Interceptor E Build—- Pursley Skin

[AfterBurners]

One thing that scares me a bit about this rocket is the pods sticking out make a great lever arm for breaking off a wing on Landing. If there's not too much I can do about it. John Pursley recommends upgrading the chute from 30 in to 36 in. Looks like there's plenty of room for a larger chut3 in the body tube. I launched in a mixture of asphalt and grass and as you might imagine the probability of landing on the asphalt is directly proportional to the amount of time finishing the rocket. Oh well. I also may put a touch of tape on the tip of the pods and on the bottoms of the caudal fins to protect it them on Landing.

You can always go with a Topflight "Thin" Mill chute or even a large "X" form chute thin mill as well. This will allow you to easily pack the chute. I'm not a big fan of the flat chutes if you launch on hard surfaces. They tend to swing the rocket underneath and when it lays "swinging" fins and wings tend to break when they hit the ground. If you were launching say of a soft surface like sod or grass then no worries.

 

[BABAR]

Little bit of orange peel on the tail cone. One of the reasons why I avoid paint in the first place. Not enough to try to redo. I'll live with it.


Here is the attachment of the shock cord to the backside of the tail cone.

The tail cone fits in pretty tight. In fact when I dry fitted I could barely get it back out again needed to use pliers with a paper towel to prevent me from scraping the paint! So I think it will be fine without gluing it in so I can take it out later

. I think this will be fairly secure for the shock cord which gets fed through the tunnel that I posted at the beginning of this thread.

it will allow me to inspect and replace the shock cord at a later date if I want to.

 

[BABAR]

Okay, any special precautions I need to take before applying Future?

I was going to put the nose cone in most of the way, put the bird on a dowel stuck in a motor casing. Dowel has hook on it so I can hang it nose down. Using a foam brush to apply the future.

 

[BABAR]

Stole (adopted? Borrowed) @BlaineS earplug antizipper idea.

https://www.rocketryforum.com/threads/blaines-kevlar-anti-zipper-using-foam-ear-plug.154996/
I used polyurethane glue instead of plastic cement

Thanks BlaineS

 

[BABAR]

PreFuture (hope I dont mess it up)

 

[mbeels]

Wow, that is flashy! There really is a lot of detail for the eye to take in, looks great!

 

[AfterBurners]

Wow, that is flashy! There really is a lot of detail for the eye to take in, looks great!

I totally agree!! Enjoy flying it!!!

 

[BABAR]

I have learned from experience not to trust the plastic attachment points nose cones so I drill my own holes.

 

[BABAR]

Well when life‘s giving you lemons make lemonade. I had a dowel inside an E expended motor casing and was using it to hold a rocket while I painted it with the future acrylic coating. Apparently the engine hook doesn’t work all that well because the rocket slipped off the motor and fell onto the concrete. Nothing too damaging to the Rocket. Perhaps I can take this as a plus. When I put the motor in I am going to tape it over the engine hook for security. I have had Estes engine hooks fail and spit motors before. So I guess better it happen now then on a flight.

 

[mbeels]

I have had Estes engine hooks fail and spit motors before.

Yeah, that's how I lost my 18/20 case.

Well when life‘s giving you lemons make lemonade.

Reminds me of my friend who was watching another friend back out of their parking spot when their tie-rod (or axle?) broke and the wheel fell off. His first reaction was "You're so lucky!" He immediately realized that a parking lot is the absolute best place for your wheel to fall off.

 

[BABAR]

WITHOUT motor but with recovery gear comes out to 376 grams (face card says 383 grams.). Still have to add rail buttons. CG is 13 INCHES. forward from the tip of the tail cone, again WITHOUT motor.

 

[BABAR]

SPEAKING of rail buttons, the instructions put on 3 inches and one 17 inches forward of the rear end of the body tube (NOT from the end of the tail cone.

These seem waaaaaay to forward for me, especially the forward one . The whole ROCKET is 39 inches including the tail cone.

Seems to me the rail length of any rocket behind the forward lug is wasted.

I am thinking going with one button about 11 inches forward of the tail cone (places it about one inch forward of the leading edge of the wing where it meets the chine), and the second 1 inch forward of the tail cone.

My rail is 2 meters, so almost 6 inches longer than a 6 foot rail.

