Trailer wind deflector

More trailer-talk....

I have a Minden-Fab / Scheder-style trailer and tow with a 200hp V6
station wagon. The front "barndoor" of the trailer is about 1.5 to 2
feet higher than the roofline of the car. The whole setup feels draggy
on the road. 65 mph is about the limit before I feel like I am abusing
things. I get about 17 mpg with the trailer, 26mpg without. I plan on
a 3000 mile round trip this summer and with gas where it is, a few
more mpg would be nice.

I was wondering if it would be worth fitting a deflector to my luggage
rails near the back of the wagon to reduce the drag and increase my
mpg a few points (and my L/D would also go up too!).

I will can fabricate something from stainless sheetmetal that would
mount to my Thule rack. Any tips or guidelines on the form of such a
deflector are appreciated. Or is this a bad idea?

Thanks,
Adam

On Apr 9, 12:19 pm, Adam wrote:
More trailer-talk....

I have a Minden-Fab / Scheder-style trailer and tow with a 200hp V6
station wagon. The front "barndoor" of the trailer is about 1.5 to 2
feet higher than the roofline of the car. The whole setup feels draggy
on the road. 65 mph is about the limit before I feel like I am abusing
things. I get about 17 mpg with the trailer, 26mpg without. I plan on
a 3000 mile round trip this summer and with gas where it is, a few
more mpg would be nice.

I was wondering if it would be worth fitting a deflector to my luggage
rails near the back of the wagon to reduce the drag and increase my
mpg a few points (and my L/D would also go up too!).

I will can fabricate something from stainless sheetmetal that would
mount to my Thule rack. Any tips or guidelines on the form of such a
deflector are appreciated. Or is this a bad idea?

Thanks,
Adam

Long ago we experimented with putting a rounded lip around the front
perimeter of a Schreder trailer. As I recall there was some
improvement measured in our coast-down tests, but I don't recall how
much and it will depend strongly on the towing vehicle. I don't know
if anyone in the group has experience with deflectors on cars. You
certainly see them on Semi-truck rigs, but they may be more fashion
than function.

Craig

.... A moneymaker for the amazing Dr. Paul B. MacCready Jr. in 1977. See
http://tinyurl.com/3vetxj . --JHC

.... not to forget Dr. Peter Lissaman and the entertaining Jack Lambie.
See SSA Final Glide July 1999 (Bruce Carmichael note). --JHC

On Apr 9, 2:19*pm, Adam wrote:
More trailer-talk....

I have a Minden-Fab / Scheder-style trailer and tow with a 200hp V6
station wagon. The front "barndoor" of the trailer is about 1.5 to 2
feet higher than the roofline of the car. The whole setup feels draggy
on the road. 65 mph is about the limit before I feel like I am abusing
things. I get about 17 mpg with the trailer, 26mpg without. I plan on
a 3000 mile round trip this summer and with gas where it is, a few
more mpg would be nice.

I was wondering if it would be worth fitting a deflector to my luggage
rails near the back of the wagon to reduce the drag and increase my
mpg a few points (and my L/D would also go up too!).

I will can fabricate something from stainless sheetmetal that would
mount to my Thule rack. Any tips or guidelines on the form of such a
deflector are appreciated. Or is this a bad idea?

Thanks,
Adam

In Hoerner's book, Fluid Dynamic Drag, he shows that the drag
coefficient of a simple box shape can be reduced by about 40% (from .
86 to .46) by rounding all the corners with a radius of about .10
times the sides of the flat front and rea faces of the box.

A deflector at the front would be good. I think the back end is at
least as important, if not more so. Why? I have pulled a variety of
trailer weights and shapes behind my 1990 chevy van. The one that
give me the lowest mileage is the one with the biggest flat plate at
the rear. And in pulling some of the nice, low profile clamshell
trailers, I have actually gotten better gas mileage than normal.

I started a plan for fairings, etc, when I was doing all my trailer
pulling with a Camaro. Now that I have the van, I am less
interested. But, I still have things started, and templates for
making a fairing for the tail end of my "egg hauler" trailer. The
trailer has the cross section of an egg, about 6 feet tall and 4 feet
wide.

