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Author Topic: Resistance Forces Other Than Aero  (Read 7479 times)
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Koncretekid
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« on: November 18, 2011, 11:58:02 AM »

We all know that drag forces are about 2/3 caused by aerodynamics, but we may not pay enough attention to the other 1/3, such as transmission losses, bearing drag, and tire deflection.  This was brought home to me when BAK posted that Bob Barker told him that the CanAm 125 that he set records with back in 1973, seized up  before the last timing light, but still set a record of 135 mph + and coasted three miles back to the pits!  He said that the rear wheel, with the chain in place, would spin for 4 minutes when spun by hand.  So I went out to my shop and because my landspeed bike was not in the shop, I grabbed the back wheel of my BSA B50 road racer which was on a rear stand and spun the wheel.  It rotated grand total of 5 seconds.  Obviously, there are some transmission losses here.

I had an old CB350 Honda front wheel under the bench, which is the drum brake equivalent of the front wheel on my Landspeed bike so I set it up in an old swing arm in a vise and tried the same thing.  It spun an amazing (or so I thought) 4 - 1/2 minutes.  The bearings are Japanese Koyos, and might even be the original bearings, which are sealed on one side only. So I popped off the outer seals and tried again.  This time the wheel spun for 9 minutes 47 seconds.  At this point I noticed that the wheel was not well balanced, so I wrapped some solder around the spokes on the light side and spun it again.  The result was over 11-1/2 minutes before it stopped spinning, and I had to watch it carefully to tell when it actually stopped.

Now these experiments are not very scientific, but because I got an order of magnitude difference by just removing the seals and re-balancing,  the results are significant.

The BSA rear wheel will never rotate very freely, because the design of the drive sprocket, which is mounted on a sleeve gear, which in turn runs on a bushing on the mainshaft, and which also rotates the layshaft and all the attached gears, has a huge amount of drag.  Luckily, when in high gear, the mainshaft and sleeve gear rotate at the same speed, so the transmission losses are confined to spinning the gears and shafts on ball and needle bearings.  Not much that can be done here without cutting the gearbox off the motor and substituting a more modern transmission, torque converter, or what have you?

The drive chain is another potential horsepower eater, but I don't know what would be better.  If I were starting over, I would go to 428 chain (from the present 520), but that would require another whole set of rear sprockets and custom made front sprockets.  Other than that, would a belt drive be more efficient?   Also, a belt drive primary is available (with some modifications to fit the B50), which might help.

Tires are also part of the equation, and I'm presently using a radial 110/70-17 front tire on the back (running counter direction to the intended direction), and a 80/90-17 bias ply on the front, both with tubes, and running 50 psi tire pressure.

So I would be interested in hearing from others on what I could do (or what you have done) to reduce these other power losses.

Tom
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« Reply #1 on: November 18, 2011, 12:54:20 PM »

I know we've discussed oil in the transmissions before.  I'm aware that the Subaru Justy that I believe still owns the Production record in I/PRO used automatic transmission fluid in place of the gear lube in the transaxle.

A trick the BMX Bicycle guys have done is to use Vaseline on their wheel bearings, and they repack their bearings every race.  Might not hold up to motorized applications, but maybe it might?  Don't know.  It would be kind of a hassle, but if you're looking to minimize your rolling resistance, that might be something to look in to.

On cars, something that gets overlooked is the straightness in the drive axles and drive shafts.  As Koncretekid noted, out of balance issues eat power, even those that might not be perceptible to someone driving a vehicle.

I would think checking the concentricity of the wheel sprocket would be a good idea.  When I rode bikes, I always assumed that they're straight, but we're looking to minimize power losses, so maybe that needs to be checked.

Crank trigger versus a distributor puts less drag on the engine.

It's chasing a lot of little issues, but if there were a silver bullet, we'd all have them in our holsters.
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« Reply #2 on: November 18, 2011, 12:54:48 PM »

I run ceramic wheel bearings in my bike. I trim the seal lip off that rides on the axle. The rusults from trimming the seal is more noticable than the high dollar wheel bearings. huh
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« Reply #3 on: November 18, 2011, 02:23:38 PM »

At some point you have to evaluate your budget.

If you are going all out then everything is a consumable that gets replaced every race.
Ceramic bearings not only in the wheels but the engine also. Expensive.

