A Sci-Fi Scratch Build - IHSF "Kessel Runner"

[lakeroadster]

Started building the Rear Stability Pod...

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[lakeroadster]

Let's talk "Drag Separation"...

The Rear Stability Pod attaches to the spool. This is a rear eject rocket. So will the spool slide out when the thrust of the rocket stops?​

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I'll have some masking tape holding the spool in place... but not much tape.​

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Likely the fuselage will be more draggy than rear eject.​

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Thoughts?​

 

[neil_w]

Likely the fuselage will be more draggy than rear eject.​

I would tend to agree with this. Drag separation should be more of an issue when you have a low-drag, finless forward section, possibly with nose weight, vs. a rear section that has extra drag due to the fins. Your front section is monstrously draggy, almost certainly much more so that the stabilizer. Hard for me to imagine that front section drag-separating from almost any conceivable rear section

 

[Azamiryou]

My mindsim says there's going to be way more drag on the main body than on the stability tail.

 

[jqavins]

I agree that the greater drag on the main body probably makes you safe, but I have one concern. You know me, I always have "one concern".

The front section is also a lot heavier. If the two parts were, hypothetically, separate at the moment the thrust stops, the rear assembly may well decelerate faster, because the lower drag is acting against a much lower mass. But they're not already separate, so the effect here is moving beyond my ability to mind sim (which it shouldn't, but sophomore statics was too long ago).

 

[NTP2]

I agree that the greater drag on the main body probably makes you safe, but I have one concern. You know me, I always have "one concern".

The front section is also a lot heavier. If the two parts were, hypothetically, separate at the moment the thrust stops, the rear assembly may well decelerate faster, because the lower drag is acting against a much lower mass. But they're not already separate, so the effect here is moving beyond my ability to mind sim (which it shouldn't, but sophomore statics was too long ago).

There are 2 fix’s for this

1 fix it (fold out tabs on the bottom or ullage motor if your being fun)

2 ignore it and hope it fixes itself

I’ll leave it to @lakeroadster for choice.

 

[lakeroadster]

There are 2 fix’s for this

1 fix it (fold out tabs on the bottom or ullage motor if your being fun)

Ullage Motors are for liquid fuel rockets in zero-g environments... which isn't the case here. Guess I'm not being "fun".​

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2 ignore it and hope it fixes itself

I’ll leave it to @lakeroadster for choice.

A bit of masking tape should be fine.​

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If I were ignoring the drag separation... I wouldn't be asking the question.​

 

[NTP2]

Ullage Motors are for liquid fuel rockets in zero-g environments... which isn't the case here. Guess I'm not being "fun".​

true, but they often serve a second purpose of pushing stages apart. and the fun part was a joke because It'd be stupidly complex and a terrible idea.

A bit of masking tape should be fine.​

that's probably the best method.

If I were ignoring the drag separation... I wouldn't be asking the question.​

its an answer to the question. eg what do I do if someone I don't like is trying to talk to me? Ignore them.

 

[lakeroadster]

1 fix it (fold out tabs on the bottom....

explain your concept of "Fold Out Tabs"​

 

[NTP2]

explain your concept of "Fold Out Tabs"​

have some tabs on the bottom of the top and boost the drag so it presses into the bottom instead of pulling away.

 

[neil_w]

I just can't imagine that the front of the rocket needs more drag. Although the last set of pictures above fooled me into thinking we were talking about the B29 here... I still think the Kessel Runner is very draggy as well. The stability tail is just a few fins.

I dunno, it just doesn't seem like a real concern to me, although as always I could be wrong because this is just intuition.

 

[NTP2]

I just can't imagine that the front of the rocket needs more drag.

I never said it was a good idea... it was a throwaway comment.

 

[lakeroadster]

I just can't imagine that the front of the rocket needs more drag. Although the last set of pictures above fooled me into thinking we were talking about the B29 here... I still think the Kessel Runner is very draggy as well. The stability tail is just a few fins.

I dunno, it just doesn't seem like a real concern to me, although as always I could be wrong because this is just intuition.

A bit of masking tape should be fine.​

 

[BABAR]

Interesting.

Although your CG for pop pod/stabilizer unit statically will hang as pictured, depending on sink rate, it will probably be stable forward end down. So should be good, will impact on tube, not boom or fins.

Maybe.

 

[lakeroadster]

Interesting.

Although your CG for pop pod/stabilizer unit statically will hang as pictured, depending on sink rate, it will probably be stable forward end down. So should be good, will impact on tube, not boom or fins.

Maybe.

