All posts by joeadmin

A new Rocket

July 30, 2018 joeadmin

Not long after the launch of March Fly, I decided to commit myself to another large and exciting rocket project. This time, to build an extremely high performance 38mm rocket.

Goals

My high level goals for this project are to:-

Build a rocket that is capable of very high altitudes for its size. (Open Rocket simulations suggest that with the most powerful motor available, it should be able to reach altitudes of ~4800 metres).
To create a rocket that can be used in multiple configurations. e.g. as a medium powered rocket, right up to high powered rocket. Also want it to be usable in two stage configurations.
To gain more experience building rockets and designing rockets with new materials and different techniques.
Ability to fly faster than Mach 1.65 when equipped with a more powerful motor when flown in single stage configuration.

Rocket Design

All rockets that I’ve built to date have been from kits. This will be my first scratch-build rocket. I think I’m up for the challenge.

Below is a screenshot of the rocket from Open Rocket.

In this screenshot, it has the smaller motor in it. Flying this motor would be good as a shake-down test.

Key Design Features

The rocket is to to be Minimum Diameter. It has to be if it is going to go high and fast.
The rocket air-frame is to be constructed out of Carbon Fibre. This is very light and very strong material.
The air-frame diameter at the back of the rocket is slightly greater than the rest of the rocket. This will allow the rocket to be staged. This is so the motor retaining plug does not interfere with the lower stage.
We have 110mm of air-frame below the fins to allow mating with other rocket.
We will not be employing lugs, buttons on this rocket. This is to minimise drag.
We will use a Classic 2 parachute by Sky Angle.
The Nose cone and the coupler will be fibreglass to allow radio signals to radiate, but the remainder of the rocket air-frame will be carbon fibre
The fins will be 2.4mm thick G10
We will do tip to tip of the fins for added strength.

Scratch-Build

Scratch Build doesn’t mean making up the build as a I go along. I am writing up some documentation to help me refine the design and the building steps. This has proved extremely important for the air-frame build already.

General Launch, L2 Certification

The big day!

March 24, 2018 joeadmin

I wrote a single page e-mail to family on the days proceedings. I decided I would share this here on the blog.

The days proceedings

Jeremy, Grandma Patsy and I got up at some crazy time 04:30 for Grandma Patsy and 05:00 for Jeremy and myself.
We had a quick bit of breakfeast -⁠ weetbix…teas and other foods.

Then I loaded all the boxes (which I had left near the front door) into the roomy Toyota Kluger… and then we set off.
We all spotted some Hot air balloons as we started our ~60min journey to Cedar Grove Road. Most of the trip was in lovely rural surroundings.
About 1/2 way into the trip we all stopped off at a small cafe in Canungra called the “Outpost Cafe”.
There Grandma Patsy got a coffee – flat white – hot in a take-away cup, and I got two slices of toast with Vegemite…sharing the facilities
with middle-⁠aged(and older) “friendly” bikies.

Then after the usual pit stop activities, we resumed our drive.

Eventually we got to Jimboomba…I was a little anxious because the road seemed to go on forever and was wondering if I’d missed some vital turn-off.
I had nothing to worry about. About 10 min later, we spied the launch site. The first thing I could see were blue portaloos. I was delighted to see them.
2 mins later we were driving into a paddock. Grandma Patsy did the honors opening the gate and then we were back together. Thanks Grandma Patsy 🙂

We met up with about 4 other chaps who kindly suggested we not park so close to the toilets. We took their advice and parked further away.

There was no equipment at this stage…and it became apparent that the arrival of the equipment was lagging. Eventually a huge truck made its way and before we knew it, Jeremy and myself were helping set up all the equipment. We stuck mostly to erecting several Gazebos. Jeremy was terrific getting the pegs and hammering them in.

We got our equipment on to a table…one nice chap said…possession is nine / tenths of the law….

Then someone stole the two tables from under us!!

Fortunately, someone loaned a table and the Tarp I brought all the way from Cairns, suddenly became valuable property!

8:30 came and the launches started. Dave, Lake, Reef and Vanessa’s father arrived…and eagerly watched. At various occasions I helped them set-up their rockets. Jeremy gave up waiting for me to get him a motor….I suggested he approach Blake with some money and ask him for some advice on what motor he required. Blake helped Jeremy with the motor purchase and I helped Jeremy assemble the motor. Jeremy’s flight went really well.

