Loc-IV build question....fins to aft centering ring

[JeffofSpace]

Hi All!

This is my first post. I am about finished with my first MPR with much much help from trolling these forums...huge thanks to all for your expertise!



I attached fins without permanently securing the aft centering ring as suggested by so many on these forums...was able to get internal fillets on both the motor tube and inside body tube (after this photo). I am now ready to attach the aft cr, and am wondering if I should attach it 1/8th inch in on the motor mount as the instructions state? Or, should I push it up the extra 1/4 inch or so and make it butt up against the bottom of the fin tabs (and epoxy to the tabs)?

Further, I am using the mma-2 adapter (will do G80-7 for first flight), but the adapter makes the motor stick out an inch lower than the stock mount...do I need to worry about changes in cg or cp with the motor lower?

Huge thanks in advance!

 

[new2hpr]

Stick it to the tabs! For a bunch of additional protection, cut a short ring of 4" coupler stock and put it in the remaining space at the rear. It will significantly protect the aft part of the airframe.

Wish my LOC IV had 38mm and TTW fins! I have the old version with 29mm and surface mt. fins!

-Ken

 

[4kids49]

Further, I am using the mma-2 adapter (will do G80-7 for first flight), but the adapter makes the motor stick out an inch lower than the stock mount...do I need to worry about changes in cg or cp with the motor lower?

Huge thanks in advance!

Jeff,

The motor should not affect CP. The small motor does not weigh much and should not affect your CG by any significant amount. It is usually a good idea though to check the CG of your fully loaded up rocket, with chute, harness, motor and everything by finding balance point of rocket and checking against known CP or rocket.

Chris

 

[JeffofSpace]

Awesome, thanks Ken and Chris.

About that mma-2 adapter...should I make a retention system for that...between the adapter and the stock mount? I do not want to permanently glue it inside the 38mm mount, but it seems it could easily shoot out the tail end at ejection charge. I have a motor retainer on the mma-2 already.

 

[Kehoes23]

Further, I am using the mma-2 adapter (will do G80-7
I think that a 7 second delay will be a bit too long for this size kit, I would check it on roc sim or open rocket :2:

 

[JeffofSpace]

Thanks, Kehoes23...the G80-7 is one of the recommended first flight motors in Loc's instructions...was thinking 4 or 5 secs would be good, though. Will run a sim and see!

 

[new2hpr]

I've flown our LOC IV on an F60-4 (Roadrunner), so I think 5 seconds should be better than 7 with the G80. Especially if you've built at all heavy. Mine is really light with the surface mount fins, all wood glue except epoxy (with microballoons) fillets.

On the motor retention, depends on your budget. Masking tape works well if you do it right. Screws with t-nuts in the aft ring is more secure. And of course, Aeropacks are awesome!

Good luck!
-Ken

 

[Handeman]

I would use a couple 6-32 t-nuts in the aft CR. Put them in from the forward side before you install it. Use a spot of epoxy to make sure they don't come loose. I would then get a couple of 1" brass 6-32 round head screws and use that with clips to hold the motor in. Use smaller clips when using a 38mm motor and longer ones when using a 29mm with the adapter. The whole setup shouldn't cost you more then a couple of dollars.

 

[qquake2k]

I always put tee-nuts in my aft centering rings. For use with adapters, I make an aluminum plate.

 

[JeffofSpace]

Excellent! Thanks, All. I think I will do a modified version of the K clip thing like Handeman described...I already have the Estes retainer on the 29mm tube (quite slick looking for a few bucks!)...I like your solution though, qquake2k. Will be sure to post picks when I figure it out.

new2hpr, I did a pretty heavy build (epoxy throughout, metal eyebolt, etcetera)...but thrustcurve shows I should get near 1000 feet on the G80...will have to do a very careful dry weight sim when I have it all set up to double check. Thanks for the food for thought!

 

[4kids49]

new2hpr, I did a pretty heavy build (epoxy throughout, metal eyebolt, etcetera)...but thrustcurve shows I should get near 1000 feet on the G80...will have to do a very careful dry weight sim when I have it all set up to double check. Thanks for the food for thought!

I agree with new2hpr that a 7 sec delay is probably too long. I fly a Sumo and G-Force to 1000 ft or less, and use 4 sec. delays. My sumo has been repaired and is on the heavy side. Simulations have their purpose, but are only as good as what is inputed (correct weights etc.). Good luck though.

Chris

 

[JeffofSpace]

Big thanks for the input, Chris. I am now thinking I will try the quicker delay for the first flight. Any recommendations for brands for g80s? I have one of the Estes, which I understand to be Aerotech.

 

[JeffofSpace]

Well, got the aft centering ring on...and maybe a big flub in the process. I put t-nuts in the ring to set up a clip system to retain the motor mount adapter (as discussed above).......but,


You astute fellows should surely see that I glued the ring down with one of the t-nuts aligned with the fin. Thus not only will I need to drill a hole down into the fin tab, the t-nuts extend inward (hitting the tab) by a few millimeters from centering ring surface flush...the ring is now at a very slight angle. the shallow side is 4.5mm in from bottom, while the deep side is in 6mm. The motor mount is already centered from fore ring and the TTW fins.

