5th Wheel aerodynamics
Jon Floyd
up our new fiver and towed it down to Texas from Kansas against strong
head winds. Along the way we noticed that the rig would decellerate and
then accellerate for no apparent reason. It sometime happened after a
bump, on smooth roads, and when 18 wheelers zoomed past. The conclusion
I reached, after trying various speeds, and noticing masking windbreaks,
was that the RV aerodynamics was the culprit.
A fiver by its nature is not an aerodynamic vehicle. Most present a huge
wind catcher to the winds. Depending on your style of RVing the lunging
or surging can reduce you joy of travel. I am looking at the various
airfoils that mount on the cab of a pickup to travel with but I am
reluctant to add that much weight to the rig just for the sake of some
weather conditions. But, as an old engineer, the problem is a challenge
and I offer some thoughts on a partial solution.
1. Obviously the best solution would be for the RV maker to improve the
"slickness" or the shape of the trailer to improve the airflow around
the RV. Think of Airstream in a 5th wheel.
2. The family of current cab mounted airfoils are, to the best of my
knowledge, not very effective, nor very light. But they do several
things that improve aerodynamics.
A. Head wind deflection over the top of the towed RV. In effect
these offer less wind resistance than the front of the RV, and if
adjusted properly add fuel economy..
B. Head wind spoilers are the small type that disrupt the wind into
the RV front thus reducing drag. Lighter but only marginally effective
for high profile fivers.
C. The final type is the wrap top cab extender that masks the entire
front of the RV. Very effective, very heavy and expensive. I have only
seen one of these in my travels so I assume they are special order from
some fiberglass fabricator.
3. There may be a market for an integrated design between a lightweight
pickup and a fiver maker. The unit would have all the advantages of a
fifth wheel and the aerodynamics of a slick class A.
4. Another design is a fiver nose cone that adds some weight but vastly
improves the aero qualities of the trailer. These aero improvers could
be offered as options by the fiver maker.
The RV market has grown lately and is projected to grow even more as the
Boomers begin to retire. I believe as fuel prices increase the appeal of
aerodynamic designs will become more important
Jon & Alma Floyd
Dodge 2500 5 spd man Cummins diesel w/ E-brake
New Horizons 31RKSSS (five star rated)
W F Sill
>I am a retired aerospace engineer and a newbie fulltimer. We just picked
>up our new fiver and towed it down to Texas from Kansas against strong
>head winds. Along the way we noticed that the rig would decellerate and
>then accellerate for no apparent reason. It sometime happened after a
>bump, on smooth roads, and when 18 wheelers zoomed past. The conclusion
>I reached, after trying various speeds, and noticing masking windbreaks,
>was that the RV aerodynamics was the culprit.
<Remainder snipped>
Jon, while the aerodynamic properties of the typical 5th wheel rv are
indeed miserable from a drag POV, I'd advise you to take up another
hobby unless you just enjoy doing huge projects for immeasurable gain.
The Big Factor is frontal area, not slipperiness. It has been well
established that appropriately-designed deflectors, installed
correctly, can slightly reduce drag and therefore improve mileage a
little.
If you are interested in a major reduction in fuel consumption, here's
a free tip: SLOW DOWN. Gains of 20% are realistically possible -
something I predict is NOT possible even if you made yer big trailer
as slippery as you can.
Much of your aircraft experience will prove to be of minimal value
when looking at your rv. You are going so slow (vs airframe
velocities) that the forces are vastly different, and ground effects
confuse the picture.
Will KD3XR ---- the Curmudgeon of Sill Hill
Before flaming, pause. I post to help rv'ers
and annoy morons. Whichever shoe fits, wear it.
Jon Floyd
W F Sill wrote:
> Jon, while the aerodynamic properties of the typical 5th wheel rv are
> indeed miserable from a drag POV, I'd advise you to take up another
> hobby unless you just enjoy doing huge projects for immeasurable gain.
> The Big Factor is frontal area, not slipperiness. It has been well
> established that appropriately-designed deflectors, installed
> correctly, can slightly reduce drag and therefore improve mileage a
> little.
