# Certing Level 2 tomorrow with a CTI K675 Skidmark!! WOOOOOOOOO!!!!

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#### Mach_Seven

##### Well-Known Member
From your earlier photo, the shroud was attached to the ebay. Do you have a photo of it on the pad? It looks like a complicated rocket and admire your bravery and perseverance.
It’s a little hard to see but it’s there. These are all the pad pics.

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#### Buckeye

##### Well-Known Member
Notice how it starts out unstable? The greater the length to diameter ratio, the more the CP moves with non-zero angle of attack. Also, I don't see the camera shroud or even a stand in and that couldn't help the CP at all.
You mean this?

s

OpenRocket does this a lot, especially with large L/D rockets. I used to fret over this, and add nose weight, which turned out to be uneccsessary. OR is overly pessimistic for CP, Rocksim may be a bit optimistic, and RasAero II falls in between.

#### dr wogz

##### Fly caster
Mach, I am sorry for your loss. But I do thank you for the education you, I, and obviously a few others are receiving!

I also thank you all for your comments & inputs on this. This is a good / educational thread, despite the cause.. And that was my (uneducated) guess: the camera shroud causing an unbalance / off-center shock wave..

Mach - think 6-million dollar man: You can rebuild him, you can save him, you can fly him another day.,.

#### wsume99

##### Well-Known Member
Well, I did a build thread in the largest HPR forum in the world and openly invited input and feedback. I sent the OR file to the prefect along with build photos and the intended motor sims two weeks before the launch for him to review. I discussed at length with the manufacturer what kind of loads this design might be able to handle. The rocket was thoroughly inspected by the prefect before launch. Green lights across the board. And I kinda know what a thrust curve is. I hope the implication isn't that I just slapped some components together and slammed in the biggest motor that will fit.

It sounds like you did your homework beforehand. One thing I'd point out is that the OEM may not have experience with your specific configuration. You lengthened the rocket and added the camera.

It looks to me that the primary failure was the airframe failure. Where the airframe buckled appears to be near the center of the longest unsupported span which is exactly where the buckling load would be the highest (as was stated earlier). Lengthening the airframe only amplifies it's susceptibility to buckling. The placement of the camera is also not ideal. You are introducing an unbalanced aerodynamic load far from the center of the longest unsupported span. This only makes buckling more likely because you are now adding a bending moment to the airframe. There is also evidence that the failure occurred near max Q. This is the exact moment where the maximum buckling load and bending moment would occur. I would bet $50 that if you mounted the camera much lower on the airframe you would have had a successful flight. The failure was caused by the confluence of buckling due to a long unsupported column and the bending load generated by the placement of the camera shroud. Moving the camera shroud lower eliminates this interaction. #### boomtube-mk2 ##### Well-Known Member 0 to 855 in 3.3 seconds. Suck on that, Lamborghini!!! That's even better than an Aprilia RSV4 Factory can do. #### Mach_Seven ##### Well-Known Member Great thread. I'll add my 2 cents.... It sounds like you did your homework beforehand. One thing I'd point out is that the OEM may not have experience with your specific configuration. You lengthened the rocket and added the camera. It looks to me that the primary failure was the airframe failure. Where the airframe buckled appears to be near the center of the longest unsupported span which is exactly where the buckling load would be the highest (as was stated earlier). Lengthening the airframe only amplifies it's susceptibility to buckling. The placement of the camera is also not ideal. You are introducing an unbalanced aerodynamic load far from the center of the longest unsupported span. This only makes buckling more likely because you are now adding a bending moment to the airframe. There is also evidence that the failure occurred near max Q. This is the exact moment where the maximum buckling load and bending moment would occur. I would bet$50 that if you mounted the camera much lower on the airframe you would have had a successful flight. The failure was caused by the confluence of buckling due to a long unsupported column and the bending load generated by the placement of the camera shroud. Moving the camera shroud lower eliminates this interaction.
$50 bet DECLINED. Your theory, combined with all the other input in this thread, leads me to this conclusion. Having lost two rockets in my last two flights, how do i go on? At least it wasn’t a total loss like the last one. But another$60 tailcone retainer gone, another $130 JLCR gone, another$130 motor case gone (I have yet to bring one home), not to mention all the typical costs and the careful and time-consuming construction. I’m still in “F*** this” mode.

