seems that wsdad isn't going for ANY kind of handling prowess, and is looking for "how can I make this work for the street" rather than "that's the most stupid thing I've ever seen".....
hollow centre watts linkage, uses same trick as a hubless wheel, large diameter roller bearing ! I was serious when I said before about the tyre contact patch load, While I agree that most of what Warpspeed was saying is true, It tends to be true because car designers often have a design which they then need to find ways to cure the problems of, rather than looking at the the problems and then finding a design which reduces them. I have an old GT40, designed by Eric Broadley of Lola fame, the plan was simple 'beat the Italians' the answer was engine behind the pilot to give 60% of the cars mass on the rear axle, the rear tyres are slightly wider than the front and it corners like it's on rails, I don't have sway bars fitted, some teams did mess around with them, but the car is actually perfectly ok without. The point is that with a rearward bias it's fairy easy to just up the width of the rubber on the rear, race cars have been doing this for years. Normal passenger cars tend to be front biased, which is more of a problem, as Warpspeed said a few pages back, bigger tyres on the front tend to look stupid, hence car designers have developed a whole bag of tricks to get round the problem, many of them end up as poor trade-offs. Ok for sure this uni-spring beam axle is not going to be up there with my mid-engineed super car with IRS and IFS on race coilovers, but it still could have every chance of being better or at least no worse than a typical production car from any of the big multi nationals in terms of handling. The only down side to the game plan might be argued that the beam is un-sprung mass, which tends to rob one of a little in terms of ride and road holding. Again you maybe able to claw that back by using very light front wheels and tyres.
Can you explain why cars corner better with a heavy rear weight bias and wide rear tires? It seems like they would do better with a balanced weight ratio and tire size. I'm sure there are as many theorys about this as there are bellybuttons but I'd like to hear your opinion, since you have some experience with your GT40.
For acceleration you need traction, and with rear wheel (only) drive, having the weight biased towards the rear is a definite advantage. For braking, a rearward weight bias is an advantage too, because you can then set the brakes up to have a more even braking bias front to rear. So for straight line performance a rearward weight bias is always an advantage. Not so for cornering. A rear weight bias will always tend towards natural oversteer, unless steps are taken to modify that natural tendency. I have never owned anything as exotic as a Lola or a Ford GT40, (replica or otherwise). My own experience with mid engined motoring, extends to owning a street driven mid engined Lotus Europa with a turbocharged 13B rotary engine. It too handled rather well, mainly because it had a fairly torsionally rigid backbone chassis, that allowed much of the roll couple to be effectively transferred to the front wheels. The main secret of building a predictable good handling chassis, (apart from the basic wheel motion geometry), is having a torsionally rigid chassis. Only then can you use antiroll bars effectively to fine tune the suspension. Hot rods have always had problems with flexy chassis rails, because that is how they were originally built. Something with a greatly extended wheelbase, could have some real limitations in the torsional rigidity department. Slingshot dragsters are a purpose built no compromise design, built to do one thing only. And copying the design for aesthetic reasons is fine, as long as you don't expect to have sports car cornering or braking ability.
Let me come at this one from another angle Warpspeed, if we were running the same size of wheel and tyre on all four corners as per production, the ideal would be C of G equa distant between the two axles, to give equal split, and equal load on the tyres, that would corner best agreed ? Ok so now if you put larger tyres on the rear with the same 50/50 split, you go in to mild understeer, so now you move the wieght back towards the rear axle, and you get back to neutral steer again. I agree with you about the chassis stiffness in part at least, however I think it's important to note that the stiffness needs to be between the points about which the axles articulate, which in the case of Wsdad's design which has the radius arms attached up near the firewall is not going to be so far away from the rear axle attachment points, so the usual problems of the flexy ladder frame are reduced. Stock pressed channel section frames had so little torsional stiffness it was scary, I know some say that if you box the rails it's ok, me, I have never gone there. A nice strong triangle made from new box section, is going to be massively stiff compaired to stock rails, if the body is bolted down solid and the motor and trans the same there is not going to be much flex. I have seriously looked at building a 'chassis-less' hot rod, using the engine/gearbox/final drive as the spine (using an IRS so the pumpkin can be fixed). same idea as an Formula 1 except longer driveline so there is room to sit behind the motor rather than infront.
