another build thread: The Launch Pad's AGM-88 HARM

[rifleshooter]

Well, kiddies, I started another rocket- the Launch Pad's AGM-88 HARM. TLP's kits seemed like a nice mid-power entry kit, so I bought this missile for its attractive looks.

This is my first TLP kit - things feel a little under built in this kit. You make your own paper tail cone (but this goes waaaaay better than you think it will) and the craft tubing supplied seems rather thin. Fins are very thin 1/8" and 3/32" stock, and I will likely finish -epoxy them in order to add strength and minimize weight. Fitment of rings was very tight and all had to be sanded to fit, which didn't break my heart.

I have found that a foaming polyurethane glue works wonders for expanding into spaces and locking together certain rings, while giving you lots of working time and a weirdly handy lubricity for screwing together parts which you don't want to bind before they're seated. I used this glue to great effect while assembling the HARM.

I am 3/4 done and have not yet photographed anything yet! Stand by for more this evening.

 

[Zeus-cat]

The components are very light because you need them that way. These 2.6 inch kits are right on the edge of stability with the Estes D12. Too much weight and the rocket will perform very poorly in flight. Go watch the video of the "Final Flight of the Phoenix" in the Low Power Forum for an idea of what can happen to one of these big rockets on a D12. That Estes kit had a few crashes and rebuilds which probably added enough weight to cause stability issues.

As I stated in that thread I no longer fly my TLP Standard AGM on Estes D12 motors. The D12 is a good motor, but these rockets are too demanding for it in my opinion. Especially after a crash or two and extra weight from repairs. The 24mm composite motors that are more powerful than the D12 are really great performers in these rockets though.

 

[rifleshooter]

The motor mount in this thing was a joke - it consisted of a clip and the motor tube. That's it - no thrust ring or anything - just a clip. I put in a home-made thrust ring (which got canted, so I'll have to figure a fix for this if there is one).

The clip is D-motor length. Sheesh. The mount does hang 1.5" into the back of the reducer, so there's plenty of room from which to hang out for something like a 24mm F-power motor.

Here's a pic of the tube, including a close shot of the bottom of the tube where my famous foaming polyurethane glue was frothing out of the top of the reducer, and I had to cut it away.

The whole thing had to be smoothed to ensure the fins would "reach around" and grab the tube and cone with no gaps.

 

[RocketManDan]

looking good so far...

 

[rifleshooter]

... is really becoming a trial.

The Estes tube marking kit is OK for working on small rockets, but when that size goes up, then you get reduced performance. I was drawing lines on the tube and they were wandering all over the place. I had to use the Mk 1, Mod 0 human eyeball to correct matters.

Eventually I resorted to the Trusty Door Frame, as it is over 1 m long and if you are careful, you can scribe a pretty straight line over that distance.

6 fins are now on. I went with 5 min Hobby Poxy, in violation of my general rule, because I need to get this one into paint today and can't baby-sit it any further.

Note on shock cord mounting - I eschewed the goofy Estes-style shock cord mounting kit for a more substantial, Quest-like arrangement of Kevlar SC tied around and looped through the forward engine bulkhead. I will "sock" the kevlar where it will likely meet the frame to prevent zippering.

 

[rifleshooter]

I am into second prime + sand.

Here's the photos I've acquired until this point.

Pics of the papered fins. Papering goes well, although primer tends to "pill" on the surface so you have to hit it with 600 grit to get a glassine finish.

Beginning fin assembly in my custom jig, which is custom-designed not to give you square fin assembly. Or it's user error - haven't figured out which yet (you do the math).

Look closely - I'm off by 1/16" (not through central axis, pisses me off). Sometimes I'm not totally warped, either. At least the fins are all axially on the centerline, which is why I see very little roll in my flight performance.

Filleting forward fins with final coat sanded Elmer's Fill-n'-Finish.

Rear fins - did not touch up filleting with Filler, promptly go holes in the fillets (white glue). Will touch up again in short order during sanding of primer.

After touch-up sanding and re-filling rear-fin fillets from second primer hit. Got the nose cone ready to go standing by. Won't put decals on this bad-boy until it flies... got a goofy feeling about this mode.

 

[El Phantasmo]

Cool fin jig/alignment guide. How do you prevent the top of the jig from creasing the tube?

 

[rifleshooter]

Cool fin jig/alignment guide. How do you prevent the top of the jig from creasing the tube?

I don't have a problem with this - the fiberboard's pretty thin and light.

 

[rifleshooter]

Flight report:

Weird.

I launched with a D12-3 Estes motor and got a nice, clean, arcing 200~ foot flight, followed by a recovery which seemed to take a while to pop out the 'chute fully. Very nice.

