L2 Hiccup

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muddymooose

Hoopy Frood
Joined
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Location
Palmyra, MI, USA
I got my L1 with a PML Ariel, loved the construction, and the cert flight went perfectly. So I built a PML Endeavor thinking I would use it for my L2 cert, but I've run into a concern. On the smallest J motor this thing will bust my local club's meager 3000 foot waiver by about 1000 feet.

So then I thought I'll fly it on an H motor at my local club launch next weekend (about 900 feet alt.) and then go to another club launch with a higher waiver for the L2 cert. What's disappointing is the closest clubs with 5000'+ waivers are all a 3 hour+ drive away.

On top of that if the SD Endeavor reaches 4000 feet on a J motor, it might be hard to track and recover especially if conditions aren't ideal.

For the L2 I'm now considering getting a heavier 6-7.5" diameter rocket that will stay under 3000 feet on a J. I had been looking at a fiberglass DD 1/2-scale Patriot or Ultimate Endeavor from PML because I've been happy with them, and going to DD now seems like a welcome challenge. I would fly it on H/I motors to get the hang of DD and then move up.

I've also researched the LOC Warlock, Doorknob, and Bruiser because I'm interested in trying something from a different company. Something fat, low, slow, and SD seems like the safe way to do an L2. I'm a little annoyed, however, that LOC doesn't provide a handy table of motors and altitudes like PML does. Yeah I can plug it all in RockSim but I would trust manufacturer data more.

So anyway I'm at a crossroad and just wanted some input regarding the direction I should consider from here.
 
One (of many) options you can try:

It's possible to use your Endeavor at your home field with the 3,000 foot waiver. You didn't mention how much it weighs or what specific motor you were considering. But if you built per the instructions you can remove the nosecone and add weight. There's a dozen ways to do this, but a simple temporary way is to throw a Ziploc of dirt or sand in the payload bay and screw the nose back on.

If you get the dry weight around 5.3 lbs and launch it on a CTI J335, it'll go about 2,880 feet.
 
One (of many) options you can try:

It's possible to use your Endeavor at your home field with the 3,000 foot waiver. You didn't mention how much it weighs or what specific motor you were considering. But if you built per the instructions you can remove the nosecone and add weight. There's a dozen ways to do this, but a simple temporary way is to throw a Ziploc of dirt or sand in the payload bay and screw the nose back on.

If you get the dry weight around 5.3 lbs and launch it on a CTI J335, it'll go about 2,880 feet.

I thought about putting on a flat-nosed cone and painting the face like a pig nose. The rocket is painted pink and black and that would go along with a pig theme.

I also simmed adding weight to the nose and/or payload section to keep the altitude down, but the required weight would make it frighteningly over-stable.

The Endeavor is 71 oz. and PML specs put it at around 4200 feet with a 38mm J350W. I upsized the fins from 1/16" to 1/8", but RockSim shows the increased drag dropping it down to only around 4000 feet.
 
I thought about putting on a flat-nosed cone and painting the face like a pig nose. The rocket is painted pink and black and that would go along with a pig theme.

I also simmed adding weight to the nose and/or payload section to keep the altitude down, but the required weight would make it frighteningly over-stable.

What's so bad about that?

The only way to go low, is to increase weight, find lower total impulse motor, or increase drag.

J350W is 700 N-sec RMS motor.
You could a touch slower and lower with J425R - 676 N-sec DMS single-use motor.
Or lower still with J420R - 650 N-sec RMS motor.

Then you can glue aerodynamic embellishments to the body, in the form of either Falcon-9 style fin brakes, or R2D2 heads plastered around the circumference of the body.
:y:

Personally, I would start with the lowest impulse motor, and add enough weight to stay under desired hight.
Also consider that the rocket is likely to fly ~10% under sim-ed height due to cross-winds and airflow imperfections.

Good luck,
a
 
+1 on just adding some weight. I flew 9 pounds on a J350 to 1500 feet for my L2.
 
I'll be adding 15 pounds of lead ballast mid-airframe in my 4" scratch L3 project to keep below a 12k waiver on a baby CTI M.
 
I am guessing your home club is Jackson? Great club, nice equipment, with super folks, but it is hard to stretch your altitude there. Your other options are Michiana, Muskegon, or Tripoli Mid-Ohio, all ~3 hrs away, as you found out. After you get your L2, you are gonna want to take your bigger projects to those fields anyway, so check them out?

