Frans, I for one and I am sure the entire Europa Club
committee would love to see you write an article for the
Europa Flyer detailing your design and flying findings.
Regards, David Joyce, G-XSDJ
Frans Veldman <frans@privatepilots.nl> wrote:
> On 06/10/2012 06:21 AM, Bud Yerly wrote:
>
>> If I do say so myself, I never have cooling issues in
>>Florida at 95
>> degree summer days using 50/50 Anitifreeze. Judging by
>>the calls and
>> email success stories, these simple techniques work
>>pretty much world wide.
>
> Although your solution might indeed work world wide it
>is less suitable
> for Europeans.
>
> There are a few reasons for this:
> 1) Your solution is focussed on more cooling air flow.
>Unfortunately
> more cooling air also means more cooling drag. More
>cooling drag means
> that higher power settings are required to achieve a
>desired cruise
> speed. Although that might not be significant for those
>living in a part
> of the world where fuel prices are only a fraction from
>what it is here,
> for many of us here the fuel price is by far the largest
>cost involved
> with flying our Europa's.
>
> In another posting you wrote:
> "135 with the old pants at 5500/34 inches at 1000 MSL,"
> "His trigear only goes 130 at max cruise."
>
> I do 130 with 27", about 155 with 34". This is a heavy
>hi-top tri-gear.
> Although I selected a very efficient prop and have Fred
>Kleins wing root
> fairings, I believe that a large portion of the
>reduction in drag is
> achieved by my modified cooling system.
>
> 2) Climate. I believe that in your area the weather is
>somewhat more
> constant than it is here. This month I have been flying
>in cruise mode
> in freezing temperature conditions (high altitude in
>Norway) and in
> prolonged full power climbs with 35C OAT (Croatia).
>Unless you use
> thermostats you can't achieve constant temperatures in
>all conditions.
>
> After numerous experiments this is what I have learned:
> 0) Cooling drag is the main drag of modern efficient
>airplanes. Imagine
> the air swirling around in the cowling, colliding in all
>kind of
> obstacles, and flowing over tubular objects (worst
>airodynamic shape
> possible) and finally leaving the airplane in the wrong
>direction and
> with the wrong speed...
> 1) The Rotax engine is for 95% liquid (oil, coolant)
>cooled. Forget
> about airflow over the engine, apart from the cylinder
>walls no cooling
> air is needed at all. Sure you can compensate for a poor
>liquid cooling
> with air flow, but it is extremely inefficient. Once you
>have the liquid
> cooling working correctly, you can close off all holes.
>That's right,
> ALL holes. This includes the two "eye's". the gills, the
>naca inlets,
> the nose wheel opening, everything. There is only one
>small opening
> needed to connect the Rotax shroud for cylinder wall
>cooling.
> 2) The main problem in the stock setup is the radiator.
>The stock
> radiator is too thick (not even to mention the tandem
>design). The
> pressure difference required to maintain enough air flow
>is too large,
> and you need very large openings to keep enough air
>flowing. I have
> tried many carefully designed diffusers but I never got
>the stock
> radiator working sufficient enough for prolonged full
>power climbs in
> hot weather.
> 3) Use an oil to water heat exchanger. This means that
>you have to focus
> on the air flow of only one radiator, and also don't
>need an oil
> thermostat and still have superfast warm-up times.
> 4) Get away with the entire "dog house". It is ugly and
>it serves no
> purpose.
> 5) Use an adjustable cowl flap to control engine
>temperatures.
> 6) Reroute the exhaust so the cowl opening points to the
>rear. I tried
> to build an exhaust augmentor but I'm not sure if it
>really works. In
> any case, the cowling air escaping around the exhaust
>opening flows in
> the correct direction and doesn't upset the air stream.
>
> So. what I'm using now is a thin radiator, mounted flush
>with the
> underside of the cowling. (Custom made, 300 Euro's). It
>is slanted so it
> follows the shape of the cowling. Because of the angle
>the horizontal
> frontal area is very small, you can say it forms a
>natural diffuser.