I glad to see you agree with me. My original compliant was the lunging or
surging that was very uncomfortable for us in the cab of the truck. I am not
overly worried about the fuel milage as much as the ride comfort. The
aerodynamic cross section is a function of drag count. The higher the drag
count the lower the slipperness. Lowering the drag count by spoiling the
wind flow impinging on the RV front may be effective. I don't know.
> If you are interested in a major reduction in fuel consumption, here's
> a free tip: SLOW DOWN. Gains of 20% are realistically possible -
> something I predict is NOT possible even if you made yer big trailer
> as slippery as you can.
The range of speeds I tried, in my attempts to reduce the surging, was from
50 -65 MPH. I never got to 70 because it was my first time with the trailer.
Excessive speed was not a problem, it was the 30-40 MPH winds on the front
of the trailer
> Much of your aircraft experience will prove to be of minimal value
> when looking at your rv. You are going so slow (vs airframe
> velocities) that the forces are vastly different, and ground effects
> confuse the picture.
Drag has existed for all shapes of all vehicles on the road for a long time.
Some fivers have been designed to reduce drag like Avion. All 18 wheel
tractors have a drage reducing shroud to improve fuel and performance. These
are aerodynamic designs for slow moving vehicles. The fact slab sided design
is the current reality should be whippable with a good lighy wind deflector.
Any reccommendations?
Jon
Thomas Stubbs
part
even at speeds as low as 30 mph--not as much as at 70, of course, but it
was found to be a much bigger component that originally thought.
I'd think that to get much improvement, you'd have to redesign the rig
from the ground up, including the tractor.
JRE
be economical and has been using them for years. You might be able to find
their research, and if you do it might help you estimate the potential
benefits.
The RV industry as a whole seems to delight in draggy aerodynamic shapes. I
think the living space and convenience will probably always win over a
better coefficient of drag, though, so I would expect them to continue to
make boxy shapes and stick AC units and other stuff out into the wind.
JRE
Jon Floyd wrote:
> I am a retired aerospace engineer and a newbie fulltimer. We just picked
> up our new fiver and towed it down to Texas from Kansas against strong
> head winds. Along the way we noticed that the rig would decellerate and
> then accellerate for no apparent reason. It sometime happened after a
> bump, on smooth roads, and when 18 wheelers zoomed past. The conclusion
> I reached, after trying various speeds, and noticing masking windbreaks,
> was that the RV aerodynamics was the culprit.
>
W F Sill
> . . . . All 18 wheel
>tractors have a drage reducing shroud to improve fuel and performance. These
>are aerodynamic designs for slow moving vehicles. The fact slab sided design
>is the current reality should be whippable with a good lighy wind deflector.
>Any reccommendations?
Yes - you can get some measurable (if not huge) gains with a
deflector, as I indicated. I suggest you research what it takes to
achieve the desired shape, size and position. . . regardless of
commercial brand. You will then be able to decide whether it is worth
the hassle. When we owned a fiver, we used one and found it
worthless and a nuisance --- but we have since learned it wasn't tall
enough nor close enough to the trailer to be effective.
David Osborn
>When we owned a fiver, we used one and found it
>worthless and a nuisance --- but we have since learned it wasn't tall
>enough nor close enough to the trailer to be effective.
The fact that "it wasn't tall enough nor close enough to the trailer to be
effective" should have been obvious early on. A cursory look at the
aerodynamic treatment on semis clearly shows that the wind deflector on the
tractor is nearly as tall as the trailer, and goes back as close to the trailer
as possible. Obviously, the closer one can get to an unbroken smooth surface
from the front to the back of the overall vehicle, the better off one is.
- - - - -
David, N8DO; FMCA 147762
djosborn at aol dot com
Paul Johnson
news:FE8506DA6A659CC8.89A7D290...@lp.airnews.net...
