landing gear – Aviation CAD TechNotes

F4F/FM2 Wildcat Landing Gear Update:

I have been busy with the Landing Gear CAD model for the F4F/FM2 Landing Gear assembly.

These images give you some idea of the progress to date. This is quite a challenging project due in part to the poor quality of a few drawings but also to the ongoing checking of dimensional relationships between the parts. Most notable is the forward Drag Link Support where you can see several red lines which is a visual indication of stated minimum and maximum tolerances. Also on this part, it is worth noting that the top pair of main holes are at 4.0625″ x/centres whereas the lower pair is at 4.1557″ x/centres…a minor variation but obviously critical dimensions.

The roller chain sprocket is a calculated profile to suit the specified roller chain; there is a smaller sprocket yet to be added to the Retracting Mechanism gearbox. This part of the project will take a while to complete and it will eventually also include the Engine mounting frame.

NAA P-51D Mustang: Landing Gear Dims

I am currently working on the Landing Gear geometry dimensions to check the data for accuracy. During the course of this research, I thought it may be of interest to share some Excel formula for converting angles shown in Deg Min Sec to decimal degrees and vice versa.

p-51 Landing Gear

The plan angle for the OLEO Strut relative to 25% wing chord is 4° 32′ 35.14″ as shown in the above sketch which translates to 4.543094 degrees.

The accuracy of the angles and dimensions in the NAA documentation is rather good with small deviations occurring of only 0.003mm when developing this in CAD. I should note this deviation is negligible and for all intents and purposes can be ignored. However, I like to get this stuff right so I have set about developing the landing gear dimensions to be as close as possible to be exact.

As I have already developed the cad geometry I measured the same angle above from the CAD system which is now giving me 4.54309673 degrees.

In Excel:

excel table

Starting from the left; in column A; I have input the angle from the cad system, then systematically converted to Deg, Min, Sec in separate cells and then converted back to a decimal angle in column E.

The equations for each cell are as shown below:

p51 Landing gear eq

Just enter the equation in the cells denoted; so for the first equation, this would be in cell B2. The latter equation works fine without parenthesis, which I included just to keep the equation tidy.

The Landing gear geometry will be recorded in a separate spreadsheet and added to the P-51 Ordinate Package. Mustang P-51 Ordinates

P-51D LG