My test of the Nav Utilities mod

[GabeTeuton]

I'm creating this page in order to not fill the mod's page with this discussion, as there are already 4 or 5 posts on there...

this is the mod's page

Now a little bit of background to justify this topic... I love to approach guided by ILS, I know there are other methods, but i just love it since it was introduced to me back in the late 90's/early 00's by Microsoft Flight Simulator, and i knew this mod since forever, so I started playing again recently and installed it when I got to the part of the space program development that needed planes, which was not much later... I like the gathering data from kerbin contracts, and the easier way for me to complete those is by plane, but when it came the time to use it, I was not able follow the altitude indicator (with the autopilot I use, which is AA), that's clearly not AA's fault, and at first doubted that I may be doing something wrong, then I started thinking about the descent rate and its relation to the Glideslope, (I also love Excel) so I got to work....

The lastest test was performed today, I started gathering data from the markers, the point for each marker represents altitude ASL, and DME (distance), the first 3 where taken from the distance displayed by selecting a target, the target was placed roughly where the mod's DME states "0", that place is accurate to where planes would touch down on the runway, a little bit after the start. A little bit ago I took another point, in this case the distance was measured only by the DME so there are 3 points in order to account for the lack of precise numbers provided in the DME (which funcionally speaking is perfectly fine):

Spoiler

First

Second

Third

The fourth one

Now the first thing to realize is that we are talking about triangles in here, the DME/distance is the hypotenuse, the altitude is of course Height, and the Base would be the linear distance between each "end" (which are at the same altitude). After that I needed to calculate the actual Base in order to complete the triangle:

Spoiler

You'll see that the chart named "correcting previous for TL" is beacuse the runway at KSC, is at 70m ASL, and that's the altitude at which I would reach "0", then by applying some trig functions i can find "θ", which is the angle of the Glideslope, and it should be around 3º, you'll see that correcting or not the θ's value is roughly around 3º, how accurate that result is could be debatable (specially because MY measurements aren't as precise as they should be), so there's no conclusive evidence to say that there's something wrong with the mod (and after going thru the data I believe that regardless of evidence, there's nothing wrong with it).

Now that I have θ calculated based on practical measurements I can do the opposite, and given θ, calculate distance from the "touchdown point" and altitude at that distance.

Spoiler

Fixing θ at 3º and using the markers distance (the actual coded distance taken from the files) just as a reference point (which are the actual reference points in the ILS approach system), i can calculate the other 2 sides of the triangle. This time I know the Base and θ, so with another trig function (which is misnamed but whatever) I can calculate the Height, or altitude, and also in orange calculate the ASL altitude, as the altitudes calculated by the functions are based of off the runway altitude so there's no point in pluging those into the autopilot, won't work don't try it (took me some random amount of time to notice when I was not hitting the runway). FYI you'll see there's no value for the hypo, because it does not matter.

Well, we are close to getting our desired Vertical Speed, now we need to calculate that base on the assumption of our own horizontal speed, why? Well because i need to reach the "touchdown point" after some X amount of seconds, and that amount has to be the same for my horizontal speed and my vertical speed.

Spoiler

That got me thinking that it works as a pretty easy function "y = mx + b", so it should be easier to calculate, and also it will allow me to verify that value, which to my amazement was exactly the same, I believe this should have been expected, but it was amazing anyway.

Now I tested this results in-game:

Spoiler

 

So when I am at 10km from the runway (measured by the DME device in the mod) precisely at the calculated altitude (after runway correction), i can set my VS to whatever result I got, and forget about it until I touchdown.

Conclusion:

The mod is fine as far as I can tell, however it would be interesting if it could show you the VS required to meet the profile starting at the outer marker and providing an altitude to "cross" it, also, it was fun to try and figure out the VS by "mathing".

Thanks!

Excel Sheet

https://drive.google.com/file/d/1GxlbaEN0mr26ZZ7JRGIMbItisGFSkf4B/view?usp=sharing

Edited April 8, 2021 by GabeTeuton
adding link