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Old 05-17-2011, 10:56 AM   #21 (permalink)
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What would be a less lengthly option?

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Old 05-17-2011, 10:57 AM   #22 (permalink)
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Does it have a supplemental fan? If so, you could proceed with a tail design anyway. Usually there is too much airflow over engines and through radiators, lots of wasted drag.

EDIT: I will be drawing up my folding boat tail design for my 5th wheel in the next week or two. It is a little shorter in height than your MH, but just as wide and blocky at the back.
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Old 05-17-2011, 11:01 AM   #23 (permalink)
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Quote:
Originally Posted by skyking View Post
I think you are missing the boat so to speak Randy. Forget the nose, concentrate on the tail. Cheaper, easier, more effective according to all accounts.
I am beginning to come to that conclusion. It is more simple, cheaper, but I did not understand that it is more important. Is that a proven and non debateable fact, that the rear is more important than the front??

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Old 05-17-2011, 11:05 AM   #24 (permalink)
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Quote:
Originally Posted by skyking View Post
Does it have a supplemental fan? If so, you could proceed with a tail design anyway. Usually there is too much airflow over engines and through radiators, lots of wasted drag.

EDIT: I will be drawing up my folding boat tail design for my 5th wheel in the next week or two. It is a little shorter in height than your MH, but just as wide and blocky at the back.
It has a 3.5 ft. manual fan with a centrifical clutch. Have you tested your boat tail on the 5th wheel? Is yes then how much did it help?
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Old 05-17-2011, 11:08 AM   #25 (permalink)
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Hard to believe, right?
Somebody posted info from a test using a brick shape. Fairing in the back was the single biggest improvement, and here is my take on why:
No matter how you smooth the flow going onto your rig, it still displaces X amount in cross section. Still 13 high and 8 wide. No way to fool that.
At the back you can "let" that air off very gently and efficiently, or let it slam shut.
If you let it slam shut the turbulence and vacuum is so great, a car can ride with almost no power input in the wake of your motorhome. IF you think about it, you could pull a smaller motorhome along behind you
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Old 05-17-2011, 11:08 AM   #26 (permalink)
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Quote:
Originally Posted by crmears View Post
It has a 3.5 ft. manual fan with a centrifical clutch. Have you tested your boat tail on the 5th wheel? Is yes then how much did it help?
I just got here myself, and have not designed it yet, let alone built it.
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Old 05-17-2011, 11:23 AM   #27 (permalink)
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Quote:
Originally Posted by skyking View Post
Hard to believe, right?
Somebody posted info from a test using a brick shape. Fairing in the back was the single biggest improvement, and here is my take on why:
No matter how you smooth the flow going onto your rig, it still displaces X amount in cross section. Still 13 high and 8 wide. No way to fool that.
At the back you can "let" that air off very gently and efficiently, or let it slam shut.
If you let it slam shut the turbulence and vacuum is so great, a car can ride with almost no power input in the wake of your motorhome. IF you think about it, you could pull a smaller motorhome along behind you
Airplanes (except for fighters) have a relatively blunt nose but a long slender tail. That seems to confirm the relative significance of the rear aerodynamics.
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Old 05-17-2011, 12:02 PM   #28 (permalink)
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Quote:
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Is that a proven and non debateable fact, that the rear is more important than the front??
Yes.

If you need to streamline a brick, add a fairing on the rear ...
Counter-intuitive, but that's how it is.


There you go :

Airflow is going from left to right, BTW

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Old 05-17-2011, 12:28 PM   #29 (permalink)
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Quote:
Originally Posted by euromodder View Post
Yes.

If you need to streamline a brick, add a fairing on the rear ...
Counter-intuitive, but that's how it is.


There you go :

Airflow is going from left to right, BTW

This is from a side view, correct?
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Old 05-17-2011, 06:24 PM   #30 (permalink)
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The tail could certainly be open to the rear for probably IMPROVED cooling flow.

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