Try something, but keep this in mind. Even at $3.50 per gallon, and
going from 17 to 19 MPG,on a 3000 mile trip, this will only save you
about $65 in gas. So, you have got to make your fairings cheap or you
spend more than you will save.

Steve

"Adam" wrote in message
...
More trailer-talk....

I have a Minden-Fab / Scheder-style trailer and tow with a 200hp V6
station wagon. The front "barndoor" of the trailer is about 1.5 to 2
feet higher than the roofline of the car. The whole setup feels draggy
on the road. 65 mph is about the limit before I feel like I am abusing
things. I get about 17 mpg with the trailer, 26mpg without. I plan on
a 3000 mile round trip this summer and with gas where it is, a few
more mpg would be nice.

I was wondering if it would be worth fitting a deflector to my luggage
rails near the back of the wagon to reduce the drag and increase my
mpg a few points (and my L/D would also go up too!).

I will can fabricate something from stainless sheetmetal that would
mount to my Thule rack. Any tips or guidelines on the form of such a
deflector are appreciated. Or is this a bad idea?

Thanks,
Adam

Every time the price of gas gets high this subject comes up - and it's a
good timely subject with today's average price at $3.37 in the US and $3.75
on the west coast. Most expect over $4 by summer although you can find $4
gas now.

The power requirement, and therefore fuel comsumption, to overcome drag
varies with the cube of speed. Simply slowing down can accomplish more than
any aerodynamic aids.

Aerodynamics is important but so is weight. If you do any amount of towing
in mountains or stop and go traffic, weight becomes the dominant factor.
I'd suggest digging through everything you carry to see if it's absolutely
neccessary. Another important factor is tire pressure. I run my tires at
the highest pressure the tires allow.

Clubs might want to consider owning a "community retrieve vehicle" available
to retrieve any club member that lands out. This strategy means that
members don't have to each own a daily driver that's also a trailer towing
vehicle. I've always thought that the really big fuel cost isn't what you
spend while towing the trailer but what you spend driving that big vehicle
around on a daily basis. If this is too socialist for you, big used SUV's
are dirt cheap right now. Buy one and park it at the gliderport so it's
available for a retrieve. Big SUV's have excellent fuel economy while
they're parked.

Bill D

On Apr 9, 2:19*pm, Adam wrote:
More trailer-talk....

I have a Minden-Fab / Scheder-style trailer and tow with a 200hp V6
station wagon. The front "barndoor" of the trailer is about 1.5 to 2
feet higher than the roofline of the car. The whole setup feels draggy
on the road. 65 mph is about the limit before I feel like I am abusing
things. I get about 17 mpg with the trailer, 26mpg without. I plan on
a 3000 mile round trip this summer and with gas where it is, a few
more mpg would be nice.

I was wondering if it would be worth fitting a deflector to my luggage
rails near the back of the wagon to reduce the drag and increase my
mpg a few points (and my L/D would also go up too!).

I will can fabricate something from stainless sheetmetal that would
mount to my Thule rack. Any tips or guidelines on the form of such a
deflector are appreciated. Or is this a bad idea?

Thanks,
Adam

I am running on mostly flat roads. The rig feels just as draggy with
no glider in the trailer. Of course in the hills everything changes.

I ran a bunch of quick "what ifs" through my CFD program. What I find
is that a roof-mounted deflector reduces the drag about 12%. One
problem is that the deflector itself creates some drag so the total
net gain is not so great.

I then tried added a full round quarter-sphere to the leading edge of
the trailer, with no deflector on the roof. This made a bigger
difference in the LE drag, dropping 30%.

In total, the air drag reduction with this type of device could be
20-25% at 65 mph. My mileage could raise from 18 to 22 mpg best case,
saving me around 30 gallons or $100 over the 3000 miles. Probably not
worth it as Steve pointed out.

/Adam

That $100 is fuel only - add in the additional load on the engine and
transmission and the cost goes up. How much depends on what you drive.

Adam wrote:
On Apr 9, 2:19 pm, Adam wrote:
More trailer-talk....

