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Hot Rods Ford Beam Axles and their Aerodynamics?

Discussion in 'The Hokey Ass Message Board' started by RileyRacing, Jul 21, 2015.

  1. So, with Bonneville being cancelled a again, and going over in my head all things speed...

    I came across a sketch I found on another forum of a belly tank type speedster with a Ford T/A/transverse style spring. It got me to thinking of how aerodynamic is was. Or isn't. I don't know.

    Murray Fahnstock's Model T Speed Secrets book has a suggestion to shape a piece of hardwood into a rounded wedge and tape it to the axle...

    To the point- does a trick like that (or drilling holes) matter? Is it worth the effort or is it worth 1/10 MPH?

    Curious to know from those who have tried.


  2. dos zetas
    Joined: May 10, 2009
    Posts: 175

    dos zetas

    Even old Indy cars like Miller Specials sometimes had streamlined fairings over the exposed parts of the axle and steering gear. Along with discs on the inside of the wheels. I've never tried, but looked at plenty of cars with the axle ends faired in.
  3. gnichols
    Joined: Mar 6, 2008
    Posts: 10,798

    from Tampa, FL

    Anything in the wind will slow you down, eh? So aero it over somehow, add fairings to the nose or frame, or use a tube axle! Drilling holes sounds like it would add more drag to me (always has but I'm no aero engineer) and negate the whopping 1 lb of weight savings and the labor costs to do it, by creating a lot of little, aggravating vortexes under the car. Besides, as I understand it, saving weight is not problem in lakes racing.
    RileyRacing likes this.
  4. Gene Boul
    Joined: Feb 9, 2006
    Posts: 805

    Gene Boul

    I asked Garlits about whether Muldowney's car was faster because her cockpit was narrower than your average man's...he said, "don't be stupid it's the tires that create the wind resistance". I think the point was concentrate on the big things and don't get wadded up in the BS!
    falcongeorge and RileyRacing like this.

  5. I agree with all the assessments so far, but figures it was worth a discussion. ;)

    And the holes idea is exactly what I thought too. Great minds and all. Lol

  6. pitman
    Joined: May 14, 2006
    Posts: 4,982


    NACA foil shapes, the 1/2 round on the front face of the axle would help.
  7. 117harv
    Joined: Nov 12, 2009
    Posts: 6,590


    The holes would not be as good as un-drilled. A truck with the tailgate up gets better fuel mileage, the bed builds up with pressure/stagnent air and the incoming slides over it. It is proven that the bottom of a jet ski, boat, etc. will go faster with a textured surface, kind of the same principle as the truck bed but water, it also removes the suction/sticking effect.

    The episode of Myth Busters where they made the dimples in the car body, that would have to help top speed, the same principle as the truck and the boat. Also, a golf ball without the dimples wont fly nearly as far.
    clem likes this.
  8. looking at some pictures of Soap Box derby cars online it appears they use streamlined axles.....must be some reason for that
  9. $um Fun
    Joined: Dec 13, 2008
    Posts: 526

    $um Fun
    from Nor Cal

    Some of the early Indy cars used a piece of shaped wood fitted to the middle of the I beam axle held on by screws from the back..

    Aero is not how you make the hole but rather how the hole is closed behind you. After a few of the lakes racers figured this out the SCTA banned mounting roadster bodies backwards.
    falcongeorge likes this.
  10. 2racer
    Joined: Sep 1, 2011
    Posts: 960


    so these bumper boobs are not for aero?
    scotty t likes this.
  11. G-son
    Joined: Dec 19, 2012
    Posts: 665

    from Sweden

    Indeed, and open wheels are quite horrible for aerodynamics. Think a Formula 1 car is a good aerodynamic shape? Think again, it's quite horrible due to the wheels (and the fact that alot of the rules in many ways are designed to keep speed down, not maximize performance). They do however have one interesting feature adaptable to a rod. All the suspension parts has a aerodynamic shape to minimize drag they cause.

    Well, both are important, but you have a good point.
    A rounded leading edge will carefully divide the ariflow and send it around both sides, a square leading edge will still make the air move out of the way but needing more force and disturbing the airflow a far greater distance around it.
    A pointed rear end (as on a teardrop shape, the lowest drag aerodynamic design) carefully pulls the airflow from both sides back together, and the "void" behind the part is filled with minimum resistance, hence almost no vacuum behind it "sucking it backwards", i.e. causing drag. A chopped off pointy end almost works as well, this is called a "kamm tail", as long as there is a good "beginning" making the air come together stagnant air can replace the chopped off tip and let air flow as if it had the full length tail.
    Other shapes create a low pressure "void" behind them, causing bigger (sometimes huge, by comparison) aerodynamic drag.

