Going for 100,000 Feet

It is meant to take images with the long side parallel to the ground. As far as a flight video goes however, that is only relevant at launch. So I will just have the videos be sideways.

Another rare warm February Day, so I was able to paint. This is done with 2 light coats of primer followed by 2 light coats then a medium coat of Chrysler Hemi Engine Orange. The paint is heat rated to 550 degrees. I will sand with 5,000 grit then wax.

EeebeeE said:

Another rare warm February Day, so I was able to paint. This is done with 2 light coats of primer followed by 2 light coats then a medium coat of Chrysler Hemi Engine Orange. The paint is heat rated to 550 degrees. I will sand with 5,000 grit then wax.

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Pretty, Be sure to take pictures 'cause that paint is going to cook off on the NC and leading edges of the fins if you put serious velocity to her. Kurt

ksaves2 said:

Pretty, Be sure to take pictures 'cause that paint is going to cook off on the NC and leading edges of the fins if you put serious velocity to her. Kurt

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Yeah. She's going to hit Mach 1.7.

This has to be one of the very best posts I've had the pleasure of reading here!!

Hellraiser said:

This has to be one of the very best posts I've had the pleasure of reading here!!

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Thank you. Flying Do this June. Hoping to have some good footage. Shwoing it off at the Rochester Museum and Science Center next weekend.

EeebeeE said:

Yeah. She's going to hit Mach 1.7.

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Ok, Mach 2.5 for 20 or more seconds will fry the paint off along with any stickers or appliques, tear the leading edge lamination away from the fin stock and cook the end of the
nosecone if it's not metal. Mach 1.7 for how long? You might be in better shape as far as your paint job goes.
It's the really high rate of acceleration down "low" that can heat the daylights out of a finish.

What I report is what Robert DeHate did to a rocket one time. Looked like it was single use from the after photos. I can't find the link up anymore otherwise I'd repost it. Kurt

Booster will not break Mach 1. Sustainer will pass Mach 1 for 5 seconds and be above Mach 1.5 for less than 2 seconds. I've seen the rocket Robert flew. He built it as if it was only going to fly once. Friction really beat it up.

Used my Raven 3 on another 2-stage project successfully over the weekend so I think I am getting close to ready tl fly "Do."

The motor choices are narrowing down to a pair of H255's or an H399 booster with an I204 Sustainer. Both are similar in combined power with the 2x H255's each having 316 NS for 632 total, and the H399 (282 NS) and I 204 (348 NS) having 630. Below are descriptions of the simmed characteristics of the flight.

The H399-I204 combination will result in an earlier separation and second stage deployment, which is beneficial because that means the booster will recover closer to the pad. Separation in this setup occurs at about 300 feet up at 0.7 seconds into the flight, and the booster will use motor ejection to deploy either a small cute or a streamer. The rocket will be travelling at roughly 545 MPH at separation. Stability of the the rocket at launch is 3.78 ca. and speed off the rail is 96 MPH. This will help reduce risk of weathercocking. The sustainer will ignite 1 second later. At this point the rocket will be approx. 1,030 AGL moving at 465 MPH. Motor burnout occurs 1.97 sec. later at Mach 1.74. The rocket should be approx. 3,650 AGL at burnout. It will coast to apogee. RAS Aero suggests Apogee to be 19,031 ft. Open Rocket suggests, 17,114.

The 2x H255 Shows speeds at separation, sustainer ignition, and top speed to be roughly the same as the other. Thew difference is that separation occurs at 630' AGL, sustainer ignition at 1,300' AGL, but sustainer burnout occurs at 3,300'. The altitude is still higher because the spent H255 weighs more than the spent I-204, creating a little more inertia. RAS Aero says 19,165 and OR says 17,171.

I am very familiar with OR and I think its projections in this situation are more accurate. However I will probably test fire the sustainer with a high-impulse F or G motor to see how it actually compares against the two programs to make sure. I can do this at NYPower.

I am concerned about coning since my fins are a little small, but the flight should still be pretty stable. This is where the H255 pair may be a perform better than the H399/I-204 because the higher seconds stage impulse will punch it through transonic space faster.

