Current Projects

Well the only ones I can easily identify are the Sahara and the Leviathan... so you got me! The one on the far left looks like an upscale Alpha (*looks* like it... not saying it is!) and the one with the similar nose on the right I would have guessed as a Panavia but the fins are not the ones used for that kit... not a partizon for sure (it's longer than the sahara and it uses the sahara's fin shape) So I am officially stumped!

Two out of six ain't bad. In order of appearance from left to right:
Estes Executioner with some modifications built this summer after the previous one flew in the trees.
Estes Sahara.
The red and black with the white nosecone hiding in back is an Estes PS II Big Bertha.
Estes Leviathan built from parts. If anyone wants the parts list and vendors let me know.
Another Executioner build in 2003.
The little guy is a scratch build made from parts that Boris gave me in 2017. It is called the Boris K. It flies great on an A8-3.

The Sahara cost me about $30.00. The Leviathan cost me more because I got an Aeropack retainer, custom cut fins and other parts I bought a la carte.

Estes is supposed to be coming out with a 50th anniversary Saturn V that is not crazy expensive. Keep an eye on their web site. I consider it a must have kit for the fanatic rocketeer. .

I started dabbling with the Saab kit I mentioned earlier in this thread. I bought some 1/8 birch wood that I will use to create my own TTW fins. This kit has two sets of four fins so it will be a bit more challenging than the usual three fins and a nose cone kit. I'm going to junk the exhaust baffle and use a 24mm motor tube. In addition I will have to cut a total of 8 fin slots. I'm still planing on upscaling this kit someday.

To help plan the build I tapped two pieces of 8x11 paper together and drew a full scale diagram. I'm wondering if anyone else has done that for a scratch build or when customizing a rocket.

I've been drilling holes in my nicely finished rockets to accommodate my new JL Altimeter 3. At least I can mod the Estes Sahara as it's not painted yet. It is very painful to try to put a hole into a finished rocket!

A few years ago, I retrofitted our entire fleet of finished model rockets with ventholes to accommodate a JL Altimeter 2. I developed a process for making altimeter ventholes which works pretty well.

First step is to decide whether to use 3 or 4 equally spaced ventholes. The answer for each rocket depends on whether the number of fins on the rocket is 4, or a multiple of 3.

Next, I extend the fin lines to the nose-end of the body tube using an appropriate sized piece of angle iron, or 90 degree wood moulding. I mark the fin lines lightly in pencil on the OD of the finished body tube (lightly enough that they won’t mar the finish, but can be wiped-off later…Sometimes I wrap the body tube OD with blue masking tape before marking the lines, if I am confident the clearcoat won’t lift off). I usually try to place the holes mid-way between the fin-lines to avoid the potential for aerodynamic interference from the fins. (However for practical purposes the fins are usually so far downstream of the venthole locations that putting them between the fin lines really isn’t necessary.)

Locating the holes axially along the body tube is a bit of an art. I typically attach my Altimeter 2 using the supplied swivel connector, either directly to the nosecone eyebolt, or to a split ring attached to the eyehole of a plastic nosecone. I normally locate the holes approximately at the position where the altimeter will hang during flight. When locating the holes, it is desirable to have them 1-2 body tube diameters downstream of the nosecone-body tube joint, or away from any decal edges, to avoid aerodynamic distortion of the pressure at the ventholes. It is necessary to have the ventholes far enough down the tube to avoid being covered-up by the nosecone shoulder (Duh!). It is also necessary to avoid having the holes at a location where they might be blocked by a stowed parachute or streamer. You want to avoid putting the holes at locations where they will line-up with the seams of a cardboard body tube (so you don’t weaken or split the tube). Finally, it is necessary to have the holes at a location where you can reach them with the tip of your finger inside the tube. (More on why this is necessary later).

Once intended hole locations are selected, I lightly mark them in pencil, check that all of the above criteria are met, then start making the holes.

