Carrot Top Belly Flop

[BABAR]

Time to practice the most sincere form of flattery, and play in @sr205347d ‘s field.

I still lack confidence in going without a port puff, and I’d rather have this backslide than auger in ballistic. So I need a light nose cone. Got this for Easter last year from my girl friend, it’s pretty light.

 

[BABAR]

 

[BABAR]

Cut nose
Shoulder

 

[BABAR]

Puff port and bulkheads
Corrugated cardboard backed up by aluminum can.

Need to block the ejection charge before it hits the glued in nose cone.

 

[hobie1dog]

interesting

 

[Raptor 2]

 

[BABAR]

@sr205347d , I am debating.

Fins are rectangles, papered 1/8” balsa

2” chord, 3 inch hemispan

Which attachment configuration seems best? Is the 120 degree angle right?

 

[Cape Byron]

Good question. Where are the experts?

 

[sr205347d]

Which attachment configuration seems best? Is the 120 degree angle right?

Any of those should work. 120 degrees works for me. I suppose as little as 90 degrees should work, but I haven’t tried it.

We are plowing new ground here. This is trial and error, mostly error. My latest is an upscale version using BT-80. First flight was good, then I had a lawn dart, after an initial successful transition to flop mode. I think it needs a lighter nose cone.

Good luck!

 

[lakeroadster]

I'd follow the K.I.S.S. principle and go with 3.

Neat build. Waterslide decal for ya..

Too late now, but a transition and a smaller BT up the center would have made it possible to "keep the greens".

Good question. Where are the experts?

 

[David Schwantz]

120 will be more stable. 90 may rock or flutter.

 

[David Schwantz]

Good question. Where are the experts?

I'm here

 

[BABAR]

I'd follow the K.I.S.S. principle and go with 3.

Neat build. Waterslide decal for ya.. View attachment 560346

Too late now, but a transition and a smaller BT up the center would have made it possible to "keep the greens".

View attachment 560347

i think for Back Slider Recovery (bSr) and possibly for Belly Flop Recovery (bFr) BT-5 is problematic. At least for bSr, the transition from stable boost to horizontal glide requires a significant shift of the effective CG (eCG) and effective CP (eCP), essentially inverting them along the length of the rocket. For bSr, this is accomplished with an eccentric intentionally discombobulating force (tempted to abbreviate that, the EIDF), which usually changes the angle of attack from near zero, where Barrowman calculations rule and lateral surface area of the body tube has little or no affect on [edit] CP (have I got that right, @neil_w?), to Center of Lateral Area Calculations (CLA) (aka”Cardboard Cut Out) calculations where body tube lateral surface area is essentially an equal factor and definitely DOES a come into play. Problem with smaller body tubes, the tube mass to lateral surface area for most paper tubes is in some way proportional (not sure if directly, but somehow) to body diameters. For same tube thickness, the lateral surface area/mass is much greater than for (edited) LARGER tubes of same thickness.

so for a longer BT-50, lengthening the tube definitely increases both lateral surface area and mass, but from CLA perspective, the eCP is shifted far more than the eCG. Because the BT-5 is effectively “thicker” in the paper component compared to diameter, the difference of shift with a longer (but smaller diameter) tube is LESS than with a proportional lengthening of a larger diameter tune (again assuming the same tube wall thickness and material.)

there are practical limits on this.

First is proportionality, for wider body tubes to get the same “SuperRoc” length to diameter proportions (Alway patent said at least 30 to 1, ideally 50 to 1) https://patents.google.com/patent/US6926576B1/en

the Length of the rocket gets challenging once you get beyond a BT-50. Optimal length for a BT-100 Rocket at 50 to 1 is about 15 feet.

second, the advantage of a larger diameter is dependent on the same wall thickness and material. I am sure the High Power Guys know why you use heavier (more thick walled or different structural material) for bigger rockets. Using the same wall thickness isn’t likely to be structurally sound for rockets of this size.

i am glad you brought this up, @lakeroadster , because you are one of the biggest proponents of the Swing Test, which is was thinking was a THIRD stability test which my first rendition of Screwball failed.

i theeeeeenk Swing Tests are the Cats Pajamas for rocket that are stable based on CLA, as a rocket stable based on CLA again I theeeeeeeenk should also be stable by Barrowman. But to do a swing test for Barrowman is harder, because you have to start with and maintain a zero angle of attack, if you go significantly off that (don’t ask me what angle is “significant”, I dunno.). I think it CAN be done, but is harder, you can’t just throw the rocket out there and start swinging it.

i don’t know if @Rktman still has his backslider, but if he was interested it would be cool to see if it fails the Swing Test. I have a tail piece from one of my back sliders, I might just play with it a bit.

this may explain why a number of people have reported rockets that failed the swing test but flew perfectly well.

and it may be that I just am crummy at doing swing tests!

