Apogee Kronos kit some things to be aware of...

[rharshberger]

So this weekend we had about twenty or so college students desiring to do their L1 certifications, they all had the new Apogee Kronos kit. The kit comes with about 6 feet of what looks to be 500-800lb kevlar (between nose and upper edge of airframe and a fairly thin plastic nose cone.

First things first the kit is a very nice looking kit made with mostly quality parts and the students did a fantastic job of assembling them for the most part, the problems arose in part due to the weak mounting method for the nose cone (the plastic loop sheared off on a number of nose cones (at least 4 iirc) due to two things IMO one was the short shock cord and the second was the students using then entire vial of BP included with the AT motors (all H115DM, H148R, and H195T). After we had 3 nose cone separations in the same 4 rocket rack the RSO (myself) put a hold on any further flights by the rockets until the cause was determined, after reviewing the parts failures it was determined to drill the nose cone base and feed the shock cord through the holes to get a bit more "meat" for the mounting. No one on the flying or spectating was in danger at anytime due to our required launch rod angles which are pre-set by the club before the flying day begins.

After the review we conducted two more flights which still broke out the nose cone bases, further discussions with the students and review of the rockets it was decided to lengthen the shock cords and reduce the powder charge by about 1/3, which seemed to for the most part solve the problem (only 1 separation in the next 4 flights).

My recommendations to any one building this kit it LENGTHEN the shock cord (5x rocket length is my preferred length) and either put a bulkhead in the nosecone (Coker style) or an eyebolt with two fender washers of at least 1" diameter.

IMO part of the blame for the failures was inexperience of the fliers, and some due to the lightweight design of the nose cone.

Please understand I am not bashing the kit (though I do like kit bashing), these are just things to be aware of for the prospective builder.

 

[OzHybrid]

Kevlar cords stop hard when they get to full length. I refuse to call them shock cords as they don't absorb any shock.....unless you incorporate some other shock removal technique. 6ft is short. I use bundles of slip knots on Kevlar. You don't need to remember any tape or rubber bands.....But at 6ft it's not even long enough to add that shock absorption.
At 6ft you're asking for a zipper too. A kit manufacturer should have known all that.
How did the manufacturer test it? Looks OK, she'll be right?

 

[KenECoyote]

Thanks for the heads up Frank!

I agree with @OzHybrid , 6' is too short, especially with "shock" cord that isn't elastic. I would lengthen and/or also apply masking tape on cord loops to help absorb some of the shock. Of course maybe the nose cone could also use a modification or redesign.

 

[Art Upton]

So this weekend we had about twenty or so college students desiring to do their L1 certifications, they all had the new Apogee Kronos kit. The kit comes with about 6 feet of what looks to be 500-800lb kevlar (between nose and upper edge of airframe and a fairly thin plastic nose cone.

Is this an Apogee made cone? Or someone else's design.

 

[rharshberger]

Is this an Apogee made cone? Or someone else's design.

Its a translucent white polystyrene afaik its not one I have seen from, Loc, Madcow, GLR etc, which are fairly thick and solid white, so I am assuming based on experience that its a Apogee specific nose cone.

 

[krislhull]

Is this an Apogee made cone? Or someone else's design.

Its a Apogee cone. per the description page for the Kronos, its one of the blow molded nosecones made for Apogee.

I was present at the launch on Saturday, and I cannot remember seeing so many failed cert flights for the same issue before. And I do agree with Rich's evaluation that the root causes of the failures was a combination of a weakly designed attachment point, combined with an insufficient length of recovery harness, and overall lack of experience in the fliers. I do find it kind of hard to truly fault the last part, though, as failures like this are how you learn. It is how I learned when I was first getting started many years ago. I do think that Apogee should supply a longer length of kevlar for the harness, and a better quality nosecone. If I were to build one of these kits, I would probably swap out the nosecone for a comparable LOC one, assuming it would be compatible with the airframe. But that is just me.

 

[Pem Tech]

Thanks for the heads up Frank!

I agree with @OzHybrid , 6' is too short, especially with "shock" cord that isn't elastic. I would lengthen and/or also apply masking tape on cord loops to help absorb some of the shock. Of course maybe the nose cone could also use a modification or redesign.

Definitely use more shock cord, I use at least 10 feet if not more. Never had a zipper or damaged tube edge with 9'16th tubular nylon.

 

[Art Upton]

Its a Apogee cone. per the description page for the Kronos, its one of the blow molded nosecones made for Apogee.

I was present at the launch on Saturday, and I cannot remember seeing so many failed cert flights for the same issue before. And I do agree with Rich's evaluation that the root causes of the failures was a combination of a weakly designed attachment point, combined with an insufficient length of recovery harness, and overall lack of experience in the fliers. I do find it kind of hard to truly fault the last part, though, as failures like this are how you learn. It is how I learned when I was first getting started many years ago. I do think that Apogee should supply a longer length of kevlar for the harness, and a better quality nosecone. If I were to build one of these kits, I would probably swap out the nosecone for a comparable LOC one, assuming it would be compatible with the airframe. But that is just me.

