burkefj's blog View Details
Archive for November, 2014
Posted by burkefj | Nov 24, 2014 @ 01:03 PM | 9,491 Views
I wanted to build another large scale rocket using foamy build techniques....Idea is to take a rocket that typically needs lot of nose weight and build it light enough to fly on smaller motors. Using sims using normal 1/4" ply, fiberglass for the nose and LOC 7.5" body tube the balasted weight ready to fly is 20 pounds for this model with a proper CG location using J-570 motor.. My goal was to try to get it close to 3.3 pounds, final result ws 4 pounds 2 oz with balast less motor, motor required will be an H-128 minimum... I'll run altimiter deployment with motor ejection as backup. The hellfire requires about 1.8x the weight in the nose for every ounce of tail weight(motor) so you need to keep the rear end light. This is full scale, the Hellfire is 7" diameter and 64" long. The advantage of building this way is you can create your centering rings and sheeted tube to whatever size you want.

Using rocksim CP calculation which is less pessimistic than barrowman estimations shows the CP to be 31" from the nose and with one caliber of stability margin, CG should be at 24" from the nose, or just in front of hte middle yellow band.

I got good deal on 18" body tubsfrom sunward for $6 (pack of 5), couplers for $3, some leftover 6" 3.9" couplers for $4 each, and a 29mm motor mount kit(provided a tube that fit into the bt-55 and three 3.9 to 29mm centering rings)and used three sheets of 6mm depron and 2 sheets of 2mm sheeting....Continue Reading
Posted by burkefj | Nov 18, 2014 @ 12:17 PM | 9,915 Views
I've been wanting to try this for a while, the work I did on my Dyna-soar/Titan II got me motiviated. I do a lot of depron RC airplane construction, my thought was to do a model that typically needs lots of nose weight or is very heavy, and see if using stringers/centering rings and 1mm depron skin I could make a large light model to fly on E-15's......

The only wood in this model are two centering rings in the upper portion that are lite ply, and the balsa coupler I used for my BT-70 upper tube since it was handy at the hobby shop, the rest is depron sheet, cardboard motor tubes and some .04 styrene sheet.

For drawing centering rings I've been simply using a strip of cardboard, put a thumbtack in one end, and measure to the needed radius, poke a hole and insert my fine sharpe and draw it directly on whatever I need to cut, no need for a compass. This can be used for drawing cones or transition shrouds as well where you need a very long radius.

I cut a 7" by 2" triangle out of 6mm depron, grooved and glued in a 1/8" carbon rod which will take the brunt of the nose cone landing force....I then added perpendicular triangles, and took turns gluing in triangle filler pieces and carving those to match the original triangle pieces a quarter at a time...eventually I had nose cone shape. I left one quadrant unfinished so I could add weight if needed, then finish it. I added a few gradually increasing centering rings to get the needed outer diameter.

I cut off a...Continue Reading
Posted by burkefj | Nov 05, 2014 @ 12:40 PM | 9,909 Views
I've been wanting to try to adapt my X-20 to a titan booster. Since the X-20 is large and lightly constructed, the booster would have to be light enough and large enough that I could use lower powered rocket motors to keep the speed down so that it wouldn't rip the X-20 apart on boost. I wanted to try a center 29mm motor tube and use depron centering rings, longerons and a 2mm skin. I wanted the all up weight without motor to be 60 oz or so less the glider. For reference 60" of standard 7.5" loc cardboard tube with a coupler weighs 60 ounces.
Lots of photos so read the whole thread to see final construction photos of the booster....
Length will be 108.5" and 8.25" for the booster to be standoff scale with the drawing I have. Ideal motor will be a 29mm H-97 or H115 that have a pretty flat mild thrust curve..

Here we go.

Here is the rocket simulation, and here is my original X-20 that boosts off a rail on E-6 24mm reloads, here is a quick video of it flying.

X-20 Dyna-Soar rocket boosted RC glider Launch Video (0 min 33 sec)


If this all works, the glider will be ejected via a piston that will also pull out the booster chute, and then I'll glide the dynasoar back. If that works ok, I may try doing an air start of the dyna-soar once released.