Bare Necessities: N5800 C-Star Flying Case

[Polyalcoholic]

https://industrialtubingresource.com/category/aluminum-tubing/7075-aluminum-tubing.html

 

[CCotner]

Thanks for the resource, but of the 5 companies it lists, one of them is a broken link, one of them is 2500lbs minimum order, one of them is Kaiser (which doesn't sell aluminum directly at any reasonable scale), and the other two all require the request-for-quote process, which generally implies a minimum order. I know I contacted one of them (Snappy I think) and they said they had a minimum order of 1 full-length extrusion.

 

[edwinshap1]

Check with IMS, or better yet head to one of their showrooms, they have the "scrap" that's actually quite large amounts of material for the consumer price/pound. I was able to get the material for a bunch of aluminum stuff from their scrap area. And if you don't find what you need in the showroom, ask if there's anymore in the warehouse, turned out to be where most of the 6061 was stored, just not enough space for every piece.

 

[daveyfire]

Or, if you're wearing closed toed shoes and pants, just go in the warehouse. I wasted so many hours in there dreaming up new projects...

 

[BLKKROW]

This may be a stupid question, but it has been stuck in my mind.

With htese kind of attempts you really need a rocket that fly's straight. Which means you need the tower to be pointing the rocket in a 0* angle of attack. I have seen people eye ball this with normal Mid/High powered flights.

But on your attempt did you use a level or some other tool to get a 0* AOA?

 

[CarVac]

This may be a stupid question, but it has been stuck in my mind.

With htese kind of attempts you really need a rocket that fly's straight. Which means you need the tower to be pointing the rocket in a 0* angle of attack. I have seen people eye ball this with normal Mid/High powered flights.

But on your attempt did you use a level or some other tool to get a 0* AOA?

What do you mean by AOA? Angle from vertical?

Angle of attack is the angle between the direction the air is moving past the rocket, and the rocket's axis.

If you mean angle from vertical, the precision of the launch pad is the least of your problems. Many rockets at LDRS left the pad perfectly straight, and then turned afterwards. (like Jim Jarvis's FourCarbYen)

Additionally, you're supposed to angle the flights away from Gerlach, not perfectly vertical.

We didn't take a plumb bob to the tower to make it vertical, but in our case, up until the 'event' the rocket appeared to be going incredibly perfectly straight.

 

[bobkrech]

That's above 100C according to MATWEB. See Attachments.

View attachment 6061-T6_MaterialData_9391.pdf

View attachment 7075-T6_MaterialData_9595.pdf

 

[CarVac]

That's above 100C according to MATWEB. See Attachments.

I see, they cross somewhere between 100 C and 150 C.

 

[BLKKROW]

What do you mean by AOA? Angle from vertical?

Angle of attack is the angle between the direction the air is moving past the rocket, and the rocket's axis.

If you mean angle from vertical, the precision of the launch pad is the least of your problems. Many rockets at LDRS left the pad perfectly straight, and then turned afterwards. (like Jim Jarvis's FourCarbYen)

Additionally, you're supposed to angle the flights away from Gerlach, not perfectly vertical.

We didn't take a plumb bob to the tower to make it vertical, but in our case, up until the 'event' the rocket appeared to be going incredibly perfectly straight.

Yes that is what I meant. I appologize I was writing my response quickly while at work and my brain must not be working correctly.

Thank you for the response.

 

[CarVac]

Before:

After:

It took a long time to dig it out:

The nosecone was perfectly fine, but you can see that the 500F engine paint was stripped entirely off of one side of the nosecone, and only partially on the other side. The Aeropoxy resin in the ablative probably is what charred to brown. The ablative did not lose any appreciable thickness, though.

Photos courtesy Allison Mis

 

[Eat, sleep, and Fly]

Before:

After:

It took a long time to dig it out:

The nosecone was perfectly fine, but you can see that the 500F engine paint was stripped entirely off of one side of the nosecone, and only partially on the other side. The Aeropoxy resin in the ablative probably is what charred to brown. The ablative did not lose any appreciable thickness, though.

Photos courtesy Allison Mis

Wait... did the case survive?

 

[CarVac]

Wait... did the case survive?

No, see how the fincan bent out? That's because the case bent outwards over the 7075 airframe tube.

 

[bobkrech]

.....The nosecone was perfectly fine, but you can see that the 500F engine paint was stripped entirely off of one side of the nosecone, and only partially on the other side. The Aeropoxy resin in the ablative probably is what charred to brown. The ablative did not lose any appreciable thickness, though.

Photos courtesy Allison Mis

That's what happens when the nosecone suddenly turns sideways at Mach 4: the upwind side gets roasted. The drag is proportional to the product of area times V^2 whereas the heating is proportional to V^3, so it takes very little time to cook off the paint, and for the velocity to drop a Mach or 2. If you have accelerometer data from instrumentation in the nosecone then you could determine how quickly it decelerated and how hot it got.