>Flow is controlled by an exit cowl flap. If the air flow
>is restricted
> by the cowl flap, the air in front of the radiator even
>doesn't "see"
> the radiator, the air flows over the surface and follows
>the shape of
> the cowling as if the radiator doesn't exist at all.
> The air leaving the radiator is recycled because it
>flows under the
> engine, taking the heat of exhaust and turbo with it on
>its way out. No
> separate openings for these items are necessary.
> The coolant is also used to cool (or heat!) the oil via
>a heat
> exchanger. Apart from the heat-up time, the oil
>temperature is always 5C
> higher than the coolant temperature, which I consider to
>be perfect. I
> keep the water at 105C and the oil at 110C in all
>conditions. This is
> the best for the engine and the efficiency.
>For cylinder cooling you can use the standard Rotax
>shroud with the
> opening under the propeller. I made my own shroud
>because of the vaccuum
> pad alternator which prevents the use of the standard
>shroud, but the
> idea is similar.
>
> After one year of using this, I can state the following
>results:
> 1) Adequate cooling in ALL conditions. I have excecuted
>a full power
> climb from 0ft to FL095 at 80 knots in an inversion
>layer with a OAT of
> 35C for most of the trajectory, with the water temp not
>exceeding 110C
> and the oil not exceeding 120C. This was with the cowl
>flap not yet
> fully open. Although not yet tested, I'm convinced that
>the cooling
> would work ok in OAT's of 45C as well.
> 2) In cruise the cowl flap is typically only half an
>inch open; i.e. it
> protrudes only a half inch below the belly of the
>airplane. Compare that
> with the huge tunnelexit of the stock XS design!
> 3) Unlimited ground operations, even in very hot
>weather.
> 4) Superfast heat-up times. 5 minutes is even in the
>winter sufficient
> to get the oil temp far enough up into the yellow arc to
>perform a take off.
> 5) Low cowling temperatures, despite the lack of
>ventilation.
> Temperatures don't exceed 60C, except briefly after
>engine shut off. In
> hot weather I open the oil tank access door after
>landing for a few
> minutes to let the hot air out.
> 6) Weight savings. I have not weighed the difference,
>but I'm sure the
> flat radiator and heat exchanger is lighter than the two
>stock radiators
> and tunnel hard ware.
>
> About the picture:
> This was the unfinished design. The final version is
>even smoother.
> The only exit opening here is the proptrusion of the
>"tunnel" against
> the belly of the fuselage. The nose wheel opening is
>sealed off and
> flush with the belly. The cowl flap can be extended
>further but this is
> the typical cruise setting. Quite a difference compared
>to the stock
> tunnel, eh?
>
> In addition of the rectangular radiator opening I have
>two round inlets.
> The one on the starboard side serves the intercooler for
>the turbo (via
> a wedge diffuser and butterfly valve). You don't need
>this inlet if you
> don't have an intercooler. The opening on the port side
>connects to the
> cylinder wall shrouds. You could use the standard Rotax
>shroud with the
> opening below the prop instead, but I made a round inlet
>on the port
> side to maintain the symmetry. In most setups you can
>ommit these round
> inlets. That would be an even cleaner nose!
> The starboard inlet also facilitates the engine air
>intake. The port
> inlet also connects to a very small auxilliary oil
>radiator. Without
> this radiator the water-oil delta T was 10C, and with
>the extra radiator
> I got my desired delta T of 5C. It is not really needed
>if you are
> satisfied with the standard delta T.
> On the top of the firewall you see a small servo, a
>similar model as the
> vertical trim servo. This servo connects via a rod to
>the cowl flap. The
> cowl flap hinges close to the radiator so even when it
>is fully open the
> angle is very low. A simple but very efficent mechanism!
>
> The front exhaust elbows are wrapped to save the cowling
>which is very
> close.
>
> If there is enough interest in this subject, I'm willing
>to write an
> article about it. There is a lot of testing, reading,
>thinking, and
> learning from failures behind this design.
> Although I have been flying a year with it now, I have
>only recently
> been able to test it in very hot and demanding
>conditions during our
> just finished round trip in Corsica, Italy and Croatia
>and overflying
> the Alps twice.
>
> More about that trip later.
>
>Frans
>
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