How much should I worry....or not? Just paint and fly the thing!?

 

[awseiger]

You *should* be OK. We all have to learn somehow. Usually, I like to think of the rear centering ring as the most important structural part, but if you have a significant amount of epoxy on your TTW fin attachment and upper centering ring, you won't have a problem, especially with 38mm motors. Anyway, it doesn't look like you've glued it in yet. If you have, you should really consider a fillet around your inner tube and motor tube.

Also, alot of people put the flat part of the T-nut on the inside of the centering ring, so it's nearly impossible to rip out. The force on the T-nuts is tremendous during ejection, more than you'd think. For your case, you should be ok. If you're worried, try to find some threaded brass inserts, these work extremely well. I have seen them used to retrofit rockets built without a retention system.

So yep, the only thing I'm worried about from what I see is the Tee nuts pulling out on the retention. Other than that, I agree. Put a coat-o-paint on and get flying! Also, I must say your fillets look quite smooth from the rear pictures.

Also, if you're going to fly with a club, you may want to put some rail buttons on there as well. Flying with a G80 though, you won't really need them.

 

[terryg]

The biggest problem is the possibily of the the T-nuts pulling out with the ejection force. This what I would do in this situation. I would coat the thread of the screws that go into the T-nut with vaseline or other grease and screw them part way into the T-nuts. I would then apply a thin layer of epoxy covering all the centering ring and the T-nuts. The vaseline will prevent the epoxy from getting into the threads of the T-nuts. This would hold the T-nuts in position and as a side benefit protect the base of the rocket from splash back of the flame off the blast plate.

 

[qquake2k]

I put the tee-nuts on the wrong way once. I coated them with JB Weld, which is stronger than normal epoxy. They haven't pulled out yet. And these are the insert nuts that can be retrofitted to an existing centering ring:

https://www.woodcraft.com/product/2001048/3631/brass-threaded-inserts-632-10-pack.aspx

 

[qquake2k]

Doghouse Rocketry has the threaded inserts, and an installation tool (scroll to the bottom of the page):

https://doghouse.blastzone.org/DogHouseRocketry/Rail_Buttons.html

And a hints page:

https://doghouse.blastzone.org/DogH...2/5/10_Installing_Brass_Threaded_Inserts.html

 

[4kids49]

Big thanks for the input, Chris. I am now thinking I will try the quicker delay for the first flight. Any recommendations for brands for g80s? I have one of the Estes, which I understand to be Aerotech.

Great job on your build. I have only used Aerotech single use and reloads in G motors. I have never used the Estes, but they are probably good. I thought I saw that they were made by AT, not sure. One thing that I like to do is get real flight data on rockets, when possible, from rocketreviews.com For something popular like the LOC IV, it is easy to get a lot of info. on what motors and delays people use. You can get a good idea on altitudes also. People don't always have a lot of alt. data for midpower rockets, but list the motor and delay. Usually they will report if something does not work. That is very valuable stuff to know before you launch yours for the first time. I have had a few adventures on first launches! Good luck with your rocket.

Chris

 

[JeffofSpace]

Thanks! Yeah, the tube is definitely still straight...I put the loaded adapter in and it slid in just as easily as it did before the aft ring was glued down. Just got the exterior epoxy on...should help with the t-nuts as well (they are also epoxied into their holes and under the flange. May do a cake of JB though, thanks again qquake2k.


I used Carpenters Wood Filler instead Bondo glaze putty for the fillets...this being my first attempt at fillets (beyond wood glue on LPR 15 years ago!), I knew I would need to get my fingers way into it...plus toxicity is an issue in the living room! Also, they are pretty much pure aero-aesthetic because the fins are internally super secure. I did one thicker coat, sanded, then a bit watered down coating for final layer, then sanded again.

Will definitely secure a shorter delay motor...I was having an issue finding stuff last week (again, new to anything above Estes "E" power). Had trouble because I ordered the kit from hobbylinc and they don't have a large motor selection...though they do have an Aerotech G80-4, but they indicate the need for the copperhead igniters (which they don't carry). I have some of the Estes sonic igniters...debating returning those and finding the motor and copperheads in one place elsewhere. Hoping to find a good source without crazy shipping costs.

 

[4kids49]

Will definitely secure a shorter delay motor...I was having an issue finding stuff last week (again, new to anything above Estes "E" power). Had trouble because I ordered the kit from hobbylinc and they don't have a large motor selection...though they do have an Aerotech G80-4, but they indicate the need for the copperhead igniters (which they don't carry). I have some of the Estes sonic igniters...debating returning those and finding the motor and copperheads in one place elsewhere. Hoping to find a good source without crazy shipping costs.