    So, basically... Anything you can do to make the air move out of the way is good. Anything you can do to reduce the frontal area, i.e. the amount of air you need to push out of the way, is also good (as long as the new shape isn't less aerodynamic). Anything you can do to make it easier for the air to fill the void your car gets behind it once all the air has been pushed out of the way is even better.
    pitman and bct like this.
  12. I like this. Thanks for a clear, simple insight.

    deuce354 likes this.
  13. I think it depends on how your life or your successes are measured?

    If you are living life .001 second at a time or .1 MPH at a stretch every little thing matters some more then others obviously. On a streeter it is pretty much purely cosmetic.

    I think on the axle just filling the axle will do as much for you as shaping a piece of hardwood into a smooth arc. One thing to remember is that there was not a lot of wind tunnel testing way back when.

    That said on the salt little things matter at least to the techs. I remember once a long time ago I was tuning a sportster that had an aluminum top end (before they came that way) and I taped the down tubes to keep the salt off the front of the motor. Bad idea that made it a streamliner in the eyes of the techs and almost got the fella kicked off the salt. Ended up I had to remove the tape and he had to pass tech all over again before he could make a pass. I doubt that it would have really made an difference one way or the other but it was what it was.
    RileyRacing likes this.
  14. I didn't get a picture of it apparently, but I was at a car show this weekend and there was an early touring car, brass era and a high end brand.

    This is relevant because the axle had a shaped wood filler piece on the front face.

    I don't see why you couldn't drill holes in your axle to mount a filler piece like this. I'm not sure if pieces on the back would be beneficial or if doing the front would be sufficient.
  15. GearheadsQCE
    Joined: Mar 23, 2011
    Posts: 2,550


    ^^^^^ And this is at 30 mph. Just imagine the effect at 200 mph. But, I bet just smoothing the axle without any other changes would be hard to quantify on something as aero as a high boy roadster.
    RileyRacing likes this.
  16. Relic Stew
    Joined: Apr 17, 2005
    Posts: 1,127

    Relic Stew
    from Wisconsin

    Here is the Blitzen Benz' axle with taped wooden fairings.

    Miller Meet 2012 101.jpg
    Miller Meet 2012 102.jpg
    patmanta likes this.
  17. I knew I saw it done on something early- couldn't remember if it was the Blitzen Benz or an early Indy T... I'm pretty certain it was both. ;)


  18. From the article those tests were run in the '90s.

    Wind tunnels were not common place way back in the '30s and only someone with a lot of money to invest or a manufacturer would have access to wind tunnel. I didn't say that it never happened just that it was not common place.

    Let me rephrase that wind tunnel testing was not common place in the car hobby back in the '30s.
    Last edited: Jul 27, 2015
  19. patterg2003
    Joined: Sep 21, 2014
    Posts: 622


    Not typical 32 roadster stuff but very interesting. Kit Planes had an article years ago on the effects of drag & the hp used to move those shapes through the air. I could not find the exact article but borrowed 3 others that may be of some interest. Even a couple of poor antenna shapes on an aircraft can take up a couple hp.

    The difference of rectangular profiled landing legs vs. streamlined is 3 - 5 miles an hour, installing streamlined wheel covers gives another 3 - 4 mph with small tires. The accumulative effect of dirty aerodynamic surfaces on an aircraft can drastically slow an aircraft & chew up a lot of hp. The same theories apply to a car.

    Best analogy I read is to consider air as a fluid like water as that is how it behaves. The air in a living room weighs about 200 lb.s. Normally people do not think of air like that. How air enters and exits cooling on an aircraft can drastically affect its performance. A blunt nosed aircraft cowl switched out for a streamline cowl with small inlets will reduce hp for cruise speeds or gain 10 - 12 mph for the same power settings. Cooling inlets are critical considerations. Improving how air flows through and around a shape can make a big difference. Wheel pants make a big difference and enough that cyclists wear similar shaped helmets to reduce drag. Adding the aerodynamic shape would allow the air to pass clean over an axle with no back suction. The bonneville strealine racers are about as clean as it gets.

    Streamline the axle with an aerodynamic shape will improve how it passes through the air & reduce hp drag about the same difference as pushing a paddle flat through water vs. on its edge. Boat building suppliers have structural foams that could be shaped and taped to keep weight low as well.
    Consider looking at parasitic & other types of drag topics on aircraft. Cars are affected by the same drag as aircraft. The more drag eliminated the more efficient it becomes so the hp can be redirected to speed. There is a Mustang II owned by Schmidtbauer that typically cruises at 180 that now cruises at 260 with the same engine all through eliminating drag every way possible. He has done talks and if he cruises at 180 now his engine is turned way down & burns a lot less fuel. Waxing an aircraft or boat can add up to 3 mph.

    This can get lengthy & complex. Considering looking up parasitic drag topics on aircraft & apply it to a car.

    Attached Files:

    patmanta and RileyRacing like this.

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