Need Advice on "H" Motor for Level 1 Cert

[Stargeezer]

Hi!

Going for my Level 1 on March 9th and I'm in the middle of building a 4" LOC Goblin. I don't want to get too crazy with 54mm or 38mm motors just yet, so looking for suggestions on a good "H" motor. I thought about getting an H115-DM sparky motor, but OpenRocket is telling me it'll only get up to maybe 900ft? Maybe less considering all the epoxy I put on it today lol.

I'm not sure what I'm after really, but maybe someone can suggest a motor that would be the best for my build? I'm still familiarizing myself with the different types. Any advice would be amazing and thank you in advance!

 

[Upsrocketman]

The biggest concern should be making sure that your thrust to weight is high enough to make a safe flight. There are some good 38mm H motors that will keep the flight low and slow, but also provide a safe liftoff. I did my L1 Cert on a 4 inch rocket a little bigger than the goblin and used an Aerotech H-219T. Kept it below 2k and had enough thrust to get off the pad safe. Take a look at final build weight and calculate what it will weigh on the pad ready to go.

Tripoli rules state a minimum of 5:1 thrust to weight. The goblin shows a finish weight of 2.5 lbs on Locs website. That may not take into account epoxy, recovery, and any other things that you may add during construction. Do a flight ready weight and add the weight of a motor to find you pad weight. That will help you choose what motor to use.

 

[Hobie1dog]

One thing to consider is a lot of places do not allow sparky motors, with all of the burn bans in place our main launch place doesn't allow them at all.

 

[Antares JS]

Hi!

Going for my Level 1 on March 9th and I'm in the middle of building a 4" LOC Goblin. I don't want to get too crazy with 54mm or 38mm motors just yet, so looking for suggestions on a good "H" motor. I thought about getting an H115-DM sparky motor, but OpenRocket is telling me it'll only get up to maybe 900ft? Maybe less considering all the epoxy I put on it today lol.

I'm not sure what I'm after really, but maybe someone can suggest a motor that would be the best for my build? I'm still familiarizing myself with the different types. Any advice would be amazing and thank you in advance!

There are 38mm G and H motors, just so you know...

Regardless, as long as your rail exit speed is okay, 900 feet sounds fine to me as long as you get your ejection delay right. It's not like you have to hit a particular altitude to get your cert - you just have to fly and recover safely.

Be sure to consider what @Hobie1dog said too. Restrictions on sparky motors seem to be getting more common. Check before buying your motor if sparkies are allowed at your launch site.

 

[Reid]

^This
I did not cert on my first attempt because I was too focused on "Low & Slow" and did not consider fully speed off the rail. I launched a chonky Minnie-Mag on an H100 and while I don't know for certain what went wrong, the rocket went up 100' or so turned and flew off to the horizon and became a lawn dart.

I rebuilt the nose cone and shot her on H143 and everything worked out fine. The H143 has less total impulse but higher max thrust because the burn time is half of the H100. So more punch to get off the rail quickly and faster to build aerodynamic drag that increases stability.

If you used all that epoxy, I wouldn't be worried about using a hotter motor to cert, it can handle it. Just sim the rocket, get the delay right, and frankly focus more on the recovery side of things. Sending it up is the easy part imho.

 

[tsmith1315]

I’d also suggest something with a little more kick to get it moving quickly. Maybe H195T or H219T, if you’re using DMS.

Besides the extra kick, these light easily and save you a half-second of nail biting at the end of the countdown.

 

[Donnager]

I’d also suggest something with a little more kick to get it moving quickly. Maybe H195T or H219T, if you’re using DMS.

Besides the extra kick, these light easily and save you a half-second of nail biting at the end of the countdown.

H283 DMS would also work very well.

 

[2-0turbo]

I'll pile on the "more thrust" bandwagon. A higher average-impulse motor with good initial kick to get it off the pad and get the fins working is preferable over a lower initial thrust, long burn motor. I love long burn motors, but everything needs to be just right when you have marginal speeds off the rod/rail. Vertical, low wind, not first flight, etc.

For CERT, better to go "bang" and get it moving and then experiment later.

I like Aerotech motors, but there are others out there. Aerotech publishes a "master motor matrix" which I've become quite familiar with makes it easy to go and select motors. For that rocket I would pick on of the following in 29 and 38mm sizes (with the H135 being a little marginal):




You can find a link to this matrix from RCS (rocketmotorparts) website: Link to Master Motor Matrix

I'm posted DMS motors, but if you're flying RMS hardware, you have even more choices (The H180 is a nice motor--I love White Lightning propellant).

EDIT: Updated the master motor matrix list--an update came out on Jan 12.

 

[waltr]

All good advice on kicking the rocket off the pad so air speed is high enough.
My LOC Goblin come in right at 3.3lbs(1500gram) with an H238 motor. Did 952feet and successful cert.
The H283 DMS (or any motor over 150N average thrust) is a good L1 cert motor. The Goblin should do about 1200 feet which is high enough since chute is deployed at apogee.

