Smallest L3 Motor

[Lowpuller]

Please fact check me.

To meet the minimum impulse requirement the motor must be an M.

In physical size the 75/5120, M1297W is the smallest motor.

Based on average thrust 75/6400, M650W is the smallest motor.


If I, uncharacteristically, were to chose to go low and slow for my L3 cert. flight, and I designed the rocket around the motor and a fairly small field size.......................the best choice of motor would likely be the 75/6400, M650W????

 

[Q-Aero]

If you don't understand why a M650W is not for a small field, you not ready for L3
11.5 seconds burning time is for a high altitude rocket

 

[dhbarr]

m1297 on a stubby rocket is what's wanted; but physical size hasn't much to do with it.

 

[markkoelsch]

Most L3 rockets are to heavy for an M650 in my experience.

The M650 is, as mentioned in a previous post, a long burn motor best suited to lighter rockets and higher altitudes.

If you are talking low and slow- can you define what you mean by that in terms of numbers?

Where are you planning on flying, what is the waiver, and what is the field like from a recovery standpoint?

As a potential L3, you should able to fairly quickly design a rocket that will meet your requirements above using Rocksim or Open Rocket. That said, a large diameter rocket with a fast burn motor would be where my intuition would lead me for a small field.

 

[Steve Shannon]

Please fact check me.

To meet the minimum impulse requirement the motor must be an M.

In physical size the 75/5120, M1297W is the smallest motor.

Based on average thrust 75/6400, M650W is the smallest motor.


If I, uncharacteristically, were to chose to go low and slow for my L3 cert. flight, and I designed the rocket around the motor and a fairly small field size.......................the best choice of motor would likely be the 75/6400, M650W????

One is low impulse the other low thrust. You really have to understand the difference. Then, learn how to simulate using OpenRocket or Rocksim (or consult tables with flight data like PML publishes) to get a good feel for motor and rocket combinations. In almost every combination which observes a safe thrust to weight ratio a lower impulse motor will result in lower altitude.


Steve Shannon

 

[claytonbirchenough]

I chose the M1101 because it was a good, "cheaper" motor to do an L3 on. It only has 5197.6 Ns of total impulse, meeting barely the requirement of 5120 Ns to be an M motor. My pre-cert flight will be on an L2200 which has about half the burn time and double the average thrust. The L2200 is 5104 Ns. I'm actually actually curious to see how the pre-cert flight compares in altitude to the actual cert flight altitude as the pre-cert I think will go straighter. But we'll have to see... more drag with that L2200 too.

I do echo the sentiment of others though, and I only cautiously do so as I don't know the OP. But if you're considering the M650 as a motor to keep everything low, some things may need to be go backed and looked at...

 

[cerving]

I'm working on my L3 with a WM Drago EX, and due to the ceiling at ROC (14,500' AGL) I've had to play around with small M's to sim it so that it stays within the waiver. Nearly all of the baby M's sim within 500' or so (M1101, M1297, M1350 DMS, M1500G)... the M650 would almost certainly blow the waiver based on total impulse (pushing 6000 Ns vs. 5200 or so for the others). It would be cool to see that 9-second burn, though, but my guess is that the last 25% or so of the burn probably doesn't contribute much to the altitude because the thrust curve is so regressive. By that time, you're pushing against a lot of air...

 

[cwbullet]

Don't let these guys discourage you. You are planning and that is good. I did this for 12 months before I built my rocket.

One recommendation: plan the rocket then buy the motor. You need to know the weight before you pick an average thrust. Impulse is important, but not as much as the average thrust and burn time to keep in on a small field. A higher average thrust is also not that important with a heavy rocket with lost of drag.

I simulated my flight hundreds of times before I purchased a motor. I tested flights with about every M motor I could purchase.

What rocket are you planning to fly and what is it's estimated final weight? Keep in mind that most flyers add about 10% of weight to their level 3 unexpectedly. I expected mine to weight about 52 pounds based on my build plan and it came in at about 58.

I hope this helps. I can SIM it for you if you send me the rocket type and you projected weight.

 

[jd2cylman]

Don't forget the CTI M1560WT. 98mm in a 2 grain case. Total impulse 5342Ns. I got one laying on the counter in my kitchen all loaded up and ready to fly.

Adrian

 

[JoeG]

You can design a rocket around a motor or buy a motor to fit your rocket. I have done both and it is way easier for me to do as Chuck suggests. I'm a little heavy handed.

The smallest M motor? Depends on what you mean by small but the M1378 Loki Red might qualify. It is a 54mm baby M coming in at 5363.0Ns. I saw a few of these at BALLS this past year and they are pretty sweet.

As pretty much everyone else has said, a 6400 case is going to hold more motor than a 5120 and more motor means going higher at least on the same rocket. Considering safe thrust margins, I'm going to bet you are generally going to go much higher on the M850 than the M1297.

