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

[orbywan]

Originally Posted by aerohead

According to Sighard Hoerner's book,your AC unit,with fairings should now be down around Cd 0.07.There is nothing lower out there.Sweet!

Thanks Phil,

I have another question if I may. I'm making good progress with the belly pan but I'm not sure how far to drop the front air dam down from the original bumper. Since this is a flat wide surface, I'm aware I'm creating drag with this, so I'm guessing getting the height of it right is muy importante.

Eyeballing it, I'd say no more than 4 inches from the bottom of the bumper/stock mini air dam, do you (or anyone) have an opinion on that? Thanks.

Rod

[aerohead]

Originally Posted by orbywan

Thanks Phil,

I have another question if I may. I'm making good progress with the belly pan but I'm not sure how far to drop the front air dam down from the original bumper. Since this is a flat wide surface, I'm aware I'm creating drag with this, so I'm guessing getting the height of it right is muy importante.

Eyeballing it, I'd say no more than 4 inches from the bottom of the bumper/stock mini air dam, do you (or anyone) have an opinion on that? Thanks.

Rod

Rod,the SAE warns us not to hang any fixed structure so low that it falls below an imaginary line angled up at 16-degrees from the point where you can first see daylight in front of the tread of the front tires.
If below,on a straight approach to a driveway ramp it would be likely to experience a ground-strike.Ouch!!!!!!!!
If your bumper is not a 'wrap-around',with as much corner radius as the nose of the RV,this would be an area for an improvement.Then the airdam itself could have the same 'wrap-around' feature.
As to the depth at which increased frontal area of the airdam starts to erase drag savings,it might be something you'd have to experiment with.
CAR and DRIVER's Crisis Fighter Pinto had about 3-inches of ground clearance.
Bondo fabricated a fabulous composite airdam for his F-150,but did have to trim it upwards a bit due to a loss in mpg.
The rubber lip on my T-100 actually flexes back and scrubs the sidewalk when I pull up to a curb.It's at about 6-inches.
Ford's Probe-IV had an 'active' front dam which lowered to within 3.25-inches of the ground at 45-mph.
The Bugatti Veyron is doing something similar.
In California,the CHP will pull you over if anything is lower than the bottom of the wheel rim.
Some Bonneville cars have zero clearance on their airdams.Side skirts ditto.
It kinda a can of worms!

[orbywan]

Originally Posted by aerohead

Rod,the SAE warns us not to hang any fixed structure so low that it falls below an imaginary line angled up at 16-degrees from the point where you can first see daylight in front of the tread of the front tires.
If below,on a straight approach to a driveway ramp it would be likely to experience a ground-strike.Ouch!!!!!!!!
If your bumper is not a 'wrap-around',with as much corner radius as the nose of the RV,this would be an area for an improvement.Then the airdam itself could have the same 'wrap-around' feature.
As to the depth at which increased frontal area of the airdam starts to erase drag savings,it might be something you'd have to experiment with.
CAR and DRIVER's Crisis Fighter Pinto had about 3-inches of ground clearance.
Bondo fabricated a fabulous composite airdam for his F-150,but did have to trim it upwards a bit due to a loss in mpg.
The rubber lip on my T-100 actually flexes back and scrubs the sidewalk when I pull up to a curb.It's at about 6-inches.
Ford's Probe-IV had an 'active' front dam which lowered to within 3.25-inches of the ground at 45-mph.
The Bugatti Veyron is doing something similar.
In California,the CHP will pull you over if anything is lower than the bottom of the wheel rim.
Some Bonneville cars have zero clearance on their airdams.Side skirts ditto.
It kinda a can of worms!

I'm not sure I understand that first paragraph, but that's OK because I get the rest and that tells me what I need to know. The first one is going to be made out of coroplast so I find out what height works and if it adversely affects the mileage, and if it scrapes. The pan is coming out sweet so far so I think I'm only going about 3 inches down from what's there now.

I'd say belly pans are kind of a can of worms also. Lots going on under there. I'm glad I did this even if the mileage doesn't go up that much, I found several 'issues' under there I wouldn't have noticed otherwise. Like a 3/4 inch wiring loom laying right on the exhaust down pipe. It's a miracle it didn't fry the whole thing. I also discovered it's time to replace all the bushings in the front end.

Most amazing discovery of the belly pan process so far? 5/16's hex head self tappers drill through frame and sub frame no problem, faster than a new titanium drill bit. Amazing. Anyway, thanks.

[orbywan]

The first stage of the belly pans is finished. If you'd like to see the results go to the first page of 'Aerodynamics' and click on 'Aero RV Belly Pans'. Thanks.

[JasonG]

To clear up some of the above,
Draw a line from where the tires hit the ground at 16deg. Don't hang nuthing there.

Normal thinking is stop the air dam level with the lowest hanging thing under there. Probably the bottom of your axle.

Self drilling sheetrock or lath screws go right through heavy truck bumper steel too !

I'm working on a similar dam here : http://ecomodder.com/forum/showthrea...dam-18663.html

[orbywan]

That looks really good Jason. I'm going to finish out my belly pans and test it again, then add an air dam so I know if it's helping or not, but I'll check this out at Lowes. I think you might be a little low in the front but what the hell do I know? If a push comes to too many scrapes you can always trim it at the next line in the flashing. Looks good.

[orbywan]

Originally Posted by JasonG

To clear up some of the above,
Draw a line from where the tires hit the ground at 16deg. Don't hang nuthing there.

Hey Jason, does the 16 degree rule apply to wheel fairings as well? Front of the wheel and behind the same wheel? Anybody know? Thanks.

[orbywan]

Now that it's cooling off I've started on the RV again. Below are photos of the right front area, mostly, on the front end, which has to be a serious vortex and turbulence generator.

So far I've built a template out of coroplast, which will be transferred to clear acrylic as soon as the plastic house cuts the piece. The parts for my extended hitch finally got here yesterday so I'll build that and drop the floor of the boat tail and vent the belly pans and then do a mileage run before I add the right side acrylic cover so I can see if I did any good on the belly pan and the rear floor of the tail.

I may take aeroheads suggestion and build a diffuser to drop the rear down instead of rebuilding the floor. It will depend on how the hitch extension goes. A drop down diffuser would be cool, because if I build it right and I accidently drag the tail, it would just fold up to accomodate the dragging and then pop back down.

The smoke generator should be here soon, that will be fun to play with. It will be an interesting winter. Winter is great here. Makes up for frying your brains out for 5 months out of the year.

[JasonG]

Originally Posted by orbywan

That looks really good Jason. I'm going to finish out my belly pans and test it again, then add an air dam so I know if it's helping or not, but I'll check this out at Lowes. I think you might be a little low in the front but what the hell do I know? If a push comes to too many scrapes you can always trim it at the next line in the flashing. Looks good.

I figured if using the pavement to trim worked for dave, it would work for me

The only thing I scrape on is the occasional curb when parking. Most of the time I back in anyway.

[93Cobra#2771]

Any updates?