 

[2-0turbo]

All good advice on kicking the rocket off the pad so air speed is high enough.
My LOC Goblin come in right at 3.3lbs(1500gram) with an H238 motor. Did 952feet and successful cert.
The H283 DMS (or any motor over 150N average thrust) is a good L1 cert motor. The Goblin should do about 1200 feet which is high enough since chute is deployed at apogee.

I did my L1 with a LOC Minnie Mag using an H135. Flight was successful, but it did a little 15-deg jog off the pad. It worked out fine, but a higher impulse motor may have helped that. The Minnie Mag is marginally stable on paper. The 4" Goblin, on the other hand, is quite stable and flies very straight from the ones I've seen. It's a great L1 choice and would likely be more stable than my MM on a similar motor.

If you feel really good about your construction and can get your hands on one, the H550 is one hell of a motor. I have one in my possession, but have yet to fly it. : )

 

[mcderek]

Hi Jess, as others have said there isn't anything wrong with a 900ft altitude cert flight. In fact it makes it easier to see all the events. If you want a sportier flight there are other H motors as suggested above or you can look at an I motor. The I205W is a good candidate. 29mm and will hit around 1,600ft.

 

[scsager]

I like the H-115DM. Both my Wife and my daughter used that motor for L1.
If you want more altitude consider one of the other Aerotech Single-Use "H" motors.
The Single-Use motors are usually the simplest and least costly way to cert if you don't already have the motor hardware
I usually recommend flying to at least 750 feet. I agree your 900 foot sim is a bit low but might be OK. The sim is only as accurate as you make it. Customize the sim to match the size, shape and weight or the ACTUAL rocket you built. Your sim is only an approximation.
Good luck!

 

[bunkermonkey9]

I did my Lvl 1 with this same rocket and mine came in at 3.2 lbs. I used a H195NT, it was a prefect flight and the blue thunder propellent will give you a nice kick off the pad.

 

[SolarYellow]

You can download a Rocksim file from LOC and open it with OpenRocket freeware. Make adjustments to mass based on your finished rocket.

https://locprecision.com/collections/rockets-4-00-diameter/products/loc-goblin
Figure out or estimate how much travel you'll have on the launch rail before leaving it. Put that into the simulation variables. Pick a motor that gives you at least 45-50 ft/sec rail exit speed and use a delay as close to the optimum calculated delay as you can get.

 

[smstachwick]

I recall one guy at Spring 2023’s ROCStock making an attempt on an H100W. That one failed, with a bit too much weathercocking and not enough thrust, I think it might have zippered a bit?

The same person upgraded to an H550ST for the next flight and it performed beautifully. I don’t think that kind of thrust is strictly necessary, but it you’re flying something really heavy that you think can take that kind of punch, it’s an option. That is a 38mm motor though, so make sure you have the mount to handle it.

Me personally, I’m still considering an H115DM for my own certification, although I’m likely to fly it in a 2.6” Astrobee D to ~2K or so. I just need to get my rocket put back together, I trashed it on an F67 while doing a few shakedown flights.

 

[Buckeye]

Hi!

Going for my Level 1 on March 9th and I'm in the middle of building a 4" LOC Goblin. I don't want to get too crazy with 54mm or 38mm motors just yet, so looking for suggestions on a good "H" motor. I thought about getting an H115-DM sparky motor, but OpenRocket is telling me it'll only get up to maybe 900ft? Maybe less considering all the epoxy I put on it today lol.

I'm not sure what I'm after really, but maybe someone can suggest a motor that would be the best for my build? I'm still familiarizing myself with the different types. Any advice would be amazing and thank you in advance!

People often suggest OpenRocket or RockSim simulations for motor selection, but that is way too time consuming and overkill for what you want to know.

Thrustcurve "Match a Rocket" (formerly Motor Guide?) answers all the critical questions in a fraction of a second for every motor known to man. Only 3 or 4 inputs required. No need to build out a rkt design file (or edit an error-riddled file from somebody else) and painfully create a "configuration" for each motor of interest one by one in OR.

Sure, you don't get wind, 6 DOF, and Cnalpha from Thrustcurve, but all that isn't really needed for a basic rocket going to 900 ft.

Rocksim has a "recommended motors" feature where you can get a similar table as Thrustcurve, but with all the fancy sim variables and constraints, if you really want all that.

https://www.thrustcurve.org/motors/guide.html

 

[DaHabes]

The biggest concern should be making sure that your thrust to weight is high enough to make a safe flight. There are some good 38mm H motors that will keep the flight low and slow, but also provide a safe liftoff. I did my L1 Cert on a 4 inch rocket a little bigger than the goblin and used an Aerotech H-219T. Kept it below 2k and had enough thrust to get off the pad safe. Take a look at final build weight and calculate what it will weigh on the pad ready to go.

Tripoli rules state a minimum of 5:1 thrust to weight. The goblin shows a finish weight of 2.5 lbs on Locs website. That may not take into account epoxy, recovery, and any other things that you may add during construction. Do a flight ready weight and add the weight of a motor to find you pad weight. That will help you choose what motor to use.

