Estes Saturn V CATO - Post Analysis?

[JPHARE]

My daughter and I built an Estes Saturn V over the winter and we have been champing at the bit to launch it. I finally got all the requisite equipment a few weeks ago (i.e. pro series launch pad, launch controller, engines, etc.). We finally got some great weather here in New England, gathered a few of her friends and went off to the local high school. Long story short, the rocket never left the pad. In fact, it ended up burning a hole in the launch plate, and lit the rocket on fire.

I've been launching rockets since the 70s and never had such a spectacular CATO (having an audience wasn't fun either; well maybe it was! We saved the Saturn V for the last launch of the day, so at least we had six successful launches of other rockets before the CATO)

Does anyone have any experience/knowledge of an Estes Saturn V CATO where it never leaves the pad? We used the recommended first engine E12-4.

I DO have one suspicion of root cause. But I would like to hold that card in my back pocket so I don't taint the "investigation."

There is video too; will post it to YouTube if there is interest...

Thanks for any feedback!

JP Hare in New England

 

[rstaff3]

It isn't the kit, it's the motor. E12's have a questionable reputation, mostly tied to specific date codes https://www.rocketryforum.com/showthread.php?139245-E12-0s-blow-up&p=1673834#post1673834

I recommend you give Estes a call. If you have the proper documentation they will send a replacement for the motor (or something equivalent). I don't know about the kit. You should also fill out ad submit a MESS form https://www.motorcato.org/

 

[Cl(VII)]

It isn't the kit, it's the motor. E12's have a questionable reputation, mostly tied to specific date codes https://www.rocketryforum.com/showthread.php?139245-E12-0s-blow-up&p=1673834#post1673834

I recommend you give Estes a call. If you have the proper documentation they will send a replacement for the motor (or something equivalent). I don't know about the kit. You should also fill out ad submit a MESS form https://www.motorcato.org/

What he said. I had a G80 CATO and destroy an Estes Nike Smoke. I sent Estes the pictures of the motor, rocket, and date code. 7 days later I had a new kit and motor. Estes does stand behind their products when things go wrong.

 

[rstaff3]

I thought the might replace their kit too but have never asked. I don't think the cover motor damage to other manufacturer's kits. That does not matter in this case.

There are a wide variety if suitable APCP motors, both single use and reloadable that will give the replacement a nice ride.

 

[Peartree]

You've got excellent advice here. Kits don't cause motor failures, motors do.

Do what the previous respondents said. File a MESS report, contact Estes customer service and provide them with date codes from the motor package (hopefully you saved it because there is at least one left), as well as pictures, and maybe a general description of the day (approximate time, weather, temperature, etc.)

Also, you probably don't want to use any motors that remain from that package in a model that you really like.

 

[rstaff3]

And, if you still can, please post the date code here.

 

[JPHARE]

Wow, all high quality replies within an hour of posting. Much appreciated guys.


I DO still have the old burned out motor and will be checking the date code after work, and reporting back here.


I was debating on whether or not to contact Estes. (My daughter and I spent a lot of time working on the rocket and are quite bummed out that it is FUBAR. Her favorite color is pink so she made sure to put a feminist revisionist paint scheme on it. See attached. Apologies to the purists out there!) It will be awesome if they replace the kit. I'll reply and let you know what they say.


So in my original post, I mentioned that I have one suspicious root cause. I really can't believe my suspicion would matter, but it IS related to launch.


To support this larger rocket, I bought the Porta-Pad E launch Pad (#2238). This comes with a 1/4" launch rod. The Saturn V kit says to use a 3/16" rod. The kit has dual launch lugs and they fit the 1/4" rod with some "slop." IMHO the fit of the 1/4" rod was similar to the scores of other rockets I've launched so I decided to throw recommendations to the wind and go with the 1/4" rod. As a mechanical engineer, I am very conscious of the critical design elements, and there was no appreciable friction between the rod and lugs. I even epoxy the launch lugs to the rocket body with the launch rod in place to make sure alignments are correct, removing the launch rod after epoxy dries. The only think i can think of is that there was some side loads that increased the static friction, and prevented lift off. But again, there is a lot of slop with the 1/4" rod.


I would hate to fault the motor if the use of the 1/4" instead of the 3/16" rod could realistically be the problem.


What do you guys think?

