Are "Hobbyline" 24mm and 29mm RMS ejection charges big enough for larger rockets?

[4regt4]

I'm in the process of building some larger MPR rockets, 2.5", BT-80, and 3". The 2.5" will probably have around 18" of body tube that will need to be pressurized (probably OK) by the ejection charge. But the 3" rocket will have some 24" of body tube between top MMT centering ring and payload bulkhead. Someone somewhere posted that the 24mm reloads have 0.5g of BP, the 29/40-120 reloads have 0.7g. I'm wondering if this will be adequate for the larger tubes I'm using. You DD guys have an easy route to ground test, but I don't want to tie the rocket to a stump and waste a reload to see if the nose cone and/or payload bay will pop off.

I did find an online calculator - https://www.insanerocketry.com/blackpowder.html - which is suggesting that the charge for a 3" tube 24" long needs to be ~1.0g. Has anybody been supplementing their 24/40 or 29/40-120 loads?

Thoughts?

Hans.

 

[SolarYellow]

Could always buy some longer MMT and build a stuffer.

 

[4regt4]

Could always buy some longer MMT and build a stuffer.

I've done that in the past, but I'm running a bit short of 29mm tube. I hate ordering just a tube from a supplier, because the USPS has blown out the rates for bigger/longer boxes. But for the 3" rocket I may just have to dig into my precious stash.

Hans.

edit: PS - the black/silver Executioner (RIP) in my avatar had a fairly long stuffer. But that didn't help a completely missing charge in a E20 SU in a flight a couple of weeks ago. Darted from ~1200ft.

 

[rharshberger]

You can always add more black powder, the chargewell will hold several grams.

 

[DeltaVee]

I've never had to supplement.... A 24/60 F35 had plenty of oomph to eject the chute on my Estes Leviathan clone (3" dia. ). I used a 24/40 F39-6 on my AT HV Arcas (2.6" dia). I did not supplement the charge. I also put alot of dog barf in the Leviathan. I figure 0.7 grams is nearly a gram... The calculator is almost certain to be a bit conservative (as it has no way of knowing how tight a fit etc. ). If in doubt, I'd supplement a bit more, but so far ive not done it... I think you'll be fine.

 

[4regt4]

I've never had to supplement.... A 24/60 F35 had plenty of oomph to eject the chute on my Estes Leviathan clone (3" dia. ). I used a 24/40 F39-6 on my AT HV Arcas (2.6" dia). I did not supplement the charge. I also put alot of dog barf in the Leviathan. I figure 0.7 grams is nearly a gram... The calculator is almost certain to be a bit conservative (as it has no way of knowing how tight a fit etc. ). If in doubt, I'd supplement a bit more, but so far ive not done it... I think you'll be fine.

Actually, the calculator ignores any sort of "fit" or whatever. It calculates pressure in a given volume. The recommended was a range of 10-15psi. I went with 12psi.

Hans.

 

[DeltaVee]

Actually, the calculator ignores any sort of "fit" or whatever. It calculates pressure in a given volume. The recommended was a range of 10-15psi. I went with 12psi.

Hans.

Fwiw... my Leviathan has about 20" between the centering ring an the nose cone shoulder. Rms 24/60 and 24/40 reload charges seem to work OK for me. I've not had an ejection failure unless I forgot to place charge... which I've only done ONCE... since you've got a chute, barf and stuff, there is a bit less volume to pressurize... not a big reduction in volume.., but it's not zero either. I've never needed a full gram, except for my upscale L1 Cherokee G. But for anything I've used 24mm reloads on, the stock charge has always been sufficient. If i had any concerns, I'd simply add some more ffff powder.

The 24 mm reload casing charge wells are limited in size so you'd just need to take care when additional powder is used.

 

[DigBaddy]

Put my Der Big Red Max up on an E28-4 with the supplied charge. Wasn't enough - nose cone popped off, but laundry was still in the tube. My only ejection failure all year in 74 flights (so far). Given that, I'll be adding a bit more BP to those loads in larger airframes.