The drag from the seals is real and trimming them counts for a lot. Oil viscosity creates drag. Use the lightest oil you think you can get away with. The trade off is wear and potential failure.

Out of balance creates drag. Make a test fixture and spin the wheels up to maximum speed. If you can't keep a glass of water on it, then re-balance. The tires should be trued so there is no run-out. The tires should be shaved to the minimum. High pressure to reduce rolling resistance.

Search for the discussions on chain wear and drag. There has been a lot of discussion. Here is two:
http://www.landracing.com/forum/index.php/topic,6295.0.html
http://www.landracing.com/forum/index.php/topic,5718.0.html

Oh, and lose weight. No point carrying excess weight.  grin
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« Reply #4 on: November 18, 2011, 02:25:19 PM »

Koncrete Kid,
I agree with you that when you have limited horse power you need to make sure that most of it is used to make you car, or bike in your case, go fast and not waste it on parasitic losses like chains and bearing seals. I did a search on roller chain efficiency and the numbers are 91 to 94% efficient and that is assuming good lubrication, and new chain and sprockets, going with something like the new Gates GT Poly Chain, which is their latest design synchronous belt design, a properly applied set up can be 99% efficient. That is well worth considering.

Ceramic bearings and hybrid bearing using ceramic balls are additional ways to reduce parasitic losses, although they are pretty spendy and going along with what fredvance said about seals I would try to design a setup which allowed you to use them without seals. Also good lubrication is important and there are some very good high speed greases available today that should be used, I have used Kluber brand before with great results on high speed spindles at over 10,000 rpm.

As I am also planning to be building a car that will have limited horse power and be chain driven and I am planning to incorporate both synchronous belt and ceramic bearing technology to reduce parasitic losses.

Rex
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« Reply #5 on: November 18, 2011, 02:50:33 PM »

Some of you know that I also play with Mountainbikes and other forms of pedal power. We have been seeing ceramic bearings being used for many years. I still have some wheels set up with ballbearings that were lapped in with polishing compound, coast like a dream.

Also, I remember a tale of a friend that ran in fairy fast karting circles told. He had some guy that hated him for how good and fast the karts he tuned went. Swore my pal was cheating until one day he got tired of the jealousy and told the guy he would show him his secret. He went over and gave the guys kart a shove and it went a few feet. Did the same to his kart and it rolled all the way across the pits! Things need to track and not bind, the other guys kart was all bound up with the four corners fighting themselves.
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Koncretekid
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« Reply #6 on: November 19, 2011, 04:37:17 PM »

Thanks for the response.

I currently use 20W50 Amsoil full synthetic in my motor, transmission, and primary chain case.  I might be able to get away with lighter oil, but keep in mind that this is an air cooled motor that runs hotter than a water cooler.  My rod bearing lasted thru about 14 runs at Bonneville over a 2 year period, and 5 runs at Loring.  It was ready to go, but didn't.

I don't plan to use ceramic bearings in the near future, but I will probably pop the seals out for the last couple of runs.

Lapping the bearings with polishing compound sounds interesting.  How do you do that and what do you use?

Also, wheel balancing will get more attention for next year.  Vibration at the handlebars last year was so bad that I got blisters on my hands.  I got the motor rebalanced for next year, but some of the vibration could have come from wheel balance issues. Tire issues (radial vs. bias ply) and size (when is bigger better?),  other than pressure did not get mentioned, but I know this is important as well.

And lastly, I read up on the Gates GT Polychain and it sounds quite amazing.  Unfortunately, their charts only go to 5500 RPM, but they do say that max belt velocity is 6500 ft/min or so, which is doable on both the primary and drive.  Changing over would be costly, so it won't get done yet.  I have no doubt that for low horsepower vehicles, this is the way to go. Converting both primary and secondary drives over to belts could free up 10% more horsepower.

Tom



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Tman
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« Reply #7 on: November 19, 2011, 05:01:25 PM »

The old bike mechanis trick was something like pear drops tooth paste followed by a SHORT spin. I have used VERY FINE polishing compound then cleaned them out real well and pack with a slick grease. The track guys used oil.
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« Reply #8 on: November 19, 2011, 09:13:19 PM »

I dont know if this would work or not in landspeed racing but at motorcycle dyno shootouts Ive seen +10hp from spraying the chain with WD40 before a dyno run compared to a run without it
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« Reply #9 on: November 20, 2011, 12:50:26 AM »

The Triumph uses Mobil 1 Racing 4T 10W-40.  It has additives for tranny gears and the ones in the bike look good during the teardowns.  This is lighter weight than 20W-50.  It might help to reduce drag in the trans and primary.

