Wayco's RW Mongoose 54 build

[DizWolf]

Yeah, yesterday was a good day. Right after I got tracking data from Scott at LOKI, I got a call from Curtis at RW. Right now I'm trying to decide if I will get a Binder design fincan or just cut the CF fins off the old rocket. Maybe I should get a set of those Space Cowboy fins from Chris Attebery.

Chop it a few inches above the fins, friction fit it on the 54/4000, put a few wraps of tape on case above all that, twist the new 60" section on top of that. Hook the harness to the top of the motor, Drill a few shear pin holes and fly it next weekend

 

[ksaves2]

Chop it a few inches above the fins, friction fit it on the 54/4000, put a few wraps of tape on case above all that, twist the new 60" section on top of that. Hook the harness to the top of the motor, Drill a few shear pin holes and fly it next weekend

Sounds like a Hillbilly repair to me!:wink: Kurt

 

[DizWolf]

Sounds like a Hillbilly repair to me!:wink: Kurt

Naw....that'd be just duct taping over the hole and calling it a day

 

[dixontj93060]

Taking the failure into account, I may not use an internal retainer at all, that would remove the weakness of the holes.

+1. Instead design for all flight profiles, commit to the right position/length, and use good structural epoxy.

 

[ksaves2]

+1. Instead design for all flight profiles, commit to the right position/length, and use good structural epoxy.

If the motor had a thrust ring that was properly seated at the bottom of the motor tube, the force on the screw holes should have been minimal. The drilling, countersinking might have weakened the structure as mentioned.
I suspect if a simple hole was drilled and small buttonhead screws used, even though that is not aesthetically pleasing as flush mounted screws, that would likely work better without weakening the structure. Might be able to get away
with 2 screws. Kurt

 

[dixontj93060]

If the motor had a thrust ring that was properly seated at the bottom of the motor tube, the force on the screw holes should have been minimal. The drilling, countersinking might have weakened the structure as mentioned.
I suspect if a simple hole was drilled and small buttonhead screws used, even though that is not aesthetically pleasing as flush mounted screws, that would likely work better without weakening the structure. Might be able to get away
with 2 screws. Kurt

How do you know it didn't happen upon recovery deployment? The damage was forward of the screw holes.

 

[ksaves2]

How do you know it didn't happen upon recovery deployment? The damage was forward of the screw holes.

I thought he said he used a punch and hammer? Perhaps that weakened the structure by cracking some of the fibers and the epoxy used to bind the filaments. If pressurization caused the blow out from the ejection charge may be it was a poorly wound tube? It's an unusual failure. Makes me pause when it comes to drilling holes now.
I've been making a dimple by twisting an awl, then use a small high speed drill to make a pilot hole and use the
final bit at high speed an light pressure to cut the final size. Kurt

 

[Wayco]

I used one of those spring loaded punches from Harbor freight. Curtis had an issue with that, CF doesn't like lateral forces, it's strength is in the longitudinal plane.
I'm now planning on friction fitting the motor casing and attaching my drogue recovery to an eyebolt screwed into the forward closure. The Loki forward closure has 1/4"x 20 threads already in it, and I have an AT forward closure with the same thread pattern. Probably won't use a CTI load, not coming up with a good method of attachment.
I watched the entire deployment sequence for that first flight and did not see anything that could have caused the damage that occurred. I really think that my method of drilling and the size of the holes caused the damage.

 

[ksaves2]

Lotsa folks use friction fit successfully. My only concern would be not to use shearpins for the apogee deployment phase and try to get away with the gentlest apogee charge that's practical. Reason I mention that is I'd like to avoid
stressing that forward snap ring groove any more than necessary. Yeah, yeah, I know, the snap ring/groove has to take 1200psi or whatever anyways. A little snap of a shockcord/harness t'aint going to hurt it. Still
I'd hate to stress a case anymore than is necessary. Especially if the L2050 is fired. The residual heat might alter the case characteristics. I concede I may be blowing needless hot air here.

