Test Launch Techniques

[nosaj13]

Hi,
I’ve working on a scratch build and I am now to the point I’m considering testing the recovery system. The rocket is a 30% scale AIM-9L Sidewinder and I’m planning on using Estes E’s. My question is should I try to ground launch (place in soft vise and launch) or are there some engines with just the recovery charge to test specifically the recovery. I have been working on the rocket for about a month and a half so you can see I would like to make sure the launch and recovery will be successful. If you have any suggestions I am open for any advice you have.
Thanks

 

[powderburner]

There are no Estes-type motors (that I have ever heard of, at least, for whatever that's worth) that are made with only an ejection charge. I don't recommend trying to doctor a used motor case either, because it would be darned near impossible to replicate the type and quantity of granular BP that Estes uses for the ejection charge. You could do a whole bunch of work and testing and still not know if a motor ejection charge will work well.

Why not do a bench test with a smaller motor? (and an adapter, to help seal in the ejection gas) You could strap down the rocket to something like a picnic table (something heavy) and do a ground ejection test. If the ejection charge from an 18mm motor will accomplish a clean deployment then you can be pretty sure that a 24mm motor ejection load will do the job. An Estes C6-anything should work great, and they are cheaper than the bigger motors (if you're going to burn a few doing ground testing)

For that matter, you could do a little flight testing with a C11 motor (and a spacer) in your "E" MMT. A C motor would keep the rocket at low altitudes, would minimize any possible danger of a bigger motor pushing an unstable rocket around the sky, and would still give you useful test results of what is probably the most critical phase right past the end of your launch rod.

After that you could try a few launches with an Estes D motor, stepping up a small amount. You will want to test flight characteristics with D motors anyway as this will be your "plan B" anytime it is a little windy, or the field is a little smaller.

Have you done any simulations yet? (rocsim, or anything else?) It sounds like you have a pretty large model rocket, and an E motor is not always a great choice for large/heavy rockets. (It has less thrust than you might think)

Edit: One more thing---I hope you used 1/4 inch launch lugs, and have a four or five foot long launch rod. Longer is better?

 

[cjl]

I'm not convinced that a ground test is either all that useful or all that informative on a rocket of this size. 30% scale means that you're looking at around 1.3-1.4 inch diameter, so I wouldn't worry at all about the motor's ability to pressurize the tube. Worry more about protecting your chute and folding it properly to avoid tangles - far more low power models have toasted or tangled chutes than have problems with getting the recovery system out.

Have you simulated or calculated the rocket's stability in some way? The sidewinder has very large canards, and will probably need noseweight to remain stable in flight. I would be much more concerned with the stability with this model than with the recovery. Also make sure that the canards are on extremely straight - they can cause much larger deviations than the main fins can if they are slightly angled.

Also, as Powderburner said, the E9 does not have as much thrust as you might hope for a heavy model, so if your rocket is on the heavy side, a D12 would actually be a better choice. The Aerotech E motors work well too, but are somewhat more difficult to use and more expensive (they aren't terribly difficult if you get the single use ones though). You'll definitely want quarter inch launch lugs on this rocket, both for the extra support and stiffness of the rod, and for the ability to use a longer (5-6 foot) rod to ensure the rocket is up to speed before it is forced to continue with purely aerodynamic stabilization.

 

[Queeg500]

what an awsome topic. Let's say you built a missile rocket from scale drawings - any missile, pick your favorite - that takes 18mm motors and it swing tests stable - motor loaded with parachute and nose weight added until stable - and the motor can carry the total weight of the rocket. so, go ahead and put a B6-4 in it and see what happens?

 

[nosaj13]

Ok thanks for your advice so far. I will try to answer your questions and also try to take your advice. Easiest first-

I did build the rocket with 1/4in launch lugs (I was not aware of the advantages of rail buttons for strait flights at the time of the MM build)

I will be flying the rocket on a 6ft rod.

I have not done any flight simulations (I’m newer at rocketry so I only had the demo version of rocksim which recently expired. I will do the simulations once I have the program.)

In regards to the issue of weight I am not saying that this is the lightest rocket ever made. I used the “stuffer tube” method to try to increase air pressure within the rocket. (Originally I was planning to make this rocket “normal” (one full section)). But I changed my plan to a “half and half” rocket to reduce its size for transport. The “stuffer tube” I added into the rocket and the plywood wings I added make the lower booster stage MUCH heavier then the upper stage. I am planning to add weight into the top section but the method of doing such is unknown to me. I did consider adding lead/copper bb’s into the upper section and gluing or expoying them in until both stages are of equal weight.

I’m not trying to break any altitude records but I do want the rocket to have some lift. My reasoning behind the “E” engines is that, the 1/3 “The Launch Pad Sidewinder AIM-9L” suggests to use “D12-3, E15-4, E30-7 and E18-4, E24-4” (This information found on the Red Arrow Hobbies website). It should be said that I have bought the Launch Pad Kit and an Aerotech RMS system that will fit the 24mm tube. So I will be able to fly my scratch sidewinder with the RMS if I need a bit more power.

My question to you is how would I secure the “C” engine in the motor mount for testing. I do have the orange spacer ring that would allow me to fly C-11’s and D’s. Would some tape on the connecting the engine to the space be enough to prevent CATO and engine back fire? (I believe the “C” engine does not hit the engine retention clip I have installed.

Hopefully I have answered all the most pressing questions and gave you some more information so you may be able to help me.

J.I.

 

[Handeman]

You don't need the spacer, or the retaining clip for that matter.

Your E engine should extend 1/4" past the aft end of the motor mount tube (MMT). Wrap three to five layers of masking tape around the aft end of your C or D motor so it cover the last 1/4" of the motor. Trim any excess flush with the aft end of the motor. (See attached photo of D12-0). This becomes your thrust ring and will keep the C or D motor extended the 1/4" past the end of the MMT. I've used this technique on motors up through G and it works fine.

You can either use the retaining clip or wrap tape so it is half on the MMT and half on the motor. I think the tape is better.

BTW, you will get some ejection debris in the top end of the MMT, but a small brush (toothbrush) or dry paper towel will wipe it clean and you'll be good to go with the E length motors.

You'll notice a slight dark ring on the tape in the pic. This motor was retained with a piece of tape across the motor and MMT. The dark ring is soot from the motor burn on the area that wasn't covered by the retaining tape.