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Estes SR71 3 cluster motor build. D12-5 and two C6-5

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mjstech

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I am just about ready to attach my 3/16 launch lug(s). I am unsure where to put it/them due to the extra motor weight. They will be installed on the 'bottom' of the rocket. I have not added the pat of clay yet. The fins are filleted many times with white glue. The paper near nose has been CA wicked. The D main will be hooked while the two C motors will be friction held with the plan of them blasting out after the delay. The two C motors have been centered with 18mm motor mounts and have the top half of the motor hook to prevent blowthrough. In these I will add a bunch of wadding to prevent the cones from burning. The cones have also been heavily superglued to the tubes to prevent them from poping off. I added a very thin layer of filler/primer that has been sanded where the body tube is under the wrap and near nose to remove any/all bumps. I plan on a full light prime and sand, gloss black, attach decals, and then flat clear.
The D12-5 has a peak thrust just under 30N and a burn time of ~1.65s the C6-5s will have a peak thrust of just over 15N each and a burn time of ~1.86s.
This is topside

This is rear angled with motors. You can see motor hook, fillets/primed topside

Here is the business end of the rocket

And one last of the rear with no motors.
 
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Gillard

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looks nice - don't fly it in anything other than a calm day, and have plenty of room.
i would recommend changing the C6-5s for C6-3s or C6-0, as with the C6-5, the C will eject after the D has deployed the parachute, and ideally you want the C to eject before.
 

Evo666

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Looking good. Can't wait for the flight pics
 

mjstech

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I plan on only flying with little/no wind, next meeting is 1/9/10. I do have C6-3's also, so I will fly with those. I will see if others in my rocket group can help take pictures or video of this for sure.
 

Verna

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YOW! :y: Questions, questions, questions.

This kit requires weight for the nc when building for a single engine. How much additional weight have you added to the nc to keep cp/cg correct?

On the D core engine; a D engine has a lot of ejection for the limited space allowed with the Estes SR-71. The stock ejection cord and plastic chute won't cut it. What kind of wadding will you be using? Not enough room for dog barf and the chute. What kind of and chute? Mylar I hope. What size chute? 10"? Shock cord needs to be kevlar. Lots of fire in a small diameter will fry the standard recovery system on this one. Before you go out to fly test pack about 8-10 sheets of wadding the chute and noce cone to make sure they'll all fit. Less than that and it's toast.

If it holds together and it might, if it goes mostly straight up you'll get about 1000'. Even though it's heavy and draggy you'll still need a large area to recover. Winds less than 5 mph!

On the nacells, friction fit is fine but you need to use boosters only, B6-0 or C6-0's and drill 2, 1/8th" vent holes right behind the cones on opposite sides.

You'll also need a 3/16ths lug and a 4' rod on a heavy base pad.

What are you using for power?

Good luck!

Verna
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dragon_rider10

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Whatever you do, make sure there are NO SOCCER GAMES anywhere within a 2 mile radius.:blush:
(and don't angle the rod at all)
 
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mjstech

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I am not sure how much clay to add to the nose. I haven't added anything yet. I dont have a scale to measure. Currently with D12-5 and C6-5s/C6-3s the CG is (by balancing it on a pen) it is just about at the joint of the two pieces wood on the nacells. This is one reason I don't know where to attach the 3/16" lug. What is optimal, 1x1", 1x2" 2x1"?
I am not sure which chute to use as stock came with an 18" plastic. Will a 10" be enough? I was thinking a 12" thin mil nylon (Top Flight Recovery) or 12" mylar (Starlight Model Rocketry). It's ok if it's a long walk.
The shock cord will be 140lb strength. (I'm not sure how long time make it, but will probably be ~30")
I plan on a 3"x3" firewall parachute protector (Top Flight Recovery) along with a little bit of dog barf and a bunch of estes recovery wadding sheets.
I plan it staying together with the amount of thick CA and going over the fillets 8-10 times with white glue. I am hoping that it will go higher than 1000' even with the extra motor/nose weight. Up to 600' is off a single C6. This will be 2x C and a D pushing it. I can't seem to find a rocksim file for it so I don't know.
I will have a very large area to recover... Rainbow Valley, Arizona (lots of flat desert with nothing around). I plan on only flying with little/no wind (early morning).
I have some C6-0s that are for multi-stage rockets. If it is important to only use booster C's I will get them. I was thinking the delay may help keep it more stable while it is still climbing. Hence why I was planning D12-5/C6-5. I will make the small vent holes wicked with CA to relieve the negative pressure at blowout on the narcells.
I may use my Estes pad weighted down with stock 3/16 rod, but if someone has a longer one I will use that.
For the igniters I plan on testing the resistance of them and use ones with similar readings. The 'power' I plan on borrowing a high Voltage/Amp remote (12V car battery fused) launcher get all 3 motors off.
 