Another thing is make sure the eyebolt is secured well as I have witnessed a couple of rockets that had the harness secured to a forward closure eyebolt "unscrew" the eyebolt on descent. That results in the sustainer going into
a free fall to smack the earth. A heavy duty swivel in the chain might help prevent this.
This could lead to a dilemma if one would want to get the eyebolt out of the closure so they could go back to using it with a rocket that has internal retention. The pricey remedy is have two forward closures for the motor. One with the eyebolt and one with the allthread.

I wonder if anyone has witnessed a friction fit motor with an apogee shockcord on the forward closure get blown out the aft end of the rocket? I'd think with enough after following harness, the rocket would tumble in drogueless o.k.
to the a nominal main chute deployment altitude.

Kurt

 

[manixFan]

...I'm now planning on friction fitting the motor casing and attaching my drogue recovery to an eyebolt screwed into the forward closure....

I know I don't have to tell you this with your experience but I just can't help myself. I've seen several recovery failures when the eyebolt unscrewed from forward closure due to twisting in the wind under chute. Pretty terrible to see a nice recovery suddenly go sideways as the fin can separates and falls to the earth while the remaining parts slowly drift away.

For my Mongoose flight at BALLS I'm using a plugged CTI motor (L265) that has an insert for a 1/4 bolt in the plastic forward closure. It's being used only for motor retention and not was a support for the weight of the rocket under chute. I don't know how strong it is and I am afraid to use lock washers to secure the recovery bolt to the forward closure like I do for normal aluminum closures to prevent the bolt from unscrewing. I also added 'safety wires' through the plastic forward ejection charge well to secure the case as a bit of insurance.

I did drill several holes in the body tube but I used the lessons you provided in this thread for guidance on how to best do it in CF. So thanks for sharing your issues to help prevent others from doing the same thing.


Tony

 

[ksaves2]

I know I don't have to tell you this with your experience but I just can't help myself. I've seen several recovery failures when the eyebolt unscrewed from forward closure due to twisting in the wind under chute. Pretty terrible to see a nice recovery suddenly go sideways as the fin can separates and falls to the earth while the remaining parts slowly drift away.

For my Mongoose flight at BALLS I'm using a plugged CTI motor (L265) that has an insert for a 1/4 bolt in the plastic forward closure. It's being used only for motor retention and not was a support for the weight of the rocket under chute. I don't know how strong it is and I am afraid to use lock washers to secure the recovery bolt to the forward closure like I do for normal aluminum closures to prevent the bolt from unscrewing. I also added 'safety wires' through the plastic forward ejection charge well to secure the case as a bit of insurance.

I did drill several holes in the body tube but I used the lessons you provided in this thread for guidance on how to best do it in CF. So thanks for sharing your issues to help prevent others from doing the same thing.


Tony

Uscrewing is a valid concern. Problem is getting the eyebolt out if using thread locker to convert back to stock or use with internal fixation with threaded rod. A jam nut is a possibility but ideal would be a threaded hole with a set screw to hold
the eyebolt in place against unwinding. I've seen some Research case forward closures with this feature. A heavy duty swivel helps too. Kurt

 

[MikeL]

Just got back from Balls – still tired from trip back to Indiana.

Flew my Mongoose 54 on a Loki L1040. Altitude per GPS was 29.2K feet above the playa. Speed was Mach 2.3.

All back with nearly a scratch…

 

[ksaves2]

Holee cow! Means I'll have to buy a K motor as my home site waiver is only 15k! What did you track with Mike? Kurt

 

[KenRico]

Time for a M !

Kenny

 

[NateLowrie]

Just got back from Balls – still tired from trip back to Indiana.

Flew my Mongoose 54 on a Loki L1040. Altitude per GPS was 29.2K feet above the playa. Speed was Mach 2.3.

All back with nearly a scratch…

Very nice. Will be putting this on the build list for sure now.

 

[tim cubbedge]

Just got back from Balls – still tired from trip back to Indiana.

Flew my Mongoose 54 on a Loki L1040. Altitude per GPS was 29.2K feet above the playa. Speed was Mach 2.3.

All back with nearly a scratch…

Did you do a tip-to-tip?

