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  #11  
Old 10-13-2013, 08:03 AM
snaquin snaquin is offline
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Quote:
Originally Posted by JumpJet
Can you please post your Open Rocket File for this model. I did a RockSim on it and it showed it to be plenty stable even with a heavy G80 motor in it.

John Boren
Estes R&D


John,

Well it turns out it was a data entry problem on my end with the OpenRocket file. I copied the Ascender file as a basis of design for creating the new Majestic file and along with it copied a mass overide that didn't belong in the Majestic design file. The corrected file is posted below for you. I weighed my built model (mass with no motors) and I come in at exactly 8.6 oz. The package weight shows 9.6 oz so I'm a full ounce below that.

I measured the CG of my built model and it falls right at the center of the letter E where I have my decal placed. That puts the CG @ 21.9" so I entered override center of gravity: 21.9 in, and override mass: 8.6 oz

With the F15-6 motor loaded I get stability: 1.72 cal

RockSim does a better job of modeling the nose cone as you can use a conical length of 7.5" with an exposed base length of 3.5" where OpenRocket I had to just use an 11.0" ogive shape. That barely makes any change on the design performance.

I can't figure out the reason for the unstable flight because same as you I determined the model does indeed indicate the model has good stability.



.
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TRA# 677 L2
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🚀 In Paint & Detail: USR Banshee
🚀 In Build Queue: Estes Doorknob w/Vander-Burn Rocketry Upgrade Kit [Sport Decor], Semroc Centurion-F, Semroc Egg Crate
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  #12  
Old 10-13-2013, 08:28 AM
snaquin snaquin is offline
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Quote:
Originally Posted by frognbuff
Have you flown a Majestic yet? I'm wondering why E15-6 is recommended but E15-8 is not. The Majestic is very light, and I'm surprised the extra two seconds of delay make such a difference. Then again, I haven't flown an E15 or F15 yet.


Bearing in mind that OpenRocket is just an estimation and that I also have just the one flight on my Majestic with the F15 engine and not the E16, refer to the first image in my last post for a possible answer.

The 6 sec delay shows 8.38 ft/s velocity at deployment which is very good. With all the same conditions the 8 sec delays shows 40.1 ft/s velocity at deployment so according to this estimation, the extra two seconds of delay do make a difference.

.
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TRA# 677 L2
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🚀 In Construction: Der Blue Maxx/Minie-Magg 5.5” & Vander-Burn MDRM Clone w/Stickershock23 Custom Decals
🚀 In Paint & Detail: USR Banshee
🚀 In Build Queue: Estes Doorknob w/Vander-Burn Rocketry Upgrade Kit [Sport Decor], Semroc Centurion-F, Semroc Egg Crate
🚀 In Repair: SLS Lil’ Hustler, SLS Aero-Dart 1969 Trim
🚀 Stay Tuned For Fall 2021 Launch Dates
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  #13  
Old 10-13-2013, 10:44 AM
frognbuff frognbuff is offline
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Quote:
Originally Posted by snaquin
Bearing in mind that OpenRocket is just an estimation and that I also have just the one flight on my Majestic with the F15 engine and not the E16, refer to the first image in my last post for a possible answer.

The 6 sec delay shows 8.38 ft/s velocity at deployment which is very good. With all the same conditions the 8 sec delays shows 40.1 ft/s velocity at deployment so according to this estimation, the extra two seconds of delay do make a difference.

.

Cool - thanks!
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  #14  
Old 10-13-2013, 08:53 PM
snaquin snaquin is offline
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Out of the five F15 engines I burned yesterday only the F15-6 engine that was used for the Majestic fight had more nozzle erosion and more soot on the nozzle end, also leaving a small ring of soot around the end of the case. These two engines came from the same package.

The engine on the left was used on the Ascender flight. The engine on the right was used on the Majestic flight. This motor was also the only one that I used that had to be forced out from the front side with a rod. The other motors could be shaken out or pulled out easily from the engine mount tube.

Did not appear to have any thrust vectoring in the photos.

Not sure if any of this helps .... I'm just making a post flight observance.

