burkefj's blog View Details
Archive for August, 2015
Posted by burkefj | Aug 19, 2015 @ 03:34 PM | 9,412 Views
This is just for information only and I'm not suggesting you do or do not try this. This is what I have done and I'm just sharing the experience.

One of the big hurdles with using the Aerotech 24mm RC rocket motor reloads is the cost of the motor casing. Since this casing is machined from a single piece of aluminum(it has a solid end) and not a tube, it is double the cost of the standard 24/40 rms casing.

The E-6, D-7 and E-7 are endburning reloads and do not come with forward seal parts since they are not needed in a solid case.

I started thinking whether or not the rc reloads could work in the standard casing with forward closure, so I bought a motor tube and the forward closure and compared dimensions. The forward closure has a little flange that holds the forward o-ring in place in a standard non rc reload. That o-ring butts up agains a .032 fiber washer to seal the front closure. For that reason, it is not possible to use the rc reload as is in the casing, as the internal length is .032 longer than the rc casing internal length. Also, due to the forward closure lip, the liner tube tends to slip over that little flange when pushed on by the nozzle, increasing this gap even further. This prevents proper sealing of the rear o-ring.(when you tighten the rear closure the nozzle flange pushes on the liner tube as it is tightened, not on the propellent grain.

I did a bit more thinking about this and was concerned about any gas blow around into the hollow forward...Continue Reading
Posted by burkefj | Aug 18, 2015 @ 08:55 PM | 8,127 Views
Here is a simple version of a Bell X-1E rocketplane. This plane started out as the second of the original X1 rocketplanes. Due to losses of other models, this one was rebuilt with a new cockpit with ejection seat, and a 4% extremely thin wing to go beyond mach 2. The wing is similar in thickness to the X-3 Stiletto.

I chose a cruciform since the wing is mid mounted. This does push the CP forward but normally the wing loading reduction is worth the tradeoff of extra nose weight. I used some strips of .03 styrene on the bottom of the fuse to prevent landing "road rash".

I installed a fully movable horizontal stabilizer since it is easy to set up on a single ply model like this. I used two 1/2" styrene .03 disks on either side of the vertical tail to support the elevator pivot, which has an aluminum tube glued through. The carbon rod goes throught that tube and is captured by small aluminum tubes on either side that glue to the carbon rod. The surfaces are then glued and taped to the rod. I used a micro servo horn from dubro glued to the carbon rod to connect to the pushrod.

I chose to use the flap area on the real wing for the ailerons and left the small outboard ailerons as decorative only.

I'm using a single 450mah 1s lipo direct to the spektrum 6115e and it seems to run the 3 hs-55 servos fine, at least for 4 flights.

Since the CG is required to be about 5/8" behind where the wing le hits the fuse, it required 4 oz of nose weight. Total auw rtf with rocket motor is just over 12 oz. It's about 37" long and 26" ws.

Flights were nominal, needed just a bit of roll trim post-boost along with some up trim. Here is the video, in reverse order of the actual flights.

Bell X-1E RC rocketplane (2 min 35 sec)

Posted by burkefj | Aug 11, 2015 @ 04:44 PM | 8,341 Views
I wanted to build another big foam rocket using depron, and chose the Pershing 1A since it has tiny fins and typically needs lots of nose weight. I had done a 5.5" version previously that flew well but wanted something a bit bigger. The plan was to try to hit 4.5 pounds fully loaded and fly on H-180 29mm motors. I used 6mm depron centering rings and stringers, 2mm skin, and a core cardboard 29mm stuffer tube that acts as a spine. the upper parachute bay is 4" by 12" long and is pml phenolic to contain the ejection charge. Ejection is by altimeter which is in a magnetic hatch area in the rocket body. The ejection charge wires go up through the stuffer tube into the parachute bay and through a little cap that fits into the top of the stuffer tube. The parachute bay can be so small because the weight is light enough that I only need a 48" lightweight chute. Fins have some select placements of carbon inbetween laminations. The cone was from a craft store and then sheeted with 2mm depron, and a carbon rod goes up through the middle to take the landing loads. The shoulder is a pml coupler and the forward recovery attachment is to a 3/32" ply plate that is glued to the carbon rod/foam cone. Since the shoulder is hollow it doesn't steal any of the parachute bay area. I have not had to add any nose weight at all in this model which is almost unheard of in a Pershing 1A. Diameter is 8" and length is around 80".

In order to do...Continue Reading
Posted by burkefj | Aug 05, 2015 @ 04:20 PM | 7,963 Views
Recently I found my plans for the XF-85 goblin I had done back in 2008, and found the video. I decided I'd build a new one as the old one was lost in a move. I started with the plans as they are posted. I decided to put in my normal 24mm rocket mount just so that I could use my same plug in motor pod with a grayson microjet.

Here is the flight video of the new version, below I give more detail on what I did:
McDonnell XF-85 Goblin RC parkjet (5 min 34 sec)

I had designed this with a fully movable elevator to give sufficient pitch control, and kept them horizontal as people have had pitch control issues when trying to use the angled tail surfaces.

In order to clear the rocket motor mount with the elevators. I extended some permanently mounted stubs and mounted the movable surfaces outboard. If you do a normally mounted motor in the tail you don't need to do that. I went with dual servo ailerons since they are simple.

I considered doing a top view as well, but that would have moved my CG even further forward.

The changes I made were to add a doubler just on the bottom half of the fuse below the wing, this gives something more substantial to land on and allowed me to hide a little carbon rod stiffener for the back half(it was a bit flexy) and allowed me to hide my nose weight. I also went with a round 1/8" carbon rod A frame wing spar setup since this version was going to weigh more than my original. AUW for this version was 12 oz. The ventral stub...Continue Reading