Non-Laminar Airflow

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BLKKROW

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This is a topic discussed a lot and is very well know.

When I saw this occurrence I thought it was very unique and had to share. Some back story, this is was from a flight on my Blackhawk 38.

This is my guess to what happened, it was about 70*f outside. The rocket had 3-4 coats of clear coat, since the rocket lawndarted I could not recover any flight data. But Open Rocket and RasAero predicted 569 ft/s or roughly 380 miles per hour.

So I can imagine as the rocket's velocity increased and reached its maximum, the outside coat on the rocket because soft and pliable.

Then when the rocket lawndarted into the ground, the dirt stuck to the outside of the rocket, according to where the coat became soft. Then nosecone was attached to the upper section with a 2-56 Nylon sheer pin.

As you can see in the picture below the sheer pin there is a void, where the dirt did not stick to the rocket. Demonstrating non-laminar flow, from the sheer pin head.

I stumbled upon this, while cleaning the parts from the rocket. I noticed the upper section had a lot of dirt attached to it, so I stuck it into my bathtub and filled it up with water. After removing the parts I noticed the dirt was not coming off, i even tried a section with a brush. So the dirt actually adhered to the rocket from the clear coat.

I blogged about this, but I figured I would show TRF just to see what everyone has to say.

Any comments? Discussion?

laminar1.jpg


laminar2.jpg
 

ClayD

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I would nto think that 380mph would heat clearcoat up enough to "soften it" maybe it wasnt cured all the way? my black krylon paint sometimes gets sticky around 190F(in the sun)
how far was the penetration into the dirt? there is emense friction stopping a rocket in say 12" from 400mph.
the spot behind the shear pin would not have the friction the other parts of the body would have as it may have created a place in the hole where the body was not compressing or riding against the dirt.

perhaps the decent was much faster? 700mph? either way, yes it does clearly show, non-laminar flow!!! really cool, thanks for posting it.
 

CarVac

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Nearly the entire rocket will be in turbulent flow because of the joint between the nose cone and body tube.
 

ClayD

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Nearly the entire rocket will be in turbulent flow because of the joint between the nose cone and body tube.
If the entire rocket is in turbulent flow, how do you expain fins working?
even the nose cone has a turbulent boundry layer... all surfaces moving through a fluid does.

saything the pin, separated the flow from the surface vs. non-laminar flow, is symatical.
 

bobkrech

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380 mph is approximately M=0.52 so the flow is subsonic. The isentropic flow equations can be used to predict the maximum temperature that could be obtained if the surface temperature reached the compressed air temperature. For Mach 0.5, T1/T0 = 1.055, 70 F = 530 R. T1 = 1.055 x 530 R = 559 R = 99 F maximum which is not going to soften clearcoat.

What happened is pretty simple. If you shot gravel into you skin at 380 mph, it would embed in your skin. Similarily if your rocket hits gravel at 380 mph, it will embed in the clearcoat.

Bob
 

ClayD

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380 mph is approximately M=0.52 so the flow is subsonic. The isentropic flow equations can be used to predict the maximum temperature that could be obtained if the surface temperature reached the compressed air temperature. For Mach 0.5, T1/T0 = 1.055, 70 F = 530 R. T1 = 1.055 x 530 R = 559 R = 99 F maximum which is not going to soften clearcoat.

What happened is pretty simple. If you shot gravel into you skin at 380 mph, it would embed in your skin. Similarily if your rocket hits gravel at 380 mph, it will embed in the clearcoat.

Bob
a black rocket is probably closer to 150 in the sun on the pad....

http://www.autogeekonline.net/forum...131-black-car-paint-temperature-full-sun.html
 
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bobkrech

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If the entire rocket is in turbulent flow, how do you expain fins working?
even the nose cone has a turbulent boundry layer... all surfaces moving through a fluid does.

saything the pin, separated the flow from the surface vs. non-laminar flow, is symatical.
The boundary layer,whether lamiinar or turbulent, is thin. Using this calculator, at 380 mph and 1' back from the nose tip, the Reynolds number is 3.5x10E6 which makes the flow turbulant and the boundary layer thickness is 0.22", and even at 4' back it's only 0.67" thick. The fin tips are out in the clean air so they're not effected.

Bob
 
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ClayD

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The boundary layer,whether lamiinar or turbulent, is thin. At 380 mph and 1' back from the nose tip, the Reynolds number is 3.5x10E6 which makes the flow turbulant and the boundaryly layer thickness is 0.22", and even at 4' back it's only 0.67" thick. The fin tips are out in the clean air so they're not effected.

