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  #21  
Old 03-13-2016, 05:55 PM
astronwolf astronwolf is offline
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Quote:
Originally Posted by wjwj
If that doesn't work, I'll try dabbling with something else. As I mentioned before, though, I am more of an RC enthusiast and not so much a rocket enthusiast, so I probably won't do too much experimenting.

Not meaning to discourage you from dabbling, but if you are not much into experimenting, I recommend shelling out the bucks for those long burn rocket glider motors and have fun with the gliders.

Long ago I once thought, "oh what's the big deal, just mix it up, pack some grains, and start flying..." I've been to local EX workshops and those guys develop some impressive motors, but not after investing a lot of time dedicated to experimentation and study, and of course spending a lot of money to learn the process. I learned first hand that it's a non-trivial process. I don't recommend cook-booking up some sugar motors just to save some money. See if you have some EX guys in your area and contact them.
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  #22  
Old 03-13-2016, 07:29 PM
wjwj wjwj is offline
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Ok, I'm going to get started experimenting this week.

Here's what I'll do: I'll build the rocket plane (design is almost done), then I'll test it out with some sugar rockets using the end-burner technique. If that doesn't work, I might try ammonium perchlorate fuel - there are some "formulas" online, and it looks like you can buy the components relatively easily.

The beauty of the internet (and Youtube) is you don't always have to experiment much - there is usually already someone who has.
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  #23  
Old 03-14-2016, 09:09 AM
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KNSU doesn't have the same level of financial investment as experimental AP but it does still have the highest cost of all. Time.
As astronwolf has said, If you're only interested in saving money but you're not so interested in the experimenting, even with the negligible cost of KNSU, then yes commercial motors are for you.

I spent a few hours on BurnSim last night and got some very encouraging results.
You will get results from this if you are determined.
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  #24  
Old 03-14-2016, 09:47 AM
kevinj kevinj is offline
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So for a point of comparison, S8E/P (RC rocket gliders with 1.1 meter minimum wingspan) models flown in FAI spacemodeling competitions are usually at or below 300g in mass.

We routinely fly on Aerotech E6 reload motors. These motors burn for 7 seconds, have a peak thrust of just under 12N and an average of 5.27N. I've flown them to 800-1200 ft.

They are slotted, end burning APCP motors, and because they are reloads and not single use motors, cost about $6 per flight on average.

kj

Quote:
Originally Posted by wjwj
Really, epoxy? Isn't epoxy flame-resistant?

Your post got me thinking, so I did some theoretical physics calculations. Here is what I know:

The rocket plane is expected to weigh no more than 300g. According to the aforementioned site, the 7sec sucrose rocket produces an average thrush of 2lbf, or 9N.

If the plane weighs 300g, its weight is 3N. Therefore, the net force of the rocket is 6N upwards.

The acceleration at that weight and thrust is 20m/s^2, or 2G. Plenty for a rocket plane, since a rocket plane, by definition, is controllable!

This calculation reassures me that if I can mimic the end-burner sugar rocket, my rocket plane has a shot at working.

(P.S. - if the rocket plane accelerates for 7sec, it would reach speeds of >300mph without air resistance. Of course, air resistance will greatly limit my speed, but still cool!)
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  #25  
Old 03-14-2016, 10:05 AM
kevinj kevinj is offline
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Quote:
Originally Posted by wjwj
Ok, I'm going to get started experimenting this week.

Here's what I'll do: I'll build the rocket plane (design is almost done)


Drop us a couple of photos.

kj
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  #26  
Old 03-14-2016, 12:21 PM
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tbzep tbzep is offline
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Quote:
Originally Posted by ///
KNSU doesn't have the same level of financial investment as experimental AP but it does still have the highest cost of all. Time.

It also has the potential to get a little hot when it's being cooked. KNSU propellant has started its share of house fires. A kitchen fire is very expensive, but not as expensive as the whole house and contents. If you do this, do it outside with a hotplate on a calm day, preferably on concrete. At the very least, have a hose handy. Use PPE (personal protective equipment) too.
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  #27  
Old 03-14-2016, 03:38 PM
wjwj wjwj is offline
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Thanks for all your thoughts. To be honest, I'll probably stick with powdered KNSU for now since the thought of cooking it scares me.

I'll also probably try some commercial motors. The problem with these is not just the price point - they don't come in the sizes I need (I'm ultimately looking for G-size motors.) Aerotech makes an F-size, but it is $25 and not reloadable (F10). The other problem is they all have ejection charges.

This is why I am experimenting. I don't mean to say that I "won't experiment." I am just saying that a homemade motor with decent performance will do for me. I don't want to spend hours upon end on the workbench experimenting, and I don't think I'll need to if the kind folks from these forums, along with Youtube, will help me. There are plenty of formulas online that I can follow, and if in the end they don't work, I can always try commercial motors. You should never discourage someone with experimenting (as I would say to any RC newbies.)
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  #28  
Old 03-14-2016, 09:53 PM
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Quote:
Originally Posted by wjwj
...The problem with these is not just the price point - they don't come in the sizes I need (I'm ultimately looking for G-size motors.) Aerotech makes an F-size, but it is $25 and not reloadable (F10). The other problem is they all have ejection charges.
...

Aerotech make a G12 in their RC range, but in the 32mm hardware.
http://www.aerotech-rocketry.com/cu...eloads/G12.html

Also available for the same hardware:
F13, F16 and F23.

To get a 'G' size with KNSU you will have a considerable weight gain. The E6 'equivalent' I modelled in BurnSim needed 36g of propellant(max that will fit in a 24/60 case) for ~35N total impulse, with optimum KNSU(ie, cooked)
Compare that to the E6 which has 22g propellant in a 24/40 case for 37.5N total impulse. A 63% increase in propellant weight and the 24/60 hardware weighs more.
The AT G12 has 51g propellant, so KNSU 'equivalent' would need ~83g.
If you're into competition flying you're at a disadvantage. Sport flying it might not bother you...
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  #29  
Old 03-14-2016, 11:46 PM
wjwj wjwj is offline
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Simon, thanks for your help. Your posts have been particularly useful.

I was not aware of these motors, but they change things a bit. I did not realize that the KNSU motors needed to be heavier. It looks like Aerotech G-12's are available in 2-packs for just $21 - not bad (although I'd have to pay that annoying HAZMAT charge.)

Perhaps I will use commercial motors. They are pretty cheap, have no ejection charge, and clearly have superior characteristics compared to the KNSU rockets.

I'll look into these more. Thanks for your help!
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  #30  
Old 03-15-2016, 12:12 AM
wjwj wjwj is offline
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Simon, here is a link to the NAR's test of the Aerotech G-12:

http://www.nar.org/SandT/pdf/Aerotech/G12RC.pdf

It gives the before and after weight. Do you know if this includes the weight of the case?

Last edited by wjwj : 03-15-2016 at 01:07 AM.
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