7.5" LOC DOORKNOB Level 2 Build Thread

[pathtouch]

I'm not judging.
View attachment 504218View attachment 504219
I'm just pointing out the obvious.

haha I guess I have a new name for it! I’ll have to get a creamsicle decal made for the backside.

 

[boomtube-mk2]

haha I guess I have a new name for it! I’ll have to get a creamsicle decal made for the backside.

Ages ago there was a brand of those called Fifty-Fifty Bars where the orange Sherbert and vanilla ice-cream were mixed in a swirly pattern.

 

[pathtouch]

We can rebuild!
We had a fun day on the lake and my buddy and myself passed the L2 exams. However when it came time to launch the wind was howling! The plan was to wait for a lull and touch off my rocket to a nice simple 700 foot flight on a J381 skidmark. Howvever one gust came up and actually created enough vacuum that my backup Eggtimer Quantum though it hit 107 feet of altitude.... and guess what my Launch Detect Altitude was.... 100 feet. OOOOOPS I'll be updating that to 200'.

Since these were backup up charges they were 3.5g of Triple 7 and that's a hot load for this rocket. Nosecone got pushed in and my cardboard couplers got pretty soaked in the water. Also might have taken out the onboard RunCam2.

That's rocketry!

Might have to wait for spring to get this cert flight done.





View attachment PadDeploy.mp4

 

[crossfire]

So you think a cross wind set off altimeter? How many vent holes did you have.

 

[jd2cylman]

Gary, he used 4 vent holes. FWIW, I always use three. Even on 4 finned rockets (which I prefer...)

 

[crossfire]

I was always told to use an uneven number of vent holes. Helps to not ge a cross wind into and out of altimeter. Use 1 or 3 vent holes.

 

[pathtouch]

I was always told to use an uneven number of vent holes. Helps to not ge a cross wind into and out of altimeter. Use 1 or 3 vent holes.

Interesting. The old recommendations from Adept, suggested never using two to eliminate cross flow and to use three or four holes. I suppose the odd number thing makes sense.

Either way we were pushing the limits on wind. The rocket was whistling while we were at the pad and I said out loud, “Think this could set off an altimeter?” Folks with much more experience told me they’ve never seen that happen haha. So we all learned about LDA settings on baro only altimeters without accelerometer

 

[crossfire]

Interesting. The old recommendations from Adept, suggested never using two to eliminate cross flow and to use three or four holes. I suppose the odd number thing makes sense.

Either way we were pushing the limits on wind. The rocket was whistling while we were at the pad and I said out loud, “Think this could set off an altimeter?” Folks with much more experience told me they’ve never seen that happen haha. So we all learned about LDA settings on baro only altimeters without accelerometer

Tommy always told me uneven number.

 

[thzero]

Interesting. The old recommendations from Adept, suggested never using two to eliminate cross flow and to use three or four holes. I suppose the odd number thing makes sense.

Wonder if staggered holes vertically would help? Even if there are an even number, it wouldn't be a direct axis through across the cylinder.

 

[pathtouch]

Tommy always told me uneven number.

Well if the man himself told you so then I’ll consider that in the next rocket! The paperwork that came with my Adept 22 (10 years ago) said three or four.

Wonder if staggered holes vertically would help? Even if there are an even number, it wouldn't be a direct axis through across the cylinder.

Then I think you run a similar risk during flight, of pressure differentials along the airframe. Adepts paperwork specifically says they should be on the same circumference line.

 

[thzero]

Interesting... one would think you'll run into pressure differentials along the airframe whether it be odd or even number of holes.

I've not seen it mentioned in other altimeters (missileworks, raven and eggtimer) that they had to be on the same circumference line that I recall, so thats interesting.

Well if the man himself told you so then I’ll consider that in the next rocket! The paperwork that came with my Adept 22 (10 years ago) said three or four.


Then I think you run a similar risk during flight, of pressure differentials along the airframe. Adepts paperwork specifically says they should be on the same circumference line.

 

[crossfire]

Well if the man himself told you so then I’ll consider that in the next rocket! The paperwork that came with my Adept 22 (10 years ago) said three or four.


Then I think you run a similar risk during flight, of pressure differentials along the airframe. Adepts paperwork specifically says they should be on the same circumference line.

Adept I use is ATLS25. Maybe 22 is different. I have always used 1 or 3 and 30 years of flying HP I never ad a altimeter fire on the pad.

 

[Buckeye]

Nosecone got pushed in and my cardboard couplers got pretty soaked in the water. Also might have taken out the onboard RunCam2.

All that damage from a short fall to the ice? Seems like you might have the same problems if the rocket landed normally under chute?

Sorry to hear about this mishap. I enjoyed your build threads and videos.

 

[DAllen]

View attachment 504391

ARE YOU SURE YOU'VE CLEARED OUT ALL THE FLAMMABLE UNDERGROWTH FROM THAT LAUNCH SITE????

 

[pathtouch]

All that damage from a short fall to the ice? Seems like you might have the same problems if the rocket landed normally under chute?

Sorry to hear about this mishap. I enjoyed your build threads and videos.

The nose cone dent is from the charge firing not the landing. This was the backup altimeter that fired. It had an extra half gram to guarantee things separated if the first charge hung up, mission accomplished! Dents already pulled out just needed a heat gun.
Once I dried out the run cam she came back to life. It’s not a forgiving landcape
That’s for sure.

ARE YOU SURE YOU'VE CLEARED OUT ALL THE FLAMMABLE UNDERGROWTH FROM THAT LAUNCH SITE????

Haha only for the first 75’ per NAR. I bought the motors from Dehate and he also wanted to make sure I didn’t set the lake on fire.

 

[pathtouch]

Video recap of the damage and of this fixes!
I know some of you guys are into the series.