> I am a retired aerospace engineer and a newbie fulltimer. We just picked
> up our new fiver and towed it down to Texas from Kansas against strong
> head winds. Along the way we noticed that the rig would decellerate and
> then accellerate for no apparent reason. It sometime happened after a
> 1. Obviously the best solution would be for the RV maker to improve the
> "slickness" or the shape of the trailer to improve the airflow around
> 4. Another design is a fiver nose cone that adds some weight but vastly
> improves the aero qualities of the trailer. These aero improvers could
While your New Horizons fiver may be well built, it is also one of the
"squarest" designs (no radius corners anywhere) and, unless they have
changed since '95 when I looked at them, they don't have an enclosed
underside (smooth bottom supposedly reducing turbulence). Take a look at
the front end design of a Spacecraft fiver per this URL:
http://www.spacecraftmfg.com/
My memory may be faulty, but I believe this design was patented back in the
70's by the founder of Spacecraft (along with fully automatic slideouts that
don't require locking bars). In addition to the "V" design that spreads the
wind along the sides of the trailer, all corners are very rounded. This is
not to say that it slips through the wind with no resistance, but what I
have gathered talking to people who have pulled both conventional designs
and the Spacecraft, it is MUCH better. Meeting a semi on a two lane road
can give me a sudden blast (slowdown) too and pulling into a headwind will
slow me as well. While I certainly agree that reducing speed has a dramatic
effect on fuel consumption, when we first picked up our Spacecraft at
Concordia, MO and pulled on to I-70, I found myself easily running 70 mph if
I wasn't careful. A bonus is that the extended "nose cone" gives you one
huge closet (they even call it a walk-in).
Paul Johnson
bill horne
Maybe that explains why I used to get 15 mpg with my old rig. My old rig
was a 305 CID 83 PU, a 14-ft nearly flatfronted TT, and a 12-ft semi-V
boat upsidedown on top of the PU. The PU got 18 mpg by itself.
--
bill
Theory don't mean squat if it don't work.
Jon Floyd
reducing the gap between the tractor and the trailer in 18 wheel design.
The big rig people have found that any gap increases drag and any roughness
on the surface of the tractor will also increase drag. So you see more rigs
with aerodynamic designs in front, skirts on the trailers and wind spoilers
on the tractors masking the trailer. The RV makers ought to pay attention.
Jon
Dick
Notice how some even put skirts between the cab and the trailer.
The flat rear of the trailer probably causes almost as much drag as the
front. One needs a pointed end back there to to really help. Have you
ever seen anything on an airplane with a flat rear section? I have
heard that on airplanes a flat frontal section will built up a layer of
air and become more aerodynamic but the rear gets very turbulent.
JRE wrote:
>
> The trucking industry seems to think that the deflectors work well enough to
> be economical and has been using them for years. You might be able to find
> their research, and if you do it might help you estimate the potential
> benefits.
>
> The RV industry as a whole seems to delight in draggy aerodynamic shapes. I
> think the living space and convenience will probably always win over a
> better coefficient of drag, though, so I would expect them to continue to
> make boxy shapes and stick AC units and other stuff out into the wind.
>
> JRE
>
> Jon Floyd wrote:
>
> > I am a retired aerospace engineer and a newbie fulltimer. We just picked
> > up our new fiver and towed it down to Texas from Kansas against strong
> > head winds. Along the way we noticed that the rig would decellerate and
> > then accellerate for no apparent reason. It sometime happened after a
> > bump, on smooth roads, and when 18 wheelers zoomed past. The conclusion
> > I reached, after trying various speeds, and noticing masking windbreaks,
> > was that the RV aerodynamics was the culprit.
> >
> > A fiver by its nature is not an aerodynamic vehicle. Most present a huge
> > wind catcher to the winds. Depending on your style of RVing the lunging
> > or surging can reduce you joy of travel. I am looking at the various
> > airfoils that mount on the cab of a pickup to travel with but I am
> > reluctant to add that much weight to the rig just for the sake of some
> > weather conditions. But, as an old engineer, the problem is a challenge
> > and I offer some thoughts on a partial solution.
> >
> > 1. Obviously the best solution would be for the RV maker to improve the
> > "slickness" or the shape of the trailer to improve the airflow around
> > the RV. Think of Airstream in a 5th wheel.
> >
> > 2. The family of current cab mounted airfoils are, to the best of my
> > knowledge, not very effective, nor very light. But they do several
> > things that improve aerodynamics.