Manufacturer's tables/sims are OK, but not gospel. They often just use the dry mass of the components in the bag and don't reflect YOUR build. As mentioned above, all that matters is motor, mass, and drag (composed of diameter and CD). Use thustcurve.org motor guide to quickly iterate through those key variables, estimate speed/altitude, and weed out bad designs for your objective.

Overstable is just fine, also, unless it is VERY windy with a WIMPY motor.
 
I would consider a bigger diameter and heavier rocket you can fly at your home field. It's always nice to be able to fly all of your rockets at your cert level at your home field.

Then again, how often would you make the 3+ hour drive to the other fields? 1, 2, or more times a year? A lot of launches are 2 day affairs so gas, hotel, and a few meals might not cost any more then a K or L motor. It might be worth building L2 rockets you can only fly L2 at the farther fields and fly them on L1 at the home field.
 
You shouldn't have to go big (6"+) to stay under 3,000'. My 8-pound 4" BBIII has flown five times now on small J motors, consistently 2,400' - 2,600'. My 4" Solar Warrior, at 9 pounds empty and a bit draggier, has flown twice on J350s to 1,700'. If you want to keep it low for your flight then I would recommend going to Thrustcurve.org and plugging in some general parameters to see what it would take to stay within your waiver.
 
So I'm not quite in the same boat as you - the launch where I was going to L2 got scrubbed - but I did start thinking about what it might take to do a "low and slow" L2, mostly because my launch site is "either it's on the field or it's in the trees". I do not like trees. Obviously, yes, a six inch rocket would get you a low flight, but that could be big. And expensive. And time-consuming.

One option (and this would be expensive and time-consuming, but certainly a possibility) is the Binder Designs Velociraptor. MikeyDSlagle just certed on his and I think it did 2800 feet or so on a baby J. I believe his was dual deploy, so if you're into that, go for it.

Another option...I started thinking "well, okay. So I asked a while back about good draggy options for a "low and slow" LPR launch for kids, partly so I'd be sure that nothing drifted over them, partly because kids get antsy when you say "Hey, hang out for a bit I'm going to go for five minutes and collect that rocket". Baby Bertha was a suggestion and it did great.

So I said "OK, what if we made a HUGE baby bertha?" You'd have to custom-cut the fins from 1/4" birch (tricky, but not awful; you could get a custom laser-cutting service to do it for you). 4" short ogive NC is $20 from Madcow (yeah, it should be elliptical but I couldn't find one of those quickly). 4 inch 4-slot BT from Madcow is $20 also. Toss in a 54mm mount, couple of centering rings, 48" chute, nice long shock cord, Nomex blanket, and use a Chute Release.... Oh, and glass the whole thing with some overkill 9-oz fiberglass, then pour 1.5kg of shot-mixed-with-epoxy in the nose cone and you have....


The Tubby Bertha!
(note - this was 100% quick-and-dirty and I fudged some stuff just to see how it would look).
My biggest concern would be making 1000% sure that the recovery harness was secure; the last thing you want is a 3lb nose cone falling from 3000 feet.

View attachment tubbybertha.ork
 
My RW Formula 200 can fly on L impulse up. With a large, heavy FG rocket like that, you could conceivably do L2 and L3 on the same vehicle. You would have to work your L2 as if it were and L3, with a TAP/L3CC, documentation, etc. But once it is built and L2 is achieved, throw and M in it and get L3.
 
My RW Formula 200 can fly on L impulse up. With a large, heavy FG rocket like that, you could conceivably do L2 and L3 on the same vehicle. You would have to work your L2 as if it were and L3, with a TAP/L3CC, documentation, etc. But once it is built and L2 is achieved, throw and M in it and get L3.