I am pretty sure that Copperheads are being phased out. I never used them. I use First Fire Jr. by Aerotech. I use Hobbylinc for G's myself, but go with what they carry. They don't carry all of the nice AT single use and reloads there. I use G77-4R (Redline), G78-4G (Mojave Green) in single use, and G76-4G and G64-4W (White Lightning) in the reloads for 29/40-120 AT motor that Hobbylinc carry. The reloads are pretty affordable. The 29/40-120 is pretty cheap from Hobbylinc. The issue for me is that I need several motors to make several launches. I don't have time at a launch to clean and reload a motor. I have two 29/40-120 motors and bring single use with me. All of the motors say HAZMAT, but I don't remember Hobbylinc charging me the fee. Maybe this has changed. You might be able to buy motors onsite at a launch with out the Hazmat, but won't get much of a discount on the motor. Best of luck.

Chris

 

[qquake2k]

I am pretty sure that Copperheads are being phased out. I never used them. I use First Fire Jr. by Aerotech. I use Hobbylinc for G's myself, but go with what they carry. They don't carry all of the nice AT single use and reloads there. I use G77-4R (Redline), G78-4G (Mojave Green) in single use, and G76-4G and G64-4W (White Lightning) in the reloads for 29/40-120 AT motor that Hobbylinc carry. The reloads are pretty affordable. The 29/40-120 is pretty cheap from Hobbylinc. The issue for me is that I need several motors to make several launches. I don't have time at a launch to clean and reload a motor. I have two 29/40-120 motors and bring single use with me. All of the motors say HAZMAT, but I don't remember Hobbylinc charging me the fee. Maybe this has changed. You might be able to buy motors onsite at a launch with out the Hazmat, but won't get much of a discount on the motor. Best of luck.

Chris

When Hobbylinc says "hazmat", it just means it can't ship via air.

 

[4kids49]

When Hobbylinc says "hazmat", it just means it can't ship via air.

Thanks Captain. Good to know.

 

[qquake2k]

Thanks Captain. Good to know.

Hobbylinc doesn't sell any motors big enough to require the separate hazmat fee.

 

[4kids49]

Hobbylinc doesn't sell any motors big enough to require the separate hazmat fee.

I do remember the slow delivery, but that can be managed. I have bought a lot of low and mid power rockets, and B, C, E, G, motors from Hobbylinc.

 

[qquake2k]

I do remember the slow delivery, but that can be managed. I have bought a lot of low and mid power rockets, and B, C, E, G, motors from Hobbylinc.

It's weird, sometimes motors take forever to get here from Hobbylinc, and other times they get here in 3 days. They always come surface mail, so I'm not sure what causes the difference. I buy almost all of my mid power motors from them, but lately I haven't been flying much MPR. We have an onsite vendor now, that sells high power. Much to the chagrin of my wallet!

 

[terryg]

Not true anymore unfortunately. F52 F40 F22 reloads and some single use engines all require hazmat shipping due the the size of the grains. Anything listed in the reloadable medium section requires a separate hazmat fee.

 

[qquake2k]

Not true anymore unfortunately. F52 F40 F22 reloads and some single use engines all require hazmat shipping due the the size of the grains. Anything listed in the reloadable medium section requires a separate hazmat fee.

Well that sucks. I haven't bought any F's in quite some time, mostly G53's, G64's, and G76's.

 

[4kids49]

It's weird, sometimes motors take forever to get here from Hobbylinc, and other times they get here in 3 days. They always come surface mail, so I'm not sure what causes the difference. I buy almost all of my mid power motors from them, but lately I haven't been flying much MPR. We have an onsite vendor now, that sells high power. Much to the chagrin of my wallet!

I just noticed you are in Northern CA. Where do you fly? I am also a NoCal. I used to fly a lot of MPR, but our LUNAR launches have become so popular that it is hard to get two flights per person in a day. I used to be able to go up with three sons and get 14 plus launches. Loving the hpr thing (except for the wallet). Tough for me to get to many launches though.

Chris

 

[qquake2k]

I just noticed you are in Northern CA. Where do you fly? I am also a NoCal. I used to fly a lot of MPR, but our LUNAR launches have become so popular that it is hard to get two flights per person in a day. I used to be able to go up with three sons and get 14 plus launches. Loving the hpr thing (except for the wallet). Tough for me to get to many launches though.

Chris

I fly with LUNAR and SARG. SARG's launchsite is in Roseville out near the casino. The SARG launches aren't usually as busy as LUNAR, but we don't have as many pads, either. You should come out sometime. They cancelled the launch this month because of fire danger, so the next launch won't be until October or November.

https://www.sargrocket.org/

 

[4kids49]

I fly with LUNAR and SARG. SARG's launchsite is in Roseville out near the casino. The SARG launches aren't usually as busy as LUNAR, but we don't have as many pads, either. You should come out sometime. They cancelled the launch this month because of fire danger, so the next launch won't be until October or November.

https://www.sargrocket.org/

Cool, thanks. I will have to check them out. I fly hpr with TCC and low mid power with LUNAR. TCC usually cancels hpr launches in my launch window. LUNAR cancels a number of hpr flights due to either fire season or rain season in my launch window. I have schedule conflicts with most of the rest of the LUNAR hpr schedule. So I definitely have a need for more launches that I could get to.

Chris