F impulse altitude record

madcow rocketry
eggtimer rocketry
SilicdyneTRF
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n27sb said:
John Coker has an excellent 2 part video on this subject. I can't do a better job than he does.
I do use an internal insert to control the ID.
[video=youtube;Lo_g1VOVAcg]https://www.youtube.com/watch?v=Lo_g1VOVAcg[/video]
[video=youtube;5KmTImQsHIk]https://www.youtube.com/watch?v=5KmTImQsHIk[/video]
Click to expand...

Thanks for the link! I'll look into that.
 
EeebeeE said:
Can you piston-launch the rocket to set a record? Also, Using an F10, your speed will not come near Mach 1, so using a heavy FG or CF rocket may not be as effective as using simple paper and balsa. Don't overthink this. A Jolly Logic altimeter and a Beeline tracker, placed in a payload section of a 24mm min. dia. rocket with papered balsa fins, a balsa nose cone and assembled with carpenter's glue will work fine. Friction-fit the motor. Take a look at this design. or buy an Apogee Aspire for $20.
Click to expand...
You can use any launcher you want to that sits on the ground and does not have any components that store energy (such as a spring or a tank of compressed air). A piston launcher is legal as it simply utilized the exhaust gas at liftoff in a better manner.

A properly designed 24 mm MD rocket should always apogee at a higher altitude than a 29 mm MD rocket using the same total impulse. It's simply physics and aerodynamics because a similar 24 mm rocket will have about 40% lower drag and more retained momentum which will extend the coast distance compared to an equivalent 29 mm MD rocket.

n27sb said:
Thank you Evan for your input. I like your Quote "History doesn't repeat itself, but it does have a tendency to rhyme. - Mark Twain "
I think it is pertinent here. Many guys have traveled this path. Here are my thoughts on each item. Some are mine and some absorbed from the generosity of forum members.
1. I think you can piston launch but it is not easy with the motors I plan to use.
2 An F10 would push me up to a 29mm frame and I would like to see what I can do in 24mm.
3. FG and CF rockets tend to be too heavy because they are usually overbuilt. By using CF in the fin can I can build lighter than paper and balsa and have a thinner fin profile. I also get better durability for the recovery phase.
4. Because all of the motors I have to choose from have too short of a delay I need my Dual Mini to deploy at max apogee. The Eggfinder GPS Is a little heavier than I would like but as it turns out I may have built the airframe too light for maximum coast so it helps out with some added weight in the nose. I probably do not need the Falcon RF tracker but some of the areas I fly in have rough terrain. Sometimes you hear the crunch of stepping on your rocket before you see it. The Falcon RF can take me to within 1 foot.
5. I plan on friction fitting the motor.
6. I like your design, I plan on trying a 29mm later to compare. Hope to fly side by side with yours one day.
7. Apogee Aspire? I think Tim makes great kits but part of the fun for me is building as much of the rocket as I can from raw materials.
How am I doing Bob?
Thanks again Evan for your thoughts. I look forward to more.
Click to expand...
You're doing fine.

The tracker is a wise idea. Too much is invested in the rocket not to include it.

There is an optimum weight for a given weight and thrust. https://www.rocketmime.com/rockets/studies.html from https://www.rocketmime.com/rockets/rckt_eqn.html Weight you rocket prepped for flight and run sims to see if adding weight increases the apogee. Used dimes and pennies for ballast. (known weights readily available).

I would suggest you look at using a Kevlar lariat loop backup for your friction fit just to make sure you don't spit out the motor casing.

The added weight and friction of any fly-away rail/rod guide should reduce altitude however it might be an interesting measurement to make.

Bob
 
bobkrech said:
I would suggest you look at using a Kevlar lariat loop backup for your friction fit just to make sure you don't spit out the motor casing.

Bob
Click to expand...
I make a small insert for the front of the engine case that allows me to mount my shock cord so even if it spits it out everything holds together.
Thanks for the idea.
 
n27sb said:
I built a launch tower but I would use a fly-away if it would help promote your stuff. PM an address and I can send you some tube.
Click to expand...

I don't want to change your plans, but it might be interesting at some point to do a comparison of results between two flights. My concern is that the fly-aways won't scale down terribly well below 29mm as a 3d-printed thing. I'll PM you.
 
n27sb said:
I don't think I have room for one. Most that I have seen are too big.
Click to expand...
Bigger than the falcon RF? My notion was "instead," not "in addition to." Because a good screamer can keep you from stepping on the rocket. Considering the unit and battery together, I assumed the screamer would weigh less than the Falcon; is that not right?
 
jqavins said:
Bigger than the falcon RF? My notion was "instead," not "in addition to." Because a good screamer can keep you from stepping on the rocket. Considering the unit and battery together, I assumed the screamer would weigh less than the Falcon; is that not right?
Click to expand...

Can you send me a link to a small one?
 
Rocket is complete, just needs a little wiring.
Rocket weight-- 2.1oz or 62g
Rocket plus electronics-- 3.8oz or 108g
Optimum weight would be 1/2 oz less but just can't get there.
It only makes a difference of 50 ft on the simulator.




photo 1-5.jpgphoto 3-2.jpg
 
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Test flew the rocket on an Aerotech E30-T. It flew straight.
2nd flight was CTI F30 LB.
About 50 ft after it left the tower if started a corkscrew. It impacted prior to deployment.
The rocksim stability factor is 2.8 Barrowman, or 3.8 Rocksim.
Velocity at departure from tower is 78 fps
Is it possible that due to the offset core of the long burn that some vectored thrust occurred or do I just not have enough stability for the
F30?
 
