Lakeroadster's 2 Stage Alpha Variant

[lakeroadster]

A scratch build Estes Alpha, but built with through wall basswood plywood fins, glued on backwards.

Then add a ring finned booster, with through wall fin supports.

Thanks to @BABAR for the backwards fin comment here that spawned this design.

 

[jqavins]

Wild.

 

[Joekeyo]

CG almost = CP. Needs work?

 

[lakeroadster]

CG almost = CP. Needs work?

Open Rocket does not calculate the change of CP, when using ring fins. In fact, there is no ring fin option* in Open Rocket at all. Therefore the CP shown is as if there was no ring fin at all.

But we know ring fins are drag making beasts. I'll build it, do a swing test and go from there. No worries.

*The ring fin shown is actually made by inserting an internal tube, and then inputting the dimensions for the ring fin)

 

[jqavins]

What about for the sustainer alone? Of course you've checked that, stupid question, just had to ask it anyway. It'll be further forward than in the unmodified Alpha.

 

[lakeroadster]

What about for the sustainer alone? Of course you've checked that, stupid question, just had to ask it anyway. It'll be further forward than in the unmodified Alpha.

1.58 Caliber with the B motors, 1.31 Caliber with the C motors

 

[BABAR]

What about for the sustainer alone? Of course you've checked that, stupid question, just had to ask it anyway. It'll be further forward than in the unmodified Alpha.

I am with Joe on this one. I suspect you will be good, and I am as you know a big fan of forward swept fins, I just didn't realize how BIG those fins are..

Unasked for suggestions are always suspect, but I have done a lot of ring fin staging.

1. Booster motor is extending far more out the back than needed. This moves CG in the wrong direction. Go with longer sustainer tube or otherwise move the sustainer fins back.

2. If you're gonna use a ring, use a RING. Make it bigger, it shows up more and will have more of a CP effect on boost. Also more drag on tumble recovery.

3. Whereas I like forward swept fins on single stage rockets and sustainers, I like rear swept PYLONS (this Buds for you, @neil_w ) for booster ring fins.

4. Purely optional, as is everything else, but cut windows on the clockwise sides of the rings right next to the pylons, you will get horizontal spin and maybe a lateral Magnus force on booster recovery (And one for @Dotini !)

 

[lakeroadster]

I am with Joe on this one. I suspect you will be good, and I am as you know a big fan of forward swept fins, I just didn't realize how BIG those fins are..

Unasked for suggestions are always suspect, but I have done a lot of ring fin staging.

1. Booster motor is extending far more out the back than needed. This moves CG in the wrong direction. Go with longer sustainer tube or otherwise move the sustainer fins back.

2. If you're gonna use a ring, use a RING. Make it bigger, it shows up more and will have more of a CP effect on boost. Also more drag on tumble recovery.

3. Whereas I like forward swept fins on single stage rockets and sustainers, I like rear swept PYLONS (this Buds for you, @neil_w ) for booster ring fins.

4. Purely optional, as is everything else, but cut windows on the clockwise sides of the rings right next to the pylons, you will get horizontal spin and maybe a lateral Magnus force on booster recovery (And one for @Dotini !)

Thanks. Good ideas for the next variant. But for this one:

1. Think of the booster motor sticking out as a mid 1970's 5 mph impact bumper.. ​

2. With the smaller ring, it's not the focal point of the rocket. And the smaller ring should be less likely to get busted when it tumbles into terra firma.​

3. It's supposed to look like an Alpha that somebody put the fins on backwards.​

4. Clockwise sides?​

​

How about no ring, and 6 booster fins?

​

​

 

[BABAR]

First, and foremost, it is your rocket, so do what you like. Since you swing test your models, you are a safe flyer, so no concerns there. I have my doubts your latest rendition will be stable without the ring unless you add a lot of nose weight.

