Horizontal Spin Recovery - with Magnus Effect?

[BEC]

One real tragedy due to a rare weak Estes Ejection Charge

It’s a little premature to call it “death”. If I can get the decal sheet, the rest of it isn’t impossible, or even all that hard to fix. I was dismayed to see that the damage on the main body tube goes further aft than I first thought, so to repair it I’ll need to cut it off just aft of the little canard fins and splice a new section of BT-55 in from there (and of course re-do the little fins).

The split in the glider’s tube at the nose can just be CA’d back together, though the tear will remain visible there.

I am in touch with Estes about this but the fellow who responded to my note seems a little stymied by the lack of a standard production code on this made-for-European-distribution C11-3. We shall see where it goes.

Now back to discussing all those very interesting recovery vehicles I saw fly yesterday.

 

[lakeroadster]

It’s a little premature to call it “death”. If I can get the decal sheet, the rest of it isn’t impossible, or even all that hard to fix. I was dismayed to see that the damage on the main body tube goes further aft than I first thought, so to repair it I’ll need to cut it off just aft of the little canard fins and splice a new section of BT-55 in from there (and of course re-do the little fins).

The split in the glider’s tube at the nose can just be CA’d back together, though the tear will remain visible there.

I am in touch with Estes about this but the fellow who responded to my note seems a little stymied by the lack of a standard production code on this made-for-European-distribution C11-3. We shall see where it goes.

Now back to discussing all those very interesting recovery vehicles I saw fly yesterday.

Was there any sign that there was an actual ejection charge? Like charring of the wadding?

 

[BEC]

I was looking through this thread and my mind drifted to when I launched my Ahpla. It's a BT-55 upscaled D-12 Alpha with a D12 booster. It doesn't fit the 50:1 design criterion at all. See photo below.

On its maiden flight, the nose cone with chute detached from the fuselage at ejection. I was expecting carnage to ensue.

The fuselage tumble recovered. It rolled about the longitudinal axis and stayed in a horizontal orientation as it was falling. How could I see that? Since one fin is black and the other two are white, it looked like a light flashing every time it made a revolution.

Think that horizontal recovery was just an anomaly, or am I in the club now?

The rocket was recovered undamaged. I guess sometimes the Recovery Gods shine upon us all.

Since I have a regular Alpha with over 100 flights on it (and several other Alphas that get air time occasionally) I have had shock cord failures. Sometimes the body falls, spinning, as yours did, and sometimes it comes in ballistic (and is therefore somewhat shorter after the sudden stop at the bottom unless flying at Sixty Acres in the winter, when it’s a core sample instead).

I can’t say why it is sometimes one way and sometimes another, even with the shock cord breaking at different points.

 

[BEC]

Was there any sign that there was an actual ejection charge? Like charring of the wadding?

Yes, there was some charring.

There is also clear indication of some kind of shock at the right time in the FlightSketch Mini’s accelerometer data: https://flightsketch.com/flights/3784/

As I got to looking at it at home last night I found a couple of complicating factors. First of all, I had installed Centuri-style baffle plates on either side of the stock coupler in the kit. The lower one (with the holes around the periphery) was loose inside the body. And I had put, apparently at two different times, one square of the wadding supplied with Q-Jets, which is a 5 1/2 inch square of parade float tissue paper, folded so as to be a sort of “chute protector”, in the model. I normally do one like this as sort of insurance for the ‘chute in baffle-equipped models. But there were two in there this time.

Still, this was the fourth flight on the model, and the maiden was made at the same site and on another C11-3 which likely I got in the same buy from AC Supply a couple of years ago. The other two flights, at Sod Blaster IV, were on D12-5s.

I have not mentioned either the wadding or baffle specifics to the fellow at Estes who responded to my customer service message this morning….

 

[BEC]

One more Super Orbital Transport post: Estes is shipping me another kit and two packs of C11-3s after my communications of the last couple of days.

