question about Mars Lander construction

[bjphoenix]

I have the Tango Papa 1.6X version and I'm asking here because the question may apply to the Estes version as well as the Tango Papa version.

First I mocked up the geometry on paper based on the written instructions and the measurements of the pieces and it seems to me that this places the pivot point for the legs too far to the rear. I suppose this is based on the given length of the parachute tube. Maybe the intent is to cut the parachute tube to fit but I didn't see that in the instructions. What I need to know is how far the pivot point should be in front of the rear bulkhead.

Second I see a photo in the instructions of the motor tube plus the vertical rods for the leg supports and rear bulkhead all assembled, but without the parachute tube. From my understanding of the construction the parachute tube would be epoxied to the centering rings over the motor tube before getting to this point in the construction. Is the photo inaccurate?

 

[Shade]

I think I understand what you are asking, the chute tube does not
extend all the way aft to the rear bulkhead but only over the two
forward most centering rings.

I will dig up my Estes and Semroc instructions and scan them.

I have not built a TP 1.6 lander... yet...

EDIT:
I attached the scan of my original Estes Plans that shows the position
of the Chute tube. Does that help or did I miss it?

View attachment ML scan.pdf

 

[troj]

I don't have mine available in front of me, but in all of them, if you follow the measurements provided, the hinges end up where they belong.

I've built both the 1.6x and 2x Landers, and don't recall a problem with positioning.

I'll have to see if I still have the instructions when I get home.

-Kevin

 

[Shade]

What I need to know is how far the pivot point should be in front of the rear bulkhead.

Approximately an inch for the Semroc/Estes versions.

I will assume that it would be scaled up proportionally.

From my understanding of the construction the parachute tube would be epoxied to the centering rings over the motor tube before getting to this point in the construction. Is the photo inaccurate?

I would say the photo is incorrect the legs have to be glued to the centering
rings before the chute tube is glued inplace. They might have omited parts
for clarity in the photo.

 

[bjphoenix]

I don't have mine available in front of me, but in all of them, if you follow the measurements provided, the hinges end up where they belong.

I've built both the 1.6x and 2x Landers, and don't recall a problem with positioning.

I'll have to see if I still have the instructions when I get home.

I have the full instructions for the 1.6X from about 10 years ago and that is what I am looking at. When I got my kit I prepared a full CAD drawing of it and Tom may have including my drawing with later versions of his kit. I recently dusted off my rocket stuff and got back in so I thought it was time to actually build my kit. The instructions are a bit hard to follow if you are just reading through and trying to visualize the pieces, plus I thought I got my motor tube mixed up with another 29mm tube and I wasn't sure if it was long enough, so I decided to check the CAD drawing. I couldn't find my original drawing file from 10+ years ago but I still have all of the parts so with a little measuring I recreated the drawing. I actually thought I would make some step by step drawings to go along with the kit construction and eventually take build photos too. When I did the drawing it seemed that the legs were too flat, and when setting on the ground the motor would touch the ground at the same time that the legs did. Plus I inferred from the slots in the body tube that the legs needed to articulate a bit, but they couldn't move up any farther because the motor was already against the ground. I moved the pieces around in autocad so that the legs seemed to droop during flight but could flatten out during landing, and this is what seemed to put the parachute tube too far forward.

I will compare my drawing with various photos I've collected and I can also post it here.

 

[bjphoenix]

I have made a few JPG's from my autocad drawing.

The first one shows the lander configuration as per my understanding of the instructions. The legs go through slots in the lower airframe and the slots define how far the legs can move up and down. The drawing shows legs at both limits of movement.

The second one shows the adjustment that I would make. I was thinking that when the legs are at maximum compression the engine nozzle should just touch the ground, then when the lander is in flight the legs are drooped back as far as possible to help with aerodynamics and stability.

Actually I'm thinking I should make an adjustment somewhere between the extremes of these 2 images. It seems that if the lander came down straight you would want the nozzle to hit before the legs bent so far as to damage the airframe, but the legs should be adjusted to provide some safety margin in case the lander comes down tilted a little bit to one side or another.