Estes Loadstar: near miss and a redesign

[Joel Shepherd]

I think the Estes Loadstar has some design issues. With or without a payload it's over-stable with the CG 3.1-3.5 calibers in front of the CP (14g payload, C6-0/B6-4 combination). This gave us a very exciting flight last weekend, where our Loadstar with two C6s, a JollyLogic altimeter and sled, lifted off and promptly rolled into a 10mph wind. The second stage carried it 600+ feet over a tree-covered hill, behind which it descended ballistically and out of sight. We heard a loud pop (ejection) and then set off to find it. Apparently it had cleared the road on the far side of the woods by 100 feet or so, ejected at 109 feet and landed as shown here: four feet away from a traffic lane!

The body tube was dented at the forward end and two of the fins had their corners ground down a bit as it slid to a stop. The booster fell close to the pad, but tore it's second fin from the body tube in three flights (apparently another known design issue).

I like staging but not the wild flights and a fragile booster. So I'm going to build a new, less aggressively stable booster and sustainer to carry the same nose cone, payload bay and adapter. It's maybe less aesthetically pleasing, but it's more likely to go up instead of over.

 

[shreadvector]

It is not overstability that is the problem. It is too low a thrust for the booster motor. They need a C11-0 or D12-0 in that booster to make that absurdly heavy two-stage payload rocket fly straight.

 

[Ronz Rocketz]

After the Cato with the D12-0, I rebuilt the booster with an 18mm mount just to see if it would fly.



I recently flew it on a B6-0/A8-3 which went to 115ft, but I was using a 30" 1/8" rod so maybe it'll fly better with a 48" 3/16" rod.

 

[Joel Shepherd]

It is not overstability that is the problem. It is too low a thrust for the booster motor. They need a C11-0 or D12-0 in that booster to make that absurdly heavy two-stage payload rocket fly straight.

That'd probably improve its velocity at the tip of the launch rod, which appears to be in the lower 20s now. That said, other than pronounced weathercocking, its flight doesn't seem to be unstable: no fish-tailing or seeking around for a course. It flew straight as an arrow ... straight into the wind. The modified design, shown in my post above, has greatly reduced fin sizes (and a slightly shorter sustainer) and still plenty of stability margin.

 

[BABAR]

It is not overstability that is the problem. It is too low a thrust for the booster motor. They need a C11-0 or D12-0 in that booster to make that absurdly heavy two-stage payload rocket fly straight.

Agree. 128 grams is over recommended max lift off for 18mm Estes C motor, plus it is draggy...another exception to the rule that Estes produces well designed rockets. Call that a back handed complement to Estes. Vast majority of their rockets do well on recommended motors. Then there’s Venus Probe, Exoskell, Outlander, etc...,. Really hoping they come out with a C5-0 soon. I don’t see Quest coming out with an 18mm composite zero delay any time in near future either.

 

[Ronz Rocketz]

Agree. 128 grams is over recommended max lift off for 18mm Estes C motor, plus it is draggy...another exception to the rule that Estes produces well designed rockets. Call that a back handed complement to Estes. Vast majority of their rockets do well on recommended motors. Then there’s Venus Probe, Exoskell, Outlander, etc...,. Really hoping they come out with a C5-0 soon. I don’t see Quest coming out with an 18mm composite zero delay any time in near future either.

Sounds like sometime this summer with the C5-0. I have the C6-0 on order but won't get here for a couple weeks. I'm tempted to try it on B6-0 again since it mostly seemed to work okay last week on a 30" rod.

 

[BABAR]

Sounds like sometime this summer with the C5-0. I have the C6-0 on order but won't get here for a couple weeks. I'm tempted to try it on B6-0 again since it mostly seemed to work okay last week on a 30" rod.

ya know, the B6-0 is likely as good and perhaps a better choice

Estes chart shows same max liftoff for B6 and C6, and at 16.4 g vs 22.7 g, you save a little weight which can’t hurt.

https://estesrockets.com/wp-content/uploads/Educator/Estes_Engine_Chart.pdf
The thrust curves are nearly identical for the first 0.75 seconds

https://www.rocketreviews.com/compare-estes-b6-to-estes-c6.html
presumably the rocket has already cleared the rod at that time, but the system will stage sooner which means that even if IS weathercocking, it has less TIME to weathercock and therefore less opportunity to go (further) off vertical.

so actually if you are stuck with an 18 mm booster, the B is definitely the safer choice.

 

[BABAR]

A significant but I think often ignored issue in the design of this rocket is the designation as a “PayLoader.” The basic concept of “PayLoader” implies the rocket is capable of LIFTING a payload. While a grasshopper, cockroach, cricket or other invertebrate passenger may have negligible mass, other payloads such as altimeters or LED lights DO have some potentially significant mass. The idea of ADDING mass to a rocket that is marginally stable simply trying to lift its OWN weight, combined with big draggy fins required for multistage stability, seems at best unrealistic.

 

[Back_at_it]

I've experienced this issue with the Loadstar but like others have said, it's not a stability issue. If flown with nothing in the payload bay and a small upper stage motor the rocket flies great.

