Boat tail mod to my enclosed trailer

[Otto]

Originally Posted by Frank Lee

The same things that have always been suggested and proven to work.

Cap on the tow vehicle if it's a pickup. The closer it matches the trailer height the better.

Boattail that isn't angled too steep to be effective.

Minimized gap between tower and trailer.

Radiussed leading edges on trailer, keeping in mind that more radius than necessary has the effect of enlarging the gap tween tower and trailer, and taking interior volume away. I forget the formula for calcing radius size but it's here somewhere.

That tail just has the appearance of being so trunciated that it would mostly exist well within the turbulent zone, thus affecting flow how? Perhaps there is some benefit from it's side panels allowing some reduction in trailing wake but really the 3-4 mpg claim mystifies me.

Sounds basically like what I and others already said, esp. the parts about leading edge radius, since my horse trailer idea is just one leading edge with as big a radius as the trailer width will allow, increasing storage volume forward and over the tongue while decreasing the truck/trailer gap into the bargain. Truncated tail as seen in OP works, may not be totally optimum, but pretty much anything to thwart con Karman vortex street in wake will help. But, if it sticks out too far aft, gets into legal problems, etc..

NASA et al have worked the truncated truck tail issue with fold-out flexible panels in Kamm tail effect. Cheap. Works. Maybe not as elegant and refined as a German sailplane, but evidently worth the effort.

OP's trailer would next benefit imho most by adding leading edge radius forward over tongue, wheel skirts and/or pizza pans on wheels, maybe belly pan to fair axle.

BTW, has anybody done a flexible Coroplast belly pan attached to trailer axle, that moves up and down with the axle? On lots of trailers, the axle is a draggy I-beam thing hanging in the breeze. Why not fair it with Coro, maybe attached with zip ties?

As

[Frank Lee]

The giant leading radius thing threw me off. My understanding of streamlining a brick (from Hucho) is that any radius above a certain minimum (that which allows "attached" flow down the sides) does no further aero good. I understand what you are saying about filling in over the tongue... just be careful with that, not only do trailers swing from side-to-side for turning, they pitch up and down over anything other than perfectly flat terrain. Figure out the maximum pitch difference tween truck and trailer ex. rear truck wheels in curbside gutter w/trailer going up a drive so that no contact occurs. For sure compromising a tad on aero is better than fixing damaged bodywork.

I'm aware of the trunciated tail panels... and this doesn't appear to be that. I still fail to see how it reduces drag in its current form; perhaps the side panels have good flow (are they angled in?) but the top and bottom are not interacting with the flow at all thus they'd do nothing. It's not about thwarting a vortex, it's about reducing the trailing wake area, and from the pic I don't see any of that.

If it truly does work then great, more power to him. We should send the case study to Hucho tho...

[aerohead]

Originally Posted by Otto

Plastic garden pool idea: Pool is round, radiused at edge of side to bottom?

Cut in half vertically, then use one half inverted to fair the upper forward roof of trailer, and then use the other half upright to fair the forward floor to leading edge wall?

PVC pipe might work to stiffen, frame the fairing?

Otto,the shape of the pool would not lend itself at all to a trailer body,sorry.
The scale of the pool is 'large' enough to form half a trailer body in thermo-formed ABS sheet compound and light.So I was just using it as an illustration as to what is possible.
A person would have to develop the wooden patterns for a vacuum table,and have the rest of the setup to make it happen.
Didn't intend to drag you into a dead-end.

[Braebyrn]

Wow, got some attention. I had about 6 hours to put this all together with just a short amount of time reading on this website, so I am really just a hack. Just thought that it is better than getting 9 mpg for the next 7500 miles.

I was clipped in a gas station by a semi last night and the pipe and some of the coroplast was broken last night. It had to be removed, so for the next 3000 or so miles, back to stock unless I get some time tomorrow.

The bottom was flush with the bottom of the trailer, but the top was not as to allow the hinges to fit there. Again quick and dirty. I also didn't want to cover the upper marker lights.

I encountered a problem that you may know about. When the boat tail (or whatever its should be called) was installed, when a vehicle passed by, or I passed a vehicle, the truck would be pushed slightly towards the passing vehicle. After it was removed, that didn't happen.

By the way, the sides of the unit were pulled lightly in towards each other. Its probably hard to see from just the one picture.

