Aerotech Motor Chart with max liftoff wt?

[JeromeK99]

Does anybody have a chart for Aerotech motors listing max liftoff weights? I can't seem to find one except for an oldie from 1999.


Jerome

 

[Kehoes23]

I believe the formula is something like this
Take a G80 motor and divide 80 by 4.14 to get thrust lbs, then divide that number by 5 to get the weight to thrust ratio (5 to 1) this number is the max weight that this motor can lift safely
I'm guessing the formula since I'm not at home, I think someone will chime in with the right formula
This is a starting point for lift off weight

 

[shreadvector]

The max wight is NOT just the maximum the motor type (average thrust) can lift off the pad, but it is the maximum wiehgt that the motor can lift off the pad and then safely reach apogee in the designated delay time ("dash number").

This is why identical power motors have lower safe maximum liftoff weights for longer delay times. Short delay = safe with heavier rockets. Long delay = crash into the ground with a heavy rocket before the ejection charge goes off, so use only in lighter rockets.

The average weights also assume average drag. Graggy rockets need shorter delays, even if kightweight, such as boost gliders.

I believe the formula is something like this
Take a G80 motor and divide 80 by 4.14 to get thrust lbs, then divide that number by 5 to get the weight to thrust ratio (5 to 1) this number is the max weight that this motor can lift safely
I'm guessing the formula since I'm not at home, I think someone will chime in with the right formula
This is a starting point for lift off weight

 

[shreadvector]

And, NO, Aerotech has not printed an updated chart in years. You can use it and extrapolate for similar total impulse and average thrust motors. This will not work for all motors since some do not have equivalents on the old chart, like the current "new" G80 which has WAY more total impulse than the old G80. That is why the shortes delay sold is the G80-7. As Gary explained so simply: if you put the new G80 into the heaviest Model Rocket (3.3 pounds) it will need 7 seconds of coasting time, so the shortest time delay is 7 seconds. Lighter rockets use longer delays.

 

[GregGleason]

Does anybody have a chart for Aerotech motors listing max liftoff weights? I can't seem to find one except for an oldie from 1999.


Jerome

I can get you close if you give me the motor you are thinking of.

Greg

 

[Area66]

I believe the formula is something like this
Take a G80 motor and divide 80 by 4.14 to get thrust lbs, then divide that number by 5 to get the weight to thrust ratio (5 to 1) this number is the max weight that this motor can lift safely
I'm guessing the formula since I'm not at home, I think someone will chime in with the right formula
This is a starting point for lift off weight

it's 4,45 if you want something simple, use this chart


View attachment 131056

View attachment 131057

 

[JohnCoker]

The common "5:1 thrust/weight ratio" rule of thumb is based on motors which develop the highest thrust at the beginning. Actually, what you want to ensure is that the rocket is flying fast enough at the end of the launch guide that its fins can keep it flying straight up. And, as shreadvector points out, it must achieve a safe altitude for successful deployment.

The only real way to know this is do a simulation to determine the speed off the launch rail (rod) and the apogee altitude. However, then you get into the problem of having to guess at a motor, then run a simulation for it, repeating for each motor. That is why I'm surprised more simulators don't offer some sort of quick-and-dirty simulation of every motor to see if it might work (and what sort of altitude you might expect), and is why I added the "motor guide" feature to ThrustCurve.org.

 

[GregGleason]

The common "5:1 thrust/weight ratio" rule of thumb is based on motors which develop the highest thrust at the beginning. Actually, what you want to ensure is that the rocket is flying fast enough at the end of the launch guide that its fins can keep it flying straight up. And, as shreadvector points out, it must achieve a safe altitude for successful deployment.

The only real way to know this is do a simulation to determine the speed off the launch rail (rod) and the apogee altitude. However, then you get into the problem of having to guess at a motor, then run a simulation for it, repeating for each motor. That is why I'm surprised more simulators don't offer some sort of quick-and-dirty simulation of every motor to see if it might work (and what sort of altitude you might expect), and is why I added the "motor guide" feature to ThrustCurve.org.