#### Steve Shannon

##### Well-Known Member
$50 bet DECLINED. Your theory, combined with all the other input in this thread, leads me to this conclusion. Having lost two rockets in my last two flights, how do i go on? At least it wasn’t a total loss like the last one. But another$60 tailcone retainer gone, another $130 JLCR gone, another$130 motor case gone (I have yet to bring one home), not to mention all the typical costs and the careful and time-consuming construction. I’m still in “F*** this” mode.
I hope you can get over your hesitancy. I certainly understand; it can happen to anyone. What I would suggest is to maybe back off from trying to push your personal envelope and fly slightly lower thrust motors until you get more comfortable. Work on consistent recoveries and uneventful flights until you get your confidence back. I certainly hope you don't give up the hobby.

#### FMarvinS

##### Well-Known Member
Mach_7 your build was very well done and I admire your intrepid approach. I also started with cardboard but soon turned to FG. You may want to consider your next build to be FG, it takes as long as cardboard rockets to build, obviously is stronger, and enables the utilization of new techniques and approaches. Although the initial costs are higher, the rocket's longevity would end up being cost effective. If you build DD, then the JLCR is not needed and future cameras can be placed internally (either lens view via port or lens only shroud outside of booster tube). I hope to see more of your future builds on the forum.

Regards,
Fred

#### Ronz Rocketz

##### NAR# 109557
It's part of the hobby...

#### tsmith1315

##### Well-Known Member
how do i go on?

If you really want to fly rockets, build something for next to nothing. Use anything you can, leftover parts, try not to purchase anything. It doesn't have to be an L2 bird. Do your own design, go basic blue jeans and T-shirt style- think fishing buddy instead of prom date. Then make it fly.
You'll feel better and you just averaged out the costs. Then improve it and fly it again.

#### 3stoogesrocketry

##### Well-Known Member
$50 bet DECLINED. Your theory, combined with all the other input in this thread, leads me to this conclusion. Having lost two rockets in my last two flights, how do i go on? At least it wasn’t a total loss like the last one. But another$60 tailcone retainer gone, another $130 JLCR gone, another$130 motor case gone (I have yet to bring one home), not to mention all the typical costs and the careful and time-consuming construction. I’m still in “F*** this” mode.

Wait till you start spending 300 per reload ....

#### Mach_Seven

##### Well-Known Member
Wait till you start spending 300 per reload ....
I would have no problem with that. A nice flight every month or two capturing some good onboard video and photos. I just can’t seem to keep a rocket long enough to enjoy it.

#### Mach_Seven

##### Well-Known Member
I hope you can get over your hesitancy. I certainly understand; it can happen to anyone. What I would suggest is to maybe back off from trying to push your personal envelope and fly slightly lower thrust motors until you get more comfortable. Work on consistent recoveries and uneventful flights until you get your confidence back. I certainly hope you don't give up the hobby.
Are you saying my current plan to purchase a MAC Performance Firestick XL and attemp a Cert 2 with an Aerotech L1000 DMS might be misguided? Go on...

#### Mach_Seven

##### Well-Known Member
Mach_7 your build was very well done and I admire your intrepid approach. I also started with cardboard but soon turned to FG. You may want to consider your next build to be FG, it takes as long as cardboard rockets to build, obviously is stronger, and enables the utilization of new techniques and approaches. Although the initial costs are higher, the rocket's longevity would end up being cost effective. If you build DD, then the JLCR is not needed and future cameras can be placed internally (either lens view via port or lens only shroud outside of booster tube). I hope to see more of your future builds on the forum.

Regards,
Fred
What do you think of the canvas phenolic Mac Performance kits use? Similar in strength to fiberglass or am I asking for trouble?

