Bernoulli Effect

[Gerdo]

If i'm getting this right, your vent sucks air out even when closed. Is it designed to do this? If so it is sucking water and dust into your TD, right? If it is designed to allow air out even when close then you are going to need air inlet vents that are water and dust proof. Maybe some kind of filter. (furnace filter, auto filter, kitchen stove vent filter) It sounds like you want to keep air moving so you don't want to seal it for travel.

[SteveH]

Bernoulli effect....yep, that's what I was counting on when I designed the profile of my teardrop. By my calculations, and they are extensive, at about 92.5 MPH, the speed at which I travel the most, my trailer becomes weightless and then my gas mileage gets really good.

[Joseph]

This would explain why I get water inside when towing in the rain but not when standing still. Who knew?! Not that I'd do without my FanTastic vent, but still...

Steenkin' science!!

Joseph

[GPW]

Gentlemen , you have replicated a giant airfoil section and for the most part , a flat bottomed airfoil which is very "lifty"...a semi-symmetrical section would be better , lessening the pressure differential between top and bottom , Fully symmetrical shaped TD would easily slip through the air without these effects .. air dam on the front bottom or the TD would help...Re-design is the answer... I love the basic TD shapes (CLASSIC) but impractical at Taladega.....

[jagular7]

Your tow vehicle has vents. Nowadays, do to the way the vehicle is designed to cut through the air, there is more turbulence with open windows than closed. All vehicles have some kind of vent. Imagine the pressure inside when sitting in a hot sun. Or the vacuum created on a chilly day. There has to be a vent system. Most new vehicles have vents in the lower areas behind the plastic bumper covers. Some are located within the door area. All these areas are not prone to turbulant air and debri. These areas are usually overalapped with sheetmetal (like door edges) or bumper covers. Pressure doesn't really care where it balances out.
Paul, you pull with a Toyota? Check the door jambs of the Truck. You should see some vents within the door and door frame. This is where the interior balances the pressure to vacuum. I think there might also be some in the back of the cab in the lower area.
About the only way to balance the pressure/vacuum within the TD is to provide a vent system. The system doesn't have to have the in-vent and out-vent right next to each other.

[angib]

Paul,

My two thoughts are:

- If you are getting too much suction/airflow through the trailer, can you block off part of the vent?

- If you want to keep the current airflow, provide an inlet that doesn't give you the same problems - put a simple air filter over it, such as a piece of open cell foam and have it suck air upwards fairly slowly so that any rain drops out. It's a bit over-the-top as drawn, but a suggested arrangement is sketched below.



Andrew

[jimqpublic]

This discussion along with the recent one on aerodynamics AND the roofer's credo of "don't put holes in a good roof" got me to thinking. Generally a bad thing.

Anyway, make a smooth roof. No vents or holes. In fact I like the idea of a squareback with a tiny spoiler/overhang so the kitchen door/hatch is protected from the elements.

But I really love the Fantastic Fan in my trailer. Why not just mount it in the sidewall as a window. I know it would interrupt the airflow there too but the side already gets turbulent air. I'm sure it would work fine- on our Chalet the fantastic fan is mounted backwards and doesn't blow open as long as it's closed snug. Mounted in the sidewall it would even work nicely in the rain (in exhaust mode).

[Melvin]

I was thinking about putting a spoiler on my TD when I was building it to stop this very thing from creating lift on the back hatch at speed. I wonder if such a deflector closer to the top front radius of your camper would spoil the effect. It would be nice if Mike would go ahead and build a wind tunnel, we have a need to create data.

A spoiler that kills the suction is going to increase drag.

[GPW]

Jim , I'm with you on the clean roof thing ... howz' about a NASA vent on the side(s) ... with a fan would be streamline , act as a vent and just sorta' look cool .... No chance for leaky' on the roof either...

Mel ... it's all a compromise.. more drag , less dust , besides with gas prices falling , a little more drag won't hurt a thing ... better than all your stuff hosed with road dust .... ecch !!!

[GHOSTSSX]

NASA vent?? Please enlighten!!!

CHUCK

[GPW]

Years ago NASA engineers designed a simple vents , that we've used on airplanes for years ... too complicated to describe ... too simple to build ...looks cool too !!! I'll see if I can dig up some info ...Be back...

[SteveH]

I think you will find it under NACA vent. Here's one article on it:
http://www.recumbents.com/wisil/nacaduct/naca-duct.htm

Used to build them as parttime work for a "friend".

[jimqpublic]

Ah, yes. When I used to ride motorcycles some of the BMW fairings had such a vent to reduce turbulence to the rider.

For the TD though we don't want it to ventilate while driving. It would look cool though.

[Melvin]

Paul,

My two thoughts are:

- If you are getting too much suction/airflow through the trailer, can you block off part of the vent?

- If you want to keep the current airflow, provide an inlet that doesn't give you the same problems - put a simple air filter over it, such as a piece of open cell foam and have it suck air upwards fairly slowly so that any rain drops out. It's a bit over-the-top as drawn, but a suggested arrangement is sketched below.



Andrew

Lots of modern cars use an airbox for engine air of exactly this construction. Look around junk yards for something easy to use about the size you want.