Bob
yes i know, it also means the nose cone joint is already in turbulent flow, and not the cause for the turbulent layer. at 380, it is probably not even affecting the rockets flow at all. I was commentin in reply to the post the "entire rocket is in turbulent flow" by carvac - which its not.

380 is speculation, and i guess on accent, which my guess is that it is much faster on decent.

"even fins have a boundary layer"

***EDIT*** MR. Bob, thank you much for posting those links! Good information on the subject matter!
 
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luke strawwalker

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Reminds me of the burn patterns on the white painted ET's on the first two shuttle flights right after ET jettison... you can really see the shockwave impingements causing localized heating on the tanks at the SRB forward attach points and orbiter nose bipod area... as well as the plume impingement burning at the bottom of the tank, and aerodynamic heating of the LOX tank ogive tip...
040612_sts1_et_02.jpg
Later! OL JR :)
 

CarVac

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yes i know, it also means the nose cone joint is already in turbulent flow, and not the cause for the turbulent layer. at 380, it is probably not even affecting the rockets flow at all. I was commentin in reply to the post the "entire rocket is in turbulent flow" by carvac - which its not.

380 is speculation, and i guess on accent, which my guess is that it is much faster on decent.

"even fins have a boundary layer"

***EDIT*** MR. Bob, thank you much for posting those links! Good information on the subject matter!
I meant to write that the entire body tube is in turbulent air, not the entire rocket.

Aside from that, all simulations of lake stakes I have ever run involve the rocket falling a great deal slower than peak upwards speed, due to energy loss.
 

G_T

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The kinetic energy of the rocket is dissipated by doing mechanical work on the ground (pushing dirt away and compressing it), mechanical work on the rocket (damage and wearing away surface material), and into heat due to friction...

Gerald
 

BLKKROW

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As stated in the OP, this was only a guess.

It makes sense it was the friction between the rocket and the dirt as it was entering the ground. That is one thing I did not take into consideration.

So either way if that was the source of the heat or the friction from the air, it does present a form of fluid dynamics.
 

ClayD

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I meant to write that the entire body tube is in turbulent air, not the entire rocket.

Aside from that, all simulations of lake stakes I have ever run involve the rocket falling a great deal slower than peak upwards speed, due to energy loss.
it depends on the terminal velocity of the rocket, and the flight profile, it can- and is not rare for rockets to come down faster than they went up, escpecialy if they dont break mach .5 on the way up.
Really all you need is terminal velocity of the rocket, and the starting speed. 60mph, starting at apogee and the ammount of time to reach terminal velocity. you could use 30mph.... if it looked strait up...

I can tell you terminal velocity on a blackhawk38 should be more than 380mph? now i am currious! Use an EX motor of equal to 1 g accelloration in rasaero to find it :)
 

BLKKROW

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it depends on the terminal velocity of the rocket, and the flight profile, it can- and is not rare for rockets to come down faster than they went up, escpecialy if they dont break mach .5 on the way up.
Really all you need is terminal velocity of the rocket, and the starting speed. 60mph, starting at apogee and the ammount of time to reach terminal velocity. you could use 30mph.... if it looked strait up...

I can tell you terminal velocity on a blackhawk38 should be more than 380mph? now i am currious! Use an EX motor of equal to 1 g accelloration in rasaero to find it :)
I don't know how to do that, so here is the file if your curious. This file is in exact measurements to my rocket.

View attachment bh38rev.alx1
 

CarVac

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blkkrow_blackhawk_lakestake.PNG

I disabled the recovery devices, and you can see that the peak "up" speed is greater than the peak "down" speed.

For a reference, at the crash the prediction shows the rocket going 390 ft/s.
 

BLKKROW

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View attachment 124509

I disabled the recovery devices, and you can see that the peak "up" speed is greater than the peak "down" speed.

For a reference, at the crash the prediction shows the rocket going 390 ft/s.
The flight did have a sight angle of attack, not enough to create a ballistic rocket. That might add a few feet per second, but that is all.

I was also thinking what about static discharge, the rocket did enter some really fine dirt almost like sand? Could that have cause it to stick so well to the rocket?

For reference the rocket entered the ground about 28-30 inches.
 

ClayD

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The flight did have a sight angle of attack, not enough to create a ballistic rocket. That might add a few feet per second, but that is all.

I was also thinking what about static discharge, the rocket did enter some really fine dirt almost like sand? Could that have cause it to stick so well to the rocket?

