Airframe Design Analysis Program
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Home > Articles & Tips Index > Model Design > Helmut Lelke's Airframe Design Analysis Program

[Courtesy of Helmut Lelke, hlelke "at"]

Helmut Lelke's Design Analysis Program (Free!)

Have you ever had the urge to design your own plane, but didn't "go for it" because you weren't sure your design would fly?  Maybe you've done designs before, but didn't feel secure enough with your usual TLAR (That Looks About Right) methods to invest all that building time, for fear of ending up with an unstable or hard to maneuver design?

CRRC club member Helmut Lelke has captured some simple design guidelines which guarantee success the first time out, without trial or error, and which work for a variety of airframes - all the way from power planes to high performance sailplanes.

Helmut's simple but powerful DOS-based program, DA (design analysis), aids in the design of model aircraft by computing important flight parameters based on your design input. You can then compare your parameters to established guidelines, making any modifications to achieve the desired results.

Running the program is simple.  (All this stuff is documented in the accompanying doc file, but here's an overview to get you interested!)

Let's collect information from the planes we're currently flying - I'll post the results so we can all learn more - how about sending me the template and results file from your favorite or not so favorite airplane, along with some info about the design (name, type of aircraft, your feel on flying characteristics)? (click any webmaster or comments link and send away!)

First you fill in the numbers for the following in a template file :

  • Stab area (including elevator)
  • Stab aerodynamic center, or AC (Helmut provides working guidelines for this if you're not sure how to calculate AC)
  • Fin area (including rudder)
  • Fin AC
  • Span, chord, sweep and dihedral angle for each wing panel

Run DA, pointing to the template file you just created, and "voila", the program writes the following to the end of the template file:

  • Projected wing area
  • Projected wing span
  • Pitch moment - how far away should the stab be from the wing
  • Yaw moment - how far away should the fin be from the wing
  • Pitch stability factor (how stable or unstable in pitch will the design be)
  • Yaw stability factor (how stable or unstable in yaw will the design be)
  • ... and a few other interesting goodies ...

So, now you're thinking, "but what would I do with all these numbers - how do I know what's good?".  Helmut's documentation gives you a set of working guidelines for ranges that are known and proven in the real world to result in well-behaved designs - so you know what to use as a target for these magic numbers.

The template file sample included in this package is a real design for a 100" sailplane that Helmut flies all the time!  As anyone who has seen Helmut fly this design can attest, it launches,  flies stably, goes UP, and stays there for a long time.

The other nice thing about this program is that it provides stability guidelines not only for "full house" aileron equipped airframes, but also gives working guideline for how to end up with a design that grooves without ailerons.

Click here if you want to see the template file for this 100" design with the output values from the program

Helmut has generously made his program and design guidelines available free of charge.

You can either download each file individually, or as a PKZIP archive.

Download DA Files

DA_WEB.DOC - this is a 34 kB Microsoft Word document with instructions, definitions of the variables that DA calculates and a variety of recommended ranges for each variable in the program.  (or click here for a 25 kB Adobe Acrobat PDF file of the documentation)

DA.ZIP - this is the main program (46 kB PKZIp archive of the DA.EXE DOS program that will run on MS-DOS and Windows systems)

DA_TEMPL.DES - this is a sample design template file - make a copy of this and alter the input parameters to match your proposed design

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