Punisher 3 Wiggle

[DHays]

Hello,

Just had a quick question. On my WM Punisher 3, I noticed that once it left the rail, it wanted to wiggle left and then right. And then it flew nice and straight. Acting tail heavy? It was flying on a K550. The flight before that on the same day it flew on a J415. It did a little wiggle but not quite as much as the K550. So, I am trying for a nice straight flight all the way. I was thinking the the average impulse of the J415 and K550 should of been enough of a kick off the pad to keep it going nice and straight. Maybe not?

The wind was probably between 5-10 MPH.
I had a little over 0.7 calibers of stability. Sounds like not enough but should be fine for the Punisher?
Do I need to go with a higher average thrust? Like a J800? Or for all of you Punisher fliers, what should be the minimum average impulse that I should stick with so I can try for a nice straight flight?
I built it stock with the exception of foaming the tail can.

My very first flight was on a H550. I thought that it flew nice and straight on that. 1,400 feet.

I know its not the rocket, it's something that I am not doing quite right.

Thank you!

 

[mikec]

I had a little over 0.7 calibers of stability. Sounds like not enough but should be fine for the Punisher?

Sounds like yours is a little tail-heavy from the foaming, mine shows 1.4 cals with a K550.

The only bad flight I've ever had was on a CTI J140 (very wobbly) but anything with reasonable TTW should be fine (the J140 was about 6:1 which was a bit low apparently.)

 

[user 30299]

The wiggling on the two motors suggests the rocket’s CG is too close to the CP. You will have instability, even with high velocity off the rail. They are heavy motors, while the H550 is a much smaller motor - so the rocket’s CG sits farther forward. Once the K and J motors burn off some mass, then the CG moves forward and the wiggling stops.

You don’t need a higher thrust motor. You just need a touch of weight (mass) added up at the nose cone.

 

[kjhambrick]

@DHays --

I can only guess without seeing it fly but I believe @mikec and @QFactor nailed it -- you need to move your CG forward.

Do you have a video of either of the flights that shows the wiggle ?

Interesting stuff here !

Thanks !

-- kjh

This is Wildman's RocSim file imported to OpenRocket and loaded with a K550 ...

Weights absolutely need tuning which will move the CG, but the CP is what it is for the rocket's shape ...



Attached is the .ork I ended up with after importing the .RKT and exporting the .ORK

 

[rfjustin]

K-2050 will solve all your woes.

 

[DHays]

K-2050 will solve all your woes.

Lol, I have been looking for one but my favorite vendor is out of them.

 

[DHays]

@DHays --

I can only guess without seeing it fly but I believe @mikec and @QFactor nailed it -- you need to move your CG forward.

Do you have a video of either of the flights that shows the wiggle ?

Interesting stuff here !

Thanks !

-- kjh

This is Wildman's RocSim file imported to OpenRocket and loaded with a K550 ...

Weights absolutely need tuning which will move the CG, but the CP is what it is for the rocket's shape ...

View attachment 615435

Attached is the .ork I ended up with after importing the .RKT and exporting the .ORK

I don't have any video. Thank you for the file and the help.

 

[DHays]

I am going to add approx 3.5 oz of nose weight to it. This will give me 1 cal. of stability with a K550. Hopefully that will do the trick. If not, I can add or remove weight, flat washers. Just need to do a test flight. Just hate to add weight to a rocket and take up more room in the nose cone since it is HED. But, if it works, then all is fine. I'll know not to foam the fin can in the future. I didn't think that it would add enough weight to worry about. It's just between the fin roots and MMT. It's a 3" airframe with a 54mm hole.

Thank you everyone for the help!

 

[kramer714]

Load up all of the recovery gear and a motor case (don't use a loaded motor). Measure the cg just by holding the rocket. Now tap the rocket against the bottom on a piece of wood, or something like that (now you know why not to use a loaded motor) , and recheck the CG, very likely it shifted down a bit when the 'laundry compresses' down. This gives you a better idea what the actual CG is at launch.

