Giant Leap Rocketry "Hardpoint" Question

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lowga

A.K.A. 'Mr. HoJo'
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I'll be using a Giant Leap Rocketry "Hardpoint" Recovery System Anchor in my 54mm minimum diameter rocket. These are very similar to minimum diameter anchors made for motor casings (without motor ejection) only these are vented to allow ejection gases to pass through them. I'll be using motor ejection only for my rocket.

The Hardpoint is made from one-piece aircraft aluminum. I have replaced the included eyebolt with a 1/4"-20 X 2" Forged eyebolt for greater strength. My question regards the mounting.

I'm considering using screws drilled through the fiberglass airframe and and the Hardpoint for attachment rather than JB Weld epoxy. This would allow me to move the location of the Hardpoint up and down on the rocket depending on which motor I'm flying, or to remove it entirely for use in another rocket. Plus i think the mechanical connection would be stronger than the Epoxy, right?

I was thinking three #4 stainless steel screws, and using a drill press to ensure the alignment of the screws.

Am I on the right track here, or is there a better option? Always grateful for the advice and expertise on this forum.
 
I screw mine in with 3 countersunk machine screws, 120 degrees apart. I use epoxied self clunching nuts adhered to the inside on the retainer, which works well. The screws are 2-56 I believe or 4-40, I will have to check later.
 
You are on the right track for your recovery point. You can mount this once based on a position that accommodates the longest motor casing that will fit in the airframe, which eliminates the need to move the Hardpoint back and forth within this rocket. The caveat is to ensure you have ample room for recovery materials. Several of us have built similar MD recovery anchor points out of coupler bits and a bulkhead, but the Hardpoint for $8 is not a bad deal.

I think you'll get more questions from the TRF community about the choice to use motor deploy as a primary for a MD rocket, but I will abstain from that topic. I would like to ask about your plans for motor retention in this MD rocket. Many of the MD anchors serve both as a recovery attachment point and as motor retention - by way of threading the top of the motor casing. For example, the Pro38 Delay/Ejection Closure Adapter for Cesaroni Casings found here:
https://www.apogeerockets.com/Building_Supplies/Motor_Retainers_Hooks/Minimum_Diameter_Retainers
 
I used the Aeropack variant of the hard point. I did what you described though the metal was so thin I used JB-Weld to affix a 4-40 nut to the inside of each hole. Works like a champ. Though I use different threaded rod lengths to adjust for different motor lengths.

I thought the hard point was intended to be Applied like an Aeropack retainer to the end of a MMT and was not aware it had a threaded opening on top and bottom.
 
The Hardpont is not intended to be applied like an Aeropack retainer. The Aeropack retainers are for dual-deploy rockets where you are not using the motor ejection. In contrast, the Hardpoint is designed with motor ejection in mind.

It can be attached directly to the end of a motor mount, but obviously in a minimum diameter rocket, I won't be using a motor mount. One of my mentors suggested mounting with screws, while another recommended using two short couplers inside the airframe--both epoxied with JB Weld with the Hardpoint wedged between them. The screws make more sense to me.

For motor retention, I'll be using an Aeropack Quick-Change that is attached with JB Weld directly to the aft end of the airframe.

I'm going with motor deployment to keep the design of the rocket as simple as possible.
 
I picked up a couple of these (38 & 54mm) in a box of surplus stuff from a club member. I used the 38mm one (I also replaced the eyebolt with a forged one) and I like the way it acts as a swivel.

I would say that using two bits of coupler would be the strongest way to attach it, followed by gluing it in (what I did).

The problem I see with the screws is that all of the load is concentrated on a few spots where the screws go through the airframe. That said, fiberglass is strong stuff and I'm sure it would work fine for nominal flights. If you have a really fast deployment it seems like it could possibly tear the screws loose or zipper the airframe.
 
I picked up a couple of these (38 & 54mm) in a box of surplus stuff from a club member. I used the 38mm one (I also replaced the eyebolt with a forged one) and I like the way it acts as a swivel.

I would say that using two bits of coupler would be the strongest way to attach it, followed by gluing it in (what I did).

The problem I see with the screws is that all of the load is concentrated on a few spots where the screws go through the airframe. That said, fiberglass is strong stuff and I'm sure it would work fine for nominal flights. If you have a really fast deployment it seems like it could possibly tear the screws loose or zipper the airframe.
 
I have a Firestorm 54 with the hardpoint, also with a forged eyebolt, glued in with generous fillets of RocketPoxy. I spaced mine for the biggest 54mm motor that I would ever fly... an AT L1000 DMS. Shorter than may CTI 54 6G case, so it's all good. I think it would be very difficult to get the holes properly lined up for multiple mounting locations, and a really hard deployment could tear the screws out of the fiberglass body tube. Glue it in and fillet the top edge.
 
