Screaming Eagle on the Prowl...er

[GlenP]

Not much work on the rocket this week. Sanded down the 2nd coat of glossy white. Got most of the crinkles smoothed out. The filled fin slots are pretty well blended in now. Looks and feels pretty smooth, but I will let it rest and continue off-gassing a couple of days, then go over it again with some 400 grit.

 

[GlenP]

Made one more pass over the body and fins with the 400 grit, ready for another coat of glossy white. Some tube spirals are still showing a little, but I don't really try to fill those up so much, I want it to look a little bit like the original white tube that was not painted, if that's even possible.

The nose cone is pretty much ready for its first coats of glossy red, but it started to rain this afternoon when I was about to mount it on a painting dowel, so that will have to wait. Also, it feels like my can of red is near the end and almost empty, so I may just get a new can and start with that. I hate it when you are using up that last little bit of the spray can and then get a splattering mess of paint on the rocket.

 

[BEC]

Glen,

Are you going to bring that out to the Raceway (E16-6) on Saturday? Or perhaps to Sixty Acres on Sunday (F15-6)? If you plan to bring it out on Saturday I'll make sure to have a 1/4 inch rod in the GSE setup.

(Painting weather should be back on Wednesday).

 

[GlenP]

I don’t think I will have this one ready to fly by Sat, but might bring my Mean Machine for a maiden flight.

And I think those are good motor and field combinations for this one too.

 

[GlenP]

Another coat of glossy white, and more spots of the crinkle. Not so bad, but hopefully after sanding them out they will go away in the next coat. Got a couple of coats of red on the nose cone also. If I can ever get a crinkle-free coat of white, then I will be able to mask off and paint the fin can blue.

Am really happy with how the Titebond Quick&Thick fillets came out on the fins and lug, they look really great after painting.

 

[Nytrunner]

Hows the weight? Of course you'll want to make sure the E16/F15 can lift it after your mods.

And if it's too heavy, there's always composites

 

[GlenP]

Looks like about 12.5 oz right now, with no engine or wadding, so that's an empty or dry weight. I was going to put in a baffle, but might not do that now to keep the weight from going up any more. I was kind of hoping I could use a 24-29 adapter and launch it on a D12, but that seems to be out of the question now. The instructions list a couple of F and G composite motor options for the stock kit (see my spec-plate decal earlier). I think the 29mm E and F BP motors should still be suitable, maybe with little or no wind for the E.

I seem to be perfecting my paint crinkle technique. I guess I am repainting much too soon after sanding, and getting down to a sub-layer of paint that has not off-gassed enough yet. The new spray layer just does not bond in those spots where I had been sanding. So, in my rush to get on more coats before a club launch on Sat, I have guaranteed that this won't be ready in time. I just don't want to launch it until I finish the paint and decals so I can get a good picture.

 

[GlenP]

After looking at some results from ThrustCurve, I am thinking this might be too heavy for the Estes 29mm BP motors. There are some good composite options that have a really steep thrust curve that would work fine but also may go way too high for my local fields, but I think I may have added just too much weight for the initial acceleration on the launch rod for the Estes BP motors.

Need to think about how I can remove some weight now after the fact. I probably could have used balsa instead of ply fins, (like the Star Orbiter uses). Now I wonder if I can size them down a little, by trimming off from the span or chord along the edge of the tip or from the trailing edge of the fins. I may cut some scraps of ply that same size to see how much total equivalent weight that might save me. I could also remove a portion of the body tube from the top.

I thought it was going to be close, now I am thinking I busted my weight target and should try to fix it.

I wonder what one of the stock Prowler kits weighs when built w/o engine? Since it requires no painting that may make some difference also.

 

[kuririn]

The Estes web site gives the empty weight as 9 oz. I weighed mine and it's 8.85 oz. Also, with an F15 motor it peaks at 2000 ft, about 850 with an E16 (for a stock Prowler).

 

[Nytrunner]

Thrustcurve gives a conservative 50 ft/s off the rod as it's go/nogo condition. (To give you an idea, my L1 flight was with a motor in a rocket that thrustcurve said was 'insufficient speed at takeoff')
What does OpenRocket say?


Something to note though, the E16 and F15 have a longer ramp up of their thrust than the D12/E12. I pay far more attention to the thrust in the 1st 1/4 second than I do the average thrust rating of the motor.
Your model weighs ~4.3-4.5 Newtons with the BP 29s in it. Moving along the curve until that point, you're looking at a quick ramp to 25N thrust. you'll expend some power in the initial burn, but by the time it's strong enough to lift your rocket, it gets going! Check out the thread on "why 5:1 ratio" for more calculations on rod/rail exit.

 

[kuririn]

BTW I don't know where Estes came up with the 2000 ft. apogee figure. I just ran the sim and it shows about 1200+ ft. on an F15. But an AT E30 with adapter shows 1100+ ft. And it gets up to stable velocity much quicker.

 

[GlenP]

For some reason OpenRocket just crashes on my Mac. I had used it on a earlier version of the OS, but I can't get it to run now.

I think I can get the weight down a little if I resort to some fin and body tube length trimming. The original Screaming Eagle body is about 1" dia and 10.5" long, so this upscale at 2" dia should be closer to 21" instead of 24", so I can trim a few inches off the heavy wall tube. I can also trim the fins down by 1/2" at the free edges, this gets them closer to the stock Prowler fin span, but still has more fin area with the 4 fins instead of 3.