#### Steve Shannon

##### Well-Known Member
Are you saying my current plan to purchase a MAC Performance Firestick XL and attemp a Cert 2 with an Aerotech L1000 DMS might be misguided? Go on...
You know the definition of insanity, right?

• Seriously, you expressed frustration at your lack of success and your loss of valuable property. It's possible to certify while minimizing the risk of either and UhClem suggested it.
• Or you can continue to attempt flights that are at the far edge of your skill level and risk additional losses.
• Or you can work on perfecting your skills incrementally until you are ready to do the cert flight and the cert flight is just another flight for you, regardless of how extreme it might seem to others. You still will have things that surprise you, but you'll probably recover enough of the pieces to learn what you did wrong and avoid it the next time.

#### dvdsnyd

##### Well-Known Member
What do you think of the canvas phenolic Mac Performance kits use? Similar in strength to fiberglass or am I asking for trouble?
Says on the Mac website that it will fly on L motors. Your best bet here would be to contact Mike directly and ask him if that particular rocket has flown on an L1000.

#### Mach_Seven

##### Well-Known Member
Says on the Mac website that it will fly on L motors. Your best bet here would be to contact Mike directly and ask him if that particular rocket has flown on an L1000.
I've got an email to Mike with a few questions about it. The LOC website said the 3" 54mm Iris could handle full K's out of the box - but apparently the airframe extension and camera shroud modifications - even with the double-walled reinforcement - was too much to bear on that K675. Mike said he'd lengthen the booster for me so it's one piece with no extension (see my post later as to why this is needed). For full K's and 54mm L's, should I double wall? Glass? Both? Neither?

And I was kidding about the L1000 cert flight. That's borderline reckless.

#### dvdsnyd

##### Well-Known Member
You shouldn't need to glass or reinforce MAC's phenolic for where you are going with that kit, but don't take mine, get it from Mike, which it sounds like you are.

#### FredA

##### Well-Known Member
If you have no problems with a $300 reload, buy yourself a$300 FG rocket to fly it in and quick messing with inferior materials.

#### Mach_Seven

##### Well-Known Member
If you have no problems with a $300 reload, buy yourself a$300 FG rocket to fly it in and quick messing with inferior materials.
No s*&%t.

Post #28 by me: "My conclusion is inadequate material strength. Fully loaded for flight without the motor this thing only weighed 6 pounds. Even with the fiberglass tip to tip and the double wall etc. Open rockets at 19 G’s, which seemed reasonable. But this thing was leaving town in a hurry. Might have been more. Shredded below the Av bay and payload section coupler. That was still connected to the air frame with the shear pins."

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#### COrocket

##### Well-Known Member
No s*&%t.

Post #28 by me: "My conclusion is inadequate material strength. Fully loaded for flight without the motor this thing only weighed 6 pounds. Even with the fiberglass tip to tip and the double wall etc. Open rockets at 19 G’s, which seemed reasonable. But this thing was leaving town in a hurry. Might have been more. Shredded below the Av bay and payload section coupler. That was still connected to the air frame with the shear pins."
If you are looking for consistency and longevity in a rocket, FredA has sage advice to transition to filament wound fiberglass airframes. Fly any rocket enough times and Murphy’s Law will eventually catch up to you. A parachute might not unfurl completely, a recovery charge might not go off, hard landing, land in an irrigation ditch etc…and FWFG rockets are much more damage resistant in these scenarios.

I once had a flight to around 4000 ft using motor eject separation at apogee and a tethered main. The motor delay didn’t burn completely to separate the rocket and the rocket came in ballistic. Despite augering a hole about two feet deep in the sod farm, the booster, motor case, retainer, shock cord, chute all lived to fly again. All I had to do is replace the shattered nose cone and cut 1/2” of frayed fiberglass off the top booster tube and the rocket flew another dozen times before drifting away and getting lost. If I had a tracker like I use now it would still be flying today. So despite costing a bit more to build initially, I was able to get flying again without buying an entire new kit.

