Level 1 certification below 750 AGM? Help.

[ChrisLentz]

I need some help with my design of my level 1 certification rocket.

Tripoli rules apply at our local club and their ceiling is only 750 feet, with waiver a little bit higher. Apparently I can attempt my level one but need to stay below 750'.

I have been building for a year now and prefer to build from scratch with little or no factory produced parts. My most recent flight was a 2.8 lb 55 inch on a G125. 798 feet and chute failed to inflate. I know I need to work on my deployment and recovery before I attempt my lvl 1. But I digress.

I understand you can't keep adding weight to the rocket or there won't be enough thrust to get it off the ground. 5:1 minimum, usually 10:1 or greater for my flights. A longer rail or rod helps with getting up to speed I understand as well but there are rational limits to both of these.

Frontal drag was the direction I was pointed. Do I put some canards on it horizontally?

How can I design a rocket with sufficient enough drag to keep an H135 below 750 feet?

Here is my youtube channel address.
https://www.youtube.com/channel/UCnoMrWiYcdHISjYBpBhfnBg

Far from professional but professionally fun.

Thank you for any assistance in advance.

 

[Buckeye]

What?!?!? What Tripoli club has a limit of 750 feet? Sounds like a place where I wouldn't waste my time for HPR. I can probably throw my rocket higher than that!

 

[DavidMcCann]

What?!?!? What Tripoli club has a limit of 750 feet? Sounds like a place where I wouldn't waste my time for HPR. I can probably throw my rocket higher than that!

If he's flying G125's, I'm guessing Canada.... a 750foot limit for L1 is weird though.

 

[DavidMcCann]

H135- https://www.thrustcurve.org/motorsearch.jsp?id=1009
H133- https://www.thrustcurve.org/motorsearch.jsp?id=655


H133 will get you L1 and will go much lower than the H135. 163Ns vs 225Ns

 

[Bat-mite]

A VMAX motor will have high thrust and a very short burn time. If you can build a 3" rocket that comes to 5 lbs. dry weight, a CTI H410 will take it to 651 feet.

 

[grouch]

Those fins look a bit wonky.

 

[MikeyDSlagle]

A VMAX motor will have high thrust and a very short burn time. If you can build a 3" rocket that comes to 5 lbs. dry weight, a CTI H410 will take it to 651 feet.

Wasn't there a safety bulletin stating electronic deploy was to be used for all Vmax flights? Or is that resolved?

 

[tsai]

Aside from weight, increasing drag coefficient is your answer. This is basically what you did in increasing the cross sectional area by going to 5.5" tubes. Tube fins or ring fin is an easy way to crank up the drag coefficient.

 

[ChrisLentz]

That was my first big rocket. Flew fine. Other than the chute problem.

 

[NateLowrie]

Aside from weight, increasing drag coefficient is your answer. This is basically what you did in increasing the cross sectional area by going to 5.5" tubes. Tube fins or ring fin is an easy way to crank up the drag coefficient.

Or just build a fat stubby rocket... I would throw together a design in Rocksim or OpenRocket before you start building. Almost any design you can come up with can be made to fly under the ceiling with the right combination of nose weight, small shape and size tweaks, and motor selection.

I am still wondering though, why such a low ceiling?

 

[ThirstyBarbarian]

You are on the right track. The two main things to look for in keeping altitude low are high drag, combined with high-thrust, but low-impulse motors. That kind of motor gives the rocket a mule-kick launch that boots it off the pad nice and fast, but burns out immediately. And then the drag starts to slow the rocket right after burnout, dropping the speed off very quickly. You get a safe launch speed, but a low altitude.

If you want to work with the rocket you have, you could add some tube fins or a ring fin. It should slow the rocket some. The problem with a lot of added drag elements is that they become hard to sim. So if you are pushing up against the ceiling, it will be hard to know for certain whether you are going to keep under it.

The simplest way to build a high-drag rocket is probably to start with a wide diameter, but keep it very lightly constructed. If you wanted to consider a kit for L1, or use one for design inspiration, something like the LOC Warlock might fit the bill. It's a 7.5" rocket, but it's not very heavy for a rocket that size. There are H motors that will boost it just fine and keep it under 500 feet. But it can also fly on a variety of H, I, J motors, so you could get a lot of use out of it when the ceiling is higher.

I started a thread about high-drag, low-mass rockets some time ago and I'll come back to post the link.

 

[bclark989]

I agree with David and Bat-mite. Get a CTI 29mm 3 grain case and fly basically any of those H's. H133, H163, and H410 would all work. I probably wouldn't recommend the H54 because if your rocket is light enough to get off the ground on 54N average, you're not staying below 750' =)

I would also agree a short stubby is the way to go. Polecat makes kits that would work if you were willing to go the kit route. Whatever you build, add nose weight until the sim has between 0.5 and 1.0 caliber stability and your altitude is within your limit.

Good luck.

