Thanks guys. I browse the RV forum religiously, there is so much good information on there. I did come across and save a lot of posts from DanH but not the second one you mentioned Charlie. I don't know how they feel, if I post stuff on there without being an RV owner? The subcowl I fiberglassed, is the back half shape of a tear drop. Much like the Vetterman setup. Should help speed up the inside cowl air to align to the tip of the tear drop, where an opening will be for the exhaust pipe. Also will allow the outside air the stay attached to the bottom and sides of the subcowl.
The perforated inner tube would face aft. The idea was to allow the slowing moving cowl air, to get sucked into the faster moving exhaust tube. But I think for now, I'll just cut the exhaust pipe short inside the bigger outer pipe. This will take place inside the subcowl. Then the bigger outer pipe will exit the tip of the tear drop, all the way down the belly of the plane. Where the pipe stops changing color from the exhaust heat, I'll cut off there. That will be my baseline.
Inside the subcowl, the front of the outer tube (
eductor) will have some type of bellmouth on it. I found a few on the internet, but I may 3D print one as a mold, then fiberglass overtop. I've done that a few times now with designing parts.https://www.summitracing.com/int/parts/vpe-10953/overview/
I have a butterfly valve on my oil outlet, which will keep temps where I want them during slow / fast speeds. Still need to make a big flap for my coolant outlet though, so it can do the same thing. This will allow me to really know if my inlets are too big / too small based on how far the flaps need to close / open to keep temps.
- Matt Boiteau
On 1/5/2019 10:49:04 PM, Charlie England ceengland7@gmail.com <flyrotary@lancaironline.net> wrote:
*Anybody have advice on how they
run their exhaust exit systems?*
- Matt Boiteau
------ Forwarded Message
--------
From: Matt Boiteau mattboiteau@gmail.com
<flyrotary@lancaironline.net>
Date: 12/9/2018 10:13:56 PM
Subject: [FlyRotary] Exhaust setup's
To: Rotary motors in aircraft
<flyrotary@lancaironline.net>
I'm at the
stage of securing an exhaust setup. How do you guys
do it?
I'll have a sub-cowl
under the belly of the plane (shape of a tear
drop), which will streamline the main cowl air
(coolant and oil outlets).
I'm thinking I exit the exhaust (2.5" pipe)
inside the sub-cowl and have a 5" wrapped
around it which ends out the sub-cowl for x
length. This should help create a vacuum and
pump out the main cowl air.
Before exiting the main exhaust pipe, should
I have perforated holes or louvers in it?
- Matt Boiteau
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Hi Matt,
I'm no engineer, but I do know a few engineers with recent hotel
time. :-)
Have you read this thread?
http://www.vansairforce.com/community/showthread.php?t=68241&highlight=cowl
This is a later thread, with postings & references back to the
link above:
http://www.vansairforce.com/community/showthread.php?t=159473&highlight=cowl
Watch Onewinglo's youtube video & try to visualize what the
air's doing wrong as it comes out of the cowl.
It's about cooling a Lyc, but cooling is cooling. It's a long
thread, but reading anything posted by DanH is worthy of respect.
Note all the attention to smoothly curved entry areas, and the
ultimate 'bluff body' (squared off) exit, with the external surfaces
parallel to the free stream around the a/c.
I could be wrong, but I see a lot of skin drag with the
tube-in-a-tube, with the exit air having to scrub on both tubes to
get out. Also a *lot* of drag where the cooling outlet air enters
the outer tube (reference: 'bellmouth' & 'velocity stack'). Is
the perforated inner tube intended to be a muffler? If so, it's
kinda like the inner tube of a Spintech muffler, but the dimpled
slots face aft in the Spintech. The spintech works great as a rotary
muffler, if that's your goal.
There's lots of NACA & NASA research on eductors, if you do a
little digging. Most of the stuff I've seen says that they can work
great at low speeds, at the expense of excess cooling drag in
cruise. A good storehouse of reading material is the CAFE
Foundation. Try here:
https://cafe.foundation/v2/tech_enablingtech_dragreduction.php
and here:
https://cafe.foundation/v2/research_reports.php
with attention to the three 'Local Flow' articles in the 2nd link.
Here's hoping I'm not making things worse,
Charlie
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