I have seen that where a rocket is loaded and the cg checked with the parachute burrito snug at the top of the bodytube, then with a quick jerk of the rocket you can actually feel the parachute sliding down. With a .7 stability it could make a difference.

YMMV

 

[user 30299]

Load up all of the recovery gear and a motor case (don't use a loaded motor). Measure the cg just by holding the rocket. Now tap the rocket against the bottom on a piece of wood, or something like that (now you know why not to use a loaded motor) , and recheck the CG, very likely it shifted down a bit when the 'laundry compresses' down. This gives you a better idea what the actual CG is at launch.

I have seen that where a rocket is loaded and the cg checked with the parachute burrito snug at the top of the bodytube, then with a quick jerk of the rocket you can actually feel the parachute sliding down. With a .7 stability it could make a difference.

YMMV

As kramer714 points out, if you could share with us the CG location (less the motor), and the rocket's loaded
weight (less the motor), a few of us could double-check the stability - and the needed weight to improve the
Punisher's stability.

 

[user 30299]

I am going to add approx 3.5 oz of nose weight to it. This will give me 1 cal. of stability with a K550. Hopefully that will do the trick. If not, I can add or remove weight, flat washers. Just need to do a test flight. Just hate to add weight to a rocket and take up more room in the nose cone since it is HED. But, if it works, then all is fine. I'll know not to foam the fin can in the future. I didn't think that it would add enough weight to worry about. It's just between the fin roots and MMT. It's a 3" airframe with a 54mm hole.

Thank you everyone for the help!

It's a short, HED rocket with a big motor capability! These are the best kinds to hone your skills!

 

[user 30299]

Lol, I have been looking for one but my favorite vendor is out of them.

I have two sitting here right now waiting to go in my own rockets . . . .

 

[kramer714]

Fun on a K1440 - ROCstock 41 Punisher Drag Race (yeah mine was the first off the pad...)

 

[rfjustin]

I am going to add approx 3.5 oz of nose weight to it. This will give me 1 cal. of stability with a K550. Hopefully that will do the trick. If not, I can add or remove weight, flat washers. Just need to do a test flight. Just hate to add weight to a rocket and take up more room in the nose cone since it is HED. But, if it works, then all is fine. I'll know not to foam the fin can in the future. I didn't think that it would add enough weight to worry about. It's just between the fin roots and MMT. It's a 3" airframe with a 54mm hole.

Thank you everyone for the help!

I've got one in stock if you need it...

 

[user 30299]

Here's the status on my Punisher . . . .



And that's from January of 2020 when it arrived at the house. Very sad.

It was brought out into the daylight last month. And hopefully will see
some build activity in the Spring (yes, 2024). I have some nice Warp motors
that will go good with it.

 

[DHays]

Load up all of the recovery gear and a motor case (don't use a loaded motor). Measure the cg just by holding the rocket. Now tap the rocket against the bottom on a piece of wood, or something like that (now you know why not to use a loaded motor) , and recheck the CG, very likely it shifted down a bit when the 'laundry compresses' down. This gives you a better idea what the actual CG is at launch.

I have seen that where a rocket is loaded and the cg checked with the parachute burrito snug at the top of the bodytube, then with a quick jerk of the rocket you can actually feel the parachute sliding down. With a .7 stability it could make a difference.

YMMV

Good point. I will definitely check that.

 

[DHays]

Here's the status on my Punisher . . . .

View attachment 615472

And that's from January of 2020 when it arrived at the house. Very sad.

It's was brought out into the daylight last month. And hopefully will see
some build activity in the Spring (yes, 2024). I have some nice Warp motors
that will go good with it.

Oh nice! you even have a tail cone.

 

[DHays]

I've got one in stock if you need it...

Thank you! I really appreciate that. I will probably hold off for now until a get a good handle on this issue first.

 

[DHays]

It's a short, HED rocket with a big motor capability! These are the best kinds to hone your skills!

Yes! so far I have my work cut out for me. Lol!

