PML 1/4 Patriot Build Thread

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I've put everything together to weigh the beast: 2100g.

CG was 36.125 inches from tip, so I added and detracted weight from MMT and piston (epoxy/quicklinks) until I got the file to 2100g and the CG showing 26.125 inches from tip.

Played around motors, and I think this is what I'm going to use. Is the velocity off the pad fast enough? Got the velocity @ deployment real low which I'm happy with for the first flight.

Can someone have a look for me?

Thanks!

Picture 1.png
 
I lift my 3kg Little John with a 123w but no wind at all, give a try on the sim to a H 242t it's the same total impulse, it should give you about the same altitude but with more pad velocity
 
It isn't enough velocity off the rod, about 1/3 low for the rule of thumb 30 mph (13.4m/s). Did you leave the rod at its default value of 1 meter (ugh...metric)? Also, on mine it weighed 4.0 lbs (~1800 g) dry, and got a good 500m level 1 flight in, but used the 5 grain H140 with an 2m rail. With the weight I'd say look at something closer to an I.
 
Thanks guys, useful information. I didn't factor in length of rod, that is something I will have to find out soon, as I don't know what the club has for HPR. How does everything else look on the sim?
 
ArthurSull said:
Thanks guys, useful information. I didn't factor in length of rod, that is something I will have to find out soon, as I don't know what the club has for HPR. How does everything else look on the sim?
Click to expand...

Well, tying into maximum liftoff thrust and launch rod velocity, the acceleration is ~5G, which is low, but as Area66 (who has much more experience than I do) pointed out, on a calm day, could be an ok flight. Ground hit is perfect, apogee deployment looks good, altitude ok (could go a little higher), speed is a little low (which may affect stability as you are right at 1 caliber at a default .3 mach, as mach number increases stability does too, until mach 1, then it drops off again).

I agree with trying the sim on the H242T.
 
the H 242 and the H 123 have boot 230 N/s total impulse, so the speed on the rod will be better and the altitude about the same.
 
Here is the Thrustcurve.org matrix for AT 38mm 20 inches mmt for 2100g 4 inch diameter rocket:

snapshot.jpg

Kenny
 
Ok! Forgot to mention I will be using Cesaroni motors, but helpful anyway as I can match them up with the best counterparts you ahve suggested from AT.

Thrustcurve looks handy, Kenny. Thanks for sharing. I'll do some more math when I get home tonight. Probably best adding some nose weight, too.
 
Thrustcurve.org is my first stop - even just weighing parts, will plug in the detail and adjust through the build .

Also will run same numbers but with smaller diameter MMT, and adjust length for the longest motor cases I have access to. For my cert used a 29mm H250G from AT that booted my Patriot straight up .

Thanks for keeping us in the loop and hope you get you a successful certification flight on the first go around.

Kenny
 
ArthurSull said:
Ok! Forgot to mention I will be using Cesaroni motors, but helpful anyway as I can match them up with the best counterparts you ahve suggested from AT.

Thrustcurve looks handy, Kenny. Thanks for sharing. I'll do some more math when I get home tonight. Probably best adding some nose weight, too.
Click to expand...

Thrustcurve will do Cesaroni motors, too. It's a great resource.
 
VARifleman said:
It isn't enough velocity off the rod, about 1/3 low for the rule of thumb 30 mph (13.4m/s). Did you leave the rod at its default value of 1 meter (ugh...metric)? Also, on mine it weighed 4.0 lbs (~1800 g) dry, and got a good 500m level 1 flight in, but used the 5 grain H140 with an 2m rail. With the weight I'd say look at something closer to an I.
Click to expand...

I would agree. I personally won't let anything go that isn't at least 28 to 30 MPH coming off of rod or rail. Calm or not. I would rather be to conservative and eliminate possible issues due to speed being to low. As also mentioned make sure you check rod or rail length on your simulation. It does make a difference.
 
Hello! I'm still alive and so is my Patriot. My girlfriend and I have just been moving house for the past few weeks and we still don't have internet at home, and work is busy so rocketry's been on the backburner.

Today I ordered my CTI 3 grain case, and a spacer so I have the option for 2 grain motors as well. I really wanted the 38mm starter kit but can't justify the price right now. I'm hoping The 3 grain should be enough to keep me going for a while, I thought the 4 grain is a little overkill right now, plus I'd have to order more spacers yada yada etc.
 
ArthurSull said:
Also, any neat ideas for adding nose weight?
Click to expand...

ALSO also, when you add a Cesaroni motor in on Openrocket, does that add the weight of the casing as well? Or should I weigh the casing/spacers and tally that up before adding in the motor on OR?
 
 
ArthurSull said:
ALSO also, when you add a Cesaroni motor in on Openrocket, does that add the weight of the casing as well? Or should I weigh the casing/spacers and tally that up before adding in the motor on OR?
Click to expand...

As far as I know, it adds the weight of the reload and case for both Aerotech and Cesaroni motors.
 
Awesome! I'm annoyed I have to add noseweight, but as my first HPR kit I think I overcompensated with the epoxy on the MMT.

Is there a surefire way of calculating how much weight to add, or is it just simply adding weight on OR until your CG is how you want it?
 
ArthurSull said:
Awesome! I'm annoyed I have to add noseweight, but as my first HPR kit I think I overcompensated with the epoxy on the MMT.

Is there a surefire way of calculating how much weight to add, or is it just simply adding weight on OR until your CG is how you want it?
Click to expand...

