RV7Guy

RV7Guy

Well Known Member
Hi Everyone,

I have a 390 with front mounted governor for my new 7. (Standard Van's cowling) I'm working the baffling utilizing the baffle kit for the angle valve 360. Everything fits very well up to the front baffle pieces. My plan is to make a plenum but I'm trying to figure out how to use the front pieces. These are the pieces that bridge the front of the case.

Stephen Christopher has been great sending me photos. Looking for other options and specifically anyone that has used a plenum with this combination.

Thanks in advance!!
 
Check out Dan Horton's installation maybe? It is a 390 with plenum.

Here is a photo I "Borrowed" from one of his posts

P3170006_zps49a737d4.jpg


Sounds like you are making progress :D
 
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RV7Guy said:
I'll get the additional part$ ordered tomorrow!!!
Click to expand...

If you really want a custom plenum, you may not use the Vans parts.

Remember, a plenum is just a volume with a lid. There are lots of ways to do a lid; the trick is developing a good inlet. Your first goal is to minimize internal flow separation, as it wastes valuable kinetic energy that would otherwise be turned into valuable pressure. The second is to minimize leakage, the same reason for the plenum lid, so the pressure doesn't leak to the lower cowl plenum without carrying away any heat.

So, decide up front if you want to go with a radically low or high Vi/Vo inlet, or stick with the stock Vans inlet, then optimize the connection between the nose opening and the plenum volume for no separation, and no leakage.

Early photo. Curved center baffle continues smooth volume expansion.



Here's the reason, an illustration from NASA CR3405. The pressure survey shows a significant loss of pressure along the inboard sides of the inlets...and aft of the center baffle wall. IMHO, there are three things going on here. The test aircraft baffle installation probably leaked badly along the inboard side, something seen a lot in RV's. It had a flat transverse center baffle wall, thus an abrupt transition to the plenum volume, guaranteeing some degree of flow separation. Last, the losses are worse in the climb, so there was probably some separation at the inlet due to AOA.



Structural tweaks after a few hundred hours. (1) Added vertical lip to plenum lid around curved front baffle wall, placing #8 fasteners in shear. Stiffer, seals better. (2) Front corners of lid clamped between plates fastened directly to the ears on #1 and #2 cylinders. Eliminated cracking of sheet baffle parts over the cylinders.

 
This is what I want to do for my next plenum, I'm functional with my current one, at least for Phase I flying, but I'm not happy with it.

Dan - what size are those inlet rings?
 
airguy said:
This is what I want to do for my next plenum, I'm functional with my current one, at least for Phase I flying, but I'm not happy with it. Dan - what size are those inlet rings?
Click to expand...

6" diameter. Low Vi/Vo inlet, inlet area is about double the outlet area in cruise.
 
That looks great Dan! what is the diffuser made out of? does it flex-move with the engine?
 
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