 

[Cl(VII)]

Holee cow! Means I'll have to buy a K motor as my home site waiver is only 15k! What did you track with Mike? Kurt

Yes, and not a big one. I got 13.9k' with a K550.

 

[MikeL]

Holee cow! Means I'll have to buy a K motor as my home site waiver is only 15k! What did you track with Mike? Kurt

I had a friend's BigRedBee GPS transmitter in the nose cone. Had a good fix from coast to touchdown.

Time for a M! Kenny

Maybe, already looking at how to modify things as to not change the overall length... We'll see. I have a bad habit of flying a lot of my rockets once and then retiring them.

Did you do a tip-to-tip?

Originally I was planning on a two layer stair-step tip-to-tip. But after reading all the threads (mainly this one), I decided to just use healthy Proline 4500 fillets.

Mike

 

[BDB]

Details! I need more details!

My mongoose is next in line on my build pile. I was planning on T2T, but MikeL and Wayco may have just talked me out of it. What did you do for motor retention? I'm seriously considering friction fit so I can fly either the Loki 54-4000 case or my CTI cases. And what about recovery? I'm dying to know!

 

[ksaves2]

Details! I need more details!

My mongoose is next in line on my build pile. I was planning on T2T, but MikeL and Wayco may have just talked me out of it. What did you do for motor retention? I'm seriously considering friction fit so I can fly either the Loki 54-4000 case or my CTI cases. And what about recovery? I'm dying to know!

Scuff the bodytube with 40 to 60 grit sandpaper BDB and use a healthy fillet of accurately measured/prepared Proline 4500. I've done it on smaller projects and am impressed. If going to use a longer sustainer tube with the intention of flying on
an L2050 or M1387 I'd probably start thinking about T2T. I believe the stock tube is not long enough for that crazy motor. Kurt

 

[Cl(VII)]

Details! I need more details!

My mongoose is next in line on my build pile. I was planning on T2T, but MikeL and Wayco may have just talked me out of it. What did you do for motor retention? I'm seriously considering friction fit so I can fly either the Loki 54-4000 case or my CTI cases. And what about recovery? I'm dying to know!

Scuff the bodytube with 40 to 60 grit sandpaper BDB and use a healthy fillet of accurately measured/prepared Proline 4500. I've done it on smaller projects and am impressed. If going to use a longer sustainer tube with the intention of flying on
an L2050 or M1387 I'd probably start thinking about T2T. I believe the stock tube is not long enough for that crazy motor. Kurt

The stock tube isn't long enough, but I wanted mine to be capable of that too, so I think I found a workaround. My motor retention is done with an aluminum rod that threads into the forward closure of the motor and a T-nut in the aft electronics bay bulkhead. This sandwiches the booster tube between the e-bay vent band, and the aft motor closure. The plan (should the rocket survive till then) is to use the several inches of the Loki 54-4000 motor case that won't fit in the booster as the coupler for an ~8" length of CF tube (electronics bay-8"extension tube-booster-aft closure) to extend the booster. Again the retaining rod will keep everything together, at least until the shred.

I also did 2 layers of CF tip-2-tip on mine too. The leading edges will also get a coat of a high temp epoxy before the Loki 54-4000 is unleashed upon it.

As for your other questions. I tracked it to 14k with an Eggfinder with no problem, and recovery was by Top Flight 30 thin mill, and a chute release (Will be adding a backup RDF beacon before going any higher though). It is set up for cable cutters, but the chute release is just so easy.

 

[BDB]

The stock tube isn't long enough, but I wanted mine to be capable of that too, so I think I found a workaround. My motor retention is done with an aluminum rod that threads into the forward closure of the motor and a T-nut in the aft electronics bay bulkhead. This sandwiches the booster tube between the e-bay vent band, and the aft motor closure. The plan (should the rocket survive till then) is to use the several inches of the Loki 54-4000 motor case that won't fit in the booster as the coupler for an ~8" length of CF tube (electronics bay-8"extension tube-booster-aft closure) to extend the booster. Again the retaining rod will keep everything together, at least until the shred.