 

[Bat-mite]

Wasn't there a safety bulletin stating electronic deploy was to be used for all Vmax flights? Or is that resolved?

Yes, and that is still in effect. Adding electronic deployment will also add weight, which will help keep the flight below the waiver.

 

[SCrocketfan]

You are on the right track. The two main things to look for in keeping altitude low are high drag, combined with high-thrust, but low-impulse motors. That kind of motor gives the rocket a mule-kick launch that boots it off the pad nice and fast, but burns out immediately. And then the drag starts to slow the rocket right after burnout, dropping the speed off very quickly. You get a safe launch speed, but a low altitude.

If you want to work with the rocket you have, you could add some tube fins or a ring fin. It should slow the rocket some. The problem with a lot of added drag elements is that they become hard to sim. So if you are pushing up against the ceiling, it will be hard to know for certain whether you are going to keep under it.

The simplest way to build a high-drag rocket is probably to start with a wide diameter, but keep it very lightly constructed. If you wanted to consider a kit for L1, or use one for design inspiration, something like the LOC Warlock might fit the bill. It's a 7.5" rocket, but it's not very heavy for a rocket that size. There are H motors that will boost it just fine and keep it under 500 feet. But it can also fly on a variety of H, I, J motors, so you could get a lot of use out of it when the ceiling is higher.

I started a thread about high-drag, low-mass rockets some time ago and I'll come back to post the link.

Great minds think alike! The Warlock would be perfect for a super low L1-an H400 with electronics might be good. If you are ok with electronic deployment, using an altimeter to deploy the main at apogee might take a bit of stress off getting the delay correct, but using motor deploy would be fine with something like an H225WT.

Weighing down a 4" rocket could work as well. I have also flown a 5.5" LOC Mini Magg on full G/small H motors, an H163 would probably keep under 750' with a bit of added weight.

 

[ThirstyBarbarian]

Here's the link. https://www.rocketryforum.com/showthread.php?132002-Low-mass-high-drag-designs

Note, my purpose in starting this thread was not the same as yours, but a lot of the same principles apply. I was trying to come up with designs for low-thrust, long-burn motors that would not go very high. But the same kind of rocket could be used with high-thrust, low-impulse motors for extremely low flights. Use a sim that has your rocket's design and actual measured weight. Then look for the lowest impulse motor that hat has enough thrust to get it off the pad at a safe speed.

Weight is is the main thing that is going to determine how much thrust you need for launch. Drag is going to determine how quickly speed is going to drop off after burnout. I was aiming for low-thrust motors, so I was focused on keeping the rocket extremely light for its size. You don't need to go to such an extreme in terms of lightweight construction.

 

[ThirstyBarbarian]

Great minds think alike! The Warlock would be perfect for a super low L1-an H400 with electronics might be good. If you are ok with electronic deployment, using an altimeter to deploy the main at apogee might take a bit of stress off getting the delay correct, but using motor deploy would be fine with something like an H225WT.

Weighing down a 4" rocket could work as well. I have also flown a 5.5" LOC Mini Magg on full G/small H motors, an H163 would probably keep under 750' with a bit of added weight.

Hey, SC! Good point about the delay for these very short flights. Some of the high-thrust motors start with a lot of delay to trim off and are hard to trim to very short delays, so electronics would be recommended.

 

[bobkrech]

The Pro29 166H163-14A would be a good choice for a motor that doesn't need electronics.

A 5.5" LOC Minni-Magg with a small amount of nose weigh should stay below 750' AGL.

 

[ChrisLentz]

I prefer to use single use motors as I am still relatively new to the hobby and don't have the resources to lose reloadable hardware.

The club is in Ottawa Canada at a grenade rage for a local training base. Very close to downtown, so it has to be low. They are currently looking for a new space to go higher.

Personally I like to try and go as high and fast as possible so this is counter intuitive but if I don't want to travel far to get my lvl 1 cert. then 750 AGM it is.

Ring fins eh? 5lb rocket? Bigger airframe?

The fellow I was speaking to from the local club insists that you can keep even an I motor below this threshold.

I guess I need to start building in ROcksim. And looking for a tube size up from my comfort level. Thanks again all who inject their wisdom.

 

[dhbarr]

Non-pointy nose is another place to look, assuming you already have enough drag at the back.

 

[RocketFeller]

This is a 46 pound, 13" diameter rocket that flew to 800' on a K:

[video=youtube;2f0r3-uCXWw]https://www.youtube.com/watch?v=2f0r3-uCXWw[/video]

 

[thomas]

I have flown a 3.2kg=7lbs rocket on a H123 to 168m = 550ft, that is a 1:4 thrust to weight ratio.
[video=youtube;Ft-QSMhWbmc]https://www.youtube.com/watch?v=Ft-QSMhWbmc[/video]

 

[ChrisLentz]

I have flown a 3.2kg=7lbs rocket on a H123 to 168m = 550ft, that is a 1:4 thrust to weight ratio.
[video=youtube;Ft-QSMhWbmc]https://www.youtube.com/watch?v=Ft-QSMhWbmc[/video]

Wouldn't that be pushing the lift off velocity to almost 'too slow'? A thread on this forum says minimum 5:1 to achieve stable flight velocity.

