Aerodynamics / MPG increase - up 16%

[austin1989us]

Originally Posted by Tango

I never was very good at math, but with any luck at all, the diesel engine, tranny and rear axle transplants I have made should take me from about 5 mpg to around 25 at a cost of 15 grand.

So...how far do I have to drive just to break even at say $4 bucks a gallon. And...just how far is the Moon anyway?

When I moved back to Houston from Anchorage me and my dad drove it in a pickup truck in a week in May. Here's a fun fact about that road trip: when you make it to Calgary you're halfway there.

If you drove from Downtown Houston to Anchorage to Houston to Anchorage to Houston to Seattle to Houston to Albuquerque to Houston to Galveston to Houston you'd be at about your break even point.

[Tango]

Originally Posted by austin1989us

If you drove from Downtown Houston to Anchorage to Houston to Anchorage to Houston to Seattle to Houston to Albuquerque to Houston to Galveston to Houston you'd be at about your break even point.

Mmmmm...now that sounds like a fun road trip!

And since I sincerely hope to put at least a quarter million miles on this rig before I die, maybe it will all have been worth it!

[ol trunt]

Hey Tango. At 60 mph, eight hours a day you should be able to reach your 1/4 mil in just a little under a year and a half. Easy peasy and well worth the effort. Its not the drive time that worries me though, its the build time -- better get cracking.

Just having a little fun at your expense. I know a bunch of stuff has gone slow for you, but all of a sudden the whole project will come together and you'll be on the road. Jack

[Tango]

Originally Posted by ol trunt

but all of a sudden the whole project will come together and you'll be on the road. Jack

Let's hope Jack! I really need get some road time in.

[austin1989us]

Originally Posted by Tango

Mmmmm...now that sounds like a fun road trip!

And since I sincerely hope to put at least a quarter million miles on this rig before I die, maybe it will all have been worth it!

How much longer do you have left? At 1,000 miles a month that'll take nearly 21 years.

It took me about 12 years to put a quarter million on my truck.

[100MPG]

Originally Posted by somewhereinusa

Putting aside that it's a really stupid thing to do for all of the safety reasons, you are STEALING fuel mileage from the guy in front.

not true. it helps reduce the drag from that vehicles air flow.

[roach711]

I was a fairly rabid bicyclist for many years and learned a lot about aerodynamics. First of all, air is a fluid, just like water, and behaves the same way. Imagine you're walking in a pool of waist deep water. It's obvious that you're pushing a wave in front of you as you push through the water, but what's not so obvious is that you're also sucking water in behind you to fill the hole you just made. Positive pressure in front and negative pressure behind.

This means that you not only have to force your way through the water but you also have to overcome the "suck" behind you. Moving through air works the same way. That's why real aerodynamics (as opposed to styling that looks aerodynamic) involves both ends of the vehicle. A water drop or a bicyclists time trial helmet are perfect examples of good aerodynamics; both have a smooth, rounded front to ease through the air and a pointed tail to gently close the gap behind. Ford wouldn't sell many cars that look like a time trial helmet though.

As far as drafting is concerned, the lead vehicle has "paid" to pass through the air and you, as the drafter, want to get into "the suck" behind it and be pulled along by that negative pressure zone. As many here have claimed, that works quite well for the drafter and doesn't cost the draftee any more. In order for both vehicles to benefit, the rear vehicle would have to move right up to the front vehicles' bumper and stay there, NASCAR style, essentially becoming part of the lead vehicle. Off the track in the real world, I don't think either driver would be very happy with that.

Driving in normal speed, close packed freeway traffic puts you into a forced draft just like a pack of cyclists. All those vehicles whizzing along together make a tunnel through the air which helps everyone.

Another thing cycling taught me is that wind resistance goes up by the square of the speed. That means that to double your speed you have to quadruple your power. Most cyclists can ride along at 10mph, many can hold 20mph, but even world class cyclists can't hold 40mph for any length of time. In general, (assuming no draft is available) freeway driving at minimum speed is just about ideal, fuel mileage-wise.

Vehicle weight costs you when changing speed (accelerating from a stop or changing speed) and when going up hill. Once up to speed on a flat road vehicle weight doesn't matter much. That's why freight trains are so fuel efficient.



Another study I saw showed that steady throttle is better, mileage-wise, than steady speed. Many people use cruise control to get steady speed and that works fine on flat roads, but in hilly areas it's better to let vehicle speed drop on the uphills and rise on the downhills, especially if there is another hill ahead. Obviously, in traffic this wouldn't be very practical.


I've been drafting 18 wheelers and winebagosauruses for decades. I stay about 2 seconds back from the lead vehicle and have never had a problem. In our cars and vans fuel mileage went up by a lot but so far with the bus I'm not seeing the same benefit. Not sure why.

[REDD]

...pretty sure you weren't drafting these, hehehe

[roach711]

There was a guy in our racing club that had a bike sort of like that. He was a big guy and could really roll the flats and the bike put him way up there so he made a BIG hole in the wind. Whenever he brought that bike to our training sessions we all fought to be the one right behind him on the road.

[cowlitzcoach]

I drove a bus from MI to WA one time.

As I was going across IA, NE, and WY I would try to draft as much as possible.

The bus had a top speed of 67 MPH and would slow down on just about any sort of grade.

Drafting behind big trucks I was able to maintain 65 MPH without having to be at wide open throttle. But as soon as a grade came up I couldn't maintain the truck's speed and dropped out of draft position.

I know it made a difference in fuel use but I didn't do enough drafting over enough miles to know for sure what the difference in fuel use was.

What I did know is many miles at less than full throttle was a lot easier on the ears.

[Tango]

Drafting works on most Formula race bikes too. But no way I would want to stay that close on the highway.