 

[DHays]

As kramer714 points out, if you could share with us the CG location (less the motor), and the rocket's loaded
weight (less the motor), a few of us could double-check the stability - and the needed weight to improve the
Punisher's stability.

Ok sounds good. It may take a day or two but I will get that info.

 

[user 30299]

Oh nice! you even have a tail cone.

Yup, I asked Tim if a tail cone would matchup nicely with the kit - he said for sure.
So I had him put a a cone in with the order.

I think it makes the rocket look cool. Adds a little weight in the wrong place, but
it improves the aerodynamics (reduces base drag).

 

[DHays]

As kramer714 points out, if you could share with us the CG location (less the motor), and the rocket's loaded
weight (less the motor), a few of us could double-check the stability - and the needed weight to improve the
Punisher's stability.

Ok, the CG fully loaded less the motor and motor case is 27-5/8" from the tip of the nosecone.
The weight is 5 lbs-9.4oz, fully loaded less motor and case.
The length from the tip of the nose to the end of the motor retainer is 48-3/4"


What I did after the above measurements, I added 3.6 oz. of nose weight, (flat washers and a longer eye bolt.) Fully loaded just as above, the CG is located at 26-7/8" from the tip of the nose. Total weight came in at 5lbs 12.6oz. I don't know if this will be good enough to try? I'll wait to see what you guys think.

The drogue and harness is tamped down towards the MMT as in a launch. Just bumped down, not packed in. Lol

Thanks again for checking this for me!

 

[user 30299]

Ok, the CG fully loaded less the motor and motor case is 27-5/8" from the tip of the nosecone.
The weight is 5 lbs-9.4oz, fully loaded less motor and case.
The length from the tip of the nose to the end of the motor retainer is 48-3/4"


What I did after the above measurements, I added 3.6 oz. of nose weight, (flat washers and a longer eye bolt.) Fully loaded just as above, the CG is located at 26-7/8" from the tip of the nose. Total weight came in at 5lbs 12.6oz. I don't know if this will be good enough to try? I'll wait to see what you guys think.

The drogue and harness is tamped down towards the MMT as in a launch. Just bumped down, not packed in. Lol

Thanks again for checking this for me!

I used RockSim 9 to check this out. I already had the basic design in there. And RockSim 9 has always
given me simulations very close to actual flight performance.

Using your numbers, without the added nose weight, I get a stability margin of 0.55 for the J415, and 0.51
for the K550 motor. I had RockSim use the Barrowman equations. And when you watch the flight simulation
in the program, the stability margins get above 1.0 right around 2 seconds into the launch.

The simulations pretty much agree with what you experienced with the two big motors; initial instability followed
by a continued straight flight.

The H550 motor gives me a 1.45 stability margin.

When I used the new weight and CG, for the added nose weight, the J415 has a stability margin of 0.76, and
the K550 has a 0.70 margin. They both reach a 1.0 margin just a little before 1 second into the launch.

So "technically speaking" you would need to add a touch more weight to get yourself nearer to 0.90 with
the rocket sitting on the pad. But that 3.6 oz. addition made a dramatic difference in the stability margin.

Honestly I think the weight you've added, and knowing you'll hit a 1.0 stability in the 1st second, you
may not see a wiggle/wobble by the time the rocket leaves the rail.

I did check the K2050 motor. It has a 0.86 stability margin for the added nose weight simulation.
So you're good to go with that motor. The K550 and K2050 use the same AeroTech 1706 case,
but the K2050 propellant weighs 674g and the K550 propellant weighs 880g.

 

[DHays]

I used RockSim 9 to check this out. I already had the basic design in there. And RockSim 9 has always
given me simulations very close to actual flight performance.

Using your numbers, without the added nose weight, I get a stability margin of 0.55 for the J415, and 0.51
for the K550 motor. I had RockSim use the Barrowman equations. And when you watch the flight simulation
in the program, the stability margins get above 1.0 right around 2 seconds into the launch.

The simulations pretty much agree with what you experienced with the two big motors; initial instability followed
by a continued straight flight.

The H550 motor gives me a 1.45 stability margin.