I was kicking around the idea of using the motor as a coupler too, but was thinking that it might need to be augmented with an "outer coupler" that was rolled from CF using the airframe as a mandrel. But what do I know....I'm still working on my L2 project. The Loki M-1378 would make for one hell of a L3 attempt, but even I'm not that crazy.

 

[Cl(VII)]

I was kicking around the idea of using the motor as a coupler too, but was thinking that it might need to be augmented with an "outer coupler" that was rolled from CF using the airframe as a mandrel. But what do I know....I'm still working on my L2 project. The Loki M-1378 would make for one hell of a L3 attempt, but even I'm not that crazy.

I didn't say it will work; I just said I'm gonna try it. Hard to get a stronger coupler than a motor case though. Also the short length of tube should keep any potential torque to a minimum...I think.

 

[manixFan]

Another Mongoose 54mm flight report from BALLS 25:

CTI L935 to 23,533 (average of Raven2 and Perfectflite CF baro altitudes) at Mach 2.3. Fin mounting area scuffed with 120 grit paper and mounted using just the Proline epoxy as directed, no tip to tip or other reinforcement.

Friction fit the motor with no issues. Ready to fly weight without motor was about 55 oz. or 3.45 pounds. I could have left out my Big Red Bee as it did not lock and I used my backup Marshall tracker to find it.

I also flew it on an L265 at BALLS but due to a wobbly tower I only got about 19,500' and 4 miles sideways. Should have been about the same as the L935.

Next year it's a Mongoose 98mm on a CTI N1560. (Assuming that the motor is available by then.) Not great total impulse but I love those long burn motors. Also a lot easier on the fins than something like the N3400. But since I'll fly that rocket on 98mm research motors as well I'll likely beef up the fin attachment over the standard Proline epoxy.


Tony

 

[manixFan]

...Flew my Mongoose 54 on a Loki L1040. Altitude per GPS was 29.2K feet above the playa. Speed was Mach 2.3. ..

Did you see a big difference between baro altitude and GPS? My baro units saw ground level at about 3500' and it's closer to 4000' at the playa. Since I did not get my Big Red Bee to lock up during flight I was wondering what kind of difference in reported altitude between baro and GPS is typical. My Raven2 and Stratalogger CF were within .5% of each other at peak altitude.

My altitude was almost exactly between what OpenRocket and RASAero predicted. How did yours pan out? That's my first time going above 20K" with less than a 3" airframe so I'm interested in how the sims compare as body sizes change.

Thanks,


Tony

 

[MikeL]

Hi Tony. Man, I missed your flights! When did you fly the L – Saturday?

I can’t say that I’ve noticed a difference in the ground level readings for the altimeters, but I have seen decent differences between what the GPS and altimeters report for the flight max altitudes. I go with the GPS’ report as we verify the ground level altitude (~3,900 for BR) before launching to make sure the GPS is functioning and has lock, and GPS data is what is required for TRA altitude records above 30K MSL. (MSL for my flight was 33,140.) My altimeters (MW RRC3 Extreme/RRC2+) were within .3% of each other, but 5% lower than the GPS. I’m not sure that it’s not due to atmospheric differences between conditions at the launch and what the altimeters were calibrated at, or the conditions at the max altitude, neither which would affect the GPS.

This was my first year using RASAero as the primary simulation reference. I was very impressed as to how accurate it was:
Speed: RA M2.2, Reported M2.3
Ascent: RA 36.3 sec, Reported 36.6 sec
Altitude: RA 28,955’, Reported 29,239’

Mike

 

[manixFan]

Hi Tony. Man, I missed your flights! When did you fly the L – Saturday?

I flew the L265 on Saturday and the L935 on Sunday along with the Loki K627 in a ShadowAero Raven3.

Thanks for the info regarding the GPS. I guess I need to make sure I can get my BRB to work properly so I can record GPS altitude. My RA sims had about the same error as yours using the baro data. I used a Featherweight Raven 2 and a Perfectflite CF for altimeters.

