Help with the Photon (LOC/Precision)

[Renaissance Man]

I am starting on my first ever non-Estes build. I went with the Photon (mostly because of the looks). I know this is an extremely basic build/instruction - but I cannot for the life of me figure out what the directions (see attached photo) are talking about with regards to the yellow cord and the eye ring. I even had my wife/brother also read it to make sure I haven't lost my mind.

I really appreciate any help and please feel free to explain it to me like I am 5!

 

[gdjsky01]

Okay I am not sure but here goes
So you have some cord.
Pick it up at the halfway point

Now make an overhand knot making a 1 inch loop at that halfway point.
Now you have a 1 inch loop at the halfway point. About a foot on one side, and a foot on the other, with the loop in the middle. Presumably the chute will attach to the loop. Well looking at the images you use the loop to secure it to the eyebolt. Which is weird because now you have a doubled up 1' SC. '1 is a really short cord. Or is there more SC?

Still per instructions... On each loose end. Just tie a single overhand knot and rub some glue in the knot.

Why the two knots, one on each end? I am not sure. I hope the instructions make the clear later on.

Estes can afford to spend $$$$ on a dedicated illustrator and tech writer. LOC I would 'guess' can not.

I'd do none of that, based on my limited knowledge of the kit.

I'd tie the cord to the eyebolt one end. The other to the nose cone or payload section, and make an overhand knot about 1/3 the way down from the top to attach the chute to.

However I am also for the most part, read and follow the instructions.

 

[kuririn]

You can secure the doubled up kevlar to the eye bolt with any knot you like. Some people swear by certain types of knots. But I think this is what the instructions are saying, in pics:
1.


2.


3.


4.


5.


The glue is to keep the end knots from unknotting and the end knots are to keep the cord from pulling through.
You may also want to put some glue on the ends of the cord then trim to prevent fraying.
PS: You may find it easier to attach the kevlar to the eye bolt before attaching the eye bolt to the motor mount.
PPS: Use yellow or white glue, never CA, as it will make the kevlar brittle.

 

[gdjsky01]

This ^^^^^^^^
Ignore me

(Tho I NEVER would have guessed that reading and looking the instructions online)

 

[Renaissance Man]

Really appreciate the replies! I also would never have guessed that is what they wanted me to do!

It seems weird to create this loop on top of the motor mount before fixing the motor mount inside of the body tube.

 

[waltr]

I've build a number of LOC kits and after reading the instructions then go and do it my way.

I do not like fully securing the Kevlar to the eye screw at the CR. What I do instead is pass the Kevlar through the eye screw and then tie the two ends of the Kevlar together. This makes one large loop through the eye screw and up to the top of the BT. This allows pulling the Kevlar around to inspect and also allows a new piece of Kevlar to be installed.

Also be sure to epoxy the eye screw onto the CR.

 

[gdjsky01]

The OP did say this was their first non-Estes kit. Tho I am not enamoured with Estes instruction that are virtually nothing but illustrations, they are way more comprehensive than most other kits. Flis was good. Rocketarium is good. Apogee is good. Semroc is good. But many others, especially HPR kits assume you already know what you are doing, and as @waltr said, will do it your way. Again, I'd have never gotten that from the instructions I read on the LOC site. Good luck and send us pictures of the build!

 

[Renaissance Man]

Ok, I have re-created the knot and set-up shown to me by kuririn above - see attached photo. I really appreciate you-all's input. I will share progress as I go - but I am slow moving given my inexperience and also child (picked up this hobby again about 9 months ago when I was going stir crazy with a young one).

I still don't really understand creating this set-up prior to even putting the motor mount into the body tube...Seems like the kevlar loop might be hard to access after its epoxied into place.

 

[kuririn]

I read the full Photon instructions. The 2 ft. long kevlar is the leader attached to the motor mount. There should also be a 6 ft. long length of kevlar to act as the shock cord. So plan accordingly. If the leader is doubled up then it is less than 12 in. long, so you may want to attach the shock cord to the leader before gluing in the motor mount.
PS Don't forget the knot to make the loop at the other end of the leader. I think the reason LOC doubles it up this way is so that if one side breaks the leader will still work with the remaining single cord.

 

[gdjsky01]

Presumably you won't have to replace it for quite a while. Though you could get a protector... I tend to lose/retire rockets before the recovery need replacement.

 

[kuririn]

I still don't really understand creating this set-up prior to even putting the motor mount into the body tube.