> > A. Head wind deflection over the top of the towed RV. In effect
> > these offer less wind resistance than the front of the RV, and if
> > adjusted properly add fuel economy..
> > B. Head wind spoilers are the small type that disrupt the wind into
> > the RV front thus reducing drag. Lighter but only marginally effective
> > for high profile fivers.
> > C. The final type is the wrap top cab extender that masks the entire
> > front of the RV. Very effective, very heavy and expensive. I have only
> > seen one of these in my travels so I assume they are special order from
> > some fiberglass fabricator.
> >
> > 3. There may be a market for an integrated design between a lightweight
> > pickup and a fiver maker. The unit would have all the advantages of a
> > fifth wheel and the aerodynamics of a slick class A.
> >
> > 4. Another design is a fiver nose cone that adds some weight but vastly
> > improves the aero qualities of the trailer. These aero improvers could
W F Sill
whined about my remark that:
>> >When we owned a fiver, we used one and found it
>> >worthless and a nuisance --- but we have since learned it wasn't tall
>> >enough nor close enough to the trailer to be effective.
Quavers the Oz from his cave:
>> The fact that "it wasn't tall enough nor close enough to the trailer to be
>> effective" should have been obvious early on. A cursory look at the
>> aerodynamic treatment on semis . . . blah, blah, blah ad nauseum.
Bull.
Had I been born flawlessly brilliant like Oz, I would have known (and
documented) all important things by the time I was 3. Had I mastered
all aspects of medicine, all branches of engineering, and forensic
usenet dissection by the time I was 4, I would certainly have by now
accomplished the highest of all possible cyberspace goals - the
approval of David H. Osborn.
As things stand, I am a failure. I'm a mere human who is obviously
and painfully inferior to the great Oz. Not being born perfect, I
found it necessary to learn a lot of stuff the hard way - making
mistakes, making more mistakes, and eventually realizing something
that has apparently escaped the razor-sharp mind (?) of the Wizard:
experience is a great teacher - but only if you learn something from
your experiences. Even Dorothy eventually figured that out.
Jon Floyd
on the road a lot then a low drag Cless A is probably the answer. If you are
going to "hub RV" or go to a region, then explore locally, while the trailer
sits still, then aerodynamic improvements are not worth the cost and weight.
For example snowbirds. I think the snowbirds won't benefit in good aero design
because they only tow twice a year. The initial cost exceeds the benefit
derived.
Producability is also a major factor. It would seem easier to build a box with
wheels, with stuff hanging on the outside, than a slick curvilinear shape that
increases manufacturing cost while increasing towability. I am sure the
manufacturers know this and have made the concious decision to sacrifice
towability for the sake of lower production costs and increased living area. I
think I am about to convince myself I will have to live with the problem.
Jon
Jon Floyd
slicker designs, but I was influenced by the ratings in the RVCG green book. J.
D. Gallant might create another catagory for RVs called Towability for trailers
and fivers for folks that intend to tow a lot. I guess it all comes down to
nothings perfect,, and you have to buy the features that will satisfy the most
need for the lowest buck.
Jon
Paul Johnson wrote:
> Jon Floyd <vest...@fastlane.net> wrote in message
> news:FE8506DA6A659CC8.89A7D290...@lp.airnews.net...
> > I am a retired aerospace engineer and a newbie fulltimer. We just picked
> > up our new fiver and towed it down to Texas from Kansas against strong
> > head winds. Along the way we noticed that the rig would decellerate and
> > then accellerate for no apparent reason. It sometime happened after a
> > bump, on smooth roads, and when 18 wheelers zoomed past. .....
> > 1. Obviously the best solution would be for the RV maker to improve the
> > "slickness" or the shape of the trailer to improve the airflow around
> > the RV. .....
> > 4. Another design is a fiver nose cone that adds some weight but vastly
> > improves the aero qualities of the trailer. These aero improvers could
Jon Floyd
problem. I tailgated an eighteen wheeler to deliberately get the buffeting in the
wake from the truck. The effect was obvious. I had not noticed before, but at
least one truck had a laminar flow vane on the top rear edge to push air into the
back of the trailer. The effect is to force air into the low pressure area
behind the tralier, thus reducing drag. That might also work for flat backed
RVs.
