Building a wind deflector

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MoInEd said:
I wonder how much an average person would pay (in $$) extra to have a better design of the trailer that would cut gas consumption, say by 20% or more....
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Have a look at Airstream trailers. A lot of dollars for the aerodynamic benefits.
 
Hi. The perfect shape is a teardrop, big in the front and a tail in back to reduce back pressure or vacuum. The airstream trailer comes close. I have installed air tabs on the back edge of my apex 194 which claim to be vortex breakers, similar to dimples in golf ball. They claim 5%. I Saw maybe a reduction from 22 lp100 km to 21.5, which is maybe 2%. As said in the postings, the square rears cause the majority of drag. Many of commercial wings have builtin flow disrupters builtin.

1.5 l p 100 km improvement is actually fantastic.

I am looking for improvements to extend my range. I have a 26 gallon tank- 20 usuable gallons. I have taken off my KO2 LT tires and switched to Michelin LTX series tires.



Keith
Retired Mech. Engineer
2015 Tundra, Forest River Apex 194
22 litres per 100km or aprox. 10.7 mpg at 60 mpg.
 
KeinNWO said:
Hi. The perfect shape is a teardrop, big in the front and a tail in back to reduce back pressure or vacuum. The airstream trailer comes close. I have installed air tabs on the back edge of my apex 194 which claim to be vortex breakers, similar to dimples in golf ball. They claim 5%. I Saw maybe a reduction from 22 lp100 km to 21.5, which is maybe 2%. As said in the postings, the square rears cause the majority of drag. Many of commercial wings have builtin flow disrupters builtin.

1.5 l p 100 km improvement is actually fantastic.

I am looking for improvements to extend my range. I have a 26 gallon tank- 20 usuable gallons. I have taken off my KO2 LT tires and switched to Michelin LTX series tires.



Keith
Retired Mech. Engineer
2015 Tundra, Forest River Apex 194
22 litres per 100km or aprox. 10.7 mpg at 60 mpg.
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Lmao im at 26 l per 100 pulling my rig as per previous post i would say your tabs need some attitude adjustments lol
4l per 100 is less than $5 difference
 
Air Tabs are a brand name that stick on the side of the trailer. Gas mileage is nice, but want range, 4 hrs driving. At 60 mph..In northern Ontario I paid $1.50 per litre and gas stations can be more than 3 hrs apart.
 

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The problem with a deflector is that you need wind tunnel time to tune the design - the optimal design is rarely what is intuitive. You actually did extremely well to get 10% on your first try - less than 5% is more typical.

While frontal area resistance is a big factor, it's not the only aerodynamic consideration. For example, you have air flow under and alongside the rig, vortexes at the rear as air backfills, and a lot of turbulence along the roof where numerous things jut up. And then there are the non-aero factors like tire rolling resistance and dragging the extra weight up grades or accelerating it from a stop.
 
All good comments. My friend is actually thinking 10% is very good and thinks with improvement to the design it can get higher. As I said, there are commercial products for this purpose but from what I read their efficacy is lower. If there was a way to reduce the gap between the deflector and trailer significantly I think it would help a lot.

I agree there are a lot other factors. I thought about improvement to the front shape of the trailer but that's more difficult. As I said, when loaded up (both trailer and car) the consumption is around 21-22L/100km, so a 10% reduction there would be interesting.
 
KeinNWO said:
Air Tabs are a brand name that stick on the side of the trailer. Gas mileage is nice, but want range, 4 hrs driving. At 60 mph..In northern Ontario I paid $1.50 per litre and gas stations can be more than 3 hrs apart.
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Last May we pulled through from Calgary to London we were warned about the lack of stations and them being closed because of Covid we took 2 large jerry cans to be safe. Ended up using them east of Medicine Hat bucking a fierce head wind lol
 
So this past few days I tested the wind deflector in the first real camping trip: 700+km (350 each way) to Rockies. Typically I average about 22L per 100km going (fully loaded and the elevation increasing) and around 18-19L per 100km coming back home.
This time I got 17.8L per 100km going and 16.3L per 100km coming back home.
That's a much better fuel efficiency than my simple 40km test run (with unloaded trailer). It's around 15-20% drop in consumption and is in line with what I had hoped for.
 
