H135W-14A motor, how to understand the data sheet

[billdz]

I'm planning to try for Level 1 certification next month. The only vendor at today's club launch sold me a H135W-14A single use motor, the only H he had. He provided me with a drilling tool and suggested I adjust the delay down to about 6 seconds.

Now I'm going to buy a rocket for the certification test, and I'd like to be sure it is suitable for the H135-14A. I'm finding the recommended motor info to be rather confusing. For example, I was considering the PML Ariel. The data sheet (https://www.siriusrocketry.com/documents/PML/ArielDataSheet.pdf) lists recommended motors and predicted altitudes. It says an H55W single-use motor will go 1601', and an H128W reload kit will go 1088'. I had thought larger numbers mean higher power, thus an H128 would go higher than an H55. Or do single use motors go higher than re-loadables? Does this mean that my single use H135 will go even higher than the H55? It was suggested that I use a relatively weak motor for the certification test, to minimize the chance or loss or damage.

Would someone please explain this to me? Thanks!

 

[blackbrandt]

Hey!

So the motors have a bit of a confusing nomenclature.

The first letter is the impulse class of the motor. In other words, it tells you the total amount of power in the motor. Every time you go up a letter, the amount of power in the motor doubles.
Scroll down to rocket motor codes on this page: https://en.wikipedia.org/wiki/Model_rocket_motor_classification


Next, the number tells you the average thrust of the motor. If you multiply the burn time by the average thrust, you get the total impulse of the motor. A higher number is a higher average thrust. So an H128 will have a higher average thrust than the H55.


Finally, the 14 is the delay in seconds between motor burnout and ejection charge.



Here's a comparison of the 2 motors: https://www.rocketreviews.com/compare-aerotech-h55w-to-aerotech-h128w.html

If you notice, the total impulse of the H55 is higher (so it has more total power).
However, the average thrust of the H128 is higher, so it will have a faster burn.

I'd recommend the H128. With a higher average thrust, it will help prevent the rocket from weathercocking too much.


I'd also recommend downloading openrocket from openrocket.sourceforge.net. It allows you to simulate the flight of your rocket, so you can see if you have a high enough rail velocity.


Let me know if this makes sense or not. I'd be happy to explain more.

 

[rcktnut]

Like mentioned OpenRocket would be a good source of info for you. Spend some time getting to know what you don't understand. Build, weigh, check your CG, sim, then adjust your delay accordingly.

 

[billdz]

Thanks Matt and rcknut, I do understand the letter/number nomenclature but did not understand how it relates to my motor. Apparently my H135 has an average thrust of 115.9N and total impulse of 225.8, both numbers higher than the H55 and the H128. See https://www.thrustcurve.org/motorsearch.jsp?id=1009. Sounds like my rocket will go even higher than the 1600' predicted for the H55? I have downloaded Open Rocket but am still learning how to use it.

 

[ThirstyBarbarian]

The letter designation defines a range, with the top end double the lower end. That's a big range, and it mean some H motors will put the rocket up about twice as high as others. For an H motor, the range is from greater than 160 Ns to less than 320 Ns. If you don't want to go too high, pick one near the 160 Ns end. The H115 is a cool single-use motor with only 172 Ns, plus it's a sparky! That's what I used, and it was perfect.

You can use Thrustcurve to designate all the parameters of your search and then sort the results. For example, you can look for manufacturer = Aerotech if that's what your vendor carries, type = Single-Use if you don't want to go use hardware or build your motor, impulse class = H, and diameter = 29 if that is your motor mount size. Then sort by impulse class. H115 is first in the list, so that is the lowest impulse Aerotech single-use 29mm H motor.

Another way way to keep the flight low and in sight for an easy recovery is to pick a larger diameter rocket with some size and drag. A 4" diameter rocket with either a 29mm or 38mm motor mount would be good. Your H135 motor would do well in most 4" rockets without going too high.

Also, about the delay drilling. Your ideal delay is determined by how your particular rocket will fly on the chosen motor. You can't just go with 6 seconds for all rockets on the one motor. Some will need more time and others less. After you build your rocket, weigh it. Get an Open Rocket design file for your rocket. Enter the weight of your built rocket as an override. Pick the motor you are going to use and run a flight simulation. Open rocket will tell you the ideal delay time. Drill the delay to get as close to the ideal as possible.

Good luck on your cert flight!

 

[billdz]

Thanks, that's good advice. Just modeled the Ariel and Open Rocket says my H135-14A will take it over 1700' high. Maybe I should add some weight or electronics so it won't go so high and I'll have a better chance of not losing or damaging the rocket?

 

[Peter Olivola]

One other point about shortening delays. Don't shorten the delay more than four seconds. The delay grain becomes unstable if you drill too far into it.