 

[lakeroadster]

i think for Back Slider Recovery (bSr) and possibly for Belly Flop Recovery (bFr) BT-5 is problematic. At least for bSr, the transition from stable boost to horizontal glide requires a significant shift of the effective CG (eCG) and effective CP (eCP), essentially inverting them along the length of the rocket. For bSr, this is accomplished with an eccentric intentionally discombobulating force (tempted to abbreviate that, the EIDF), which usually changes the angle of attack from near zero, where Barrowman calculations rule and lateral surface area of the body tube has little or no affect on CG (have I got that right, @neil_w?), to Center of Lateral Area Calculations (CLA) (aka”Cardboard Cut Out) calculations where body tube lateral surface area is essentially an equal factor and definitely DOES a come into play. Problem with smaller body tubes, the tube mass to lateral surface area for most paper tubes is in some way proportional (not sure if directly, but somehow) to body diameters. For same tube thickness, the lateral surface area/mass is much greater than for smaller tubes of same thickness.

so for a longer BT-50, lengthening the tube definitely increases both lateral surface area and mass, but from CLA perspective, the eCP is shifted far more than the eCG. Because the BT-5 is effectively “thicker” in the paper component compared to diameter, the difference of shift with a longer (but smaller diameter) tube is LESS than with a proportional lengthening of a larger diameter tune (again assuming the same tube wall thickness and material.)

there are practical limits on this.

First is proportionality, for wider body tubes to get the same “SuperRoc” length to diameter proportions (Alway patent said at least 30 to 1, ideally 50 to 1) https://patents.google.com/patent/US6926576B1/en

the Length of the rocket gets challenging once you get beyond a BT-50. Optimal length for a BT-100 Rocket at 50 to 1 is about 15 feet.

second, the advantage of a larger diameter is dependent on the same wall thickness and material. I am sure the High Power Guys know why you use heavier (more thick walled or different structural material) for bigger rockets. Using the same wall thickness isn’t likely to be structurally sound for rockets of this size.

i am glad you brought this up, @lakeroadster , because you are one of the biggest proponents of the Swing Test, which is was thinking was a THIRD stability test which my first rendition of Screwball failed.

i theeeeeenk Swing Tests are the Cats Pajamas for rocket that are stable based on CLA, as a rocket stable based on CLA again I theeeeeeeenk should also be stable by Barrowman. But to do a swing test for Barrowman is harder, because you have to start with and maintain a zero angle of attack, if you go significantly off that (don’t ask me what angle is “significant”, I dunno.). I think it CAN be done, but is harder, you can’t just throw the rocket out there and start swinging it.

i don’t know if @Rktman still has his backslider, but if he was interested it would be cool to see if it fails the Swing Test. I have a tail piece from one of my back sliders, I might just play with it a bit.

this may explain why a number of people have reported rockets that failed the swing test but flew perfectly well.

and it may be that I just am crummy at doing swing tests!

I meant just a smaller tube at the very tip, then a transition back to whatever body tube you feel is best.

 

[BABAR]

I meant just a smaller tube at the very tip, then a transition back to whatever body tube you feel is best.

I don’t know if she gave me more than one, but I only HAVE one, and it has now been decapitated.

 

[BABAR]

I meant just a smaller tube at the very tip, then a transition back to whatever body tube you feel is best.

Just noticed your new Avatar. Nice tribute to three heroes of space flight.

 

[lakeroadster]

Goofing around.... I tossed a streamer in it just... well... because.

 

[lakeroadster]

Just noticed your new Avatar. Nice tribute to three heroes of space flight.

