GoDevil 54MD Snag

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Jasons

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Evening folks,
Running into a problem. After several successful ground tests. On my last flight, it appears the G-force of launch is packing my main chute, lines etc. up against my charge wells and not shearing the (2) 2-56 pins. Only explanation I can come up with considering the ground tests went so well. Anyone experience this? Possible fixes?

Jason
 

o1d_dude

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As to the chute, you could build a “chute shelf” to prevent the laundry from traveling rearward under power and compressing itself against the pyro charge.

You did say the ground tests worked well, right?
 

Cameron Anderson

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I had a similar issue with my Wildman Mach 2. I did extensive ground testing but when it came to launch I only got a partial chute extraction. It is hard to simulate G shock from launch in ground testing.
 

Jasons

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That chute shelf may actually work. Its interesting, yes, the tests were flawless. First flight with these kind of forces. Cameron, did you implement any changes to get better results on your Mach 2?
 

Cameron Anderson

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That chute shelf may actually work. Its interesting, yes, the tests were flawless. First flight with these kind of forces. Cameron, did you implement any changes to get better results on your Mach 2?
I went through probably five major design changes before I flew on an L1000 last year (first and only flight...the up part was spectacular). Several times since I've tried to redo the setup to get something I like but no luck...I tried adding a small drogue, I tried a streamer, a different packing method, different charge set up. Nothing delivered consistent ground test results. My friend used a reefed main chute with redundant cable cutters on his Mach 2 and had great results. I am considering stealing his set up.
I want to fly my Mach 2 again on the K455 in September so I'm going to start fiddling with it again in August, but all I've learned so in several hours of tinkering far is how much I hate MD (but I can't stay away! It's an addiction).
I ordered the GoDevil 54 a few days ago, it literally arrives tomorrow, and I am already dreading it.
 

Cameron Anderson

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That chute shelf may actually work. Its interesting, yes, the tests were flawless. First flight with these kind of forces. Cameron, did you implement any changes to get better results on your Mach 2?
If you can fit it, a piston in your upper air frame for your main deployment should work to clean up your ejection. I use pistons religiously (where I can fit them).
 

Jasons

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Trial and error then I suppose, thanks for the info. MD is cool but challenging, which is ok too. Have had an overall great experience with this GoDevil..you will enjoy it.
 

tfish

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I'm not familiar with how the ejection charges are setup (blowing recovery gear up into a closed end) on a Go Devil 54. Below is how I set up my ejection charges on most of my...... LOW Altitude... roughly below 23K MSL..... min dia rockets. I place the charges on top of what I want to blow out of the tube. The photos are of a 54mm min dia rocket with a reefed chute. I balloon for the ejection charges. Balloons and finger tips from gloves are the least efficient containment method for BP..(it scatters a lot of the BP) But I like this method because it places the charge on top of the object and blows it out the opening.

In the below photos the nose cone houses all of the electronics. The charges are set up to blow the nose cone off.

20200407_152039.jpg
20200407_152227.jpg
20200407_150431.jpg


The above photos were mocked up for photos only..you might notice the charges had been fired and the cable cutters are not 'open'.

as with any new deployment setup...do a bunch of ground tests prior to flight.

Tony
 
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rharshberger

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My guess is that the chute is getting wedged into the airframe (the ejection charge can still blow off the nose cone) and the nose cone and shock cord are just not enough to get it moving. Chutes dont get pushed out of airframes by the ejection charge, they slide out on their own unless a piston or some other method is used to force them out. Depending on the size and material of the chute combined with a nomex protector the laundry may not be able to overcome the friction keeping it from sliding out of the end of the parachute bay. Ejection gasses will simply go path of least resistance which means around the chute to exit the airframe.
 

Dipstick

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Interesting, I had exactly the same problem with a min diam. 54mm scratch build. Ground test was flawless but in flight it didn't shake out.

I simply upped the charge a bit on the next flight, never thought about it being the chute packing...
 

cerving

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Maybe a really big streamer would work... it would help you find it better, too.
 

OverTheTop

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I ran single-ended dual deploy on mine (actually a 54mm Tomach, but same-same). NC electronics would blow the NC (with a small drogue) off at apogee. Main would stay in the airfram until the mid-bay electronics blew the bundle out. Worked OK.
 

blackjack2564

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Jason...how much BP are you using and where?

One of the failure modes I see...is just the ground test & not figuring the dynamics of flight into the charge. i.e. not enough BP.

