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  #41  
Old 07-17-2017, 07:33 PM
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az_gila az_gila is offline
 
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Quote:
Originally Posted by alpinelakespilot2000 View Post
Hi Gil-
Just for a reference point, I just installed an AntiSplat cowl flap a couple days ago. It increases the exit air by about 11.2" square inches and in 65% power cruise it seems to have about 2-3 knots of cruise penalty. That said, I generally wouldn't need it at cruise (just climb) and, additionally, since the flap hangs down in the slipstream my un-expert opinion would surmise that just cutting back the cowl exit would have less of an impact on speed than does a cowl flap. Again, though, I wouldn't really know for sure.
Hope this helps.
Thanks, the cowl flap or louvers are the backup position if needed...

Did you get a good reduction in CHTs during climb?
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  #42  
Old 07-17-2017, 08:07 PM
alpinelakespilot2000 alpinelakespilot2000 is offline
 
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Originally Posted by az_gila View Post
Thanks, the cowl flap or louvers are the backup position if needed...

Did you get a good reduction in CHTs during climb?
Yes, but I didn't do repeated runs to accurately quantify it.

With that qualification, sustained climb on an 85F+ day full or near-full throttle would normally have me pushing 400 or more. With the cowl flap open I could climb 5000 without surpasing 385 or so. Likewise, oil temp in climb stays down about 15-20F less than it would in climb without the flap. However, once at cruise and with the flap closed, the oil continues to climb in the direction to what I was used to seeing. Still looking for in-cruise solutions to higher-than-desired oil temps on hot days.

Again, though... the above are just off-the-cuff observations that I would not put too much faith in until I can do some more careful testing.

Just another observation, Gil... I would not put excessive stock in the "your baffles must not be well-sealed" advice. That could certainly be true, but my sustained searching on this issue over 5+ years flying is that every engine is different and what works for one doesn't always work for another. In addition, your home base is probably close to the most extreme in the US, so there's no way you're going to see temps as low as a lot of others report. Finally, there also seems to be a divide between the advice you might get from someone like Mahlon Russell and what you might get from someone like Mike Busch on CHT limits. Both know a lot more than I ever will, and I have great respect for and try to follow the advice of both, but I think Mahlon's might be a little bit more universally practical on this particular issue.

Good luck though. Thanks for all your contributions to this forum.
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Last edited by alpinelakespilot2000 : 07-17-2017 at 09:33 PM.
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  #43  
Old 07-18-2017, 07:24 AM
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Originally Posted by alpinelakespilot2000 View Post
Just another observation, Gil... I would not put excessive stock in the "your baffles must not be well-sealed" advice. That could certainly be true, but my sustained searching on this issue over 5+ years flying is that every engine is different and what works for one doesn't always work for another.
Sorry, but the Lycoming cooling charts are not wrong...and whatever cooling issues a builder may suffer are not based on luck of the draw.
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  #44  
Old 07-18-2017, 09:38 AM
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Originally Posted by DanH View Post
Sorry, but the Lycoming cooling charts are not wrong...and whatever cooling issues a builder may suffer are not based on luck of the draw.
Dan, could you describe the "cylinder fin flashing problem" that does exist at various levels on many cylinders as a "luck of the draw" issue?

A variation in airflow between the fins right next to the CHT sender location could cause at least an indication of a CHT variance. The other possible variation is flashing on the cylinder side that has minimal depth fins - my old picture from my Tiger -

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  #45  
Old 07-18-2017, 11:39 AM
alpinelakespilot2000 alpinelakespilot2000 is offline
 
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Originally Posted by DanH View Post
Sorry, but the Lycoming cooling charts are not wrong...and whatever cooling issues a builder may suffer are not based on luck of the draw.
My only point, Dan, was that there's a lot more than baffling that may impact engine temps. Sufficient fuel flow, proper mixture distribution (especially for carbed engines that are prone to wacky distributions), inlet air vs. exit air, proper oil temperatures, etc. I'm not at all arguing that good baffling is not an important, maybe the most important factor, just that there are other things that can also play into it as well.
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  #46  
Old 07-18-2017, 12:54 PM
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Originally Posted by DanH View Post
Sorry, but the Lycoming cooling charts are not wrong...and whatever cooling issues a builder may suffer are not based on luck of the draw.
Yes, and to add to that, the baffle system execution is one of the biggest variables in the entire RV line. People always say theirs are "sealed", but invariably they are not.

And as long as Van continues to ignore the "zero fin depth issue" with their poor baffle design, we will continue to fight that issue as well.

Address those two fundamental issues, and the "luck of the draw" aspects (casting flash, for example) will become noise level.
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  #47  
Old 07-18-2017, 01:00 PM
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Originally Posted by Toobuilder View Post
Yes, and to add to that, the baffle system execution is one of the biggest variables in the entire RV line. People always say theirs are "sealed", but invariably they are not.

And as long as Van continues to ignore the "zero fin depth issue" with their poor baffle design, we will continue to fight that issue as well.

Address those two fundamental issues, and the "luck of the draw" aspects (casting flash, for example) will become noise level.
Speaking of which, is there a thread on the High CHT subject that has pics of someone installing or the installed washers for the washer trick for the rear cylinders? For some reason I'm having trouble visualizing how this is implemented.
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  #48  
Old 07-18-2017, 01:41 PM
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Originally Posted by az_gila View Post
Dan, could you describe the "cylinder fin flashing problem" that does exist at various levels on many cylinders as a "luck of the draw" issue?
Yes...in terms of what we get off the UPS truck. How it gets installed and flown is builder choice.

That flashing provides an interesting illustration. The average aluminum baffle achieves little more than rough proximity to the ends of the fins, very often not touching them except in a few places, as well as leaving leak paths out the side edges of the wrap. To make things worse, Lycoming inserts rubber combs in the bottom fins, which block the passages even more than flash, and push the wrap away from the fin tips.

Ok, partially block the passages between fins with flash or rubber combs, and where does the air go? Was the problem the flash, or the loose-fitting wraps allowing air to bypass the pinched paths at the flash? If the wraps were really sealed to the ends of the fins, the air would just squeeze through the narrow places...a local increase in velocity, increasing turbulence, an arguable plus.

First fit attempt, my own baffle wrap, cyl#4. Bend at the big arrow is non-existent as the wraps come out of the box, and you can see the gap prior to the comb.



Quote:
Originally Posted by Auburntsts View Post
Speaking of which, is there a thread on the High CHT subject that has pics of someone installing or the installed washers for the washer trick for the rear cylinders?
Left front and right rear cylinders. Read here, as well as the links: http://www.vansairforce.com/communit...ad.php?t=93949
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Last edited by DanH : 09-03-2018 at 07:22 AM.
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  #49  
Old 07-18-2017, 02:48 PM
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Left front and right rear cylinders. Read here, as well as the links: http://www.vansairforce.com/communit...ad.php?t=93949
Dan, I was actually asking a more literal question-- How is the washer installed between the cylinder and bafflle in the no fin area?
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  #50  
Old 07-18-2017, 03:39 PM
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Dan, I was actually asking a more literal question-- How is the washer installed between the cylinder and bafflle in the no fin area?
On the mounting screw. Here the screw point is just above my left index finger.

Of course, the washer spaces the tin away from the head at the black rectangle as well as the no-fin depth area in the red circle. Airflow at the black rectangle is just a leak. That's why I referred you to how to make a bypass duct instead.



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Last edited by DanH : 09-03-2018 at 07:28 AM.
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