The fire was on the 27th... gone but not forgotten.

 

[BABAR]

Hmmm, with shoulder and glue a little heavier than I expected.

Still lighter than one of my old Viking nose cones. Got a deal on a dozen Vikings 10 years ago, love the cones. For this bird though, I like the carrot for a number of reasons

It is lighter

This is still to me a bit experimental. Flight possibilities as follows, in order of anticipated likelihood

1. Back Slide

2. Belly Flop

3. Unstable and skywriting from get go.

4.stable up and unfortunately down, i.e. Ballistic

#3 is bad, but doesn’t worry me that much, as those usually don’t generate enough forward kinetic energy to be a problem.

#4 I really don’t like, so while I like Viking cones I’d rather have something rounded and a bit squishy.

 

[BABAR]

Glued in with polyurethane glue and set upright.

The run off should spread over the bulkhead. I think the combo of thin aluminum plate on the hot side and the foaming glue (which should form a “plug”) on the other side should seal the forward end and leave the port as the only exit for ejection charge.

 

[BABAR]

Needed a 60 degree fin guide since I am going with @lakeroadster KISS principle for fin attachment. Most important thing is they be straight. I didn’t want to mess with a sanded bevel. Now I just had a V8 oh crud moment, @Rktman ‘s dihedral technique would have been perfect, but I already cut them. The joint has to be straight, not strong, as the fins will be glued to the rocket body. And hey, I can cover the joint with the launch lug, since I needed a bit of a stand off anyway as the carrot nose cone is a tad wider than the tube.

I am using parchment paper to keep things from sticking.

 

[lakeroadster]

Love that fixture.... slicin' and dice'n

 

[sr205347d]

1. Back Slide

2. Belly Flop

3. Unstable and skywriting from get go.

4.stable up and unfortunately down, i.e. Ballistic

5. The ejection charge "puff" by random motion, causes the rocket to enter stable forward flight AOA, resulting in a lawn dart.

6. The rocket enters good Belly Flop AOA, but rocking or bobbing causes the rocket to enter stable forward flight AOA resulting in a lawn dart.

See my comments in the other thread.

 

[Rktman]

i don’t know if @Rktman still has his backslider, but if he was interested it would be cool to see if it fails the Swing Test. I have a tail piece from one of my back sliders, I might just play with it a bit.

Was able to do the swing test with my backslider. And the result was [drum roll]...
as you suspected, it was UNstable. With a fresh B4-2 installed, it insisted on orienting itself tail-first in the direction of the swing. I tried repeatedly to face its nose cone forward, but as soon as the airflow hit it, it swung its fins "forward".

Given the result, I find myself fascinated that it nevertheless launches straight and "stable" every time.

 

[BABAR]

Was able to do the swing test with my backslider. And the result was [drum roll]...
as you suspected, it was UNstable. With a fresh B4-2 installed, it insisted on orienting itself tail-first in the direction of the swing. I tried repeatedly to face its nose cone forward, but as soon as the airflow hit it, it swung its fins "forward".

Given the result, I find myself fascinated that it nevertheless launches straight and "stable" every time.

I think this is good proof that, as @sr205347d say, the “transition” is not an alteration of the “monolithic “ rocket anatomy, but an alteration in angle of attack. I struggle getting my mind around @sr205347d doing it with no “puff”, but unsound to argue with success.

Mine is done

 

[BABAR]

Finis!

 

[lakeroadster]

 

[lakeroadster]

Piloted by....

​

 

[BABAR]

No video, but hand tossing it off the balcony with an expended motor casing resulted in flat or tail first landings. Of course, I don’t know if it is VERTICALLY stable, but the balcony tests were encouraging.

tail first landing on such a short drop likely means it WILL either Belly Flop or Back Slide, as when it picks up speed with such an asymmetric fin can the drag will almost certainly lift up the tail.

 

[sr205347d]

No video, but hand tossing it off the balcony with an expended motor casing resulted in flat or tail first landings. Of course, I don’t know if it is VERTICALLY stable, but the balcony tests were encouraging.

tail first landing on such a short drop likely means it WILL either Belly Flop or Back Slide, as when it picks up speed with such an asymmetric fin can the drag will almost certainly lift up the tail.

Let us know how it flies!