trailer aero

[fredvance]

I am thinking of building an enclosed trailer for my bike. I want to make it as slick as possible. If I V the front will a sharp edge on the nose cut the air better than a rounded one.  Fred

[Seldom Seen Slim]

Fred --

Thanks for asking the question.  I don't have the answer, but'll be looking carefully at the responses.  I'm in the market for a new race trailer and want to have good aero.  Every time I ask an owner or a dealer I get a not-very-trustworthy answer.  "Hey, the truck pulls it like the trailer isn't even there" isn't what I want to hear.  What I'll believe is a report from someone telling me how many gallons of fuel he used to pull to and from Bonneville a couple of trips -- so we get a REAL performance figure.

Just this morning my ability to report like that died on me -- my PDA, which had a running fuel log of the last 120,000 miles on my pickup, went into hibernate mode and, upon rebooting, all data was lost.  Dang!

Back to the trailer -- I want to know fuel consumption numbers from the various configurations of trailer, with the "tow-ability" a second question.  I know that the front aero piece called a "Noze Cone" (trademarked name) helps with my big trucks -- and I therefore assume it'd make a difference on a trailer.  As for the V front end -- I haven't seen any data that's reliable.

Post your comments, boys and girls, and let Fred and me see if there really is a difference.  Thanks.

[Sumner]

I am thinking of building an enclosed trailer for my bike. I want to make it as slick as possible. If I V the front will a sharp edge on the nose cut the air better than a rounded one.  Fred

If you are planning on staying "sub-sonic" I would make it rounded.  A lot is going to depend on what the air is like coming off of the back of the tow vehicle.

Jon, when my dad died at 94 he still had every data log of mileage, date, gallons to fill, and location since the 20's for every car he owned.  None of them ever went into hibernation or lost their data.  They weren't very high tech........ a little notebook and a pencil and my mom made the entries usually  .

c ya,

Sum

[Glen]

Terry Nish has vortex generators on the race car trailer that cleans up the trailering air. I think if you look on the www.nishmotorsports.com they are listed.

[Seldom Seen Slim]

Yes, Sum, I yield the point.  My '89 GMC Jimmy has a spiral notebook in the glovebox showing every maintenance, all the fuel, and so on -- since the truck was brand new.  The battery has gone dead (even been removed) from the vehicle numerous times and that paper log is still accurate.

I got the PDA when the current truck was new, bought the Fuel Minder program, and thought I had the world by the tail.  Then I learned that the fuel program wasn't quite as good as I had hoped, but it served well enough.  I'm bummed by the loss of phone numbers and all, and for them the PDA has an advantage over paper in that it';s easy to change data without resorting to an eraser on the end of the pencil.

So -- hey, everyone, if you want me to have your phone number/address/email or whatever -- send it along in a PM or straight email to me:  jonwennerberg@nancyandjon.org

Ta-ta for now.

[SPARKY]

Jon,----the secret to most aero and especially trucks is MOVE the AIR ONCE!!!!!!!!!!!  Some big rigs have BAT WINGS to enclose the joint between the truck and the trailer.  Taper the rear of the trailer with a ramp and rroof and two doors that form a V and move the wheels inside.  ("Wortex generators"  good German term) on the rear at the transition point!!

[Seldom Seen Slim]

Glen, I've seen the vortex generators, I've talked with the folks at Nish, and I've talked to other folks that have run the generators.  Nobody has shown me the hard data to prove that the things work, and like a Noze Cone, like the V front on a trailer, like all those things -- until I see some solid proof -- I don't believe it.  I'm not saying they don't -- I'm saying I'm not buying a trailer with a $500 - $1,000 added front end in the hopes that it makes a difference.

[PorkPie]

the size you need a round front shape is the right solution......a v nose make sense above 600 mph....any idea how much the speeding ticket would be for 600 mph.....

Round is fine - and if the "round" is a opening radius and goes proper tangential into the side panels you will get a clean shape.