Any good reasons NOT to move the forward lug site (button in this case) back 6 inches?

 

[BABAR]

@neil_w , thrustcurve definitely goes along with you on this, says the Estes motors won’t hack it. The new ThrustCurve won’t even display motors that don’t work.

E20 gets it off the 2 meter rail at 16.5 m/s for 173 meters. Apogee at 4.4 seconds is pretty close to the 4 second delay option

E30 20.1 m/s for 209 meters. Apogee at 5.1 seconds is a bit late for the 4 second delay.

Also chute recommendations?

The stock chute is 24 inches

I made a Mylar Chute which is two pieces of Mylar taped, shroud lines passed OVER top of canopy for strength. It’s ellipsoid, 28”x36”, with 8 shroud lines.

It packs easily.

The rocket has about 9 inches long by 2 inch diameter recovery compartment (11 inches forward of the forward centering ring (essentially a long stuffer tube or chimney forward of the motor mount), subtract 2 inches of nose cone shoulder.

I figure I will use plent of wadding and burrito wrap the chute.

I could also get a chute from Top Flight while I am getting my motors, the thin mil are not much more expensive, they also have the X chutes which look cool (I think you have to have a swivel to use them, but that’s okay)

https://buyrocketmotors.com/recovery/
My launch site I about 300 yards diameter (roughly 3 football fields wide and tall.)

Pursley recommends a 36” chute. I want to get it back without breakage, but I also want it to land IN the field!

Will probably launch on a day with winds 5mph or less (we have some nice winter morning here.). Not sure how likely this bird is to weathercock, I think I have lost more rockets to that than from drift.

I am leaning toward the E20-4 and getting a 36” thin mil orange Top Flight chute

https://www.buyrocketmotors.com/top-flight-thin-mill-parachute/
Maybe get the blanket too? Says 6x6” for up to 2.56” airframe (this bird is 2”.)

 

[mbeels]

WITHOUT motor but with recovery gear comes out to 376 grams (face card says 383 grams.)

So that's less than a pound, pretty light.

Maybe get the blanket too? Says 6x6” for up to 2.56” airframe (this bird is 2”.)

I'm not sure if 6x6" would be large enough for a full burrito wrap, but maybe. I think that those body tube size guidelines are for using the nomex blanket wadded up like wadding.

Also chute recommendations?

The stock chute is 24 inches

I'm not sure, depends on how soft the landing surface is. My gut tells me one size larger, and maybe your 28"x36" ellipse would be pretty good. Sure would be visible.

 

[BABAR]

So that's less than a pound, pretty light.



I'm not sure if 6x6" would be large enough for a full burrito wrap, but maybe. I think that those body tube size guidelines are for using the nomex blanket wadded up like wadding.



I'm not sure, depends on how soft the landing surface is. My gut tells me one size larger, and maybe your 28"x36" ellipse would be pretty good. Sure would be visible.

I have used the gold Mylar for a lot of chutes. On a Sunny day it is absolutely gorgeous coming down.

 

[BABAR]

Okay, Beauty Shots (at least to me.) Not perfect, but since I RARELY put much work into finishing a rocket (this is probably a record) I am probably posting more than I should, but it also shows some different photo techniques, with mirror photos and outdoor night-time flash, with the distant background (except for the new houses across the lake.....grrrrrr, coming out black as out of range of the flash.

 

[kuririn]

Beautiful job!

 

[neil_w]

Bravo, looks great.

How many coats of Future?

 

[Nytrunner]

SPEAKING of rail buttons, the instructions put on 3 inches and one 17 inches forward of the rear end of the body tube (NOT from the end of the tail cone.

These seem waaaaaay to forward for me, especially the forward one . The whole ROCKET is 39 inches including the tail cone.

Seems to me the rail length of any rocket behind the forward lug is wasted.

I am thinking going with one button about 11 inches forward of the tail cone (places it about one inch forward of the leading edge of the wing where it meets the chine), and the second 1 inch forward of the tail cone.

My rail is 2 meters, so almost 6 inches longer than a 6 foot rail.

Any good reasons NOT to move the forward lug site (button in this case) back 6 inches?