For about 4 hours I set-up the rocket. Everyone was looking in…Jeremy was taking photos. Grandma Patsy helped as much as possible, making sure no one got too close. I was a little nervous having this awesomely powerful motor on the table and people casually walking past it. But we were following procedures to a tee.
I had my instruction manual with check-boxes and pictures…and only after inspecting all components, did I actually start assembling components. So many things were checked and re-checked.

Then at about 12:30….the launch pad that I wanted to use was vacated…their rocket went up…and then splashed down into the Logan river….(only about 4 hrs later did some university students practice their swimming skills to pull that rocket…a 4 metre beast…from the river. Lucky they don’t have crocodiles down this way!!).

I didn’t take any photos myself… I wanted to see it through my own eyes and be in the moment…so to speak.

Recovery

After the flight, Jeremy, Lake and myself bounded up the paddock, through long grass to recover it. 30 min later, we were talking back….Lake was holding the Nose cone, Jeremy was holding the large Parachute and I holding the rest of the “bits” as best as I could….across the muddy river bed in my best Black shoes (well almost the best…the ones I wear to Darwin for work).

Hot, tired, sweaty and alive. 2 litres of fluids later…felt a bit more alive…Sweet feeling of success.

It was not quite over though….

Videos

I do have a few small videos of the launch.

https://youtu.be/o3FykRAwLEA

https://youtu.be/SZSu98DQ_H8

Here is a larger video – with more details on the whole build/launch.

Alas I do not have photos or videos of it coming down…. But I assure you….it was seamless.

Here are the best screenshots I got of it coming down.

Coming down...top part of it. — Coming down…top part of it.

Flight Data

As you can see, it reached an altitude of 3528 feet. Very impressive.

Recovery, Rocket Building

Creating sleeves for the Shock-Cord

February 10, 2018 joeadmin

I wanted to protect the shock-cords from the brutal heat of the ejection charge. I knew I can purchase nomex variants, but I didn’t have any place I could purchase them easily and I thought I’d try my chances and make something that might provide them “some” protection at minimal cost.

The solution needs to provide some protection for a few flights. It doesn’t need to be so strong it will last 20 flights. i.e. something modest is satisfactory.

Materials

I did some research on materials and it seems that:-

Wool is not flammable
Cotton is probably not too bad a material at resisting fire.
There are some Polyesters that are impregnated with some compounds that make them inflammable.

I ended up finding a material that is a blend of Wool and Polyester – not perfect, but something that could provide some protection over 2 or 3 flights before requiring replacement.

Creating the sleeve

It was quite a simple process, however I thought it would be important to show some photos below of what I did.

Comparing pinned fabric with shock-cord to make sure the shock-cord will fit inside it.

Sewing the sleeve with my sewing machine, using the pins as a guide and removing them as I approach them.

Trimmed the sewn sleeve - make it look neat. — Trimmed the sewn sleeve – make it look neat.

Shock-Cord bowline knot around the Quicklink.

Sleeve fits snugly around the whole bowline knot. Later on, I use zip-ties to hold it in place and reduce chance of hot gases going up length of sleeve.

How does it fair?

The result of two ejection tests. This sleeve needs to be replaced.

Cut open of sleeve shows interior is fairly untouched. The Shock-Cord looks like it is relatively good health

L2 Certification, Rocket Building

Parachute Sizing + Shock Cord

February 3, 2018 joeadmin

Drogue Parachute

Very particular about having a Drogue parachute used at the top of the flight. They are supposed to be built to survive extra forces. The choice of Drogue parachute is important because when the main parachute is ejected, I don’t want the rocket travelling too quickly. Some websites have said 50 to 60 mph (which translates to 22.3 ms-1 to 26.8ms-1. Open Rocket raises alerts when I hit about 22ms-1. I’d prefer to keep it within range that doesn’t produce warnings inside Open Rocket. This meant a Drogue at very minimum = 28″. Probably can’t get a 28″, so would be a 30″ Drogue.

Cert-3 Drogue Chute

I have since this found a parachute called SkyAngle CERT-3 Drogue. The main website is:-

http://www.b2rocketry.com/Cert-3.htm

The Drogue Parachute has a Cd of 1.16, but this is based on just the area of the ‘cap’, not the whole parachute. (This is not how parachutes are normally done; people usually use the whole canopy area. The website has a link to a calculator to get decent speeds:-

https://descentratecalculator.onlinetesting.net/

I put in weight of rocket as 8 kg – this is for my L2 flight. I selected the 24″ Cert-3 Drogue. Results are:-

Descent rate:

70.26 ft/sec
21.41 meters/sec
77.09 km/hr
47.9 mph

This is good. It indicates that the speed is less than 50 miles per hour.

