Blackhawk 29 Crash - Raven Data Included

[TZ250]

Everyone,
Please help me to diagnose the problem that I had last weekend with my Blackhawk 29's first flight. I used a CTI F240, a LOC 29mm-24mm adapter with tape on the motor and the adapter for a very tight friction fit, a streamer for motor ejection at apogee, -3 seconds on the delay and stock settings from the Raven.

The Blackhawk 29 disappeared off of the rail, but just above the rail everything came apart. It was hard to tell what happened because it happened so quickly.

Someone at the launch thought that the F240 had a manufacturer's defect. I don't know.

The Blackhawk is fine and suffered no damage. The motor case was ejected and not found.

Thank you for your help.

View attachment Nov_26_2011_C.FIPa

 

[cavecentral]

High thrust motors go hard and fast. With the missing case, I wonder if it and/or the adapter pushed through the motor mount and rammed into the bulkhead causing separation? Failure at the thrust ring level.

 

[gregm]

Possibly drag separation?

I can't view the data here at work. How close to burnout would you say things went wrong?

 

[TZ250]

Wow. I had not considered that. Thank you.

I will make some changes to avoid that problem in the future!

 

[TZ250]

Possibly drag separation? How close to burnout would you say things went wrong?

Possibly, that was mentioned at the launch. It's difficult to tell how close to burnout because the motor has a 0.3 second burn time.

https://www.thrustcurve.org/simfilesearch.jsp?id=1837

Picture linked from www.thrustcurve.org

 

[gregm]

I have a Blackhawk 29 that is slated to fly on an I800. Drag separation is my #1 concern. While the parts fit is good, I wouldn't trust it not to come apart at burnout. Either at the payload, nose cone, or both.

 

[TZ250]

I have a Blackhawk 29 that is slated to fly on an I800. Drag separation is my #1 concern. While the parts fit is good, I wouldn't trust it not to come apart at burnout. Either at the payload, nose cone, or both.

The I800 is 38mm. Which Blackhawk do you have?

https://www.thrustcurve.org/simfilesearch.jsp?id=1406

 

[maxvelocity]

If you had a drag seperation why would your case eject? Unless you had a very loose fit

 

[DAllen]

Shear pins?????

 

[gregm]

The I800 is 38mm. Which Blackhawk do you have?

https://www.thrustcurve.org/simfilesearch.jsp?id=1406

Kosdon 29mm I800. :wink:

Believe it is certified as an I560 if I remember right.

 

[gregm]

If you had a drag seperation why would your case eject? Unless you had a very loose fit

A lot of force involved if it took a hard turn off the rail, right?

I would not be at all surprised if the case was flung loose, if drag separation was the issue of course.

Don't know there is any way to know for sure other than to try the flight again.

I can't fly my I800 until MWP next year so maybe I will pick up the F and see what happens.

 

[maxvelocity]

Yea it could happen I guess but id think the motor would have to be a little loose. Those little casings are light and if it had a good friction fit I would think itd take a whole Lotta whip to get it out. At least with my friction fits. I can barely pull them out. Id guess the instant kick of the F240 shot through the adapter. Those are some mean little motors. Too bad you couldn't find the case and adapter that would answer a lot of questions

 

[gregm]

Yea it could happen I guess but id think the motor would have to be a little loose. Those little casings are light and if it had a good friction fit I would think itd take a whole Lotta whip to get it out. At least with my friction fits. I can barely pull them out. Id guess the instant kick of the F240 shot through the adapter. Those are some mean little motors. Too bad you couldn't find the case and adapter that would answer a lot of questions

Another thing I have noticed is that friction fitting motors in composite tubes is not as easy as phenolic or paper tubes.

I lost a Pro29 one grain motor at MWP. I couldn't move it once it was in the rocket but it wasn't there when I recovered it. With phenolic and paper tubes there is some flex that allows for an even tighter fit. I found it a lot more difficult with the glass mmt to reach the point where I could get the motor in the tube tight enough but without catching the masking tape. I had even sanded a nice bevel on the end of the tube in the hopes it would assist in easy motor installation.

It is entirely possible that the adapter failed, the burn of this motor is asking a lot of paper tubing.

 

[Jeroen_at_CTI]

I used a CTI F240, a LOC 29mm-24mm adapter with tape on the motor and the adapter for a very tight friction fit, a streamer for motor ejection at apogee, -3 seconds on the delay and stock settings from the Raven.

The Raven data looks normal. Did you set the delay to 15-3s (3s removed)? That should be fine too.

Jeroen

 

[mikec]

Drag separation is not really the issue people make it out to be, except in extreme cases of very heavy upper sections and/or very draggy lower sections. I'd look elsewhere for an explanation.

drag separation force:

Fsep = a [ M / (1+R) - M1 ]

Where:
a = max deceleration
M = total mass of rocket
M1 = mass of lower section
R = drag ratio of upper and lower sections

If Fsep is +, then there is a drag separation force, if - then there isn't.

Thus we can define the Derimiggio-Newton 1st law of Drag Separation:
If M/(1+R) < M1, then the sections won't drag separate period.

 

[Adrian A]

Looking at the data, there isn't much of a clean thrust before things go haywire. It looks to me like it was a CATO, maybe due to nozzle clogging? Right at ignition there was an accel spike over 90 Gs, followed by a thrust dropout for about 20 msec and then another big spike. The accelerometer only goes to about 90 Gs, so those highest spikes were likely higher than that. How much did the rocket weigh on the pad?

