"Wind Vane" boattail

[j-c-c]

Originally Posted by freebeard

A two-axle big-*ass RV isn't a good test case. What other options?

• Plan taper abaft the rear axle with length added to preserve interior space
• Twin-tail flaps rather than a boat tail
• Active Coanda nozzles.

Explain why an RV as described is not a good test case.

[freebeard]

Lack of plan taper, copious frontal area.

OTOH the boat tail would be half a block long so maybe it would be.

[j-c-c]

Originally Posted by freebeard

Lack of plan taper, copious frontal area.

OTOH the boat tail would be half a block long so maybe it would be.

So a truncated boattail (Kamm tail?) shorter than half a block would offer no benefits?

[freebeard]

Now your talking. An unhinged truncated boat tail?

There may be an opportunity to put air brakes on the sides of the truncation. Then they could be operated independently, on the lee side [or opposite?]. A-B testing would answer that question.

An air brake on a taper wouldn't have to increase the overall width so no taking out maiboxes.

[j-c-c]

Originally Posted by freebeard

Now your talking. An unhinged truncated boat tail?

This is my thread, I want it hinged.

[freebeard]

So.... airbrake flaps would have two hinge lines.

Needs a pic. If you truncated and hinge the boat tail, on a vehicle body with "two axle, large relatively rear overhang applications with "average" drivers in cross wind situations" wouldn't the result be a rear wall or cavity that faces to the left or right?

Originally Posted by aerohead

I'd first want to verify the threat posed by crosswind and gust.

Opportunity or threat? Enquiring minds.

[j-c-c]

Yes, but the "flap" would hinge (freely, but damped an amount TBD) to seek its own equilibrium for whatever crosswind is present, and also reduce side area to be effected by crosswinds, all the while reducing drag, hopefully.

[freebeard]

I would trust aerohead's scrutiny.

[aerohead]

Okay, so we're limiting the discussion to either tongue-pull, or fifth-wheel, dual-axle RV travel trailers?
Since I only do computer twice a week, I'll throw out some general comments, in hope that they're germane to j-c-c's crosswind concerns:
1) Since there exists no commercially-available boat-tail technology available for 'any' type of RV in the marketplace, I'm still perplexed a bit about the issue of crosswind effects associated with 'rigid' boat-tails.
2) Commercially-produced, single-axle, boat-tailed RV trailers like the Teller-Bowlus 'Papoose' and 'Road-Chief' are reported to be extremely stable platforms when towed.
3) The up-coming, LightShip L1, with an 81-inch boat-tail, has been thoroughly aerodynamically engineered. We can await third-party test reports, as those with access to this trailer make observations available.
4) Anyone interested in adding a boat-tail to any trailer would be highly encouraged to 'clean-up' the trailers forebody, with the addition of some sort of gap-filler, as seen with 18-wheelers, BamZipPow's single-wheeler, some of my monstrosities, and now, LightShip 1L's example.
5) The addition of this forwards 'aerodynamic mass' would compensate for the aerodynamic mass added by the following boat-tail.
6) A boat-tail can only be effective if the onset flow coming to it is already turbulent-free.
7) It follows that, any potential aerodynamic yaw-moment induced at the 'rear' by the tail, would be offset by an opposing induced yaw-moment above the tongue on a tongue-pull trailer.
8) Fifth-wheel trailers attach nearly directly over the rear axle of the tow vehicle. Other than a roll-moment, which 'can' tip a rig over, because of their sharp upper side-to-roof intersections, I'm unsure whether or not forward yaw effects are even experienced. Around 15% of the trailer weight is added to the static weight already acting downwards on the rear tires.
9) I've pulled fully-boat-tailed trailers equivalent to coast-to-coast across the USA, experiencing up to gale-force crosswind in the Texas Panhandle, Phoenix, Arizona haboob wind storms, and been inside large dust devils near Tonopah, Nevada without event.
I'll await further information.

[freebeard]

I'll await further information.

Thanks but my reading of the remit is: "My concern and focus was geared more towards typical RV two axle, large relatively rear overhang applications with "average" drivers in cross wind situations.'

Sound like a singular motor home or pickup camper.