Well, 1 reason not to move the button back is that you'll have plenty of rail length regardless. 6" difference on a 2m rail really shouldn't make a bad difference in exit velocity for a rocket that small.

1 reason for moving it back anyway is that for a rocket that small, you can probably put the forward button/lug wherever you want it. The masses and forces involved at this scale just aren't that serious
(I think I've invoked the BABAR corollary again)

It's common to put the forward button near the CG and CP for larger rockets. Loading underslung on the rail, a button is desired near the CG so it's more of a direct force instead of a twisting moment. When standing on the pad, a button near the CP again reduces twisting from wind trying to catch the rocket.

 

[BABAR]

Bravo, looks great.

How many coats of Future?

2 coats. Note: Pursley warm about getting glue on the skin. I did some fillets with white glue which dries clear (mainly around the front ends of the wingtip pods, the rear section of the wing goes through the wall of the mid pod the forward end of the wing just abuts the pod, the rear end of the pod has no attachment at all. The Future finish gives a nice clear gloss to vinyl and paint, but looks a but milky over the glue fillet, which was previously transparent.

 

[BABAR]

Well, 1 reason not to move the button back is that you'll have plenty of rail length regardless. 6" difference on a 2m rail really shouldn't make a bad difference in exit velocity for a rocket that small.

1 reason for moving it back anyway is that for a rocket that small, you can probably put the forward button/lug wherever you want it. The masses and forces involved at this scale just aren't that serious
(I think I've invoked the BABAR corollary again)

It's common to put the forward button near the CG and CP for larger rockets. Loading underslung on the rail, a button is desired near the CG so it's more of a direct force instead of a twisting moment. When standing on the pad, a button near the CP again reduces twisting from wind trying to catch the rocket.

Thanks
Makes sense. I will put it at the CG with motor in, which is still likely to be waaaaaay back from the instructions.


Interestingly, I have found with my long gap stage rockets I need Two buttons on the booster (logical, as it is the last to leave the rail.). OTOH, a long gap stage rocket for me is about 6 feet long. Even through CG is still forward o CP, the length of the Rocket combined with fins even when small of the sustainer creates a significant moment force which tends to bend the rocket (it’s BT-50 tubing.). Adding a THIRD rail button, placing it on the sustainer, does very little for stability (it is actually near the forward end of the rail) but does a LOT for support while it is sitting on the pad awaiting launch.

 

[modeltrains]

He immediately realized that a parking lot is the absolute best place for your wheel to fall off.

Also a much better place than middle of I-70 to have a timing chain break.
Spiffy looking rocket.
Will have to make a note of the optional shock cord attachment method.

 

[BABAR]

Mass at 450 grams with aerotech E20-4 motor (50 grams) and 36" X chute

 

[les]

Nicely done!

 

[BABAR]

Mini buttons Sharpied black at 12 inches (actual CG with motor and 36" X'chute) and 1.5 inches (vs instructions 17" and 12".)

 

[neil_w]

That really is a convincing air scoop design.

 

[SCooke123]

Turned out great! I hope your first flight is a good one.

 

[BABAR]

Well, she's finally officially a rocket.
Winds today 3-5 mph, about as good as it gets here.
Not a cloud in the sky.
Great shout outs to @neil_w for motor choice, the E20-4 got it off the pad with authority
to @AfterBurners for chute choice (36" Top Flight X chute, packed nicely, and dropped it nice and gentle, fortunately into the grass)
and to @Onebadhawk for a perfect swivel that held up to the ejection charge and allowed the X chute to rotate easily (I've see a flight where a swivel wasn't used, it wasn't pretty.)

Couple of teaching points, I had to mash the button for a while, really was expecting a misfire, but once she lit she took off like a bat outa hell. Had I not kept pressing the button I think I would have given up on that igniter.

Also be careful chasing rockets with a camera, I almost tripped and face planted.

Only down side was I DID lose my hat, I forgot to pick it up after getting the rocket (being excited about a successful flight), and I am guessing somebody "found" it later. Oh well.

 

[neil_w]

Great flight!!!

What kind of launch controller are you using?

 

[BABAR]

Great flight!!!

What kind of launch controller are you using?

Pratt Go-Box with 12 volt battery. Usually works great. I don’t think it was controller issue. I launched 8 rockets after this with the new Estes starters with no problems.