Rookie HPR mistakes

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Scrapmaster87

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1) Forgetting to attach the booster recovery harness to the payload section. The 14" drogue was enough to prevent damage on the 3lb booster and the 1.5lb payload section had the most gentile landing it will ever have.
2) Rushing through prep and forcing a sloppily folded main chute into the payload section. Main failed to deploy, same rocket as number 1, no damage, thing is built like a tank.
3) Mixing epoxy on autopilot. I was making glassed plywood stock for fins the other day when I noticed something was off when I was mixing my final batch. Since my final batch wasn't a full 3oz dixie cup, I actually had to think about the 2:1 mix I was using. Since right now I'm using 10cc syringes, a full cup is 4 full squirts of resin and 2 squirts of hardener... I did 3 squirts of resin and 1 squirt of hardener... then my muscle memory reached for my mixing stick when I was thinking of the next 5ccs of hardener... This is when I realized that that the previous 3 batches were made with a 4:1 mix instead of the 2:1! I still mixed the final batch correctly and followed through with a deep vacuum bagging for the practice. Its been 2 weeks and the board is still tacky on 1 side... not sure what I'm gonna do with this, it'll make ok centering rings...but i just print my rings anymore...
4) Shooting clear too soon (crinkled with layer beneath)
5) Shooting clear too heavy (runs!)
6) Repainting over clear (nothing sticks well!)
 
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Chas.alpha1

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I'd say one of the most common is mis-application of materials. It can go both ways, but I think most often for people new to HPR is to over-build.

For example, it is very easy to read over some of the great build threads of big, fast, giant-motor projects and go down the rabbit hole that your first HPR needs to be built with 3 layers of 10oz fiberglass tip to tip, when in reality, most L1 rockets are fine with just cardboard and wood glue.


I definitely overbuilt my L2 cert rocket to insure there would be no construction issues with firing a J500, but other than that I agree with everything you said. It's very easy to get overly conservative at the cost of considerable loss of performance.
 

green dragon

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Once I have had my rocket on the rail before I realized I didn't have a motor in it.

Check rail buttons to ensure they are firmly attached...check again. Had one pull off while removing a rocket so I could install the motor that I had forgot at my pit area.
Just curious how you could arrive at the pad without the motor installed ?

RSO should catch this = as they are REQUIRED to check motor retention, meaning they should note the empty hole ?

"rookie RSO " mistake ?
 

CoyoteNumber2

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Just curious how you could arrive at the pad without the motor installed ?

RSO should catch this = as they are REQUIRED to check motor retention, meaning they should note the empty hole ?

"rookie RSO " mistake ?
If there's no motor installed, I doubt it poses much of a safety hazard.
 

C.O.B.H.C.

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Forgetting to clean out the inside airframe of my PML Phobos and the piston jammed but it still partly separated rocket so it just had hard landing. When flying PML Q-Tube it is important to clean out the tube every so often to make sure the piston still slides freely.
 

Glasspack

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Scrapmaster ............ was that 14" or 14'

It just seems; a 14 inch Chute is to small to safely land 3 pounds !!
Calculator puts it at like 37.29 mph ground impact !! Good Job on the Build then !!! :)

I am currently trying to figure out the drouge for my LvL2 Model............
 

Scrapmaster87

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Scrapmaster ............ was that 14" or 14'

It just seems; a 14 inch Chute is to small to safely land 3 pounds !!
Calculator puts it at like 37.29 mph ground impact !! Good Job on the Build then !!! :)

I am currently trying to figure out the drouge for my LvL2 Model............
It may have been 2.5lb, but yes it's built like a tank. My design philosophy thus far is that the main chute's purpose is to serve as a curtosey to whatever the rocket land on.
 

green dragon

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If there's no motor installed, I doubt it poses much of a safety hazard.
Still should have been noticed by the RSO. ( who, as I noted, is required to check motor retention - and certified motors if not a research launch, meaning they need to see the motor.
 