I second the H219T. I used it for my L1 in a 4" SuperDX3 (5 Lb.). TTW of 10:1 off the rail, 8:1 average. 1,000' altitude. It's also DMS, which keeps it simple.

 

[dpower]

I second ThrustCurve for getting a rough idea. You can even search for common public Rockets, there are a few LOC 4" Goblins already on there, just keep in mind that weight can vary quite a bit, so you'll want to create your own entry once your build is complete. These are the results for one public entry at 56 oz, 6' rail. 50 ft/s is the default safe velocity off the rail, I set it to show only 29 mm AT motors.

 

[cbrarick]

Use the H238 single use. It will actually go lower then a long burn motor due to base drag. You should, however put the rocket into rocksim or open rocket and truly get a idea what will work and what won't.
Wimpy motors and draggy rockets are a recipe for disaster. You may not have enough speed off the rail to be safe, or you may weathercock badly turning it into a rainbow shot.

 

[loopy]

There's always the H550...

 

[tsmith1315]

Use the H238 single use

H283?

 

[cbrarick]

H283?

https://wildmanrocketry.com/collections/motors-aerotech-38mm-single-use/products/h283st

 

[Stargeezer]

We're launching in March on a big sod farm and yes sparky motors are allowed where I'm going.

 

[GalantVR41062]

Part of the high power journey is proper motor selection.

A lot of factors go into this and without more information it's hard to nail down the "good" motor for the certification attempt.

Building an accurate simulation of the rocket (I use open rocket) and making sure each part matches your build and the final weight and center of gravity match the built rocket as close as possible.

I then make adjustments to surface finish and the like as I fly the rocket to match real life flight profiles to better simulate other flights I have not done yet.

I do not know for sure but it sounds like you are building the rocket with a 54mm mmt. If you do not own or have access to reload hardware and limited to single use options look into this motor: Aerotech H169WS-13A 29mm SU motor, looks like a punchy option for a 4" model weighing 5-6lbs.

 

[Ronz Rocketz]

I recall one guy at Spring 2023’s ROCStock making an attempt on an H100W. That one failed, with a bit too much weathercocking and not enough thrust, I think it might have zippered a bit?

The same person upgraded to an H550ST for the next flight and it performed beautifully. I don’t think that kind of thrust is strictly necessary, but it you’re flying something really heavy that you think can take that kind of punch, it’s an option. That is a 38mm motor though, so make sure you have the mount to handle it.

Me personally, I’m still considering an H115DM for my own certification, although I’m likely to fly it in a 2.6” Astrobee D to ~2K or so. I just need to get my rocket put back together, I trashed it on an F67 while doing a few shakedown flights.

I've heard the H550ST to be called a "blow the fins off" motor. Might need to fiberglass the fins to prevent flutter of the large Goblin fins.

My 4in LOC Patriot went to 1500ft on a H195T at 2758g. Generally, the sparkies have less power and the Blue Thunder have more.

The grass farm sounds awesome. IMHO, a rocket landing in a tree or on a power line and is recovered, that's a pass. An unfurled chute is a fail. A 2in zipper is a pass. A 12in zipper is a fail. However, that's up to the evaluator to decide. Fortunately, my cert flight was a success. The following two flight, not so much but did manage to stick the landing on the Bounty Hunter.

 

[cbrarick]

I've heard the H550ST to be called a "blow the fins off" motor. Might need to fiberglass the fins to prevent flutter of the large Goblin fins.

no, not only no but your comment lacks any sort of science.
Why do we continue to promulgate these myths?

it's a standard 3FNC rocket with not so huge fins. It's 4 inches in diameter, so it's draggy anyhow. it will be fine. the only question would be how you glued your fins on - did you prep the area of the fillets before you used whatever glue you used. It doesn't need to be epoxy as even carpenter's glue will provide a stronger bond then the cardboard it's being glued to.

 

[JRL303]

H180 or H123 depending on motor tube size and or adapters.

 

[Ronz Rocketz]

no, not only no but your comment lacks any sort of science.
Why do we continue to promulgate these myths?

it's a standard 3FNC rocket with not so huge fins. It's 4 inches in diameter, so it's draggy anyhow. it will be fine. the only question would be how you glued your fins on - did you prep the area of the fillets before you used whatever glue you used. It doesn't need to be epoxy as even carpenter's glue will provide a stronger bond then the cardboard it's being glued to.

You sound offended and I apologize.

 

[dmaaero]

29mm H115DM-7
8' rail
Looks good on RockSim
I really need your exact weight, and CG, Post that when you finish the build and i will check again.

 

[RobertH3]

I've seen 4 or 5 level 1 certs on the H550ST. Nice and loud, quick lighting, and excellent rail exit speed. LSO's tend to like that, especially on first flights of new models. 2 of our club members level 1'd on the H550ST with Apogee Zephyrs - no structural issues there. The Goblin will be draggier than the Zephyr and won't go as high.