Light 'n Tight II - Av Bay Rebuild - Wild Child

Recently flew my Wildchild DD with the Missile Works 3D printed sled, the RRC2+ and the Lipo battery combo. Ran two #8 threaded rods and used the Doghouse Rocketry Anchor Posts on each end for recovery harness (1/4" kevlar) connection. A Perfect Flite Thin Mil chute fit nicely into the tiny upper airframe. Ran ematches from the altimeter to 2gr charge wells (also from Doghouse Rocketry)--direct connections, no terminal blocks of any kind. G76 took it to 2000' and change, and it dual deployed perfectly. Next flight on an H268R!

Cool! How much was did it weigh on the pad?

Greg

Greg,
Newbie question here..On the bulkhead caps would a grove milled into the wood around the piece that fits into the coupler and fitted with an O-ring be useful or is BP gas/crud incursion into the AV-Bay via the bulkheads not a problem with the stepped bulkhead?

rharshberger said:

Greg,
Newbie question here..On the bulkhead caps would a grove milled into the wood around the piece that fits into the coupler and fitted with an O-ring be useful or is BP gas/crud incursion into the AV-Bay via the bulkheads not a problem with the stepped bulkhead?

Click to expand...

Hmmmm ...

Well, it's complicated. The short answer is, "it can". I've actually thought about doing that, but backed away from the idea. It makes more sense to do place an O-ring on items that have a high flexural stiffness, and are resistant to deformation under pressure. That said, I think even things with a lower flexural stiffness may benefit. The problem is that you cannot look at just the pieces, you have to look at the assembly, as a system, and try to understand how it behaves under deployment events. To do it right, you would have to run tests to get data points, maybe high-speed video to see how it reacts under pressure. Many of us are just not equipped as hobbyists to do that. I'm certainly not. Basically, we do the best we can and adjust when necessary.

That said, the more significant area of leak path (at least from my limited experience) has been the all-thread port and the e-match port. For the time being, I think time is better spent making sure that those areas are addressed before the cap tenon area is looked at.

Greg

Last night I did so more work. I decided to forgo the "paper in the tube" location method and chose to go with only the "fine tune" option. I tapped the switch plank to a 2-56 screw size, then used some 120 grit to scuff up the area of placement inside the av bay tube. As far as the epoxy, I went with JB Weld for this join. The reason is that this area is black and I was fearful that too much heat would weaken the joint. It may be an unfounded fear, but I went with my gut instinct.

After placing the JB Weld on both surfaces to be joined, I placed the switch plank inside the av bay tube. It took about 5 minutes to finally locate the tiny 2-56 hole and engage the screw that would hold it place. After fully seating the screw, I backed it out to inspect it. There was epoxy on the threads. Not good. I cleaned up the screw with acetone and applied some Mobil 1 motor oil on the threads and threaded the screw back in place. I applied a little bit of torque on the screw to make sure the switch plank was fully seated in the av bay tube. Then after about 2 hours of curing, I broke the screw free and re-tightened it, and repeated that action another two hours later.



This morning, I broke the screw free and tightened it again. At this point, I think I'm home free regarding the question of "can I get the screw out".

That leaves only one manufacturing task left to do to complete the av bay. That is to re-tap the screw switch to the final 6-32 threads.

Man, I hope this all works.

Greg

I was able to tap the screw switch up to 6-32 threads.

So now came the moment of truth. Would the system actually work when I fully seated the screw?

I got the common head screwdriver and went to work, and eventually I heard the friendly beep. Just once, then it died. Oh well, I knew the battery was on its last legs, so I swapped it out for a new one. I then tightened the screw and got no tone. Oh. No. The switch must not work. So, just to make sure, I shunted the switch terminal. Still no joy, so maybe the switch was ok after all. So maybe there is a problem with the power supply. So I took the MAWD off the sled and put a fresh 9V (classic box battery, not the small battery) to verify the power supply. I touched the battery to the wires and still, no joy.

The MAWD must be dead. Sigh.

There go the plans to fly it this weekend. Oh well. Better for it to fail now than at 1,400 feet.

Greg

Nooooooo, that sucks. Sorry to hear this after all that work.

Well, to say I was disappointed would be a first-order understatement.

I have had some good correspondence with PerfectFlite as of late to resolve this issue and I am hopeful that it will fly again.

Again, this MAWD unit has only flown once, even though I bought it back in 2007. It looks to me that it's in great condition.

Greg

Interesting that the altimeter would just die...
If you are interested I have a MAWD for sale over on the yard sale for $60.
Check it out I think that is a fair price. Also have 6 other types in that listing.
MAWD works great, I have flown it three times all with great sucess.
Flew to over 10k twice and over 5k once, the 10k flights were past mach, so mach delay works.

Jimmy F. said:

Interesting that the altimeter would just die...
If you are interested I have a MAWD for sale over on the yard sale for $60.
Check it out I think that is a fair price. Also have 6 other types in that listing.
MAWD works great, I have flown it three times all with great sucess.
Flew to over 10k twice and over 5k once, the 10k flights were past mach, so mach delay works.

Click to expand...

Thank you for the offer. On Friday afternoon I shipped the MAWD back to PerfectFlite for evaluation, per the manufactures directives. So perhaps there is still hope that this MAWD will fly again. BTW, I'm very happy with how PerfectFlite has responded to my inquiries. The response has been timely, professional and helpful. It has made me happy about my choice to fly PerfectFlite.

Regarding the launch that I would have flown the revised av bay at, the winds were at the safety limits so it wasn't an optimal day to do a test. So, even that worked out in a way.

Greg

PerfectFlite contacted me yesterday as they received the package and ran some checks. The bottom line is that the MAWD altimeter is fine, but the switch leads I was using for the MAWD test (that is outside of the av bay) were somewhat corroded and not twisted well. Ultimately that led to a 7.47 volt drop in that part of the circuit. So yep, it wasn't going to work. Bottom line: Don't assume the wires work as advertised. Test them. Thankfully this lesson was learned on the ground and not in flight.

There is another question though with my switch setup and how robust it is. That's because it worked, then it seemed not to. I need to run some tests to see if there is a voltage drop in that part of the circuit. I at least need to run them so I can get a baseline figures of what the "factory fresh fabrication" results are.

Greg

I ran some electrical checks on the switch system and the bottom line is that the JST portion performs great but the screw switch I designed was intermittent. An intermittent electrical connection is at best a nuisance, but in flight applications it is totally unacceptable. Rather than trying to fix it, I removed it. Or at least as much as I could (that JB Weld is pretty tough stuff to remove).

I am leaving the "home brew" switch and moving on to OTC solutions. In this case it will be the SS-10/10T which I ordered from Mouser.com.

I don't know how I'm going to mount it yet. I'm just hoping there is enough room.

Greg