For larger 75mm motor, L1395-BS-0, we are looking at a total weight of approximately 10.7kg. When I put these numbers into the decentrateCalculator, I get:-

Descent rate:

81.26 ft/sec
24.76 meters/sec
89.16 km/hr
55.4 mph

So this might be okay too.

How does this fair with calculations?

I would like to see if I can get similar results using well known equations.

Velocity = SQRT(8 * m * g/(pi * p * Cd * D * D))

m = 8

g = 9.81

pi = 3.1415

p = 1.22 kg/m^3

Cd = 1.16

D = 0.61cm (24″)

Putting this all in, we get:-

V = 19.5ms-1.

This does not agree with above calculated values. It is slightly under.

What are the Risks with a 24″ Drogue Chute?

The main concern is that the speed of the rocket is such that as the main parachute is ejected, it shreds it, or it damages the rocket in another way, e.g. rips out the shock-cord.

It is probably helpful to also list what we consider to not be a risk

Shredding of the Drogue

We can probably do a small calculation to determine the approximate forces that the rocket will experience due to the deployment of the main parachute.

F = ma

m = 8kg

a = Delta V/ Delta T

Delta V = 6 – 22 = -16ms-1

Delta T = 0.25 seconds (BIG GUESS)

We assume the acceleration is constant

a = -16 / 0.25 = 72 ms-1

F = 8 * 64 = 516 N

64kg force = 141 lb

According to :-

https://publicmissiles.com/PMLRecoveryComponentsFAQ.pdf

The shround lines for parachutes > 48″ can take 300lbs of force.

60″ Chutes are even stronger, though there is no figures quoted.

With this in mind, even if a chute opens in 0.25 second, we are looking at a force that is probably survivable.

Main Parachute

Lots of websites suggests a landing speed of about 5 ms-1. I’m probably not going to get that, but I’m thinking I’ll get close using a 84″ PML parachute. 84″ is ~215 cm diameter. Open Rocket simulations produce a landing speed of ~5.9ms-1. I’m going to have to accept this.

Eventually I decided to go for a Cert-3 SkyAngle Large parachute. This was something Blake from AusRocketry was suggesting. I was very glad in the end to get a Cert-3 SkyAngle parachute because it is 61″ across, compared to the 84″ across….this means it is easier to pack into the airframe payload compartment. I believe me, space is a premium in that compartment.

How does this fair with calculations?

I would like to see if I can get similar results using well known equations.

Velocity = SQRT(8 * m * g/(pi * p * Cd * D * D))

m = 7.8

g = 9.81

pi = 3.1415

p = 1.22 kg/m^3

Cd = 1.26 (From the B2rocketry website)

D = 1.55m (61″)

Putting this all in, we get:-

7.3ms-1

This seems high, but if I use:-

https://descentratecalculator.onlinetesting.net/

Mass: 7.8kg

Parachute: SkyAngle Cert-3 Large

I get:-

17.53 ft/sec
5.34 meters/sec
19.23 km/hr
11.95 mph

I trust the decent calculations more than my own calculations. I suspect my D dimensions were incorrect.

Will the Cert-3 Large parachute survive or will it shred?

Now I’m obviously concerned that the 22ms-1 speed of the rocket might be too much for the main parachute. Above 20ms-1, Open Rocket shows warnings. I can see other people in posts, e.g.

http://www.rocketryforum.com/showthread.php?28347-Maximum-Parachute-Deployment-Speed

say that they have done drogueless at 24ms-1 suggesting that upper limit is 30ms-1.

Other Concern

If the Main parachute takes 5 seconds to deploy (and this is all quite possible), then at a speed of 22ms-1, the rocket will have potentially travelled 110metres (360 feet). So if I set the rocket to deploy at ~700 feet, will still have another ~110 meters to go. I think this is satisfactory.

I am contemplating changing the deploy to 1000feet. It will give it a bit more time to open.

Shock Cord

Many people suggest Tubular Nylon. It is extremely strong. AusRocketry says 9/16 version of this machines has a max tensile strength of 2000lb (that is lb, not lbf). Another site with same size material has a strength of 1500 lb. So not sure why there is a discrepancy, but perhaps I should question the AusRocketry value.

