V1

[KenG]

Cowlflaps,

In the case of most light twins these aircraft are not certified with a V1 or a V2 speed. FARs Part 23.51, 23.67, 25.107 and 25.121 explains
how aircraft are certified and how the manufacture is to determine these speeds. While V1 is determined by the manufacture with specific runway
performance in mind, it is not dependent on the length of the runway. That is V1 for a 2,000 foot runway is the same as for a 13,000 foot runway. Just
on the prior you may not have accelerate-stop distance. That being said there is no real way to compute a V1 for an aircraft that does not have one.
(again this is done by manufactures.) While LeftCoaster gives a technique for determining a V1 speed this is based on accelerate-stop distance only
and a distance that is based on a selected length of runway. This does not take into consideration accelerate-go distance and accelerate-go over a 50'
obstacle. These are all tests that a manufacture must perform with highly qualified test pilots.

The best bet is to try and find real world V1, VR and V2 speed and hope that the person who did the aircraft dynamics modeling got it right. In the
past I have worked with various modelers on aircraft performance on various King Airs. This is not an easy task as you fix one thing, cruise speed and
a given altitude and it will throw off acceleration time performance during the take-off roll. While pilots do have a good number of charts available
to us we often do not have all of the charts used during certification. It is always a compromise.

If you absolutely cannot find any good Vspeed numbers then you might have to try various methods of computing a set of numbers. I would always
recommend that you start with ISA condition from an airport at sea level. There are a couple of scenery files that are designed for testing aircraft
performance with runway distance markers. The first set of Vspeeds I try to find are VS0 and VS1 as I can then interpolate some numbers from them such
as VREF and VR. On a large airplane with multiple flap position I will find the stall speed for each position. This goes into a chart. I then repeat
the test at the same weight at ISA+30 and again at ISA-30 and record the numbers again. I then follow these tests up with VMCA testing again at ISA,
ISA+30, and ISA-30. (You can go into the aircraft config file and look up the stall speeds these should match your ISA flaps up and flaps full down
speeds.) I perform these tests as close to the ground as I can. 400' AGL is optimal. (No I would never try this for real at 400'.) Ok I now have my
stall speed at various flap configurations. By multiplying them by 1.3 I can compute the VREF. If the VREF speed is below VMCA+3 then VMCA +3 is my
VREF speed. I also have a basis for starting to compute a VR speed. For VR I start with 1.1 X the stall speed in take-off configuration. For V2 I can
compute a V2 speed is 1.2 times the stall speed in the takeoff condition. Again all speeds should be above VMCA. I then test to see if under ISA
conditions at 400' and with one engine failed I can achieve the following climb gradients: 2.4% for twins, 2.7% for three holers, and 3.0% for four or
more engines. If the airplane can not perform to these standards at ISA and MTOW then I would not perform engine out in this aircraft.

Whew, we now have a bunch of VR, V2 and VREF speeds through charting straight line between the numbers for ISA -30, ISA and ISA +30 we can
extrapolate number for temperatures in between. Performing the stall tests at 5,400' and 10,400' I can also extrapolate the difference for altitudes
between SL and 10,000'. Finally I would test at minimum fuel and load and a loading right in the middle of minimum and MTOW at each temperature and
altitude and finally I have a set for numbers from ISA -30 to ISA +30 from SL to 10,000' that can be used.

However I have not touched V1. This is because V1 is a decision speed and based on engine failure on VEF. VEF is determined by the manufacture in the
certification process. So here is where some flying policy comes into play. Airlines who operate heavy equipment have come to realize the danger
associated with high speed aborts, in such they recommend continuing the take-off in most cases where speed is equal to 10% below VR, unless such
take-off with put the passengers at greater risk (fire or big parts coming off the airplane.) Thus for V1 you would be safe making it 10% less than
VR. Now with those speeds we can start to makes some distance measuring first with accelerate-stop tests at each temperature and weight (and airports
close to the altitudes, Denver International and Lake County are close.) Then followed by accelerate-go tests. If you reach an altitude, temperature,
or weight in which the aircraft lumbers and will not takeoff then you have found the maximum performance of the airplane and you should not attempt
take-offs under those conditions.