Second, I am with you that I like the casing sticking out a bit on single stage and on SUSTAINERS. Great way to take the brunt of the initial impact when recovering with a forward deployed chute or streamer. IMO the fallacy on your thinking here is how this booster will recover. It is TUMBLE recovery UNLESS you put the windows on the ring, in which case it will be horizontal spin (we will discuss the windows in a moment.) Classic Estes two stage kits (at least some of them) actually had a REAR END motor block, as two stage rockets had an occassional habit of ejecting the rear motor at staging WITHOUT separating the stages. Sustainer lights, flame shoots out the length of the booster (with little thrust due to massive Krushnic effect), usually cooks the booster, and unless the delay is short the whole thing comes in fast if not frankly ballistic.

In any case, since the booster is going to randomly tumble at worst, and if you do the windows, come down horizontal at BEST, the chance it is going to land on your extended booster bumper is pretty darn low, so all you accomplish is pushing CG back with no benefit (again, IMO.)

Next, regarding a large ring taking the focus off the forward fins, yes, I guess so. If you want the attention to be on the forward fins, fly it as a single stage and keep the ring out of it. Beauty is in the eye of the beholder, if you think a longer ring detracts from the forward swept fins, then for you that is absolutely correct.

Next, disagree that a smaller ring (lengthwise) is less likely to break than a larger ring. The larger ring will have greater surface attachment to the pylons. You DO have to make sure you get the grain direction on the pylons right, I learned that lesson for you with my first ring bird where grain was exactly wrong, and the ring broke off as could easily be expected. But a larger (lengthwise) ring is likely to be STRONGER than a smaller ring, and unless you have too tight a space between the ring and the body (short pylons or too many pylons, IMO three pylons in the optimal number) rings DEFINITELY have more positive effect on CP, exception being if it gets TOO long, when, like long skinny tube fins, the drag is such there is no airflow through the "tube" center and they act like cylinders.

From an aerodynamic standpoint, I'd put the tail end of your pylons AT the tail end of the rocket (move it back just a tich), keep the forward sweep of the TAIL end of the pylons, and go neutral at the forward end (so forward edge of fin sticks out 90 degrees.) I'd then extend the length of the tube fin accordingly. I would also put an engine block in the REAR end of the booster (i usually use a 1/8 inch piece of body tube or motor mount tube if not minimum diameter, snip out a section, and glue it it.) This will slightly RECESS the motor, not enough to cause Krushnic, and increase probability of successful separation (pretty much 100% prevents rear ejection of the expended booster motor at staging. Some people say nothing is 100%, this is pretty darn close). Again emphasize this is an AERODYNAMIC recommendation. I you don't like the "look", then it's a no go from an aesthetic standpoint. In any case, unless you device a way of putting a streamer or chute on your booster (lots of ways to do it), your booster is NOT going to come down "keister-first" and land on the casing.

Finally, as for the windows, see pic 3 on post 1

Bail Out Bill and the Horizontal Spin Recovery Rocket | The Rocketry Forum

the "windows" are placed either all clockwise, or all counterclockwise, immediately adjacent to the pylon. Either will work as long as ALL are placed to the same "side" relative to the pylon. Bail Out Bill is a much longer rocket than your booster, but with ejecting the nose it was unstable enough post deployment that it initially started to tumble. It is amazing how little "windowage" it takes to get the rocket to so into a horizontal spin. Without the windows, the rocket even without the nose cone would have been stable and done a core sample, even though it may have started unstable it likely would have become stable because the body is so long that CG would still be forward of CP. @Dotini has done me one better and come up with a consistent way of getting great horizontal spin WITHOUT dumping the nose cone.

In any case, although I don't have test results to prove it, LOGICALLY (emphasize LOGIC doesn't always mean CORRECT), horizontal spin with a RING is likely the optimal recovery for a black powder booster WITHOUT its own chute or streamer. Rationale: without horizontal spin, the booster tumbles randomly, so the drag surface presented to the fall vector is constantly changing. the OPTIMAL presentation is horizontal, as this presents the maximum fin surface to the falling airflow vector. HORIZONTAL spin automatically orients the rocket horizontally, thus keeping a constant maximum drag configuration to the air stream.

You can do this WITHOUT a ring if you use @Dotini 's brace method, my ring method has the advantage that even though the spin has a lot of kinetic energy to dissipate on impact, there are no "edges" to catch, so usually it just spins on the ground until friction slows it down.