To make the holes, I start with a very sharp sewing needle, and gently but firmly push the needle thru the body tube from outside to inside. (Using a thimble to push reduces fingertip distress.) After the first push thru, I use a piece of sandpaper and my fingertip to knock down the cardboard volcano on the ID of the tube, to remove anything that could snag the recovery system. (I find using a fingertip better than trying to do it with sandpaper wrapped around a dowel...So finger length often ends up being the deciding factor in determining how far down the tube the holes end-up.) After sanding, I then push thru the needle again, sand again, push thru again, etc. repeating a few more times until the holes are clean. I then move on to gradually enlarge the holes using a succession of slightly larger items…straight pins, small nails, larger nails…using the same push thru/sand/push thru/sand process, until the desired size is achieved. (A micrometer comes in handy to measure the various pins and nails used to make sure you get close to your desired hole size.) After the final sizing step, I take a conical bit from my Dremel tool set, and BY HAND, use it to break any burrs on the outside surface of the holes, by centering the tip of the bit in each hole, and slowly working the bit back and forth by hand. At the end of this process, I have a set of nice clean holes of the desired size, with no damage to the finish on the exterior of the rocket.

Notice that all of this is done by hand, without using any power tools. I found this to be a prudent precaution. My experience has shown that using power tools on delicate work with model rockets often leads to trouble as bad things can happen fast. Hand making the holes makes for more precise positioning, and avoids inadvertent damage to the finish due to slips.

After retroactively making altimeter ventholes for all of our legacy rockets, I made it a point going forward to put altimeter ventholes into every new rocket during the initial build, before finishing. When making ventholes on new builds, I use a similar process, but take the added step of applying CA to the selected hole locations (locally saturating the tube) before making the holes. In addition to strengthening the tube, I find this results in neater holes with fewer fuzzy burrs. (I didn’t use CA on the retrofits…just carefully pushed thru the existing finish, gradually sized the holes, and sanded the tube ID between steps.)

This method has worked well for me so far on many rockets with cardboard tubes, up to mid-power rockets. Give it a try.

Thanks for the tips.... they should be very helpful.

According to pundits on the rocketry forum, you evidently don't really need multiple holes unless you're relying on altimeter based ejection systems so that an errant breeze doesn't pressurize the altimeter bay. That said, a single hole can be done if you keep the area of the hole the same... I put three on my Sahara, but I opted for one on the Ventris as this rocket is finished... and figure I could tolerate one messy hole.

There is a nice piece on the topic here:

www.vernk.com/AltimeterPortSizing.htm

The article suggests a 1/4" hole for every 100 cubic inches of volume of the altimeter bay. Then in order to scale to the volume you actually have you use this:

A1 = V*(Aref/Vref)

Where A1 is the ultimate hole area you need, V is the actual altimeter bay volume, Aref is the area of a 1/4" hole and Vref is 100 cubic inches. With this in hand, what you end up with (after some manipulation and so long as you're restricting yourself to a single hole) is:

D1=Dref * sqrt(V/Vref)

So if your volume is 20 cubic inches you get D1 =.25*sqrt(20/100) = .111" or just under 1/8th inch (.125) After pluggin my ventris nose cone hole I calculated the volume there to be about 10-13 cubic inches which brings a single hole of just over 5/64".

The article has the math shown to do multiple holes and so on... very informative. Using CA for my Sahara produced nice holes... I drilled a pilot hole using my dremel on low speed, soaked and then step drilled the holes from there. Sanding produced very clean holes. For my finished Ventris, I used a 1/16" drill by hand open a hole up. I then used a new knife blade to trim back the fuzz above the tube. Then side-soaked (using a very very fine tip) the hole with thin CA. I oped for a single 3/32" hole in this case even though calculations showed that 5/64" would be enough. The hole was pretty clean but I did use the blade to carefully trim the paint that got flexed. A nice sharpie application and I was good to go... since the payload was painted black.

My original plan of using velcro tape to hold the altimiter in place is just not going to work to my satisfaction and I'll have to build a cradle or harness (or buy one from JL).