Modified Estes V2 Center of Gravity Question

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Skp

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I have finished an Estes V2 with the exception of the nose wght.
I have cut the fins to scale and added the pods.
The livery is from Operation Backfire.
The string attached to the rocket is the CG while it is fully loaded with parachute, chute release, JL alt3 and an Aerotech F35-8W 24/60 reload(the largest motor I imagine ever using)
I am aware that openrocket does a very poor job of figuring the CP of a boattail rocket.
Rocksim uses an average bt dia that gives a closer approximation of the CP, but according to the Apogee Newsletter that I read, it is still conservative.
I did the swing test and when started pointed forward it remained forward. When it was started tail first, it tried to turn nose forward, but was not able to make the turn.
I understand that the swing test is also conservative, and that a rocket may fail the test and still fly stable.
I have rail buttons for longer guidance at liftoff.
I believe that it will fly stable as is.

I will also load with a D12-5 and string test it, as well as with a E9-6.

I have a launch on Sunday and would appreciate community input regarding experience with the V2 CG point.
V2 COG.jpg
 

Pointy_end_up

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I worried over this myself. I went through a lot of different references and different ways to calculate it. Best I could come up with was between 35 - 37 cm from the nose for the CP. I ended up putting lead in the nose to get the CG at 25.6 cm from the nose with a D12. It flew perfectly straight in a cross wind. Don't know if I have the optimal CG/CP relationship but I do know it worked with this CG. Hope that helps.
 

Skp

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I worried over this myself. I went through a lot of different references and different ways to calculate it. Best I could come up with was between 35 - 37 cm from the nose for the CP. I ended up putting lead in the nose to get the CG at 25.6 cm from the nose with a D12. It flew perfectly straight in a cross wind. Don't know if I have the optimal CG/CP relationship but I do know it worked with this CG. Hope that helps.
That is helpful. Did you modify the fins to be more scale accurate, or were they stock?

I have done the swing test with a D12 and E9. When started pointing in the right direction they both were solid going forward. If turned sideways or backward it does not correct.

I put 34 grams of clay ON the nose cone and is easily passed the swing test, correcting to nose forward regardless of initial orientation. The CG was 33cm from the nose with a D12 installed, which is farther back than yours was, and only 1 cm ahead of your most conservative CP estimate.
 

Skp

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I remember getting stable flights if the C/G is a half-diameter in front of the leading edges of the fins.

Peter Alway
With the D12 loaded, I have the CG about .75 of a diameter ahead of the leading edge of the fins.
I am about 95% confident that this will fly fine on a D12 without any additional nose wght.
I will of course bring some clay with me, discuss it with the RSO and submit to his authority.

Thank you for your input and I will report back with it's maiden flight.
 

Skp

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I ran the CG of about .75 of a diameter above the fins past our Mindsim guy and he felt there would not be an issue, the RSO hardly gave it a second look. So out the rail it went on a Estes D12-5

[YOUTUBE]/k0FuHm6qKsQ[/YOUTUBE]
FlightGraph.png

The next step will be to work out weight I can add to it that will place the CG at about the same place for an Aerotech F35 and see what it does for the smaller motors.
 

Howie

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I had the same kit, with scale fins. I say had, as the second time I flew it on an F35-8, aliens snatched it out of the sky. It had 16 previous flights on motor ranging from a C11-3 up to the aforementioned F35 reload, and all were stable. I use Rocksim and here is a screen shot of that kit's fin form and CG / CP numbers:

IMG_9480.JPG

Mine weighed 172g empty - I think the weight I have stated here included an JL Altimeter 2 /3 included as I don't ever believe I flew mine without that. In case the CG / CP numbers aren't legible, they are 12.46" and 16.82" respectively.

I see you added the fairings for the tip fins, those look good. I'm finishing my 5.5 LOC V2 and considering adding those. If you made those lightly, they may have a positive effect on stability. Last week I posted a thread in the Rocketry Electronics and Software forum regarding the stability effects on those fairings. Here's the link:

https://www.rocketryforum.com/showthread.php?140409-Rocksim-Question-CP-for-pods-and-fins

Hope this helps!
 

Daddyisabar

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The Mindsim guy was too enthralled with the nice paint job and good looks of the rocket. If it looks that good it must be stable.
 

Howie

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Something I did with my V2 and you might want to consider is removable nose weights. That way the rocket performs well on small motors but has enough weight forward when needed for larger motors. I used one or two wooden pencils, trimmed short enough to fit inside the nose cone and inserted through the hole at the base. A couple strips of duct tape sealed that hole to keep them in.
 