 

[CarVac]

That's what happens when the nosecone suddenly turns sideways at Mach 4: the upwind side gets roasted. The drag is proportional to the product of area times V^2 whereas the heating is proportional to V^3, so it takes very little time to cook off the paint, and for the velocity to drop a Mach or 2. If you have accelerometer data from instrumentation in the nosecone then you could determine how quickly it decelerated and how hot it got.

Unfortunately, while we have retrieved all of the data, it's not all useful.

The lateral accelerometer traces clipped even before the rocket visibly started coning. It wouldn't take much to clip them: I just calculated that at 30g (the Raven's limit) and 4000 ft/s (the Raven's estimation of the speed right before the 'event'), the radius of curvature would be 16,666 feet.

 

[mannyskid]

That's what happens when the nosecone suddenly turns sideways at Mach 4: the upwind side gets roasted. The drag is proportional to the product of area times V^2 whereas the heating is proportional to V^3, so it takes very little time to cook off the paint, and for the velocity to drop a Mach or 2. If you have accelerometer data from instrumentation in the nosecone then you could determine how quickly it decelerated and how hot it got.

I have a feeling that their nose cone heating damage happened during flight. I don't know if anyone got any really good shots of their flight, but here is a cropped version of one of Chris' shots of my flight:



You can see that my nose cone did a pretty similar thing to theirs, it was thrown off of the airframe after it went unstable. My nose cone damage doesn't look a lot like theirs, my paint is damaged pretty uniformly around the whole cone. I think that the reason the paint is burned off on one side is because it was spinning at an angle at high mach.

 

[CarVac]

I have a feeling that their nose cone heating damage happened during flight. I don't know if anyone got any really good shots of their flight, but here is a cropped version of one of Chris' shots of my flight:

View attachment 142267

You can see that my nose cone did a pretty similar thing to theirs, it was thrown off of the airframe after it went unstable. My nose cone damage doesn't look a lot like theirs, my paint is damaged pretty uniformly around the whole cone. I think that the reason the paint is burned off on one side is because it was spinning at an angle at high mach.

I concur with Manny.

Bob, you can't see it in the photos, but there are clear diagonal streaks across the boundary between brown and white at about the same angle that the rocket was coning, from the brown side towards the white side.

 

[REK]

You guys had to point your rocket away from the launching range is that correct? If so about how many degrees would you say you had the rocket pointing away?

 

[CCotner]

You guys had to point your rocket away from the launching range is that correct? If so about how many degrees would you say you had the rocket pointing away?

We did our best to eyeball the 5 degree tilt to the northeast (away from Gerlach) that is required by law.

 

[CCotner]

We did our best to eyeball the 5 degree tilt to the northeast (away from Gerlach) that is required by law.

Ok, maybe it isn't required by law. I swear last year when I was getting ready to go to XPRS, I read some requirement by the BLM or the FAA that all black rock launches >50kft or some such be 5 degrees away from gerlach... but I can't find any evidence to suggest that wasn't a hallucination.

 

[REK]

Ok, maybe it isn't required by law. I swear last year when I was getting ready to go to XPRS, I read some requirement by the BLM or the FAA that all black rock launches >50kft or some such be 5 degrees away from gerlach... but I can't find any evidence to suggest that wasn't a hallucination.

I dont know why, but I got the feeling that it is required by law.

 

[CCotner]

I swear I read 5 degrees somewhere, and it was an explicit exception for Black Rock high-altitude flights (like the explicit exception for Black Rock that exempts record attempt rockets from having to have safe descent speeds).

 

[REK]

Well wherever its from I am certain its a rule we all have to follow and of course as a rule it is covered by law probably. Safety first as they say.

 

[bobkrech]

I have a feeling that their nose cone heating damage happened during flight. I don't know if anyone got any really good shots of their flight, but here is a cropped version of one of Chris' shots of my flight:

View attachment 142267

You can see that my nose cone did a pretty similar thing to theirs, it was thrown off of the airframe after it went unstable. My nose cone damage doesn't look a lot like theirs, my paint is damaged pretty uniformly around the whole cone. I think that the reason the paint is burned off on one side is because it was spinning at an angle at high mach.

I concur with Manny.

Bob, you can't see it in the photos, but there are clear diagonal streaks across the boundary between brown and white at about the same angle that the rocket was coning, from the brown side towards the white side.

What I said is not in disagreement with your statement. It the angle of attack was near zero, the paint damage would have been symmetric. The nose cone had to be at a high angle of attack, probably close to perpendicular, to have had the observed damage. High angle coning or flat spinning at high Mach will make the diagonal streaks that you say occurred.

