Starbust on E9s?

[Samuron]

I'm finishing up an LOC Starburst, and while the whole point is to fly it on Fs, I was thinking of test flying in on E9s just becuse they're easy to come by.

I have seen all kinds of launch reports on the web from people who say their Starbursts flew great using E9, but I have to admit I'm confused buy it.

The rocket has a stated weight of about 20 oz., which by everything I've read would require at least 28 newtons of thrust, or half again as much as the two E9s would put out.

Am I missing something? Does anyone have personal experience with this?

 

[DynaSoar]

Originally posted by Samuron
I'm finishing up an LOC Starburst, and while the whole point is to fly it on Fs, I was thinking of test flying in on E9s just becuse they're easy to come by.

I have seen all kinds of launch reports on the web from people who say their Starbursts flew great using E9, but I have to admit I'm confused buy it.

The rocket has a stated weight of about 20 oz., which by everything I've read would require at least 28 newtons of thrust, or half again as much as the two E9s would put out.

Am I missing something? Does anyone have personal experience with this?

You're trying to use the 5:1 rule, right? There are very few motors it applies to.

Any motor that starts with a kick followed by a lower level sustained burn is designed that way to get a larger mass moving than the 5:1 rule would suggest. An E9 has about 1/2 more average thrust during the first half second than during the following 2.5 seconds. One E9 will burn like a 13 during this time, two of them like 26. In that half second it'll get up to stable speed, which is all it needs to do given sufficient thrust after that to keep it at that speed.

LOC says it'll fly on two D12s so I wouldn't worry about it, but I would use a long rod. My sims say it'd take most of that half second to get up to speed and it'd need at least 5 foot of rod.

 

[Chilly]

I'd think it would work. I've flown an Arreaux several times on E9-4's. Works great in calm winds off a 5' rod.

 

[Samuron]

Thanks for the help, folks.

I knew I was missing something; I had never looked at the thrust curve. I'll take your advice and keep it low on a 6' rod.

 

[DynaSoar]

Originally posted by Samuron
Thanks for the help, folks.

I knew I was missing something; I had never looked at the thrust curve. I'll take your advice and keep it low on a 6' rod.

You can find thrust curves for most presently certified low/mid motors by going to the list of certified motors at https://nar.org/SandT/NARenglist.shtml and clicking on the engine size (E9, etc). That links to the data sheet, including the thrust curve.

You can also use the flight profile estimator at https://www.rocketreviews.com/cgi-bin/myemrr/rsim01a_form.cgi
Give it your rocket's diamater and weight without motor, then pick the engine out of the list (a little out dated, but most are there), check the "full flight profile table", and it'll give you speed and altitude results for every 1/10 second up to apogee. It knows the thrust curves automagically. You can give it different rod lengths and stable speeds to check those too.

Unfortunately it doesn't do multiple motors. But you can add the impulse of multiple motors and use a motor on the list that comes close in impulse and has a similar thrust curve.

 

[Zak Orion]

My wife has a Starburst and all she has flown in it is E9's(6 flights). So far the only problem she had is on the last flight only one engine ignited(still flew but not pretty and definately not high enough). I should add that we launch it on a 6' rail(had a rail before we had a 1/4" rod).

Here is a pic:
https://mars-rocketry.com/v-web/gallery/album21/starburst

 

[cjl]

It'll work fine. Estes says an E9's max lift weight is 15.0 ounces. Two would easily lift a 20oz rocket. BTW - the E9 has a 25n spike for the first 1/4 second of power, and then a 10n sustainer for the rest of the 2.8 sec. burn. It is actually more like an E11 or E12.

 

[Samuron]

I'm happy to report that a Starburst does indeed fly BEAUTIFULLY on E9-6s.

I launched it today at Rainbow Valley, my first launch of a new rocket in 30 years. Two flights off a 6' 1/4" rod, picture perfect, making me a BAR officialy.

Thanks for all the input!

 

[RocketboyG80]

Glad to hear it. Clusterted E9's are always impressive due to their long burn time. Attatched is a pic of my modified LOC Graduator on two E-9's.

 

[bsexton]

I've only flown my Starburst on E30's which are getting more difficult to come by. I would be very reluctant to fly this on D12's, but it is good to know that the E9's work well. I would have thought the 4 second delay would have been more appropriate, but I will try the 6 second delay.

 

[Samuron]

Mine was just peaking over at apogee with ejection at 6 seconds; 4 would have been way too short.

I agree with you about the D12s, although a lot of websites say it works.

 

[lalligood]

Originally posted by Samuron
Mine was just peaking over at apogee with ejection at 6 seconds; 4 would have been way too short.

I agree with you about the D12s, although a lot of websites say it works.

If a rocket will safely fly on a cluster of E9s, then it should fly safely on the same number of D12s. While the burn is shorter, the average (& initial) thrust is higher than the E9s. They would just need a shorter delay (like a 3- or 5-second delay). Go through the same deductive reasoning as what you did for the E9s...you'll see that it'll work

 

[Samuron]

I believe it, but I decided not to go lower than the E9 just in case I didn't get them both lit. Rocsim predicts only about 250' with 2 D12s; I figured if only one lit I'd end up hitting someone.

I do know it can be done though; I found a CATO rocketry site that reported success, but with the following warning:

"A note to flyers of the Starburst: 2xD12 is the minimum power for this bird!"

 

[bsexton]

I launched my LOC Starburst on a pair of E9-4's this past weekend and the flight was perfect! The 6 second delay would have been a little long but the 4 second delay was perfect for my flight. I also launched from a 6' rod.