I always do my first flight low enough to see all events and make sure they function.
Flown enough min. diam. to know how much BP to use on new ones, just by size/diam. There are always some quirks that come up depending on altitudes flown, but after you gain experience, ya just know.
Your issues are most likely simple, ya just haven't figured it out yet.Having a mentor goes along way,
Even if several peeps build the same rocket, rarely do they ever build the same.
I too use glove fingertips in all but extreme flights...[over 20,000ft]
 

Buckeye

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Evening folks,
Running into a problem. After several successful ground tests. On my last flight, it appears the G-force of launch is packing my main chute, lines etc. up against my charge wells and not shearing the (2) 2-56 pins. Only explanation I can come up with considering the ground tests went so well. Anyone experience this? Possible fixes?

Jason
This is a good thread. I recently had a couple near-minimum diameter rockets exhibit perfect ground tests and initial flights, yet the nose cone did not budge for main deployment during the next flight. And yes, I even had redundant charges that both fired!

I attributed the problem to cold weather and not enough containment of the charge canister (centrifuge vial), causing incomplete burn of the BP. However, my ground tests were damn cold, too. Now I am starting to think parachute shifting/jamming is the problem. I like the piston idea. I will try that. Or, my parachute packing sucks, and I need a new technique

I'll note that this is only a problem in my Madcow fiberglass rockets. The fiberglass is heavy and needs more chute, and thus does not pack very nicely in small airframes. Packing a smaller chute in a cardboard frame of same diameter never gave me issues.
 

Glasspack

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Jason...how much BP are you using and where?

One of the failure modes I see...is just the ground test & not figuring the dynamics of flight into the charge. i.e. not enough BP.

I always do my first flight low enough to see all events and make sure they function.
Flown enough min. diam. to know how much BP to use on new ones, just by size/diam. There are always some quirks that come up depending on altitudes flown, but after you gain experience, ya just know.
Your issues are most likely simple, ya just haven't figured it out yet.Having a mentor goes along way,
Even if several peeps build the same rocket, rarely do they ever build the same.
I too use glove fingertips in all but extreme flights...[over 20,000ft]

Jim,

For those of us that have charge canisters already mounted on the bulkhead..., what is your thought on placing the igniter on top or in the middle of the powder charge as opposed to the bottom of all the powder; before its all packed tight and taped up for flight. I have read other tests that show the powder can get blown outward, and of course some of it may not burn. Thinking if the fire started in the middle or the top ….any blown powder would have to go through the flame, theoretically helping create a full burn of the powder. My LVL 2 model is not minimum Diameter but I worry about so many things......

Thank you
Paul
 

crossfire

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I like to put match about half way in charge holder. It's worked for me. Back in the day we used to place charge down below chute in the booster tube. It kind of makes sense charge fires pushing everything out of the tube.
 

OverTheTop

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For those of us that have charge canisters already mounted on the bulkhead..., what is your thought on placing the igniter on top or in the middle of the powder charge as opposed to the bottom of all the powder; before its all packed tight and taped up for flight.
FYI I always have my eMatches on the top of the BP.
 

Glasspack

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Over the top... Then Is there some truth to all of that thought of powder being blown out with out burning ?
it was a very convincing article I was read ………...
 

Buckeye

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Jim,

For those of us that have charge canisters already mounted on the bulkhead..., what is your thought on placing the igniter on top or in the middle of the powder charge as opposed to the bottom of all the powder; before its all packed tight and taped up for flight. I have read other tests that show the powder can get blown outward, and of course some of it may not burn. Thinking if the fire started in the middle or the top ….any blown powder would have to go through the flame, theoretically helping create a full burn of the powder. My LVL 2 model is not minimum Diameter but I worry about so many things......

Thank you
Paul
I like to put match about half way in charge holder. It's worked for me. Back in the day we used to place charge down below chute in the booster tube. It kind of makes sense charge fires pushing everything out of the tube.
FYI I always have my eMatches on the top of the BP.
Over the top... Then Is there some truth to all of that thought of powder being blown out with out burning ?
it was a very convincing article I was read ………...
Same here, that way the unburnt powder has pass through the burning powder to get out ofcthe charge well.
OK, this may be a good practice to pack BP and matches, but it does not explain why the ground tests work and the flight doesn't.
 
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OverTheTop

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Then Is there some truth to all of that thought of powder being blown out with out burning ?
I have read an article somewhere where testing was done in a vacuum chamber and the mass of the system weighed after setting off the charges (and letting gases out). The results showed that more BP was burned (lower final mass of system) if the match was on top of the powder. I can't remember where I read the article unfortunately.