Now, let’s consider the situation where we have some Black Powder ignite and produce a pressurized chamber. Energy is neither destroyed or created, so we need to account for it. Energy would go into:-

Breaking the shear pins
Heating/moving air as its bursts the components apart
Imparting energy into nose cone
Imparting energy into the Avionics Payload

We would expect the Nose Cone and Avonics may to be sent in opposite directions (conversation of momentum) and the Shock-cord to be stretched to its maximum length and then it would produce an equal and opposite force, that keeps the components tethered. This Shockcord is effectively like a spring – and like a spring it stretches and absorbs energy. We can work out what forces are in the ShockCord based on the energy it absorbs.

$F = \sqrt {2kE}$ .

k = Spring Constant

E = total energy

F = force that the Shock-Cord is experiencing.

If the force (F) is excessively large (exceeds the rated strength of the Shock-Cord), then we have a problem.

So how much Energy is being absorbed?

The Black Powder produces a pressure and we know the volume of the tube. We assume that the Blackpowder ignites completely and the production of all these gases occur before any venting can occur. All ideal (and unlikely in the real world) but this gives us a conservative look at it.

Now, E = PV = nRT

P = 10psi = 10/14.7* 101325 ~ 69,000 Pa

V = 0.049 * 0.049 * 3.1415 * 0.41 = 0.0031m^3

E = 69,000 x 0.0031 = 213 Joules

This is a fair amount of energy.

If k = 30,000 (and this is a BIG GUESS)

F = sqrt (2 * 30,000 * 213) ~ 3600 N = 367 kg = 807 pounds

This is well short of 1500 lb or 2000 lb (AusRocketry).

Of course this all hinges on choice of k and I’m not sure if this is a good value.

Polishing, Rocket Building

Polishing the rocket

January 27, 2018 joeadmin

The sprayed clear coat, while rather flat, is nevertheless pitted. So I decided that I should try and improve the finish. To do this I needed to sand and polish it.

What the clear coat looks like

The clear coat looks like the surface of orange. This makes the light look distorted. The eye piece was very good at showing me the imperfections.

Photo of unpolished paint work through eye piece. Note the distortion in the light.

Infact this is often referred to as “Orange Peel”. I suspect the Orange Peel I see isn’t as bad as some coats, but I still wanted to remove it.

Removing the imperfections

The first thing I have to do is remove the imperfections. This I did by using 1200, 1500 and finally 2000 grit sand paper.

I could probably have used 1000 grit come to think of it, but using 1200 grit made me feel a bit better as I didn’t want to risk going through the clear (though there is almost no risk because of the thickness of the clear coat).

The result was a smooth surface without any pitting that was very dull. I admit the dullness did concern me a little. Would I really be able to get that shine back?

Polishing

I used the following product for polishing.

This is the polish I used to bring up the shine. I had to use a LOT of elbow grease. Fingers get very sore.

And I used a lot of manual rubbing (circular motion) to bring out the shine.

I decided against a machine to polish it. I just didn’t want to risk ruining the paint work. Even if I had a machine, I still needed to get into some of the hard spots.

Occasionally, the result was poor and this was because I had not sanded the surface sufficiently. So I sanded it a bit more and this resulted in excellent results. See two photos below, one of an un-polished fin and the other of a polished fin.

Fin that hasn't been sanded and polished. Note the blurred appearance of items in the reflection. — Fin that hasn’t been sanded and polished. Note the blurred appearance of items in the reflection.

This fin has been sanded and polished. Note how we have a cleared view of objects in its reflection.

The Nose cone

The orange peel on the nose coat was much less a problem. Not sure why. Anyhow, I decided to polish this as well and got pretty good results.

L2 Certification, Painting, Rocket Building, Tools

A Second Paint Job

January 27, 2018 joeadmin

In the first paint session I managed to paint the nose coat with base coat and clear coat. I base coated the booster, but had some issues and ran out of blue base paint.

The second paint job is to complete the painting tasks. For the second paint session I decided to purchase a gravity-fed spray gun.

$30 dollar spray gun - Gravity fed. Well worth the investment. — $30 dollar spray gun – Gravity fed. Well worth the investment.

For the second paint session I purchased new :-

1 litre of blue paint
0.5 litres of thinner
0.5 litres of hardener (activator)

Second batch of paint products for painting booster using new Gravity Fed spray gun.

Unfortunately I didn’t take too many pictures during the second paint session. I was too busy concentrating on the job. The base coat (blue) went fairly well. I have a photo of the booster hung up below.

Photo during painting. Using the gravity fed spray gun.

