First launch of my first scratch build

[Chud]

So this past week I finished my first scratch built rocket. After many name suggestions, it went on the launch pad with the name Betelgeuse.
Here is what happened.....
I got everything set up, started the countdown and hit the launch button. (I ended up using the E-9 motor)
Initial take off was great up until about 40 feet, then the rocket took an immediate, very sharp turn and continued it's flight basically parallel to the ground....just a slight angle upward. I maintained a visual on the rocket for the entire flight. At apogee...the chute deployed but the rocket continued to fall as if no parachute. Ended up the chute strings ripped through the chute. So I watched the free fall as long as I could and then went hunting. I ended up finding the rocket pretty close to where i thought it would be. It was about 15 feet up in a tree.
Once I got it down, I checked it for damage. One of the forward fins was sheared off. Other than that, the rocket was just fine.
So here is a question....why would the rocket do an aggressive turn like that and fly parallel to the ground? I was thinking either the fin came off right after takeoff, or it came off when it hit the tree. I have not been able to find the fin. My thought is, if the fin detached right after takeoff....I should have found it as I launched from a nice sized field. I think that that particular fin was just a bit misaligned from the others....could that have caused the sharp turn and the shearing? Other than that...i was pleased it actually flew. Even after going parallel, the rocket seemed to remain straight during it's flight. Thoughts/ideas anyone? Thanks!
Pic of the rocket

[blackbrandt]

How does the nozzle of the motor look? If a little bit of junk got deposited on the nozzle, that might be your problem.

[Chud]

Funny you ask. Once I got the rocket out of the tree...I noticed the motor was not there. Not sure how that happened unless a branch move the retainer and it came out. So I'm not sure. I am positive the motor was fine throughout the duration of the flight....I am sure I would have noticed a motor that was still burning come out of the rocket. Thanks!

[Rocketbuilder]

Between this and the solar flare incident Roger mentioned, it seems some strange force is affecting the flight of model rockets across the nation!
I seriously doubt the fin came off in flight; how did you mount the fins? Unless you used, like, a glue stick or something, I think it would be fine. A slight misalignment shouldn't cause a fin to be sheared off.
I'd agree that it was most likely the motor nozzle, either getting a pice of debris from the propellant stuck in it, or an imperfection in the clay causing part of it to break off. Without recovering the motor, it's impossible to know.
However, there is another possibility. While I've never had it happen to me, I have heard of the "thumb friendly" engine hooks getting in the way of the exhaust cone, deflecting the thrust and causing a sharp turn like you described. If you want, you can cut off that part of the motor hook, leaving only the part that retains the engine.

[kruland]

The rocket could easily have weathercocked. My guess is the rocket was marginally stable. The forward fins are nearly the same size as the rear fins which moves the CP forward quite a bit. And with the weight of the E9 it could easily have been marginally stable. Have you tried modelling it in OpenRocket or RockSim to check?

As for the motor, was the hook fully engaged? If it were not, the force of ejection could have blown it out.

Kevin

[blackbrandt]

I have had that problem with the engine hook before. I figured out if you wrap a piece of tape around the motor hook and tube, it holds the hook on pretty effectively.

[[POW]Eagle159]

However, there is another possibility. While I've never had it happen to me, I have heard of the "thumb friendly" engine hooks getting in the way of the exhaust cone, deflecting the thrust and causing a sharp turn like you described. If you want, you can cut off that part of the motor hook, leaving only the part that retains the engine.

This happened to me on a scratch built tube fin rocket before, 3 nice flights then 1 that went totally off.

[Chud]

With this rocket I did not use open rocket or rocksim. The front fins are roughly half the size of the rear. I do agree that the margin of stability could have been an issue....but that overall it was stable. i do know that the CG and CP were close, but within the 1 tube diameter apart. As for the motor hook...all checked out to be okay at prelaunch. I am thinking that the ejection blew the motor out. I will use some tape for the hook and motor next time. I guess the only way to really find out is to finish repairing/replacing the missing fin and try it again! I am leaning in the direction of some debris in the motor nozzle.
Thanks everyone for your replies.

[Bone Daddy]

Bones

[Chud]

Wow. Bone Daddy, your reply is the kind of stuff I need to hear....thank you. I do want to point out though, that I have not "concluded" it was a motor malfunction, simply leaning. But I must say, since my original post the possible stability issue has become more of a concern that I will explore.
I have started to sim this in OR. I am new to OR so still learning but agree that it shouldn't be very hard. I must admit, the thought of flying it again only on the assumption of motor malfunction, is a bit scary now.....what if the rocket turned again, this time just off the launch rod and headed right for someone.
Your criticisms, suggestions and opinions are wise and appreciated...thank you.