My level three rocket was near 6300' on an M1297. 7.5" cardboard rocket weighing 45 pounds. YMMV.

 

[cbrarick]

Please read "modern high powered rocketry 2" it will help your questions be more informed.

Having said that, have fun with your L3, make something that stirs your heart without going exotic. Do what you do best and leave your experimenting for your second flight....

Good luck!

 

[Crumb fire]

Cti makes a 5198M1101P, (75mm/4 grains) which seems to be the lowest of "total impulse" M reloads.
"Do what you do best and leave your experimenting for your second flight...."...+1

 

[DavidMcCann]

The Loki M 1378 is only 5361 Ns. And it's 54mm, that's makes it the smallest right?

 

[markkoelsch]

The Loki M 1378 is only 5361 Ns. And it's 54mm, that's makes it the smallest right?

Smallest diameter.

 

[jimzcatz]

The Loki M 1378 is only 5361 Ns. And it's 54mm, that's makes it the smallest right?

Nope, Loki M1200 Spitfire. 5123 ns.

 

[cwbullet]

I was just speaking from experience. I paid for 2 motors for my level 3 because the rocket was a little heavier than I expected. The first motor I bought on special and saved a ton, but it has too little thrust for my safety comfort zone.

I ordered a second motor and used it for my level 3. I have used the first motor since, but I could not use it for my level 3 rocket.

You might be better at estimating the amount of adhesive and foam you use to build it. I significantly underestimated.

 

[Q-Aero]

A M1297W with, let say a 8" 50 pounds Patriot will reach around 3400 feets, that's not bad for a small field

 

[Dave A]

Did my L3 on an M1297 in a 50#, 6" IRIS, awesome flame and flight

 

[watermelonman]

I am surprised how much lower the M1350 measures than the M1297, wonder if there was pronounced variance in opposite direction for each, or differences in the testing equipment. I have also been surprised at how much more performance my rockets have gotten out of the M1101, not like you can buy one these days though.

All are excellent all around baby M options. The M650 is a special motor for specific rockets. In fact iter keeps promising an M650 glider!

 

[Lowpuller]

A motor comparison with a little help from AT and Thrust Curve.



The above weight is based on rocket less motor but the simulation assumes rocket plus motor.

Based on this simulation looks like;

M650W wins the prize for SLOW

and

M1550R wins the prize for LOW

For the best of both worlds looks like the M1297W takes the cake! With the M1550R a close second.

 

[rharshberger]

A motor comparison with a little help from AT and Thrust Curve.

View attachment 308554

The above weight is based on rocket less motor but the simulation assumes rocket plus motor.

Based on this simulation looks like;

M650W wins the prize for SLOW

and

M1550R wins the prize for LOW

For the best of both worlds looks like the M1297W takes the cake! With the M1550R a close second.

M1297W a thing of beauty....



iirc 37lbs RTF, 7800' max altitude, and 908fps. It jumped off the pad in a blink, the first two photos are consecutive frames.

 

[Lowpuller]

Nice rocket and nice photos, what type of rocket is it?

 

[DavidMcCann]

Nope, Loki M1200 Spitfire. 5123 ns.

yea but thats 76, which is bigger....

 

[cwbullet]

A motor comparison with a little help from AT and Thrust Curve.

View attachment 308554

The above weight is based on rocket less motor but the simulation assumes rocket plus motor.

Based on this simulation looks like;

M650W wins the prize for SLOW

and

M1550R wins the prize for LOW

For the best of both worlds looks like the M1297W takes the cake! With the M1550R a close second.

That sounds like a good choice.

 

[Dave A]

That sounds like a good choice.

I'm sure the AT reloads will be easier to find. M1297 has nice, big flame.

 

[rharshberger]

Nice rocket and nice photos, what type of rocket is it?

Its a scratch built Upscale of the Estes Cherokee-D, built with FG wrapped Loc 5.38" airframe and the Loc 5.38L nosecone. Graphics by Stickershock.

 

[CoyoteNumber2]

M1297W a thing of beauty....

View attachment 308555View attachment 308557View attachment 308556

iirc 37lbs RTF, 7800' max altitude, and 908fps. It jumped off the pad in a blink, the first two photos are consecutive frames.

Remember when the M1297 used to be an L1120?

 

[markkoelsch]

Remember when the M1297 used to be an L1120?

Yes, I remember. A very full L, and then improved processing and a little more propellant and the M1297 appears.

 

[CoyoteNumber2]

Yes, I remember. A very full L, and then improved processing and a little more propellant and the M1297 appears.

Where/how was the extra propellant added? Smaller core, longer grains, denser?

 

[markkoelsch]

Where/how was the extra propellant added? Smaller core, longer grains, denser?

It would not be number of grains. I am not certain if it was better density or smaller core