Big project-F250 pulling 20x8.5 enclosed trailer

[Christ]

Phil -

Trying to help out, I looked through a few of your old posts.

You've got this post here:

Originally Posted by aerohead

1986 SAE Paper 860211: 4.25-inch minimum radius needed for attached flow at leading edges,vertical or laid-back nose lowers Cd by 0.01

For those interested, the arrows next to the username redirect you to the original post.

[Christ]

Also this:

Originally Posted by aerohead

When I posted this originally,I forgot an important tidbit.In most fluid books of my day,the example of E.Moeller's work on the nose of the 1951 Volkswagen Van was always cited.The Volkswagen began quite literally as a "brick-on-wheels" with a drag coefficient of 0.76.With some clay,Moeller sculpted the front of the Volkswagen with generous radii,and the Cd dropped to 0.42.With the exception of the HUMVEE,there are no current production vehicles that possess square leading edges.Today,the example of the VW serves to demonstrate the significance that a little softening of leading edges has meant in the meantime.

And googling found me this:
http://www.scribd.com/doc/20056364/I...Carried-Out-To

Which makes reference to an empirical front end design by Hucho and Janssen, and the refinement testing involved.

I can't find a site that gives any Hucho - specific info without costing me the purchase price of the book...

[aerohead]

Originally Posted by Christ

Also this:



And googling found me this:
In This Chapter the Modifications That Were Carried Out To

Which makes reference to an empirical front end design by Hucho and Janssen, and the refinement testing involved.

I can't find a site that gives any Hucho - specific info without costing me the purchase price of the book...

In the FLOW-IMAGES galleries,there are some color shots of the VW Rabbit which Hucho,Jansen,and Emmelman were involved with.There is also an overhead ( plan view ) of the Rabbit nose in smoke.
You can see what little radius is required to prevent separation.
One of the SAE papers reported 80-mm in full-scale for leading edges.I think that translates to 4 and a fraction in inches.
But there is a formula,something like 0.03 X width = R.
I didn't expect to be here today but we finished early in Dallas and I got in before traffic formed.I'll try and remember for next time.

[slowmover]

"What other easy things can I do to help out. Been reading a lot, but not sure where to start".


Maybe you know all this and have already done it. These are the "is it plugged in" questions.

The cheapest is driver. 8-mpg average is a gas motor average for that rig weight and shape. 11-12 would be reasonable. The truck industry average between best and worst drivers, controlled, is 30%. Only thing that matters is on-time for cheapest cost. First guess is that you're driving too fast. Anything above 60-mph hurts too much, so keep speed down while in motion, trip plan all stops for fuel food (2-hours max), and pay closer attention to tire pressures/brakes/alignment and get the hitch dialled in.

Driving no more than about 10-under the limit on the Interstate (except in 55-mph states) keeps one out of the packs of cretins on the road. It is not only legal, but prudent. You have right-of-way, so use it. It also helps avoid lane changes, "brake tests" and allows you to pay closer attention to road condition, weather and traffic. Set the cruise between 58-62 mph. Widens peripheral vision as well. All to the good. The only measurement is how much fuel to move X-weight Y-miles. Speed hurts. Stopping/starting hurts more. You'll make it up by planning all stops in advance for rest/fuel/food. Every two hours, max. Plan your route for majority "truck designated" miles (Trucker Road Atlas). I'd rather travel an extra 15-miles on the Interstate than cut across town, for example. Avoid "scenic" and no-shoulder roadways. Discipline pays.

Fatigue sets in by 6th hour, and driver performance declines. So long as you are, overall, making 50-mph per tank of fuel you are good (use hourmeter). Anything over 600-miles per day is too far. Avoid any night driving if at all possible (respect civil dawn and civil twilight). Fatigue -- as you already know -- tears up performance. Zero idle time.

As to tires do not inflate to maximum (a mistake) but optimize to load. Tires pressure/temperature takes 1.5-hours of steady state driving to stabilize (a tire consultant tells me), so look for an ideal rise of only 3-psi after that point. 5-psi is okay, but one can come down a touch. Find out what is best for your rig. Do not exceed vehicle manufacturers numbers for full load, front or rear on the truck. Tire sidewall numbers don't mean much. Need weight PER WHEEL to send an email to manufacturer to get recommended pressures. Work to fine tune from there. Same for trailer.