 

[DMehalko]

When i fly a 29/40-120 case in say a loc 4" goblin, i typically bump to 1.4/1.5g

 

[DeltaVee]

When i fly a 29/40-120 case in say a loc 4" goblin, i typically bump to 1.4/1.5g

So I am able to fill a 24/40 or 24/60 red cap with at LEAST a full gram of ffff black powder... (I was not sure it'd fit!). A full gram does not quite fill up the red cap up to the ridge that latches onto the charge well, and if you carefully tap it down a bit, leaves about 3/32" between the powder level and the lip of the cap so you could put a fraction more in. So if in doubt, blast it out!

 

[loopy]

I've never had issues, but I typically don't fly my 40-120 in anything bigger than 3 inch diameter. But I know things like the Sumo and G-Force were designed for that case, and I don't think they had any issues.

 

[DeltaVee]

I've never had issues, but I typically don't fly my 40-120 in anything bigger than 3 inch diameter. But I know things like the Sumo and G-Force were designed for that case, and I don't think they had any issues.

Neither have I (had any issues). However I think it's nice to know you can bump up the amount of black powder somewhat... IF you have to.

 

[T-Rex]

Hi, I'm Terry and I'm a BP addict.....
I've gotten into a bad habit of bumping up the charge in most of my hobby reloads. Have had a couple "energetic" deployments. Knew I had a problem when the forward centering ring went with the nosecone & laundry on a 4" Patriot that I flew on a G80.
Be careful, it can be a slippery slope.....

 

[waltr]

When i fly a 29/40-120 case in say a loc 4" goblin, i typically bump to 1.4/1.5g

Same here on the 4" LOC Goblin.
I add BP to the charge that comes with the reload to 1.2gram. Push the motor frw end into the red cap with 1.2gm BP. Turn over and tap the case to settle the BP and push the cap all the way on.

 

[4regt4]

Hmm.. OK. The online BP estimator gives 1.5g for a 4" body tube of length 20" (which I'm crudely guesstimating for the Goblin) at 12PSI. So looks like I'll basically follow the estimates given using that estimator.

Hans.

 

[Joekeyo]

For what its worth, I flew a Sumo (4" dia.) on a 29mm AT G76. This uses the standard 29mm EC. It worked fine. The Sumo has an ejection piston. I expect this would increase the EC efficiency.

 

[rharshberger]

For what its worth, I flew a Sumo (4" dia.) on a 29mm AT G76. This uses the standard 29mm EC. It worked fine. The Sumo has an ejection piston. I expect this would increase the EC efficiency.

Pistons increase ejection charge efficiency by a significant amount.

 

[Tech 68]

If you've got a used motor case laying around like this, you can test the 29/40-120 max quantity on the ground.

 

[4regt4]

If you've got a used motor case laying around like this, you can test the 29/40-120 max quantity on the ground.

View attachment 543564

Actually, I just remembered that I have a defective 29/40-120 tube and forward closure laying around. I could rig up a charge in that, running the igniter wires out the back like you show.

Hans.

 

[JRL303]

I'll chime in. I don't use the red caps. I use masking tape to make a larger cylindrical BP container, fill it with BP and crimp it closed. Never had an issue with this method.

 

[Lotronex]

I've launched my Super Big Bertha 3 times, on the Hobby Line reloads. The first time was on a 24mm, nose cone popped off, but laundry never came out, I assumed it was just an under powered charge. The second time was a 29mm, but it weather-cocked and turned into a cruise missile. It did eject the chute, but it got ripped off instantly. Third and final time was another 29mm, great boost, heard the event, but just lawn darted. I really wanted to put a stuffer tube in, but I needed to have the repairs done by the weekend for our final launch of the year, so I didn't. At this point I'm just going to cut it down and stick it on a shelf.

 

[waltr]

Actually, I just remembered that I have a defective 29/40-120 tube and forward closure laying around. I could rig up a charge in that, running the igniter wires out the back like you show.

Hans.

Not sure this will work since without a delay element the BP is not contained in the charge well.
Maybe a big wad of wadding will do instaed of a delay element.

 

[4regt4]

Not sure this will work since without a delay element the BP is not contained in the charge well.
Maybe a big wad of wadding will do instaed of a delay element.

Shouldn't be needed. The little hole in the forward closure can easily be plugged. The igniter leads will occupy most of the space, and a drop of wood glue (dried before the BP is poured in...) should seal it up just fine. Or if the igniter leads are not fed out through the hole, just a pinch of toilet paper should plug it up.

Or a wad of cheese, that usually plugs me up.

Hans.

 

[waltr]

Yes, any of those will work.