Figured out the discrepancy between the two programs. I still had the field set at 3,981 feet in altitude... Black Rock. Set it back to 891 feet, which is Potter NY, and the two sets of sims are within 100 feet of each other. Both below 18,000'. Makes me a lot more comfortable. Still will test fly the sustainer. Probably on a G250.

EeebeeE said:

I am concerned about coning since my fins are a little small, but the flight should still be pretty stable. This is where the H255 pair may be a perform better than the H399/I-204 because the higher seconds stage impulse will punch it through transonic space faster.

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But I thought your stability was over 2 cal for the whole flight? I read somewhere that small fins are fine as long as you use enough nose weight to keep it over 2 cal for mach flights.

TRFfan said:

But I thought your stability was over 2 cal for the whole flight? I read somewhere that small fins are fine as long as you use enough nose weight to keep it over 2 cal for mach flights.

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In theory yes, however one thing that sims don't account for is coning. This can be a pretty significant issue when you have small fins and excessive nose weight.

littlemisterbig said:

In theory yes, however one thing that sims don't account for is coning. This can be a pretty significant issue when you have small fins and excessive nose weight.

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I do have a lot of nose weight. (5 oz.), but the motor weight is also high comparatively bringing the entire launch weight of the sustainer to 28.7 oz. After the fuel is spent it is still about 20 oz. or so. Comparatively, PML makes a solid plastic nosecone that is the same size and weighs 4 oz. Mine is 2 oz. more including the weight. This isn't an outrageous amount. Plus, this will have some spin which should also help stabilize the flight.

Another thing I think contributes to coning is excessive length, giving way to overstability. Saw a bunch of college student builds and all of their rockets seemed to be 8+ feet long with 3" fins and high impulse motors. The greater the distance between the nose and the thrust, the larger the radius of the cone. My sustainer is 28" long. I would have made it shorter if I could. Essentially, it is a "powered boosted dart."

The sustainer test flight should give me some good data. Thinking of a G250 in the test to simulate the initial thrust of the booster. That should give me a good indication. Sims to 3,600' in OD and 3,650' in RAS Aero. I will use the same electronics configuration as in the planned flight. The only thing I will not be able to duplicate is the launch weight.

littlemisterbig said:

In theory yes, however one thing that sims don't account for is coning. This can be a pretty significant issue when you have small fins and excessive nose weight.

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Is there a way to predict coning?

Think of a rocket as a pendulum. If the pendulum has alot of rotational inertia (weight more distributed towards the end of the rocket), its inertia as it crosses vertical during a correction can be greater than the restoring forces of the fins so the rocket overcorrects and repeats. Add a little spin and the wobble turns into a cone. The cone is unstable because once this happens the centripetal force of the weights at the ends of the rocket will want to widen the cone angle.

To avoid coning:
Concentrate weight near the CG of the rocket instead of the ends.
Do not use 3 fins, instead use at least 4 or 5 of the same area so that you have at least one or two fins more perpendicular to wobble motion of the rocket.
Spin the rocket like hell.

jderimig said:

To avoid coning:
Concentrate weight near the CG of the rocket instead of the ends.
Do not use 3 fins, instead use at least 4 or 5 of the same area so that you have at least one or two fins more perpendicular to wobble motion of the rocket.
Spin the rocket like hell.

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The other thing you need to do is to give it a lot of high impulse initial thrust to get it moving. At least a 15:1 Thrust-Weight ratio so that when it leaves the rail, the speed gives it more stability.

In this case, because of its short length, long payload, and large motor...the whole thing is heavy. The sustainer is a 28" long, 29mm minimum diameter FG rocket that weighs 1.8 pounds when loaded and the parachute bay, where there is the least concentration of weight is only 2.5" long. When the booster is added to the configuration, the CG is almost in the center of the sustainer motor and the rocket weighs 2.75 pounds.

An H399 booster still gives it a 39:1 Thrust-weight ratio and by the time it leaves the rail it is doing just shy of 100 MPH.

I do have 3 fins, but even so, they are about 90% as high as the airframe is wide. Normally you want about 110% or so. These are pushing the envelope, but not near as bad as fins that are 75% or less. The subsequent rockets will have larger fins in relation to the size of the rocket...but not much larger.

