AERODYNAMICS

O

omoore

New member
Mar 21, 2018
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New Bern, NC
I just returned from a two-day drive on I-95 (in my car). It struck me that
most of the long haul trucks had a variety of wind deflecting
devices--front air dams, long panels between the wheel to reduce air under
the trailer, and curving shields over the rooftop AC. Has anyone tested if
any of these would improve our MPG? I have two rooftop storage units, for
instance. It would be easy to make a deflector to lessen air resistance--if
it would improve mileage.

Oliver
'74 Glenbrook
Patterson Stage II engine
Alcoa wheels
Honda generator
 
> It would be easy to make a deflector to lessen air resistance--if it
> would improve mileage.

As the GMC MotorHome being fairly aerodynamic already, I doubt you will
see much improvement. Better make sure all the parts that are relevant
for optimal engine tuning are in place, you are not running any
unnecessary devices that consume energy, and you only travel with stuff
in your coach that you really need.

But I am sure others with real technical knowledge will chime in and
provide more insight.
--
Best regards

Olly Schmidt
PGP KeyID: 0x4196BF22
'76a 26' Eleganza II - Virginia, US
'73 23' Sequoia - Schleswig-Holstein, Germany
 
Search airtab.com. Due to the curved rear cap on the GMC probably less gains. Might help on trailing edges of rooftops etc.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
Being that as an Aero Space Mechanical engineer does not qualify to do a
good evaluation ,
however I associate with an Engineer that does Practical Designs for
Formula cars in Europe.
He feels the rear is a major area that need to be addressed.
Basically he was telling me that a sharp corners will do wonders.
In my opinion I have a hard time seeing that.

On Thu, Feb 4, 2021 at 9:53 AM Olly Schmidt via Gmclist <

> > It would be easy to make a deflector to lessen air resistance--if it
> > would improve mileage.
>
> As the GMC MotorHome being fairly aerodynamic already, I doubt you will
> see much improvement. Better make sure all the parts that are relevant
> for optimal engine tuning are in place, you are not running any
> unnecessary devices that consume energy, and you only travel with stuff
> in your coach that you really need.
>
> But I am sure others with real technical knowledge will chime in and
> provide more insight.
> --
> Best regards
>
> Olly Schmidt
> PGP KeyID: 0x4196BF22
> '76a 26' Eleganza II - Virginia, US
> '73 23' Sequoia - Schleswig-Holstein, Germany
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.gmcrvparts.com
1-800-752-7502
 
Sharp corners, perhaps causing laminar air flow similar to a golf ball dimple.

Randy Hecht
Roswell, GA

1974 Canyon Lakes GMC Motor-coach

>
> Being that as an Aero Space Mechanical engineer does not qualify to do a
> good evaluation ,
> however I associate with an Engineer that does Practical Designs for
> Formula cars in Europe.
> He feels the rear is a major area that need to be addressed.
> Basically he was telling me that a sharp corners will do wonders.
> In my opinion I have a hard time seeing that.
>
>> On Thu, Feb 4, 2021 at 9:53 AM Olly Schmidt via Gmclist <

>>

>>> It would be easy to make a deflector to lessen air resistance--if it
>>> would improve mileage.
>>
>> As the GMC MotorHome being fairly aerodynamic already, I doubt you will
>> see much improvement. Better make sure all the parts that are relevant
>> for optimal engine tuning are in place, you are not running any
>> unnecessary devices that consume energy, and you only travel with stuff
>> in your coach that you really need.
>>
>> But I am sure others with real technical knowledge will chime in and
>> provide more insight.
>> --
>> Best regards
>>
>> Olly Schmidt
>> PGP KeyID: 0x4196BF22
>> '76a 26' Eleganza II - Virginia, US
>> '73 23' Sequoia - Schleswig-Holstein, Germany
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
>
>
> --
> Jim Kanomata
> Applied/GMC, Newark,CA
> jimk
> http://www.gmcrvparts.com
> 1-800-752-7502
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
Before the accessories go on, the coach is very aerodynamic. Resistance is roughly the same as the corvette of the area, drag coefficient of about
.3. Of course, .3 times the area of the thing is a fair amount to push through the wind. JI wouldn't be looking for any great mileage gain though.
Jimmy the K's degree in in aerodynamics, he might could help you.

--johnny
--
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
 
I don't recall (paging Bill Bryant) if the drag coefficient of ~0.3 was for the 1/8 scale model, but it was for a naked GMC - no mirrors, no wind
wings, no rooftop AC, vents, pod, roof rack, door hinges, awnings, etc. With all of that stuff I don't have a clue what the GMC's coefficient would
be, nor how it would compare to any other RV. It's a good bragging point, though. ;)

Richard
--
'77 Birchaven TZE...777;
'76 Palm Beach with 18,477 verified miles;
‘76 Edgemonte
 
You would be well served to insure your tire pressures were on the high
side of correct, keep your loaded weight as low as possible, drive 55 mph.
Keep your engine well tuned-up, and install the EBL Fuel Injection with a
re-curved distributor that was matched to your final drive gearing. Also,
be sure that you have no brakes dragging, and your wheel bearings are
freshly packed and properly adjusted. That should account for 3 to 5 mpg
better mileage.
Jim Hupy
Salem, Oregon

On Thu, Feb 4, 2021, 2:39 PM Richard via Gmclist
wrote:

> I don't recall (paging Bill Bryant) if the drag coefficient of ~0.3 was
> for the 1/8 scale model, but it was for a naked GMC - no mirrors, no wind
> wings, no rooftop AC, vents, pod, roof rack, door hinges, awnings, etc.
> With all of that stuff I don't have a clue what the GMC's coefficient would
> be, nor how it would compare to any other RV. It's a good bragging point,
> though. ;)
>
> Richard
> --
> '77 Birchaven TZE...777;
> '76 Palm Beach with 18,477 verified miles;
> ‘76 Edgemonte
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
Hard to believe in the sharp rear corners being good. Like a basic semi trailer box. Companies like Trailer Tails have add on fold out baffles to
eliminate the square edges to reduce drag
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
My Ford V-10 powered Phoenix Cruiser averages 8.5 mpg while towing my 2010 Honda Fit. Without the toad, it moves up to near 9 mpg. Honda does not seem
to hurt the mileage.
If I would slow down a little, I could improve mpg. I do find off the Interstate, mpg goes up due to slower speeds and not fighting drag.
--
2012 Phoenix Cruiser model 2552
KA4CSG
 
My 2014 F550 rollback tow truck with the Triton v10 and 4 sp auto trans
never gets above 7. Usually 5 -6 mpg.

Sully
Bellevue wa.

On Fri, Feb 5, 2021 at 3:29 PM Thomas Phipps via Gmclist <

> My Ford V-10 powered Phoenix Cruiser averages 8.5 mpg while towing my 2010
> Honda Fit. Without the toad, it moves up to near 9 mpg. Honda does not seem
> to hurt the mileage.
> If I would slow down a little, I could improve mpg. I do find off the
> Interstate, mpg goes up due to slower speeds and not fighting drag.
> --
> 2012 Phoenix Cruiser model 2552
> KA4CSG
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
There might be something to the squarer back end claims....drive in the rain or wet roads and try to see out the rear window.

That being said i dont think more than about 10 mpg is gonna happen no matter unless yoir cruising on flat road, no wind, everything closed, no A/C,
holding 62.5mph etc.....and maybe you might get q2....lol.

I always find it fumny when people talk MPG on a behicle....my thought is....if you wanna drive, it costs money, doesnt matter what the mpg is.
--
Rich Mondor,

Brockville, ON

77 Hughes 2600
 
8 to 10 is about it. It's what I get with a carb equipped 26 foot Royale
with a 403. Anytime I push the speed up in the 75 mph range, it is a whole
bunch worse than that.
Jim Hupy
Salem, Oregon

On Sat, Feb 6, 2021, 2:52 PM 6cuda6--- via Gmclist
wrote:

> There might be something to the squarer back end claims....drive in the
> rain or wet roads and try to see out the rear window.
>
> That being said i dont think more than about 10 mpg is gonna happen no
> matter unless yoir cruising on flat road, no wind, everything closed, no
> A/C,
> holding 62.5mph etc.....and maybe you might get q2....lol.
>
> I always find it fumny when people talk MPG on a behicle....my thought
> is....if you wanna drive, it costs money, doesnt matter what the mpg is.
> --
> Rich Mondor,
>
> Brockville, ON
>
> 77 Hughes 2600
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
I got 10.3 ONCE on a fishing trip into Canada. Driving 300mi at 50-55mph. Thought we'd never get there. Otherwise 7.5-9 depending on if I am towing. I
don't keep track of it any more. It is what it is.
--
Larry
78 Royale w/500 Caddy
Menomonie, WI.
 