Jon
Dick wrote:
> I expect the truckers find it worth while because of their mileage.
> Notice how some even put skirts between the cab and the trailer.
>
> The flat rear of the trailer probably causes almost as much drag as the
> front. One needs a pointed end back there to to really help. Have you
> ever seen anything on an airplane with a flat rear section? I have
> heard that on airplanes a flat frontal section will built up a layer of
> air and become more aerodynamic but the rear gets very turbulent.
>
> JRE wrote:
> >
> > The trucking industry seems to think that the deflectors work well enough to
> > be economical and has been using them for years. You might be able to find
> > their research, and if you do it might help you estimate the potential
> > benefits.
> >
> > The RV industry as a whole seems to delight in draggy aerodynamic shapes. I
> > think the living space and convenience will probably always win over a
> > better coefficient of drag, though, so I would expect them to continue to
> > make boxy shapes and stick AC units and other stuff out into the wind.
> >
> > JRE
> >
> > Jon Floyd wrote:
> >
> > > I am a retired aerospace engineer and a newbie fulltimer. We just picked
> > > up our new fiver and towed it down to Texas from Kansas against strong
> > > head winds. Along the way we noticed that the rig would decellerate and
> > > then accellerate for no apparent reason. It sometime happened after a
> > > bump, on smooth roads, and when 18 wheelers zoomed past. The conclusion
> > > I reached, after trying various speeds, and noticing masking windbreaks,
> > > was that the RV aerodynamics was the culprit.
> > >
> > > A fiver by its nature is not an aerodynamic vehicle. Most present a huge
> > > wind catcher to the winds. Depending on your style of RVing the lunging
> > > or surging can reduce you joy of travel. I am looking at the various
> > > airfoils that mount on the cab of a pickup to travel with but I am
> > > reluctant to add that much weight to the rig just for the sake of some
> > > weather conditions. But, as an old engineer, the problem is a challenge
> > > and I offer some thoughts on a partial solution.
> > >
> > > 1. Obviously the best solution would be for the RV maker to improve the
> > > "slickness" or the shape of the trailer to improve the airflow around
> > > the RV. Think of Airstream in a 5th wheel.
> > >
> > > 2. The family of current cab mounted airfoils are, to the best of my
> > > knowledge, not very effective, nor very light. But they do several
> > > things that improve aerodynamics.
> > > A. Head wind deflection over the top of the towed RV. In effect
> > > these offer less wind resistance than the front of the RV, and if
> > > adjusted properly add fuel economy..
> > > B. Head wind spoilers are the small type that disrupt the wind into
> > > the RV front thus reducing drag. Lighter but only marginally effective
> > > for high profile fivers.
> > > C. The final type is the wrap top cab extender that masks the entire
> > > front of the RV. Very effective, very heavy and expensive. I have only
> > > seen one of these in my travels so I assume they are special order from
> > > some fiberglass fabricator.
> > >
> > > 3. There may be a market for an integrated design between a lightweight
> > > pickup and a fiver maker. The unit would have all the advantages of a
> > > fifth wheel and the aerodynamics of a slick class A.
> > >
> > > 4. Another design is a fiver nose cone that adds some weight but vastly
> > > improves the aero qualities of the trailer. These aero improvers could
Chris Bryant
<<..>>
>1. Obviously the best solution would be for the RV maker to improve the
>"slickness" or the shape of the trailer to improve the airflow around
>the RV. Think of Airstream in a 5th wheel.
>
>The RV market has grown lately and is projected to grow even more as the
>Boomers begin to retire. I believe as fuel prices increase the appeal of
>aerodynamic designs will become more important
I know *nothing* about them, but there is apparently a new
company releasing a very interesting looking fifth wheel. The url is
http://www.lamarr.com/ .
Again- I know nothing other than what is on the website.
--
<<reply to address is good>>
Chris Bryant
Bryant RV Services- DeLand, Florida mailto:brya...@totcon.com
On RVing-RV TV about RVs, by RVers: http://www.onrving.com
c...@hotpop.com
both fore and aft.
