Ducted Rocket Experiments

[TheAviator]

I noticed something interesting. I tried to unbend the pipe by hand and noticed that the slag readily flakes off the stainless steel, exposing clean surface. It did not corrode the pipe or pit it or react with it.

Interesting! That would lend some credibility to my hypothesis that the slag is aluminum oxide (and probably some metallic aluminum now that I think about it.) As for corrosion, the chlorine takes time to corrode the metal. For example, the fasteners on my rail launcher were fine when I put it away, but when I got it back out again, only the fasteners that had been in the plume were moderately rusty. Nothing a quick wipe down with some soapy water after the launch wouldn't solve, probably.

 

[GlenP]

...a quick wipe down with some soapy water after the launch...

...or maybe right before the launch? That works for cast-iron Dutch ovens over the fire at least!

 

[rocket_troy]

As for corrosion, the chlorine takes time to corrode the metal.

At ambient temperatures at least. At typical rocket exhaust temperatures, HCl will generally have an effect on metals similar to that of sunlight on vampires, but I agree, the slag (Al2O3) is obviously suppressing rapid corrosion.

TP

 

[iter]

Well what do you know. An Aerotech 75mm phenolic liner is a light friction fit into the 70mm duct on the Habu. No room for additional tape or air gap. Maybe a light coat of heat paint. It's strange how completely unrelated parts fits so perfectly together.

Ari.

 

[Cape Byron]

It's strange how completely unrelated parts fits so perfectly together.

I blame the Metric system...

 

[iter]

Did a static burn with the 75mm phenolic liner. This works well! Liner was hot to the touch after the burn, but I could hold it in my hand. No damage to the foam. The liner shows some ablation, but I expect it's usable for multiple flights. The motor is an F25W-9. It's essentially a smaller version of G40, closest equivalent I had on hand. Less propellant. On the other hand, it randomly had a long delay grain, which produces as much heat stress as a real grain (it burns slower so the hot gas stays in the tube longer, especially without external airflow).

Overall this looks promising.

 

[burkefj]

And it whistles!

Did a static burn with the 75mm phenolic liner. This works well! Liner was hot to the touch after the burn, but I could hold it in my hand. No damage to the foam. The liner shows some ablation, but I expect it's usable for multiple flights. The motor is an F25W-9. It's essentially a smaller version of G40, closest equivalent I had on hand. Less propellant. On the other hand, it randomly had a long delay grain, which produces as much heat stress as a real grain (it burns slower so the hot gas stays in the tube longer, especially without external airflow).

Overall this looks promising.

 

[iter]

And it whistles!

Yeah, that's the audio clipping. DSLR has great optics and very basic audio. In reality it sounded like a normal motor, maybe a little throatier with the foam acting as a resonator.

 

[iter]

Ablation photos.

First image--forward end closest to camera. It's hard to get the whole length in focus on a phone camera. MMT's aft end is exactly at the liner's forward end. Nozzle sits maybe an inch inside the liner. The first observation is that the first 4" or so have no charring at all and hardly even any soot. The first blister is 7" in.

Second image--looking from aft to forward. This is the burnt end. Blisters seem to form in longitudinal lines. I assume it has to do with the tube's construction layers. Or maybe it's where the Mach diamonds hit the walls :=) Perspective makes it look like blisters go all the way up the tube, but again, the first (forward) 7" of the liner are completely blister-free.

 

[TheAviator]

Ablation photos.

First image--forward end closest to camera. It's hard to get the whole length in focus on a phone camera. MMT's aft end is exactly at the liner's forward end. Nozzle sits maybe an inch inside the liner. The first observation is that the first 4" or so have no charring at all and hardly even any soot. The first blister is 7" in.

Second image--looking from aft to forward. This is the burnt end. Blisters seem to form in longitudinal lines. I assume it has to do with the tube's construction layers. Or maybe it's where the Mach diamonds hit the walls :=) Perspective makes it look like blisters go all the way up the tube, but again, the first (forward) 7" of the liner are completely blister-free.

That's so cool to see. Happy glider driving!

 

[iter]

Flew the Habu on a G40W at Seymour this weekend. Photo by Harry Spears.

 

[aerostadt]

Overall, how did the flight do? How was the liner degradation, glider duration, and maneuverability, etc. ? Picture looks great!

 

[David Schwantz]

BVM Heat shield, the paint stuff, is heavy. Would need many coats. But the BVM ceramic blanket is very light weight. Could just wrap around the outside of the liner if need to.

 

[iter]

Yeah, well, I had mixed results. The liner was a hard press fit into the airframe, and it stayed on during the static burn, even needed some force to remove after. On the flight, it spit out the back about halfway into the burn. I have Harry Spears to thank for this incredible photo sequence. In addition to the liner flying out, you can see exhaust flame through the foam fuselage--it looks like it's glowing white-hot. CG shifted way forward and I struggled to bring it down safely.

 

[iter]

Considering the sequence of events, the airplane is in surprisingly good shape. The nose broke off and there's dirt embedded in the fuselage, but that's largely cosmetic. The inside of the fuselage is burnt up, but less than I expected. Incredibly, elevator linkage still works. Airflow through the duct must be a bigger factor than I anticipated, seeing as any foam survived there at all.

There is some structural weakening where foam burned. I'm considering options. Maybe I use a foaming polyurethane glue to install the liner permanently--it can replace some of the missing foam and the liner becomes part of the structure.

In terms of performance, I think I'm getting about what you can expect out of this airframe. The closest comparison I have is Vulcan. Vulcan is heavier by a pound but cleaner aerodynamically. The smallest motors I've flown in Vulcan were G54 and G69. G40 would be a struggle in Vulcan, but flew Habu easily. Aerodynamically, the airframe handles a G40 easily. I think it would do even better on a CTI mellow like H42 or H53.

 

[iter]

Did I leave everyone speechless?

 

[burkefj]

Dude, you sharted your liner! hahahaha

See, it was better if I didn't say anything

Keep it up!

Did I leave everyone speechless?

 

[aerostadt]

Interesting concept having the motor moved internally so far forward. Even though a G40 burns for only about 2 seconds, it puts out a lot of fire and smoke. Repairs tend to make things heavier as you know. Thanks for sharing.

 

[iter]

See, it was better if I didn't say anything

I promised you additional information, I gave you additional information :=)

 

[iter]

Two good flights in as many days. G40 at Seymour, TX (a TNT launch) and G54 at NDRCC

 

[burkefj]

The g54 is pretty good how's the liner holding up?

 

[iter]

The g54 is pretty good how's the liner holding up?

The liner is holding up pretty well. I bet it's good for a dozen flights. We'll see how that works out in practice.

Some more photos from Seymour by Harry Spears.

 

[aerostadt]

What is the weight of this plane? Are you inputting any controls at lift-off?

 

[iter]

@aerostadt : I try to interfere as little as possible on the way up.

Flying on H54 at Hearne yesterday. Video by Brett Noake: