My path to level 2. A painkiller, a Scion, and a whole lot of time. (Successful!)

depending on weight, at 5 pounds an I600R (which is just about full) Gets it to 4K

Winter seems to finally be losing its grip. I've managed a couple flights in the backyard with an Estes Richocet (fun little rocket), and it looks like the snow pack might be clearing out enough at Dad's farm to get some mid power flights in again soon. Unfortunately, I didn't have much luck at the local metal suppliers in finding 1010 rail, looks like I need to order it online. I'll get that done in the next day or two here.

But I don't feel like the time is right just yet to start on the Painkiller 3 build. I'd like to get a few more flights with my 24mm and 29mm birds first.

Now that I'm looking at working up some deployment charges for ground testing, here's a question I've wondered for a while but never got around to asking.....

Why measure the size of recovery charges in grams, and not grains? Being a reloader, my brain thinks of grains whenever I see a powder callout. All my powder measures are in grains, as are my scales.
Makes me a bit skittish of using the wrong unit of measurement, so I think it will be appropriate not to use abbreviations.

-Hans

Because we have been told since childhood were suppose to use the metric system. Just kidding. You're doing the testing, use what ever measure you want, just remember which one you used.

All my powder scales are in grains, so the choice is pretty clear. The calculators I've seen so far are giving me @2.5 grain charge sizes for the PK micro built for dual deployment. I'll probably just stick with feeding a dribbler onto a scale for this weight. I usually do rifle charges in the 35-45 grain size, so my volumetric measures aren't set up for weights this small.

Now I just need to determine what size centrifuge tube for this charge weight. Shouldn't be too hard to figure out.

-Hans

If you have a centrifuge tube, use that as a measure. Most are marked in Cubic Centimeters, or CC. One cc of volume works our to be very close to one gram of BP. Most of us use the cc volume measure on the centrifuge tubes to measure our BP. I certainly do. It is technically a cubic centimeter, but we call it one gram.

As jeff2space said, just remember and use the same measure when you ground tested the charges with and then measure them for flight the same way. It doesn't matter if you use grains, grams, ounces, or how many Barbie Doll drink cups you use, as long as you use the same amount each time you fly.

I see why those little tubes are so popular, cheap and very easily adapted. For the PK Micro, the .5ml size looks like it will be perfect. I'll need larger for the PK3, but that's a while off anyway.

Very little left to take care of before the micro gets its maiden flight. Basically I just need to fit a shear pin, order some motors, and get the launch rail sorted out.
Right now I only have a 4' rail, so some of the lower impulse motors are giving me slow speeds off the rail than I'd like to see according to open rocket.
Looking at an F39-6 for the maiden flight now. This is giving me around 45 ft/s off the rail, with a 1,000ft apogee.
I'm just really going bonkers here waiting for some milder weather. It's either always really cold, or really windy, every weekend.

-Hans

Hah, my L2 was full of electronics. Everyone has different capabilities and many of us have different goals.

I reload as well and the initial question of "why?" occurred to me as well. The first charges I made were in grains, then converted to gram equivalent. My powder scales are calibrated in grains, but there's also cheap electronic scales that will do grains, grams, or oz.

It took me a while to determine the answer to why, but I think I did. We're pressurizing a MUCH MUCH larger area, and when we do, it's to SIGNIFICANTLY lower pressures. Consider: If you overthrow by 0.1grains in a small-volume pistol cartridge --like 9mm, for example-- there's a measurable performance difference. I was working up a load for my .45; it was that additional 0.1 gr which made the difference between reliable and spectacular.

However, in a rocket, the container in which the powder is held is secondary. And that's what tripped me up at first: I was like: I've got to get this amount of powder in this amount of space, so yeah, I should be doing grains... right? I tunnel-visioned in on the ejection charge holder, dismissing the airframe compartment. Then I realized: we don't CARE what the pressure inside the container is --ONLY that in the airframe compartment. Now, compare the volume of even a rifle casing --let's take a decent-sized, often-reloaded one here, like .30-'06-- to a nominal parachute compartment... 3.9" x 17".

.30-'06= 0.27 cu in.
3.9 x 17= 203 cu in.

That's what? 750 times bigger? Thereabouts?
And the pressures we're dealing with: with reloading... 15,000-70,000 PSI vs. Rocketry: 10-20 psi.

Grams is simply a more efficient and useful range of measurement for this application than grains. The resolution measuring in grains gives you yields no better results than the gram range, and, while you, I, and a few others may be more accustomed to measuring in grains when we're dealing with powder for reloading applications, it's wholly unnecessary in rocketry applications. Yes, it's a departure from our experience... but that's not a bad thing --if anything, I think it lends a greater appreciation for each application!