#### Rocketjunkie

I just posted the YouTube link here in the thread. The on board didn’t record for some reason. I 100% confirmed the camera was recording before we launch. No files recorded though.
Probably lost connection before the camera finished recording the video. The video was NOT recoverable, even with paid versions of card recovery software. That part of the memory card was also permanently lost (about 8 GB). I had it happened when I shredded the Deuce98. This rocket has glassed plywood fins.
Wow, I know you said it took a hard right but I was not expecting a 90 degree turn. Hurts to see it.
Probably lost a fin. That's why it took the 90 deg turn. Seen it happen many times and with a cardboard rocket, the damage to the rest of the rocket occurs from aerodynamic forces. I've been flying cardboard rockets for over 30 years and still do. You can use a motor 1/2 the size as a fiberglass rocket the same size. With the introduction of dual deploy in 1995, I was able to double the motor size (and altitude) for the same amount of walking

#### Mach_Seven

##### Well-Known Member
Probably lost connection before the camera finished recording the video. I had it happened when I shredded the Deuce98. This rocket has glassed plywood fins.
Probably lost a fin. That's why it took the 90 deg turn. Seen it happen many times and with a cardboard rocket, the damage to the rest of the rocket occurs from aerodynamic forces. I've been flying cardboard rockets for over 30 years and still do. You can use a motor 1/2 the size as a fiberglass rocket the same size. With the introduction of dual deploy in 1995, I was able to double the motor size (and altitude) for the same amount of walking
Unlikely for the reasons discussed at length in this thread. That fin can was glassed to the end of the motor mount, well forward of the fins.

#### FMarvinS

##### Well-Known Member
Hi Mach_7- I have no personal experience with Mike's products but he and his kits have good reputations. I agree with FredA and I suggest that you consider for example Wildman kits. Quite a few 2.6 inch and 3 inch diameter kits have 54mm motor mounts which accept K and L motors. These kits run about $109 to$199. Additional expenses would accrue due to acquisition of kevlar cords, parachutes, altimeters etc; however, similar expenses occur with cardboard kits. The range in build difficulty is from easy to moderately more involved. Furthermore, I and probably many others have experienced faulty landings and the strength and resiliency of FG is significantly better than card board and often these rockets can be rebuilt or fixed.
As Steve recommended these kits enable flights from J through L motors and are platforms that enable incrementally increased difficulty with experience.
Good Luck!

Fred, L2
ICBM, S.C.
KG4YGP

#### FredA

##### Well-Known Member
Post #28 by me: "My conclusion is inadequate material strength. Fully loaded for flight without the motor this thing only weighed 6 pounds.
Weight alone is not that much on an indicator - I fly 5-pound rockets on L-1200's.

#### Ronz Rocketz

##### NAR# 109557
That's the problem with long threads. Not everyone reads through it all so you can expect redundancy.

The cover article in Sport Rocketry had an interesting expose about a multiple camera rocket and the problems associated with it.

#### Mach_Seven

##### Well-Known Member
Weight alone is not that much on an indicator - I fly 5-pound rockets on L-1200's.
Right. Of course. It was more of an unsettling feeling at the lack of bulk and heft on this big thing in my shop. “Why so light? Oh yeah. Because it’s made of cardboard.” Then my bowels would lurch a little bit.

#### Mach_Seven

##### Well-Known Member
That's the problem with long threads. Not everyone reads through it all so you can expect redundancy.

The cover article in Sport Rocketry had an interesting expose about a multiple camera rocket and the problems associated with it.

Nice find! Thanks! Camera is mandatory for me.

#### Mach_Seven

##### Well-Known Member
You shouldn't need to glass or reinforce MAC's phenolic for where you are going with that kit, but don't take mine, get it from Mike, which it sounds like you are.
He told me the same thing. I had a nice conversation with him. I learned a lot about canvas phenolic. Lighter than FG but 5x stronger than carboard.