EeebeeE said:

I do have 3 fins, but even so, they are about 90% as high as the airframe is wide. Normally you want about 110% or so. These are pushing the envelope, but not near as bad as fins that are 75% or less. The subsequent rockets will have larger fins in relation to the size of the rocket...but not much larger.

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Having the fins be at least, or just over, a body diameter is one thing. From what I can tell, your three fins have relatively short root chords, and no tip chord. Personally, I'd either increase span or switch to 4 fins. I'd take the slight performance hit over losing the rocket.

How does "speed" give more stability? Isn't stability strictly determined by fin area/location and mass distribution?

Anything interesting in the raven file from the 2 stage flight this weekend? Did it fire the igniter output at the expected time?

N

Good paper here, if you are math and physics challenged or impatient you can skip to the recommendations on page 10.

https://rsandt.com/media/Sounding Rocket Fin Design to Mitigate Roll Lock-In.pdf

littlemisterbig said:

Having the fins be at least, or just over, a body diameter is one thing. From what I can tell, your three fins have relatively short root chords, and no tip chord. Personally, I'd either increase span or switch to 4 fins. I'd take the slight performance hit over losing the rocket.

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That's a reco that should have been made 6 months ago.

jderimig said:

Good paper here, if you are math and physics challenged or impatient you can skip to the recommendations on page 10.

https://rsandt.com/media/Sounding Rocket Fin Design to Mitigate Roll Lock-In.pdf

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The stability of the sustainer is more than 2.5. By the time it reaches mach 1, the stability will be closer to 2.8. I have two programs that are both widely respected that say this will fly. I have FinSim saying that the fins will experience minimal flutter.

I am concerned about coning, slightly, but I also know these things. A top speed of Mach 1.7 is NOT hypersonic, where most coning shreds occur. The weight is evenly distributed throughout the rocket. The design is stable, but not overstable.

Yes I have only 3 fins, but at this point, I have a built, sanded, and finished rocket. Recommendations such as more fins, larger fins, larger tip chord, etc. are irrelevant at this point. This is what I have and I am beyond reasonably sure it will fly successfully.

Wingarcher said:

How does "speed" give more stability? Isn't stability strictly determined by fin area/location and mass distribution?

Anything interesting in the raven file from the 2 stage flight this weekend? Did it fire the igniter output at the expected time?

N

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Speed gives more stability because the CP moves aft as the rocket accelerates, creating a greater distance between CG and CP. Also, consider Newton's First Law. This is the stability simulation which backs up that the rocket becomes more stable as it increases in speed.



Pilot error on the Raven 3. For some reason the delay was set at 5 seconds instead of 1. I have reprogrammed, reset, and rechecked the setting is now at 1 second. So yes...the Raven fired "correctly," even though the timing was incorrect.

EeebeeE said:

Yes I have only 3 fins, but at this point, I have a built, sanded, and finished rocket. Recommendations such as more fins, larger fins, larger tip chord, etc. are irrelevant at this point. This is what I have and I am beyond reasonably sure it will fly successfully.

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I hear ya. My hybrid rocket attempt is also 3 fins and small profile (span ~100% or less of airframe diameter). However with my design the good thing is my mass in more concentrated towards the center of the rocket, but my CG moves backwards as the tank drains during the burn. I have high static margin (~4-5 cals) though.

Will test fly at NYPOWER on a J. That's what test flights are for.

EeebeeE said:

The stability of the sustainer is more than 2.5. By the time it reaches mach 1, the stability will be closer to 2.8. I have two programs that are both widely respected that say this will fly.

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The Cp through the transonic region moves forward considerable. Depending on the mass distribution of your motor, the rocket can end up unstable above Mach 0.9. A min-diameter rocket (fly the motor) doesn't shift the Cg much; a big dumb rocket (motor is mostly behind the Cp) shifts the Cg forward as it burns. Therefore, the transonic stability problem is mostly seen in min-diameter rockets.

Another factor is the shape of the nose cone. The fins can end up within a cone of turbulent air. A long ogive shape gives minimal airflow separation. A conical nose could have airflow separation along the whole rocket, masking the effect of the fins. Small fins may not be in the steady air stream. A coning action in that case will occur as the fins wander out of the turbulent airflow.