The key is going to be consistency. I pulled my trailer to drumheller 2 weeks ago used 1/2 tank of fuel pulled it home used a 1/4 tank
Then i pulled my trailer to lethbridge and back the following weekend and home i used 1 tank of fuel in total, difference is lethbridge is twice as far away as drumheller .
So why such a difference? One is flat driving one is very hilly, one day was windy driving one day was not.
And driving to Lethbridge the speeds are higher but i used less fuel.
 
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Its too subjective
Front wind
Side wind
Tail wind
Flats of saskatchewan
Hills of northern ontario
Temperatures air and humidity
Ac on? Off?
Tire pressure
Barometric pressure

Cost? Materials a few hundred bucks
Time? $100 hr x 15 hrs at least
Fuel $1.16 -$1.40 liter

Study window? Several weeks/trips
 
Steve I understand what you say but this trip from Edmonton to Rockies I do at least 4-5 times each summer and the numbers have always been in the same range. The drop with the deflector was way more than a noise. Looking at it from an engineering viewpoint, the weight of my trialed is 2/3 of my tow vehicle yet when hooked up the gas consumption was more than 3 times normal. Most of it I suspect is due to the drag, I.e. head pressure of air (extremely bad shape of the trailer). So even a slight measure to reduce the drag should have noticeable improvement in gas consumption.
 
MoInEd said:
Steve I understand what you say but this trip from Edmonton to Rockies I do at least 4-5 times each summer and the numbers have always been in the same range. The drop with the deflector was way more than a noise. Looking at it from an engineering viewpoint, the weight of my trialed is 2/3 of my tow vehicle yet when hooked up the gas consumption was more than 3 times normal. Most of it I suspect is due to the drag, I.e. head pressure of air (extremely bad shape of the trailer). So even a slight measure to reduce the drag should have noticeable improvement in gas consumption.
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No offense my dad is an engineer charted recorded graphed everything and i mean everything - he still has mileage logs from our trip to San Diego in 1976 ( i love rummaging through them all and i have inherited the same phyco tendencies lol i love to compare) but until you are comparing environmental conditions which is why a wind tunnel comes into play your findings are inherently inaccurate. Please dont take me wrong i love the idea - but in order to work properly your defector needs to be much closer to the trailer ie mounted to the trailer to work but then you have the 3ft void between your audi and the trailer which causes drag.
Keep trying though and i will keep busting your chops till you get it right lol.
Like i said i loved those things as a kid they were supper cool 😎
 
Put the reflector in front of the camper. Getting the right angle with take time to test and adjust. Your sides are still getting hit by air going down the road. Your fighting a losing battle for minimal gain.
 
TheBar said:
I had a 3" bug deflector on my last new truck. It was almost vertical maybe 80 degrees is why I think it worked. At 40 mph it didn't do much but at 70 June bugs went up over the roof instead of splattering on the windshield. But the biggest shocker was behind a truckload of bricks. We saw a brick come rolling down the load then bounced and came directly towards the windshield at my passenger. He dove for cover but when the brick passed over the bug deflector it shot up over the roof. Luckily nobody was behind me. So air deflectors do re-direct air but they must increase drag to some degree. I would think the size and slope is critical to that balance.

Where a Class C cab roof meets the curved underside of the cabover bunk has to be a wind trap. This conversation has me thinking a bug deflector at the front of the hood might direct the airflow higher to the sloped front of the bunk and eliminate some drag. A 3" deflector has to cause less drag than that 12" air trap.
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No engineer here but I agree. I believe the windshield from tow vehicle already deflects a huge amount of air up and over the trailer.
 
Thank you for this post. I will be copping your design as I tow an R-pod with a VW Atlas. We towed a 1972 Apache hard side pop up that weight #2000 for 15 years behind 2 Caravans and an 2018 Atlas. We got 18 mpg since there was very little wind resistance so I feel I have a good base line to go off of for weight vs mileage. Both the van and the Atlas got 22-24 mpg empty. I bought the R-pod last year and it weights #2500, so a good weight comparison with the old camper. I dropped down to 12 mpg on average with a 2000 mi trip to use as a base. Both the VW and Audi are the same vehicle just different badges this should be a good match. I know will never get the same mileage as I did with the pop up but I was hoping for 15mpg and this will help. The new vehicles are just as aerodinamic in the rear as they are in the front so the air slipping off the roofline goes down and has to fight it's way back up the trailer so this is as good of a solution as you can get. I've been a heavy truck tech for 32 years and have seen the changes in the industry and how much a little bit will save over the long run. Again thank you, you have saved me so much time in designing and texting this.
 

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