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-   -   Photos: Really good baffle seals (https://vansairforce.net/community/showthread.php?t=141528)

rvsxer 10-14-2016 07:24 AM

This is a really good thread. C'mon, there must be more engine baffle pics out there. Don't be shy. Yes, I have an ulterior motive. Guess what I'm working on right now... Redoing the forward baffling and seals near the inlets on my -6.

rockwoodrv9 10-14-2016 07:49 PM

I looked at the pictures Dan posted showing some issues with the baffling on that RV. From looking and the narrative, I would think the plane would overheat so bad and have so much drag, it wouldn't fly. Yet, it does. In fairness, the cowling was off for some reason.

It is either a testament to the design of the plane or engine - or both. Im working on my baffling and plenum now and so paranoid about holes and air leaks, it is driving me nuts. I worry about cooling so I guess it is a good thing to go nuts this time!

I have a James cowl and BillL built a beautiful plenum for me. I have everything going for me possible so hopefully I will stay cool enough. I will get some pictures posted. In my opinion, it is looking pretty good.

LettersFromFlyoverCountry 10-16-2016 09:17 AM

Enjoy the critique on that plane at the fly-in. What's the "proper" way to do this area, assuming the incorrect way is published somewhere and that's what so many people are using?

rv8ch 10-16-2016 02:13 PM

Inlet baffle seals
 
I'm also looking for the right way to do this - the instructions are very vague in this area, and if there is an obvious right way that's tried and tested, I'd like to use it.

keen9a 10-17-2016 09:08 AM

Quote:

Originally Posted by DanH (Post 1109582)
Keep 'em coming folks.
Example; this from NASA CR3405; pressure coefficients measured in four areas of an upper plenum volume:


Dan, there is a key word in this figure that you are missing. This is Total pressure coefficient. Total pressure is the stagnation pressure of the flowing air. Through the throat area of the inlets, the flow velocity is at it's maximum, and therefore the static pressure is much lower than the total pressure.

I don't have data, but I find it hard to believe that the inboard side of the inlet has higher static pressure than the stagnated air behind the spinner.

Ron RV8 10-21-2016 11:24 AM

Looks good...

It would be really nice to see some pictures of how you dealt with the inlet transition and ramps... My CHTs are running a little higher than I would like and this is where I have trouble visualizing exactly what to do...

Quote:

Originally Posted by Toobuilder (Post 1109255)
I have not yet addressed the area around the ring carier, but as far as I'm concerned, this is how you do the perimeter:





One piece of rubber and even clamping at the fasteners assures minimal leakage. I have a few hundred hours on it now and the edges of the seal show perfect contact with the upper cowl.


DanH 10-21-2016 05:20 PM

Quote:

Originally Posted by keen9a (Post 1119350)
Dan, there is a key word in this figure that you are missing. This is Total pressure coefficient. Total pressure is the stagnation pressure of the flowing air. Through the throat area of the inlets, the flow velocity is at it's maximum, and therefore the static pressure is much lower than the total pressure.

Figure 44 is a 0.3 Vi/Vo inlet. By definition, velocity (and thus remaining dynamic pressure) in the inlet throat is low, only 3/10's of freestream velocity. Static + Dynamic = Total, thus if dynamic is low, static must be high.

There's a natural tendency to think of inlets as a choke point, the narrow passage in the Bernoulli tube illustration...high velocity, low static pressure. It isn't so. Just for fun, carefully add up the measured area of the passages between the fins on your cylinders. My 390 cylinders only total about 23 sq inches of flow area, all four together. Add 12 for the oil cooler scat hose, for a total of 35. The inlets total 56.5. The exit is about 30 in cruise configuration, and about 46 in slow mode.

Radical example? Maybe, but again, go measure some Van's inlets. They're all fundamentally external diffusion, Vi/Vo <1. For sure, none are Vi/Vo greater than 1, which would be required to drop static pressure below freestream static at a point aft of the inlet plane.

Quote:

I don't have data, but I find it hard to believe that the inboard side of the inlet has higher static pressure than the stagnated air behind the spinner.
A very localized condition? Interesting theory. You seem to be arguing that a baffle flap on the inboard wall can be fastened to the sheet metal, and it will blow outward against the fiberglass. Care to measure static pressure on each side of that flap, and prove or disprove? I'll give you an incentive. The volume around the nose case, forward of the front baffle wall, is part of the lower cowl volume, which is indeed above freestream static. Not a lot, but...

AlexPeterson 10-26-2016 09:18 PM

Well, I'm not sure mine qualify for the thread's title...

I added fillets to the lower outboard inlet areas:



These baffle seals have 1540 hours, no meaningful wear:



A little wear on this:




Years ago, I rigged up a manometer in the cockpit, and calculated that I was getting nearly full pressure recovery on the top. I run very cool cht's and oil. CHT's with OAT of 60F at altitude might be around 320F at a power setting of 8gph, KTAS 168 or so.

rv8ch 10-27-2016 12:42 AM

Inlet baffle seals
 
Thanks Alex, those are probably the most clear pictures of the way to do the baffles around the inlet that I've seen, and clear up a lot for me.

Marc Bourget 10-27-2016 04:08 AM

Mr. Peterson said:

Years ago, I rigged up a manometer in the cockpit, and calculated that I was getting nearly full pressure recovery on the top. I run very cool cht's and oil. CHT's with OAT of 60F at altitude might be around 320F at a power setting of 8gph, KTAS 168 or so.[/quote]

Do you have any data? Does your "full pressure" mean the dynamic pressure at the speed you were measuring?

mjb


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