For tumble recovery, impact point is purely random, you have no idea what is going to hit first.

a final advantage of a bigger ring, makes it easier to find on the ground. Tumble recovery rockets and boosters don't have the advantage of chutes or streamers fluttering on the ground to help you find the rocket.

Wishing you two straight trails and two short walks!

 

[jqavins]

You DO have to make sure you get the grain direction on the pylons right, I learned that lesson for you with my first ring bird where grain was exactly wrong, and the ring broke off as could easily be expected.

What is the right direction? I'd think that parallel to the leading edge, just like a regular fin, would be fine. Actually, it seems like the only wrong way would be parallel (or nearly so) to the ring and body tube. Is there more to it that I'm missing?

[M]y ring method has the advantage that even though the spin has a lot of kinetic energy to dissipate on impact, there are no "edges" to catch, so usually it just spins on the ground until friction slows it down.

If one could get the CG of the booster with the spent engine to hit the middle of the ring that it should roll along the ground with a little luck.

 

[BABAR]

What is the right direction? I'd think that parallel to the leading edge, just like a regular fin, would be fine. Actually, it seems like the only wrong way would be parallel (or nearly so) to the ring and body tube. Is there more to it that I'm missing?
If one could get the CG of the booster with the spent engine to hit the middle of the ring that it should roll along the ground with a little luck.

You are correct that the guaranteed WRONG direction is parallel to long axis. Been dere, done dat.

for rings that don’t extend either forward or aft of the forward or aft end of the Booster body tube, perpendicular to the long axis will always work. For rings that extend aft of the tail end of the body tube, the standard “parallel to leading edge” rule would likely be best.

 

[lakeroadster]

First, and foremost, it is your rocket, so do what you like. Since you swing test your models, you are a safe flyer, so no concerns there. I have my doubts your latest rendition will be stable without the ring unless you add a lot of nose weight.

Second, I am with you that I like the casing sticking out a bit on single stage and on SUSTAINERS. Great way to take the brunt of the initial impact when recovering with a forward deployed chute or streamer. IMO the fallacy on your thinking here is how this booster will recover. It is TUMBLE recovery UNLESS you put the windows on the ring, in which case it will be horizontal spin (we will discuss the windows in a moment.) Classic Estes two stage kits (at least some of them) actually had a REAR END motor block, as two stage rockets had an occassional habit of ejecting the rear motor at staging WITHOUT separating the stages. Sustainer lights, flame shoots out the length of the booster (with little thrust due to massive Krushnic effect), usually cooks the booster, and unless the delay is short the whole thing comes in fast if not frankly ballistic.

In any case, since the booster is going to randomly tumble at worst, and if you do the windows, come down horizontal at BEST, the chance it is going to land on your extended booster bumper is pretty darn low, so all you accomplish is pushing CG back with no benefit (again, IMO.)

Next, regarding a large ring taking the focus off the forward fins, yes, I guess so. If you want the attention to be on the forward fins, fly it as a single stage and keep the ring out of it. Beauty is in the eye of the beholder, if you think a longer ring detracts from the forward swept fins, then for you that is absolutely correct.

Next, disagree that a smaller ring (lengthwise) is less likely to break than a larger ring. The larger ring will have greater surface attachment to the pylons. You DO have to make sure you get the grain direction on the pylons right, I learned that lesson for you with my first ring bird where grain was exactly wrong, and the ring broke off as could easily be expected. But a larger (lengthwise) ring is likely to be STRONGER than a smaller ring, and unless you have too tight a space between the ring and the body (short pylons or too many pylons, IMO three pylons in the optimal number) rings DEFINITELY have more positive effect on CP, exception being if it gets TOO long, when, like long skinny tube fins, the drag is such there is no airflow through the "tube" center and they act like cylinders.