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Verna

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>I don't have a scale to measure.

You will need a scale accurate to 1/10th oz. but all you need to do on something like this weigh the additional parts and add only that much. These projects are fairly easy, just build as the directions say but in this case substituting parts as needed to account for the factors already discussed. You want 2 lugs where the instructions say to put them, one about 1" behind the nc and the other at the end of the main bt.l

>I am not sure which chute to use as stock came with an 18" plastic. It's ok if it's a long walk.

Ok on the walk but I was thinking about getting the recovery system in there with the nc on correctly. I'd go with the Top Flight 12" mylar (Starlight Model Rocketry). I just don't think you can get more than that in there loose enough to deploy.

>The shock cord will be 140lb strength. (I'm not sure how long time make it, but will probably be ~30")

Sounds good.

>I plan on a 3"x3" firewall parachute protector (Top Flight Recovery) along with a little bit of dog barf and a bunch of Estes recovery wadding sheets.

If a test fit allows it all, go for it.

>I will have a very large area to recover... Rainbow Valley, Arizona

I'm jealous of that!

> I have some C6-0s that are for multi-stage rockets. If it is important to only use booster C's I will get them.

Do that, you really need the boosters, only. Ejections will fry the an cell cones and most likely split the tubes too even if they kick out. Friction fit them only to the point of staying in for launch. The burn through of the boosters will kick them out with no problem.

>The 'power' I plan on borrowing a high Voltage/Amp remote (12V car battery fused) launcher get all 3 motors off

Sounds good to me! Get some photos.

Verna
www.vernarockets.com
 

mjstech

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in the stock location would you recommend 2x 1" 3/16 lugs then?
thanks for your help on this also.
 

mjstech

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Thanks, I just wish my finishing(paint) skills were as good. I just need to take my time with paint and not over do it in one coat.
 

Peartree

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Just a warning from Micromeister's experience in clustering this rocket. The two C's are enough to fly this bird even if the center motor does not ignite. Unfortunately, only the center motor deploys the recovery system. If the center motor fails to ignite...


well, you get the idea.
 

mjstech

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Yeah, I hope to get all 3 going. I did see another post somewhere about a duct made under the paper on the nacells to have those allow for recovery. I think that person was flying with 2 motors. If I do make another one of these I may try that.
 

mjstech

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I am currently attaching the 2x 1" 3/16" lugs in the stock location with thick CA, then CA fillets. I'll then white glue finish fillets. It looks like I got them plumb. I'll get some pics when it is dry enough.
 

Micromeister

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Yeap! It may be a little late for your current build, but I've learned that it's a much better set-up to vent the two pod C6-7's into the core BT-50 through fabricated 1/8" x 3/16" brass rectangles soldered into a flat vent added to the center section of the balsa standoffs. works like a champ and haven't crashed another SR-71 since. I've litterally warnout 3 or 4 models since without a single crash. Have to admit I haven't used a D12 core as 3- C6's puts the model close to out-of-sight and made for some very long hikes to get it back:)

SR-71-e1-sm_FS 3-32 x 3-16th ducts 160dpi_01-07.jpg


SR-71-e2_Ducting parts FS 300dpi_04-02-96.jpg


013-sm_SR-71 Blackbird 3C+_03-10-88.jpg
 

GregGleason

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John,

Oh no!

That was a very sad end to a very nice Blackbird.

Do you think something like monofilament line or cotton thread on the center motor's nozzle as a "hold down" point, where it would not launch unless it burns through the line, would be a future solution for this kind of cluster?

BTW, when I was in the USAF, an SR-71 did a slow speed fly by over the runway of the base. It put one engine in AB then back out, and then repeated it for the other engine. Each afterburner flame was as long as the aircraft, with visible Mach diamonds. :cool:

Greg
 

mjstech

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Now those are the pics I saw! Awsome build. My b-day is 4/2, which is why I sorta remembered also. 1988/1996, sheesh, I got into rockets with my dad in 92/93 when I was 11 or 12.
On your 'death of a SR-71' was that before you added vents to the kits?
I didn't add the steel heat disks, I will load up a bunch of wadding in the nacells. I am hoping that with friction fit on my C6-0s fit they will self eject. The intake cones have a bunch of CA holding them also.
You listed the stock nose as 15g, and in another pic you list that you added 30.4g. How did you come up with that conclusion if you remember.
Do you remember which rod you used to use? What about getting all three motors to fire? What about your chute, what size/type was it?
I know it's going to be a long walk with D and 2xC. Luckly we launch in the desert with nothing around, and in the mornings there is no wind.
For my first launch I may just run a D and see how it goes.
If I build another one of these I will probably make it 3xC and will add the vents.
 