OK, this maybe a good practice to pack BP and matches, but it does not explain why the ground tests work and the flight doesn't
Very true. I personally have not suffered the problem but I blow the NC of first, the chute coming out of the airframe later. Other people may have a standard dual-deploy perspective.
 

blackjack2564

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Always put match on top to prevent blowing BP out and up into airframe.
If put in bottom you blow a column of BP into your chute and risk damage from 2nd stage of burn.

These photos taken from the high speed video show an initial blast..then
Screen Shot 2020-07-15 at 7.36.52 PM.png


Yes that is the BP being blown out and up! Even though several layers of electrical tape were used to contain! Note time stamp is all at 33 seconds. This happens so fast it appears as one flash at normal speed.


Screen Shot 2020-07-15 at 7.37.10 PM.png
Screen Shot 2020-07-15 at 7.37.28 PM.png
.column of BP being thrown up and the secondary flash of the column continuing to explode.
This happens so fast it would appear to be only one.
Mendal of Rocket Junkies charge containers did the testing when he made us some for the 3/4 scale Nike Smoke project.
I found the match on bottom video but match on top is lost on U tube. However suffice to say it showed a single neat clean charge going off with none of the effect shown in first video. NO secondary flash.

Watch it and learn! I have been telling folks this for years

 
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blackjack2564

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Now to address the other issues....
Smallest charge I use is .5 gram in 38mm minimum in charge holder long and thin like gun barrel. Highly directional and more ump.than finger tip which is omni directional.
Same for 54mm but with .75 BP Head end deploy also in finger tips
Same size used in 75mm with .75 grams...but only 4in of space between motor and bulk plates,, drogue and cord packed between holders. Use 3 4-40 shear pins. in NC the drogue charge really hits hard and don't want to shake out main.
It doesn't sound rational but it is...lol

How tight or loose coupler fit makes a difference. With a marginal charge and a loose coupler...in flight the pressure on NC from air passing over it, can hold it in place and charge pressure leaks by...this won't happen on ground testing or as I say "dynamics of flight"

There are technical terms and calculations to describe all this, I gave you the shade tree mechanic version.
Many other issues we can talk about....next time ya see me at a launch...I hate typing and searching for this stuff. It's been posted numerous times over the years

There is a good discussion of all this starting at bottom of pg 2 from my Nike build thread; https://www.rocketryforum.com/threads/excelsior-the-3-4-scale-nike-smoke-success-flew-today.144294/

Click on pics to enlarge...full size got lost during forum change over.
 
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blackjack2564

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Here is my 54mm Mach-2 minimum charge holders.. 1.75 long .5 hole for charge.
apogee uses holders.
main at low altitude uses finger tip charges. get detail in making them can be found right at top of high power under the sticky...Cj builds DarkStaretc..go to index and all is there.
Hope all this helps guys. still need info on what size yours charges are for what size rockets and how much area being pressurized to figure out what went wrong..
Good luck and have fun.

DSCN0287.jpg
DSCN0469.jpg
DSCN0287.jpg
DSCN0282.jpg
 

David Schwantz

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I have the Go devil 54 also. Only one flight so far on a K550W. Recovery was perfect. I do not use charge wells on the MD stuff. I place my charges in vials with the long wire so that I can put them behind the chutes. It is my guess that I just "blow" everything out this way. So far have not burned holes in a chute like this. Good luck.
 

David Schwantz

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Always put match on top to prevent blowing BP out and up into airframe.
If put in bottom you blow a column of BP into your chute and risk damage from 2nd stage of burn.

These photos taken from the high speed video show an initial blast..thenView attachment 424632

Yes that is the BP being blown out and up! Even though several layers of electrical tape were used to contain! Note time stamp is all at 33 seconds. This happens so fast it appears as one flash at normal speed.


View attachment 424633View attachment 424634.column of BP being thrown up and the secondary flash of the column continuing to explode.
This happens so fast it would appear to be only one.
Mendal of Rocket Junkies charge containers did the testing when he made us some for the 3/4 scale Nike Smoke project.
I found the match on bottom video but match on top is lost on U tube. However suffice to say it showed a single neat clean charge going off with none of the effect shown in first video. NO secondary flash.

Watch it and learn! I have been telling folks this for years

This is exactly why you get powder burns when the gun barrel is to close to the target.
 
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