I hope this will get the weight down and reduce the weathervane tendency with the smaller sized fins, which were about the size of my original 80% of 2X scale that I had drawn initially. Wish I stuck with that plan now. Will be a challenge to trim these fins, now that they are already attached to the body. The smaller fins will reduce the plywood weight by about 0.7 oz, not sure how much the 3" removed section of body tube will account for, if much at all.







Even for the stock kit 9 oz, ThrustCurve says the F15 is not acceptable, with 47 ft/sec at the end of the rod, so I take those results with a grain of salt. But, I do want to get my weight down to 12 oz or less, if possible.

 

[dhbarr]

Slightly longer rod? It's pretty close.

 

[GlenP]

Yes, that is also a good option. I wasn’t even thinking about that. I was trying to get it to work with the stock launcher that came with the Prowler launch set, but it would be fairly easy to get a longer rod for that, very good idea.

Modify the launcher instead of the rocket, that had not even occurred to me.

 

[GlenP]

That 3" section of the body tube I just removed, takes the stock Prowler body from 24" to 21" and closer to 2X the length of body+fin can of the Screaming Eagle. Would you believe that section of the heavy wall tube weighs 0.3 oz? That gets me back down to 12 oz. I might not have to trim the fins that much if at all, but could just sand down the free edges a little bit, like 1/8" or so. Shock cord anchor and engine retainer were not attached yet to the body and engine mount, but I included them on the scale. Will add a little bit of epoxy weight after they get mounted.

 

[Nytrunner]

47 is fine, just dont launch in 15 mph wind

 

[GlenP]

I mounted the shock cord and engine retainer. Lots more sanding. And did some artwork for my decals. To give some credit for the stock kit, I will add some Prowler decals along with the Screaming Eagle, on the opposite sides of the fins. The Estes kit body tube comes pre-printed hot pink with some transparent peel-and-stickers. So, I tried to make my own version for waterslides with the pink highlights in the transparent portions. We'll see how they turn out when I print them. I may apply them on top of the metallic silver Trim Monkote as well.

 

[GlenP]

or maybe one of the fins like this, on the launch lug side:

 

[GlenP]

Pink rocket with a prowler logo that looks like a black panther...

a Pink Panther?

Now I get it. Very clever.
Looks like they are out of stock on the Estes web site again.

 

[kuririn]

I found a Rocsim file for the Prowler and an OR file for the Screaming Eagle at EMRR. So I did a "quick and dirty" file for your kitbash (hope you don't mind) since your sim program is down. Maybe you can tweak it when your program is back up.
Also attached a .pdf summarizing the sims I ran in OR for different motors.
Also four pdfs of different motors in Rocsim. It gives more info than OR, most notably the distance to minimum stable velocity.
PS The Rocsim summaries say Prowler but it's for your kitbash: I forgot to change the name of the file.

 

[GlenP]

Cool, thanks! Looks like the sim data uses a default 3' launch rod. The 1/4" rod that comes with the E series launch pad is 4' long. But I can probably replace that with a 6' rod, if needed.

I am pretty much done trying to paint anything with Rustoleum 2X paint/primer. I am just getting crinkle coats that I have to sand off and start all over again every time. It leaves deep crevices where the paint did not bond at all on the crinkle lines and filling those back in again is nearly impossible. Time to switch to Krylon or something else. Just wasted another good weather painting day.

 

[Nytrunner]

What were the humidity and temperature conditions?

 

[GlenP]

I waited for a moderate weather day, probably in the 50s or so. I think I discovered that I must wait a full 48 hours after painting to sand, then wait another full 48 hours after sanding for the next coat. When I paint immediately after sanding, I think that I may be painting over a deeper layer that was just exposed by sanding that has not offgassed enough yet, maybe? I got a much better coat this time around. The white is pretty much done on the body, so the fin can is ready for the blue. I still need to clean up that spot on the nose, but it looks much better now. Those spots on the nose started where I had sanded the plastic seam.

 

[Nytrunner]

I've had a few of your frustrations as well. It is a trickier paint to get used to and develop a routine for, and the over 55deg under 85% humidity is critical.

Despite that I still go back to it for the wide color selection available at walmart, and the finish achievable with patience. I find it helpful to break my rockets into sections (booster, payload, nose, etc..) and make a painting schedule so I don't get antsy and try to rush things.

 

[GlenP]

Yeah, I decided to work on some other rockets while waiting in between sanding and painting, to give it time to cure. Not going to rush it.

 

[Hugh Cronin]

Try Ace Hardware Premium paint. I got great results with their primer and paint. No crinkles no runs no drips. Put on multiple lite coats.

 

[Hugh Cronin]

 

[GlenP]

Wow, that rocket looks fit for a King. Majestic even. I will have to give that paint a try, ACE is where I usually shop for paint and glue, for hobby stuff as well as for home and garden stuff.

 

[neil_w]

Rusto 2x paints need long cure times but even more so on plastic parts.

I don’t think I’ve ever given less than 4 days before sanding, and usually 5 days to a week (or longer) before recoating. Knock on wood I haven’t had a single crinkle-coat yet.

Primers and metallics seem to dry a lot quicker.

 

[BEC]

I have had the occasional crinkles with Rusto 2x, most often on plastic parts. Washing them thoroughly before priming seems to help (though I realize now I didn't do that on the CM or the fins of my Saturn V that I shot primer on a week or so ago)