Later!

--Coop

You know, that really does put it into perspective.... you're right, I'm so used to dealing with things in the range of tens of thousands of psi, where even a slight measurement error can cause big issues. While recovery charges are still a serious matter, they aren't at the level of precision needed by reloading.

Time to start sourcing parts for the Painkiller 3 soon, I'm getting into a serious build mood now that weather is improving.

Lots of contradictory info out there on sizing the recovery harness, which has me nervous about doing a permanent job of bonding it to the motor mount with epoxy.

-Hans

HHaase said:

You know, that really does put it into perspective.... you're right, I'm so used to dealing with things in the range of tens of thousands of psi, where even a slight measurement error can cause big issues. While recovery charges are still a serious matter, they aren't at the level of precision needed by reloading.

Click to expand...

Glad to be of assistance --and you're right: nowhere near the level of precision. Look forward to the remainder of the build!


Later!

--Coop

HHaase said:

Time to start sourcing parts for the Painkiller 3 soon, I'm getting into a serious build mood now that weather is improving.

Lots of contradictory info out there on sizing the recovery harness, which has me nervous about doing a permanent job of bonding it to the motor mount with epoxy.

-Hans

Click to expand...

In a 3" rocket, I'd not worry about the bonding to the MMT. It's a reliable and convenient place to mount the shock cord--not to mention, unless you have real small hands and arms, you may have difficulty using quick links or the like in such a confined airframe. As far as length... pick one that makes the most sense to you. Some will put forth a good argument for long cords. Some put a good argument for shorter ones. Could always go long, and cut it down as you see fit...


Later!

--Coop

I'm not as worried about length, it's thickness and weight capacity that confuses me here. Likely going to make a short y-harness with heavier Kevlar just a hair shorter than the tube, and extend from there with a quick link. This will settle my two concerns of making sure it's strong enough, and preventing the non-replaceable section from getting damaged by the edge of the tube.

-Hans

1/4" Kevlar should be plenty strong for this--and the Y-harness is a good approach.


Later!

--Coop

Living in the middle of nowhere is a bit of a drag on the hobby for me, no doubt about it. Nearest clubs are 3-4 hours away. I haven't found anybody on this forum yet that is local to me to get a club started in the area. Too new to the State to know local farmers enough to get permission to use their fields. Really putting a damper on my progression here.

What a strange day yesterday. I don't know which was more odd.... Getting my daughters 'der red max' out of the tree with a 20 gauge shotgun (shot the branch, not the rocket), or using rhubarb leaves as wadding in the painkiller micro. Left my bag of dog puke at home... Oops.

But I did bump up my largest motor flown, with F23's in the mega mosquito. Also finally had the first flight with the PK micro. E18W was a bit slow off a 4 ft rail, weathercocked a bit. Next flights in the PKM are planned on F39's. I'm also thinking I've reached the maximum practical altitudes at Dad's farm. Hitting 1000ft or so is giving me some decent walks in all but the calmest wind. I haven't hit any of them yet, but I am learning very well exactly where all the slough's are. If I go much higher I will start potentially landing in water.

Adding up my total burn for the year it's already 50% more than 2014. That's as of the first day of summer, so plenty of time left to go for more. But I think my certifications will probably be in 2016 due to funding, available time, and logistics of getting to the nearest club launch. New target for 2015 is multiple flights in the G range, with the PK3 build during the cold season for an early 2016 laungh. I'll need another rocket for the G motor target, as I don't have anything in the right size/weight class that will stay low enough at home. So I just ordered an Estes Scion to fill that role. It's going to do double duty as a prototype build for the Painkiller 3 as they're both 3" rockets, so I can plan out the av-bay and electronics layout on something I can more easily test fly.

Build on the Scion is going well. Since it's a relatively unknown PSII kit, I decided to do a separate build thread on it.
So far I'm quite happy with how it's coming together.

I'm seriously considering going for my L1 with this one on the 25th at TSM.
Just need to build an openrocket file for it, as I couldn't find one. Should be easy, just base it off the Leviathan.

https://www.rocketryforum.com/showthread.php?127069-Estes-Scion-Dual-Deploy-Build-Thread.

Edit: Sims out to right around 1,750ft with a couple different CTI motors in the H range.
The 168H54 longburn is the likely choice I think. Only hits 9G maximum, about 250mph.
Nearly the same peak altitude as the 3 grain classic, but over a full second more burn.
I'll look at it again when I have a better idea of the final flight weight.

