Factoring drag into design

[jon p]

I am building a larger teardrop that I can live in for extended periods. It will be 6ft wide x 10-11ft long. Is there anyone here knowledgable of drag such as an aeronautical engineer?

I am only 5'6" tall so would like to build it where I can stand in it. I am only willing to do so if it won't have a huge effect on the drag. I have read the drag is worse on transmissions and mpg than the weight of the trailer.

Also as far as rounded corners go which is better aerodynamically. I have saw some teardrops that are "reversed" and wondering if the normal option or "reversed" option would be better in regard to drag.

[bobhenry]

I started on a trolly look trailer in early 09 and a fellow just had to have the frame $$$$$

So I sold it !

I had the floor cut and it had a round nose and tail vertically but leaving the roof flat to be able to install a trolly top thru it.

I still wonder if the round nose and tail would have eliminated the drag coeffiecient enough to matter. The trailer was 6 foot wide and it was
about a 2 to 2 1/2 foot radius on both ends so it was not quite a full semicircle.

[Dusty82]

I'll certainly be watching this thread for answers as the sheep wagon basically has a flat, square front end. I considered drag a little bit, but obviously not all that much.

[starleen2]

So Jon P - ya' worried about drag? we need to know what you are towing with - It makes a difference. I have towed with a jeep commander and a jeep wrangler - with the same trailer - And I can tell the difference between the two - one is narrower and shorter than the trailer - the other same width and height of the camper.

[jon p]

So Jon P - ya' worried about drag? we need to know what you are towing with - It makes a difference. I have towed with a jeep commander and a jeep wrangler - with the same trailer - And I can tell the difference between the two - one is narrower and shorter than the trailer - the other same width and height of the camper.

Yea my thoughts are the same as yours on this. If the trailer and vehicle are close to the same height it seems to me that drag will be decreased. However I imagine that at the same height the wind will still be able to drop between the rear of the vehicle and the front of the trailer if there is a long tongue. Right now I drive a 2000 Cadillac STS but I am building this trailer to last my lifetime and I know the car wont.

[planovet]

Sometimes I think we tend to over-think this stuff. All the engineering mumbo jumbo tends to fly over my head (no offense to those who are engineers). My tear has a curved front surface, not because of aerodynamics or the "drag coefficient" but because I liked the look better.

[jon p]

Sometimes I think we tend to over-think this stuff. All the engineering mumbo jumbo tends to fly over my head (no offense to those who are engineers). My tear has a curved front surface, not because of aerodynamics or the "drag coefficient" but because I liked the look better.

I am not one to care much about looks or flashy designs. I want to be able to save money on fuel by not cutting my mpg in half. If its going to knock me from my >20mpg current avg. down to 10mpg then I may as well buy a larger travel trailer with more luxuries. I am hoping to only lose a few mpg by going with the teardrop. Thanks for posting the images and drag coefficients. I wonder how to apply those to a trailer because the car is already creating pockets of air that will be impacting the trailer in different locations. It seems those coefficients would only apply if the trailer was in front of the vehicle.

I think what I really need to figure is how much the larger pockets of air are able to drop between the rear of the car and the front of the trailer. From where it would initially impact the front of the trailer is where I would need to start the largest arced curve. At least thats the way it seems to me....

I read that these are the most aerodynamic motorcycle haulers on the market....
http://www.ironhorsetrailers.com/
It doesn't seem to matter much if the back half of the trailer is flat as long as the front is round. That is confirmed by comparing the half circle and full circle drag coefficients above.

[Bucko6]

For what it is worth, I think your MPG expectations are too high. My tow vehicle is a full size crew cab pickup. On the highway empty, I get about 20 MPG. When I tow my 30' travel trailer it drops to 10 to 12 MPG. When I tow my teardrop, I was only getting 14 to 16 MPG. Keep in mind I run 70 MPH empty, 60 with the 30' and about 65 with the tear. Profile is important, look at how manufactures round the front profile of new factory travel trailers. I think overall frontal area is important too. My tear could hide behind my pickup but the air behind the tow vehicle will drop back down and meet your trailer head on. For your best shape, think airplane and keep the frontal area small. My guess is no matter what you do, you are going to knock off about 25% of your unloaded MPG.

[jon p]

For what it is worth, I think your MPG expectations are too high. My tow vehicle is a full size crew cab pickup. On the highway empty, I get about 20 MPG. When I tow my 30' travel trailer it drops to 10 to 12 MPG. When I tow my teardrop, I was only getting 14 to 16 MPG. Keep in mind I run 70 MPH empty, 60 with the 30' and about 65 with the tear. Profile is important, look at how manufactures round the front profile of new factory travel trailers. I think overall frontal area is important too. My tear could hide behind my pickup but the air behind the tow vehicle will drop back down and meet your trailer head on. For your best shape, think airplane and keep the frontal area small. My guess is no matter what you do, you are going to knock off about 25% of your unloaded MPG.

I could live with 16mpg, but not 10mpg. Has anyone on these forums made a spherical front design like the ironhorse trailers I listed above or an airstream, but out of wood. Would seem difficult to bend the wood not just two-dimensionally, but also 3-dimensionally.....

[eamarquardt]

I just finished an all day drive (mostly hwy miles) and got 21 mpg in my Ford Windstar van. I then drove about 200 miles with my utility trailer behind me (see album). The trailer (empty) weighs a ton (literally as it has two frames and dumps like a dump truck plus dual wheels for more rolling resistance/drag) and is not aerodynamic at all. With the trailer hooked up and with a 500# load in it on the return trip, I got over 17 mpg for the 200 mile trip.

I think that unless you are pulling something really obnoxious you wont see that much of a difference. Partially because your tow vehicle will be "blazing the trail" in front of your trailer.

Theory is great but real numbers are better. Anyone else have some good data?

Cheers,

Gus

[jon p]

So far I am thinking of mimicking this outer design.....

http://www.roamingtimes.com/a/consumer/ ... railer.asp

[kennyrayandersen]

Yeah, that's not easy -- you'd probably want to do that part out of foam and fiberglass, or get access to an English wheel if you want to do it out of metal.



One other thing to consider is that if you look at really early airstreams and aero trailers rather than have an exact curve they use a series of flat segments to approximate a doubly curved surface. If you had three singly rounded surfaces in the corner, aerodynamically speaking you'd probably already get the same approximate drag as the quarter spherical one.



However, less well known is that the front matters some, but the back is where it's at. The back has much more influence regarding the overall CD than the front. In the front the air builds up and makes it's own pseudo shape, but a flat in the back causes tons of turbulent flow (drag).

[jon p]

However, less well known is that the front matters some, but the back is where it's at. The back has much more influence regarding the overall CD than the front. In the front the air builds up and makes it's own pseudo shape, but a flat in the back causes tons of turbulent flow (drag).

I'm a little confused on this one. Your comment here doesn't seem to align with the picture table posted above by planovet. The semi-circle actually has less drag than the full-circle....

[PaulC]

In a perfect world all the talk above makes sense BUT your trailer/TD will always be travelling in "dirty" air. This argument has been raised here to the point that my best advice to you is to build it, put the drawbar on the front of your tow vehicle and push the thing down the road. Then, and only then, will aerodynamics be of any effect.
Cheers
Paul

[madjack]

In a perfect world all the talk above makes sense BUT your trailer/TD will always be travelling in "dirty" air. This argument has been raised here to the point that my best advice to you is to build it, put the drawbar on the front of your tow vehicle and push the thing down the road. Then, and only then, will aerodynamics be of any effect.
Cheers
Paul

+1 .....................................................................