Wow, this is the PNC-74a. It is sold as being a superior cone with a better attachment for the shock cord instead of Estes nose cones . Defiantly the 'recovery harness' needs to be about 3 times the length, 18-24 feet.


https://www.apogeerockets.com/Build...-Nose-Cones/PNC-74A-For-3-0in-Thin-Wall-Tubes

 

[Rocket-Fan]

Their kit description says ...

"Extending the theme of ruggedness and reliability, the Kronos comes with 10 feet of 300# Kevlar shock cord".

Length of rocket is 51" so looks like 13-17ft of shock cord would be more appropriate.

Edit: link to kit

 

[rharshberger]

Wow, this is the PNC-74a. It is sold as being a superior cone with a better attachment for the shock cord instead of Estes nose cones . Defiantly the 'recovery harness' needs to be about 3 times the length, 18 feet.


https://www.apogeerockets.com/Build...-Nose-Cones/PNC-74A-For-3-0in-Thin-Wall-Tubes
View attachment 675692
View attachment 675685

Same cone sold by BMS and formerly Mercury Engineering from the description. Makes sense it did look familiar....the white red and black ocket in this picture uses the same cone (modified of course).

 

[martinjaymckee]

Hey, Kronos designer here. The PNC-74A used on the Kronos is not the same as the BMS nosecone - though that was our weight reference. It's an in-house Apogee design. We have done dozens of flights with this nosecone from moderate F to H, and never seen the shearing issue ourselves. I know of only one other time it happened. I have been trying to keep track after that one report however.

I always fly with the kevlar Z-folded and taped, so the loads the nose cone sees are reduced. We have begun adding that procedure to some of our higher power kit instructions. We'll certainly keep an eye on things and consider respecifying the Kevlar in the Kronos, as it has proven much more popular in the L1 range than we had expected. It could certainly stand a beefier recovery system for maximum reliability on H power.

 

[Glasspack]

I emailed Apogee Rockets to let them know about the short commings with the Kronos Kit....
(Or at least areas for improvement) Tim from Apogee will be looking into fixing this issue......

Here was the reply.....
_____________________________





Hello Paul,

Thank you for letting us know, we were not aware of this issue. I will send Tim the link as well.

Brendan Campbell
Customer Service

Apogee Components
4960 Northpark Dr.
Colorado Springs, CO 80918

Ph: 719-535-9335

 

[spullen]

Hello,

I work for Apogee Components and just wanted to let everyone know we are updating the kits later this week and re-specing it with a longer and more sturdy kevlar shock cord. This should help with recovery another wonderful thing is put a chain of crochet knots in the kevlar. Then as it ejects it pulls the knots out which absorbs shock.

 

[KenECoyote]

Hey, Kronos designer here. The PNC-74A used on the Kronos is not the same as the BMS nosecone - though that was our weight reference. It's an in-house Apogee design. We have done dozens of flights with this nosecone from moderate F to H, and never seen the shearing issue ourselves. I know of only one other time it happened. I have been trying to keep track after that one report however.

I always fly with the kevlar Z-folded and taped, so the loads the nose cone sees are reduced. We have begun adding that procedure to some of our higher power kit instructions. We'll certainly keep an eye on things and consider respecifying the Kevlar in the Kronos, as it has proven much more popular in the L1 range than we had expected. It could certainly stand a beefier recovery system for maximum reliability on H power.

I emailed Apogee Rockets to let them know about the short commings with the Kronos Kit....
(Or at least areas for improvement) Tim from Apogee will be looking into fixing this issue......

Here was the reply.....
_____________________________





Hello Paul,

Thank you for letting us know, we were not aware of this issue. I will send Tim the link as well.

Brendan Campbell
Customer Service

Apogee Components
4960 Northpark Dr.
Colorado Springs, CO 80918

Ph: 719-535-9335

Hello,

I work for Apogee Components and just wanted to let everyone know we are updating the kits later this week and re-specing it with a longer and more sturdy kevlar shock cord. This should help with recovery another wonderful thing is put a chain of crochet knots in the kevlar. Then as it ejects it pulls the knots out which absorbs shock.

I have a degree in Marketing Management and I applaud Apogee and those involved with this kit for their AMAZING responsiveness. Heck, this was only posted here today!

 

[rharshberger]

I have a degree in Marketing Management and I applaud Apogee and those involved with this kit for their AMAZING responsiveness. Heck, this was only posted here today!

I concur well done Apogee!

 

[martinjaymckee]

Just FYI, we are updating the Kronos kit with 16' of 750# Kevlar (up from 10' of 300#) and already-built kits will have inserts added to the instructions to add further suggestions to increase flight success. Once we have worked through the stack of the current instructions, we will - of course - be folding the modified instructions into the booklet.

Please do reach out and let us know about any issues you may have with our products (especially in cases like this when there seems to be a pattern). It's our goal to help people to be successful.