^ This (+1).

Greg

 

[JeromeK99]

I was hoping there was one out there that I missed. The AT header cards list the max liftoff weight.. so the data does exist! Not sure why they don't want to share it.

I'm not looking for a specific rocket.. just a reference. I have Rocksim and sim stuff out. It would be nice to have a chart to see if a motor is even practical before doing half a dozen sims.

I was aware there was more to it than a simple equation.

And as John said, it would be great if a sim program would just load up every motor that fit, and highlight what works! That would be a very useful feature!

Thanks anyway!

Jerome

 

[Area66]

it would be great if a sim program would just load up every motor that fit, and highlight what works! That would be a very useful feature!

Jerome

the Madcow apps do it, for now it work only on Iphone, Ipad and Ipod , I just enter the diameter and the weight of the rocket and it give me a choice of motors and appogee

 

[JohnCoker]

And as John said, it would be great if a sim program would just load up every motor that fit, and highlight what works! That would be a very useful feature!

Give this a try: ThrustCurve motor browser

I agree that this would be really good as a smartphone app so that you can use it at the launch site. (Especially because the on-site vendor might have different stock than your first choice.)

 

[bobkrech]

I was hoping there was one out there that I missed. The AT header cards list the max liftoff weight.. so the data does exist! Not sure why they don't want to share it.

I'm not looking for a specific rocket.. just a reference. I have Rocksim and sim stuff out. It would be nice to have a chart to see if a motor is even practical before doing half a dozen sims.

I was aware there was more to it than a simple equation.

And as John said, it would be great if a sim program would just load up every motor that fit, and highlight what works! That would be a very useful feature!

Thanks anyway!

Jerome

They are not commonly used anymore because it doesn't work in a lot of situations, but the one you can do in your head is to take the average thrust in newtons and divide by 25 to get the weight of the rocket in pounds......

The reasons why are listed below.

1.) The minimum recommended thrust to weight ratio is generally considered as 5:1, so if your motor develops 5 pound of thrust you can launch a 1 pound rocket. Unfortunately it only works on calm days, and on rockets that are not excessively heavy or draggy.

2.) A more accurate assessment shows when the wind increased over 5 mph, to prevent weathercocking, the thrust to weight ratio needs to be equal to or greater than the wind speed in mph. While this may seem excessive it insures the apparent wind is at a near zero angle of attack when the rocket leaves the rod. See https://www.nar.org/pdf/launchsafe.pdf for the details.

3.) The rule of thumb don't work for draggy rockets or heavy rockets because there is not provision for variations in the time to apogee which determines the proper ejection delay.

4.) Free simulation programs and other aids are available. The simplest ones require only the rocket diameter and weight, an estimated drag coefficient and a thrust curve, and they will predict the time to apogee so you can select an appropriate delay.

5.) These readily available and accurate aids have made the not so accurate lift-off weight tables obsolete.

Bob

 

[bill_s]

And, NO, Aerotech has not printed an updated chart in years. You can use it and extrapolate for similar total impulse and average thrust motors. This will not work for all motors since some do not have equivalents on the old chart, like the current "new" G80 which has WAY more total impulse than the old G80. That is why the shortes delay sold is the G80-7. As Gary explained so simply: if you put the new G80 into the heaviest Model Rocket (3.3 pounds) it will need 7 seconds of coasting time, so the shortest time delay is 7 seconds. Lighter rockets use longer delays.

Not exactly. 4.7" dia. at Cd=.5, 24 oz. wants a 5.5. sec. delay. At 7 it's over -50 fps at apogee. ADDING 10 oz. reduces that to -46 fps. Reducing the weight makes the delay even worse, but increases altitude down to an optimum of 17 oz. ... reducing weight even further beyond that and altitude starts to drop. Of course, Aerotech doesn't make any rockets themselves that fat and light ... my rockets sim best on lower thrusts, all else equal, but 137 N-s is not equal .