Skp

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I had the same kit, with scale fins. I say had, as the second time I flew it on an F35-8, aliens snatched it out of the sky. It had 16 previous flights on motor ranging from a C11-3 up to the aforementioned F35 reload, and all were stable. I use Rocksim and here is a screen shot of that kit's fin form and CG / CP numbers:

View attachment 319757

Mine weighed 172g empty - I think the weight I have stated here included an JL Altimeter 2 /3 included as I don't ever believe I flew mine without that. In case the CG / CP numbers aren't legible, they are 12.46" and 16.82" respectively.

I see you added the fairings for the tip fins, those look good. I'm finishing my 5.5 LOC V2 and considering adding those. If you made those lightly, they may have a positive effect on stability. Last week I posted a thread in the Rocketry Electronics and Software forum regarding the stability effects on those fairings. Here's the link:

https://www.rocketryforum.com/showthread.php?140409-Rocksim-Question-CP-for-pods-and-fins

Hope this helps!
Thank you for the additional data to look at. The farthest back I have read that someone balances their V2 at is the boattail/bodytube line, but I would only be willing to try that after A LOT of successful flights with progressively less nose weight.
 

Skp

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Something I did with my V2 and you might want to consider is removable nose weights. That way the rocket performs well on small motors but has enough weight forward when needed for larger motors. I used one or two wooden pencils, trimmed short enough to fit inside the nose cone and inserted through the hole at the base. A couple strips of duct tape sealed that hole to keep them in.
That is something that I have thought about. I think I've been bitten by the V2 bug.
 

Skp

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The Mindsim guy was too enthralled with the nice paint job and good looks of the rocket. If it looks that good it must be stable.
Well it was a very risky flight, you saw the bleeding paint lines.:wink:
 

Skp

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Time to Bump the WAC? Electronic staging and deploy.:confused:

Skin over frame? There is real possibilities here.:)

Control vein motor mounts? When :flyingpig:

Scale launch vehicles with armored half track control car? Scale OCD would quickly make me look like :bang:
I will have to look at skin over frame.
 

Howie

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That is something that I have thought about. I think I've been bitten by the V2 bug.
There are other kits you should try if so. I've built the 5.5" Loc R2 kit, which is a stretched V2. It's flown several times and I'm finally getting it's final finish done. It will be V2 #31 flown from White Sands, NM. Here's the paint scheme:

IMG_9422.jpg
 

Skp

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There are other kits you should try if so. I've built the 5.5" Loc R2 kit, which is a stretched V2. It's flown several times and I'm finally getting it's final finish done. It will be V2 #31 flown from White Sands, NM. Here's the paint scheme:

View attachment 319945
I suspect that if I were to start to spend that much money on rockets, my wife would prefer I get back into buying more firearms.:D
 

Daddyisabar

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I will have to look at skin over frame.
We bumped the WAC on and A8 with the Booster on a G64. Still low enough to see everything well. Simple timer and all motor eject.

You could use the control veins as motor retention.

We did a "skin over frame look" with cut vinyl. Not scale but a good look. Need access to a really good vinyl cutter. Takes a lot of patience to install the wraps. But it looked like the real thing, not smooth at all, but kinda wrinkly. Make the access doors usable for your electronics. A real skin over frame high power job would be awesome. Can't recall it even being attempted. You would have to be the ultimate V2 maniac!


Scale support vehicles rule!

feuerleitp01.jpg
 

Skp

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We bumped the WAC on and A8 with the Booster on a G64. Still low enough to see everything well. Simple timer and all motor eject.

You could use the control veins as motor retention.

We did a "skin over frame look" with cut vinyl. Not scale but a good look. Need access to a really good vinyl cutter. Takes a lot of patience to install the wraps. But it looked like the real thing, not smooth at all, but kinda wrinkly. Make the access doors usable for your electronics. A real skin over frame high power job would be awesome. Can't recall it even being attempted. You would have to be the ultimate V2 maniac!


Scale support vehicles rule!

View attachment 319947
You are tempting me sir, you are tempting me. Maybe a joint project.
 

Daddyisabar

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You are tempting me sir, you are tempting me. Maybe a joint project.
It would be good to get a team together with mad skills.

The old one had a carbon fiber tail cone and centering rings. For fins it was finished and embossed Balsa over a fiberglass core. TTW with nice big epoxy/micro balloon fillets for a nice scale look. Even the WAC had laminated fins.
 
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