Chuffing

[Last Ox]

For a separate discussion of rail speed/safe vertical flight, I measured 480fps video of more than 100 flights. Erratic flight (by otherwise stable rockets) looked largely random, and the two biggest sources of randomness I could identify (but not measure) were wind gusts and failure of motors to light cleanly and come to thrust as designed. I did not have anything helpful to contribute on ignition but am glad to see a thread on the subject.

We can choose to fly when wind is benign, but how can random perversity in motors be avoided? I can guess that scrupulously protecting grains from humidity and oil might be a good idea. I've seen some encourage doubling up igniters. I was unaware of the connection to a specific propellant. It would be great to know when the factory seal was broken on motors and how they'd been stored between then and launch. Honestly though, I can see in a video that a motor does not light cleanly, but it would be tough to work out the effect on the thrust curve (vs nominal) during the critical period from when thrust balances weight and the rocket leaves the rail. Most chuffing motors fly OK.

24" scratch build, flight card lists an E26-10W but does not state the rocket weight.

View attachment _Chuff.mp4

I believe this is one of those things that resist exact science and thereby keep the hobby interesting.

 

[NOLA_BAR]

AT White Lightning propellant seems the most susceptible to oxidation and chuffing. If you look at the grains, they will having varying amounts of oxidation on the surface as a whitish powder. I typically remove this with fine sanding, then as mentioned lightly coat the top of the grain and a bit of the slot with a pyrogen dip. With SU or White Lightning Q-Jet motors, not sure there is much you can do other than QC the igniter and proper placement.

Now here is a question, why aren’t these motors and grains vacuum sealed at the manufacture? Would this add significantly to the cost?

 

[dhbarr]

the two biggest sources of randomness I could identify (but not measure) were wind gusts and failure of motors to light cleanly and come to thrust as designed.

This is actually a pretty useful finding, as longer rails and higher exit speeds both reduce these failure modes.

 

[Handeman]

Speaking of which... At a launch on Sunday, I had an Aerotech RMS motor where the ignitor lit, but somehow did not ignite the motor. I inserted another ignitor, but the motor did not "catch". I am thinking there's now oxidation on the motor, which is preventing the second ignitor from starting the motor. I am thinking I can disassemble the 24/40 case enough to slide in an emery board into the slot and file off just the oxidized portion and then re-assemble and use the motor next month. Can I get away with this, or am I fooling myself into thinking this could work?

That can certainly work. I seldom fly Hobbyline reloads any longer, but when I did, I got past the poor performance and lighting reliability of copperhead igniters by sanding the grains, even brand new ones. The key is to leave the dust in the slot. The dust from sanding the slot is what augments the igniter.

The dust from sanding propellant grains is what I call "pixie" dust. Dropping about 1 cc (1 gm BP equivalent, 1/2 a centrifuge vial) into a single 75mm grain with 1" core and a bare ematch is how we get a quick and consistent ignition on our vertical EX test stand.

 

[Tractionengines]

We can choose to fly when wind is benign, but how can random perversity in motors be avoided?

It can't....Ok. In all seriousness, it can be helped, but it can't be avoided. Any "help" will cost $... the more you want to avoid the possibility of a chuff, and making sure you have full thrust at the moment of liftoff the more $ it will cost.
____________________

The motor MFGs can put more effort into sealing out ambient air. But that will take better plastics with lower permeability, then package with a desiccant pack, while working inside a nitrogen "drybox". Each would have a pink/blue moisture indicator to show if it was contaminated when opened. It comes with a log sheet that the flyer completes when they open the motor and every minute of air exposure is tracked. There are set expiration dates, that motors can't be used after. If the Indicator, or open time, or expirationdate, are exceeded, then the motor must be scrapped at the flyers expense. When taking the rocket to the RSO, you submit your certification that none of those conditions exist under penalty of law. .... etc. etc. etc....

Then we need launch pads with positive hold down of flights. There needs to be a data entry point of what nominal thrust needs to be produce, in what amount of time, before the flight is released. Clusters would need to have verification of which motors are lit, and which, if any, can be omitted and still have a nominal flight..(oh and this all needs to be done within a brief fraction of a second, since our total burn time can be well less than a second total). etc. etc. etc

Personally I would rather, live with our safety distances, safety codes, have some general recommended storage and use guides. Then we accept the chances that our HOBBY MOTOR may have less than perfect performance, while keeping cost per flight as low as possible.

 

[rharshberger]

For a separate discussion of rail speed/safe vertical flight, I measured 480fps video of more than 100 flights. Erratic flight (by otherwise stable rockets) looked largely random, and the two biggest sources of randomness I could identify (but not measure) were wind gusts and failure of motors to light cleanly and come to thrust as designed. I did not have anything helpful to contribute on ignition but am glad to see a thread on the subject.