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Micromeister

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Now those are the pics I saw! Awsome build. My b-day is 4/2, which is why I sorta remembered also. 1988/1996, sheesh, I got into rockets with my dad in 92/93 when I was 11 or 12.
On your 'death of a SR-71' was that before you added vents to the kits?
I didn't add the steel heat disks, I will load up a bunch of wadding in the nacells. I am hoping that with friction fit on my C6-0s fit they will self eject. The intake cones have a bunch of CA holding them also.
You listed the stock nose as 15g, and in another pic you list that you added 30.4g. How did you come up with that conclusion if you remember.
Do you remember which rod you used to use? What about getting all three motors to fire? What about your chute, what size/type was it?
I know it's going to be a long walk with D and 2xC. Luckly we launch in the desert with nothing around, and in the mornings there is no wind.
For my first launch I may just run a D and see how it goes.
If I build another one of these I will probably make it 3xC and will add the vents.
The Death of an SR-71 was before adding the pod venting. it was my First Clustered SR-71. I'm now on my 4th. 2 & 3 were litterally warn out by flying. #2 logged 23 flights, burned thru the main body tube at several places on her last flight. #3 logged 27 flights. I reinforece the area around the vents toward the front with Medium CA during construction which seems to help on this model the main motor mount burned thur the BT-50 and shroud..... Guess Nothing lasts forever with that much after burn LOL!!!!
#4 only has a few flights, and was reinforced in the motor mount area with CA as well.
Yes NO matter how tightly you friction fit the pod C's they will Self Eject at burn thru. B6-0's do as well:)

To return the models CG to it's original postion I added nose weigh that was equal to ALL the added materials, rings, discs, vents etc. and 1/2 the Max. extra motor weight, In my case the mass of a single C6-7, you'll need to add the extra mass difference between C6-5 and D12-5 or 7 as well. Over all for my model these added up to 30.4g. Each of my altered Clustered SR-71's has varied a bit in E-weight because of variences in epoxy used, and other material masses. I feel it is important to get accurate weights of everything before assembly so our added mass numbers comes out correctly. So far each of my 4 have been vary stable in flight even on the windest of days, showing very little of the weathercocking we hear so much about with the unaltered model.

My models have all flown from 1/8" x 36" stainless rods. This model leaves the rod Very fast, I have not had any problem with rod whip or tip off on any flight.

Believe it or not I alway use the Stock 18" Estes plastic chute with my SR-71's I do substitute my own trim monokote silver tape discs for the supplied discs and tie an overhand knot in the end of each shroud line about 1/2" for the end, which is coiled around the disc in a half loop then burnished down under the tape disc with a round end tool to the canopy. As the motor extends well below the wing/fins on this model it takes any part of a hard landing. but the 18" chute seems to bring them down at a gentle enough rate to prevent damage.

Getting all three motors to light is generally not a problem as I ALWAYS use a relay ignition system with a HD 26amp/hr Gelcell at the launcher. Remember the rule of thumb is still 2amps/igniter even with the new Quest Q2g2 igniters. It is also wise to use the heaviest/shortest clip-leads you can manage. May I suggest down loading Tech-Tip 006 "Clustering BP motors" from the Library section of narhams.org. I wrote this tech-tip to answer many of the clustering questions you've just ask. This Tech-Tip will help explain what has to happen in that first split second to make all these things work. The Death of a SR-71 was completely my fault as I did NOT check the igniters for that flight...BEFORE and AFTER installing them in the motors and one last time on the pad. Had I done so I might still be flying SR-71 #1 ;)

I wish you luck on recovery, I can't imagin how high it's gonna go with a D12 and a par of C6-7's in the pods. I'm sure it will still be moving UP at a pretty good clip at ejection. For that reason you may want to go with a sawn nylon chute but the Core BT-50 is pretty tight so you may have to reduce the size to say 14"?
Good Luck I hope to hear some interesting flight reports real soon...
Happy Clustering
 
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cbrarick

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Can you give us more detail on your vents? Did you scratch build them or did you get them? I want to use them in my next build...
 