How are you going to tie on the kevlar leader if your motor mount is already glued in place?

Seems like the kevlar loop might be hard to access after its epoxied into place.

Built according to the instructions, it is permanent and inaccessible.
There are methods for making the kevlar replaceable, like waltr posted above.

 

[Renaissance Man]

I read the full Photon instructions. The 2 ft. long kevlar is the leader attached to the motor mount. There should also be a 6 ft. long length of kevlar to act as the shock cord. So plan accordingly. If the leader is doubled up then it is less than 12 in. long, so you may want to attach the shock cord to the leader before gluing in the motor mount.

There is a 6 foot length of kevlar in the kit as well! I guess I just don't understand why there are two different lengths/widths of kevlar when it would seem simpler to just make a single 7-9 foot length of kevlar to act as the shock cord and attach directly from the eye bolt on the MM to the parachute and nose cone.

 

[waltr]

Even on kits with a single piece of shock cord I do a Loop to the motor mount's eye bolt the extends a few inches above the booster section BT. This loop part is replaceable since this part takes much the the ejection charge heat.

I do not agree with LOC on how they show to attach it to the eye screw.
Also, 6 feet on Kevlar seems to be on the short side of a minimum of 3:1 total rocket length.

 

[bjphoenix]

I was going to rejuvenate an old rocket recently so I taped a hobby knife to a long stick and used it to cut out the old shock cord. I used a couple of thin sticks and a few pieces of wire to feed the old shock cord down into the tube and through the screw eye.
Many years ago I was building a 2.6" diameter rocket and thinking about how I was going to feed the shock cord down into the tube and through the screw eye. My daughter was watching and she grabbed one end of the cord, stuck her hand down the tube and put the cord through the screw eye.

 

[Renaissance Man]

A quick photo update about the Photon build! I have the motor mount in place, fins in place, internal and external fillets applied, and purchased a motor retainer to place against the aft CR. You can even see the kevlar loop attached to the shock cord.

With the photos comes more basic questions...like: what prevents the motor from ejecting itself forward into the body tube of the rocket after ignition? This kit does not have a motor retaining ring inside of the motor mount like the Estes kits I have built.

 

[kuririn]

With the photos comes more basic questions...like: what prevents the motor from ejecting itself forward into the body tube of the rocket after ignition? This kit does not have a motor retaining ring inside of the motor mount like the Estes kits I have built.

There is no forward thrust ring in most mid power rockets so that you can use different lengths of motor casings. There is a flange molded into the back of most composite motors that acts as a rear thrust ring. On black powder motors there is no rear thrust ring so you have to add one on with 1/4" masking tape.
Top: Composite motor with molded flange (rear thrust ring)
Bottom: Black powder motor with masking tape wrap on rear end

 

[techrat]

I am also building the LOC Photon and also noticed that. At first, I considered building in a thrust ring and then said "screw it". I'll just use composite motors in this guy. All the plastic motors have the thrust ring built-in. Soak the end of the 24mm tube with some CA to make it nice and stiff, and when it's dry it will take whatever those 24mm composites have to give. FYI: I found the tail of the rocket to be heavy, so I added a little nose weight to balance it out. It should fly nicely when I'm done.

 

[waltr]

Yes, and all the Re-loadable cases have rear thrust rings.
One you start using this system you will not want to go back to the Estes method.

 

[Renaissance Man]

FYI: I found the tail of the rocket to be heavy, so I added a little nose weight to balance it out. It should fly nicely when I'm done.

Going to keep asking noob questions...

1. How did you do calculations to figure this out or just have enough experience to know it was heavy in the rear? How did you "add a little nose weight"?

2. Are you using the launch lug or the rail guides? There are no instructions for the latter so I am almost certainly going with launch lug. I don't understand why I have to cut it though and can't leave it as a single tube?

3. What composite motor are you considering using with it?

Thanks!!

 

[kuririn]

1. How did you do calculations to figure this out or just have enough experience to know it was heavy in the rear? How did you "add a little nose weight"?

On the Loc webpage for the Photon there is a link labelled "Rocksim". Download the file and unzip it. Then download either Rocksim ($125) or Open Rocket (free). Open Rocket will run Rocksim files. They are simulation software programs that will show you a number of important parameters on your rocket, such as center of pressure, center of gravity with certain motors, speed off the rod/rail, optimum delay time, etc.
If you load a motor and the CG is too close to the CP (or worse, behind it) then it will be unstable and you will have to add nose weight. Usually done by epoxying lead sinkers or bbs into the nose tip. If your nose cone is polypropelene then epoxy will not stick to it. Then I use expanding foam.