Canadian gasoline is the "good stuff" no corn juice. Automatic 15 -20%
improvement in mileage.
Don Garrity says it best. "Gasoline goes in the tow rig, you drink the
alcohol, and Nitromethane is for racing."
Jim Hupy
Salem, Oregon

On Sat, Feb 6, 2021, 6:00 PM Larry via Gmclist
wrote:

> I got 10.3 ONCE on a fishing trip into Canada. Driving 300mi at 50-55mph.
> Thought we'd never get there. Otherwise 7.5-9 depending on if I am towing. I
> don't keep track of it any more. It is what it is.
> --
> Larry
> 78 Royale w/500 Caddy
> Menomonie, WI.
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
Sort of on subject...no square ends, but great mileage.

I got over 11mpg on some of the segments of my homeward trip from
Pittsburgh after picking up my 23 footer. Coming across flat-lands with
one (or 2 or 3 or more) hellacious tailwinds.
Ron Clark

> There might be something to the squarer back end claims....drive in the rain or wet roads and try to see out the rear window.
>
> That being said i dont think more than about 10 mpg is gonna happen no matter unless yoir cruising on flat road, no wind, everything closed, no A/C,
> holding 62.5mph etc.....and maybe you might get q2....lol.
>
> I always find it fumny when people talk MPG on a behicle....my thought is....if you wanna drive, it costs money, doesnt matter what the mpg is.

--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus
 
I average 8.3 to 9.0 MPG with a GVW of 17,102 lbs. (Depending on hills.) 78 Royale 403. Always towing Linda's 5,000 lbs plus Chevy Uplander lift van. Pulling my 24ft enclosed car hauler. With shop/car inside. Just under 7 MPGs. GVW is then in the 24,000lbs range.
Bob Dunahugh
78 Royale
4 COPO Yenkos

________________________________
From: Gmclist on behalf of Larry via Gmclist
Sent: Saturday, February 6, 2021 7:59 PM
To: gmclist
Cc: Larry
Subject: Re: [GMCnet] Aerodynamics

I got 10.3 ONCE on a fishing trip into Canada. Driving 300mi at 50-55mph. Thought we'd never get there. Otherwise 7.5-9 depending on if I am towing. I
don't keep track of it any more. It is what it is.
--
Larry
78 Royale w/500 Caddy
Menomonie, WI.

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GMCnet mailing list
Unsubscribe or Change List Options:
http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
My record was 12 (11.98something) driving the freeway homefrom Asheville. Freeway the whole way,downhill the whole way, and cruise set at 55. I was
trying. Normally, about 9 in the 26' bobtail, a bit over 8 with a toad behind.

==johnny
--
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
 
to James Hupy. Re Canadian Gasoline. I believe for all brands in Toronto they now all contain Ethanol EXCEPT the Premium 91 Octane.
A lot of pumps are labelled like this On the 87 Octanc may contain up to 10% Ethanol, the 89 Octane may contain up to 5% Ethanol
and on the 91 Octane Contains No ethanol. We also have 93 and 94 octane I believe they get this by adding Ethanol to the Ethanol
free 91 Octane as the 93 and 94 do contain Ethanol. It is expensive to use the 91 just to avoid Ethanol in a vehicle that really doesn't care.

I keep planning to do some back to back long distance comparison with 87 Octane and 91 but it never works out. My 2007 Dodge Grand Caravan
3.8 L motor doesn't seem to care. If I get the motorhome back on the road maybe I can get more performance info.
--
DAVE KING
lurker, wannabe
Toronto, Ontario, Canada
 
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