Not to suggest that the above can not be arranged, but as per NAR L3 cert requirements:
1.0 Flyer Requirements
1.1 Any individual attempting NAR Level 3 Certification must be a Level 2 high power certified NAR member in good standing.
An individual may not submit a design for a Level 3 Certification project review to the L3CC until Level 2 certification has been successfully accomplished.

https://www.nar.org/high-power-rocketry-info/level-3-certification/

YMMV,
a
 
Not to suggest that the above can not be arranged, but as per NAR L3 cert requirements:
1.0 Flyer Requirements
1.1 Any individual attempting NAR Level 3 Certification must be a Level 2 high power certified NAR member in good standing.
An individual may not submit a design for a Level 3 Certification project review to the L3CC until Level 2 certification has been successfully accomplished.

https://www.nar.org/high-power-rocketry-info/level-3-certification/

YMMV,
a

Gotcha. There might be a way to pull it off, but my brain hurts thinking about it. :grin:
 
Not to suggest that the above can not be arranged, but as per NAR L3 cert requirements:
1.0 Flyer Requirements
1.1 Any individual attempting NAR Level 3 Certification must be a Level 2 high power certified NAR member in good standing.
An individual may not submit a design for a Level 3 Certification project review to the L3CC until Level 2 certification has been successfully accomplished.

https://www.nar.org/high-power-rocketry-info/level-3-certification/

YMMV,
a

That’s NAR. Tripoli allows a flyer to attempt L3 with a previously flown rocket. https://www.tripoli.org/Level3





Steve Shannon
 
Only semi-serious here, but the answer is obvious. Fins. All the fins. Split fins, tube fins, ring fins, stack 'em all on and get the drag coefficient high enough that you'll stay under the waiver. Plus you'll have lots of people wondering what the heck you're launching. Just make sure the outermost fins are extra beefy so they don't get broken on landing!

I have a bad habit of designing my next rocket based on a name. All The Fins is now going into the project hopper.
 
Only semi-serious here, but the answer is obvious. Fins. All the fins. Split fins, tube fins, ring fins, stack 'em all on and get the drag coefficient high enough that you'll stay under the waiver. Plus you'll have lots of people wondering what the heck you're launching. Just make sure the outermost fins are extra beefy so they don't get broken on landing!

I have a bad habit of designing my next rocket based on a name. All The Fins is now going into the project hopper.

Oh this could be fun. In my head: 2 inch main BT, some big trapesoidal fins with BT-60 tube fins at the tips. And tube fin canards. And tiny finlets near the nose like the King Kraken, just because.
 
For Max drag, carve a u-channel in the front of any fin thick enough to take one. Or use a half tube split lengthwise.
 
For Max drag, carve a u-channel in the front of any fin thick enough to take one. Or use a half tube split lengthwise.

I'm intrigued with this and previous replies, but wouldn't one have to potentially explain to the RSO how such changes will keep it under the waiver? Wouldn't one have to somehow sim this?

Going back to the simplest solution to keeping a PML Endeavor under 3000' on a small J...IIRC my Rocksim data said I'd have to add something like 3 pounds to the payload or nose to keep it legal. The dry rocket weight is 4.5 pounds, and adding 3 pounds to the front end would make the CG something like 3-4 body diameters ahead of the CP...like I said earlier, extremely over-stable. It has been mentioned that this isn't a big deal in calm air. What sort of wind starts to make weathercocking a problem with this setup?
 
I am guessing your home club is Jackson? Great club, nice equipment, with super folks, but it is hard to stretch your altitude there. Your other options are Michiana, Muskegon, or Tripoli Mid-Ohio, all ~3 hrs away, as you found out. After you get your L2, you are gonna want to take your bigger projects to those fields anyway, so check them out?

Manufacturer's tables/sims are OK, but not gospel. They often just use the dry mass of the components in the bag and don't reflect YOUR build. As mentioned above, all that matters is motor, mass, and drag (composed of diameter and CD). Use thustcurve.org motor guide to quickly iterate through those key variables, estimate speed/altitude, and weed out bad designs for your objective.

Overstable is just fine, also, unless it is VERY windy with a WIMPY motor.

Thanks for the helpful reply. Jackson is my home field, and the people and launch site are great except for the modest 3000 foot waiver. I'm open to launching at the more distant clubs, since a 3-hour drive is no big deal if I'm going to spend a whole day.

I like to think my liberal use of epoxy and overbuilding makes my rockets heavier and draggier, but I don't know exactly by how much. Since increasing the fin width from 1/16" to 1/8" only resulted in the hypothetical J launch going from 4200' to 4000', it would seem like a couple ounces of epoxy wouldn't make a big impact either.