So, if I did get a chance tomorrow to put another one together, how should I make it? Flush with the top, flush with the bottom? More of a point? It was about 36" from the trailer and I did pick up some LED tail/turn signals to be legal.

Thanks,
I will try and check back later tonight.

Rick

[KamperBob]

Braebyrn, a good starting point is Phil's overlay template. Orange4boy did a nice illustration of how to use it; however, I believe the side view was not enlarged enough to place the reflection plane at ground level; still, the illustration should be helpful.

Aerodynamic Streamlining Template: Part-C

Cheers
KB

[Braebyrn]

Ok, left the boat tail off and made a nose cone with the thought of taking up the space between the truck and the trailer also. On a semi, it is easy to take up that space since they pivot a lot further back than a tow behind trailer.

I also put on a front air dam and side skirts that is about three inches from the ground. With those mods, I went from 9 to 12mpg towing the trailer.

Next time it will be the nose cone and the boat tail mods and maybe the wheel covers, wheel skirts and undercarriage sealing.

[Varn]

Braebyrn

Sounds like you are going to save 500 dollars in 7500 miles. Keep it together and don't drive on gravel roads. Good job.

Some of us are just driving the sow's ear of a silk purse.

Originally Posted by Braebyrn

Ok, left the boat tail off and made a nose cone with the thought of taking up the space between the truck and the trailer also. On a semi, it is easy to take up that space since they pivot a lot further back than a tow behind trailer.

I also put on a front air dam and side skirts that is about three inches from the ground. With those mods, I went from 9 to 12mpg towing the trailer.

Next time it will be the nose cone and the boat tail mods and maybe the wheel covers, wheel skirts and undercarriage sealing.

[JasonG]

Originally Posted by Braebyrn

Wow, got some attention. I had about 6 hours to put this all together with just a short amount of time reading on this website, so I am really just a hack. Just thought that it is better than getting 9 mpg for the next 7500 miles.

I was clipped in a gas station by a semi last night and the pipe and some of the coroplast was broken last night. It had to be removed, so for the next 3000 or so miles, back to stock unless I get some time tomorrow.

The bottom was flush with the bottom of the trailer, but the top was not as to allow the hinges to fit there. Again quick and dirty. I also didn't want to cover the upper marker lights.

I encountered a problem that you may know about. When the boat tail (or whatever its should be called) was installed, when a vehicle passed by, or I passed a vehicle, the truck would be pushed slightly towards the passing vehicle. After it was removed, that didn't happen.

By the way, the sides of the unit were pulled lightly in towards each other. Its probably hard to see from just the one picture.

So, if I did get a chance tomorrow to put another one together, how should I make it? Flush with the top, flush with the bottom? More of a point? It was about 36" from the trailer and I did pick up some LED tail/turn signals to be legal.

Thanks,
I will try and check back later tonight.

Rick

The pulling together is the airflow rushing between the trailers creating a vacuum.
This sounds crazy but, dont fight it. Let them pull together and they will seperate when the pass is complete.
fighting it will lead to sway and a potential comming together as the air flow destabilizes.

9MPG -12MPG ?
You should be getting better than that, although you are going 75MPH.
I get 12-14 with that thing V

[euromodder]

Originally Posted by Braebyrn

I also put on a front air dam and side skirts that is about three inches from the ground. With those mods, I went from 9 to 12mpg towing the trailer.

It doesn't look very impressive in mpg, but in metric lingo you've gone from 26.1 L/100km to 19.6 L/100km, saving 6.5 L every 100km.

You've taken a compact car off the road with these mods.

[Braebyrn]

Originally Posted by JasonG

The pulling together is the airflow rushing between the trailers creating a vacuum.
This sounds crazy but, dont fight it. Let them pull together and they will seperate when the pass is complete.
fighting it will lead to sway and a potential comming together as the air flow destabilizes.

9MPG -12MPG ?
You should be getting better than that, although you are going 75MPH.
I get 12-14 with that thing V

Well about the only thing to fill in the gap on my setup is to put a flexiable connection between the truck and the trailer. Something that is on springs or maybe surgical tubing imbedded in a vinyl wrap. That way there is no drag behind the truck.

I tend to drive 64 at the most even when the speed limit is 75. Seems to get the best right around 60-64 now with the new parts I put on the truck.

Funny thing is when just driving the truck, I am getting around 21mpg on the highway at 60. Thats with the air dam, side skirts and mods on the bumper and grill area.