.
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TRA# 677 L2
NAR# 85518 L2
SAM# 0052

🚀 In Construction: Der Blue Maxx/Minie-Magg 5.5” & Vander-Burn MDRM Clone w/Stickershock23 Custom Decals
🚀 In Paint & Detail: USR Banshee
🚀 In Build Queue: Estes Doorknob w/Vander-Burn Rocketry Upgrade Kit [Sport Decor], Semroc Centurion-F, Semroc Egg Crate
🚀 In Repair: SLS Lil’ Hustler, SLS Aero-Dart 1969 Trim
🚀 Stay Tuned For Fall 2021 Launch Dates
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  #15  
Old 10-14-2013, 12:48 AM
Initiator001 Initiator001 is offline
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Quote:
Originally Posted by snaquin
Also good to know about the EB-20. I figured that was the one you used from one of your other posts. I need to pick up a few from Semroc.



.


To prevent any backpressure issues with the EB-20 Semroc baffles I punch extra holes in the baffles.

I haven't notice any burning/soot on the parachutes.
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  #16  
Old 10-14-2013, 03:09 AM
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Royatl Royatl is offline
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Quote:
Originally Posted by snaquin
Out of the five F15 engines I burned yesterday only the F15-6 engine that was used for the Majestic fight had more nozzle erosion and more soot on the nozzle end, also leaving a small ring of soot around the end of the case. These two engines came from the same package.

Did not appear to have any thrust vectoring in the photos.

.



The soot on the nozzle end probably came from the rocket flipping around.

Is there any way you can get the camera to focus on the nozzles, not the label?

It may only take a brief, severe thrust vector to knock the thing to the point where the fins stall out and it slows to a speed that the fins can't recover. It sounds odd that the empty motor was tight in the rocket.
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  #17  
Old 10-14-2013, 09:38 AM
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JumpJet JumpJet is offline
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Default RockSim File

The Majestic I have here made from a kit weighs more then what's stated on the box. Attached is my RockSim file for it. I get quite different results that the Open Rocket file posted. I used the RockSim Calculation Method instead of the Barrowmen, since I was told it was more accurate.

I did not include launch lugs on this design but I can't see that making much difference. I choose materials for each component to represent as close as possible the actual weights of the parts.

With engine unloaded and loaded the CG is right where it is stated on the RockSim file. The Mass of my rocket is correct as well.

Can someone explain why we have such different results.

By the way the copy of Open Rocket I have on my machine would not open the Open Rocket file posted in this thread.


John Boren
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  #18  
Old 10-14-2013, 10:57 AM
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Shreadvector Shreadvector is offline
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Was there a motor block or thrust ring installed? Just curious if the motor could have moved forward under thrust and the result would be a "Krushnic Effect" with lower thrust - and possibly vectored if the aft motor retaining ring started to melt.

I have seen several of these rockets flown with the F15-6 motor and they all were extremely stable.

I have seen them flown off the 6 foot long steel rods that our club uses as well as individual pads using the Estes rod which is a bit shorter.

Quote:
Originally Posted by snaquin
I hope you have better luck with your first flight with your Estes Majestic than I did today. Yesterday, I also assembled mine with the recommended CA and 30 minute epoxy used sparingly following all the assembly instructions. I used the recommended first flight engine, F15-6 and the PSII wadding, starter and plug.

I flew in calm conditions with rod close to vertical. The smile in the picture was short lived. Shortly after it came off the rod it went unstable and cartwheeled through the air for a pretty good distance landing between my vehicle and the vehicle parked next to me and was damaged when it thumped on the ground and ejected it chute near the spectators standing nearby.

I'll be contacting Estes soon to request a different PSII kit. I'm really not comfortable repairing mine and flying it again.

Perhaps yours will fly better since you have the added weight up front with the Semroc baffle on yours. I ran it through OpenRocket last night and it didn't show stable without added nose weight but I ignored that thinking it was a data entry problem on my end and it should be stable since I assembled the Majestic per the instructions without any modifications.



.
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  #19  
Old 10-14-2013, 11:45 AM
Rex R Rex R is offline
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@jumpjet
looks like you should update your open rocket, they changed the design file format (to a zip based one) with the 13.05 release.
Rex
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  #20  
Old 10-14-2013, 12:28 PM
Initiator001 Initiator001 is offline
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Quote:
Originally Posted by Shreadvector
Was there a motor block or thrust ring installed? Just curious if the motor could have moved forward under thrust and the result would be a "Krushnic Effect" with lower thrust - and possibly vectored if the aft motor retaining ring started to melt.



The Estes PS II E2X kits include an orange spacer ring for use in the motor mount tube when using the E16/F15 motors. The kits are set up to handle the Estes (re-labeled AeroTech) G40 and G80 motors which have longer cases than the E16/F15 motors.
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