Warpspeed: A rear weight bias will always tend towards natural oversteer, unless steps are taken to modify that natural tendency. Do you think a roll bar is the only effective way to do this or do you think the large rear wheels and skinny front wheels will get it done? Perhaps a combination of both? mid engined Lotus Europa with a turbocharged 13B rotary engine. Sounds pretty exotic to me!!! I wouldn't turn down a ride in one! The main secret of building a predictable good handling chassis, (apart from the basic wheel motion geometry), is having a torsionally rigid chassis. Only then can you use antiroll bars effectively to fine tune the suspension. I agree with you about the limitations of a flexy chassis on the street. I had plans to triangulate the rails ahead of the engine and hide it with a sheet metal cone shaped "hood." Instead of 2 large rails, I had planned on three smaller tubes. Inside, my radiator, battery, a small gas tank and a few other things were going to be hidden (maybe even a shaft driven A/C compressor and alternator ). See the first picture. I had not taken into consideration that the radius arms puts the flex back near the engine, instead of out on the front corners of the chassis. This would be especially true if I can figure out a way to use the friction shocks. If I do the same with some rear hairpins, the chassis "rails" could be made very strong for a short couple of feet, just to connect the two hairpins, with out very much weight penalty. Chassis flex would not matter, except for the area between the hairpin mounting points. Something with a greatly extended wheelbase, could have some real limitations in the torsional rigidity department. As far as the suspension is concerned, the car would only be a couple of feet long. Do you see any problems with it? See the second picture. Slingshot dragsters are a purpose built no compromise design, built to do one thing only. And copying the design for aesthetic reasons is fine, as long as you don't expect to have sports car cornering or braking ability. You're right. I am trying to take something inherently designed to go straight and make it corner better for the street. I recognize it will never be as good as other basic layouts. I just want it to be safer and turn quicker than if I had left it as originally designed. A car that wants to go straight when I want to turn scares me, but they sure look cool. That sounds like a really good idea. I like that design. (God thought of it first, using backbones and legs.) I see a couple of drawbacks for the street, though. I'm not trying to discourage you, I'm just wondering if you've found a way around these. 1. If you are T-boned, you are squished between the other car's bumper and your chassis. 2. Would the stress on the block warp it enough to cause problems with bearing clearances? I vaguely remember reading somewhere that Lotus tried that but had to make the block thicker. The added weight made it impractical. How has the F1'ers solved this problem? What if you built a tube cage or tunnel back bone for the stock engine, tranny and rear end to sit in?
I had figured on a full cage arround passenger compartment, but agree that the T bone thing is a bit scarey. As to the classic chestnut of an engine block not being designed to take chassis forces, and hence if it could twist the block, well it's true that there are engines out there that would not stand being used as a chassis. Fortunately iron block hemi's are not in that list, plenty enough metal to take the forces involved, No way could I put together a frame as strong or stiff as a casting that is near half inch thick all over. Bit of a lardy old lump, hence the wanting to try and redress things by not having a heavy frame in addition to an all ready heavy engine. I have made quite a few parts for the build, but only bolted a limited number of parts together as yet, Got to work out a way of mounting the steering box off the side of the motor, and bend up the cage before there is anything much to show, most of it is just a whole pile of brackets and heavy aluminum plates. Aim is to start with a very mild 300bhp (or less), and then maybe start playing with pulleys to get more as felt needed. The frame-less thing is nothing new, But I have just never seen it done for a hot rod.
"Frameless" worked pretty well with big block Chevies too . WSDAD, keep in mind that the hairpins only resist roll if they are pretty much parallel to the chassis centerline. The more they are angled inward (as in the photo in the post above), the less geometric roll resistance they provide.
