Gilles et al,
..... and I respectfully bow to your testing and experience.
The importance of the coolant system is certainly not lost on me. While
you are probably not aware of it, I have done a lot of work to develop a
fully ducted water/oil radiator with full diffuser, nozzle and cowl flap
in an effort to reduce cooling drag and improve cooling efficiency.
If the Rotax published literature is to be believed, the 9 series
engines should be able to run for up to fifteen minutes on a reduced
power setting in the event of a coolant loss, to enable the hapless
pilot to reach the ground safely. Indeed they justify the unusual
configuration that combines the complexity of water cooled cylinder
heads with inefficiency of air cooled cylinder barrels for that reason.
Your experimentation and the experience of coolant failure of others
begs an interesting question, if the Rotax air cooled barrels do not
offer any increased endurance in the event of coolant loss - why use
air-cooled barrels?
Water cooled barrels would offer far better heat distribution and thus
less localised distortion and allow tighter tolerance pistons that in
turn would develop greater power with less noise.
With regards to thermostats, your comment were perhaps intended for the
original poster. I was referring to the scenario from a previous poster,
where the coolant has been lost and the engine is still running. Under
these conditions you can reasonably expect the oil temperature to rise
(to possibly critical levels) and I was trying to indicate that a
synthetic oil could possibly withstand these extreme conditions.
Nigel
On 04/06/2014 11:24, GTH wrote:
>
> Nigel Graham a crit :
>> I would be very interested to hear how successful this is once fitted
>> and tested (either on or off list).
>> With regards to oil over-temp should the water coolant be lost, I
>> think you might be surprised how resilient a modern full-synthetic
>> oil is (which can be used in a 9 series engine as long as you don't
>> run 100LL). On a reduced power decent I think you would get away with
>> it.
>
> Nigel and all,
>
> I respectfully beg to differ with the above statement.
> As some listers here may know I've been conducting extensive oil and
> water cooling tests on a 914.
> Whereas in-flight heat rejection through oil and water actual numbers
> are not totally in agreement with the Rotax ground bench numbers, the
> coolant plays a key role, and total loss of coolant is definitely a
> major issue. I seriously question the chances of engine in-flight
> survival for more than a very short time at idle.
> If you happen to have solid data on experiments on Rotax engines with
> partial or total loss of coolant I would be much interested and
> willing to publish them on Contrails !
>
> Concerning the coolant thermostat option, the question is, do you
> value lightness, simplicity and low drag or not ?
> And above all, do you have ample cooling, since the idea is to always
> provide excess cooling and just throttle the oil flow to help oil
> warming up.
> A thermostat helps oil *warming*, not cooling, at the price of
> additionnal weight and constant cooling drag penalty.
> As I understand that some Europa builders experience marginal cooling,
> they may wish to first fix the cooling airflow issue.
>
> FWIW,
> Best regards,
|