That's how I do it, with Open Rocket. I try to make sure all the weights are as accurate as possible, then add nose weight until I get at least one caliber of stability with the heaviest motor I plan to use.
 
ArthurSull said:
Awesome! I'm annoyed I have to add noseweight, but as my first HPR kit I think I overcompensated with the epoxy on the MMT.

Is there a surefire way of calculating how much weight to add, or is it just simply adding weight on OR until your CG is how you want it?
Click to expand...

Assuming you have accurately put the weight , diameters, and lengths into a roc-sim file including mass for epoxy , chutes, shock cords, electronics ext you will get very accurate readings in roc-sim or open rocket, this will give you over-all stability empty. Then add in the smallest motor size ( lightest) that you think you will fly as that will give you the worst case of mass needed to add. You can that adjust that mass to give you desired caliber of stability.

When I follow this procedure, I am surprised at how often I don't need to add weight or it is less than I thought.
 
Rrwjr said:
Assuming you have accurately put the weight , diameters, and lengths into a roc-sim file including mass for epoxy , chutes, shock cords, electronics ext you will get very accurate readings in roc-sim or open rocket, this will give you over-all stability empty. Then add in the smallest motor size ( lightest) that you think you will fly as that will give you the worst case of mass needed to add. You can that adjust that mass to give you desired caliber of stability.

When I follow this procedure, I am surprised at how often I don't need to add weight or it is less than I thought.
Click to expand...

Keep in mind that heavier motors will move the CG aft. That's why I always sim with the biggest motor in Open Rocket.
 
qquake2k said:
Keep in mind that heavier motors will move the CG aft. That's why I always sim with the biggest motor in Open Rocket.
Click to expand...

I see where what I posted could cause a mistake. If you would use a larger motor in diameter that isn't necessarily a long motor in relation to the size of the rocket you could make a mistake in nose weight. I am currently working on a 38mm Super Jart and when I stuff a longer 4 grain motor inside the rocket I am more stable than a single grain motor. So therefore i dont need any nose weight. This is based on the motor length is a much high proportion of the overall length of the rocket with a 4 grain than a single grain. In this case motor length is over 50% of the actual rockets length so therefore its mass is spread out across much more of the rocket due to its size.

I also should mention I use Roc-sim way more than open rocket and maybe there is a difference there. Thanks qquake for making a clarification that allowed me to see my statement could be incorrect and for also being professional about how you communicated it.
 
Rrwjr said:
I see where what I posted could cause a mistake. If you would use a larger motor in diameter that isn't necessarily a long motor in relation to the size of the rocket you could make a mistake in nose weight. I am currently working on a 38mm Super Jart and when I stuff a longer 4 grain motor inside the rocket I am more stable than a single grain motor. So therefore i dont need any nose weight. This is based on the motor length is a much high proportion of the overall length of the rocket with a 4 grain than a single grain. In this case motor length is over 50% of the actual rockets length so therefore its mass is spread out across much more of the rocket due to its size.

I also should mention I use Roc-sim way more than open rocket and maybe there is a difference there. Thanks qquake for making a clarification that allowed me to see my statement could be incorrect and for also being professional about how you communicated it.
Click to expand...

I never considered that. I can see where a long motor in a short rocket would increase the stability, because it's adding weight forward. Thanks for pointing that out.
 
qquake2k said:
I never considered that. I can see where a long motor in a short rocket would increase the stability, because it's adding weight forward. Thanks for pointing that out.
Click to expand...

Most of my rockets are like that.

I wonder why....
 
Whilst building furniture for our new flat I found a spare length of all thread rod in my tool box. Just perfect for aligning the launch lugs. It fits snugly into the lug and using that in conjunction with the string from nose method and of course a good old fashioned straight line drawn on the BT, I'm going to put on the lugs this afternoon.

Washing BT and lugs, then scuffing both surfaces up real rough, then using my Devcon Epoxy.

IMG_20130901_120823.jpgIMG_20130901_120831.jpg
 
Conformal launch lugs glued on, with the help of the rod.
Scuffed up the BT with rough paper and crosshatched with a hobby knife to help with the bonding.

15.jpg16.jpg
 
Now, here's an updated OR file, with 100g of added nose weight to bring the stability over 1cal.



Everything looks right to me. This is probably the motor I'm going to use for cert, an I170, it's also the biggest I can use as only got a 3g case.

Picture 2.png

In terms of adding nose weight, I saw this in a local hobby shop today. Reckon it'd be easier than glueing in lead shot with epoxy, what do you think?

https://www.hobbystores.co.uk/default.asp?WPG=HOB_HomePage1&itemid=F-GPMQ4485

or there is this liquid gravity stuff too, which might work better:

https://www.horizonhobby.com/products/liquid-gravity-weight-system-DLMBD38
 
On the nose weight, the first is probably lead. Lead, being poisonous, should not be used as weight in a rocket IMHO since we can never 100% assure safe recovery. In the event of loss, shred, cato, etc the lead gets into ground water and wild life, it's not good for anyone. Brass is a good choice, as is steel or bismuth. If you use shot, mixing shot sizes will allow a higher packing density, as the highest you can get with the same size is ~74%, but expect ~65% for random.
 
Thanks, I'll look into it. Also, kudos on thinking about the environment. I'd never have thought. Mind you I daren't think of a CATO for this. :puke:
 

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