For reference the rocket entered the ground about 28-30 inches.
pure sand is what is considered "non-compressable" soil. Its not really "dirt"... its used under foundations because it doesnt settle like normal soils do.
its great for stopping bullets too, its why you use sandbags as barracades. I have some sand at home that i shoot into.
Since your impact zone was like "dirt" with a component of sand, i would say the really hard silica of the sand, just cut right into the paint on your rocket, and that is why it stuck. the other dirt was compressable enough that it didnt.
(Sand is the best "dirt" for energetic dissapation" -because it does not give, when it does it just fractures, there for you can just get finer and finer sand, and never compress it more than it is)... it's a perfect ballistic media.

28-30" really seems far for something that didnt go all that fast. but then again the FG nose cones really go all in!

Rasearo is a great tool. I love it because its so freindly to my ex motors. (it could be easier to the Rasp.eng file) but is just perfect imo.
i am curious the parameters Carvac used was. Launch angle, altitude, ect. Most rockets are not launched at 0 degrees, and probably more like 3 to 4 degrees. (on a 6' rail, is damn near impossible to see 5degrees.) on a 4' tower, it would be even worse. a look of the surface winds, along with apogee velocity are good areas to look as well.

It really sucks there isnt any data... ( i am a data lover...)

again thanks for sharing this , it does boggle.

Clay
 
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CarVac

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The sims: 2182 ft ASL, 100 F, 29.96 inches Hg, 2 mph wind, 8 ft rail, and 3 degree tilt.

That said, not much really changes when I set it to 0.
 

BLKKROW

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pure sand is what is considered "non-compressable" soil. Its not really "dirt"... its used under foundations because it doesnt settle like normal soils do.
its great for stopping bullets too, its why you use sandbags as barracades. I have some sand at home that i shoot into.
Since your impact zone was like "dirt" with a component of sand, i would say the really hard silica of the sand, just cut right into the paint on your rocket, and that is why it stuck. the other dirt was compressable enough that it didnt.
(Sand is the best "dirt" for energetic dissapation" -because it does not give, when it does it just fractures, there for you can just get finer and finer sand, and never compress it more than it is)... it's a perfect ballistic media.

28-30" really seems far for something that didnt go all that fast. but then again the FG nose cones really go all in!

Rasearo is a great tool. I love it because its so freindly to my ex motors. (it could be easier to the Rasp.eng file) but is just perfect imo.
i am curious the parameters Carvac used was. Launch angle, altitude, ect. Most rockets are not launched at 0 degrees, and probably more like 3 to 4 degrees. (on a 6' rail, is damn near impossible to see 5degrees.) on a 4' tower, it would be even worse. a look of the surface winds, along with apogee velocity are good areas to look as well.

It really sucks there isnt any data... ( i am a data lover...)

again thanks for sharing this , it does boggle.

Clay
Trust me 28"-30" inches was the depth, I measured the dirt line.

When I walked up to the rocket after my brother found it, I was in awe of how far it dug into the ground. It also hit the perfect spot, it penetrated right into a desert grass area that had some water under the soil, probably the softest part. Seeing how all around it was large gravel mixed with the dirt.

I also highlighted where my minds eye was seeing the airflow/dirt flow.

laminar1.jpg
 
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bobkrech

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The flight did have a sight angle of attack, not enough to create a ballistic rocket. That might add a few feet per second, but that is all.

I was also thinking what about static discharge, the rocket did enter some really fine dirt almost like sand? Could that have cause it to stick so well to the rocket?

For reference the rocket entered the ground about 28-30 inches.
By definition, a rocket is on a ballistic trajectory once the engine has burned out, and it remains ballistic until a recovery system is activated, or in this case when it impacted the ground because the recovery system failed to function, because the only forces acting on the rocket are aerodyanmic drag and gravity.

The impact velocity will be no greater than the terminal velocity of the rocket, and may be lower if the altitude does not provide sufficient height to accelerate to terminal velocity.

Terminal velocity is the velocity where the drag force of the rocket equals the rockets weight so no further acceleration is possible.

F,drag = 1/2 CdArhoV2 = mg = weight

v,terminal = sqrt[(2mg)/(CdArho)] where mg is the weight of the rocket, Cd is the drag coefficient, A is the cross-sectional area of the rocket and rho is the density of the atmosphere.

The terminal velocity of a rocket should be lower than the peak ascent velocity as the sectional density of the burned out rocket is lower than that of a rocket containing unburned propellant, and the rocket is continually experiencing drag forces during flight.

