Ha ha.... I wondered who was going to be first out of the closet, me or
Fran=92s. Fran=92s and I have been collaborating on a journey of discovery
for
the last couple of years.
I have been reluctant to share what I have been doing, mostly because up
until now I have only been able to tell everyone what doesn't work! Both
Fran's and I can share funny stories of tuft test showing air flow out
where it should be flowing in, some take offs where we couldn't get back on
the ground quick enough due overheating and lots of work and re work.
For me, I am still works in progress, but over the next winter I plan on a
fourth iteration over next winter which will be a similar design to Fran=92
s.
If I can persuade my friend Graham Singleton to come and visit, it might
even a new carbon fiber cowling :)
At a high level the sources of design material we used were:
- Kays & London wedge diffuser
- Kuchemann & Weber trumpet diffuser
- Cooling design notes from the Central States Canard Group
- Taper diffuser design from the Canard group
- Oil Streaking presentations from the Central States Canard
Group
- Think Vs. think radiator notes from Rotary Engine forums.
- Cooling Vs flow data from Rotax and Laminova
Our design criteria was:
Cooling that works in all phases of operation:
- Ground
- Climb
- Cruise
Operates over a range of -5c to 40c
Offers the lowest drag possible
This ultimately dictated a few design solutions:
*
*
*Cowl Flap. *
This is the only way we could get cooling over a large speed range and
ambient temperature.
*Laminova liquid oil heat exchanger.*
In one of the design iterations that Fran's had created he had the oil and
water radiators separated. Although this provided plenty of oil and liquid
cooling it caused a long cycle time to bring the oil temperature up to
operating temperature. The Laminova solves this problem. One problem that
Fran's and I have not been able to solve is the need for a small axillary
oil radiator.
*Thick Vs. Thin Radiators.*
I was ultimately able to make the thick radiator work with a Kuchemann &
Weber trumpet diffuser, but I intend to abandon this. From our research we
have discovered that 70 to 80% of the heat exchange occurs in the first
20mm of the radiator.
*Diffused Inlets.*
At first glance Fran's cowl appears to have no diffuser on the inlet side
of the radiator, however it works very well. After reading the design
notes for the Kays & London wedge diffuser our hypothesis is that because
the coolant radiator is at an angle to the relative wind it behaves like a
wedge diffusers.
*Other thoughts & observations.*
Fran=92s has been flying a working solution for nearly a year and his desig
n
can be used as is. I am doing some experimentation with a single diffused
inlet that provides the engine combustion air, inter cooler and the engine
shroud. Given the level of effort this has proved to be I wouldn=92t
recommend anyone copying what I have done, and it remains to be seen if it
even works.
Over next winter I plan on removing the thick radiator and I expect that
this will be a lower drag configuration over what I have.
Pointing the exhaust back is offers a lot of drag reduction. I have some
photographs that show the exhaust plume on the old style exhaust shooting
out nearly 2 meters. For monowheel the exhaust needs to be much longer so
that carbon monoxide does not find its way into cabin via the tunnel.
Unfortunately this was complex bit of stainless steel to fabricate.
When my cowling is fully open it is the same angle as the standard
cowling. I see 8 knots difference between fully open and fully closed.
This isn't an exact comparison because when my cowl flap is open air will
spill around the side and I expect this would be higher drag than the
original cowl. I have done a number of long cross country trips and for
the same manifold pressure settings I am seeing about 5 knots increase in
my cruise. I have Warp drive blades and I do not wing root fairings so my
set up is not as efficient as Fran=92s.
Regards, Paul
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