Sometimes a person wants to keep the seals.  One trick is to replace the double lipped ones with single lip seals.  Also, taking the spring out of the seal can help to reduce friction.  Do not do this with engine seals.  They are designed to withstand crankcase pressure and they can leak during racing use if they are modified.

What sort of ignition and charging system are you using?   
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Koncretekid
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« Reply #10 on: November 20, 2011, 06:20:52 AM »

I dont know if this would work or not in landspeed racing but at motorcycle dyno shootouts Ive seen +10hp from spraying the chain with WD40 before a dyno run compared to a run without it
Methinks the chain in question might have needed a good cleaning and WD-40 is probably a good choice.  It's very light, and might be good for one run, but would probably have to be re-sprayed before each run.

Bo,
If 10w-40 is a good choice for the transmission and the primary, maybe straight 10w or the above mentioned ATF would be even better.   Has anyone tried ATF with a wet clutch? In high gear on the BSA, the mainshaft is locked to the sleeve gear, so theoretically, the only load is on the bearings which are ball at each end of the mainshaft, the rest of the gears are rotating but with no load.  Another problem I have is a third bearing on the mainshaft known as an outboard bearing, which replaces the seal holder behind the clutch.  Seemed like a good idea at the time, to mitigate flexing of the mainshaft, but in hindsight, it is practically impossible to have all three bearings perfectly aligned without some friction.  For sure I could pop the seals on this bearing, as very little oil from the primary would escape, and then only onto the chain.

I run total loss ignition with a Boyer.  BTW, the seals on the wheel bearings don't have springs.  I'm thinking that they could be removed, sanded on the inside to give a few thousandths of clearance, and replaced to keep out the majority of the salt and dirt.  I still would, of course, want to replace before the next event.

But on the subject of bearings, I know there are different classes, the better ones have tighter tolerances.  Would the lower tolerance ones be more likely to self align and therefore be more frictionless?

Tom

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« Reply #11 on: November 20, 2011, 10:33:37 AM »

Tom,

Recognizing that you don't have a lot of space to run this type of thing, and ignorant to the rules of the class (special construction, isn't it?), is an oil cooler or reservoir a possibility?  An extra quart would fill the cooler, and probably let you go lighter on the oil viscosity.

It's always a worry - British castings and what not.
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« Reply #12 on: November 20, 2011, 11:42:12 AM »

Tom,

running ATF in the trans is possible, the issue will probably come down to "shear stability" in the oil. It will break down and make shifting difficult. For short duration it should be fine (not over the road).

Another consideration would be to narrow the gears in the trans to minimize gear meshing/parasitic losses.
Ceramic hybrid bearings can help. Full compliment has more contact and depending on the load can be very efficient.

Something about chain efficiency, more it is consistancy, if the chain has short or long links along the length it will create heat and absorb HP. Also, if the chain is stretching this indicates either the wrong size, incorrect center distance or wrong material/construction of chain. I found using very small chain, high quality with CNC machined sprockets on karts the chains stopped heating up. Search up RK chain, I hear it is made for bikes now.

John
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« Reply #13 on: November 20, 2011, 12:30:07 PM »

on bikes  it takes a while to get the chain sides to not drag on the sprockets
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« Reply #14 on: November 20, 2011, 10:56:13 PM »

Tom, vibration has been a problem on that bike.  Lots of people like to use motocross bikes for desert racing.  Usually the MX bikes have a magnetic rotor on the crank end and it spins inside of the coils.  This provides little flywheel inertia.  This results in some engine vibration and it is no big deal for MX bikes.  The races are short, unlike desert races.  We put external flywheels on a lot of desert racers.  The coils were inside of the rotor.  The bikes vibrated less and were easier to ride.  The total loss system has no coils and where the coils used to be would be a great place for a flywheel.  The flywheel mass might reduce engine vibration.  Just an idea.

 
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