Problem is the rocket becomes too heavy for the C6-0 to get moving off the short Estes launch rod when you have a payload or another C6-7 motor on board. It really needs a D12-0 booster.

If you want to stick with a C6-0 booster, replace you short launch rod with a 4ft piece from the hardware store then try flying it on a C6-0/A8-5 combo. She'll fly great. When the time comes, upgrade the booster to 24mm and let her rip..

 

[Joel Shepherd]

Well ... since I tend to learn best by ignoring advice and discovering first-hand what goes wrong ;-) (which then makes me think more deeply about the advice afterwards), I might try doing the rebuild in the first post (much smaller fins, shorter body tube) but with the same motors and see what happens. Simulations seem to show that it'd gain another 2-3 mph or so off the end of a 36" rod and it does pull the CP more than a caliber closer to the CG but still well within stable limits. But I hear the collective wisdom in this thread and others that more speed off the rod -- more power or less weight -- would make the biggest difference, compared to trying to tune the CG-CP positions. So, if/when that fails, and since the hope is to boost something heavier like an altimeter, it'll be time to try a lighter and/or higher-powered design.

 

[BABAR]

Well ... since I tend to learn best by ignoring advice and discovering first-hand what goes wrong ;-) (which then makes me think more deeply about the advice afterwards), I might try doing the rebuild in the first post (much smaller fins, shorter body tube) but with the same motors and see what happens. Simulations seem to show that it'd gain another 2-3 mph or so off the end of a 36" rod and it does pull the CP more than a caliber closer to the CG but still well within stable limits. But I hear the collective wisdom in this thread and others that more speed off the rod -- more power or less weight -- would make the biggest difference, compared to trying to tune the CG-CP positions. So, if/when that fails, and since the hope is to boost something heavier like an altimeter, it'll be time to try a lighter and/or higher-powered design.

Your method is sort of like figuring how long it takes to microwave a potato.

stick it in the microwave on high for one hour, and measure the time it takes to explode.

subtract two minutes.

Use this time for all subsequent potatoes of the same size.

 

[neil_w]

Your method is sort of like figuring how long it takes to microwave a potato.

stick it in the microwave on high for one hour, and measure the time it takes to explode.

subtract two minutes.

Use this time for all subsequent potatoes of the same size.

Or...

 

[BABAR]

Sounds like sometime this summer with the C5-0. I have the C6-0 on order but won't get here for a couple weeks. I'm tempted to try it on B6-0 again since it mostly seemed to work okay last week on a 30" rod.

You have inside knowledge that Estes IS going to put out a C5-0? That would be great!

just out of curiosity, doesn’t look like it would be that hard to put a 24mm motor in the booster. I might then lengthen the sustainer, the added mass of the additional body tube is minimal, and stretching the forward end gives more of a CG shift without as much weight. Plus adding a payload actually INCREASES stability so long as you can maintain the speed off the rail, which should be easy with the larger motor.

 

[Ronz Rocketz]

You have inside knowledge that Estes IS going to put out a C5-0? That would be great!

just out of curiosity, doesn’t look like it would be that hard to put a 24mm motor in the booster. I might then lengthen the sustainer, the added mass of the additional body tube is minimal, and stretching the forward end gives more of a CG shift without as much weight. Plus adding a payload actually INCREASES stability so long as you can maintain the speed off the rail, which should be easy with the larger motor.

I’m just going by with what Bill S said at NARCON. I’ll see if I can find it.

I originally installed a 24mm mount until the D12-0 Cato blew it out. I decided to try the 18mm instead (because I like pain). Almost tried it today but the wind picked up.

 

[Ronz Rocketz]

I lied. He said it's not a 2021 release.

 

[Ronz Rocketz]

If you want to stick with a C6-0 booster, replace you short launch rod with a 4ft piece from the hardware store then try flying it on a C6-0/A8-5 combo. She'll fly great. When the time comes, upgrade the booster to 24mm and let her rip..

When I launched the Loadstar at night last week, I couldn't find my rods which is why I used the 30". Surprisingly worked okay and the booster didn't land too far away from the launch pad so was easy to find in the dark. Fortunately, the rods are cheap at Home Depot.

 

[Joel Shepherd]

just out of curiosity, doesn’t look like it would be that hard to put a 24mm motor in the booster. I might then lengthen the sustainer, the added mass of the additional body tube is minimal, and stretching the forward end gives more of a CG shift without as much weight. Plus adding a payload actually INCREASES stability so long as you can maintain the speed off the rail, which should be easy with the larger motor.

True but the last thing the Loadstar needs is more stability. Heavier motors in the back might change the equation a bit, but the fins still are oversized (with regrettable consequences for the booster as well).

In any event, my goal isn’t to blow up a series of microwaves with hot potatoes (LOL) but if the simulations show that smaller fins and a shorter body has an adequate stability margin and is less prone to weathercocking ... what’s the harm in trying? If it works, great, if it doesn’t then there’s another failure to learn from, and Loadstar IV can trust in thrust.

I appreciate the insights either way.