[Scotty Dog]

UM, anyone think maybe that paint job might play a part in this?
Anywhoo..
Glad there was No Harm No Foul even tho it didnt go as expected.

[jungmann1]

Try flying it on a D12. Higher impulse and lighter weight should help out with both a weathercock and/or CG/CP relationship issue.

[kruland]

If it was a front fin which tore off, I'd remove the other two before trying again.

If you need help with OR, post away. Send me the dimentions etc and I'll take a stab at it.

Kevin

[Chud]

UM, anyone think maybe that paint job might play a part in this?
Anywhoo..
Glad there was No Harm No Foul even tho it didnt go as expected.

Hey now. It was an easy visual to look for....it stuck out like a sore thumb as I was hoping.

[qquake2k]

I too am thinking a stability issue. E9 motors aren't so good for heavy, marginally stable rockets. Also, how long was your launch rod? For a rocket that length, I'd want at least a four foot rod, six feet would be even better. I'm real curious to see the Open Rocket file.

[Chud]

Hello all.....UPDATE!
Yesterday evening I launched my repaired scratch rocket for the second time. I want to thank Bone Daddy and especially Kevin for their help. Kev...redid the OR and did it right this time. Everything looked good in the sim so I went for it. Hardly any wind, 4 ft launch rod btw, and anxious. It was a great launch, flight and descent. I would estimate the performance was pretty close to the sim results. Unable to find any definitive reason for the botched first flight, debris in the motor nozzle seems likely. So yep...reanalyzed everything, repaired the sheared fin, and had a great launch. Thank you all for your help!

[kruland]

Glad to hear it! It is a pretty rocket - I hope to see it fly.

Kevin

[Coop]

Great! Glad this one worked! Congratulations!


Later!

--Coop

[luke strawwalker]

With this rocket I did not use open rocket or rocksim. The front fins are roughly half the size of the rear. I do agree that the margin of stability could have been an issue....but that overall it was stable. i do know that the CG and CP were close, but within the 1 tube diameter apart. As for the motor hook...all checked out to be okay at prelaunch. I am thinking that the ejection blew the motor out. I will use some tape for the hook and motor next time. I guess the only way to really find out is to finish repairing/replacing the missing fin and try it again! I am leaning in the direction of some debris in the motor nozzle.
Thanks everyone for your replies.

You do realize of course that the CG should always be ahead of the CP by AT LEAST one tube diameter AT A MINIMUM correct?? Maybe you worded it incorrectly, but if not, then that's likely your problem!

I'd go with bigger rear fins or smaller front fins... forward fins are REALLY destabilizing.

I had a D12-D12 two stager do something similar one time... we chalked it up to ROD WHIP, which is when a slender launch rod bends under the weight of the rocket and springs back straight basically as the rocket leaves the pad, pushing the rocket off course. As fast as the rocket's moving, it'll usually continue to swing sideways til it's about 20 feet up or so, by which time the fins keep it going straight-- horizontally in this case... it staged and continued on the same nearly horizontal flight path until gravity pulled it over and it impacted under thrust about 200 yards downrange...

That might've been what happened to yours... or it could be ground effect... you didn't mention the terrain or any buildings or trees or whatever on the flying field... sometimes buildings or trees will have a "wind shadow" that stretches up to a couple hundred feet away, depending on the wind, terrain, and building/tree size/grouping, etc. When the rocket ascends out of this wind shadow, it suddenly gets hit by a sideways wind that tips it over sharply and can result in a near-horizontal flight, especially in a rocket that's either overstable and prone to weathercocking, or sometimes one that's nearly neutrally stable with undersized fins or a CP that's too close to the CG.

Just some other things to think about! Building your own is one of the coolest parts of rocketry, but you have to really understand the forces and aerodynamics and all...

later! OL JR

[dlazarus6660]

If your still looking for ideas, I say aliens and their spaceship were hovering above to watch your flite and got in the way!

[DRAGON64]

That spiral pattern really plays tricks on the eyes... at least in the photo it does. Nice build. Scratch building has it's advantages and disadvantages... most importantly, you get to design and build pretty much anything you want... as time goes by and you collect more parts, scratching out a rocket gets easier... BUT! You soon find that you have amassed a huge inventory of "stuffs" and you realize that you need a "bigger boat" No matter how fast you build, you cannot stay ahead of the curve, cause your stuffs just keeps growing and growing (like the blob)... build it, and they will come.