So, before buying/building anything, get Open Rocket and sim a few kit designs (there are several libraries around.) Generally, play with rockets of different diameters to find one that will allow a 10 second delay or longer. That will probably be a 4" diameter design, but you need to try a few to get a feel for the software as well as the different kits. Another feature of a 4" design vs. 3" or smaller is the drag limiting factor that will keep altitude from getting too high. You really don't want to lose sight of your L1 cert flight or have to hike too far to retrieve it.

 

[Coop]

First--here's wishing you the best on the cert flight.

If you don't have the rocket yet, figuring the motor--much less the delay--is an iffy proposition at best. It would be a neat trick to get that to 6sec delay with the CTI DAT tool, as they'll take off 3, 5, 7, 9 seconds... Which isn't going to give you a delay length of 6 seconds without modifying the tool which --forgive the assumption-- seems a little advanced for your level of experience at this time.

The H-135 is a good little motor; I fly them often in rockets weighing just under 3lb or so to roughtly 1,300 ft. My Bucky Jones loves that motor.

My recommendation is to get yourself a simulation program and run the sims. Without getting off the couch to go check, I'd say most sport rockets in the 2.6-3.3 lb range with a 29mm+ MMT will go between 1100 and 1500 feet--ish. I seem to remember 435FPS range as the speed I would usually see.

Later!

--Coop

 

[DavidMcCann]

A 3" rocket weighing around 48 oz will go around 1600 feet.

Basically, anything you can fit that motor in is going to fly just fine. Don't over think this.

H55, H135, H 128..... you're not going to be able to make any reasonable comparison based solely off those numbers. A slow burn with a low number may actually push higher than a higher number on a faster motor. Or not. Depends on the rockets drag, weight, optimal mass, etc.

id live to know how the vendor suggested a delay on a motor you don't even have a rocket for, lol.

 

[DavidMcCann]

Coop- h135 single use is an AT motor champ

 

[jrkennedy2]

id live to know how the vendor suggested a delay on a motor you don't even have a rocket for, lol.

I was wondering the same thing...

 

[Coop]

Coop- h135 single use is an AT motor champ

My mistake; I saw the H135, and thought it was the CTI H135 4g white reload.

Later!

--Coop

 

[GrouchoDuke]

I flew that motor in a PML Quicksilver for my L1 cert and it was great. My rocket is 42oz (without the motor) & went to 2400' with it with a 10 second delay. Like others have said, the motor should do fine in anything that says it'll take an H. Worry about the delay after you build a rocket, weigh it, and run an OpenRocket sim on it. Here's the launch:

[YOUTUBE]USlect3lDak[/YOUTUBE]

One thing that really helped me a bunch was Mark Canepa's book. I had a million questions when I got into high power (not that long ago) and it answered most of them...or at least got me thinking in the right direction. Amazon has it if you're interested: https://www.amazon.com/dp/1412058104/?tag=skimlinks_replacement-20 (Avionics development moves fast, so that stuff is a little dated though.) As you know, this forum & the people here are also awesome.

 

[T-Rex]

I ran several kits through simulations using the H135W motor. I had difficulty finding anything that I would consider a first kit for HP that didn't reach 1500ft or greater, and the majority required a delay of 8 seconds...

I would encourage you to do some reading and maybe consider a different motor for your cert flight if you are concerned. I used a cardboard Madcow 4" Little John on an AT 238T to 1600ft for mine. It really isn't all that high. Open Rocket is your friend. Rocketry Reviews has a library of simulation files.

 

[Bat-mite]

A little something extra to throw in.

A simple way to look at thrust and impulse: thrust is for weight (how heavy is your rocket), and impulse is for altitude (how high do you want to go).

Assuming you want a nice, safe 5:1 thrust:weight ratio, the H135 has 26 pounds-force. Divided by 5, and you get about 5.2 pounds maximum liftoff weight, which includes the motor, hardware, laundry, etc. The motor is about half a pound, and let's say your retainer, harness, chute, quick-links, etc., come in at about a pound. 5.2 - 1.5 = 3.7. So you want a rocket whose built weight does not exceed 3.7 pounds.

But there's the other end. Just yesterday I saw someone try to cert Level 1 using a cardboard rocket and an AT H550. That's 550 Newtons of thrust, and I think the rocket weighed no more than 2 pounds on the pad! That motor is designed to lift a 20-pound rocket. With about a 50:1 thrust:weight ratio, you can imagine the motors ripping forward through the CRs and out the top of the airframe, which is what happened.

I also recently saw a college group trying to cert Level 1. There were about 15 flyers, and they only had two motor cases to share among them. The first person up launched her rocket to about 5000 feet on a breezy day, and it was never seen again. So make sure you have your recovery figured out.