From an aerodynamic standpoint, I'd put the tail end of your pylons AT the tail end of the rocket (move it back just a tich), keep the forward sweep of the TAIL end of the pylons, and go neutral at the forward end (so forward edge of fin sticks out 90 degrees.) I'd then extend the length of the tube fin accordingly. I would also put an engine block in the REAR end of the booster (i usually use a 1/8 inch piece of body tube or motor mount tube if not minimum diameter, snip out a section, and glue it it.) This will slightly RECESS the motor, not enough to cause Krushnic, and increase probability of successful separation (pretty much 100% prevents rear ejection of the expended booster motor at staging. Some people say nothing is 100%, this is pretty darn close). Again emphasize this is an AERODYNAMIC recommendation. I you don't like the "look", then it's a no go from an aesthetic standpoint. In any case, unless you device a way of putting a streamer or chute on your booster (lots of ways to do it), your booster is NOT going to come down "keister-first" and land on the casing.

Finally, as for the windows, see pic 3 on post 1

Bail Out Bill and the Horizontal Spin Recovery Rocket | The Rocketry Forum

the "windows" are placed either all clockwise, or all counterclockwise, immediately adjacent to the pylon. Either will work as long as ALL are placed to the same "side" relative to the pylon. Bail Out Bill is a much longer rocket than your booster, but with ejecting the nose it was unstable enough post deployment that it initially started to tumble. It is amazing how little "windowage" it takes to get the rocket to so into a horizontal spin. Without the windows, the rocket even without the nose cone would have been stable and done a core sample, even though it may have started unstable it likely would have become stable because the body is so long that CG would still be forward of CP. @Dotini has done me one better and come up with a consistent way of getting great horizontal spin WITHOUT dumping the nose cone.

In any case, although I don't have test results to prove it, LOGICALLY (emphasize LOGIC doesn't always mean CORRECT), horizontal spin with a RING is likely the optimal recovery for a black powder booster WITHOUT its own chute or streamer. Rationale: without horizontal spin, the booster tumbles randomly, so the drag surface presented to the fall vector is constantly changing. the OPTIMAL presentation is horizontal, as this presents the maximum fin surface to the falling airflow vector. HORIZONTAL spin automatically orients the rocket horizontally, thus keeping a constant maximum drag configuration to the air stream.

You can do this WITHOUT a ring if you use @Dotini 's brace method, my ring method has the advantage that even though the spin has a lot of kinetic energy to dissipate on impact, there are no "edges" to catch, so usually it just spins on the ground until friction slows it down.

For tumble recovery, impact point is purely random, you have no idea what is going to hit first.

a final advantage of a bigger ring, makes it easier to find on the ground. Tumble recovery rockets and boosters don't have the advantage of chutes or streamers fluttering on the ground to help you find the rocket.

Wishing you two straight trails and two short walks!

Thanks for the reply. I'm thinking I'll build the rocket and swing test it without the ring fin, just as an academic exercise to test stability.

Then add the ring fin and swing test it again.

As The Boy Wonder would say "Holy Ring Fins, Batman". Neat idea.

Questions:

A) I wonder if it would work with nice large radi in the corners of the opening, instead of being square, well, at least on the edge of the opening away from​

the fin (see below).​

B) So cut three openings in the ring (since it has three ring supports) and basically remove 60 degrees of the ring at each opening. Correct?​

C) Do you think six fin supports and 6 ring holes would be better, or worse, in regard to obtaining a horizontal recovery of the booster?​

 

[BABAR]

The windows don’t need to be square, and really don’t need to be very big, especially for a short booster section. The just need to be near the pylon, and RADIALLY all on the same side of each pylon. (Hence the “all clockwise” or “all counterclockwise” comment.)

doing these with a short nose to tail length ring is harder, as the windows weaken the ring.

increasing the number of pylons will almost certainly improve the spin rate, BUT I don’t think it is necessary, it really doesn’t take much to get these to spin for short boosters. More challenging for long gap boosters (I have done 18” boosters with 15” gaps routinely successfully.) the effect is a positive feedback loop. As the rocket tumbles, the windows occasionally catch the random motion just right, which imparts a leeeetle bit of spin,which imparts a sliiiiight tendency to go horizontal. With this slight tendency the windows are slightly better oriented to catch the motion just right, which spins it a bit more…. And so forth, until finally the rocket is perfectly horizontal (perpendicular) to the falling vector.

increasing number of pylons also will increase the effectiveness of the fins on boost——- up to a point. Especially with a medium length ring, if the cross sectional area of each section (body tube inside, ring outside,pylon on each side of section), too many pylons and the area gets so small the drag goes sky high and they don’t work as fins, the effect is the same as a flat disc.

