Hello and a question?

[Lonnie Utah]

Hi everyone,

First time poster.

About a year ago my 12 y/o boy scout son bought a rocket kit from hobby lobby to complete the "space exploration merit badge" where Requirement #3 is "Build, launch, and recover a model rocket.* Make a second launch to accomplish a specific objective." He had such a good time with it, he parlayed it into two other badges, electronics and movie making. As part of the process, we've built his own launch controller and several Arduino based altimeters (with a custom printed circuit board.) Our next project is designing an Arduino based altimeter and GPS transmitter along with a corresponding base station receiver.

We had an exceptionally nice day yesterday for Feb so headed out to the soccer fields where we normally fly. He'd recently gotten an deal on an Estes Amazon and wanted to test it out. He decided to do a double launch with his ESAM-58 (comparable size weight) We put our small altimeters in the nose cones and launched both of them. Both of them ended up being ground strikes. The body tube of the amazon was torn/damaged by the impact. We launched the ESAM again without the electronic package with similar results. Ground strike. I'm including the flight data below.




As you can see, both rockets flew ballistically and less than 120' in altitude. (the tracks end early because either the battery came off the altimeter or the microSD card was dislodged by the impact.) I know these are heavy rockets for these engines. But we've flown the Esam on B4-4's before with good results. The question is, did we get a bad batch of engines? Seems like it to me. Trying to figure out if it's worth an e-mail to Estes or not.

Anyway, looking forward to learning alot from the smart folks here...

 

[smstachwick]

Hi everyone,

First time poster.

About a year ago my 12 y/o boy scout son bought a rocket kit from hobby lobby to complete the "space exploration merit badge" where Requirement #3 is "Build, launch, and recover a model rocket.* Make a second launch to accomplish a specific objective." He had such a good time with it, he parlayed it into two other badges, electronics and movie making. As part of the process, we've built his own launch controller and several Arduino based altimeters (with a custom printed circuit board.) Our next project is designing an Arduino based altimeter and GPS transmitter along with a corresponding base station receiver.

We had an exceptionally nice day yesterday for Feb so headed out to the soccer fields where we normally fly. He'd recently gotten an deal on an Estes Amazon and wanted to test it out. He decided to do a double launch with his ESAM-58 (comparable size weight) We put our small altimeters in the nose cones and launched both of them. Both of them ended up being ground strikes. The body tube of the amazon was torn/damaged by the impact. We launched the ESAM again without the electronic package with similar results. Ground strike. I'm including the flight data below.

View attachment 631114View attachment 631116


As you can see, both rockets flew ballistically and less than 120' in altitude. (the tracks end early because either the battery came off the altimeter or the microSD card was dislodged by the impact.) I know these are heavy rockets for these engines. But we've flown the Esam on B4-4's before with good results. The question is, did we get a bad batch of engines? Seems like it to me. Trying to figure out if it's worth an e-mail to Estes or not.

Anyway, looking forward to learning alot from the smart folks here...

The best indication of motor trouble, data-wise anyway, is accelerometer data. The reading should reflect the certified thrust curve.

The ESAM is built around an Estes BT-60 tube that commonly accepts 24mm and 29mm motors (C-G range or even larger) when used in other kits such as the Hi-Flier XL and Star Orbiter.

The Amazon is built around a BT-56. Uncommon today, but its close equivalent the BT-55 commonly accepts motors in the C-F range.

Neither are built for performance, being built around big, heavy, draggy tubes. The Amazon also sports a heavy plastic fin can and motor retainer.

I think the B4-2 and B6-2 motors, with their shorter delays, would be better fits for these larger rockets making low hops. Double-check your field dimensions and see if you have the room to upgrade to C power, as well.

In a few months you may also have an option to fly a Q-Jet by AeroTech B14-3T, currently in development. The extra thrust might get it up more confidently.