Yes but easier to rebuild than repair. Repairs usually add weight
 
n27sb said:
Test flew the rocket on an Aerotech E30-T. It flew straight.
2nd flight was CTI F30 LB.
About 50 ft after it left the tower if started a corkscrew. It impacted prior to deployment.
The rocksim stability factor is 2.8 Barrowman, or 3.8 Rocksim.
Velocity at departure from tower is 78 fps
Is it possible that due to the offset core of the long burn that some vectored thrust occurred or do I just not have enough stability for the
F30?
Click to expand...
Static stability shouldn't be a problem with numbers llike those, and I shouldn't think static instability would cause corkscrewing anyway. Vectored thrust coud cause it I guess, but lots of people use offset cores without epidemics of corkscrewing, so I'd look for some other cause. So now begins the questioning.
  1. How was the weather?
  2. How well centered were all the payload weights?
  3. How precicely did the fins match, for size, shape, and position?
  4. Had there been any damage after the first flight?
2. and 3. are things that people have a little bit imperfect all the time without problems, but I bring thm up because they can cause radially asymetric forces. If I wanted to build in a subtle defect in the hopes of corckscrewing, the frst thing I'd try would be an off center weight, and then an asymetric airfoil on just one fin.
 
Last edited:
markkoelsch said:
I think you need more fin. A bit larger, or go to four fins.
Click to expand...
Thanks Mark, I think I will add more fin.
After close inspection of the nozzle it looks like there was an obstruction blocking about 30% of one side of the exit. The photo does not show how bad it really was.
I have seen this before but never this much. I think a more stable rocket would have overcome this. I have seen a "wiggle" at about 100ft after launch on other rockets I have used this motor in.
Next time I think I will use the CTI F51 since it is a center core. performance should be as good if not better.
nozzle.jpg
 
jqavins said:
Static stability shouldn't be a problem with numbers llike those, and I shouldn't think static instability would cause corkscrewing anyway. Vectored thrust coud cause it I guess, but lots of people use offset cores without epidemics of corkscrewing, so I'd look for some other cause. So now begins the questioning.
  1. How was the weather?
  2. How well centered were all the payload weights?
  3. How precicely did the fins match, for size, shape, and position?
  4. Had there been any damage after the first flight?
2. and 3. are things that people have a little bit imperfect all the time without problems, but I bring thm up because they can cause radially asymetric forces. If I wanted to build in a subtle defect in the hopes of corckscrewing, the frst thing I'd try would be an off center weight, and then an asymetric airfoil on just one fin.
Click to expand...

Weather was perfect, I am pretty sure the other items were in good shape because of the prior flight. I just posted a photo of the nozzle, I think this was the problem.
Thanks for you input. Any other thoughts?
 
n27sb said:
Test flew the rocket on an Aerotech E30-T. It flew straight.
2nd flight was CTI F30 LB.
About 50 ft after it left the tower if started a corkscrew. It impacted prior to deployment.
The rocksim stability factor is 2.8 Barrowman, or 3.8 Rocksim.
Velocity at departure from tower is 78 fps
Is it possible that due to the offset core of the long burn that some vectored thrust occurred or do I just not have enough stability for the
F30?
Click to expand...
I agree with Mark. The corkscrew is most likely coning, and I don't think it's unexpected. It looks like your fins are too small in span and with the motor core being asymmetric the probability of roll-pitch coupling is enhanced. I also prefer 4 fins instead of 3.

What was the stability with the F30 versus the E30? The F30 is heavier at 102 g and a 54 g burnout weight than the E30 at 47 g with a 25 g burnout weight. Does the stability change with velocity?

Bob
 
Bob/Mark I agree.
Stability is better on a lighter E30 (4.2)
I am laying up a new BT as we speak. I am making the BT 2 inches longer and going to 4 fins with enough span to get a barrowman of at least 4.
I just figured out that Rocksim has a feature that calculates optimum weight. If I run a CTI F51 I can add a 1/2 oz from where I was and be right on the money.
tube.jpg
 
bobkrech said:
I agree with Mark. The corkscrew is most likely coning, and I don't think it's unexpected. It looks like your fins are too small in span and with the motor core being asymmetric the probability of roll-pitch coupling is enhanced. I also prefer 4 fins instead of 3.

What was the stability with the F30 versus the E30? The F30 is heavier at 102 g and a 54 g burnout weight than the E30 at 47 g with a 25 g burnout weight. Does the stability change with velocity?

Bob
Click to expand...

Screen Shot 2015-05-15 at 9.27.03 AM.jpg
Getting ready to cut fins. hope this is enough.
 
What is your top speed according to Rocksim? Perhaps this is naïve but, assuming you're subsonic, wouldn't an elliptical nose cone give better results?
 
jqavins said:
What is your top speed according to Rocksim? Perhaps this is naïve but, assuming you're subsonic, wouldn't an elliptical nose cone give better results?
Click to expand...

Rocksim gives a little less altitude with the elliptical.
 
Had the opportunity to fly a new version today. Nice flight, almost vertical. I had opted to leave the deployment computer out but the 12 second delay did not work. It looks like it only delayed about 8 seconds at most. So the flight was stopped short at a vertical velocity of about 170 mph. This flight used a streamer so no damage. I plan to re-try this in a few months with my Altus Metrum Easy Mini. Probably could have exceeded 5000 ft. The Eggfinder GPS walked me right to it. Even though it was only 100 yards away, nobody saw it land. I got paperwork signed by the Tripoli Prefect so I think I can submit this for a National record. 4176.5 ft This busted my past local club record using an "F" motor of 2850 ft.
fx1-2.jpgScreen Shot 2015-10-10 at 3.37.56 PM.jpg
 
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