This post will be a bit long and possibly a little off-topic but hopefully some here will find it interesting and perhaps a few programming types may even find it useful.

First a little bit of History:

A long time ago, when I was working on my F6F-3 Hellcat project, I really didn't know much about AIR files.

To get something to use for the Hellcat, I simply took the stock P47D and modified it to get the level of performance I wanted.

Just about all testing was done via Autopilot including service ceiling testing.

One of the last things I did back then (and I still recommend it today) is to fly it around without autopilot to see if the handling is as expected. It was.... to a point. As soon as I tried to fly it at higher altitudes close to 30,000 feet which were easily within the performance capabilities, I found that the stability was so poor that it could not easily be controlled. THIS WAS NOT RIGHT.

It took me a while, but it also helped that I had a couple 1/72 scale models of both the Hellcat and the Thunderbolt on my desk.

In looking them over, one rather obvious thing was that the Stabilizers on the Hellcat were much larger than those on the Thunderbolt. Out came the dial calipers and I had a pretty good estimate for the actual areas for the Hellcat.

When I changed that parameter, the stability greatly improved.

A couple nights ago, after testing a new gauge I was programming, I decided to have a look at a very old project. It is a very small jet / rocket plane and since I don't know much about CFS Jet AIR files, I have never had much success working on that aircraft. This time, I figured I would do something different; I copied in the Learjet AIR file and Sound files to use as a starting point.

The problem now is that most of the parameters didn't match. I also didn't have any reference material to get the correct numbers, so all I could do was estimate.

How often have we found drawings for an odd aircraft and been able to build it but didn't have any good specifications for it?

I have run into that quite a few times especially Japanese aircraft where drawings are available but dimensions are not so easy to find.

Heron's Formula

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A few years ago, when my Son was taking a math class in High School which I remember as being pretty close to the old "Functions" class that I had in High School, he needed a little help.

He was trying to derive formulas from equations and I took a look through the chapter in his math book.

Sometimes they give interesting tidbits that are somewhat related.

In this case, they gave an example of calculating the Area of a Triangle using something called "Heron's Formula".

The idea is that given the Lengths of the three sides of a Triangle, the Area is a simple formula.

I thought about it a bit and a couple weeks latuer came up with a practical use for it in Aircraft Design with Aircraft Factory 99.

First of all, a bit of background:

A "Part" in Aircraft Factory 99 is a listing of the (X,Y,Z) coordinates of each vertex of the Polygon that is that Part.

If you have a triangular Part, then it is pretty easy to calculate the lengths of the sides.

if you ignore the Z offset, you have the triangle projected onto the X-Y plane..... Flattened.

The calculation is easy, but such a Utility is not terribly useful; Most interesting Parts are not Triangles.

If one is working with a project in AF99, it is quite easy to trace the edges of a Structure or Component such as a Wing or Stabilizer. (See attached image for a simple example.)

If this is done properly, then a fairly simple Utility can go through the resulting Part (Polygon) and break it up into sets of triangles and calculate the area of each triangle.

In the attached example, we get the following

Triangle1 - Vertices 1,2,3

Triangle2 - Vertices 1,3,4

Triangle3 - Vertices 1,4,5

.....and so on.

It is generally possible to find an appropriate polygon that represents the object reasonably well.

Even a well placed concavity in the polygon will not break things.

This may not be the exact area dimension from the actual aircraft but it probably is not far off.

I wrote this utility several years ago as mentioned before.

I called the utility "AreaHero" after the author of the formula: Hero of Alexandria.

For this mini jet / rocket, I now have a practical use for it.

Thoughts?

- Ivan.

Hope you all have a pleasant holiday with family and close friends.

- Ivan. ]]>