When I used the new weight and CG, for the added nose weight, the J415 has a stability margin of 0.76, and
the K550 has a 0.70 margin. They both reach a 1.0 margin just a little before 1 second into the launch.

So "technically speaking" you would need to add a touch more weight to get yourself nearer to 0.90 with
the rocket sitting on the pad. But that 3.6 oz. addition made a dramatic difference in the stability margin.

Honestly I think the weight you've added, and knowing you'll hit a 1.0 stability in the 1st second, you
may not see a wiggle/wobble by the time the rocket leaves the rail.

I did check the K2050 motor. It has a 0.86 stability margin for the added nose weight simulation.
So you're good to go with that motor. The K550 and K2050 use the same AeroTech 1706 case,
but the K2050 propellant weighs 674g and the K550 propellant weighs 880g.

Excellent! You have provided me with some very helpful information. I might go up to 4 oz. and give that a try. And, it looks like I will need to keep an eye on the propellant weight as well on motor selections. I see a K2050 in my future!

Thank you so much again!

 

[user 30299]

Excellent! You have provided me with some very helpful information. I might go up to 4 oz. and give that a try. And, it looks like I will need to keep an eye on the propellant weight as well on motor selections. I see a K2050 in my future!

Thank you so much again!

Here's some extra info from the simulations.

I always start off with a fixed Drag Coefficient (Cd) of 0.60. I found that to be a good middle of the
road number when working with a new design or someone else's build. And I used an 8 ft. rail length.

• The H550 shows a max altitude of 1,529 ft., and a rail exit velocity of 106 ft./sec. In the ballpark for your actual launch of 1,400 ft.
• The J415 shows a max altitude of 6,705 ft., and a rail exit velocity of 77 ft./sec.
• The K550 shows a max altitude of 8,268 ft., and a rail exit velocity of 99 ft./sec.
• The K2050 shows a max altitude of 7,079 ft., and a rail exit velocity of 161 ft./sec. (don't blink when the LCO pushes the button)

Do you know the actual altitudes for your J415 and K550 launches?

 

[cwbullet]

• The K2050 shows a max altitude of 7,079 ft., and a rail exit velocity of 161 ft./sec. (don't blink when the LCO pushes the button)

And, you should hope those fins are attached well.

 

[kjhambrick]

I used RockSim 9 to check this out. I already had the basic design in there. And RockSim 9 has always
given me simulations very close to actual flight performance.

Using your numbers, without the added nose weight, I get a stability margin of 0.55 for the J415, and 0.51
for the K550 motor. I had RockSim use the Barrowman equations. And when you watch the flight simulation
in the program, the stability margins get above 1.0 right around 2 seconds into the launch.

The simulations pretty much agree with what you experienced with the two big motors; initial instability followed
by a continued straight flight.

The H550 motor gives me a 1.45 stability margin.

When I used the new weight and CG, for the added nose weight, the J415 has a stability margin of 0.76, and
the K550 has a 0.70 margin. They both reach a 1.0 margin just a little before 1 second into the launch.

So "technically speaking" you would need to add a touch more weight to get yourself nearer to 0.90 with
the rocket sitting on the pad. But that 3.6 oz. addition made a dramatic difference in the stability margin.

Honestly I think the weight you've added, and knowing you'll hit a 1.0 stability in the 1st second, you
may not see a wiggle/wobble by the time the rocket leaves the rail.

I did check the K2050 motor. It has a 0.86 stability margin for the added nose weight simulation.
So you're good to go with that motor. The K550 and K2050 use the same AeroTech 1706 case,
but the K2050 propellant weighs 674g and the K550 propellant weighs 880g.

@QFactor --

Very nice analysis !

It is a lot of fun to follow along in threads like these.

I always learn something

Do you mind posting your RocSim .RKT File ?

The .RKT file I downloaded from the Wildman Punisher3 Page has a few mass overrides, and the length is 49 inches instead of 48.75 inches.