Micromeister

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Can you give us more detail on your vents? Did you scratch build them or did you get them? I want to use them in my next build...
Hopefully this won't be viewed as Hi-jacking the thread.

Not sure what else I can say about the vents? I guess I got the idea from the venting used on the Trident. but needed a way to transmit the HOT gases from the outer pod tubes into the main. This was easy on the Geo-Sat HLV and Deep Space Transport using the same cardstock matching plate method as the Trident. The SR-71 however needed something more.
The Vents were custom fabricated from 3/32" x 3/16" x.014" thin wall rectangular brass tubing from the hobby store rack or from www.smallparts.com #U-RCTB-1.
The Trick to venting is to as closely as possible match the square inch area of the ID of the largest motor "casing" we plan to use. this ensures no overpressure log jams. in this case with 18mm motors it takes 4 pieces to make up each vent. I tried joining them first with CA, then epoxy but they just wouldn't stay together. ended up soldering them into a single unit by placing them on a heat resistant sheet, pinning 4 oversize pieces in position, heating the group and flowing 50/50 solder into the seams. after cooling a little clean up work with 120grit sandpaper brought them to a single 3/16" thickness matching the balsa pod standoffs of the SR-71.

Positioning needs to be close to the core motor forward end and far enough up to share FP wadding while leaving plenty of room for the recovery system. Because the Pod motors are a bit further foreward this has to be measured closely. I chose also to slant the vents Up I don't recall the exact degree but the 1st photo I uploaded earlier is full size so you should be able to tell for there. Cutting and trimming was done with a fine tooth Razor saw and X-Acto miter box. the brass cuts and sands fairly easily.
The vents are epoxied in place as part of the SR-71 pod spacers and protrude only slightly into both Pod and Main Body tubes. Attachments were with epoxy and fillets of 30 minute epoxy were added.
I've used the same pair of Vent tubing in the last 3 models. Sanding off the old epoxy and re-installing in the new pod standoffs.
Thats about it I think. Hope this helps with your next builds.
 
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Peartree

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3 E-9's? Sheesh, did you have to have Kiwi's in your recovery team?
 

mjstech

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Micromeister,
Thanks for posting the techtips location. Your info about cluster launching was really helpful. So were the other tips too. I am also glad you posted the information on what with and how you made the vents.

Emir,
Awsome scratch build. I can't even imagine 3xE9s. Have you had any issues with not having all 3 motors fire?
 
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mjstech

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(from Emir's link)
>Blackbird XL launched on 1 x E9-6, Mild wind speed, (Approx 5km/hr), Model >weight was 500g loaded.
>It got to the top of the launch rail, and started flipping, and then nose cone >came off, which flipped it faster.
>Total height about 9’ off the ground, landed about 10’ from the launch pad. >Then ejection charge fired whilst on the ground.
>Which I was happy with that, as there was no damage to the model.

Hahah, I hope mine doesn't do that.

Nice idea about the booster motor mounts to be able to vent. Did you ever do the 3 x F35 cluster (24mm RMS) with the expected height 3000'?
 
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EMiR

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Did you ever do the 3 x F35 cluster (24mm RMS) with the expected height 3000'?
No not as yet, pretty much every launch event since i finished, has been too windy, plus I'm trying to convince myself that its a good idea :)

As far as all 3 motors firing at the same time, the old BP motors pretty much kick in at the same time, everytime. It will a different story with AP motors tho.
 

mjstech

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I have primed, sanded, and painted with gloss black.
My final black coat looks very nice. My camera isn't doing it justice. I used enamel spray paint.
The rocket is very shiny, I will add the decals and top coat with a flat clear coat. Then attach my recovery items. I still plan to launch this on 1/9.
Does anyone have a recommendation for the flat clearcoat? How about tips for the decals?



 

cbrarick

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Krylon has an enamel flat clearcoat.... so it won't mess up your enamel black..
 

Samuron

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Does anyone have a recommendation for the flat clearcoat? How about tips for the decals?
Hey Mark,

I think you asked about the clearcoat yesterday at the meeting, but we never got back to it.

I like to used Testors GlossCoat laquer before putting on decals, to give them a perfectly smooth surface and prevent silvering. Then, top the decals off with Testors Dullcoat.

However, do a test on some scrap painted with your enamels first; I've never had GlossCoat craze enamel paint, but it's better to make sure.
 
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