Estes Magnum BT-70 upscale

What is it with me and Magnum maiden flights ending in disaster? LOL. I have a video of the flight that I'll be posting soon.

Looks like what probably happened is that the stages separated too easily. There was enough venting between the motors but perhaps not enough venting through the back of the booster. I had drilled a few holes through the centering rings but perhaps they were too small. I noticed before flight that the booster slid on and off very easily so I actually put a couple small pieces of tape on to snug it up a little. Not enough apparently. There are a couple burnt spots on the rear CR of the sustainer and the C11-5 nozzle was a little sooty but not much which told me that the sustainer didn't get hit with much burning BP chunks at all.

Two possible solutions I'm thinking of, perhaps both, are: 1. Need a way of holding them together a bit longer. 2. Vastly increase the venting back through the booster.


Here's the damage:


Surprisingly, the top half is relatively fine. The nose cone stuck in the dirt a good 3 inches and wedged into the payload bay 2 inches, nearly crushing my firefly altimeter. This was very hard to pull back out, but I finally got it separated tonight.



For the rebuild/repair of the body tube, I don't think I have quite enough BT-70 on-hand and no couplers left so I'm going to have to order some new parts. Maybe I'll take the opportunity to install a baffle while I can as well.

Video is up now. That's my son doing the countdown and pressing the launch button. Also my rocket retriever:wink:

Watching this again, you can hear my acceptance of the inevitable doom: "Oh well..."

[youtube]4mvxq4HL9kU[/youtube]

:sad: Better luck with MkII!

It sounds like small vent holes plus a loose coupler were a lethal combination. I also think you will do better with an F15-0. I just don't like the E16-0 because the case is half empty. That's a longer gap between the two motors and a lot of air that can expand, creating pressure that needs to be vented.

BDB said:

It sounds like small vent holes plus a loose coupler were a lethal combination. I also think you will do better with an F15-0. I just don't like the E16-0 because the case is half empty. That's a longer gap between the two motors and a lot of air that can expand, creating pressure that needs to be vented.

Click to expand...

I'm thinking that's exactly it. I just might go for an F15-0... in addition to larger vent holes and snugging up the coupler. Extra BT-70 and a baffle are probably going to arrive in a few hours so the repair should commence tonight.

I had this idea for another possible solution. I worked up an adapter in OpenSCAD that would hold the two motors together securely and provide adequate venting. A kind of funnel for the burning BP particles as well. This would be 3D printed out of (i believe) ABS. Not sure how durable that would be in this role though. A vented manifold.

I started with a basic transition shape that both motors will "nest" into. I also added two opposing slots like BDB cut into the E16 on his Magnum II.


I'm tempted to try some sort of static test with this, or whatever I come up with. Staging 29mm to 24mm Estes motors has become a mini obsession as once this becomes easier, it opens up some cool options.

I like the coupler idea a lot. You can static test it. I've seen videos where people did it to see if they could stage BP and AP motors. They just fastened them to a fence post. I'll see if I can find the video. I've always wanted to do it.

Finished up the rebuild! Not going to paint just yet until it's flown successfully.

This time, I installed a baffle and replaced the Estes-style mount with an LOC-style kevlar loop attached with a fiberglass strip.




Here it is, whole again! I'll have to snug up the fit between the nose block and the payload tube as it got loosened from the impact last time.




It also occurred to me last night a simpler way of staging these two motor sizes. Since the major issue is that they don't nest together like 24mm and 18mm do, and you can't tape them, why not cut a short section of 29mm motor casing, sand out the interior so that it will nest with a 24mm, and tape that to the 29mm booster?

Took about 2 minutes to cut with a hacksaw:


Then I used sandpaper on a dowel connected to a drill but I suppose you could do it with a dremel. Lots of sanding to get it to fit.



Then I cut notches for some venting as well as clearing the engine hook I have on the sustainer motor mount.



This is how they will connect internally. The adapter gets taped on and the 24mm motor nests inside. Seems so simple, I really hope this works. I don't want to let my success rate fall below 90%.




Here is how it will be installed in the booster. All I need then is to slide the booster on, using the "blue fins" as a guide to keep it aligned. Using engine hooks in this particular design eliminates friction fit but adds complexity. Just need to align the hook with the slots in the adapter and it's all good.




I also drilled some extra larger holes through the booster for better venting. Here you can see the previous three holes and the larger new ones.

I predict success! :wink:

TangoJuliet said:

I predict success! :wink:

Click to expand...