I have a Minden-Fab / Scheder-style trailer and tow with a 200hp V6
station wagon. The front "barndoor" of the trailer is about 1.5 to 2
feet higher than the roofline of the car. The whole setup feels draggy
on the road. 65 mph is about the limit before I feel like I am abusing
things. I get about 17 mpg with the trailer, 26mpg without. I plan on
a 3000 mile round trip this summer and with gas where it is, a few
more mpg would be nice.

I was wondering if it would be worth fitting a deflector to my luggage
rails near the back of the wagon to reduce the drag and increase my
mpg a few points (and my L/D would also go up too!).

I will can fabricate something from stainless sheetmetal that would
mount to my Thule rack. Any tips or guidelines on the form of such a
deflector are appreciated. Or is this a bad idea?

Thanks,
Adam

I am running on mostly flat roads. The rig feels just as draggy with
no glider in the trailer. Of course in the hills everything changes.

I ran a bunch of quick "what ifs" through my CFD program. What I find
is that a roof-mounted deflector reduces the drag about 12%. One
problem is that the deflector itself creates some drag so the total
net gain is not so great.

I then tried added a full round quarter-sphere to the leading edge of
the trailer, with no deflector on the roof. This made a bigger
difference in the LE drag, dropping 30%.

In total, the air drag reduction with this type of device could be
20-25% at 65 mph. My mileage could raise from 18 to 22 mpg best case,
saving me around 30 gallons or $100 over the 3000 miles. Probably not
worth it as Steve pointed out.

/Adam

On Apr 9, 8:19*pm, Adam wrote:
More trailer-talk....

I have a Minden-Fab / Scheder-style trailer and tow with a 200hp V6
station wagon. The front "barndoor" of the trailer is about 1.5 to 2
feet higher than the roofline of the car. The whole setup feels draggy
on the road. 65 mph is about the limit before I feel like I am abusing
things. I get about 17 mpg with the trailer, 26mpg without. I plan on
a 3000 mile round trip this summer and with gas where it is, a few
more mpg would be nice.

I was wondering if it would be worth fitting a deflector to my luggage
rails near the back of the wagon to reduce the drag and increase my
mpg a few points (and my L/D would also go up too!).

I will can fabricate something from stainless sheetmetal that would
mount to my Thule rack. Any tips or guidelines on the form of such a
deflector are appreciated. Or is this a bad idea?


Speaking as someone who lives in the UK, it strikes me that a change
of tow vehicle could produce major fuel savings all the time. I mean
- 26mpg at best! My car is perfectly capable of towing my glider in
it's trailer at UK legal speeds, without the trailer it does almost
50mpg, with it it drops to low 40s. Surely similar vehicles are
available in the US?

BTW not sure if you are leaving the roofrack on all the time. Taking
it off when you don't need it will improve your mpg.

On Apr 11, 4:42*am, Cats wrote:
On Apr 9, 8:19*pm, Adam wrote:





More trailer-talk....

I have a Minden-Fab / Scheder-style trailer and tow with a 200hp V6
station wagon. The front "barndoor" of the trailer is about 1.5 to 2
feet higher than the roofline of the car. The whole setup feels draggy
on the road. 65 mph is about the limit before I feel like I am abusing
things. I get about 17 mpg with the trailer, 26mpg without. I plan on
a 3000 mile round trip this summer and with gas where it is, a few
more mpg would be nice.

I was wondering if it would be worth fitting a deflector to my luggage
rails near the back of the wagon to reduce the drag and increase my
mpg a few points (and my L/D would also go up too!).

I will can fabricate something from stainless sheetmetal that would
mount to my Thule rack. Any tips or guidelines on the form of such a
deflector are appreciated. Or is this a bad idea?

Speaking as someone who lives in the UK, it strikes me that a change
of tow vehicle could produce major fuel savings all the time. *I mean
- 26mpg at best! *My car is perfectly capable of towing my glider in
it's trailer at UK legal speeds, without the trailer it does almost
50mpg, with it it drops to low 40s. *Surely similar vehicles are
available in the US?

Don't forget the US gallon is 3.78 l, and yours is 4.54 l per Imperial
gallon... This explains some of the apparent disconnect.

Some of us do tow with Jetta TDIs and get reasonable mileage.
Dan