HHaase said:

Build on the Scion is going well. Since it's a relatively unknown PSII kit, I decided to do a separate build thread on it.
So far I'm quite happy with how it's coming together.

I'm seriously considering going for my L1 with this one on the 25th at TSM.
Just need to build an openrocket file for it, as I couldn't find one. Should be easy, just base it off the Leviathan.

https://www.rocketryforum.com/showthread.php?127069-Estes-Scion-Dual-Deploy-Build-Thread.

Edit: Sims out to right around 1,750ft with a couple different CTI motors in the H range.
The 168H54 longburn is the likely choice I think. Only hits 9G maximum, about 250mph.
Nearly the same peak altitude as the 3 grain classic, but over a full second more burn.
I'll look at it again when I have a better idea of the final flight weight.

Click to expand...

The H54 should be a really fun motor for the Scion. One warning though, it's offset core moonburning grain geometry means the thrust is slightly angled at liftoff. I've flown it 3 times in my MDRM and two of the flights have arced a bit because of the low thrust and angled initial thrust. Once the rocket builds up velocity, however, the long burn is really cool and makes for a really impressive flight. Here's a liftoff pic where you can see the angled thrust, it flew great though:
https://flic.kr/p/u6oQfx
If it helps, my MDRM weighs around 36 oz empty and hit 985 feet and 198 MPH on an H54 flight that arced a bit. 9G maximum sounds about right, the same flight was 9.2G peak and 3.5G average.

Hmmm, didn't know that about the offset core. Is it something easy to see visually, so you can plan and predict the direction? Given the constant wind out here, it would be nice to give it a bit more upwind push.

HHaase said:

Hmmm, didn't know that about the offset core. Is it something easy to see visually, so you can plan and predict the direction? Given the constant wind out here, it would be nice to give it a bit more upwind push.

Click to expand...

You can't see it with the motor built, but you could probably mark the position of the core before putting the motor back together. Unfortunately I don't know which way the thrust angles relative to the core, but maybe someone else can provide feedback on that. The offset is pretty small, so the rocket will still go generally in the direction you angle it. In the photo above most of the angle is due to wind and the initial angle, it's just more pronounced because of the slow burn and offset core. You could definitely angle it upwind, it just may wobble or angle off course a bit. Alternately, the H42 or H53 mellows would also be a long burn, but I don't think they have offset thrust.

Just shot an e-mail to one of the vendors that handles TSM launches, to see which motors he'll have available in time.
Also contacted the prefect to confirm with him that I'll be able to make the attempt, as I've never flown with them before.
Wife has given me the thumbs up, so the pieces are falling into place for a level 1 attempt in 19 days.

Scion will definitely be ready in time with motor ejection, though I'm still going to try and get the av-bay ready for a DD launch. Not going to rush it though. I'll work at a comfortable pace, and whichever way the rocket is ready to go.... is the way it's going to go.

Good luck on your attempt. You seem very conscientious so you got er whipped. No worries, enjoy your levels.

Not much left to do for prep work on this flight, basically just need to ground test the charge weights. Still waiting on a couple pieces of hardware for the scion before I can do that.
In the mean time I'm familiarizing myself with the Raven, which is pretty darn slick of an altimeter system. Otherwise I'm down to just cosmetics on the build. It feels darn good.
The important part is I don't feel rushed, and am enjoying the process still.

Still a lot to do in the next two weeks, but it all feels attainable without pressure. Ask me again on the 22nd how I'm feeling

-Hans

In South Dakota winds, I'm surprised you're leaning toward longer-burning motors like the H-54. It's going to arc, and weathercock. Particularly with a drilled delay, you stand a fair chance of a zipper. I'd suggest you consider something with a higher average thrust and shorter burn time. Not necessarily V-max (however, if that floats your goat, have at it), but the white motor --H163-- would be my personal choice in that case size, along with some antizipper techniques incorporated...

I hate to suggest something that might stress you out or cause you to second-guess your attempt (particularly if the wife has given the thumbs up), but talk to other fliers more familiar with the local conditions about your motor choice, and see what they say --I haven't been in SD in a long time so my memory may be spotty...


Later!

--Coop

Ironically, all the 29mm 3 grain CTI H motors (except the V-max) sim out within about 25ft of each other for apogee.
But I have been leaning toward a higher average impulse just for the reasons you mentioned.
My original concern was the rocket being too light weight for the higher impulse motors, but now that I've been researching what other people fly Leviathan's on, and with a better idea of the final weight, I think more impulse is in order.