Jon Floyd
trailer squats! Does it auto level? Anyway it shows great promise and is
definately a head turner.
Jon
Badkitty
> I know *nothing* about them, but there is apparently a new
>company releasing a very interesting looking fifth wheel. The url is
>http://www.lamarr.com/ .
Wow. Looks like Darth Vader's fiver!
John KD7KBL
Bothell, WA
USA
ICQ# 25096533
castle...@icqmail.com
http://www.radiohound.net
"What do you mean you can't solder with a propane torch and a butter knife?"
mark...@my-deja.com
flat. RV's have all kinds of parasitic drag up on top from AC's,
Antennas, vents, etc. Not the deflector would do much good in that
kind of "dirty" air.
I did recently see someone iwth a fiver that had some sort of flexible
skirting going from the cab and sides to the trailer. Including the
top. Dunno' how he turned, though.
Mark
In article
<920FFA3F4F2D1F12.74BF9873...@lp.airnews.net>,
> > > > 1. Obviously the best solution would be for the RV maker to
improve the
> > > > "slickness" or the shape of the trailer to improve the airflow
around
> > > > the RV. Think of Airstream in a 5th wheel.
> > > >
> > > > The RV market has grown lately and is projected to grow even
more as the
> > > > Boomers begin to retire. I believe as fuel prices increase the
appeal of
> > > > aerodynamic designs will become more important
> > > >
> > > > Jon & Alma Floyd
> > > > Dodge 2500 5 spd man Cummins diesel w/ E-brake
> > > > New Horizons 31RKSSS (five star rated)
>
>
Sent via Deja.com http://www.deja.com/
Before you buy.
F150Owner
>That is true and as it happens was one of the ways I proved it was an
>aerodynamic
>problem. I tailgated an eighteen wheeler to deliberately get the buffeting in
>the
>wake from the truck.
I'm new to 5th wheeling and I knew that there would be a lot of wind drag on
the outfit. What no one told me about was the turbulence in the bed of the
pickup from the 5th wheel. When I had a travel trailer I always placed the
small wood 2x4 pieces of wood in the truck bed for use with the trailer jacks.
They never blew around or moved.
When I towed the 5th wheel with these "loose" items in the bed, it looked like
a scene from the movie "Twister" when I got up to about 65mph. The wood was
hitting my truck bed and sidewalls.
Regards,
DH
Please remove KILLSPAM from my email address when replying - Thanks.
David Osborn
>I'm new to 5th wheeling and I knew that there would be a lot of wind drag on
>the outfit. What no one told me about was the turbulence in the bed of the
>pickup from the 5th wheel. When I had a travel trailer I always placed the
>small wood 2x4 pieces of wood in the truck bed for use with the trailer
>jacks.
>They never blew around or moved.
>
>When I towed the 5th wheel with these "loose" items in the bed, it looked
>like
>a scene from the movie "Twister" when I got up to about 65mph. The wood was
>hitting my truck bed and sidewalls.
That's exactly why "louvered tailgate" mileage-comparison test results
conducted without a fifth-wheel trailer attached are likely meaningless when
one is attached!
wade
"David Osborn" <djos...@aol.commnet.net> wrote in message
news:20001013094703...@ng-fz1.aol.com...
Jon Floyd
the wind above the face of the RV. In addition I have replaced the solid gate
with a non-louvered wire mesh tailgate. The aerodynamics of any fiver can be
adjusted by lowering the front of the fiver with respect to the truck, but I have
not tried that, yet.. Another problem is the wind build up on the face of the
basement, as a function of the "wraparound" wind flowing into the bed of the
truck from around the cab.
I believe a louvered tailgate would direct the wind downward and then become a
high pressure drag on the bottom of the trailer that is not at all aerodynamic.
My idea is that any wind that gets into the bed of the truck should be allowed to
flow into the face of the basement that will then force the winds out the sides.
I have not tested these theories yet, but eventually I will get into a situation
that will prove me right or expensively wrong.
I have 3 2x4s in the back of the truck for the same reason. I also have an
extended kingpin hitch that will allow me to turn the fiver around in the turning
radius of the truck, even after backing into a severe jacknife. That obviously
changes the aero characteristics of the truck bed. I nay have to put the 2x4s in
the basement.