I recommend wRASP for things like max. liftoff and "sanity checks" unless you have an Open Rocket file. Only takes a couple minutes.

 

[JeromeK99]

Does anybody have a chart for Aerotech motors listing max liftoff weights? I can't seem to find one except for an oldie from 1999.


Jerome

I was hoping there was one out there that I missed. The AT header cards list the max liftoff weight.. so the data does exist! Not sure why they don't want to share it.

I'm not looking for a specific rocket.. just a reference. I have Rocksim and sim stuff out. It would be nice to have a chart to see if a motor is even practical before doing half a dozen sims.

I was aware there was more to it than a simple equation.

And as John said, it would be great if a sim program would just load up every motor that fit, and highlight what works! That would be a very useful feature!

Thanks anyway!

Jerome

Thanks guys for all the math... :eyeroll: but I was just asking if anybody new if there was a chart available.

Like I said, I have Rocksim... and I use it.. just realized how stupid it was to have to sim a dozen motors or do a bunch of math :eyepop: before a sim lol


Jerome

 

[bill_s]

I also got one recently that I didn't at all agree with the number they had. I think it was the G53-5FJ reload package. Maybe the number listed was for a -10. It didn't agree with the reccomendations for their own rockets either.

 

[Mikeyk]

Does anybody have a chart for Aerotech motors listing max liftoff weights? I can't seem to find one except for an

 

[Mikeyk]

I could use some help with this. I can't seem to buy a G-89, or any Pro series 2 motor bigger then an F. I need a simple chart. I know an eE 12 will lift the weight. I'd just like to know what a g-80 would do with 15 1 oz of rocket...engine weight factored in. I worked all day. Newton is dead. A chart. Motor, vs weight...approx altitude. I'm sure there will be a simple guy like me who can set up a program in 10 mins and get paid for it. Will shake your hand!

 

[Tractionengines]

I could use some help with this. I can't seem to buy a G-89, or any Pro series 2 motor bigger then an F. I need a simple chart. I know an eE 12 will lift the weight. I'd just like to know what a g-80 would do with 15 1 oz of rocket...engine weight factored in. I worked all day. Newton is dead. A chart. Motor, vs weight...approx altitude. I'm sure there will be a simple guy like me who can set up a program in 10 mins and get paid for it. Will shake your hand!

Go here enter rocket data, and rail length get quick list of usable motors.

https://www.thrustcurve.org/
The thrust curves of many motors do not work well with the rule-of-thumb equations. So best to just run quick and easy SIM.

 

[mikec]

10+-year old thread. Max liftoff weight is a combination of thrust and delay time. This Aerotech catalog ( https://d11fdyfhxcs9cr.cloudfront.n...echquestcatalog2021.16pages_1639435758852.pdf ) has max liftoff weight for all of the Quest and Aerotech low and mid-power single-use motors as of a couple of years ago.

Agreed that thrustcurve is a better way to go.

 

[Wayco]

John Coker is (and has been) a member here for many years. He has made many improvements to Thrustcurve over those many years, and it's the best way to get a quick and accurate estimate of anything you need to know on all motors that fit your rocket.
Sharon and I have 75 rockets listed on it, and use it extensively when we prep for a launch. I also print out a copy of it and include it in my log book file for each rocket I take to a launch.

 

[bobbyg23]

I was hoping there was one out there that I missed. The AT header cards list the max liftoff weight.. so the data does exist! Not sure why they don't want to share it.

I'm not looking for a specific rocket.. just a reference. I have Rocksim and sim stuff out. It would be nice to have a chart to see if a motor is even practical before doing half a dozen sims.

I was aware there was more to it than a simple equation.

And as John said, it would be great if a sim program would just load up every motor that fit, and highlight what works! That would be a very useful feature!

Thanks anyway!

Jerome

Thrust curve will list what is safe and not safe.