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  #151  
Old 11-12-2012, 11:26 PM
DanH's Avatar
DanH DanH is offline
 
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Quote:
... if it's truly over center, that means it would be jammed, right? I'm confused on why you describe it this way.
Perhaps a poor choice of words. Let's try a picture.

The highest load on the door linkage would be when the door is closed, because that's when internal cowl pressure is the highest.

If we arrange things so that the arm linked to the door becomes parallel to the link as the door reaches the closed position, there is no resting load on the actuator. That's good for the plastic gears, which are subject to a bit more heat than the designer intended. Even better, as the door nears closure and resistance rises, this sort of arrangement provides a progressive increase in linkage ratio. Thus a little bitty actuator can pull the door shut without strain.

Top is door open, bottom is door closed.

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Last edited by DanH : 07-17-2018 at 05:42 AM.
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  #152  
Old 11-13-2012, 01:05 AM
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Aha! Had to go back to your original photos and blow them up and compare with your diagrams, bit I get it now and also see how the over center arrangement with the door closed relieves stress on the actuator.
Thanks
Erich
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  #153  
Old 11-13-2012, 06:09 AM
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Default Sweet!

Brilliant invention, Dan.

Can I come and spend a week with my -10 and mess with its exit?

Best,
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  #154  
Old 11-13-2012, 06:32 AM
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Great mod Dan. 4 kt increase is a pretty significant drag reduction. I think I know what Bob Axsom will be doing this winter
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  #155  
Old 11-13-2012, 06:49 AM
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Dan since you had your cowl manometer-ized I would be interested in knowing the cruise pressure differences between iterations of the cowl exit.
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  #156  
Old 11-13-2012, 08:41 AM
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Quote:
Originally Posted by erich weaver View Post
Aha! Had to go back to your original photos and blow them up and compare with your diagrams, bit I get it now and also see how the over center arrangement with the door closed relieves stress on the actuator.
Here's one with the door more than half open. As the actuator pulls on its center arm to close, the arms on the ends will eventually parallel the linkage rods. Linkage ratio goes to infinity.

The black heat shrink thing on a wire is a temperature probe. The actuator was subject to about 160F in this location. As you can see the location shields it from radiant heating.



Quote:
Originally Posted by Kevin Horton View Post
Great mod Dan. 4 kt increase is a pretty significant drag reduction. I think I know what Bob Axsom will be doing this winter
Thanks, but, well, let's remember this was a shakedown cruise. To use Bob's excellent example, accurate measuring is needed. In addition to airspeed, it would be nice to cycle the door and measure a lower cowl pressure rise and an exit velocity increase.
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Last edited by DanH : 07-17-2018 at 05:45 AM.
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  #157  
Old 11-13-2012, 11:30 AM
RV8R999 RV8R999 is offline
 
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Point of clarification...

I believe the 4kt increase is from a door open to door closed position not an adidtional 4kt increase over the previous exit of same area without a door installed, correct Dan? Unless this exit has smaller area than previous??

Dan's idea, as was mine, was to shrink the exit as small as possible for cruise drag reduction with acceptable penalty in CHT while adjusting the door open for the WOT climb condition to provide CHT margin.

Last edited by RV8R999 : 11-13-2012 at 11:53 AM. Reason: more
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  #158  
Old 11-13-2012, 11:51 AM
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Quote:
Originally Posted by RV8R999 View Post
I believe the 4kt increase is from a door open to door closed position not an adidtional 4kt increase over the previous exit of same area without a door installed, correct Dan?
I added the red for emphasis.

Quote:
Originally Posted by DanH View Post

Pushed over and established the usual settings for fast cruise, WOT, set RPM, lean to 100-125 ROP for power, trim, altitude hold on. Indicated TAS settled in at the usual 181 knots, which is what I had with the previous exit.

Now the good part.....thumbed the switch to close the door, and picked up four knots....
As I read this, he gained the 4k above his normal speed/power settings.

I wonder if there is going to be a max speed increase, and if so, how much.

Pretty sure that is what most folks are interested in
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Last edited by Mike S : 11-13-2012 at 11:54 AM.
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  #159  
Old 11-13-2012, 12:28 PM
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Quote:
Originally Posted by RV8R999 View Post
Point of clarification...
I believe the 4kt increase is from a door open to door closed position not an adidtional 4kt increase over the previous exit of same area without a door installed, correct Dan?
Again, the numbers are preliminary, but with the door closed it appears to be faster than previous. A few GPS triangles will tell the tale.

Remember, the fixed exit area (what remains with the door closed) has been reduced as compared to the previous fixed exit. Even the tailpipe clearance bump has been reduced. I also added an internal flange to capture the trailing edge of the horizontal intake fairing; you can see it below the actuator in the above photo. Sealing that joint means one less loss of internal cowl pressure,as the previous exit panel was bulging outward along that line. Increased internal pressure + smaller exit = increased exit velocity = less cooling drag.
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  #160  
Old 11-13-2012, 12:44 PM
RV8R999 RV8R999 is offline
 
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yep, with smaller exit would expect speed increase.

So here is the test - how small will you go? I'm going to reduce mine an additional 15%.
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