But I was told no decals are available. As I noted above, I could fix the current one for a lot less effort than building a new one if I could just get the decals. If I scan them when they get here, is anyone able to print a set from a scan (I don’t need the whole set) and send them to me for a reasonable fee?

 

[Dotini]

It was a great experience for me to launch at 60 Acres with @BEC and @BABAR, not only to demonstrate HSR, but especially to learn from and get to know my friends here at the forum. I picked up on several ideas and products I was not familiar with. Thanks, guys!

Since my regular launch partner is still in Germany, our test and development program has been a bit stalled. Today the inspiration hit me to bash an HSR fin can from the plastic unit issued in the Estes Mongoose kit. I've used these fin cans on 5 other rockets so far, so I'm familiar with how rugged they are - including being fit for backslider use. Now I'm adapting the unit to HSR for hopefully a quick and easy build of a durable HSR in the BT-50 size. With a cored out balsa transition, I believe this is plenty of fin area for BT-55 forward tubes.


Reversed Estes Mongoose fin can. Heavy duty coupler. The fin structural angle is .040" Lexan corner guard (bullet proof) from local hardware store. Tip extension is 0.25" PETG, very flexible.

Edit:

Short tube ahead of fin can is thick wall unit from Rocketarium.

 

[Dotini]

Longitudinal turbulators may activate additional Magnus effect. We'll know if it works by the effect on descent rate. Tube is interchangeable with other models. These turbulence generators are 14" 5/32 polystyrene angles from Evergreen Scale Models, weight about 0.058 oz each.


This BT-50 model has just over 11.65 square inches of fin area. Overall length is projected at 45". Launch lugs are 3/16".

 

[BABAR]

“Turbulators”?

don‘t mix up the B with a D.

 

[Dotini]

“Turbulators”?

don‘t mix up the B with a D.

The D word could be warranted! My models often are not very successful. Such is the nature of experimentation, of rocket science at the humble, happy, hairy hobbyist level. These strakelets or drag generating devices are intended to be analogous to the seams on a baseball - to enhance or activate the lift generating regions around the horizontally spinning tube. It won't be long before the unforgiving stopwatch renders its harsh verdict on little old Wernher von Dotini.

Clearly I'm experiencing difficulty with fin durability. The present model is a return to a fin can which has been reliable in the past in the backslider role, but now with added spin inducing modifications. Chances are it's stretching the envelope too far. We'll see and be the wiser by next week.

 

[lakeroadster]

“Turbulators”?

don‘t mix up the B with a D.

If it's brown... float it down.

 

[BABAR]

The D word could be warranted! My models often are not very successful. Such is the nature of experimentation, of rocket science at the humble, happy, hairy hobbyist level. These strakelets or drag generating devices are intended to be analogous to the seams on a baseball - to enhance or activate the lift generating regions around the horizontally spinning tube. It won't be long before the unforgiving stopwatch renders its harsh verdict on little old Wernher von Dotini.

Clearly I'm experiencing difficulty with fin durability. The present model is a return to a fin can which has been reliable in the past in the backslider role, but now with added spin inducing modifications. Chances are it's stretching the envelope too far. We'll see and be the wiser by next week.

Brings a new meaning to the term “fecal-turbine interaction”!

 

[Dotini]

Brings a new meaning to the term “fecal-turbine interaction”!

Yes, I'm tired of excessive fin damage. Your idea of the windowed box might work.

For fin material, I'm having good luck with styrene so far (it's flexible), but I'm still looking forward to the best root design. A simple butt join with Gorilla glue followed up with fillets seems plausible so far. I've used tee-section roots with some success as well.

 

[BABAR]

Yes, I'm tired of excessive fin damage. Your idea of the windowed box might work.

For fin material, I'm having good luck with styrene so far (it's flexible), but I'm still looking forward to the best root design. A simple butt join with Gorilla glue followed up with fillets seems plausible so far. I've used tee-section roots with some success as well.