 

[Adrian A]

In the last couple of years, there have been quite a few failures with the N5800 in high-performance rockets, and a lot of them have very similar characteristics, including, significantly, exponentially-increasing lateral acceleration before the breakup. My previous thinking about these is that they were due to airframe weakening due to aeroheating, leading to coupler buckling. But thinking about the thermal time constants some more, and especially for this aluminum-structure rocket, the hypothesis that I like better now is that the center of pressure is moving forward significantly when the rocket is at high speed (> Mach 2.5). I just downloaded data from another repaired Raven today that survived a Mach 3 breakup, and it also clearly shows the lateral acceleration increasing exponentially near the end of the burn, starting at about 2900 feet/second and getting up over 20 Gs immediately before the breakup.

I have heard an anecdotal rule of thumb that the fins should stick out more than 1.25 calibers for effectiveness at higher Mach numbers. Does anyone have some CFD capability or know of some controlled experimental results that can back this up?

 

[CarVac]

In the last couple of years, there have been quite a few failures with the N5800 in high-performance rockets, and a lot of them have very similar characteristics, including, significantly, exponentially-increasing lateral acceleration before the breakup. My previous thinking about these is that they were due to airframe weakening due to aeroheating, leading to coupler buckling. But thinking about the thermal time constants some more, and especially for this aluminum-structure rocket, the hypothesis that I like better now is that the center of pressure is moving forward significantly when the rocket is at high speed (> Mach 2.5). I just downloaded data from another repaired Raven today that survived a Mach 3 breakup, and it also clearly shows the lateral acceleration increasing exponentially near the end of the burn, starting at about 2900 feet/second and getting up over 20 Gs immediately before the breakup.

I have heard an anecdotal rule of thumb that the fins should stick out more than 1.25 calibers for effectiveness at higher Mach numbers. Does anyone have some CFD capability or know of some controlled experimental results that can back this up?

I have alternately heard that using 4 fins is superior once north of Mach 3.

 

[daveyfire]

Dave Triano and Frank Kosdon flew a series of 98mm minimum diameter rockets at Balls about 10 years ago. The motors were similar to N5800s in total impulse and burn time, with carbon fiber cases. The rockets looked like upscaled Shock Value kits. All experienced shreds very similar to a classic N5800 shred. Dave later said the failures were caused by instability due to forward Cp shift at high Mach. (He had a friend at ETH run some CFD for him.)

Anecdotally, SS3 had four fins that stuck out about 1.25 calibers, and was stable at M=4.2.

 

[scatsob]

Yeah but we all know that rockets with three fins fly higher than ones with 4 . On a serious note, when I was designing the fins for my last altitude attempt I found that fins with higher aspect ratios gave more desirable results with respect to stability and low surface area. As a result my fins had a 7" root chord and 5" span on a 4" rocket. I think very low aspect ratio fins are popular because the large root chord allows for maximum adhesion with fins that are glued on. Aluminum fincans solve that problem.

 

[GregGleason]

The IRIS sounding rocket went to Mach 7 with a 75 pound payload. The fins (4) were at ~1.46 calibers.

I don't have the velocity of the IQSY Tomahawk, but it likely was hypersonic as well. The fins (4) were at ~1.53 calibers.

Greg

 

[David de Bruyn]

I did mention something like this earlier, but apparently it was accounted for.

In any case, you can imagine at high Mach numbers that the air would form a cone around the rocket. If the fins do not stick out far enough they will have less of an effect as the air density at closer to the tube will be much lower. Im mincing words here - it's late and I dont feel like drawing pictures :/

In any case, it does seem common at high g flights with low caliber fins. It is probably also also relative to the length of the rocket as well as the "sharpness" of the cone.

Then again, it could be the motor...

 

[CCotner]

I did mention something like this earlier, but apparently it was accounted for.

In any case, you can imagine at high Mach numbers that the air would form a cone around the rocket. If the fins do not stick out far enough they will have less of an effect as the air density at closer to the tube will be much lower. Im mincing words here - it's late and I dont feel like drawing pictures :/

In any case, it does seem common at high g flights with low caliber fins. It is probably also also relative to the length of the rocket as well as the "sharpness" of the cone.

Then again, it could be the motor...

We consciously played the game with tiny, tiny fins because of the extreme performance gain we expected to see by reducing cross-sectional area.

It is entirely possible that, due to inadequate simulation accuracy in RASAero, the rocket was becoming less stable. However, the exponential lateral acceleration we experienced was clearly before the event which led to dynamic instability; the dynamic instability clearly originated at the ~2.7s event that David has identified to be common to every single N5800 flight we can find data on. So while we were experiencing static instability shifts that might have been more severe than RASAero predicted, they did not cause the subsequent dynamic instability (pitch-roll coupling and 'coning') which ended the flight.