Alignment on BOTH truck and trailer axles should be set, tires wheels balanced on BOTH, shocks should be like new on BOTH vehicles, and trailer brakes should be perfect (not only in adjustment, but in measured voltage/amperage at each wheel drum). I've yet to see a recommendation for adjusting trailer brakes exceed 5,000-miles. And bearings usually call for maintenance at 3-5,000. I'd make them all perfect. Yours may be equipped with Nevr-Lube bearings, but at least do the brakes often. Personally, I'd re-wire both the truck power to the trailer, and the complete trailer brake system. They're never as good as they should be (unless they're disc units). Ideal brake performance means lesser/finer measured inputs by driver.

You need the weights of the truck and the trailer, separately, as well as both when empty and loaded. Also the trailer tongue weight. And then the rig as hitched. Proper hitch rigging is found less than 10% of the time studies show, going back decades. Use a CAT Scale. Have a look at both calculators and threads on RV.net to set up hitch. Look for posts by Ron Gratz over there. Use the formulas. Improper hitch rigging is not only a safety deficiency, but causes the front end to catch more air and worsens trailer response. Scale tickets are a deductible business expense.

Set up correctly you can drive with two fingers assuming a decent hitch (not the friction bar type). If not, more work is needed for adjustment (or, my preference, a better hitch). If you can get BOTH truck and trailer just slightly, just barely nose down it'll be a help (by actual measurement, not eyeball). Both before and after being hitched. If not, I'd modify the hitch receiver and ball mount if the usual adjustments don't work.

To start spending money I'd go first for a P3 or, better, a MAXBRAKE brake controller. Be sure trailer leads truck brakes slightly. Test in gravel, too, if you can (need observer to tell you which brakes are locking first). MULTI-VEX mirror inserts would be next (vision trumps everything else in towing), and then AIRTABS would be worthwhile as an experiment, as, anything that keeps trailer tail from twitching is worth trying. I would also try a front air dam on the truck (after blocking grille). The 2WD's I've measured -- Ford, GM and Dodge -- are all at least 7" of clearance with stock air dams. I've seen at least one extra deep sheet metal air dam retrofitted. 4WD's sit way too high so it might help. Be sure the accountant sees any of this for deductions (repairs/maintenance, etc).

Get tires optimized for on-highway performance next time you need some. Never seen any complaints about MICHELIN and I average above 80,000 per set with mine. (And get a real wheel and rotate the spare in and out. Use no patched tires to tow with, make that one the spare).

See if you can't find a used HENSLEY ARROW hitch for sale (better, a PRO PRIDE). The difference is amazing. It's some bucks, but if times get flush I couldn't recommend anything to make a larger improvement in the overall performance of the rig. PULL RITE is slick as well. The "easier" your rig is to drive, the more time/attention you can give to the tiny adjustments to keep efficiency high.

I averaged 15+ mpg with a 34' 7,500-lb trailer at 63 mph. Could have broken 16 by slowing slightly. I averaged 19 with a 12-foot 6x6 enclosed trailer at around 3,800-lbs. Granted, both were "aero" trailers in comparison. Yours is "ugly" for fuel economy. Look forward to your experiments.

[aerohead]

Originally Posted by aerohead

In the FLOW-IMAGES galleries,there are some color shots of the VW Rabbit which Hucho,Jansen,and Emmelman were involved with.There is also an overhead ( plan view ) of the Rabbit nose in smoke.
You can see what little radius is required to prevent separation.
One of the SAE papers reported 80-mm in full-scale for leading edges.I think that translates to 4 and a fraction in inches.
But there is a formula,something like 0.03 X width = R.
I didn't expect to be here today but we finished early in Dallas and I got in before traffic formed.I'll try and remember for next time.