 

[jqavins]

[T]he effect is a positive feedback loop. As the rocket tumbles, the windows occasionally catch the random motion just right, which imparts a leeeetle bit of spin,which imparts a sliiiiight tendency to go horizontal. With this slight tendency the windows are slightly better oriented to catch the motion just right, which spins it a bit more…. And so forth, until finally the rocket is perfectly horizontal (perpendicular) to the falling vector.

It sounds like this would have to happen faster than you make it sound if it's going to work for a booster. Since separation occurs at only a few tens of feet up, there's not much time for a gradual build-up of the effect.

 

[lakeroadster]

It sounds like this would have to happen faster than you make it sound if it's going to work for a booster. Since separation occurs at only a few tens of feet up, there's not much time for a gradual build-up of the effect.

Approx...

120 feet apogee for the B powered booster​

310 feet apogee for the C powered booster​

​

​

 

[jqavins]

I was speaking more generally. Yours is higher than I expected, so change "a few tens of feet" to "quite a few tens of feet".

BABAR, is that enough? I guess so, huh? Since you've done it before, and all.

 

[Dotini]

How far are you into the build? Any pix yet?

 

[BABAR]

I was speaking more generally. Yours is higher than I expected, so change "a few tens of feet" to "quite a few tens of feet".

BABAR, is that enough? I guess so, huh? Since you've done it before, and all.

It really is surprising how quickly it occurs. I am not good at documenting stuff, I have a couple of altimeters that I have never even flown. But even for my 18” boosters it works, I’d guess they stage at 100 feet or so, minimum diameter my standard booster is a C6-0 for BT-20. I agree it might not work for B6-0. My usual sustainer BT-5 rocket is A8-3, sometimes A8-5 if I can get them.

for A non-gap or short gap booster like @lakeroadster ‘s design, the booster is so unstable at separation that it immediately starts to tumble, so the effect starts to kick in pretty fast. Also, at separation the booster still has significant kinetic energy carrying it UPWARD, so it doesn’t start to fall immediately bit it DOES IMMEDIATELY START TUMBLING, so there is more time to kick in then you think.

things are different for black powder single stage and sustainer deployment. In those rockets, one of three possibilities.

1. perfectly timed ejection (smart or lucky) at apogee, deploys at zero vertical and maybe horizontal velocity if it didn’t weather cock. Rocket IMMEDIATELY starts to fall, but takes a while to build up speed. If chute or streamer gets out and is packed right, plenty of time to deploy as it starts to fall.

2. Early ejection. Bird still going up. Again, plenty of time to deploy, although may cause a zipper or torn shroud lines or other damage.

3. Late ejection. This is the one that really may be bad. You have all the velocity issues of early ejection, but now the rocket is already moving down. If deployment isn’t fast, it may hit ground before full deployment.

 

[jqavins]

In those rockets, one of three possibilities.

1. perfectly timed ejection (smart or lucky) at apogee, deploys at zero vertical and maybe horizontal velocity if it didn’t weather cock. Rocket IMMEDIATELY starts to fall, but takes a while to build up speed. If chute or streamer gets out and is packed right, plenty of time to deploy as it starts to fall.

2. Early ejection. Bird still going up. Again, plenty of time to deploy, although may cause a zipper or torn shroud lines or other damage.

3. Late ejection. This is the one that really may be bad. You have all the velocity issues of early ejection, but now the rocket is already moving down. If deployment isn’t fast, it may hit ground before full deployment.

All that is true, of course, and super super basic. Did you have a point here about horizontal roll recovery?

 

[lakeroadster]

Thanks to Alan Hall over on The Rocketry Show Facebook page for the idea of calling this rocket the AHPLA (Alpha spelled backwards).

So it shall be written, and so I shall photo-chop it.

 

[lakeroadster]

All that is true, of course, and super super basic. Did you have a point here about horizontal roll recovery?

As I read @BABAR response, I thought that's what his first 2 paragraphs addressed?