The big differences this time was :-

The use of gravity fed spray gun with regulator. This meant I could actually get the air coming out at the right pressure. With the previous gun, I had no really control over the pressure (well I had no knowledge of what it was set to).
More base coat to experiment with
Lowered the whole rocket about 15cm to make it easier to paint. Arm won’t get as sore.
Had special tray for cleaning gun between base and clear coat
Purchased 4 litres of thinner specifically for cleaning the gun. So now I don’t have to use the precious thinner that is supposed to be used for the paints.

Rather than waste valuable thinners used in painting, decided to purchase some, just for cleaning.

Problems experienced during painting

Unfortunately I did get a few runs with the clear coat and I’m very sure it is because I went over the fin-cam too many times. i.e. three passes, when two passes would have been sufficient. The spray was open wide and there was more overlap than I expected. This is due to my inexperience.

I decided not to sand back down to base and do it all again. I decided to just remove the obvious runs and polish the rocket.

Removing the Runs

I removed the large runs by applying some polyster filler compound. After 20 mins it was set and I sanded it down using grit 400 sand paper. This meant I was only sanding the runs and not the area around them. It worked very well. Then I sanded it down with 1200, 1500 and then 2000 to removal all remaining traces of the runs. There is still some undulation of the clear coat because of the flow of the clearcoat, but it is only slightly undulating and is very smooth.

Reflecting on the results

So while I didn’t get the best result, I did learn a lot on what went wrong and how to remedy some of the issues I created. I have to remind myself this is my second paint job in my life. It went reasonably well considering!

Avionics, L2 Certification, Rocket Building, Testing

Testing out the Ejection charges

January 27, 2018 joeadmin

I purchased the following eMatches to test out the ejection charges.

https://ausrocketry.com.au/igniters-e-matches/j-tek-lf-electric-match-24-inch-60cm-1.html

The recommended firing current is 1 Amp. The Duracell battery I want to use should be able to supply this without any trouble. I wish to conduct three tests:-

Test 1 – firing igniter standalone
Test 2 – Fire igniters from the Raven 3
Test 3 – Ejection test of drogue parachute.
Test 4 – Ejection test of main parachute.

To perform all these tests I created a test-fire box using old Cat-5 cable and some old parts lying around. Here is a movie describing what I made.

It isn’t neat/tidy, but very functional and safe. I can install all deployment charges without having the battery connected at all.

Test 1

I wanted to convince myself that the igniter would work on one of these nine volt batteries with this ignition system. Below is a video showing this.

The remaining tests will come in other posts.

L2 Certification, Painting, Planning, Rocket Building

Preparation of area for painting

December 2, 2017 joeadmin

Painting is to commence on the Sunday (3rd Dec 17), but decided to spend a few hours on the Saturday making sure everything was ready and I’m familiar with the operation of the tools.

Making sure the Compressor works satisfactorily
Looking at the operation of the Spray Gun
Making sure the rocket is level and at appropriate height
That we will be able to paint the Nose Cone while the rocket remains hanging

It was a good thing we checked because I noticed that:-

The rocket was not at the right level, it was too high and this would result in tired arm.
The Nose Cone jig was right on top of the rocket, and this would mean I couldn’t hang it up and paint it at the same time. So I moved it to the right

All these might seem like small points, but they all go to help make it a successful paint job.

Here are some more pictures of the area where I will be painting the rocket.

Tape on inside to reduce amount of paint getting on inside of air-frame.

Backing masking tape so that paint doesn't go onto inside of air-frame. — Backing masking tape so that paint doesn’t go onto inside of air-frame.

Toothpick to reduce amount of paint going into threads.

Rocket suspended from garage door at just the right height. Nose cone is also suspected from eye-bolt to the right.

Just double checking that the level of the rocket seems to be at a comfortable height.

L2 Certification, Painting, Planning, Purchasing

Selection and Purchase of Paints and Equipment

December 1, 2017 joeadmin

One of the next tasks is to paint the rocket. I’ve decided to use Two-Paks. I purchased some painting supplies from ColorTek in Cairns.

Two-pak paints – includes gas-can sprayer, Thinner, Primer and hardener.

I’m not sure what colours I want to paint the rocket, so I’ve had to delay the purchase of these.

Painting hardware

I was thinking that I would need to purchase a spray gun and compressor; however my wonderful neighbour has offered to loan me his. Initially thinking that I should use his for priming and purchase my own gun for the base coat and clear, but now thinking we might be able to use his Spray-gun for all coats. His spray-gun is 1.5 mm orifice which means it is sits between the 1.3 mm good for base paints and 1.7 mm which is good for Primers. So his spray gun should be suitable for all coats (primer, base coat and clear).