Speed: RA 2,436 ft/sec, Reported: Raven2 - 2,583, PF CF 2,447
Altitude: RA 22,329 ft, Reported: Raven2 - 23,589, PF CF 23,476

I was pretty happy that the altitude reported by the two altimeters was within 0.4% of each other. The average of the two altimeters was about 5% higher than the RA II predicted altitude. Your GPS data was less than 1% off than RA so a much better agreement.

I also just got my 98mm Mongoose in the mail today. Man, that is a loooonng box! Lots of what I did for the 54mm Mongoose will be applied to that rocket as well.


Tony

 

[MikeL]

Shoot, I missed them both. Saturday I was out for a long time helping retrieving my friend’s 75mm MD N. Sunday, if you saw a 6” Purple and Yellow Eagle Claw go on an O, I was out helping with that one. Sorry that I missed both of yours.

If you don’t already, one thing we do is to make sure that the GPS unit has lock before putting it in the nose, and then leave it on. Verify again that is has lock before launching. It seems to make a difference on how fast it reacquires lock after liftoff.

Man, if I bought a 98mm Mongoose - my wife would kick me all the way down and half way back our 300' driveway! And she's L2! I'm envious!

Mike

 

[ksaves2]

Shoot, I missed them both. Saturday I was out for a long time helping retrieving my friend’s 75mm MD N. Sunday, if you saw a 6” Purple and Yellow Eagle Claw go on an O, I was out helping with that one. Sorry that I missed both of yours.

If you don’t already, one thing we do is to make sure that the GPS unit has lock before putting it in the nose, and then leave it on. Verify again that is has lock before launching. It seems to make a difference on how fast it reacquires lock after liftoff.

Man, if I bought a 98mm Mongoose - my wife would kick me all the way down and half way back our 300' driveway! And she's L2! I'm envious!

Mike

Other thing to do is replace that keep alive button cell on the board every now and then. That little thing under that metal clip. Push it out with a fine screwdriver. (I do it every year or sooner as explained in the next sentence.) If I find that it takes a long time for the unit to get a fix out on the open. I'll replace the button cell and the cold acquisition time is shortened. It might also mean that if the unit is locked-out during high G flight the warm acquisition time could be very short if the keep alive button cell keeps the details of the satellites ephemerides (positions) intact in memory when it comes out of blackout. The re-acquisition might be instantaneous as opposed to starting from a cold mode.
Also, if ones unit gets fast fixes out in the open and doesn't or loses lock when put in a stationary nosecone, could be the nosecone material or paint could be attenuating the incoming signal. Less likely could be the satellites positions are suboptimal based on the receiving antennas orientation. Carbon fiber is notorious for attenuating and also the Rf might not "get out". The attenuation is frequency and power dependent.
More info here: https://gpstracklog.com/2013/09/good-satellite-days.html and here: https://freegeographytools.com/2007...tellite-geometry-effects-on-position-accuracy

With the Trimble planning software and a downloadable ephemeris table, one can predict the "Dilution of Precision" (DOP) and the likelihood of being able to have a good lock on a launch day. The lower the DOP the higher the accuracy.
This might be overkill for many but if going to push a tracker to the extreme, knowing up front where the GPS constellation is going to be can provide some assurance of precision.

Sport flier = probably overkill.

Kurt

 

[manixFan]

Other thing to do is replace that keep alive button cell on the board every now and then....With the Trimble planning software and a downloadable ephemeris table, one can predict the "Dilution of Precision" (DOP) and the likelihood of being able to have a good lock on a launch day....

I replaced the button cell battery the day of the launch so it was fresh. It could have been the mounting in the nosecone - I'll have to do more work on that.

Holy cow do I ever learn a lot of stuff on this site. The GPS prediction site is pretty cool. And I can hardly wait until the next party when I can start talking about 'Dilution of Precision' and then my wife tells me it's time to go home. Seriously, good stuff to know though.

And MikeL, I do remember the Eagle Claw. My K627 flight was the second to the last of the launch so I was there for all the other launches. The name Eagle Claw reminded me of fishing when I was a kid.

I unpacked the Mongoose 98 today. The fins are a ridiculous 1/4" of laminated CF. I think they weigh more than the rest of the rocket. If I get those things on right it will take one heck of a motor to flutter them off.


Tony