[Tango]

Drafting works on most Formula race bikes too. But no way would I want to hang that close on the highway.

[magnakansas]

Drag coefficients are calculated a number of ways none of them are exact on paper. Some test methods are better than others. Length comes into play also.

example two buses, one a 24' short bus and one 35' bus. same nose, same body other wise. I would expect the longer bus to have better drag numbers.

The trailing side is most important. Do you see many fish with flat butts? Some whales and dolphins have pretty blunt noses/fronts, but not flat cut off rear ends.

I bought the 1954 wayne because of the rounded tail end. I wish the front window was sloped more, but I am not going to redo that can of worms. I have enough to get done already.

I am trying all I can do setting up the drive train to keep engine rpm low as possible in top gear, and at peak torque in the gear below top gear.

When you put an under tray on a bus that never was designed for one, you can create heat problems for the engine/transmission. In my case, the front radiator/engine/transmission, need enough air to keep cool. When you under tray, you also need a place for the air to get out. smoothly.

The turbulent air is the bigger hurt. Low speed aerodynamics testing is easy with scotch tape, pieces of yarn 8" long and a trip down the road. Place tape in the middle of the yarn and stick it to the bus. Do this where ever you want to see what the air is doing. Best scenario is the yarn blows towards the back of the bus. Worst is when the yarn blows to front of the bus.

After you learn what the air is doing, then you can begin to decide how to shape the air.

If you can under tray front to back I don't think an air dam will do much.

If you can't under tray then put a deep air dam and cut off one inch at a time and then test. Keep the air dam (frontal area) as little as you can and keep full benefits of the air dam.

Disc covers - smoothies - on the rear duals will help.
Short wheel nuts on the fronts will help.

When you have an area of the yarn going all over the place, that is an area to put stuff were aerodynamics will not matter much. Like a CB antenna, Marker lights, door handles, mirrors.

I expect to find trapped air built up under the hood of my 1954. Getting that air out will help cooling engine transmission.

I already know I will use side cameras, do something different about the big turn signals sitting on top of the fenders, under tray, and something to blend the bottom rear air back up to the air flow.

I will probably make side skirts for the rear wheel wells, I have been looking at some of the old buses that have what looks like rear fenders about an inch deep on the sides... I would like to graft those on, with fender skirts. They will look neat painted a contrasting color and the skirts will go better with that look. Kinda like the rear on a Cord 812

One thing I will try is to put a tear drop on the front beam axle. The profile will look a lot like a wing strut if I can do it.
Some sort of taper tail behind rear duals. A fairing behind them will get shredded if a tire fails.....

If you have an inner fender liner for wheels and keep the liner as close as you can to the tire, that will help.

Rib tread tires are better than tires with lugs. Tires with deeper tread are worse ... for aerodynamics, nother whole story bout hydroplaning, or light snow/slush conditions.

Skinny better than wide for aerodynamics. I want to run 225 70 19.5, for less engine rpm, I am going with 245 width. The wider tire also weighs about 25 lbs more, or 150lbs more for all six.

Front radiator buses, an air dam may aid in cooling. The air dam may help to lower the pressures behind the radiator. For that to work, you have to effectively "seal" areas on the front to reduce air flow around the radiator, make the air go through it.

From testing on road cars, I find, at about 35 mph things start to change with air flow, many cowl induction hoods don't seem to do any thing below that point and do what they need to above that point.

Law of diminishing returns. Target the big stuff first. You get to a point where the time, effort, money don't seem to gain much.

NACA ducts are designed to be effective and low drag, They have a very specific profile in order to work well. Coolers, engine oil, engine coolant, transmission coolers, could be all ducted so that they will add energy to forward motion if very well designed. Most of us will never be able to do it. probably not worth effort, because if you get it wrong enough you will over heat stuff that is expensive to repair.

I am pleased to have found this thread. I hope that somebody else finds what I have written, interesting.

william

[cowlitzcoach]

William, it appears as if you have really thought things through on trying to minimize the coefficient of drag for your bus.

The basic problem is a bus is a big brick shape that by design is very un-aerodynamic. Some buses are notably better than others. Your rounded '50's vintage Wayne it going to be much better than the later Wayne Lifeguard bus bodies that were the definition of square box.

I am not sure exactly what you mean when you refer to under tray.

I am going to assume you mean stuff hung under the sides of the bus.

The smoother you can make the side profile the slippery-er the bus will be.

Having all of the bottom of the lower skirt the same depth will help with making the air flow smoother.

[magnakansas]

imagine, if you will the entire bottom of the bus smooth, no axles, drive shafts, exhausts, exposed. The side mirrors add drag. The rear axle housing, shock absorbers all are licked by the air stream, they add drag. So, if I could I would make a horizontal plane as low as the rear axle, front axle to get them out of the air flow. If that would be practical. I am supposing the front axle on my f450 chassis is going to be too low to be practical to smooth over, so I will attempt to put a fairing on it.

[ennonne]

Have you read this thread:

http://www.skoolie.net/forums/f13/ae...ics-18789.html

In that thread, I posted a link to the "AeroRV". He saw some impressive gains in economy with a boattail. All kinds of good aero stuff at that site if you poke around.

[RoadRallyBus]

I just drove our Skoolie (E450 Bluebird conversion) from the South Coast (Houston) to Niagara Falls. We did about 500 miles per day for 5 days including the Chesapeake causeway. Next trip is from East to West. I have a few years of fluid dynamics modeling. 1) Add air dam to front bumper. 2) AVS bug deflector to front hood (this will help deflect air over the windshield). 3) Diffusers across the front windshield and back of bus. Golf balls have dimples to make them go farther and faster. Diffusers do the same.