 

[falingtrea]

Since you were using a motor adapter, I assume the rocket was built with a larger motor mount than 29mm? Next question is was just the case missing, or the case and adapter? If both were missing, and the adapter has no external thrust ring, it is quite possible that your motor came loose under thrust and shot through the rocket. The two thrust spikes Adrian mentioned could be initial thrust and then when the motor hit the upper bulkhead on it's way out. I would not trust a friction fit with a high thrust motor.

 

[Mad Bomber F/X]

The I800 is 38mm. Which Blackhawk do you have?

https://www.thrustcurve.org/simfilesearch.jsp?id=1406

Tim makes a 38mm Blackhawk. I have mine slated to fly on a I800 also, a CTI 38mm 4 grain V-Max.

 

[TZ250]

Since you were using a motor adapter, I assume the rocket was built with a larger motor mount than 29mm?

The Blackhawk 29 is a minimum diameter rocket. The motor adapter is used to adapt down to the 24mm CTI 3 grain case.

Next question is was just the case missing, or the case and adapter?

The case and adapter are both missing.

It looks to me like it was a CATO, maybe due to nozzle clogging?

Adrian, thanks for reviewing the data. The nozzle initially had a small amount of flash in it, but I removed that when I reassembled the motor.

How much did the rocket weigh on the pad?

IIRC, it was 412g.

 

[UPscaler]

Kosdon 29mm I800. :wink:

Believe it is certified as an I560 if I remember right.

You are awesome!




TRM


Braden

 

[Adrian A]

The Blackhawk 29 is a minimum diameter rocket. The motor adapter is used to adapt down to the 24mm CTI 3 grain case.





The case and adapter are both missing.




Adrian, thanks for reviewing the data. The nozzle initially had a small amount of flash in it, but I removed that when I reassembled the motor.




IIRC, it was 412g.

So when the accelerometer was pegged, you were (temporarily) getting about 100 lbs of thrust out of the motor, which is about twice what it was designed to produce. Another possibility could be blow-by setting off the deployment charge right away.

 

[llickteig1]

Drag separation is not really the issue people make it out to be, except in extreme cases of very heavy upper sections and/or very draggy lower sections. I'd look elsewhere for an explanation.

drag separation force:

Fsep = a [ M / (1+R) - M1 ]

Where:
a = max deceleration
M = total mass of rocket
M1 = mass of lower section
R = drag ratio of upper and lower sections

If Fsep is +, then there is a drag separation force, if - then there isn't.

Thus we can define the Derimiggio-Newton 1st law of Drag Separation:
If M/(1+R) < M1, then the sections won't drag separate period.

Don't throw too much math at the situation. If a rocket airframe isn't properly vented, the sections can separate due to internal airframe pressure, especially during high-accelleration launch. It isn't really drag separation, but it behaves a lot like drag separation.

--Lance.

 

[Adrian A]

Or keep using the math, but don't forget the differential pressure term. It can be substantial. I had a rocket come apart at Mach 1 at 10,000 feet due to the combination of differential drag and insufficient venting. The altimeter happened to be vented to the inside better than it was to the outside, so its pressure recordings were a smoking gun after I recovered it.

 

[crossfire]

Hello
I flew my all carbon Shadow Raven at MWP-9 on a Kosdon J-1500. I can't remember how long the case was as it belongs to Dave from Shadow, I think around 40" long. The motor was so long that it only went in as far as the bulk head in the booster tube. The motor hung out the back of the rocket by about 1". All I did was friction fit the motor and than used some of Shadows silver tape which went about 1/2" on to motor case and 1/2' on to the body tube. The motor never moved. The flight went to 10500'
GP

 

[troj]

Take a look at the inside of the rocket.

Is there exhaust residue or BP residue over the entire interior of the airframe? If so, that means one of two things -- an ejection charge pushed the motor out, or the motor shot up through the airframe.

If there's no residue, then things were apart by the time a charge fired, and drag separation becomes a more likely culprit.

-Kevin

 

[TZ250]

Take a look at the inside of the rocket.

Kevin, based on your statement, I took a closer look inside the airframe. I looked at it when I pulled it from the corn field, but I was in a hurry.

The good news is that everything is still here and I don't have to buy new parts (other than a sheared threaded rod). Also, it proves the fantastic quality of the vendors that I bought from. The Wildman Blackhawk 29 held together perfectly, the CTI motor fired as expected, the Raven accelerometer recorded 92 g's (but it probably received more) even though it's rated for 70 g's. Thanks guys! I'm also glad that there are many knowledgeable and friendly members here that are willing to help.

Despite my crash, this makes me want to fly the F240 even more. It's a cool little motor!

I'm glad that I made this mistake because I have learned a great deal about rocketry since the flight. The changes I will make will prevent this mistake from happening again.

Soooo, this is what I found.

 

[bandman444]

So you did find the case?

Bryce

 

[jd2cylman]

So you did find the case?

Bryce

Yes he found it. Inside the rocket. See it in the pics.

 

[TZ250]

So you did find the case?

Yes. I should have explained that the top picture shows the inside of the airframe with my smallest flashlight hanging inside. The second picture is just a close-up crop of the first picture. We can clearly see the 29mm - 24mm motor adapter, nozzle and rear closure. The third picture shows the case and adapter after I pushed it out with a dowel rod.

 

[bandman444]

Sorry I guess I missed when you said you found the ejected case.

Bryce