 Lancair crash at SnF
Michael Ash <mike@mikeash.com> wrote in
news:1209240958.122432@web1.segnet.com:
> In rec.aviation.student WingFlaps <Moreflaps@> wrote:
>> On Apr 27, 6:04?am, Dan_Thomas_nos...m wrote:
>>> ? ? ? ? Lots of people had the impression you were talking about the
>>> dreaded downwind turn, with all the talk about the energy required
>>> to accelerate to maintain airspeed. The energy required, as pointed
>>> out in a much earlier post with several very good references, is so
>>> tiny that it's not worth fooling with at all.
>>
>> Perhaps you could put a number on that? Could you try a gliding turn
>> with stopwatch and altimeter and compare that to a straight glide?
>
> In the optimal 45-degree-banked turn the load factor will be about
> 1.4. Your best glide speed and min sink speed will increase by the
> square root of that, or 20%. The glide angle remains the same if you
> increase your airspeed appropriately, so your sink rate will also
> increase by 20%. So instead of 650fpm you'll be coming down at 780fpm.
> At 78kts (65kts best glide speed from previous post plus 20%) and a 45
> degree bank you're making a circle a bit over 500ft across which will
> take you 13 seconds to complete half of. The extra sink rate from the
> turn will therefore cost you 30 feet over what you would have
> experienced in a straight glide for the same amount of time.
>
> You'll also lose about 80 feet to accelerate from 65kts to 78kts. But
> you'll gain this back at the end, so as long as the end of your turn
> ends at a reasonable height it can be ignored.
>
> The numbers will, of course, vary between aircraft but it would appear
> that the extra energy loss due to the turn itself isn't all that
> significant. If 30 feet is the difference between making it and not
> making it you probably should not be turning around in the first
> place.
>
> Did I miss anything?
>
45 degrees isn't enough unless you have a very nice gliding airplane or
are starting from a good height to begin with.
Bertie |