F-Motor Record???

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jhurst7
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F-Motor Record???

Postby jhurst7 » Sat Aug 20, 2016 9:48 pm

Hello,

I was thinking over the past few days, what motors would be required to break the sound barrier. So I started with an F-40. Although the F-40 didn't break the sound barrier (304m/s on a 26°C day), it did reach an Apogee of 5,662 feet (1726m). Which, I checked back on the Tripoli website, would be a record by 250 feet. I've just got a few questions;

1. Have I missed anything major, I've got parachutes, planning on wadding instead of piston ejection, altimeter, but is there anything else I've missed?

2. The rocket reaches Mach .89 which from my understanding is transonic. Would there be any transonic turbulence which may affect it?

3. Would the fins being attached to the rocket body and not through the wall be enough to hold them on?

4. Would packing the parachute in the nose cone affect its deployment?

5. I have a small tail cone on the end, what kind of motor retainers and aft closures be used on a minimum diameter rocket?

6. Would an Altimeter One reading be enough to officially break the record?

I think I'll definitely have some more questions, but that's all for now, any help would be much appreciated.

-James
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Happy Heyoka
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Re: F-Motor Record???

Postby Happy Heyoka » Sun Aug 21, 2016 12:47 am

You might want to check that stability value - somewhere between 1 and 2 calibres (body diameters) between CP and CG as a minimum is the usual rule of thumb.
OpenRocket can also do a stability plot over time in the simulation (as it goes transonic, that goes through a dip).

Increasing stability through a nose weight (moving the CG forward) will increase mass; through body length or fin size (moving the CP back) will increase drag. Both of those will decrease your maximum velocity.

On your question, MD rockets don't have the usual fin mounting but sometimes have a slotted body with the insides flush... so fillets etc are important (extra mass again). Check out Lister's 24mm MD design for ideas (amongst others).

Also don't forget to add the mass of the altimeter... and at 5000', you're definitely going to want a beeper or tracker or something to help you recover it (-> more mass).

btw - all this is theoretical from my point of view - haven't built anything yet that's gone faster than about Mach 0.8.
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jhurst7
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Re: F-Motor Record???

Postby jhurst7 » Sun Aug 21, 2016 8:13 am

Yeah, it's all theoretical for me as well, I just got my Level One Cert.

As for the stability, it remains relatively constant throughout, taking a dip at apogee.

Also, an Altimeter is included in the OpenRocket, the large box with an up Arrow. I modeled it off an Altimeter One.

As for GPS tracking, would I absolutely need it? The rocket comes down at 6.5m/s (I know, a bit hard) but the flight time is 271 seconds (4 minutes 31 seconds) so could I visually track where it goes down? Is the launch site at Westmar very clear? With a strong wind of 12km/h, it drifts around 650m on the way down. I could probably run under it or just be close to it and see where it comes down.

I've also got another question; what material should I use? I'm currently using carbon fibre just because I wasn't sure what to use so any help there would be good. I'm also unsure as the maximum acceleration is 310m/s (31g) and that seems pretty tough.

Thanks

-James
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Re: F-Motor Record???

Postby SpaceManMat » Sun Aug 21, 2016 9:57 am

jhurst7 wrote:Hello,

I was thinking over the past few days, what motors would be required to break the sound barrier. So I started with an F-40. Although the F-40 didn't break the sound barrier (304m/s on a 26°C day), it did reach an Apogee of 5,662 feet (1726m). Which, I checked back on the Tripoli website, would be a record by 250 feet. I've just got a few questions;

1. Have I missed anything major, I've got parachutes, planning on wadding instead of piston ejection, altimeter, but is there anything else I've missed?

2. The rocket reaches Mach .89 which from my understanding is transonic. Would there be any transonic turbulence which may affect it?

3. Would the fins being attached to the rocket body and not through the wall be enough to hold them on?

4. Would packing the parachute in the nose cone affect its deployment?

5. I have a small tail cone on the end, what kind of motor retainers and aft closures be used on a minimum diameter rocket?

6. Would an Altimeter One reading be enough to officially break the record?

I think I'll definitely have some more questions, but that's all for now, any help would be much appreciated.