At least here in Australia, a road registered hot rod must have a separate chassis that takes all the suspension loads, and it must at least "resemble" the original pre 1948 vehicle chassis that the hot rod is supposed to represent. Backbone chassis are interesting. Usually a big box section runs down the length of the car, and driver and passenger sit either side, with the transmission tunnel very high and wide, as in my own Lotus. The other way to do this, is to make the central box section wide enough to actually sit inside, as in the "tub" of an open wheel race car. The idea of returning all the suspension loads to a "virtual" central bulkhead, using torsion bars is also a very interesting idea. But the loads at the suspension mounting points will be much higher than otherwise, requiring some very rigid structure. It also does not really lend itself to a long wheelbase vehicle. But it is still an interesting idea. If I was doing this, I would probably build an independent front end with some very long skinny wishbones that reached right back to the central "point" in the chassis. These wishbones would consist of upper and lower swing arms, and a long pair of drag links that would look like a four bar from the side view. The springs and shocks could be mounted inboard and hidden from view. This has a few advantages. Minimum unsprung weight, extreme rigidity, you can put the roll centre anywhere. Visually it could be made very clean. Look at the quadraduce front suspension design. Something like that, but without the front drive shafts. http://www.streetrodding.com/index.cfm/f/siteContent.view/id/2107
Sounds like a good way to put all the extra weight of a Hemi to work for you. The idea is unique enough to make it into some national magazines, IMHO. I think it will be fun coming up with innovative ways to mount things using dual purpose brackets - such as alternator / headlight (with built-in turn signals) or radiator / shock mounts, etc. In stead of mounting the steering box to the motor, can you mount a light rack and pinion unit to the axle? Would that be outside of the style you're shooting for? https://www.hyperracing.com/product.asp?prodid=16-500
One of the 'ideal' suspention models had each wheel on a virtual arm the pivot of which was located at the C of G ( or at least very near it ). The ideal model was a way of evaluating designs rather than an aim, but certainly designs which act more like the ideal model show superior results. The Rear end of the GT has uprights which are held on double arms and huge long bars which are fixed back at the firewall, so it's rear end it pretty well as the front end Warpspeed has just mentioned, the lower unsprung mass is part of that game too, beam axles are heavy things, where as slender uprights with wide spaced ball joints on tubular arms, tend to be some what less mass hopping up and down. A beam axle can never match IFS or IRS, but as far as these things go, making a front one in light tube does go a fair way to redressing the issues as far as this design goes. Simple is still often the best answer if never the perfect one. More joints and linkages you have, the more there is to flex, break, wearout, and generally do things you would rather it didn't. I have played arround with a load of diffrent stuff on the rear end, and to be honest one of the best repeated results has been home made semi-trailing arms. I know a lot would turn in horror, but it's very simple, it's way better than a beam axle and it's not impossibly complex to get the geometry right like a double A arm. Sure the roll centre is probably way higher than might be nice, but it's a very simple design, just one arm with a hub welded on the end, with only one articulation point, one set of bushes, if far enough apart not even that heavily loaded, sure there are more complex ways of doing things which might in theory work better, but simple is easier to get right. In the same way I see Wsdad's mono spring, sure it's not the way many would go, but I figure that it's very simple nature and lack of complex linkages may mean that it works way better than a first glance might suggest. I have never had anyone spot the lack of a chassis once the body is on. Normally you have to point it out and even then it takes an age before the penny drops, sometimes it does not even then. As long as there is a indentification plate on something frame like near the motor somewhere the 'man' seems to be ok with running this set up on uk roads, but I never go far beyond the back roads where I live, and as I say no one ever spots the lack of a frame, I have been running my Subaru round for years with a beam bolted to the transaxle which carries the body and the upper shock mounts, and four tubes bolted off the front of the motor which carry the fuel tank, radiator and a motorcycle headstock. Probably the simplest trike I ever built. Works fine, keep it simple. I will get the bracket made, probably best not to switch to rack and pinion now, horses, midstream etc. It's only that the only thing I could find which had had a steering box, ( everything in the UK having been rack and pinion for at least fifty years pretty well ), has the arm on the other side, so while it's easy enough to make an arm to go the other way, it also means that the whole box has to be inverted to get the arm to move the right way when the steering is turned, so the bracket not only has to hold the box to the side of the block but has to do it with the box the other way up and round so the mounting face is now facing outwards. I would have done it by now but the block is on the bench with the side I need to get to facing the wall, I just need to turn it round sometime, ( easy to say ! )
