Aero RV (custom boat tail for '95 Ford E-350 Class C motorhome)

[ennored]

I do tow, some. Three different trailers, a car 4 down, a small 4x8 golfcart trailer, and a 24' enclosed. Good news is the hitch ball ends up about 24" from my zero line for a tail. A 36" tail will fit nicely. I envision it as a three sided tail, being open in the middle. Could leave the hitch alone, still be able to put bikes on the back "inside" the tail. Measurements have been taken, sketches have been drawn, etc. The Monaco Vesta has a very small tail, still waiting on an email response on how it actually works. There's an RV show in a few weeks, there's usually one there. I might have a tape measure in my pocket...

Cool thing is that I can remove my current rear cap and fab up a trial tail. See how it works, both in aero/MPG and towing impact. The enclosed trailer won't really benefit as the tail will direct air right onto the front of the trailer, but I don't tow it much, and it would be a bit of a gap filler. I can put the OEM cap back on if it doesn't work out. Or modify it if it works. It's already fiberglass, and very close to square. A single mold could be made that three pieces could be pulled from, 2 sides and a top. We'll see, one step at a time.

If this family could build a whole RV in 4 months, I can build a tail, right?

http://www.youtube.com/watch?v=dil4_PzS9mA

(They used boat building techniques. Folks could use the same methods. I know a guy who builds racing hydroplanes, planes, and racecars. I'll surely be visiting him to see what he would do.)

[orbywan]

Originally Posted by ennored

I do tow, some. Three different trailers, a car 4 down, a small 4x8 golfcart trailer, and a 24' enclosed. Good news is the hitch ball ends up about 24" from my zero line for a tail. A 36" tail will fit nicely. I envision it as a three sided tail, being open in the middle. Could leave the hitch alone, still be able to put bikes on the back "inside" the tail. Measurements have been taken, sketches have been drawn, etc. The Monaco Vesta has a very small tail, still waiting on an email response on how it actually works. There's an RV show in a few weeks, there's usually one there. I might have a tape measure in my pocket...

Cool thing is that I can remove my current rear cap and fab up a trial tail. See how it works, both in aero/MPG and towing impact. The enclosed trailer won't really benefit as the tail will direct air right onto the front of the trailer, but I don't tow it much, and it would be a bit of a gap filler. I can put the OEM cap back on if it doesn't work out. Or modify it if it works. It's already fiberglass, and very close to square. A single mold could be made that three pieces could be pulled from, 2 sides and a top. We'll see, one step at a time.

If this family could build a whole RV in 4 months, I can build a tail, right?

Exactly! Sounds like you have a plan and the right attitude. Cool video. They did a really good job on the nose and blending the sides into the frontal shape. Too bad they didn't add a boat tail. With their energy, numbers and skills, it would have been short work.

[gezundheit]

is there any formula based on the vehicle length? i have a 1978 25ft.pace arrow
and remembered that your rv is that size also.so,how did you arrive at your
fishtails length? what confused me was reading about that european trucking
groups 53ft.trailer and their fishtail.they sized theirs at 2 meters or 6ft.and said
it was the correct size for getting the lowest drag.now i'm thinking,if they are
correct,does that apply to any sized vehicle? anyway,i know you have been
asked this question before but i figured to ask again since you are the man.
regards,brian.

[orbywan]

Originally Posted by gezundheit

is there any formula based on the vehicle length? i have a 1978 25ft.pace arrow
and remembered that your rv is that size also.so,how did you arrive at your
fishtails length? what confused me was reading about that european trucking
groups 53ft.trailer and their fishtail.they sized theirs at 2 meters or 6ft.and said
it was the correct size for getting the lowest drag.now i'm thinking,if they are
correct,does that apply to any sized vehicle? anyway,i know you have been
asked this question before but i figured to ask again since you are the man.
regards,brian.

There are mathematical formulas for just about every aspect of aerodynamic design, including the optimal length for a boat tail, but if you're going to build something that is actually going to be driven on the road, the length has to be confined to what is practical and/or legal.

In the USA, trucking regulations limit the length of a boat tail on a 53 foot trailer to 18 inches, I believe, which is not even close to optimal. My vehicle is the same original length as yours so I based the length of the boat tail partly by applying the proportions of the Dryden van study, and partly by the limitations in departure angle and strikes incurred when you start driving a 25 foot RV off road.

As far as being the man, aerohead and possibly several other of the aero geniuses that frequent this site would possibly qualify for that title, I'm just a guy with a mig welder and the cajones' to use it. ha.

[gezundheit]

thank's for the reply.i like your interpretation.there is this outfit that makes airtabs,looks like it would work on my roof a/c as well as the front of the coach too.this whole group
is very inspiring.the fact that you do stuff is what keeps me coming back.

[orbywan]

Originally Posted by gezundheit

thank's for the reply.i like your interpretation.there is this outfit that makes airtabs,looks like it would work on my roof a/c as well as the front of the coach too.this whole group
is very inspiring.the fact that you do stuff is what keeps me coming back.

Some people will tell you airtabs are a waste of time. I don't know about that, I haven't read up on them at all, but I would say remember what the Dryden and many other tests have shown. The biggest gains are to be had at the rear of the vehicle and in this case in the rear of the a/c fairing as well most likely.

I think you'll have more success building fairings and boat tails than you will sticking airtabs on things but what the heck, go where the spirit moves you. A lot of people never get past the I'm gonna do this and I'm gonna do that stage.

[wyatt]

Originally Posted by orbywan

In the USA, trucking regulations limit the length of a boat tail on a 53 foot trailer to 18 inches, I believe, which is not even close to optimal.

I remember reading that as long as the extension is not increasing cargo volume, that on semis and the like, a 4' extension is allowed for aerodynamic pruposes. I have seen a number of extensions on semis that are more than 18" in length, and reports say that the 4' versions are good for about 7% FE increase.

[orbywan]

Originally Posted by wyatt

I remember reading that as long as the extension is not increasing cargo volume, that on semis and the like, a 4' extension is allowed for aerodynamic pruposes. I have seen a number of extensions on semis that are more than 18" in length, and reports say that the 4' versions are good for about 7% FE increase.

I wasn't sure about the length, but I'm glad they allow 4 feet, that's more like it.

[ennored]

The 48" TrailerTail is what I included in my plot a few posts up:



The graph is in inches, in plan view, of the various tails noted.

(I didn't scale the Trailer Tail length down to the Dryden van width (80"/102"), but it's a straight plate at 15°, really no need to.)

[ennored]

I've been poking around looking for other examples or large aerodynamic vehicles. High speed trains came to mind. Some of the latest bullet trains look pretty bizarre. I think the front and rear of them are the same so there may be some compromise relative to that? Nose seems long, tail seems short. One conclusion is aerodynamics aren't so important as the frontal area is relatively low, but then why would they have the wild looking noses at all? Aero has to play a role at such high speeds, right?

The red one in the middle is the newest design. An E6 Shinkansen.



Anyone know any more about trains?