As per previous conversation, I still agree that wider fins (technically bigger “hemi-span” fins) are more efficient. However, I think the difference in efficiency can be countered by using an increased number of NARROWER hemi-span fins (6 or 8), perhaps with longer chord length (front to back.). Gonna cost you a bit more drag (though perhaps no more than your braces or spars.). The narrower fins will have a lower moment or leverage on impact, this less likely to break. and if you make them with a longer chord they should be stronger, spreading the same stress over a greater length. Preferably you’d like a smaller radius of curvature for more effective “turbulation.” do your relatively thin plastic fins come is smaller sizes? Mine were obviously far to heavy.

the ring idea would definitely help, but as you mentioned it has a high drag cost. OTOH, you can overcome drag with bigger motors to get same altitude without outflying the field size.

 

[BABAR]

A while back @cwbullet was looking for things to 3D print. A mongoose style fin can with curved fin modification, BT-5 or BT-20 scale, might interest him.

 

[Dotini]

As per previous conversation, I still agree that wider fins (technically bigger “hemi-span” fins) are more efficient. However, I think the difference in efficiency can be countered by using an increased number of NARROWER hemi-span fins (6 or 8), perhaps with longer chord length (front to back.). Gonna cost you a bit more drag (though perhaps no more than your braces or spars.). The narrower fins will have a lower moment or leverage on impact, this less likely to break. and if you make them with a longer chord they should be stronger, spreading the same stress over a greater length. Preferably you’d like a smaller radius of curvature for more effective “turbulation.” do your relatively thin plastic fins come is smaller sizes? Mine were obviously far to heavy.

the ring idea would definitely help, but as you mentioned it has a high drag cost. OTOH, you can overcome drag with bigger motors to get same altitude without outflying the field size.

I will go ahead with a new build involving fins with the chord roughly twice the span. I may do six, but probably not. I will make them of styrene angles, although I would use Lexan if I could get it.

Below is a successful model but with limited testing. The fins are Lexan angle, .7 x .7, so span of 1.4 and chord of 2", 11.2 square inches and not as much area as I'd like.


This 24mm fin unit has not seen much use, but seems very rugged so far. Joints are styrene angles.

 

[BABAR]

have you had any spin failures (failed to spin due to inadequate surface area) or unstable on boost rockets (again due to inadequate surface area?)

Because of the high length to diameter ratio, I think these rockets require very minimal surface area for BOOST stability. Plus the curved or especially ANGLED fins provide a lot of surface area far off centerline where it is most efficient.

 

[Dotini]

have you had any spin failures (failed to spin due to inadequate surface area) or unstable on boost rockets (again due to inadequate surface area?)

Because of the high length to diameter ratio, I think these rockets require very minimal surface area for BOOST stability. Plus the curved or especially ANGLED fins provide a lot of surface area far off centerline where it is most efficient.

Never had a failure to spin. Some spin faster than others. That model with canard fins you saw at 60 Acres did appear to exhibit a bit of weathercocking.

 

[BABAR]

narrower semispan fins should weathercock less. I also think, at least based on cardboard cut out stability, that increasing number of fins causes LESS weathercocking than a smaller number of fins with same total surface area. Tube fins, for example, are known to be usually less efficient but also less prone to weathercocking.

 

[cwbullet]

A while back @cwbullet was looking for things to 3D print. A mongoose style fin can with curved fin modification, BT-5 or BT-20 scale, might interest him.

If someone makes a rocksim or open rocket, I can make a fin can.

 

[Dotini]

Here's a tested HSR fin can which has had a ringtail added. I expect this to be quite durable.


Below is the Mongoose bash ready for HSR duty.

 

[Dotini]

Here comes the new "Window Box" or square ringtail HSR fin can. It will fun to test, and looks like it would be very sturdy and easy to repair in the field. Fins are .050" polystyrene angle. Loads of fin area, weight 1.27 oz.