To the Vortex.....Vortex are to break the vacuum behind the vehicle when you got too much turbulences on the rear end...in other words....bad rear end aerodynamic.......the old aerodynamic rule says...it's not important how you go into the air....it's important how you got out of the air......but if the airflow, coming from the front to the rear, is clean....it's easier to go properly out of the air.........what means....throw the Vortex into the garbage bin.........

[Uncle Jimbo]

For whatever its worth. We'r running a 1997 GMC Suburban, that I call "da boat". We pull a 6x12 Timberwolf lowboy cycle hauler. Without the trailer & with some of my work tools, on the hwy I get 15-16 mpg. The ironic thing is, with the trailer, bike, tools, etc, I still get 15mpg so long as I keep it at 65mph. - - Go to 70mph and it dives to 13 1/2to 14. I did make up a spoiler/(vortex generator?) that we mount on the rear roof of the GMC when pulling the trailer. It seemed to save a strong 1mpg comparred to not using it. I have no "hard data" other then the mpg checks that we do on most every fill-up. OOoops, air conditioning ! I forgot, turn the air on and loose another 1 - 1 1/2. Its confounding to me though, how little difference there is with this mpg thing with trailer or with out, at least as far as "da boat" goes.  Iam guessing it has to do with speed.

[Sumner]

For whatever its worth. We'r running a 1997 GMC Suburban, that I call "da boat". We pull a 6x12 Timberwolf lowboy cycle hauler. Without the trailer & with some of my work tools, on the hwy I get 15-16 mpg. The ironic thing is, with the trailer, bike, tools, etc, I still get 15mpg so long as I keep it at 65mph. - - Go to 70mph and it dives to 13 1/2to 14. I did make up a spoiler/(vortex generator?) that we mount on the rear roof of the GMC when pulling the trailer. It seemed to save a strong 1mpg comparred to not using it. I have no "hard data" other then the mpg checks that we do on most every fill-up. OOoops, air conditioning ! I forgot, turn the air on and loose another 1 - 1 1/2. Its confounding to me though, how little difference there is with this mpg thing with trailer or with out, at least as far as "da boat" goes.  Iam guessing it has to do with speed.

"da boat" is probably pushing all of the air out of the way and it probably doesn't come together again until behind that trailer.  Does the mileage go down at 70 the same with or without the trailer.

I get 20 mpg with my truck at 75 without the teardrop trailer and 16-17 with it at 75.  If I'm in Calif. and running around 65 with the trailer it will go up to 18-19.

c ya,

Sum

[SPARKY]

The diffrece in HP required for a 24' Ryder rental truck to be able to maintain 55 vs 70 will astound you; nearly a 1/3 more, and have any reserve left for passing, climbing a hill, or slight head wind.

[panic]

"the "round" is a opening radius and goes proper tangential into the side panels"

That's what I would try first. The nose is an ellipse, with the minor diameter to match the width of the trailer, and the major radius determined by the practical length between the existing trailer front and the back of your tow (at any angle - be careful).
That's the obvious side; the front-to-top can also be improved with any radius (bigger = better), especially if the distance from the tow to the trailer is too large to bridge with a cover from the tow roof.
The bottom is a puzzle, since the cd will improve with any aero contour - but do you want air passing under the trailer?

[SPARKY]

Trucks that compete in the truck fuel millage contest have upside down nose cones in front of the trailer tandems and BELLYPANS, and Wipers on the tires to try to slow down or stop the rotational air on the tires.

[PorkPie]

A suburban is a brick in the air.....and moving a brick faster cost mpg.....

A spoiler and a vortex are two totally different things.....a spoiler is a kind of a wing and helps a lot to get a better mpg.....a vortex are small - two by three inches - plastic shapes which people add on the end of the side panels to interupt the turbulences.......a spoiler/wing clean the airflow.......

[isiahstites]

The diffrece in HP required for a 24' Ryder rental truck to be able to maintain 55 vs 70 will astound you; nearly a 1/3 more, and have any reserve left for passing, climbing a hill, or slight head wind.

Agreed! I drove one from Alabama to San Diego once and experienced the same thing.

Scott