 

[AfterBurners]

Not the same motor, but I remember I had an engine cato one of my rockets and I think it was actually a scratch build, not even an ESTES kit.

ESTES not only sent me a new pack of motors, they also sent a kit equivalent to the one I built!

You tell me what company does that!

 

[djs]

I'm not a mechanical engineer, but I would be very surprised that launch lug "slop' would have caused the rocket to hang up on the rod. Take a look at the expended motor- if it has the nozzle blown out, or not looking "normal" compared to the unused one, it's definitely the motor. In this case, it blew out the back end of the nozzle, which prevents the motor coming up to pressure. Thus the "fire but no thrust" that you saw. I've had this happen before with bad motors.

 

[JPHARE]

Just got the date code for the motor in question: A 07-25-16

Doesn't seem to be on the list of known bad batches. Before we indict the engine, I'd like to get opinions about the launch rod issue (see my previous post.)

Thanks!

 

[rstaff3]

Friction on the rod will not cause a CATO. It may result in a lawn dart or the like, but no boom. Generally, if the rocket slid freely, you were likely good. I have had a rocket with a single 3/16 lug bind on a 1/8 rod, but that generally won't happen if you have a really long lug or more than one.

 

[Oberon]

You say it was a "CATO where the rocket never leaves the pad" but your last comment implies you're worried about the possibility that it hung up on the launch rod.

Did it blow up as soon as it was lit, shooting fire out both ends of your rocket (indicates motor failure typical of E12s)? Or did it burn normally on the pad (indicates the rocket got stuck)? Third possibility is the nozzle end cap of the motor blew out, which would result in a sputtering flame and no thrust, but not an immediate top-end blowout (ejection charge would fire eventually). Should be pretty obvious by the leftover motor case.

 

[terryg]

Estes E9 and E12 motors have always been more failure prone then their smaller motors.

 

[rstaff3]

You say it was a "CATO where the rocket never leaves the pad" but your last comment implies you're worried about the possibility that it hung up on the launch rod.

Did it blow up as soon as it was lit, shooting fire out both ends of your rocket (indicates motor failure typical of E12s)? Or did it burn normally on the pad (indicates the rocket got stuck)? Third possibility is the nozzle end cap of the motor blew out, which would result in a sputtering flame and no thrust, but not an immediate top-end blowout (ejection charge would fire eventually). Should be pretty obvious by the leftover motor case.

Great point, syntax may be an issue here.

 

[JPHARE]

Sorry if I used the term CATO too liberally or incorrectly.

I will post a link to the video in a few hours. If a picture is worth a thousands words, a video must be worth a googolplex (approximately.)

This is what happened:

When the launch button was pressed, the engine ignited. The rocket rotated (along vertical axis of course) about 90°, while the rocket engine continued to burn (which eliminates friction issues in my mind). After the normal burn period, and delay, the ejection charge popped off the top section. (The crowd cheered!) All of this happened while the rocket remained on the launch pad. There was never any vertical displacement of the main rocket body. The engine is about four inches up inside the rocket body, so all that cardboard and plastic in the cavity provided great fuel for the motor. The bottom caught fire. THAT is what I am defining as "catastrophe"!

Like I said, I'll post a link to a video ASAP.

Thanks again. Great responses guys...

 

[djs]

Definitely sounds like a failure of the nozzle on the motor. Do you have a picture of the motor bottom end?

 

[JPHARE]

The motor seemed to burn correctly (boost, coast, ejection phases at correct times). And the nozzle is still in the casing, and looks nominal. The launch plate has a beautiful hole in it where the thrust was focused. So I don't think that was a problem.

Will post pics and a video later tonight.

 

[mikec]

Sounds like Krushnic effect to me.

 

[dhbarr]

We don't mean "the nozzle of the engine was recessed four inches" I hope?

 

[Charles_McG]

If the motor is up inside the body, it sounds like the motor block ring didn't adhere to the motor mount properly. Or was positioned wrong. Is there an engine hook in this kit?. If there is, what became of it?

Once the motor pushed its way to a new stopping point, the Krushnik effect would sap it of thrust and prevent liftoff.

 

[JPHARE]

Yes. To be accurate it is recessed 3-3/8" by design. Seemed a bit odd to me, but that's what the instructions say. There is an assembly that fits in that cavity for display purposes that shows the five F1 engine nozzles. To be removed for launch.