Me too! Great idea modifying the 29 mm casing so it nests into the 18 mm motor.

Ok... I like what I am seeing here...

However, I have a few questions:


Please keep in mind, I'm running on a sleep deficit here, and only just woke up... Where the hell is my coffee?

K'Tesh said:

Ok... I like what I am seeing here...

However, I have a few questions:

Why do you have to tape the improvised part to the booster's motor? Can't you glue it in? or is the booster's motor tube too short for that?

Would you get any improved performance if you cut additional notches in the improvised part?

Did you use TTW fins for the booster? If so, are the centering rings in the booster really even necessary?​

Please keep in mind, I'm running on a sleep deficit here, and only just woke up... Where the hell is my coffee?

Click to expand...

That's a-o-k.
Yes the boosters motor tube is way too short and it has a reverse motor hook. However I was thinking I might be able to glue it on to the sustainers motor mount. Only if I know it works though

When I had just 3 dowels, there was plenty of venting which also allowed the burning BP chunks to go flying all over instead of into the nozzle above. I'd like to try keeping them contained as much as possible.

As far as the centering rings, I suppose they wouldn't be totally needed for centering as i went with TTW. However boosters tend to either float down or fall like a rock. I wanted to build it like a tank since being stout came in handy for my regular Magnum's booster.

Where's that fist pump smiley?
I went ahead and set up a static test with an E16-0 and C11-5. Worked great! I took two videos, one 4K@30fps and another 160p@320fps. I'm in the process of editing them together and will post the video. It was really cool to see BP staging up close and at 10x slower normal speed.

Cabernut said:

Click to expand...

Wow!!! Congrats.

I really like how it turned out. You really can see how energetic the staging event is. The booster flew back about 20ft. I also noticed upon examining the slo mo footage, that the booster nudges back a tiny bit just before staging happens. Perhaps this little nudge is when the BP actually blows forward to the sustainer, and the "poof" is due to the massive pressure buildup when it ignites?

[youtube]s-REbMX4wYQ[/youtube]

Cabernut said:

I really like how it turned out. You really can see how energetic the staging event is. The booster flew back about 20ft. I also noticed upon examining the slo mo footage, that the booster nudges back a tiny bit just before staging happens. Perhaps this little nudge is when the BP actually blows forward to the sustainer, and the "poof" is due to the massive pressure buildup when it ignites?

[youtube]s-REbMX4wYQ[/youtube]

Click to expand...

That is a terrific video! The Estes Magnum is probably my favorite kit and your upscaled version is splendid. It's just plain "sexy"!

As for the problem of direct staging when the motors are of differing sizes, I did something similar when I rebuilt my Estes Renegade booster with a 24 mm motor mount to replace the woefully inadequate 18 mm mount. I glued a short section of a spent D12 casing to the 18 mm B6 motor as an adapter. It worked like a charm with a C11-0 to a B6-4 but when I tried it with a C11-0 to a C6-5...no staging occurred and the sustainer lawn darted. Right now she's in dry dock along with most of my fleet while I recover from this damn shingles!

Cabernut said:

I really like how it turned out. You really can see how energetic the staging event is. The booster flew back about 20ft. I also noticed upon examining the slo mo footage, that the booster nudges back a tiny bit just before staging happens. Perhaps this little nudge is when the BP actually blows forward to the sustainer, and the "poof" is due to the massive pressure buildup when it ignites?

[youtube]s-REbMX4wYQ[/youtube]

Click to expand...

Is it just me or did the booster thrust look like it was squirrelling?

snrkl said:

Is it just me or did the booster thrust look like it was squirrelling?

Click to expand...

You mean right after ignition? They tend to do that I've noticed. I assume it settles out before rod clearance though.

I suspect that happens when the starter ignites the BP on one side of the "divot", leading to offset combustion for the first few milliseconds or so.

tmacklin said:

That is a terrific video! The Estes Magnum is probably my favorite kit and your upscaled version is splendid. It's just plain "sexy"!
C11-0 to a C6-5...no staging occurred and the sustainer lawn darted. Right now she's in dry dock along with most of my fleet while I recover from this damn shingles!

Click to expand...

I aggree, That Magnum is one nice looking bird. The Estes Magnum was probably my second or third two stage rocket. (The first was the Scorpion).

The C11-0 is notorious for staging issues. I think the problem is the motor has more pressure during staging that pushes the motors apart faster which prevents staging. It is VERY IMPORTANT to vent the booster. The tape the motors together is not reliable. Have a gap between the motors with lots of venting.