-James


2. At .89 your NC and Leading edges should see supersonic air speed and asociated shock waves.
3. Yes, if you do it right.
4. I assume this is motor deploy only. You of course need to make sure that there is nothing to snag the chute on the way out. When the charge goes off both the chute will be pushed into the NC further. You need to have the chute attached on the shock cord between the body and the NC, when the cord is pulled far enough the chute will be pulled out of the NC provided the NC has enough momentum to overcome the friction. You also need to be carefull about the charge size, because there is very little space the charge is likely to be too energetic and may eject your NC too hard breaking the cord.
5. Not sure you can get a tail come retainer that small, you may have to use a tail cone and figure out another way to retain you motor. Either a min dia retainer or friction fix. Check Aus Rocktery site for both items, also the Aero Pack web site.
6. Chech the ARMS / Tripoli website for their respective rules on allowable altimeters. Pretty sure altimeter 1 is ok.
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Re: F-Motor Record???

Postby jhurst7 » Sun Aug 21, 2016 10:34 am

I know that you can change the delay on some CTI motors, would I be able to change the ejection charge size on any motors?

Also, I've noticed that the ejection charge is only 4 seconds, is there any way to extend the delay or would I have to do the ejection electronically?
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Re: F-Motor Record???

Postby SpaceManMat » Sun Aug 21, 2016 2:07 pm

Yes you can change the charge on CTI. You remove the round charge well cover. Carefully remove and measure the charge, add a bit of dog barf. Put the cover back on and add some ca glue.

You probably want to consider using a streamer recovery and also look at optimising your weight to maximise weight OR can do this. 200g is very low are you sure about the part weights? Also your stability is a bit low, as its a short stubby rocket it can probably be a bit low, but keep in mind that to maximise altitude you need to prevent weather cocking. If your speed of the rail is low and your stability is low then you will definitely have issues.
QRS: 124
AMRS: 32 L2 RSO
Highest Altitude: 13,647 feet
Fastest Flight: Mach 1.55
Largest Motor: CTI 1115J530 IM
Current Project: X Wing

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Re: F-Motor Record???

Postby jhurst7 » Sun Aug 21, 2016 7:04 pm

SpaceManMat wrote:
You probably want to consider using a streamer recovery and also look at optimising your weight to maximise weight OR can do this. 200g is very low are you sure about the part weights? Also your stability is a bit low, as its a short stubby rocket it can probably be a bit low, but keep in mind that to maximise altitude you need to prevent weather cocking. If your speed of the rail is low and your stability is low then you will definitely have issues.


I'm not sure what you mean by weight OR, could you please specify? I'm pretty sure about the part weights, my only problem is maybe I haven't taken the reload casing into account? However, one of the motors I was thinking of using was an Apogee F10 which is a single use. Would I be able to use that and get it shipped in somehow or is that too hard? The other motor I was thinking of using was an Aerotech F10, which Blake doesn't seem to have.

The stability stays at around 0.7 throughout so that shouldn't be a problem.
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Re: F-Motor Record???

Postby SpaceManMat » Sun Aug 21, 2016 7:51 pm

Sorry little bit of a typo, OR has an optimizer tool. You need to configure it to find the weight that results in the optimum altitude.

Talk to Blake about special motor orders, you can't just import them yourself.

.7 stability is almost certainly too small.
QRS: 124
AMRS: 32 L2 RSO
Highest Altitude: 13,647 feet
Fastest Flight: Mach 1.55
Largest Motor: CTI 1115J530 IM
Current Project: X Wing

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Re: F-Motor Record???

Postby jhurst7 » Sun Aug 21, 2016 8:32 pm

On the optimization tool, for some reason, I can't select the components to optimize. I think I'm doing something wrong. What do I do?
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Re: F-Motor Record???

Postby Viking » Sun Aug 21, 2016 8:57 pm

Your stability will improve some when you add another 30mm to the air frame length.
OR's motor 'shadows' for the Aerotech hobbyline motors do not include the forward closure.
For the F40 (29/40-120) you need to add another 30mm for the delay grain, charge well and cap.
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Re: F-Motor Record???

Postby SpaceManMat » Sun Aug 21, 2016 9:49 pm

jhurst7 wrote:On the optimization tool, for some reason, I can't select the components to optimize. I think I'm doing something wrong. What do I do?