We can choose to fly when wind is benign, but how can random perversity in motors be avoided? I can guess that scrupulously protecting grains from humidity and oil might be a good idea. I've seen some encourage doubling up igniters. I was unaware of the connection to a specific propellant. It would be great to know when the factory seal was broken on motors and how they'd been stored between then and launch. Honestly though, I can see in a video that a motor does not light cleanly, but it would be tough to work out the effect on the thrust curve (vs nominal) during the critical period from when thrust balances weight and the rocket leaves the rail. Most chuffing motors fly OK.

24" scratch build, flight card lists an E26-10W but does not state the rocket weight.

View attachment 602430

I believe this is one of those things that resist exact science and thereby keep the hobby interesting.

Doubling up igniters is not necessarily a good idea as it IS possible to CATO a motor with an igniter especially if two of them can overpressurize the motor, its also one more wire for the motor to have to spit out as it comes up to pressure, if those two wires snarl together and block the nozzle it can lead to a CATO. Keep it simple use the right size igniter for the motor, if its an older motor check for oxidation on the interior of the top grain if its present scrape carefully to remove. I fly lots of old AT whites and reds and with a good ignitor they usually light first shot, the ones I have the most issues with are the disposables where scraping the core is harder to do.

 

[SolarYellow]

In a G64, I use a slice of compressed black powder from an uncased C6. (unwind the cardboard) The dark stuff is the BP and the grey section is the delay(don't use)
This gives you an igniter to supply the heat to get it started and a small amount of easy to light propellant to keep it going for long enough to become self-sustaining combustion.

Since doing that, I've had ignition first time on every G64. This is similar to the head end pyrogen augmentation inside most Cessaroni motors.

Another possibility, for those who happen to have quantities of it around, may be the addition of one or more chunks of larger-kernel, slower-burning smokeless to the ignitor. Haven't tried it yet, but intend to. A smaller, readily adjustable version of the Pyrodex pellet. Look for videos showing the difference in how smokeless burns vs. BP at ambient pressure. The smokeless burns much more slowly and produces much more flame.

 

[Grog6]

For those outside the US; most countries restrict guns, but military ammo is abundant.That ammo is nitrocellulose and guanidine or nitroglycerin, both added to increase power. silver paint is aluminum powder. Let it dry in a thick coat, and powderize; mix the mil-type gunpowder with a solvent, acetone dries quickly. If you get a clear yellow layer, be careful with it. It could be nitroglycerin. I have not had this problem, however. This will set anything on fire.
If this info is restricted, mods, please delete, or move to restricted. And I won't post such if it's uncool.

 

[SolarYellow]

If you can research out what powder is in said ammo, a single-base powder will be only nitrocellulose, no nitroglycerin. So should avoid the problem mentioned above.

https://en.wikipedia.org/wiki/Smokeless_powder#Composition

 

[kjhambrick]

There was a interesting flight a couple months ago at a club launch where a chuff of the motor sent the rocket off the launch rod, and then as it fell back down the motor ignited. Somehow the rocket still went straight up (maybe at a little angle, but still). It was interensing.

EDIT: Dang ! I missed @Last Ox's post in this thread ! Sorry about the redundancy but I love that video !

Maybe this one that @Last Ox recorded with his high-speed camera ?

This deserves at least a quick look. A 3:1 combination goes up at 2g. There is lots of PFM (I prefer to think of it as chicken bones and toads' blood - I used PFM for many years professionally) involved in whether a rocket flies straight, but there is zero in kinematics equations. At 2g, you do not hit 45fps inside of 16 feet. A very light rocket may burn enough fuel to alter the 3:1 ratio, but that is about it.

The ratio is based (so far as I know) on published average thrust. The thrust that controls lift-off dynamics is the part of the curve between the weight of the rocket (liftoff) and the time the guide(s) leave the rail. This is rarely the same as average thrust, or even 'initial thrust' (based on the first half second). I'd hope that whenever a verified simulation shows a 3:1 rocket hitting 45fps sooner than nominal, the thrust curve data will show a thrust during this window that is enough above average (on which 3:1 was based) to account for the difference. Many black powder motors are made to do very well in this regard, Q-Jet motors may need to be used with care.

Lots can happen, the rocket below RSO'd comfortably, on an E22 motor. This motor nominally builds thrust slower than some, but in this case took pretty much forever from first motion (hop?) to reach average thrust. It went off the rail at only 31fps but flew just fine (in 7-10mph of variable wind). T:W was nominally above 10:1, computed average acceleration was 2.3g over the length of the rail (ignoring the first hop) - on the upper half of the rail, more than 10g.

View attachment 598961

In keeping with the topic of the thread, my impression is that 45fps is a thumb rule that usually works. I doubt anyone could put enough data into a sim to account for the cases where it doesn't. Based on a sample of about 100 launches, quite a few rockets do just fine on much less that 45 fps, and a few outliers (proven designs, with good track records) have trouble well above that speed. Gusty wind is not the flyer's friend, and if in doubt and a longer rail is handy . . .

