Today's Message Index:
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1. 02:15 AM - Re: Re: Cooling issue (GRAHAM SINGLETON)
2. 06:10 AM - Re: Re: Cooling issues XS 914 on the ground (nigel_graham@m-tecque.co.uk)
3. 11:44 AM - Re: Re: Cooling issues XS 914 on the ground (Fred Klein)
4. 07:43 PM - Re: Re: Cooling issues XS 914 on the ground (Frans Veldman)
Message 1
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| Subject: | Re: Cooling issue |
Just make one change at a time Roland, then measure and see if it works.Ver
y tempting to install more than one good idea while on the job.Graham
On Monday, 22 August 2016, 7:35, Roland <schmidtroland@web.de> wrote:
Bud,
no plug&play indeed. And I also fully agree, that a compromise has to be fo
und (ideally the best one) with a fix setup.
I'm just happy, that I finally (after >5 years of ownership) managed to fin
d a good compromise for me, although I did many things unconventionally and
even some different to your suggestions ;-) . I have now a good basis=C2
- for further little improvements - if one day I ever should have the fee
ling that I miss tinkering (at the moment I write this, I cannot imagine it
).=C2-
Happy landings
Roland
PH-ZTI
XS TG 914
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=459740#459740
S -
WIKI -
-
=C2- =C2- =C2- =C2- =C2- -Matt Dralle, List Admin.
Message 2
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| Subject: | Re: Cooling issues XS 914 on the ground |
Hi Fred,
I waited for more informed respondents but it's all gone eerily quiet.
As you are aware, I have developed my own cowling and cooling ducting -
so have spent a lot of time researching this problem.
There is no prescribed ratio as such. The dimensions will be defined by
the aircraft speed at which the cooling should be most efficient
(climbing, full power - probably around 80kts (41 m/s) and the speed at
which you can get air through the radiator (a lot less than 41 m/s -
your radiator manufacturer should be able to supply this data). In the
cruise of around 120 kts, the air will be whistling by at about 62m/s.
The surface area of the radiator is dictated by the amount of heat you
need to dump (you'll get this from your engine supplier), though I guess
you've already sourced a rad.
The purpose of the divergent duct (a diffuser) is to slow the air down
and raise it's pressure, before presenting it to the radiator at a speed
that can be passed through the radiator matrix that is fast enough to
absorb the heat, but not so fast that the airflow stalls and causes drag
(like the standard Europa). So the eventual size of the duct opening
will be arrived at using a ratio of flying speed to
best-airflow-through-rad speed.
The next bit sounds simple - just make up a divergent duct to join the
opening to the radiator ........ but as in all things aviation, there's
a "gotcha". The diffuser walls cannot diverge more than 7.0 degrees from
the free airstream (deduced buy experiment and verified by subsequent
CFD analysis), or the boundary layer breaks away and goes turbulent -
causing huge cooling drag. Once the air has cleared the radiator, it
needs to be speeded up again and it's pressure reduced to rejoin the
outside air at as near as possible, the same pressure (pressure
recovery) any miss-match here will cause drag This is done by passing it
through a convergent duct (a nozzle). Since the air is being forced into
a reducing cross section, it can withstand a far sharper convergent
angle before the boundary layer goes turbulent - typically around 15 to
25 degrees. (have you ever noticed the different inlet/outlet cone
angles of a vintage aircraft venturi?)
How much you need to slow your air down dictates how long your
narrow-angle duct should be. In my case it was about 2.5m - putting the
radiator just in front of the tailplane, clearly not a viable option. I
had to get the air into my cowl, slow it down, pass it through the
radiator, speed it up and exhaust it in just under 600mm. in the space
in the centre tunnel. I think I have devised a way of meeting all of
these requirements within the challenging space constraints, though as I
haven't been able to test it out yet, will keep it under my hat for the
time being!
Hope this is of some help.
Nigel
On 20/08/2016 20:49, Fred Klein wrote:
>
> As an aside to this conversationcan anyone tell me the ratio of the area of the
inlet to the area of the face of the radiator?
>
> This would be of interest as I grapple w/ cooling issues related to my non-standard
engine install (a MPEFI, liquid cooled, 1.8L RAM Sube.
>
> thanks in advance,
>
> Fred
>
>> On Aug 20, 2016, at 11:12 AM, h&jeuropa <butcher43@att.net> wrote:
>>
>>
>> CORRECTION! Ours is also a 13 row oil cooler. I based the previous answer
on a photo where part of the cooler was actually hidden from view. We were just
at the airport and verified. When we mask off, there are 6-7 rows showing.
>>
>> Sorry for any confusion. Heather
>>
>>
>>
>>
>> Read this topic online here:
>>
>> http://forums.matronics.com/viewtopic.php?p=459689#459689
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>
>
Message 3
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| Subject: | Re: Cooling issues XS 914 on the ground |
> On Aug 22, 2016, at 5:52 AM, nigel_graham@m-tecque.co.uk wrote:
>
> I waited for more informed respondents but it's all gone eerily quiet.
As you are aware, I have developed my own cowling and cooling ducting -
so have spent a lot of time researching this problem.
Nigel=85thank you for your thoughtful (and informed) reply=85I=92m aware
of the =937% solution=94 to the flow in the inlet duct and issues
related to the desire for non-turbulent flow. I will respond to your
message w/ photos and comment, perhaps best handled w/ a personal email
since out discussion will focus on non-standard engine/cowl
combinations.
Fred
Message 4
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| Subject: | Re: Cooling issues XS 914 on the ground |
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Hash: SHA1
Hi Nigel,
> The purpose of the divergent duct (a diffuser) is to slow the air
> down and raise it's pressure, before presenting it to the radiator
> at a speed that can be passed through the radiator matrix that is
> fast enough to absorb the heat, but not so fast that the airflow
> stalls and causes drag (like the standard Europa).
You describe a divergent diffuser. Later it was discovered that you
can also make a wedge diffuser, by placing the radiator at a steep
angle, and a horizontal sheet of metal meeting the end of the
radiator. This accomplishes the same effect, slowing the air down and
increasing the pressure. The air goes indeed into turbulent flow, but
this is just what you want inside the radiator; turbulent air carries
heat more easily away. One of my experiments was to use the original
radiators but in a wedge setup and it gave a huge improvement, while
the required radiator opening was much less.
A later discovery (not by me but in general) was that you can also
create a natural wedge diffuser by placing the radiator at an angle...
and leaving the horizontal separator away. This simply means you can
mount the radiator inline with the angled shape of the lower cowling.
It sounds a bit strange at first sight, but once you realize that the
function of a diffuser is to convert a small opening with high speed
air to a large opening with low speed and higher pressure, you will
see that the same happens with a very steeply angled radiator in free
air. The frontal surface is much smaller than the surface of the radiator.
Thinking like air molecules: hitting the radiator they are scooped up,
to pass through them, but when there is no more room for air molecules
the remaining air molecules just see a solid angled "plate" and just
follow the shape of the lower cowling as if there is no radiator at
all, so it causes no drag.
Anyway, it works perfectly well. And it is done this way in many
modern aircraft.
Hope this gives further insight.
Greetings,
Frans
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