I put an E9-4 into the bird, and launched - although the wind had picked up from ~1-2 mph to perhaps 5 mph, the bird leapt up off the pad pretty quickly and arced within 100 feet. It nosed over and flew into the deck under power. The arc was away from the prevailing wind - so it didn't weather cock.

I'm thinking that the extra weight and length of the E-motor was "pushing the tail around" which suggests there was not enough weight in the NC to allow stable flight. I'll post a video up here within a couple of hours.

Damage is pretty severe - NC's trashed, and the first 4" of BT are obliterated. I want to buy a coupler and a few inches of new body tube. Due to the amazing papered fins, they're in perfect shape despite two breaking off at the BT (they can be re-glued without too much drama).

I will repair, use Open Rocket to build a replica, then seek to weight it so it can be stable under power of an E - F 24 mm reloadable motor. Any suggestions you can spare will be appreciated.

 

[Zeus-cat]

As I said in my earlier post, these kits are tough to fly on D12 motors. It sounds like you had a light build so the D12 flight was OK. You said it arced, which is not an uncommon flight profile for my TLP kits.

Therer is no way I would ever fly one of my TLP kits on an E9 unless it was one of the 1.6 inch diameter kits. The 2.6 inch diameter birds are just way too heavy for an E9. Sorry to hear that yours crashed, but I am not the least surprised by that.

 

[rifleshooter]

Why would these birds be harder to fly on a higher-powered motor?

Here's the video:

[YOUTUBE]DD0ovFjl6qc[/YOUTUBE]

TLP claims to be OK with flying these birds on F-motors. What would happen if I put an F-motor in it? Would it loop?

 

[Rex R]

the problem is the E9 thrust curve...it is a remarkable motor in the right bird, but when push comes to shove it is not the motor to use. an E15 or E18 would have been my choice. sorry to see tthat happen to a nice looking rocket.
rex

 

[qquake2k]

I'm so sorry. What a shame.

 

[Zeus-cat]

You have learned a valuable lesson the hard way (like many of us here do). You need to look at all the parameters of a motor before using it. An E9 has more total thrust than a D12, but it has less average thrust throughout the entire flight profile. As Rex R has said, the E9 is a great motor, but like all motors it must be used properly.

If a D12-3 had trouble producing a straight up flight on your rocket, then the E9 flight was doomed before the start. The D12 has a higher peak thrust and a higher average thrust than the E9. It will safely lift heavier rockets than the E9. The E9 burns longer than the D12 which is how it gets to be an E class motor.

My rules of thumb are that if a rocket flies great on a D12-3 (straight up and chute deployment near apogee), then it does not fly on an E9. The E9 would not get the rocket going well enough to deploy the chute in time (like your flight). However, if a rocket flies well on a D12-5, then it is a candidate for an E9-4 or An E9-6. I use a software simualtion to detemine if the rocket can use either of these motors.

 

[Zeus-cat]

I just watched the video. The damage doesn't look too bad to me. Just slice off the front end of the rocket, stick a coupler in there and a new forward section and you should be good to go. My TLP Standard has had that same repair by the way. The only difference was that mine bit it on a D12-3. I tend to build heavy; and with a repair or two they get even heavier. She only flies on E18s and up from now on. And she flies great on E18s; 500 feet straight up. And I mean straight up; not arced over like on a D12. And she bolts off the pad too.

Yours might be to heavy for the D12 after the repair. If the rocket is right on the edge for weight for the D12 after the repair; you need to think long and hard about using D12s. 2.6 inch diameter rockets are a lot more draggy than smaller rockets. A BT-50 or BT-60 rocket will fly much better than the same weight BT-80 sized rocket.

The two concerns I would have for the composite E and F motors are the strength of the motor mount and the balance issue. I think you beefed up the motor mount so that should not be a problem. The weight of the E and F motors isn't that much more than the D12, but you should check out the stability in Open Rocket or some other package.

 

[rifleshooter]

The real problem here wasn't with the kit, it was with the rocketeer.

E is bigger than D. When I look at my alphabet up near the blackboard, that's what it says, anyway. Must have more power, right?

Apparently, you have to actually understand how this stuff works, and not just take a half-assed guess at it. The Estes E-motor burns much, much longer and delivers more average thrust, but lower spiked thrust than the D12-3 that I flew the bird initially on. I didn't know this, and put the wrong engine in the bird.

Whoops!

The D12-3 is a great first motor for this bird as the flight was great. I do predict that a nice 24mm RMS or single use high-impulse E-G motor would drive this bird quite nicely into the sky.

Fins are repaired. Body tube and repair coupler are ordered. I will put a new NC I have laying about that's a little heavier and an inch or so longer. I will dummy all these changes in OpenRocket to see if the CP/CG situation will still be kosher.

Then, I will shoot video, attempt not to step on the bird when it comes down, and post it here for all to see.

 

[SacEsq]

Why would these birds be harder to fly on a higher-powered motor?