7lbs is not terribly out of my capacity

 

[thomas]

Well, the 5:1 rule is not a scientific law. The velocity at the end of the rail was 15m/s which is slow but ok.
You could use an H238 than you have 7.7:1.

 

[BDB]

It's completely possible. I flew a 4", 6# rocket to approx. 700' a couple months ago using a Loki H144 for my L1.

 

[boatgeek]

What everyone else said. You can also add drag by sticking relatively small pieces of the hook side of sticky back velcro to the rocket. I'd probably put it on the fins near the tip so it's in the clearest airflow. On the body tube between the fins is another good place. Whatever you do, it should be symmetrical around rocket centerline so it doesn't pull the rocket one way or the other. This is hard to simulate well, but test flights on a high-thrust G motor should get you into the ballpark.

CTI motors are nearly as easy as single use. I would highly recommend borrowing a case for a flight if you can. It opens up so many more options than single use.

 

[ChrisAttebery]

I have flown a LOC Warlock on an H242 with a shortened delay to about 600'.

 

[mpitfield]

I prefer to use single use motors as I am still relatively new to the hobby and don't have the resources to lose reloadable hardware.

The club is in Ottawa Canada at a grenade rage for a local training base. Very close to downtown, so it has to be low. They are currently looking for a new space to go higher.

Personally I like to try and go as high and fast as possible so this is counter intuitive but if I don't want to travel far to get my lvl 1 cert. then 750 AGM it is.

Ring fins eh? 5lb rocket? Bigger airframe?

The fellow I was speaking to from the local club insists that you can keep even an I motor below this threshold.

I guess I need to start building in ROcksim. And looking for a tube size up from my comfort level. Thanks again all who inject their wisdom.

Or plan a drive down to one of the US clubs in upstate NY. I live in To and have a similar challenge as you, our local club NAPAS lost it's field and we are looking for a new one. However I joined two US clubs, URRG and MARS, both have great fields and waivers for a L1 cert. They are both roughly a 4 hour drive from where I live, so a bit more for you, however some of the members of your club also fly down there so you should ask their opinion.

 

[ThirstyBarbarian]

You can definitely design a rocket to fly an I motor to less than 750 feet. In fact, you could fly a motor of pretty much ANY impulse class to less than that. As I mentioned earlier, the main things are drag, and the thrust curve of the motor. Mass is also a major factor, of course. It's not the total impulse or impulse class --- it's a combination of all the factors.

I would say there are going to be basically two approaches to the problem.

One way would be to go the motor approach where you pick a L1 type rocket with a draggy design --- big diameter, short, fat, but still a pretty standard design. And then you look for a motor with a very short burn, but enough kick to get it off the pad safely. High-thrust plus short burn equals relatively low impulse. The rocket will take off fast, but there is no sustaining thrust to keep it going, so it should slow down quickly and not go very high. Because drag is not a big factor in speed off the rail, you are trying to match the motor to the weight of the rocket. Pick one that can get that mass off the rail at speed, then let gravity and drag start slowing it down right away.

if you are limited to motors that have a long sustaining thrust (or you like those motors), then you are going to have to rely on drag. An extreme example would be a saucer design. Even though the motor keeps pushing, the saucer has so much drag it never goes very fast, and and soon as the thrust is done, it pretty much stops coasting immediately. That's the approach I was taking with the thread I linked to above. So I was working with things like foam core and easter egg nosecones to make something extremely draggy, but very light, that could be lifted safely with low thrust.

You probably don't want to L1 with a saucer, so unless you want to get into some nonstandard designs, very lightweight materials and building techniques (like foam core and Easter eggs), the motor approach would probably work best. Aim for a big L1 rocket that can fly on the upper end of L1 motors, or even some L2 motors, and then look for a motor in the H or lower I impulse class that has enough thrust to lift it, but burns out in a second or less. If you are sticking with Aerotech DMS motors, then think in terms of Blue Thunder propellant that goes off like a shot. If you are willing to branch out, there are a lot of other choices too.

Because you are working with this specific low ceiling, and you are also trying to use a motor within a specific motor class range (L1 motor), you are definitely going to need to use a sim program to work within those constraints. I like Open Rocket, because it is free.

 

[DavidMcCann]

Wouldn't that be pushing the lift off velocity to almost 'too slow'? A thread on this forum says minimum 5:1 to achieve stable flight velocity.

 

[jimzcatz]

Yes, and that is still in effect. Adding electronic deployment will also add weight, which will help keep the flight below the waiver.

I understand this is suggested, not required. I saw several vmax flights last weekend no electronics. F and Gs though