Notes on a micro Silly Putty based DT timer for 6" to 8" clg's.
Aluminum tubes (from K&S) are cut with a single edge razor blade. De-burr the inside edges.
The main shaft is crimped with pliers to create a drag paddle. Paddle is 5/16" long and should just fit inside the 1/8" o.d. tube body.
All the parts to make a micro timer. The balsa plug will seal the putty in place.
The drag flap is cut from an aluminum pop can with scissors. Sand the edges smooth.
Rear bearing glued onto the main shaft with CA.
Front bearing fitted to body with CA. File the end flush and de-burr.
You can see the paddle inside the body. It should be set back about 3/32" from the end (to allow room for the balsa plug).
Silly putty. Enough for lots and lots of timers!
The reinforcement ring that fits onto the end of the shaft is carefully drilled with a 1/32" diameter hole. I use a pin vise for control. A small drill press would be ideal.
Install the ring and drill through the shaft carefully.
1/32" music wire pin is CA'd in place (be careful not to get any glue in the bearings!). The excess shaft material is cut flush with the ring.
Push some silly putty into the end with a 3/32" music wire pin until it is packed tight. Rotate the shaft a few times and push the putty back in.
Clear away a small amount of putty from the end so that the balsa plug will have room.
CA the balsa plug into the end.
Plug cut off flush with the aluminum body. Seal with thin CA.
The finished timer!
The timer is very light.
This is how much the aluminum drag flap weighs.
Flap and timer combined.
My StingerII weighs 4.8 grams without a timer.
Marking out the nose for the timer installation.
The timer pocket is cut out and sanded smooth.
The timer is installed with thick CA.
A small pin is added to the top of the body. Motivation is a 5/16" diameter medium weight orthodontic band.
Drag flap is atached with thick CA to the left side of the fuselage (same side as the glide turn). This spins the glider down in a hurry!
Weight after timer installation. Due to the removal of a large amount of nose lead, the timer only added 0.1 gram!
0.015" glass fiber plate added to left side to reinforce the nose and to act as a wind shield for the front of the drag flap. 1/64" ply is a good substitute. Small amount of clay is a fairing. Note the flap is extended into DT position.
AUW is now 5.0 grams. 5/16" medium dental band gives a DT time of ~ 100 seconds at 0 degrees C for just under 1/2 turn on the timer arm. (tested in my refrigerator!)