Good luck and have fun!

 

[ThirstyBarbarian]

A simple way to look at thrust and impulse: thrust is for weight (how heavy is your rocket), and impulse is for altitude (how high do you want to go).

That's a good simple way to think of it. And when the OP asked about the H55, the purpose of a motor like that is to send a very light rocket very high, or a very light rocket on a long burn. There are a lot of rockets that could fly on an H135 that are just too heavy to get off the ground on an H55. And there may be some rockets built for an H55 that would be too lightly constructed for an H135 (although I expect most would hold together fine.)

 

[ThirstyBarbarian]

I ran several kits through simulations using the H135W motor. I had difficulty finding anything that I would consider a first kit for HP that didn't reach 1500ft or greater, and the majority required a delay of 8 seconds...

I would encourage you to do some reading and maybe consider a different motor for your cert flight if you are concerned. I used a cardboard Madcow 4" Little John on an AT 238T to 1600ft for mine. It really isn't all that high. Open Rocket is your friend. Rocketry Reviews has a library of simulation files.

You are right that 1600 or 1700 feet is not extraordinarily high. It's high, but it's definitely not unreasonable. A lot of cert flights are probably in that range. As long as the field is reasonably big, it should be OK. Maybe ask a few people to help keep an eye on it throughout the whole flight to the landing. Also a Jolly Logic Chute Release could help to keep the walking and searching area small.

 

[r66astro]

I flew that motor in a PML Quicksilver for my L1 cert and it was great. My rocket is 42oz (without the motor) & went to 2400' with it with a 10 second delay. Like others have said, the motor should do fine in anything that says it'll take an H. Worry about the delay after you build a rocket, weigh it, and run an OpenRocket sim on it. Here's the launch:

[YOUTUBE]USlect3lDak[/YOUTUBE]

One thing that really helped me a bunch was Mark Canepa's book. I had a million questions when I got into high power (not that long ago) and it answered most of them...or at least got me thinking in the right direction. Amazon has it if you're interested: https://www.amazon.com/dp/1412058104/?tag=skimlinks_replacement-20 (Avionics development moves fast, so that stuff is a little dated though.) As you know, this forum & the people here are also awesome.

I love my Quicksilver! Used it for my level one also, use Stratologger and Jolly Chute release. Used Aerotech single use H100 only 2100 feet but was an extremely windy day.. I have yet to use motor ejection. Did my level 2 last weekend in Ft Myers, Fl with a Wildman Eagle claw4. Used RRC3 and Stratologger. Just did single deploy with TAC1 72" chute worked very well. So I think QuickSilver is a great level one rocket
Bill

 

[Buckeye]

id live to know how the vendor suggested a delay on a motor you don't even have a rocket for, lol.

Heehee. No kidding!

I'll give my usual spiel: How experienced are you with MPR, reloads, and other non-Estes stuff? Mid-power rocketry is a good place to learn before going for HPR L1. Understanding motor designations is absolutely critical to this hobby (A simple mix up of a B6-4 and a B4-6 can destroy your Estes rocket, too). In addition to Canepa, read Stine, Coker's website, and Apogee newsletters to get your foundation.

Forget OpenRocket. That is like shooting a fly with a bazooka at this point. You don't even have a rocket. Quickly figure out basic rocket properties (mass, diameter), expected performance, and even test every motor imaginary in Thrustcurve Motor Guide.

 

[Nytrunner]

Wildman's site has a nice quickview of the motor specs and its thrustcurve.
As you get more familiar with the motors and their behavior, it'll get easier to pick motors for your rocket (or for some people, to build a rocket for a specific motor).

https://www.wildmanrocketry.com/ProductDetail.aspx?product=3917

Personally I look at the first ~half-second of the thrust profile. Sometimes that first portion will be lower or higher than the "average thrust" of the motor. Doing that allowed me to have a perfect certification flight of my 5.3# loaded rocket on an H120: by the avg. thrust alone, it would have been marginal, but in that first half-second, the motor put out ~130-150 N.

 

[MikeyDSlagle]

I'm with Nytrunner on this one. I look at the first .5 or .25 of the profile. You need that initial oomph to get your rocket up to speed before it leaves the rail.

I'm no expert on impulse or thrust or motors or all the numbers and letters or what not, so I will tap out now. LOL.

Mikey D

 

[GrouchoDuke]

I love my Quicksilver!

They're great and they look cool. I'm really surprised I don't see more posts about them. @AeroAggie just did his L1 cert with one on an AT H100W out at KloudBusters.

 

[JohnCoker]

This explanation of motor statistics may help.