 

[pathtouch]

Hey! Three months later things have thawed out in the north east and summer rocket season is here. I was able to drive up and meet the nice group of folks at Tripoli Cherryfield, and launch the Doorknob for a successful L2 certification.

CTI J381 Skidmark
Weight on the Pad: 18.5 lb
The Eggtimer Quantum said 768 feet
The Adept22 Beeped out 679 feet
Plenty stable even with moderate winds, no nose weight required.

I would recommend some more impulse if you're going dual deploy. By the time my drogue was settled the main charges were deploying. My nose cone actually swung around and back through the main chute shroud lines and foiled the main a bit. Between a half main, a drogue, and the robust fiber glassing the rocket was completely unscathed even though it touched down between 30-40 feet per second. Good enough!

Now looking for the next motor. I'm thinking the biggest 54mm Aerotech I can get to try out some my new hardware I'd love to hear peoples favorites.

 

[TheTank]

Hey! Three months later things have thawed out in the north east and summer rocket season is here. I was able to drive up and meet the nice group of folks at Tripoli Cherryfield, and launch the Doorknob for a successful L2 certification.

CTI J381 Skidmark
Weight on the Pad: 18.5 lb
The Eggtimer Quantum said 768 feet
The Adept22 Beeped out 679 feet
Plenty stable even with moderate winds, no nose weight required.

I would recommend some more impulse if you're going dual deploy. By the time my drogue was settled the main charges were deploying. My nose cone actually swung around and back through the main chute shroud lines and foiled the main a bit. Between a half main, a drogue, and the robust fiber glassing the rocket was completely unscathed even though it touched down between 30-40 feet per second. Good enough!

Now looking for the next motor. I'm thinking the biggest 54mm Aerotech I can get to try out some my new hardware I'd love to hear peoples favorites.

Which Hardware?

 

[pathtouch]

Which Hardware?

54mm - 2800 or 2560.
I also have a 1280 case and the adapters for everything 426-2800 but might as well go big!

 

[TheTank]

54mm - 2800 or 2560.
I also have a 1280 case and the adapters for everything 426-2800 but might as well go big!

In that case to go full send..L1090W in the 2800 case… or K700W in the 2560 or K1275R also in the 2560 would be my choice for a rocket that size/weight.

 

[Tim51]

Congratulations - welcome to L2!

 

[pathtouch]

Finally got around to modding my nose cone with a tracker sled. I cut the bottom off and installed a 1/4” bulkhead with some t-nuts to accept a 29mm payload. The bulkhead actually sits on the nose cone shoulder inside and then I epoxied it in. Also added a 1/4” ubolt for the recovery attachment point. As a bonus I gained 6” of space for packing the main chute. Wish I did this originally! Can’t wait to try the Featherweight gps tracker. I have a K1050 lined up for the next launch

 

[DMehalko]

54mm - 2800 or 2560.
I also have a 1280 case and the adapters for everything 426-2800 but might as well go big!

the L1090 is a great 54mm motor! I wish they had more L loads for the 2800 case….

 

[Hobie1dog]

Thanks for the video congratulations

 

[JohnCoker]

Has anyone heard any other source of the recommendation of "not two" or "an odd number" of vent holes? I also heard it from Adept back in the day, and followed it over the years. However, I've never heard a convincing reason nor heard it from other manufacturers, so it could be just a quirk of the Adept units.

Anyone have an independent source for this rule of thumb?

 

[JackC]

Has anyone heard any other source of the recommendation of "not two" or "an odd number" of vent holes? I also heard it from Adept back in the day, and followed it over the years. However, I've never heard a convincing reason nor heard it from other manufacturers, so it could be just a quirk of the Adept units.

Anyone have an independent source for this rule of thumb?

Yes, try Vern Knowles website. He has an article about that.

 

[Tim51]

Has anyone heard any other source of the recommendation of "not two" or "an odd number" of vent holes? I also heard it from Adept back in the day, and followed it over the years. However, I've never heard a convincing reason nor heard it from other manufacturers, so it could be just a quirk of the Adept units.

Anyone have an independent source for this rule of thumb?

This is something I've wondered about. Canepa (2004) implies one hole might be vulnerable to the possibility of wind gust, and two should be avoided:

"Is a single port better than multiple ports? Probably not, at least according to those who maintain that multiple ports reduce the likelihood that an unusual wind gust through a single hole might cause the altimeter to misfire. Although this is always possible, most rocket altimeter bays should work fine with a single port. But if more than one port is used, always use at least three, and space the ports equally around the diameter of the airframe, on the same plane"
(Canepa, MHPR2, p.139)

However, searches for an original source on this seem to be circular - a 2009 thread on Australian Rocketry points out that the above is basically the same advice to that given by Adept, Perfectflite and Missileworks:

https://forum.ausrocketry.com/viewtopic.php?t=1415
Fwiw I've always used four holes, but, allowing for the placement of screw switch(es) on the vent band, the ports are on the same plane but not directly opposite each other.

 

[Steve Shannon]

Beautiful job. I don’t know how I missed this, but you’ve done a great job!

 

[JohnCoker]

Yes, try Vern Knowles website. He has an article about that.

I found this article: https://www.vernk.com/AltimeterPortSizing.htm
He has charts for the size when using 3 or 4 holes, but I didn't see any discussion about the number of holes.

 

[pathtouch]

I think it’s important we all remember had I not messed with the LDA setting and left it at 200 feet it wouldn’t have gone off on the pad.
Sure at the limit, 20mph wind gusts on this particular rocket tricked the altimeter into thinking it was 107 feet AGL, it’s a non issue for properly configured altimeters. I don’t think I’ll shy away from four holes anytime soon on four fin rockets.