-Hans

HHaase said:

Ironically, all the 29mm 3 grain CTI H motors (except the V-max) sim out within about 25ft of each other for apogee.
But I have been leaning toward a higher average impulse just for the reasons you mentioned.
My original concern was the rocket being too light weight for the higher impulse motors, but now that I've been researching what other people fly Leviathan's on, and with a better idea of the final weight, I think more impulse is in order.

-Hans

Click to expand...

The CTI Pro29 166H163-14A White Thunder motor is a good all-wind motor for the 3" Estes Scion weighing 18 oz. without the motor. This motor give the rocket a a maximum acceleration of 30 G off the pad and will apogee at ~1860' with a 7 (high wind) or 9 (low wind) (-7 or -5) second delay.

Having said that, IMO this rocket is a bit light for a L1 cert flight because it will drift a lot in a high wind. If you use a parachute that give a 15 fps descent rate, in a 10 mph wind the rocket will drift 1' sideways for every foot of altitude, and in a 20 mph wind it's 2' sideways for every foot of apogee. That's 620 yard with a 10 mph wind and 1240 yards in a 20 mph wind so you want to have a pretty big field on a windy day (or you don't launch which is the experienced flyers solution.)

A 4" diameter rocket weighing 3 pounds without the motor will apogee at 1000' with the H163 or H410 (which is the all-weather 3G-Pro29 motor for a 4" 3 pound rocket). My definition of an all-weather motor is a motor that accelerates at > 20G in a given rocket which insures minimum weather cocking into the wind.

Use the motor guide at https://www.thrustcurve.org/ to plan your flights. It's quick and easy.

FYI - I think you are confusing total impulse with average thrust. Total impulse to the total push of the motor. The average thrust is the total impulse divided by the burn time. In the 3G Pro29 casing, the H410 with fast burning Vmax propellant burns for ~0.4 seconds while the H63 with a standard burn rate White Thunder propellant burns for ~1 seconds and the H87 Imax propellant burns for ~2 seconds. The H54 uses a slow burning long burn propellant that burns for ~3 second. All of these motors have approximately the same total impulse (force multipled by burn time) but the thrust (force) is much greater for the fast burn propellant than the slow burn propellant in the same casing.

For example, here is the decoding for the recommended CTI Pro29-3G 166H163-14A White Thunder motor. CTI is the manufacturer, Pro29-3G indicates a 29 mm diameter motor casing with 3 propellant grains, 166 is the total impulse in Ns (newton seconds), H is the impulse class (160 Ns < H <=320 Ns), 163 is the average thrust in N (newtons), and 14 seconds is the longest ejection delay for the motor. The delay can be adjusted by -3, -5, -7 and -9 seconds with the Pro29 DAT (delay adjustment tool) to provide 11, 9, 7 and 5 second ejection delays.

Bob

Bob;

I've actually been doing sims with Open Rocket throughout the build. The Scion has also been built as a full dual-deploy using a Featherweight Raven. Final built weight, without motor, comes to right around 760 grams.

Originally I wanted to go with the H54 as I was concerned about having too high of an average impuse for the airframe, given that this is a thin-wall 3" cardboard body tube with a 'recommended' motor of an F15-4. That was before I had enough info to figure out the actual flying weight. Now I'm leaning toward a higher average impulse after I had a chance to weigh it with the full av-bay and deployment gear. Right now I'm looking at the H90 if the wind is fairly calm, and going with the H133 or H163 if it's breezy. All depends on what I see from other flights that morning, forecast currently calls for 7-9.... but that's a week away. I'll make the motor call at the field depending on actual conditions.

-Hans

P.S. I did an edit on the thread title, figured it fits more with where I actually went with things.

Tested the deployment charges today. I could probably go a bit lighter, but honestly I think these are going to work just fine.
A CTI charge for 29mm motors is 18.5 grains, these are 15 grains on the apogee and 12 on the main.
Full extension on the recovery lines, only a touch of recoil on the apogee when it hits the end of the line.
Both chutes pulled out clean and cleared out of their nomex after exiting the tubes.

I'll keep the motor charge in place as a backup, with an un-drilled delay.

[video=youtube_share;SOJ8CqLpqaA]https://youtu.be/SOJ8CqLpqaA[/video]

Had to do a last minute addition of nose weight after I did the final stability calculations, and the scion is now ready to fly. Weather looks perfect, tomorrow I try for L1