It really is surprising how quickly it occurs. I am not good at documenting stuff, I have a couple of altimeters that I have never even flown. But even for my 18” boosters it works, I’d guess they stage at 100 feet or so, minimum diameter my standard booster is a C6-0 for BT-20. I agree it might not work for B6-0. My usual sustainer BT-5 rocket is A8-3, sometimes A8-5 if I can get them.

for A non-gap or short gap booster like @lakeroadster ‘s design, the booster is so unstable at separation that it immediately starts to tumble, so the effect starts to kick in pretty fast. Also, at separation the booster still has significant kinetic energy carrying it UPWARD, so it doesn’t start to fall immediately bit it DOES IMMEDIATELY START TUMBLING, so there is more time to kick in then you think.

 

[BABAR]

Thanks to Alan Hall over on The Rocketry Show Facebook page for the idea of calling this rocket the AHPLA (Alpha spelled backwards).

So it shall be written, and so I shall photo-chop it.

View attachment 490402

Sounds Klingon

 

[lakeroadster]

Sounds Klingon

Well the fins do have a bit a of the bat'leth look. Maybe they have a fighting spear called Ahpla?

The Ahpla does have the Klingon Fighting knife, D'k tahg look.

 

[jqavins]

Yeah, I'd say the D'k tahg far more than the bat'leth.

 

[BABAR]

if “Qapla” means ”Success”, maybe “Ahpla” means “Good Luck.”

or it may simply refer to Blood Wine Sangria, I dunno.

 

[jqavins]

or it may simply refer to Blood Wine Sangria, I dunno.

That's blood wine with a little prune juice.

 

[lakeroadster]

I ended up doing an upscale to allow use of 24mm motors. Not a big change, but one I felt was worth the effort.

Started on the drawing package today. See post 31 below. Keep in mind they are preliminary, so feel free to cuss and discuss. Constructive comments are always appreciated.

@BABAR could you take a look at the ring and see if you think the opening will be adequate? I spent some time running through various scenario for making the opening in the rings, and I think drilling holes and using a Dremel to fine tune them makes a lot more sense than trying to cut the opening with a x-acto knife.

Sure is nice having the time to create some CAD models and drawings.

Thanks..

John

 

[BABAR]

I ended up doing an upscale to allow use of 24mm motors. Not a big change, but one I felt was worth the effort.

Started on the drawing package today. I posted them below. Keep in mind they are preliminary, so feel free to cuss and discuss. Constructive comments are always appreciated.

@BABAR could you take a look at the ring and see if you think the opening will be adequate? I spent some time running through various scenario for making the opening in the rings, and I think drilling holes and using a Dremel to fine tune them makes a lot more sense than trying to cut the opening with a x-acto knife.

Sure is nice having the time to create some CAD models and drawings.

Thanks..

John

View attachment 490512

View attachment 490499View attachment 490500View attachment 490501View attachment 490502View attachment 490503View attachment 490504View attachment 490505View attachment 490506View attachment 490507

That looks great! Plenty of cross sectional area room in each section for good air flow. I think the longer ring will give you a lot more stability, and the pylons will act effectively as fins as well. Your cut outs look to be just the right size too.

Having 6 pylons will add a good bit of strength to the ring structure. Doesn't guarantee that it won't break, it's gonna build up a lot of kinetic spinning energy. My theory though is that the ring allows it to "slide" when it hits the ground (possibly roll), as opposed to @Dotini 's design which uses braces as his designs come to a rather abrupt stop when they hit.

Ring design also allows for a lot of surface area (both ring and pylon) with far less potential for weathercocking. The pylon fins are shielded (at least the parts inside the ring) from lateral wind forces.

 

[Dotini]

In my humble opinion, the booster has become plenty interesting enough to warrant its own tube and nose cone.

 

[jqavins]

It's been a while, and I forgot about your beautiful assembly drawings.

Is the long coupler, item 6 on sheet 3, for structural reinforcement? If so, I think it's overkill, unnecessary weight. As we all know, most LP rockets use stock tubes with no such reinforcement and do fine, unless they dirt dive. Will the coupler add enough strength to survive such an event? Is that your purpose?

Finally, aren't the leading end chamfers on the launch lugs backwards? Don't you want the lug profile to be a trapezoid, not a parallelogram?