I was able to force the dry mass of the Wildman.RKT model to 5 lb, 9.4 oz and the no motor CG moved forward to 27.2 inches by adjusting / removing some of the original mass components

And after those adjustments, and adding the 3.6 oz of nose weight at 5-inches past the tip of the nose, I ended up with the CG at 26.25 inches so I am close to your file now but I am not sure about the mass distributions.

I am also getting higher altitudes across the board but not too bad, I suppose ...

That is an awesome rocket !

Thanks for letting me play along, @DHays !

-- kjh

What I ended up with:

Sim Summaries:

# Title     | Wildman Punisher 3
# Command   | /home/konrad/prj/app/dev/blueraven/tst/get-or-sims.sh -SA -T Wildman Punisher 3 -D 3.1 in -L 49 in -o /home/tmp/Punisher_3-sum.txt /home/tmp/Punisher_3.ork
# Sorted by | Altitude
# RunDate   | Wed Nov 15 06:03:14 CST 2023
#
# Config       |      zMax |     vRail |      vMax |   GMax |      Mach |     tBurn |   tApogee |     tLand |     vLand | MotSize | Delay | SimName
  H550ST       |      1563 |     116.5 |     335.7 |  21.45 |      0.30 |       0.6 |       9.8 |      39.8 |      25.1 | 38x213  |  14.0 | H550
  J415W        |      8264 |      86.0 |     982.9 |  14.44 |      0.89 |       3.4 |      21.1 |      82.1 |      26.5 | 54x314  |  14.0 | J415
  K2050ST      |      8578 |     182.0 |    1202.8 |  59.24 |      1.08 |       0.8 |      20.5 |      80.5 |      27.3 | 54x383  |  none | K2050-STP
  K550W        |      9786 |      98.4 |    1134.6 |  19.92 |      1.02 |       3.4 |      22.3 |      89.8 |      26.9 | 54x410  |  18.0 | K550
#
# Rocket Name      = Punisher 3
#
# Diameter         = 3.1 in
# Length           = 49 in
# Dry Mass         = 2641 g
# CD               = 0.52
#
# Config From      = K550
# Site Latitude    = 30.617158375589348
# Site Longitude   = -97.49690197952224
# Site Altitude    = 643 ft
# Site Temperature = 60.0 F
# Site Pressure    = 998 mb
# Wind Speed       = 10 mph
# Speed of Sound   = 1116 ft/sec
#
# Rod Length       = 120 in
# Rod Angle        = 0.0 deg
#
# Command Line     = /home/konrad/prj/app/dev/blueraven/tst/get-or-sims.sh -SA -T Wildman Punisher 3 -D 3.1 in -L 49 in -o /home/tmp/Punisher_3-sum.txt /home/tmp/Punisher_3.ork

 

[ac2fv]

Here's my 3" Punisher waiting to hit the sky in April 2024.... can't wait!

 

[user 30299]

And, you should hope those fins are attached well.

Looking at the simulation, the K2050 motor would hit its max velocity (1186 ft./sec) under that first 1.0 second
of the launch. The K550 motor simulation showed a max velocity of 1085 ft./sec, also under that first 1.0 second .

If DHays has additional flight info from the K550 launch, then maybe we can see how accurate the sims are?

Since his Punisher survived the K550, it has a good chance of surviving the K2050.

But it maybe a good precaution to have people up and out of their seats on the Punisher's first K2050. Better safe than sorry.

 

[cwbullet]

Looking at the simulation, the K2050 motor would hit its max velocity (1186 ft./sec) under that first 1.0 second
of the launch. The K550 motor simulation showed a max velocity of 1085 ft./sec, also under that first 1.0 second .

If DHays has additional flight info from the K550 launch, then maybe we can see how accurate the sims are?

Since his Punisher survived the K550, it has a good chance of surviving the K2050.

But it maybe a good precaution to have people up and out of their seats on the Punisher's first K2050. Better safe than sorry.

I agree—definitely not a newby build. I have built several that will take a K2050, but my 5.5-inch Bertha did not. That is a lesson to always label your motors (if you assemble them at home) and that is a different story.