I plan to launch the Endeavor without a payload (except the Altimeter3) on an H and then an I at the Jackson launch on Saturday to get an idea for how it flies on those motors. Winds are forecast to be around 12 mph. If the H goes well I might add a pound to the payload for the I launch to see how it behaves.
 
Only semi-serious here, but the answer is obvious. Fins. All the fins. Split fins, tube fins, ring fins, stack 'em all on and get the drag coefficient high enough that you'll stay under the waiver. Plus you'll have lots of people wondering what the heck you're launching. Just make sure the outermost fins are extra beefy so they don't get broken on landing!

I have a bad habit of designing my next rocket based on a name. All The Fins is now going into the project hopper.

Sounds like fun. I'm now intrigued with custom building a purposely fat, heavy, finny monster that stays low on even the biggest motors. The L3s in my club seem to enjoy this approach to keep L and M motors under the 3000 foot waiver. Giant, disgusting things you would never think could fly that can do the most beautiful things with aerodynamics.
 
I'm intrigued with this and previous replies, but wouldn't one have to potentially explain to the RSO how such changes will keep it under the waiver? Wouldn't one have to somehow sim this?

Exactly. The more the rocket deviates from 3FNC with crazy add-ons and shapes, the less capable is the drag calculator in the simulations. So, you really don't know the drag impact without doing iterative experiments. Diameter and mass effects, on the other hand, are easily simulated. Use Thrustcurve.

I know that lots of guys add a bunch of mass to keep the altitude down, but adding 100% of the rocket mass with additional lead just seems wrong to me. Band aid engineering.

I would build a rocket dedicated to L2 motors, but still capable of a safe, shakedown flight on an L1 motor. I did this with Madcow Frenzy and drove to a bigger field for the L2 cert flight.
 
When I was starting out I had some PML motor tables, but as I started flying altimeters found that they were more of a rough suggestion. They’re not terribly accurate since everyone builds differently. If you haven’t used the Thrustcurve motor guide yet, you’ll want to check it out (as many others have suggested). It’s a very easy tool to use. With a few inputs you’ll get a table of all the motors in the MMT diameter with altitudes and suggested delay times. There’s even a simple safety check to confirm a motor will provide enough velocity off the rail for a stable flight. I’ve used Open Rocket and found that there are so many places to tweak something unintentionally, it throws off the simulations. There are pros here that can make RockSim and Open Rocket sing. I’m not one of them so I lean on Thrustcurve and found it to be more accurate for me.

If you run a 4” rocket at 4.5 lbs and an average finish, Thrustcurve says it will go just a hair over 3,000 feet on the smallest 38mm J motors. I’ve used it enough to believe that’s closer than the 4,000 feet you’re getting from RockSim.

I like the idea of doing some test flights on H and I motors with a pound of ballast in the rocket. That’ll give you a real world idea of how the rocket will perform. Just make sure you use a punchier motor like a white thunder so you can get the safe velocity off the rail. 5.5 lbs is enough weight to be a problem with lower thrust H and I motors. You’ll be able to use the ALT3 to confirm altitudes and adjust your CD to get the sims accurate.

Something to remember regarding the added weight: if you add something like a bag of dirt to the payload section, that weight will be sitting on the forward bulkhead of the coupler. While it will move the CG forward, it won’t move it forward as much as if you were to add it to the nosecone. That will help reduce the overstability you’re concerned about. Although as other posters have mentioned, that’s only an issue if it’s windy and you’re using a lower thrust motor.
 
Thanks for the recommendations on the Thrustcurve motor guide. I compared numbers to launches I've done in the last few weeks and it looks accurate. I've written down the numbers for the H and I motors I plan to use Saturday and I'll check them against the Altimeter3 numbers.

I did see the Loki (I've been partial to Loki thus far) J396 should put the Endeavor at 2988 feet, or 2805 feet with a pound of weight. Unfortunately I installed the PML Kwik-Switch motor mount so a 38-740 motor case is too long. Luckily I see CTI J motors that use the Pro38-5G case will *just* fit, and a pound of payload will keep it around 2850-2900 feet.

Knowing all this I think I'll shoot for launching the Endeavor on a CTI J270-J335 with a pound of weight at my local field, maybe in November. I would be pushing 3000 feet on that tree-lined field with single-deploy, however, so I would probably only go ahead if the wind was light.
 
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