|The tests were carried out here in order to clarify the
question whether the split flaps can be re-closed partially or entirely
without exceeding the allowable cylinder temperatures above the cylinder
temperature reversal heights during climb with combat power.
Since this evidence could not be provided by direct measurement of
cylinder temperatures due to too great difficulties, the required cooling
pressure gradient was taken as a reference.
As the comparison of the flown Δ px values with requirements for hottest European summer day by the engine manufacturer shows, the cooling pressure drop with internal air intake ranges from not quite to nearly sufficient in
climb, while the use of external intakes result in a certain, albeit at a higher altitude is only slight excess.
It follows that a reduction of the cool air outlet cross section by operating the split flaps above 7000 - 8000 m cannot be made.
As the plot of the Δ px
values determined in level flight with closed split flaps shows, even here the required cooling pressure gradient no longer
exists, for internal intake above 9300 m and for external intakes above 9950 m, so that from the altitudes stated the split flaps must be opened
the flaps are not closing 100% if the pre-load is not constantly checked and readjusted, and a small opening angle already creates
an adequate drop off, these measures should not occur.
The following consideration applies to normal inner air intake duct. With GM 1 - addition there is not enough Δ px
generated with existing production fan, so that an increase of the
cooling air outlet cross section or at higher altitudes a more
pressure-creating fan is necessary.
With the present design, in climb with open split flaps, with GM 1, a
sufficient Δ px could be created by increasing the speed, for example, at 8000 m from 260 to 310 km/h (see graph 2), however, then, while
taking in account the speed increase by ~ 80 g/sec GM 1 addition,
at approximately 10300 m, the speed is equal to the level speed achieved
with combat power, and thus the limit is reached.
Level flight with GM 1 with closed split flaps, taking into account a Δ px
increase of 20 to 25 mm water column due to the speed increase from GM
1, result in the need to open the split flaps from 8500 m on more and more with increasing altitude in order to
obtain a sufficient cooling pressure gradient, whereby the speed gain due to
GM 1 - addition for the most part is lost again.
The limit here is also in ~ 10300 m, where the split flaps are fully open, in addition, the Δ px required can not be provided, so that, as already mentioned, a greater outlet
cross-section or a variable fan becomes necessary.