Larger rockets tend not to survive problems with dynamic stability. Their higher longitudinal moments of inertia require more corrective force from the fins than a smaller, less dense, rocket. Testing with a subscale rocket won't necessarily predict dynamic stability problems.

jsdemar said:

The Cp through the transonic region moves forward considerable. Depending on the mass distribution of your motor, the rocket can end up unstable above Mach 0.9. A min-diameter rocket (fly the motor) doesn't shift the Cg much; a big dumb rocket (motor is mostly behind the Cp) shifts the Cg forward as it burns. Therefore, the transonic stability problem is mostly seen in min-diameter rockets.

Another factor is the shape of the nose cone. The fins can end up within a cone of turbulent air. A long ogive shape gives minimal airflow separation. A conical nose could have airflow separation along the whole rocket, masking the effect of the fins. Small fins may not be in the steady air stream. A coning action in that case will occur as the fins wander out of the turbulent airflow.

Larger rockets tend not to survive problems with dynamic stability. Their higher longitudinal moments of inertia require more corrective force from the fins than a smaller, less dense, rocket. Testing with a subscale rocket won't necessarily predict dynamic stability problems.

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Agree with what you are saying. The stability of the sustainer in this case is most important. It starts at 2.5. However also as the fuel gets spent, the CG also moves forward, which is why both RAS Aero and OR see an overall increase in stability even through mach. Since the sustainer fires when the rocket is approx. Mach 0.6, propellant mass is reduced to the point that stability increases to about 2.7 ca. at mach 1.

Also, this rocket is more geared toward the learning curve than a subscale test. The subsequent rockets will have ogive nose cones, and probably a little larger fins. Plus those boosters will be larger in diameter than the sustainers.

The reason for a conical nose cone on this effort was because this was the only FG nose cone I could find. I would have preferred ogive, but most manufacturers didn't produce them or sell them individually. Someone gave me this nose cone. It needed a little TLC, but it was far better than plastic.

jderimig said:

I hear ya. My hybrid rocket attempt is also 3 fins and small profile (span ~100% or less of airframe diameter). However with my design the good thing is my mass in more concentrated towards the center of the rocket, but my CG moves backwards as the tank drains during the burn. I have high static margin (~4-5 cals) though.

Will test fly at NYPOWER on a J. That's what test flights are for.

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Looking forward to see it go.

Any progress?

TRFfan said:

Any progress?

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Funny you should ask... I was going to make an update today anyway.

Working on the electronics. As you probably have seen the nosecone and the payload tube are glued together and this is set up as single deploy. This eliminates the need for threaded rods which in addition to being heavy, take up a lot of space in an area that is roughly only 8.6 cubic inches (141 cc's). Space management is critical.

The sled is made from a 1/16" thick piece of balsa, sandwiched between two sheets of 6 oz. FG. It only weighs 0.25 oz. (7 grams), and it is very strong. I am using a LIPO battery to power the Raven. Small but still needs to be managed well. For instance the altimeter on one side and the battery on the other are too wide and will not fit into the airframe...bt if I fit the altimeter battery on the opposite side of the tracker, and the tracker battery on the opposite side of the altimeter, then I am fine.

So this is how everything lays out. The sled extends into the coupler tube. It will have a bulkhead on the aft end and the separation charge will be connected there. I am using flat wire to run the staging charge and the sustainer ignition. I have an idea as to how to connect everything there but it needs testing.

On one slide of the sled I will have the altimeter battery, the altimeter, and the onboard camera. On the other side I will have the transmitter, transmitter battery, and the magnetic switch for the altimeter. There is about 2" of sled left at the aft end to run the wiring for the charges. I will use 30 ga. wire for this. A single #4 sheetmetal screw will hold the coupler to the airframe. and the video camera peep hole will serve also as the vent for the altimeter.

A couple more shots of the sled. Wiring is finished. The magnetic switched was raised so that it was closer to the airframe making it easier to turn on. Also, it was cleaner to have the wires run under it than over it.

The entire electronics sled with components and wires along with the video camera not in these photos only weighs 2.3 oz. I think it came out well.

I really recommend using more than one vent hole if at all possible. I had ONE vent hole appropriately sized drilled in the nosecone for a stratologger. It was a windy day and the ejection charge blew 3 times before my stubborn self drilled another 3 vent holes.