 

[Lonnie Utah]

Thanks for the reply! Upon reading it, I forgot to mention that while our Arduino has a built in accelerometer (GY-521 a 3-Axis Accelerometer Gyroscope Sensor Module), the altitude data is recorded using a BMp-280 barometric pressure sensor. We weren't recording accelerometer data yesterday.

Where we fly regularly is basically 700'x700' directly, but if you count the baseball fields in one direction and the open space across the street in another, it's closer to 1200'x1300'. We've launched two stage rockets without difficulty there before. Within an hours drive we have miles of wide open space including the local rocket club flying field (which we've used when they aren't having official events.

 

[aerostadt]

Check out the Utah Rocket Club at https://www.uroc.org/ There is a club rocket meet scheduled for St. Pat's Day, March 16th.

 

[kenstarr]

Welcome from Cache Valley. Hope you can make it to the march launch aerostadt posted about!
Ken

 

[Huxter]

Welcome!

Did you say if the nose cone popped or not?

Plastic parachutes and Utah in Feb are not a good combo - the parachutes do not unfurl well. Thin-mil rip-stop nylon is the way to go - in any weather!

Sounds like your son is very good with electronics and rocketry - well on his way to becoming an engineer - I'd be a proud papa - congrats dad - great job!

 

[smstachwick]

Thanks for the reply! Upon reading it, I forgot to mention that while our Arduino has a built in accelerometer (GY-521 a 3-Axis Accelerometer Gyroscope Sensor Module), the altitude data is recorded using a BMp-280 barometric pressure sensor. We weren't recording accelerometer data yesterday.

Where we fly regularly is basically 700'x700' directly, but if you count the baseball fields in one direction and the open space across the street in another, it's closer to 1200'x1300'. We've launched two stage rockets without difficulty there before. Within an hours drive we have miles of wide open space including the local rocket club flying field (which we've used when they aren't having official events.

You should have plenty of room for rockets with motors as large as Type D, only counting the smaller dimension. I’d be wary of counting the street in those dimensions unless traffic is very sparse and very slow, you don’t want to startle drivers and cause an accident.

But given the area available even with a conservative estimate, I’d say don’t be afraid to up the power. Just check stability and be mindful of wind drift.

 

[Hobie1dog]

to the forum

 

[cwbullet]

welcome

 

[Lotronex]

Hi @Lonnie Utah,
One thing you can do is simulate these rockets in OpenRocket or RockSim, and see how well they perform next to the data you got from the altimeters. You can adjust your computer models to match what your rockets mass and center of gravity actually are and see how close the engines actual performance was to the theoretical numbers.

 

[JeffBigg]

Welcome to the forums.

 

[lr64]

I'm a bit fuzzy. Did the ejection charge go off or not? Seems like, if the time units along the bottom of the graph are seconds, there was plenty of time for the chute to pop out and open.

 

[Lonnie Utah]

I'm a bit fuzzy. Did the ejection charge go off or not? Seems like, if the time units along the bottom of the graph are seconds, there was plenty of time for the chute to pop out and open.

It did. But only after both rockets had arced over and impacted the ground. It blew the body tube upwards after they had gone nosecone first into the soft ground. Outside the safety issue it presented, it gave both of us a good laugh. But that's why I thought there was a issue with the engines. The boost portion of the flight should have been higher. Fwiw, the air temp was in the mid 40's.

It's been a while since I've looked at the code, but I think the altimeter records on 0.1 second intervals? I'll look in the AM and report back.

 

[Art Upton]

Those really needed a B6-2 in my humble Opinion with the added equipment.

Do get OpenRocket Sims, your Son will like it: https://openrocket.info/

 

[Lonnie Utah]

Hi Art,

While I won't disagree (in fact, I agree with you), a couple of things. The payload package we've designed only weighs around 17 grams, so it's pretty light (just over 1/2 oz). I know we're flirting with the maximums here, but it should have given better performance than what we saw.

Second, after the original "incident" we launched the ESAM again, this time with out a payload and it preformed exactly the same. We had a ground strike before the ejection charge fired. Based on Estes own recommendations, without a payload the rocket should have flown fine on a B4-4. We've flown it in that configuration before without incident.