I found an old instruction PDF online at: https://www.estesrockets.com/media/instructions/002157_SATURN_V.pdf

These instructions vary slightly from the ones that came with the kit, but the main steps are the same. Look at step 4 and you'll see what I mean about the recessed engine mount.

Also, I see that they recommend a 1/4" launch rod in the older instructions. Seems odd that they would change that to 3/16 for the newer instructions...

 

[Cl(VII)]

I looked at the directions for the kit and it says to recess the motor tube about 3 3/8" inside the back of the rocket. I assume that is what you mean by 4" inside. My bet is now Bernoulli Lock, although the Krushnic effect folks may have the answer too.

A brief explanation of both rocket destroying phenomena here: https://rocketry.wordpress.com/2006/10/17/the-krushnic-effect-and-the-bernoulli-lock/

Basically if you don't have enough gap between the rocket base and the blast plate you can suck tight and you won't go to space today.

 

[JPHARE]

The motor started in its nominal position (3-3/8" up inside the body) and it remained there. All motor and mount components started and ended in the same place. No failures there.

I did NOT have the rocket positioned with a gap above off the launch plate before launch. I am starting to wonder if there was some physics effect in the closed cavity. I thought about it before launch, but ASSUMED there would be plenty of pressure to lift off...

 

[dhkaiser]

Was it something like this? Estes replaced the launch pad and motors...

https://www.flickr.com/photos/dhkaiser/15671416056

 

[Cl(VII)]

The motor started in its nominal position (3-3/8" up inside the body) and it remained there. All motor and mount components started and ended in the same place. No failures there.

I did NOT have the rocket positioned with a gap above off the launch plate before launch. I am starting to wonder if there was some physics effect in the closed cavity. I thought about it before launch, but ASSUMED there would be plenty of pressure to lift off...

Yep, Bernoulli lock. You had almost the worse case scenario setup for this with a wide based rocket, recessed motor mount, low thrust motor, and no gap with the plate. Sorry it got toasted. I hope this doesn't discourage your daughter from rocketry. Good on you too for going with the pink paint job she wanted.

I came very close to doing a similar thing with a rocket once (TLP Krypton in my case). Were it not for a club member catching me (I think it was Chas) it would have likely sat and burned in front of me. Bernoulli lock in particular is a very counter intuitive phenomenon, so don't feel too bad about it.

 

[JPHARE]

DHKAISER:

Mmmm, not quite like that... I'll post the vid soon and you'll see for yourself

CCL(VII)

Yeah, I think you're hitting the nail on the head. Bernoulli Lock or Krushnic Effect (or combination of both, seemingly related.)

 

[rstaff3]

Yup, it now sounds like Bernoulli lock to me too. I discovered that the hard way on my 4" NCR Archer on a G80. It stayed firmly on the pad and the bottom got nice and toasty.

A 4" recess in a 4" rocket will not have a significant impact on performance. It is common for kit builders to recess the motor up to one caliber (the BT diameter) on scale rockets with either smallish fins or forward mounted fins.

 

[JPHARE]

Great job guys. I am comfortable with the conclusion of Bernoulli Lock.

I read the article above about Bernoulli and Krushnic, and my situation rang true with many statements.

"A very dramatic phenomenon where your rocket makes a tremendous amount of noise and smoke but doesn’t go anywhere!" - Check.


"This happens when the motor is recessed into the body tube by more than one tube diameter." - Check.


"it almost always destroys the lower body tube beyond use." Check.


"...where the rocket seems to be “glued” to the pad at liftoff." Check.


"This afflicts larger, flat-bottomed rockets launched too close to pads with flat blast deflectors." Check.


"This is quite possible as a 2″ dia.rocket has, potentially, over 45 lbs (200 N) of suction available to hold it back, while a 3″ rocket has over 100 lbs (460 N)!" Check.


"... when launched from an Estes Porta-Pad with its perfectly matching round blast deflector." Check.


Good to know that after 40+ years of my amateur model career, that I still don't know everything. (Don't tell my wife!)

 

[rstaff3]

Well, you have a wife and by definition know nothing. Are you sure you aren't Jon Snow?

 

[rstaff3]

BTW, no need to fill out a form or call Estes