2. Are you using the launch lug or the rail guides? There are no instructions for the latter so I am almost certainly going with launch lug. I don't understand why I have to cut it though and can't leave it as a single tube?

You can use either one or both. For this little guy lugs are sufficient. The advantage of rail buttons is that a rail is stiffer than a rod and is not subject to "rod whip".
Cutting the longer lug into two smaller ones and gluing them farther apart will more effectively reduce the torque of the rocket around the rod. Like one really long launch lug. Not really needed for this little guy IMHO.

3. What composite motor are you considering using with it?

Play around with OR or RS and see what motors work. You want a motor that has enough speed off the rod to be stable, with a delay close to the optimum, and an apogee that fits your flying field. That's the beauty of these sim programs. You can try different motors without actually burning them up. And it's fun!

Going to keep asking noob questions...

A wise man once said that the only dumb question is the one that is not asked.

 

[techrat]

1. How did you do calculations to figure this out or just have enough experience to know it was heavy in the rear? How did you "add a little nose weight"?

2. Are you using the launch lug or the rail guides? There are no instructions for the latter so I am almost certainly going with launch lug. I don't understand why I have to cut it though and can't leave it as a single tube?

3. What composite motor are you considering using with it?

#1) I held it in my hand and it felt rear-heavy. If it's that bad with no motor, it'll be much worse with one. I'll give it a swing test before I fly it, but judging from how it feels versus my other rockets, I can just tell. I cut a little slot in the nose, added some steel BB's and then used Gorilla glue. Once that dried, I sealed up the slot with the original plastic and some Testors plastic glue.

#2) Launch Lug. Why mess with success?

#3) Any Quest Q-Jet, Like an E-26 should be enough to make things work. The rocket is 165grams right now (but unpainted), so, still lighter than my Big Daddy, any Q-Jet in "E" for 24mm will work fine.

 

[kuririn]

I ran the Photon Rocksim file from the Loc website using Open Rocket.
Here's a screenshot.

Simmed with three different motors.
Estes D12-5
730' apogee
5.08 sec. optimum delay (very close to motor delay)

Estes E12-6
1185' apogee
5.95 sec. optimum delay (again very close)

Aerotech E20-7
1442' apogee
6.55 sec. optimum delay (close again, I think this motor only comes in a 4 or 7 sec. delay)

BUT...............
Notice that there is no nose weight in the nose cone.
And the calibers of stability for each sim with motor loaded are all less than 1.0.
(Caliber of stability = distance between CG and CP / diameter of airframe).
So you would have to add some nose weight to fly stable.
So pick the heaviest motor you intend to fly and add enough nose weight to achieve a safe caliber of stability. I like to shoot for 1.5 or higher.
And of course, the added weight will change the values in the sim (lower apogee, shorter optimum delay, slower speed off the rod, etc.).
Have fun!

 

[waltr]

Now that you have the OR sim you have the location of the CP. I like to mark this on the rocket after painting. A small dot and circle in line with the launch lug is a good place. Then at a club launch you can show the RSO the CP and CG is easy to find to ensure them the rocket is stable.

 

[Back_at_it]

Verify the weight of the components in your rocket. The sim has the nose cone listed at 1.60oz. Mine was actually actually much lighter. I also changed up the motor mount and moved the upper ring to the top to the motor tube. Internals fillets were also added which added more weight on the rear so by the time I was done my CG was right at the CP.

I added .60oz (17 grams) to get to CG up to about 17.5 or 1.09cal. with an E12-6 in the tale. I can tell you that it flies great on the E12-6 with this .60oz of nose weight.

I actually have another one I need to build for a friend in the hobby (he prefers to fly over build). Was thinking on doing a build thread on it.

 

[Renaissance Man]

Ok, I have been messing around with OpenRocket for the last week or so (and have changed some of the default colors) and have found it super useful if a bit buggy (but also free! - so no worries). I loaded the Rocksim file from the LOC site and then made several edits as I found that there were a few inaccuracies. The calculated weight of the rocket without a motor is 165 grams. Currently my completed rocket (prior to being primed and painted) is 170 grams - so at least it is fairly close? I unfortunately did not weigh each component prior to starting the build.

Here is a screenshot with simulation findings with the biggest motor I can imagine flying with it: Aerotech F32T-6



I figure I need to add a bit of weight to the nosecone, but want to do it in an easy fashion. Any thoughts?