ETA: I just check our altimeter code, as I thought, it writes in 0.1 second intervals...

 

[smstachwick]

Hi Art,

While I won't disagree (in fact, I agree with you), a couple of things. The payload package we've designed only weighs around 17 grams, so it's pretty light (just over 1/2 oz). I know we're flirting with the maximums here, but it should have given better performance than what we saw.

Second, after the original "incident" we launched the ESAM again, this time with out a payload and it preformed exactly the same. We had a ground strike before the ejection charge fired. Based on Estes own recommendations, without a payload the rocket should have flown fine on a B4-4. We've flown it in that configuration before without incident.

ETA: I just check our altimeter code, as I thought, it writes in 0.1 second intervals...

Anytime you’re adding payloads, making modifications, or even just being pretty liberal with the glue, you can expect a change in the rocket’s behavior, sometimes a drastic one.

OpenRocket is fantastically easy to use and as accurate as the data you put in. Get a good measurement of your “empty” weight and CG, and an accurate aerodynamic model, and you’ll get a better idea of what performance you can expect on each motor type. This is when rocket science becomes science and not merely a consumer item or a toy.

For the record, swapping in a B4-2 motor is the very first troubleshooting thing I’d do, especially if the altitude achieved is only 120ft. A B6-2 might be next if that’s unsatisfactory before upping the power to something like a C6-3.

 

[neil_w]

How much did the rocket weigh, without motor? This is the single most important factor, surprised no one has asked yet.

 

[Lonnie Utah]

How much did the rocket weigh, without motor? This is the single most important factor, surprised no one has asked yet.

3.45 oz without payload. 4.0 oz with payload.

 

[smstachwick]

3.45 oz

Yeah, that’s right on the estimated maximum lift (3.5 oz). Combined with the abnormally high drag of such a large-diameter model, I don’t find that result surprising at all.

 

[Antares JS]

3.45 oz without payload. 4.0 oz with payload.

That's right at the borderline for a rocket to fly safely on the B4-4, according to Estes. Throw in the fact that those rockets are larger diameter and therefore a bit on the draggy side for 18mm power, and no wonder you're crashing. Use a two second delay or upgrade to a C.

 

[Lonnie Utah]

That's right at the borderline for a rocket to fly safely on the B4-4, according to Estes. Throw in the fact that those rockets are larger diameter and therefore a bit on the draggy side for 18mm power, and no wonder you're crashing. Use a two second delay or upgrade to a C.

View attachment 631419

Whelp. I'd say that settles it. Exactly why I signed up! Thanks everyone. Cheers.

 

[neil_w]

Whelp. I'd say that settles it. Exactly why I signed up! Thanks everyone. Cheers.

Not so fast.

I mean, I can easily say off the top of my head that 4 oz is too heavy for a B4. Nonetheless, let's dive a little deeper. One quick comment first: 1/2 oz is a large chunk of weight for a low-powered rocket. Don't assume that because your payload seems pretty light that it is insignificant.

Anyway: I entered a rough but decent approximation of the ESAM into OpenRocket, and used your given mass values. Here's the flight with a 4 oz rocket:


Predicted apogee is remarkably close to your 120'. Velocity off rod is quite slow: how close to vertical was your rocket's ascent? Predicted ideal delay is 2.13 seconds, so your 4 second delay was clearly too long. However, let's take a look at the altitude plot:


Even though deployment was quite late, it still looks like you should have had some margin before the rocket hit the ground. So, we know that a B4-4 is the wrong motor for this rocket, but I don't have a good explanation why ejection was so late.

Removing the payload we get this:



Again, not a good flight but also not ejecting after impact. So clearly there were other factors at play that are not immediately obvious. A batch of motors with extra long delay, non-vertical flight, enhanced gravity field at your launch site, etc.

Once in a while someone will assert that OpenRocket is really only for MPR and HPR fliers, because who needs it for LPR. This is a good example where it provides some useful insight into motor selection for a straightforward LPR rocket.