 

[BABAR]

you and I may be on both Perfectly good but completely non-interersecting pathways regarding rings and horizontal spin.

for me, the idea is that the ring PREVENTS the angled or curved fins from hitting the ground at all, and allows the rocket to CONTINUE to spin, even for a fraction of a second, so the dissipation of energy is spread out from near instantaneous to short put finite. I think this requires the ring to be at both the forward and rear ends.

your technique, on the other hand, I think SHOULD spread the load from the one impacted fin to ALL the fins, which also should be a good “fin preserving“ strategy.

 

[Dotini]

you and I may be on both Perfectly good but completely non-interersecting pathways regarding rings and horizontal spin.

for me, the idea is that the ring PREVENTS the angled or curved fins from hitting the ground at all, and allows the rocket to CONTINUE to spin, even for a fraction of a second, so the dissipation of energy is spread out from near instantaneous to short put finite. I think this requires the ring to be at both the forward and rear ends.

your technique, on the other hand, I think SHOULD spread the load from the one impacted fin to ALL the fins, which also should be a good “fin preserving“ strategy.

Here's a new design for you to consider. It could very easily accommodate a ring at both ends. As is, it has 18 inches of fin area and weighs 0.77 oz.

BT-50 tube. Fins are 0.025" Lexan angles. Roots are 5/32" polystyrene angle. Fillets to be added.

A potential benefit of this design is a maximum diameter of only 2.9". This along with light weight should reduce the landing torque exerted on the fins.

 

[BABAR]

I like it.

Can you get the petg pre-colored, I know you like your rockets to look good as well as fly well.

 

[Dotini]

I like it.

Can you get the petg pre-colored, I know you like your rockets to look good as well as fly well.

I'm trying to move away from PETG (shipping tubes). Too thin, brittle, low quality.

Real Lexan is the best - bulletproof!

I think you can Lexan sheet in various colors and tints. With the present model I'm using clear 4' corner guards available from hardware stores for about $5.

 

[BABAR]

I'm trying to move away from PETG (shipping tubes). Too thin, brittle, low quality.

Real Lexan is the best - bulletproof!

I think you can Lexan sheet in various colors and tints. With the present model I'm using clear 4' corner guards available from hardware stores for about $5.

Nice ”repurposing”. How are you attaching these to the body tube again?

 

[Dotini]

Nice ”repurposing”. How are you attaching these to the body tube again?

I'm using 5/32" polystyrene angles from Evergreen Scale Models. They are 14"long and come in various quantities. I bought an economy pack of 10. I'm using medium CA for glueing the fins to the angles and for gluing the angles to the tube. I'll use original Gorilla Glue for the fillets.

 

[BABAR]

I. I'll use original Gorilla Glue for the fillets.

by “original Gorilla Glue” do you mean the polyurethane glue that foams up? I love it for internal foam centering rings, but even with my low standards of craftsmanship I haven’t been able to use it on visible Exposed surfaces . Do you let the fillets dry and sand them down?

 

[Dotini]

by “original Gorilla Glue” do you mean the polyurethane glue that foams up? I love it for internal foam centering rings, but even with my low standards of craftsmanship I haven’t been able to use it on visible Exposed surfaces . Do you let the fillets dry and sand them down?

Yeah, it foams a bit. I minimize that by applying the least amount with a sharpened 1/16" dowel, then immediately smoothing it with a finger. I try to never sand glue.


Fully cured original Gorilla Glue fillet.

 

[Dotini]

Landing torque inputs and rotational inertia are two areas of fin design we havent yet explored. The current specific goal is reduced fin breakage in HSR rocketry.


Left, new BT-20 model to hopefully replace the X-8 seen in several videos in this thread. (It's now retired due to a cracked fin.)
New model is under 2.5" maximum diameter, yet has 12.5 square inches of fin area.