Bob
 

BLKKROW

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By definition, a rocket is on a ballistic trajectory once the engine has burned out, and it remains ballistic until a recovery system is activated, or in this case when it impacted the ground because the recovery system failed to function, because the only forces acting on the rocket are aerodyanmic drag and gravity.

The impact velocity will be no greater than the terminal velocity of the rocket, and may be lower if the altitude does not provide sufficient height to accelerate to terminal velocity.

Terminal velocity is the velocity where the drag force of the rocket equals the rockets weight so no further acceleration is possible.

F,drag = 1/2 CdArhoV2 = mg = weight

v,terminal = sqrt[(2mg)/(CdArho)] where mg is the weight of the rocket, Cd is the drag coefficient, A is the cross-sectional area of the rocket and rho is the density of the atmosphere.

The terminal velocity of a rocket should be lower than the peak ascent velocity as the sectional density of the burned out rocket is lower than that of a rocket containing unburned propellant, and the rocket is continually experiencing drag forces during flight.

Bob
I understand, that since the rocket did not come under parachute it was ballistic. What I meant by the term, was that since the AOA was not significant the rocket flew up under the power of the motor. Then it arced over, so the motor was not providing any thrust on the downward part of the flight.

I cannot explain it well, its like throwing a football vertical, it will reach its peak then come back to earth. Unlike if you throw the football towards a friend 80 yards away its arced so it does go vertical but the ball is still under the power of the thrower once it reaches the receiver.
 

ClayD

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Trust me 28"-30" inches was the depth, I measured the dirt line.

When I walked up to the rocket after my brother found it, I was in awe of how far it dug into the ground. It also hit the perfect spot, it penetrated right into a desert grass area that had some water under the soil, probably the softest part. Seeing how all around it was large gravel mixed with the dirt.

I also highlighted where my minds eye was seeing the airflow/dirt flow.
my 38mm rocket that weights 1lb punched through a paver and 8" into soil. (So i am not doubting) , it is just an impressive display of energy is alls I'm sayin! :)
 

CarVac

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I understand, that since the rocket did not come under parachute it was ballistic. What I meant by the term, was that since the AOA was not significant the rocket flew up under the power of the motor. Then it arced over, so the motor was not providing any thrust on the downward part of the flight.

I cannot explain it well, its like throwing a football vertical, it will reach its peak then come back to earth. Unlike if you throw the football towards a friend 80 yards away its arced so it does go vertical but the ball is still under the power of the thrower once it reaches the receiver.
What??? A football loses horizontal velocity as it flies in a ballistic arc. Also, rockets (should) fly so much more vertically than a football that the horizontal velocity is usually a negligible component of the impact speed.
 

BLKKROW

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my 38mm rocket that weights 1lb punched through a paver and 8" into soil. (So i am not doubting) , it is just an impressive display of energy is alls I'm sayin! :)
Totally! I was amazed when I pull the remains of the rocket out of the hole.

There was enough force that the 3 plastic rivets where destroyed from the Av-Bay under its own weight and momentum. Then the craziest thing, was the 3/16" steel rod that was used as an attachment point for the shock cord in my nosecone. It was bent so much that it was almost at a 90* angle. This was from all the laundry/av-bay sliding forward and bending it.

When I saw this, I was so happy that it did not land through someone, or someones car.
 

BLKKROW

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What??? A football loses horizontal velocity as it flies in a ballistic arc. Also, rockets (should) fly so much more vertically than a football that the horizontal velocity is usually a negligible component of the impact speed.
I understand it loses velocity, but the ball still has some energy from the initial throw. Compared to it being thrown completely vertical, when it reaches its maximum altitude then tumbles back to earth under the potential energy from its height above the ground.

I am talking about shifting from kinetic energy to potential energy. Which is what every rocket "should" do, compared to a rocket that has a AOA of 45* lets say that rocket when it reaches the ground, will still have some kinetic energy and potential energy.

Sorry for all the misunderstandings, I love science and can explain it well in my head. But putting it to words is my downfall.
 

troj

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Remember, all thread is VERY weak in compression, and quickly turns into a spaghetti noodle. It's only beneficial under tension
 

BLKKROW

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Remember, all thread is VERY weak in compression, and quickly turns into a spaghetti noodle. It's only beneficial under tension
I was talking about 3/16" cold rolled steel rod. Not all thread.
 
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BLKKROW

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The width of the coupler, I just measured it at 38.3mm.

Also it was 1/4", sorry I have been writing an english essay all day. This thread really helps me get through it :)

Did my last post help you understand what I was trying to get across?
 

CarVac

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Your wording was far from correct, but what you were thinking of was not strictly wrong.
 
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