Jon
F150Owner wrote:
> I'm new to 5th wheeling and I knew that there would be a lot of wind drag on
> the outfit. What no one told me about was the turbulence in the bed of the
> pickup from the 5th wheel. When I had a travel trailer I always placed the
> small wood 2x4 pieces of wood in the truck bed for use with the trailer jacks.
> They never blew around or moved.
>
> When I towed the 5th wheel with these "loose" items in the bed, it looked like
> a scene from the movie "Twister" when I got up to about 65mph. The wood was
> hitting my truck bed and sidewalls.
>
Richard Wiebe
front (hitch point of the 5th wheel}. I would think you want the bottom
of the "front area" as near to level as possible. If you go up a
inclined drive (IE - a gas station entry) - aren't you more likely to
damage the bottom of the trailer with the top rear end of the truck box?
I also remember a thread about tuning the air deflector. You place a
string from the top of the windshield to "a point 4 in. above the top
front edge of the 5th wheel". Your deflector bottom and top edges
should both touch the string. This tunes both the position (on the
truck roof) and the "angle of deflection".
I am not sure if this is the best method. But - it sounds better than
just "strapping it on the roof". I also wonder how many do not tune the
position - then complain about the poor results?
I might be interested in getting one - if I thought they would be
worthwhile.
Getting older (and wiser) - but - it beats the alternative!
Jon Floyd
Richard Wiebe wrote:
> As one thread suggested - you reduce the wind resistance by lowering the
> front (hitch point of the 5th wheel}. I would think you want the bottom
> of the "front area" as near to level as possible. If you go up a
> inclined drive (IE - a gas station entry) - aren't you more likely to
> damage the bottom of the trailer with the top rear end of the truck box?
I have been told that the optimum is the front shouild be about 1 inch
lower than the rear of the trailer as measured from the edge of the trailer
to the ground. Oviously the normal seperation of 7-10 inches from the
trailer overhang to the top of the rail should not be reduced to too narrow
a margin.
> I also remember a thread about tuning the air deflector. You place a
> string from the top of the windshield to "a point 4 in. above the top
> front edge of the 5th wheel". Your deflector bottom and top edges
> should both touch the string. This tunes both the position (on the
> truck roof) and the "angle of deflection".
The type of deflector I have has twin spring loaded struts that pushes the
deflector up out of the way of the fiver front when in low speed
conditions. At highway speeds the deflector is pushed down in tune with the
air pressure impinging on it. The unloaded starting angle is adjustable as
a function of the strut ends pin holes. The manufacturer reccomments tuning
that angle by driving for a while then observing the bug hit line. (I'm not
making this up) Raise the angle until the bug hit line disappears on the
front of the trailer. Your technique may not work due to the bounced air
being redirected by linear winds above the deflector.
> I am not sure if this is the best method. But - it sounds better than
> just "strapping it on the roof". I also wonder how many do not tune the
> position - then complain about the poor results?
As I have described, the deflector I have is not mounted to the top of the
cab. Instead it comes as a self contained unit that mounts into the front
stake holes on the bed rails. The steel box beams are adjustable to extend
the deflector above the cab but floats above it. As an old engineer this
seemed to be a more elegant answer than the fixed strapon type.
> I might be interested in getting one - if I thought they would be
> worthwhile.
We head south in 8 days and I'll let you know how it works out. I have not
adjusted the trailer/truck height yet so I still have some fiddling around
to do.
> Getting older (and wiser) - but - it beats the alternative!
You got that right!
Jon
Badkitty
>As I have described, the deflector I have is not mounted to the top of the
>cab. Instead it comes as a self contained unit that mounts into the front
>stake holes on the bed rails. The steel box beams are adjustable to extend
>the deflector above the cab but floats above it. As an old engineer this
>seemed to be a more elegant answer than the fixed strapon type.
Jon:
I'd be very interested in the name of the manufacturer and model of
your deflector.
Jon Floyd
believe it is also available from Camping World. I want you to understand I am
in no way associated with the company. I don't even know if it works and it is
currently an experiment.
Jon