Tube.... What Tube?​

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[jqavins]

Interesting.

Although your CG for pop pod/stabilizer unit statically will hang as pictured, depending on sink rate, it will probably be stable forward end down. So should be good, will impact on tube, not boom or fins.

Maybe.

Tube.... What Tube?​

 

[lakeroadster]

View attachment 683103

Yeah, that's what I thought you folks were saying.​

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There is no way that tube will be pointing down once things settle and the chute is deployed. The motor is spent and the lever arm of the stability pod will mean the stability fins will be pointed down.​

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The fuselage does the ground contact, nose first,​

followed by the spool, fins first,​

followed by the chute.​

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11 fps decent rate isn't enough for the pod to fly into the wind.​

 

[jqavins]

Yeah, that's what I thought you folks were saying.​

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There is no way that tube will be pointing down once things settle and the chute is deployed. The motor is spent and the lever arm of the stability pod will mean the stability fins will be pointed down.​

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The fuselage does the ground contact, nose first,​

followed by the spool, fins first,​

followed by the chute.​

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15 fps decent rate isn't enough for the pod to fly into the wind.​

I agree, the fins won't be effective and make the tube point down. I was just answering your question "What tube?"

 

[lakeroadster]

Stability Warp Pod Installation

I shimmed the rocket body level and then installed a 5/16" dowel into the launch lug to establish the C/L. Then, shimmed up the area just ahead of the Stability Fins and marked a 5" c/l for the rods. I used masking tape to hold the fins in their rotational orientation and then preliminarily applied some glue where the dowels slid through (2) 3/8" dia. holes in the rear spool bulkhead.​

 

[BABAR]

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11 fps decent rate isn't enough for the pod to fly into the wind.​

7.5 mph wind. Yeah, not much.

I’ve seen many rockets coming down under streamers and some chutes that were completely horizontal, the nose cone was coming down first.

 

[lakeroadster]

7.5 mph wind. Yeah, not much.

I’ve seen many rockets coming down under streamers and some chutes that were completely horizontal, the nose cone was coming down first.

Apples and Oranges... or should I say Nerf Balls and Oranges?​

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Front eject, with a chute, coming down horizontal, nose cone first ​

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[lakeroadster]

Rear Stability Warp POD.... Glue fillets

 

[lakeroadster]

Finished Rocket, awaiting paint for the Pod. Probably going to use High-Temperature Paint... maybe some header paint.

 

[Daddyisabar]

High temp hemi orange. Paint will still burn if in danger zone but it is a cool color. Burn from first flight on the body shaft of Sharknader. One of the four booster motors CATOED first flight, maybe making it even worse. Thin hardwood dowels are no match for too close in rocket motor flame plumes.



Never underestimate the power of the toy rocket propellant! Gosh darn it! I shoulda canted dem motors just a bit. Just too dern lazy and building fast and easy. High heat paint done NO dern good!. Silly 3M lable paper fin covering. A sooty cluster mess after second flight. Serves me right for such poor design.


But for some unknown reason it was nice and stable off the pad. No worries Mr. RSO. Traditional 4F4NC tractor cluster safety.

 

[BABAR]

Apples and Oranges... or should I say Nerf Balls and Oranges?​

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Front eject, with a chute, coming down horizontal, nose cone first ​

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I’ve always liked the phrase, Kumquats and Avocados.

In this case, however, Au contraire!

Comparing this to a standard front eject, the physics isn’t that different.

For forward eject, when I’ve seen horizontal position of body, the nose cone was the part with greatest density to drag ratio, so nose cone falls first, kind of dragging everything behind it. Your rocket body is kind of a big heavy nose cone equivalent, and like you picture, drags the motor mount unit and chute behind it.

For forward eject body descent, the cord runs out the front of the body, so might as well be attached. For these, the body CG is in the tail, and CP is also in tail. In event of a broken cord with body separated from chute and nose cone, these would either tumble or if long enough maybe come in ballistic.

Your tail unit has the CP at the tail, and the CG FORWARD.
While the CG is behind the attachment point, it’s far less than the attachment point for the standard forward deploy rocket.

Put another way, technically your motor mount unit when deployed IS stable, and if jettisoned would come in ballistic.

Your attachment point is ahead of CG, so statically it would hang tail down. But this is not descending under static conditions.

The question is whether a 7.5 mph wind is sufficient to achieve stability. I’d argue it wouldn’t take much wind to flip it forward end (motor tube end) down. Seems MORE likely with your design (Kumquat) than with a forward deploy rockets (Avocados.)

 

[Dotini]

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