The Leading Edge by Goro Tamai

[NeilBlanchard]

I got to see the 2nd Edition of Hucho from the MIT library, via my wife who is a librarian at Harvard. I now own the 4th edition that I bought from Amazon. Here's the Amazon UK page for it:

Aerodynamics of Road Vehicles: Amazon.co.uk: Wolf-Heinrich Hucho: Books

If you can find the 2nd edition (used?) then buy it. I think it had several very useful things that seem to be edited out of the 4th edition; including several pages on air flow inside the wheel well with a spinning wheel. But, I think only the 4th is available new - and it is certainly well worth buying, in my opinion.

[sheepdog 44]

Any recommendations? I'm interested in HPV style wheel fairings.

[aerohead]

Originally Posted by NeilBlanchard

I got to see the 2nd Edition of Hucho from the MIT library, via my wife who is a librarian at Harvard. I now own the 4th edition that I bought from Amazon. Here's the Amazon UK page for it:

Aerodynamics of Road Vehicles: Amazon.co.uk: Wolf-Heinrich Hucho: Books

If you can find the 2nd edition (used?) then buy it. I think it had several very useful things that seem to be edited out of the 4th edition; including several pages on air flow inside the wheel well with a spinning wheel. But, I think only the 4th is available new - and it is certainly well worth buying, in my opinion.

Neil,here are some highlights of wheel drag from 2nd Ed.:
*Wheels and wheelhouses essentially double the drag of a low-drag car.(VW's long-tail 'flow' body goes from Cd 0.0915,to Cd 0.14 when wheels are added)
*The closer the wheelhouse volume is to the volume of the wheel the lower the drag.
*The drag coefficient of the wheel does not vary as it is submerged within the bodies wheel well,only a drag reduction due to lower frontal area is actively involved.
*Open wheels,such as with Rumpler's Tropfenwagen,can double the drag (from Cd 0.14,to Cd 0.28,as per Wolfgang Klemperer's measurements of the Tropfenwagen at the Zeppelin Werke).
*Rear skirts cut drag if flow is already attached upstream.
*Front skirts,as,Adler-Jaray,Probe-IV,and AeroCivic can cut drag (9% with respect to Ford's Probe-IV).
*Just moving the wheels out flush with the body sides can mean up to a 16% drag reduction.
*Drag coefficients approaching those of basic bodies of Cd 0.07-0.09 can only be achieved through integration of the wheels into the body (2013 Cambridge University CUER eco racer is a current example,@ Cd 0.11,also NUNA series,and PACCAR.)

[aerohead]

Goro Tamai's book arrived today.Amazon had been sold out,and after a week and a half UPS delivered here at Copy-Pro.
I got a new one,just under $49 which included shipping.
More grist for the mill.

[NeilBlanchard]

Originally Posted by aerohead

Neil,here are some highlights of wheel drag from 2nd Ed.:
*Wheels and wheelhouses essentially double the drag of a low-drag car.(VW's long-tail 'flow' body goes from Cd 0.0915,to Cd 0.14 when wheels are added)
*The closer the wheelhouse volume is to the volume of the wheel the lower the drag.
*The drag coefficient of the wheel does not vary as it is submerged within the bodies wheel well,only a drag reduction due to lower frontal area is actively involved.
*Open wheels,such as with Rumpler's Tropfenwagen,can double the drag (from Cd 0.14,to Cd 0.28,as per Wolfgang Klemperer's measurements of the Tropfenwagen at the Zeppelin Werke).
*Rear skirts cut drag if flow is already attached upstream.
*Front skirts,as,Adler-Jaray,Probe-IV,and AeroCivic can cut drag (9% with respect to Ford's Probe-IV).
*Just moving the wheels out flush with the body sides can mean up to a 16% drag reduction.
*Drag coefficients approaching those of basic bodies of Cd 0.07-0.09 can only be achieved through integration of the wheels into the body (2013 Cambridge University CUER eco racer is a current example,@ Cd 0.11,also NUNA series,and PACCAR.)

Thank you Phil - I specifically remember the illustration of the air flow within the wheel well in the 2nd edition, and I looked for it in the 4th - as far as I could see, it is not in the 4th edition.

The 2nd bullet point is the one that stuck with me. Keeping the wheel well tight to the spinning wheel is the main takeaway.

[Frank Lee]

*The closer the wheelhouse volume is to the volume of the wheel the lower the drag.
*The drag coefficient of the wheel does not vary as it is submerged within the bodies wheel well,only a drag reduction due to lower frontal area is actively involved.