Under the (benign) conditions given for this poll, I can only say that many rockets, especially with 'front loaded' motors, would probably do fine on as little as 10-15fps (but If I were qualified as a NAR or TRA RSO - and I am not - I would probably not sign off a first flight at less than 5:1 without a credible sim showing 3-4 times that speed, or as light hobby rockets with lots of stand-off).

Note that the motor chuffs then snuffs then finally lites and off she goes ...

Very nice video that @Last Ox captured there !

-- kjh

 

[kjhambrick]

Another possibility, for those who happen to have quantities of it around, may be the addition of one or more chunks of larger-kernel, slower-burning smokeless to the ignitor. Haven't tried it yet, but intend to. A smaller, readily adjustable version of the Pyrodex pellet. Look for videos showing the difference in how smokeless burns vs. BP at ambient pressure. The smokeless burns much more slowly and produces much more flame.

One thing about smokeless powder is that it burns at MUCH higher pressures than BP or Pyrodex when confined ...

I've never tried smokeless powder around a composite motor but all the warnings about using smokeless powder ammo in damascus barrels (*) raises a red flag for me ...

-- kjh

(*) - maybe smokeless powder and damascus barrels is just an old wive's tale: Damascus Barrels - Rumors & Facts but why take chances with antique firearms ?

 

[rharshberger]

One thing about smokeless powder is that it burns at MUCH higher pressures than BP or Pyrodex when confined ...

I've never tried smokeless powder around a composite motor but all the warnings about using smokeless powder ammo in damascus barrels (*) raises a red flag for me ...

-- kjh

(*) - maybe smokeless powder and damascus barrels is just an old wive's tale: Damascus Barrels - Rumors & Facts but why take chances with antique firearms ?

Damascus barrels and smokeless powder is not a wives tale its FACT dont do it, the line between enough and too much is highly variable by gun construction since no two guns are constructed the same and Damascus barrel were made either by hand or very early industrial age and the processes were not exactly consistent. Consistent enough for the lower pressures of BP but not for smokeless. The difference between smokeless and BP if they were rocket motor reloads would be black jack vs blue thunder (warp9 might be too hot).

 

[OzHybrid]

It seems there are many hurdles for you guys. There is much I admire about Australia... It certainly isn't as easy to pursue this hobby there as here. At least it seems that way...

It throws up a few challenges...... But it's a lot of fun.

But when you guys say" just use a pyrodex pellet" ( insert picture of Australian with large veins in forehead)........

 

[prfesser]

One thing about smokeless powder is that it burns at MUCH higher pressures than BP or Pyrodex when confined ...

I've never tried smokeless powder around a composite motor but all the warnings about using smokeless powder ammo in damascus barrels (*) raises a red flag for me ...

-- kjh

(*) - maybe smokeless powder and damascus barrels is just an old wive's tale: Damascus Barrels - Rumors & Facts but why take chances with antique firearms ?

Smokeless powder burns very fast at high pressures, but I wouldn't hesitate to stick a little onto a motor to enhance ignition. The motor is open at one end, so I don't think high pressures would be much of a big deal. Just an opinion.

 

[kjhambrick]

@RocketScientistAustralia --

When you dissect an Estes BP Motor and slice slivers off the Black BP Grain, does it tend to crumble or does it slice nicely ?

Thanks

-- kjh( I need to find something to replace the Thermalite that I am no longer allowed to own without a license in the U.S.A. )

 

[DeltaVee]

@RocketScientistAustralia --

When you dissect an Estes BP Motor and slice slivers off the Black BP Grain, does it tend to crumble or does it slice nicely ?

Thanks

-- kjh( I need to find something to replace the Thermalite that I am no longer allowed to own without a license in the U.S.A. )

I'm not really advocating this but having dissected a C6-7 many moons ago, just chipping pieces off would cause it to crumble, some of which you'd be able to use... however I'd imagine it'd be possible to use a very fine toothed razor saw (X-acto or Zona) to hack off a disk without igniting the grain... but you'd want to do it VERY slowly and VERY cautiously I would think!

 

[Handeman]

I'm not really advocating this but having dissected a C6-7 many moons ago, just chipping pieces off would cause it to crumble, some of which you'd be able to use... however I'd imagine it'd be possible to use a very fine toothed razor saw (X-acto or Zona) to hack off a disk without igniting the grain... but you'd want to do it VERY slowly and VERY cautiously I would think!

What size motors are you trying to augment and why?

I've never found any Hobbyline motors that ever needed any type of augmentation other than using an emory board to file the slot and leave the dust in there. I've never had a supplied igniter in a AT HPR reload fail to light the reload either.