My brother pointed this out to me also and it troubled me for quite a while. I almost scrapped the idea because of it. But if you look at the suspension, the forces are actually at the corners. This is kind of hard to visualize and hard for me to explain, but I’ll try. First, let's deal with the spring in the middle, "as far from the wheel as possible," as you rightly said. Then we'll examine other parts. 1. In theory, when both wheels go up at exactly the same time on a perfectly smooth road, the force of the spring is transmitted equally to each wheel. There's no instability there due to the distance of the spring from the wheels. Please don't point out that there's no such thing as a perfectly smooth road - just humor me for now. 2. When the axle is pushed perfectly sideways, the flat part of the spring resists any sideways movement of the axle. The leaf is several inches thick in that plane and cannot bend. Even though it's a long way from the wheel, it's ok because it is pushing in line with the load. It's pushing through the axle to the wheel. No problem. (Imagine you're squishing a bug on the floor with the end of a broomstick. The bug will feel the same weight whether you grab the broomstick at the top, middle or bottom. Your hand is the spring and the broomstick is the axle.) 3. When one wheel is pushed back, as if hitting something it can't roll over, the leaf spring is useless because it's so far away from the wheel. The wheel has a mighty lever that the spring is unable to resist, no matter how thick it is. That's what the hairpin does. It resists the "pushing back" force of the tire. Because the hairpin is mounted very close to the wheel, it’s stable. The other end of the hairpin is mounted on the frame several feet behind the wheel. One would think this would be a problem, being mounted so far away. It still works OK though, because the hairpin is in line with the force of the wheel. (Imagine the bug is on the wall this time and the broomstick (the hairpin) is pushing into our poor little abused friend. It still doesn't matter whether you hold the broomstick in the middle or end, the bug will be equally pissed. The only way I can see that this might be morally OK is if the bug were some sort of Beetle from Germany. No one but hippies care if you crush Beetles. Muah-ha-ha-ha! Just kidding - I like Beetles.) 4. When one wheel is raised, as in rolling over a bump or if the body rolls in a corner, the leaf spring is too far away to do any good. Again, the wheel has a mighty lever, rendering the distant leaf spring useless. The hairpin is also useless by itself. It just goes up and down with no resistance. However, if you add a torsion spring to the end of the hairpin by the wheel, it pushes the wheel back down. Now attach the other end of the torsion spring to the other hairpin near the other wheel and you’ve got yourself a sway bar. The torsion spring is the axle. You can't get any closer to the wheel than the axle. Because the torsion spring and the hairpin are both mounted so very close to the wheel, they stabilize it in all the places that the distant leaf spring fails. If we were relying solely on the leaf spring for stability, it would be a disaster. Because the leaf spring is pushing in line with the lines of force acting against it and because the wheel is mounted so close to the hairpin and torsion spring, it’s stable. At least that's the theory. We'll see once it's built. Here's a close-up of a nice looking 3 link on Ewald’s dragster (Thanks 64Dodge440!).
One thing you may (or not) want to consider is that Ewalds front end follows the NHRA rule requiring front suspension and 1 shock per wheel. A lot of designs were tried to follow the letter of the rule but were in effect solid mounted front axles before the rules allowed them. Garlits had 1 mounted with cushions similar to Ford motor mounts. I don't remember what year the rules changed allowing solid front ends but in my experience most dragster front ends (spring or torsion bar) didn't "work" once the chassis were built to flex - the flex was the suspension. Mounting this setup to a rigid frame will be a different deal.
I've been considering a Mumford linkage for the front of my A project. There should be room behind the axle, especially as most of the Mumford linkage is below the frame mountings.
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