Since this second point refers to ride height and not how far out the sides wheels are, it seems to contradict the prior point, since a lower ride height causes the wheel to fill up the well more.

[SvdM]

I bought The Leading Edge at the end of last year. I have noticed one or two contextual errors too. I bought it after I helped with the design for a body for a Cruiser-Class solar car that will be running here in the South African Solar Challenge (Sasol Solar Challenge) Latest News

When I designed the car I was asked to create something car-like rather than full-on Challenger. The client liked some concepts sketches that didn't strictly adhere to the best aero knowledge I've been able to glean from you aero-powerhouses here and I had to go ahead as is and didn't have a lot of time to do it in (not my dayjob).

From Tamai's book I noticed that the induced drag of this car would probably outweigh the skin-drag, but it is so far a very interesting read (even for a non-Engineer) on how engineering teams really go to the nth to get the drag as low as possible and what they need to do to accomplish it. An interesting part is their use of side-winds to 'sail'.

I am not very involved in this project apart from the initial SW-model, but I do pop in every now and again to see how they're doing.

[aerohead]

Originally Posted by Frank Lee

Since this second point refers to ride height and not how far out the sides wheels are, it seems to contradict the prior point, since a lower ride height causes the wheel to fill up the well more.

Frank,you're correct.
The message I took away was that you'd minimize the wheelhouse as best you can,with an eye on active suspension,bringing the tire up into the body for it's lowest drag configuration on the highway when it counts the most.
Cogotti's (sp?) test model showed about a 0.078 drag increase when his big honkin' wheel wells and wheels were added to his drop car.
Buchheim,when he did the VW 'Flow' body (long-tail),adding the minimized wells and wheels pushed the Cd from 0.0915,to 0.14,only a 0.0485 drag increase.
--------------------------------------------------------------------------
The report on the VW Jetta hybrid land speed record car said that the mirror delete,wiper delete,lowering,and narrow tires did not affect the Cd,only a CdA reduction from frontal area.
Tamai reports that The GM Impact land speed record car,with same mods as the Jetta,except for a covered cowl and 0.5-meter boat tail,went from Cd 0.19,to Cd 0.14 if you calculate at a constant frontal area.(not really the case).They don't break out the contribution from 'hiding' the tires a bit.Wish they did.
Finally,early in Tamai's book,he mentions that the wheel fairings,even though they add frontal area and wetted area,do produce an overall drag reduction.So it looks like the wheels/wells are something worth investing time with.Hope he expands on all this later.Hucho really doesn't get into it.

[aerohead]

Originally Posted by SvdM

I bought The Leading Edge at the end of last year. I have noticed one or two contextual errors too. I bought it after I helped with the design for a body for a Cruiser-Class solar car that will be running here in the South African Solar Challenge (Sasol Solar Challenge) Latest News

When I designed the car I was asked to create something car-like rather than full-on Challenger. The client liked some concepts sketches that didn't strictly adhere to the best aero knowledge I've been able to glean from you aero-powerhouses here and I had to go ahead as is and didn't have a lot of time to do it in (not my dayjob).

From Tamai's book I noticed that the induced drag of this car would probably outweigh the skin-drag, but it is so far a very interesting read (even for a non-Engineer) on how engineering teams really go to the nth to get the drag as low as possible and what they need to do to accomplish it. An interesting part is their use of side-winds to 'sail'.

I am not very involved in this project apart from the initial SW-model, but I do pop in every now and again to see how they're doing.

I was reluctant to buy the book,but now that I'm getting into it a bit I also find it very interesting.
Contextual comments seem to be compensated for later as he fleshes out his text.I'm reading every word,as I never know when I'll run across a 'caveat.'
So far I'd say the book is a 'BUY' recommendation.For it's cost,we get a pretty good section on fluid mechanics and really complete work on boundary layer theory.
I have to bear in mind that this book is about solar racers,and as long as I do,there's no disappointment.
Hope you enjoyed your design experience on the racer.There's a lot to consider with a rulebook competition vehicle.

[aerohead]

I'm at page 178 and the book's already paid for itself.
There is so much information associated with underbody flow that the book,along with Hucho's would be enough of a 'library' or anyone interested in exploring really low drag.
Since these areas could not be modeled analytically with CFD,most of the data is from empirical wind tunnel studies and road testing.
It's a treasure trove and I hope Goro Tamai will accept my apology for my lukewarm reception after reading preparatory comments.
The book is invaluable!