 

[DeltaVee]

What size motors are you trying to augment and why?

I've never found any Hobbyline motors that ever needed any type of augmentation other than using an emory board to file the slot and leave the dust in there. I've never had a supplied igniter in a AT HPR reload fail to light the reload either.

I think this might be for the larger motors... this is something that the Aussies were doing because it costs too much to cannibalize a blue thunder slug and they can't get stuff like that which is available from QuickBurst... I use the latter myself. I've had issues even when filing off the white stuff from WL motors so I went with quick dip enhancement of igniters, propellant grains themselves etc... and/or my own igniters

 

[kjhambrick]

What size motors are you trying to augment and why?

I've never found any Hobbyline motors that ever needed any type of augmentation other than using an emory board to file the slot and leave the dust in there. I've never had a supplied igniter in a AT HPR reload fail to light the reload either.

@Handeman --

What a great idea !

Thanks Jeff !

-- kjh( I was complaining about giving up my Thermalite for HPR Motor Augmentation )

 

[rharshberger]

What size motors are you trying to augment and why?

I've never found any Hobbyline motors that ever needed any type of augmentation other than using an emory board to file the slot and leave the dust in there. I've never had a supplied igniter in a AT HPR reload fail to light the reload either.

+1, and I use pretty small BKNO3V/ProCast ignitors on my 18mm-29mm Hobbyline motors not "scientifically" sized just whatever I have that fits the small nozzles. I will use the supplied ignitors as long as they ARE NOT Copperheads....

 

[Handeman]

+1, and I use pretty small BKNO3V/ProCast ignitors on my 18mm-29mm Hobbyline motors not "scientifically" sized just whatever I have that fits the small nozzles. I will use the supplied ignitors as long as they ARE NOT Copperheads....

Oh, that's too bad, I have a whole fist full of Copperheads I could send your way.

Actually, I never had much trouble with copperheads. I always sanded the slots to generate dust, and cut a 1/2" x 1" piece of the cardboard header off the bag with a small slit in the center. Slide the copperhead through the slit and clamp the alligator clips, one above the slit and one below. Worked almost every time.

 

[kjhambrick]

Oh, that's too bad, I have a whole fist full of Copperheads I could send your way.

Actually, I never had much trouble with copperheads. I always sanded the slots to generate dust, and cut a 1/2" x 1" piece of the cardboard header off the bag with a small slit in the center. Slide the copperhead through the slit and clamp the alligator clips, one above the slit and one below. Worked almost every time.

I too had pretty good luck with copperheads in 18/24/29 mm Hobby Motors.

But I always used a cigarette lighter to split the two foil strips from the central strip of insulation at the tail of the CH.

The cigarette lighter method was easy peasy back when I smoked ... I always had at least one working lighter in my pocket.

But now that I don't smoke anymore, I don't want to have to keep a working lighter in my range box just to prep copperheads

And I don't want my 3-going-on-4-year old granddaughter getting the idea that flames are OK around rocket motors ( she is a rascal ).

The cardboard from the AT Packages is much more substantial than the thin paper I've heard other fliers suggest.

The problem I had with thin paper or with masking tape is that alligator clips on club launchers are liable to bite thru thin paper causing a dead short and no ignition.

I've always got at least one AT Package Header in my trash bag and I already use the lower corners of the rather substantial AT Plastic Bags for ejection charges ...

I'll do my small part -- Full recycling of the AT Packaging is environmentally sound

I'll definitely try your alternating cardboard insulation instead of the cigarette lighter method next time ( all my old motors have copperheads ).

Thanks again @Handeman I'll let you know how it goes after our burn ban has been lifted and we can fly rockets in Central TX again !

-- kjh

 

[kjhambrick]

+1, and I use pretty small BKNO3V/ProCast ignitors on my 18mm-29mm Hobbyline motors not "scientifically" sized just whatever I have that fits the small nozzles. I will use the supplied ignitors as long as they ARE NOT Copperheads....

@rharshberger --

What do you use for blanks to create ProCast ignitors ?

Or where do you get ready-made ignitors for the very small Hobbyline motors ?

Thanks !

-- kjh( I think I want some )

 

[rharshberger]

@rharshberger --

What do you use for blanks to create ProCast ignitors ?

Or where do you get ready-made ignitors for the very small Hobbyline motors ?

Thanks !

-- kjh( I think I want some )

For small ignitors like 18mm or 24mm I use 30 gauge wire wrap wire that I twist into pairs myself, then I use 36 to 40 gauge nichrome (usually 38ga) as the bridge wire using the wire wrap method and then dip in thin pyrogen. For larger ignitors I uses 22 or 24 gauge shooters wire fore the wire. No solder just wire wrapping the nichrome bridge around the two lead wire conductors.
The solder type ematch blanks are too wide to fit through small nozzles.