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Ejection deflector for Motor eject helicopters and Air Brakers

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BABAR

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One of my more recent air brake rockets twice failed to deploy the blades, something relatively uncommon for my birds.

Here is a “hat” to put on the motor (which will also have a streamer on it so I can FIND it!)

The upper cylinder has a piece of aluminum can facing the motor’s ejection charge, the sticks are carbon fiber rods. The idea is the that ejection charge will be directed OUTWARD, so it should assist the rubber bands (which work 99% of the time, I think the displacers on the rocket are just too small and not giving enough leverage.
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BABAR

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jqavins

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Would you show it installed? In the pictures here, I don't see where the gas goes. Also, it would appear that the carbon rods are on the outside of the motor, and wouldn't that keep you from inserting the motor/deflector assembly shown in the first pic?
 

BABAR

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shockie

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Would a length of bt with exhaust holes around the periphery with a nose block on top work?

Is this holding down the blades at launch?
 

MadRocketer

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Would a length of bt with exhaust holes around the periphery with a nose block on top work?

Is this holding down the blades at launch?
That method has worked for me. Six .25” holes evenly spaced at the engine end vented the gas well, but more may have been better. The block still made it 8 inches to the end of the tube and nearly past the rubber band “fence” to keep it put.
 

BABAR

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Would a length of bt with exhaust holes around the periphery with a nose block on top work?

Is this holding down the blades at launch?
In answer to first question, yes, in fact I have designed some like that.

most of my Helis and AirBrakes have been “tubeless”, no motor mount or any tube at all. I have had two (over say 13 years) catch fire, I now put Mylar or foil on the inside of the rotors when I go motor eject.

this “hat” controls the blast, directs it laterally so it assists in blowing the rotors out.

For question 2, no, hat has nothing to do with motor retention.

the rotors are held by burn rubber bands in boost phase (the rubber bands also serve as a motor stop.). Although with the hat in place, the bands do go between the rods.

 

PatD

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That's a very interesting helicopter design.

I
Actually an aerobrake design. Wierd watching them come down, little bit of potato chipping, no rotation, slow and controlled.
 

BABAR

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Wierd watching them little bit of potato chipping, no rotation, slow and controlled.
okay, I googled it and am still lost

what in reference to rocket recovery is “potato chipping”?
 

PatD

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okay, I googled it and am still lost

what in reference to rocket recovery is “potato chipping”?
Sorry, a ref from skydiving years ago. Basically applied to beginners that don't yet control very well. As they descend they roll from side to side and fwd/aft. Don't know where it started, just used the phrase like others did. 😁
 

georgegassaway

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The main issue is not enough leverage for the rubber bands to pull. Make the Stops/leer arms stick out a lat farther out. Also, tat is a heck of a super-long rubber band, which makes me wonder if the pull force is very good to begin with.

I'll note that what you are doing is pretty much like Rotaroc-style helicopter model, just without any blade angle to make it rotate (I made such a model long long ago, no rotation). So check out the article and plans for this A sized model.




Another thing is that if models like that reach apogee then are coming down sort of fast when they eject, or weathercock and never do "slow down" at apogee as they do for a vertical flights, the air pressure makes it very hard for the blades to deploy. So, use a very short delay and try to fly so it will not weathercock, so it can be mostly vertical (and hopefully not quite at apogee yet) when it ejects.

Also, I often rig one blade with a lot more force than the other two blades have (such as two rubber bands, no one). That way, the blade with the really strong band pull will tend to try to deploy out more than the other two, and that by itself will usually cause the model to achieve an angle of attack it to the airflow that causes more drag and more angle of attack until finally it flips and deploys.

I do not have warm feelings about the ejection charge force method you are trying out, being very effective in helping to deploy the blades. I like the ingenuity though.
 

jqavins

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Sorry, a ref from skydiving years ago. Basically applied to beginners that don't yet control very well. As they descend they roll from side to side and fwd/aft. Don't know where it started, just used the phrase like others did. 😁
Now I'm even more confused, but only in an academic, irrelevant way.

At first I assumed it was a kind of flex in the non-blades that I did not expect would happen. I've heard a saddle curve (more precisely, a surface containing a saddle point) sometimes called a "potato chip". Could a strip of balsa ever do that? I wouldn't have thought so, but...

But I don't see any way to relate it to a parachute or the motion under it. :dontknow:
 

BABAR

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The main issue is not enough leverage for the rubber bands to pull. Make the Stops/leer arms stick out a lat farther out. Also, tat is a heck of a super-long rubber band, which makes me wonder if the pull force is very good to begin with.

I'll note that what you are doing is pretty much like Rotaroc-style helicopter model, just without any blade angle to make it rotate (I made such a model long long ago, no rotation). So check out the article and plans for this A sized model.




Another thing is that if models like that reach apogee then are coming down sort of fast when they eject, or weathercock and never do "slow down" at apogee as they do for a vertical flights, the air pressure makes it very hard for the blades to deploy. So, use a very short delay and try to fly so it will not weathercock, so it can be mostly vertical (and hopefully not quite at apogee yet) when it ejects.

Also, I often rig one blade with a lot more force than the other two blades have (such as two rubber bands, no one). That way, the blade with the really strong band pull will tend to try to deploy out more than the other two, and that by itself will usually cause the model to achieve an angle of attack it to the airflow that causes more drag and more angle of attack until finally it flips and deploys.

I do not have warm feelings about the ejection charge force method you are trying out, being very effective in helping to deploy the blades. I like the ingenuity though.
Appreciate the expertise. In fact, the inspiration for my Air Brake series actually WAS a scratch helicopter that, likely due to messed up pitch angle from loose blades, didn’t spin, and came down just fine. None of my helicopters are airfoiled, so it is quite possible most of my designs, whether they spin or not, are relying on air brake drag rather than helicopter blade lift to slow descent. Not gonna win any duration contests, but they are fun to fly, and as you say, “contest or sport, it‘s all good.”

agree the ejection force is not sufficient to deploy the blades alone. I DO however think it helps, just moving the blades out one cm from midline provides better leverage for the pull bands. Agree that ejection past apogee definitely impinges deployment as airflow tends to hold rotors closed.

the “hat” device not only uses a force that is otherwise wasted (the heat is used to burn the retention bands), it also directs the hot ejection particles to a more localized portion of the rotor, so I can beef up the insulation/fire protection there. Previously with my tubeless or “motor mount less” designs, the entire internal surface of the blades was at risk. Fires were rare, but I did have at least two. Now I am either using foil or Mylar tape for protection (Mylar doesn’t do as much, but it helps.)

I wish I had access to (or the personal drive to build) a wind tunnel, I would like to see the difference in drag between my pyramid nose cones and your nose cone and hub arrangement. The latter is not very aerodynamic.

I came up with the integrated fin-rotor about the same time Jim Flis put out the TiddlyWink. Did anyone else independently come up with this? It’s a real win win, more surface area for brake or airfoil, also no residual fins on the dangling tube to resist rotation.
 

PatD

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But I don't see any way to relate it to a parachute or the motion under it.
No parachute involved in an aerobrake or helicopter designs usually. I was talking about the motion of an aerobrake rocket on recovery. They rock back and forth under the "blades" with no rotation. The appearance sparked my memory of skydiving.
 

jqavins

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That I got, the two rotating motions are similar. It's the term, "potato chip" that I don't get. Since my sadle curve hypothesis was blown, now that I know the term comes from sky diving slang, now that I know it's about the motion and not about geometry, what's that motion got to do with a potato chip? But it's not important.
 
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