Here's the video:

[YOUTUBE]DD0ovFjl6qc[/YOUTUBE]

TLP claims to be OK with flying these birds on F-motors. What would happen if I put an F-motor in it? Would it loop?

OUCH!!! Loved the background music tho LOL

 

[Zeus-cat]

The real problem here wasn't with the kit, it was with the rocketeer.

E is bigger than D. When I look at my alphabet up near the blackboard, that's what it says, anyway. Must have more power, right?

Apparently, you have to actually understand how this stuff works, and not just take a half-assed guess at it. The Estes E-motor burns much, much longer and delivers more average thrust, but lower spiked thrust than the D12-3 that I flew the bird initially on. I didn't know this, and put the wrong engine in the bird.

Whoops!

The D12-3 is a great first motor for this bird as the flight was great. I do predict that a nice 24mm RMS or single use high-impulse E-G motor would drive this bird quite nicely into the sky.

Fins are repaired. Body tube and repair coupler are ordered. I will put a new NC I have laying about that's a little heavier and an inch or so longer. I will dummy all these changes in OpenRocket to see if the CP/CG situation will still be kosher.

Then, I will shoot video, attempt not to step on the bird when it comes down, and post it here for all to see.

By jove, I think he's got it!

 

[RocketManDan]

... is really becoming a trial.

The Estes tube marking kit is OK for working on small rockets, but when that size goes up, then you get reduced performance. I was drawing lines on the tube and they were wandering all over the place. I had to use the Mk 1, Mod 0 human eyeball to correct matters.

Eventually I resorted to the Trusty Door Frame, as it is over 1 m long and if you are careful, you can scribe a pretty straight line over that distance.

6 fins are now on. I went with 5 min Hobby Poxy, in violation of my general rule, because I need to get this one into paint today and can't baby-sit it any further.

Note on shock cord mounting - I eschewed the goofy Estes-style shock cord mounting kit for a more substantial, Quest-like arrangement of Kevlar SC tied around and looped through the forward engine bulkhead. I will "sock" the kevlar where it will likely meet the frame to prevent zippering.

You should get a large angle for drawing those lines...check out the local hardware store.

 

[hornet driver]

Man I hate seeing that. Looks reparable and that's a good thing.

 

[Daddyisabar]

The stock motor mounts are fine for E and F composite motors. Many TLP flights and no problems. No additional nose weight is needed if left stock. Keep the weight off the hind end! If they fly in an arc on a D-12 they will fly in a bigger arc on an F-24 or F-12:eyepop:. As always it depends on the model and wind. My HARM is still in the bag so I don't know how it flies, but it sounds like it too might have the tendency like a lot of other TLP kits to arc a bit. The big fins forward look really cool but for some rocket science reason they always seem to make the TLP rockets more unpredictable than my Stormcaster or Big Daddy:bangpan:. Silly sports scale fliers, usually happy if it just goes up and comes down under some sort of recovery.:blush:

 

[John Beans]

My Estes Executioners were always marginal, too. Especially when I modded them heavily (two stage variants, baffles, payload sections, etc.).
One solution for slow flying, marginally stable rockets: the E30T. I say treat yourself once in awhile...
--John

 

[rifleshooter]

You should get a large angle for drawing those lines...check out the local hardware store.

RMD, I purchased the straightest lumber in Lowe's and created my own 34" section of straight angle:

That's what's in my shop now. I suspect lines will be much easier now!

 

[rifleshooter]

OK, so Discount Rocketry just delivered my Nike Smoke 2.6" Model Rockets.us kit, along with my repair BT-80 tube and coupler.

I should have the rocket tuned up here in short order.

The replacement NC is about an ounce heavier and an inch longer. The TLP guy says it will work great. I will OpenRocket the whole deal first, though!

 

[rifleshooter]

Well, team, I put the rocket back together without so much as a fare-thee-well of pictures to document my efforts.

It was really pretty easy.

I painted and decaled the bad boy. Using a non-TLP nosecone left me with it being slightly oversized; it's not too scale. The original NC wasn't a scale job anyway as I have seen pics of the actual missile and the shape is clearly an odd one.

Here are the photos from my completed effort.

 

[qquake2k]

That turned out awesome!

 

[Serpico]

That did come out awesome - nice job on the rebuild. Like all the details this time around!

 

[jungmann1]

Purty!

 

[[POW]Eagle159]

What is the Cg of that beast? Can you also give a reference of where it is on the rocket?

I can't see how it is stable!

I love how it all turned out, perfect job!!!

 

[rifleshooter]

What is the Cg of that beast? Can you also give a reference of where it is on the rocket?

I can't see how it is stable!

I love how it all turned out, perfect job!!!

Thank you all!

I haven't done the Openrocket calculations yet or measured CG, but will before Saturday because there's a club flight.