K'Tesh

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Forgot to secure the nosecone to the recovery bay on a zipperless design.

While the nosecone was tethered to the rest of the rocket, both it and the bay separated from the sustainer trapping the parachute inside the bay. I got lucky, I had just enough altitude for the parachute to extract itself and deploy an instant before it was too late. The flight was filmed, but the battery on the camera quit right at the moment the parachute came out and opened, only about 20 feet off the ground.

On the plus side, I didn't have to walk far to recover it... Intact.

 
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thobin

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Putting tape down on both side of your wing fillet??? Now you have a ridge of epoxy to sand down or fill. If you sand it you just divot out the body tube and wing. Mounting your engine tube flush with ether centering ring top or bottom. Effectively eliminating one glue joint from the engine mount to the ring and eliminating the possibility of adding a motor retainer.

TA
 

OverTheTop

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Not turning off Windows Update and having a major update take over 40 minutes to apply in the field, running on battery. Compounding matters was the fact I didn't have my power supply to charge the laptop with me, since it wasn't going to be on for very long :(.

Make sure your PC is up to date before going on a launch, and turn off Windows Update!
 

Mike Haberer

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My first HPR was obviously on my cert flight and it went well. However, the next time I used a DMS motor I forgot to drill the delay. I lawn darted my 1/4 scale NCR Patriot. It's been rebuilt and flown several times, just now getting to painting the airframe and putting on the decals (18 months later). Pic is after I cut the damaged part of the airframe off. The nose cone was demolished. \

20201202_091102.jpg
I don't think I'll ever forget to drill a delay again...



.
 

Grog6

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I have a question.
What type of construction is required to handle transonic flight?
I know how to do the calcs, but materials numbers are hard to find.
So, I'm asking what works reliably?
 

OverTheTop

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A reasonably built cardboard rocket will do well. Fins probably need to be stronger than just plain balsa. Maybe papered balsa, or perhaps a model plywood will be sufficient.
 

Mike Haberer

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Below are some tables I found on the internet from some academic papers that provide shear modulus and other values for plywood and fiberglass. I use them in a spreadsheet that a TRF'r put together a while back based on an article in an Apogee Newsletter a few years ago (search for fin flutter topics on the forum).

I use both the spreadsheet and AeroFinSim to calculate fin flutter values for scratch builds. The spreadsheet provides more conservative values than AeroFinSim. In general, unless you are going above Mach 2, heavy cardboard (e.g., LOC or Blue Tube) and plywood (1/4" for fins) is all you need. Using fiberglass or carbon fiber isn't really needed unless you go well beyond transonic. This has been stated by others on different threads on the forum. (Note: fin design makes a huge difference in fin flutter dynamics. Some designs are very robust; change the design and they'll fail, all else being equal. In my design iterations, keeping the tip cord = 0 is the key.)

At some point, I should build a design that threads the needle between the spreadsheet and AeroFinSim numbers and keep upping the ante until it fails to actually put some empirical data to the estimates. All it would take is dialing down the plywood fin width by 1/16" of an inch from a design that works to one that will fail. So much to do, so little time....
 

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green dragon

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Or, since the DMS delay was pretty much ok as-is, since you never drilled it, you never thought to instal the ejection charge powder, oops....... will only do that once, also :(
 

FlyBy01

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Or, since the DMS delay was pretty much ok as-is, since you never drilled it, you never thought to instal the ejection charge powder, oops....... will only do that once, also :(
I almost did this myself; I luckily remembered just before putting the ignitor in.
 

manixFan

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I have a question.
What type of construction is required to handle transonic flight?
I know how to do the calcs, but materials numbers are hard to find.
So, I'm asking what works reliably?
When you ask about 'construction', that can be construed as either materials or methods. Others have mentioned materials, so I'll mention methods. Based on my personal observations and experience, if you are going above Mach and want top performance:

  • all joints should be as clean and tight as possible - tube ends square and flush, nose cone diameter exactly matches body tube, etc.
  • keep the rocket as short as possible - reduces drag and bending stresses on body
  • fin alignment is crucial - any misalignment greatly increases stress on the fin
  • make sure leading edge of the fin won't delaminate at speed (if using a layered fin structure)
  • fin profiles and fillets should be as uniform as possible
  • keep surface protuberances to a minimum
  • the smoother the surface the better, painted with high temp paint such as brake caliper or engine paint or an epoxy clear coat
  • use a fin shape that has been successful for others - the Mongoose is a good example or a zero tip chord as mentioned above
  • a boat tail helps reduce base drag
  • make sure all electronics/batteries can survive high G flights (mounting especially)
  • start small and work your way up in size

It's not hard to break Mach 1 and survive. But things get quickly out of hand above Mach 2 and Mach 3 seems be like a brick wall. But really, this is a discussion for another thread.


Tony
 

Grog6

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So construction-wise, avoid "pinning" features that will hold a shock wave.
So is blue tube sufficient for the body tubes?
What nosecone works well?
I destroyed many plastic ones over the years when I was a kid; big engine- light rocket==Confetti,lol.
 

SDramstad

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Putting tape down on both side of your wing fillet??? Now you have a ridge of epoxy to sand down or fill. If you sand it you just divot out the body tube and wing. Mounting your engine tube flush with ether centering ring top or bottom. Effectively eliminating one glue joint from the engine mount to the ring and eliminating the possibility of adding a motor retainer.

TA
I use rocketpoxy for fillets and I pull the tape off 10 to 15 minutes after I apply the rocketpoxy. At that point it will flow enough to eliminate ridges from the tape line but thick enough not to flow where I don’t want it.
 

ChicagoDave

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10,000% easier to fix the fillet when the epoxy is still green than to fix it after it's cured.. Use Isopropyl Alcohol. Dip your gloved finger (or other tool) in the alcohol and run it along the ridge to smooth it out. Do this before the epoxy gets past the leather stage and you'll blend that into the body tube / fin perfectly. If you have lumpy / bumpy fillets use the same process to smooth out the surface of the epoxy. Take your time, go slow and you can get your fillets to almost perfection without touching sandpaper.

Also use the alcohol and paper towels to dissolve excess epoxy, drips and other epoxy "oops".
 

thobin

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Guess I never had a problem with it going where I needed it and leveling out on its own.


1629844820185.png
 

debonairbear

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My biggest mistake was not looking at the thrust curve for an H115 when I attempted my L1 certification. I lost the NCR Big Brute (built with epoxy) I had built for that attempt an hour before and switched to a MDRM I built with wood glue and had launched on an F50. The fins shredded on the way up in a spectacular fashion. We thought the motor had CATOed because we thought we saw flames as it flew apart, but the motor was intact. View attachment 467652View attachment 467653View attachment 467650View attachment 467651
Even had you looked at the thrust curve, how would you have known that it would shred? is there a rule of thumb to follow?
 

Joekeyo

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Weld is only for bonding metal components. Use it for that, and don't use it for anything else.
Is that so or is that the mistake?

My rookie mistake was that I expected JB Weld is the same as I remember from years ago. The JB weld I remember was a putty, not a paste. Am I right on this or has my memory did a mash-up again?

What I bought was paste. It was an ugly mess getting the paste into the little hole in the nose cone. My plans were to make little putty snakes and drop them in the hole, then tamp them down with a dowel rod. That didn't work with the sticky goo.
 

Grant_Edwards

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My rookie mistake was that I expected JB Weld is the same as I remember from years ago. The JB weld I remember was a putty, not a paste. Am I right on this or has my memory did a mash-up again?
JB Weld is a company that produces about 70 different adhesive products. They make 6 or 7 different epoxy puttys. They also make dozens of types of "liquid" 2-part epoxies, various silicone and RTV products, tire patches, copper gasket paste, thread-locker, and so on.
 
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