 

[lr64]

Here's a graph of the B-4's nominal performance:
https://estesrockets.com/cdn/shop/files/B4_thrustcurve.webp?v=1677879807
Looking at your graphs, with a lot of hand waving and rough estimation, it seems like the motor may have put out something in the ballpard nominal thrust at first. If the air drag really is bad, maybe there's nothing wrong with the motor. But that wouldn't explain why it flew ok on that engine before if it weighed the same back then. Just how high were those other flights when the ejection charge went off?

In any case, IMHO, plastic fin cans are an abomination and ordinary plastic has no business at the back end of a rocket. ;-) I don't know if balsa fins and no can would have saved the rocket, but it wouldn't have hurt.

I found an Openrocket file for the ESAM here:
https://www.rocketryforum.com/threads/kteshs-openrocket-files.123564/page-16#post-1931489

Running that, Openrocket thinks it will be ok at 4 ounces, but at 5 ounces it hits the ground before deployment. So the motor wouldn't have to underperform by much to cause a crash like this. A delay in the ejection charge of about a second would put it on the ground before deployment even at 4 ounces.

 

[Lonnie Utah]

Not so fast.

The plot thickens....

Eta: just weighed the Amazon an it's slightly heavier at 3.55 oz sans payload

 

[smstachwick]

The plot thickens....

It always does. Just wait until you start digging around into glue threads. Everyone seems to have their favorite and some can be…passionate about their choice.

Currently there’s a big argument going on over whether to include base drag in stability calculations.

 

[Lonnie Utah]

Just wait until you start digging around into glue threads. Everyone seems to have their favorite and some can be…passionate about their choice.

Good. After blowing the nose cone off a 220 Swift on Sat, the kid informed me I was using the wrong glue. Lol. (We found all the parts and launched it again with the nose cone taped on.)

Needless to say, we had quite the day. On the plus side, he had a wonderful flight of his Gryphon that one of his cousins got him for Christmas.

 

[smstachwick]

Good. After blowing the nose cone off a 220 Swift on Sat, the kid informed me I was using the wrong glue. Lol. (We found all the parts and launched it again with the nose cone taped on.)

Been there, done that. Putting together a 3-inch diameter Big Daddy rocket with hot glue (which melts, obviously) and then flying it on an E9 is a great way to never make any friends at all on the range.

Needless to say, we had quite the day. On the plus side, he had a wonderful flight of his Gryphon that one of his cousins got him for Christmas.

I never got glide recovery to work. My Scissor-Wing Transport did a passable 737 MAX impression on the first flight, so that was the end of that.

 

[lr64]

Glide recovery CAN be made to work. The last time I saw my Fliskits Nanite, it was going up in a thermal at 7 in the evening. Unfortunately, I didn't get it trimmed right until everyone else had left. It's probably best to try tossing gliders by hand, over long grass, to check the trim before giving them hundreds of feet to build up speed as a lawn dart.

 

[Jmhepworth]

For a new member of the forum, you generated a lot of useful discussion. Nice.

I hope we see you out at Frank Hunt Field in March. It’s fun launching at the soccer park (that’s where I fly most of my low power rockets with grandkids because we don’t have to wait for a club launch). But it’s even more fun to launch with others, including model rockets. Although we launch a lot of high power rockets, nobody looks down on those who launch from the model rocket area. Just be aware that adults have to join either NAR or Tripoli (NAR comes with a printed magazine and Tripoli comes with an online magazine) as well as UROC. It’s about insurance. Kids still get to launch low power for free and a Tripoli Junior membership is pretty cheap for kids 12-17 who want to launch high power. And you could have the same discussion with experienced fliers there as you’ve been fortunate to have here.

 

[Lonnie Utah]

I hope we see you out at Frank Hunt Field in March.

I don't think we'll make it for March, he's starting his Eagle Scout project soon. He's got to finish it for an event Mid-May, and the timeline is going to be tight.

We'll catch another one though.