In this case, I was thinking about the kit as a very large MPR kit, rather than the small HPR kit that the community has taken it as. That's on me for misreading the market. But, we're always glad to find ways to improve.

Cheers!

 

[OzHybrid]

Just FYI, we are updating the Kronos kit with 16' of 750# Kevlar (up from 10' of 300#) and already-built kits will have inserts added to the instructions to add further suggestions to increase flight success. Once we have worked through the stack of the current instructions, we will - of course - be folding the modified instructions into the booklet.

Please do reach out and let us know about any issues you may have with our products (especially in cases like this when there seems to be a pattern). It's our goal to help people to be successful.

In this case, I was thinking about the kit as a very large MPR kit, rather than the small HPR kit that the community has taken it as. That's on me for misreading the market. But, we're always glad to find ways to improve.

Cheers!

Like no-one would put a K in a bull pup.....

 

[WizardOfBoz]

Our TRA prefect, Dennis, counseled for a long cord - can't recall the rule [on edit: 5x the length of the airframe*] but my DX3 ended up with 4' of 1/2" tubular kevlar to the bulkhead and 20' of 9/16 tubular nylon to the nose cone. Sewn loops fasrened with soft shackles. Other rockets like an Argent, a PSII Nike Smoke and an EZDD all have long kevlar cords. 3/8 and 1/4". Even my little Patriot uses a very long Kevlar cord. 1.5mm I think. But it's 10 feet long.

* 5 x airframe is an easy formula but shouldn't it be more mass related?

 

[rharshberger]

Our TRA prefect, Dennis, counseled for a long cord - can't recall the rule [on edit: 5x the length of the airframe*] but my DX3 ended up with 4' of 1/2" tubular kevlar to the bulkhead and 20' of 9/16 tubular nylon to the nose cone. Sewn loops fasrened with soft shackles. Other rockets like an Argent, a PSII Nike Smoke and an EZDD all have long kevlar cords. 3/8 and 1/4". Even my little Patriot uses a very long Kevlar cord. 1.5mm I think. But it's 10 feet long.

* 5 x airframe is an easy formula but shouldn't it be more mass related?

It should be testing related, mass will only get you the tensile strength needed for say, a 50G event (which is my worst case on "standard" performance flight) but determining how much shock cord YOU need is determined by ground testing and your setup preferences. Strength of the two recovery harness anchor points should also be a factor.

Typically I go with 5x airframe length but no less than 10' of 2mm kevlar (I have lots of rockets what only use 10' kevlar shock cords but all the rockets are stubbies or dual deploys with minimal ejection charges).

 

[Buck]

I also had an issue with my Kronos on my first flight with it. The nose cone and loop cracked but luckily did not separate, so the rocket was recovered undamaged. Since then I have added 5 more feet of shock cord, bought another nose cone and installed Apogee's 3'' nose cone bulkhead and sled for my tracker. I haven't had a chance to fly it yet, but will probably give it a go in a couple weeks. FYI, First flight was on a ''G'' motor.

 

[Buckeye]

Just FYI, we are updating the Kronos kit with 16' of 750# Kevlar (up from 10' of 300#) and already-built kits will have inserts added to the instructions to add further suggestions to increase flight success. Once we have worked through the stack of the current instructions, we will - of course - be folding the modified instructions into the booklet.

Please do reach out and let us know about any issues you may have with our products (especially in cases like this when there seems to be a pattern). It's our goal to help people to be successful.

In this case, I was thinking about the kit as a very large MPR kit, rather than the small HPR kit that the community has taken it as. That's on me for misreading the market. But, we're always glad to find ways to improve.

Cheers!

Thanks for the quick updates!

A longer cord is a good idea for both MPR and HPR use. Apogee advertises ebays and nose bays for the 3" thin wall tube, so the mass of this rocket can really jump with the added payloads. 29mm is a grey area, and people will be tempted to put an HPR motor in it, especially L1 newbies trying to cert on the cheap.

 

[WizardOfBoz]

29mm is a grey area, and people will be tempted to put an HPR motor in it, especially L1 newbies trying to cert on the cheap.

I think that this is a really important observation. The TRA Prefect I mentioned above (Dennis K.) counseled against my using an Estes Argent for L1 as being "a little light". I took the hint and built a mad cow super DX3. That is (IMHO) an almost perfect L1 rocket, as its big enough to be impressive but also to keep an H180 from sending it to 10000 feet. The key point is that there's an almost qualitative difference between L1 HPR and lower powered rockets.

I write math models of disease for a living. We always counsel newbies in the field, when writing models of kids, that "a child is not a small adult" meaning that the physiology is quantitatively different. That's the lesson I took from Dennis: A good L1 rocket is NOT a 20% upscale of an Estes Alpha. Or any small rocket with a 29mm motor mount. And most failure modes for L1 qual are different. Except for one: you can lose both an Estes Alphas launched on a C6-5 and a DX3 launche on a J270. Losing the rocket is the common failure mode.