Thanks to all for the advice. After hearing both schools of thought, I think the argument about spreading out the load by using epoxy to attach the Harpoint makes sense. I'm waiting on the CTI 54mm 6 grain case to come in--so I'll need to estimate the best spot to place it.

Grateful, and learning so much.
 
Thanks to all for the advice. After hearing both schools of thought, I think the argument about spreading out the load by using epoxy to attach the Harpoint makes sense. I'm waiting on the CTI 54mm 6 grain case to come in--so I'll need to estimate the best spot to place it.

Grateful, and learning so much.

CTI have drawings of all the cases on their site, with lengths for each as well to help remove the guesswork: https://www.pro38.com/drawings.php
 
I have used the hard points for years, never changed out the bolt, never drilled one for screws. Always just epox them in at the end of the motor tube. Never had a failure, never. They cost less than 20.00 each. I would never switch one from rocket to rocket. I have crashed rockets, cut out the hard point and used it on another build. BTW, I have put a hard point in a short 38mm tube, added cr's and a coupler. I glued the coupler into the airframe and I worked fine. For me, I try and not overthink something like this. JMHO Tim Thomas L3
 
Tim,

Great advice from an L3! I certainly am guilty as heck of overthinking nearly every aspect of this stuff. For my L1, I must have spent two hundred hours researching every aspect, working on the build, etc. After my certification flight was over, I remember thinking. "Good lord, I could have built this with wood glue in a few hours, and been done with this months ago."

Trying to do better on my L2 project, but still have that fear of making a mistake.

In the end, it's still just rocketry--and not really that different than the low power, mid-power stuff I've been doing for a lifetime.

I'm going to take your advice, and just build the darn rocket, without worrying myself to death in the process.
 
For motor retention, I'll be using an Aeropack Quick-Change that is attached with JB Weld directly to the aft end of the airframe.

Well, now you are no longer minimum diameter. How will you launch the rocket - tower, flyaway guides? The motor retainer cap (now the largest diameter on the rocket) may cause issues.

Since you are making an order to Giant Leap, consider the Slimline.
 
Sorry for the confusion. I have no desire to make this thing a true minimum diameter bird. It was chosen for strength of construction and survivability. The fiberglass airframe, and molded fiberglass fin can were what made it attractive as a platform.

I'll be using Acme Conformal Rail guides to launch the rocket. The Aeropack motor retainer is the widest element on the airframe but only by a little. The Slimline would be a better choice if I was going for the highest performance, but that really isn't a consideration.

To be honest, I wouldn't mind flying it with some ballast to keep the altitude down-and keep the rocket in sight. I've heard of people flying sand and even water as ballast but have no real idea how this works. Not much about it in High Power books either.
 
Les,
I have found out the hard way, don't overthink the small stuff. The hard point is a cool part. Well built and strong. If you can straighten out that eye, you have other things going on that are bad, very bad. For me, I love to build. I love to fly. Put a motor in that bad boy and 'Let'er eat'!! Always, have fun. The more flights you have, the more you learn. Tim
 
Les,

You sir are doing it right.
Your approach of being meticulous and asking questions of things that you aren't sure of is the correct way.
You will gain knowledge of HP quickly this way and have safe fun flights instead of dangerous confetti displays that those who do not do.
 
Why not use an Aero-Pac motor retention/with cap. [thought kit came with one?]
Glue it on rear of airframe.
Just slide in 54/38 adaptor & done.

Why do you need the hard point?

What do instructions say about recovery?
 
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This is what I do where needed on minimum:
Cost pennies. use scrap section of coupler..glass or phenolic. Cut another smaller section and remove a slice so it will fit inside. Glue recovery Y-harness between the 2.

Slide into position and either glue or use screws/rivets to hold in place...not through the coupler above it , so placement is easy & does not require finding holes. Just pull tight against the screw/removable rivet.
Locate just above longest motor you wish to fly.

DSCN5005.jpg DSCN5007.jpg

DSCN5009.jpg DSCN5013.jpg


Make simple 54/38 adapter with scrap of MM tube...only need a short section. Notch CR and glue recovery Y-harness to tube. Install and held in place with rear rail button screw [in my case] add 1 screw in yours, since using conformal guides.
You don't need tail cone, just 3 CR's /....one for airframe [thrust plate] and one fit inside for rear & 1 for front. [coupler 2]

This is fancy one with snap ring to hold motor in. [tape on lip, cause I friction fit to hold adapter in]

DSCN0293.jpg

Stupid simple one.
Insert motor, wrap a couple turns of masking tape in front, so motor can't come out.
Insert into airframe. Use 1 screw to hold in place.

I'm old school & just friction fit the whole adapter ...done this on M-motor size adapters.
This is my 38/29. don't have pics of large one.

DSCN5528.jpg DSCN5530.jpg

So there are a few of my way of doing it I have several more. Just think outside the darn box.
"It is rocket science" If you plan on moving up to L-2.
 
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