Message text written by "Paul Atkinson"
>I am just wondering what you 914 powered flyers consider to be an adequate
minimum runway length. The figure I have generally been quoted is 450
meters
or 1500ft. I get the impression that this is a generic figure that will do
for any Europa regardless of powerplant.
Having read several accounts of 914 powered Europas with VP props leaping
into the air like homesick angels, I wonder if any of you are happy
operating from shorter strips, and how much benefit there is from the extra
power and VP prop over say a 912 with fixed pitch. For comparison mine is a
monowheel classic which will have a Wilksch WAM120 and an MT prop, and I
will be operating from elevations of 500' or less, most of the time.
Any comments gratefully received.<
I agree with the comments so far on this subject. Be aware that as there
are several factors, all of which can affect take-off run and some of which
can affect landing run. When some of these are added together in certain
conditions it is possible to end up with with distances which are double
the standard numbers. The CAA provide an excellent booklet giving
recommended factors for this. Although they only give an approximate idea
it provides a way of predicting whether the length available is sufficient.
Remember that the take-off distance available to 50ft (TODA) can be more
relevent than the take-off run available (TORA) if there are any trees or
even hedges at the end of the runway.
The factors and their affect on take-off and landing run and distances
required (TORR/TODR & LRR/LDR) as published by the CAA are as follows:
Factor TORR/TODR Correction LRR/LDR Correction
Weight 2% per % 1% per %
Temperature 1% per deg C 0.5% per %
Pressure Alt 1% per 100ft 5% per 1,000ft
Headwind 7% per 5kt 7% per 5kt
Tailwind 20% per 5kt 20% per 5kt
Up Slope 5% per % 2.5% per %
Down Slope 2.5% per % 5% per %
Dry Grass Add 20% to hard rwy figures Not
published
Wet Grass Add 30% to hard rwy figures Not
published
Soft Ground Add 25% to hard rwy figures Not published
To apply these factors the performance for an individual aircraft needs to
be measured for a known set of conditions (ideally fairly standard
conditions ie. typical average weight, 15 degC, typical airfield pressure
alt, zero wind or small head component, level hard runway). When
subsequently calculating the performance on the day remember to apply the
corrections in the correct sense. To avoid a lot of work with a calculator
I have produced a spreadsheet which will apply the corrections. This sheet
also does the weight and balance calculations having inserted fuel load (in
volume), pilot & pax weights and baggage weight. If anyone is interested I
could look at making it available. Naturally it would be free to Europa
Club members but a small donation to the club funds would be appreciated
---From non-members.
Finally when it comes to the actual take-off in limiting conditions the
following two checks during the take-off run will help assess the stop-go
decision as applied to Europas:
1. 25kts by 25% TORA
2. 35kts by 50% TORA
If these are not acheived the take-off must be aborted. Of course to
measure this markers need to be placed or the positions otherwise defined
along the runway.
Whilst most of us rarely operate close to the performance limits regularly
it is nice to know how much margin you have in hand. For instance if a
Europa needs 200m take-off run in standard conditions at MAUW, it will need
400m with the following conditions (Temp +30degC, Press Alt 3,000ft, 4kt
tailwind, 2% up slope, soft grass). If there is a hedge at the end of the
runway the standard TODR might be 300m so to clear the hedge in the above
conditions you would need 600m. That is without a safety factor of 33%
which the CAA recommends so the margins can become reduced quite
significantly.
Food for thought?
Nigel Charles
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