 

[Back_at_it]

Ok, I have been messing around with OpenRocket for the last week or so (and have changed some of the default colors) and have found it super useful if a bit buggy (but also free! - so no worries). I loaded the Rocksim file from the LOC site and then made several edits as I found that there were a few inaccuracies. The calculated weight of the rocket without a motor is 165 grams. Currently my completed rocket (prior to being primed and painted) is 170 grams - so at least it is fairly close? I unfortunately did not weigh each component prior to starting the build.

Here is a screenshot with simulation findings with the biggest motor I can imagine flying with it: Aerotech F32T-6

View attachment 551897

I figure I need to add a bit of weight to the nosecone, but want to do it in an easy fashion. Any thoughts?

Once the rocket is completed. Primed, Painted etc. Put the largest motor you plan to fly in it then check the CG then compare that to the sim. You are showing the CG at 45.3cm with a 94cal which is fine. If you want to add nose weight, the easiest way I have found is to add BB's, lead fishing weights or other small objects inside the nose cone. I've seen people use nuts, washers, small screws etc. then hold them in place with epoxy.

 

[Renaissance Man]

Alright team...next questions regarding issues with instructions again (step 5 & 6 as shown in screen-shot below).

1. LOC directions have the END of the shock cord being attached to the parachute and the nose cone being attached proximal to that, is that standard way of doing it? Remember I am used to Estes where nose cone serves as attachment site for the parachute AND the shock cord.

2. I have included some pictures of the green parachute and the orange shute protector. The directions never even mention the parachute protector at all....where does this piece of the recovery system fit in?!

3. How does one tie shroud lines to the nylon parachute? Is it really this "anchor hitch knot"? Won't tying the shroud lines like this cause the piece of the parachute from the hole to the outer diameter be folded awkwardly (see last picture with my high tech annotation)?

Thank you all so much for all the guidance. I probably should have gotten a kit that holds my hand a bit more to start after just doing Estes.

 

[techrat]

The orange do-hickey is the Nomex chute protector. Think of it as re-usable recovery wadding. Slide it over the shock cord (should be a slit to do that). When you are going to launch, throw in a couple of pieces of wadding and/or dog barf. When you bundle the chute, wrap the nomex blanket around the chute like a burrito. This will protect the chute from the ejection gasses. It can be re-used again and again. Because of it, you don't need as much wadding, but still use some to protect the shock cord.

You can attach the chute to the nosecone like any Estes rocket. You can use any knot you like, as long as it works. And yes, it'll bunch up the end of the chute where you tie the knot. That's life. Or you can substitute an Estes plastic chute if that makes your life easier. Remember, parts is parts, mix and match, make it your own.

 

[kuririn]

1. LOC directions have the END of the shock cord being attached to the parachute and the nose cone being attached proximal to that, is that standard way of doing it?

There is a thread recently that discusses that very issue:

Questions during my build LOC IV LOC Precision

Ok, i have started the build and im sorta stuck on this whole parachute assembly. The instructions are kind of typed strange so im not sure what they mean: "Attach shock cord to forward ring eye bolt. Pass loop through eye bolt, then pass shock cord through it’s own loop as shown. Don’t get any...

www.rocketryforum.com

The Loc method in the instructions is not the way most of us do it, but I believe it will work. Personally, I would attach the end of the shock cord to the nose cone, tie a loop in the shock cord about a third of the way down from the nose cone, and attach the chute to that loop. This does two things: Removes the plastic loop on the nose cone as the chute connecting point. The loop is a frequent point of failure. And by separating the chute a further distance from the nose cone it helps to prevent tangles in the shroud lines from the nose cone weaving in and out. Some people drill two holes in the base of the nose cone and fish the shock cord through them and tie it on. instead of using the plastic loop.

2. I have included some pictures of the green parachute and the orange shute protector. The directions never even mention the parachute protector at all....where does this piece of the recovery system fit in?!

The shock cord threads through the buttonhole of the chute protector. Parachute is above.
I don't think the protector they give you in the kit is big enough to wrap your chute in. So just cup your chute into the protector and slide it into the airframe. Some people add a little bit of wadding for insurance.

3. How does one tie shroud lines to the nylon parachute? Is it really this "anchor hitch knot"?

Again, you can do it like the instructions, it will work. Personally I tie a looped knot like the Estes chutes. Optional drop of glue to prevent unravelling. All kinds of fancy knots, people have their favorites. More than one way to skin a cat.