You need to expand on the item you want to optimise and the choose the property of that item such as mass, position, length etc. Then you can add that property. At this stage you can also set the min and max values you want to alow for that item. Next select the simulation that you want to optimise for. I usually set the min stability but this tends to be only a suggestion. The optimiser should default to mazimising altitude. The. You should hit the Start optimisation button. I find the optimiser a bit fiddly to use but it is quite handy.
QRS: 124
AMRS: 32 L2 RSO
Highest Altitude: 13,647 feet
Fastest Flight: Mach 1.55
Largest Motor: CTI 1115J530 IM
Current Project: X Wing

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Re: F-Motor Record???

Postby jhurst7 » Wed Aug 24, 2016 8:28 pm

I finally was able to use the optimize tool, thanks for the help Matt, and I have added the extra 30mm for the delay, charge and cap, thanks Viking.

I now have a slightly different design, and a bunch more questions.

1. For some reason, my speed has dropped, from 304m/s to 197m/s, while my apogee has increased, why has this happened?
2. If it does travel at this speed, what materials should I use? My original design consisted of carbon fiber, but now the whole rocket is Quantum Tubing, would this be a good material to use?
3. I've also got my fins hanging out the back a few centimeters. That should be fine when it hits the ground right?

That's about all for now.
Thanks

-James
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Re: F-Motor Record???

Postby SpaceManMat » Wed Aug 24, 2016 9:24 pm

1. When the motor stops you want your rocket to have as much momentum as possible to carry the rocket to its highest altitude. When your rocket is light it will go faster but the drag will increase so you suffer larger losses to drag. By increasing mass you have reduced the speed and therefore the drag to obtain a better altitude.
2. QT is pretty soft, but as your staying away from transonic speeds it would be ok. The issue I can see is that you would probably want to increase the size of your fillets to make sure it had enough QT material to hold the fins on. The main point of QT is to make it easy to obtain a nice finish to you rocket.
3. Combined with the use of QT this would be bad. Far too easy to snap a fin off. If you where building an all Fiberglass or carbon fiber and used tip to tip reinforcement with fiberglass / carbon fibre cloth then it would ok I would expect.

Also I think you've killed your stability there somehow.
QRS: 124
AMRS: 32 L2 RSO
Highest Altitude: 13,647 feet
Fastest Flight: Mach 1.55
Largest Motor: CTI 1115J530 IM
Current Project: X Wing

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Re: F-Motor Record???

Postby Viking » Wed Aug 24, 2016 11:35 pm

jhurst7 wrote:1. For some reason, my speed has dropped, from 304m/s to 197m/s, while my apogee has increased, why has this happened?

Because motor.
Your original sim was with an F40 which has ~68N max. and ~38N average thrust.
The new motor is a tad over 90mm long, which would be about right for the Apogee F10 you have mentioned in another post.
While both motors have similar total thrust, the F10 has only ~23N max. and ~11N average thrust but much longer burn time (7s Vs 2s for the F40)
Less max thrust = less acceleration (for a regressive thrust profile)
Less max and average thrust = less velocity.
Longer burn and less drag(due to less velocity as as Matt explained above) = more altitude.
New motor also explains some of the weight reduction.
Simon
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Re: F-Motor Record???

Postby jhurst7 » Tue Sep 13, 2016 9:00 pm

After some optimizing and some thinking, I have changed the design slightly. The apogee on a single use Apogee F10 is 2009m or 6591ft. The old record was 5407ft.

It has a stability of 0.99 and at burnout, the stability is around 1.9. This seems like plenty of stability. As you can see in the picture it has a tail cone. So, what I was thinking to do is glue the tail cone on with some slow setting epoxy, putting some tape on the inside of the body tube and then sliding in the motor from the top. The max stress put on the friction fit would be 2.3kg, which isn't much. One of the problems with that, however, is that the motor may burn through the plastic casing and it might fly out. I've never used a composite single use motor before, so I don't really know what will happen with it. Will this work?

Also, what materials should I use? Fiberglass seems like a good idea, but what about some obscure ones like Acrylic or PVC or Polystyrene. Would these work?

And finally, what paint smoothness should I use. I currently have it at 20μm, however, I'm not really sure what to put it at. Any help with that would be great.
Thanks

-James
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