Boy! I wasn't even close! My memory is FUBAR.
Hucho has two reports:
the first occurs on page 181.A table is presented and the formula presented is Radius divided by the square-root of the area of the face you're streamlining.The minimum drag occurs for values around 0.4.

The second reference is on page 423,Figs 11.25 and 11.26.The drag relationship is for radius divided by width ( which also happens to be the height) and minimum occurs in the neighborhood of 0.06- 0.10.

[KamperBob]

Originally Posted by 5.0 Junkie

I haven't gotten a chance to tow it much yet. I'll have a whole week full of it coming up.

I have a commission only sales job and needless to say, things are pretty rough now. Gauges are on the list.

7500# isn't much for the truck, but it pulls like twice that due to pushing so much air.

Junkie, I tend to agree with slowmover. Let's sort out your drag factors. When you say 7500# that's the GVWR right? What is your scale weight? More importantly, how fast do you drive when towing?

The single biggest factor is you. You may have some bad habits you don't realize. Powerful trucks happily do whatever you ask. They don't sass. They just guzzle and go. Once you have ScanGauge feedback, I bet you will start seeing improvement just because you're paying attention to what it is you care about optimizing.

One more question. How attached are you to this truck and to this particular trailer? Is there possibilitiy of trading either one for something else?

Cheers
KB

[DON-BUR]

Originally Posted by botsapper

My aero mods on the trailer package. Must first address the truck fairing. There is a retractable hinged top to serve as a bow fairing. Many truck cab designs use this retracting fairing combination. To seal off as much gap between the trailer & fairing, there is another cone fairing/storage on the top front on the trailer. An adaptation of Don-Bur teardrop profile is added on top of the flat trailer top. And at the end there are hinged foldaway panels that extend the trailer for your on road long-tail configuration. Front & rear spats for the bogeys, and wheel covers compliment the whole package.

Take your pick or add all of the aero treatments.

(Conceptual ideas only)

We are delighted that our Teardrop roof shape should reach the hallowed halls of Ecomodder; however, you should note that the Don-Bur Teardrop is protected under Registered Design 000709423-0001 and patent 0707243.2.

You may ask - "hasn't this been done before with the Teardrop trailers being pulled behind cars?". The answer is that with the domenstic versions, the Teardrop shape encompases just the trailer. The Don-Bur Teardrop shape encompases the entire vehicle and, as such, forms a smooth curve over both tractive unit and trailer.

We will prosecute any individuals found to be infriging our copyright and/or patent.

Don-Bur

[5.0 Junkie]

Trailer axles weighed right around 7500# while hooked to truck. I just went over truck scales. Truck axles together were right at 8300#.

I am a Heavy Duty Equipment Specialist for Hunter Engineering. Needless to say, truck is aligned perfectly and tires were done on the latest balancer. They also had relatively low runout.

I drive around 65 most of the time. I have recently installed a custom tuned chip with a 60hp tow tune. Mileage is now around 9.5 most of the time. Chip helped some and slowing down a bit helped some too. The 7.3l gets decent mileage under 2000rpm, or 66mph or so. Above that and it starts dropping quickly.

I'm going to skirt the fenders on the trailer soon. I'm likely going to put on airtabs just to calm the trailer down. It is quite a handfull in windy conditions or around a large truck. I have a boattail design in my head and a framework to help out the front of the trailer. I am also trying to find the fringe material or similar to put on the lower edges of the trailer to see if that helps some.

I have a weight distribution hitch with 1 sway control. It is set up per instructions. What setup were you referring too and how would one of those other hitches help over what I have?

[MetroMPG]

Originally Posted by DON-BUR

We are delighted that our Teardrop roof shape should reach the hallowed halls of Ecomodder; however, you should note that the Don-Bur Teardrop is protected under Registered Design 000709423-0001 and patent 0707243.2.

We are equally delighted to be warned of potential legal consequences! (I think this might mean we've finally "made it.")

I realize you are only protecting your company's hard work, and having read this discussion know that the truck/trailer owner hasn't expressed any interest in redesigning the plane of his trailer's roof.

[5.0 Junkie]

Don't worry about me. I'll buy a hotshotter truck long before I ever attempt that.