The Prontosaurus is reimagined

[Dotini]

Four decades ago I built but mercifully never flew the Prontosaurus, chambered for 3 E's. It likely would have broken up in flight.

Now, nearly a year after being born again in rocketry, I'm once again irresistibly dabbling into the realm of mid-power, having started a fleet of 3 clustered models utilizing D motors and various tube diameters. However, it occurred to me that I've never launched and successfully recovered a scratch built rocket of greater than C power. That's why I've started Prontosaurus 2, a large, primitive and easy-to-build rocket built around around a single E motor mount, but blocked to accept the basic Estes D. This will get me started at the ground level for my clustered D's to come.

Foreground, the extinct Prontosaurus, never survived my Paleolithic era. Background, the Prontosaurus 2, fledging wings.


My region is emerging from historic monsoons, and now I'm itching to finish and fly a new fleet of rockets.

 

[Dotini]

Prontosaurus 2, my first scratch BT-80 model, is coming together, and to me it has a pleasing heft and look. Weight of components seen below is 8.6 oz. I'm hoping for an altitude of 800' or so with a D12, which should work very nicely at my 500' x 500' field. I could use an Estes E, probably at 60 Acres, but I've heard worrisome comments about its reliability. Any truth to that?


Supernumerary coupler is to reinforce motor mount installation and beef up tube in front of motor. Overall length is about 36". I plan on using a 24" Xform chute. Big enough?


Fins are 1/8" basswood, spin tabs are thin birch plywood from Finland.

A lurid fluorescent pink and black roll pattern paint job is coming as weather permits.

 

[teepot]

So I'm a little confused. If you put an engine block for a D you won't be able to fly E's. Block it for E's and use a spacer to fly D's.

 

[Dotini]

So I'm a little confused. If you put an engine block for a D you won't be able to fly E's. Block it for E's and use a spacer to fly D's.

Yeah, I got confused with the names of parts I'm not used to using. Sorry about that.
At the moment, the motor mount has a green spacer in it to "block" the D motor in place. If I remove the green spacer, I can use an E. Note: I do not plan on using an E in this model. I expect it might blow the fins off!

 

[Dotini]

I'm adding a stuffer tube both for better recovery and for added weight. I'll also add ballast to the nose cone so that I get closer to the estimated maximum lift weight for the Estes D12-3.

Van Milligan says the sleeve on the stuffer tube will help prevent it from being the first part on the rocket that wears out.

 

[kyle]

Unless you need the nose weight for cp/cg reasons I might think again about adding it if it's just to get closer to your intended motor's max lift-off weight. Closer to max lift-off weight is closer to "not gonna work" weight. Add in a little variance in motor performance and the planned optimized flight could become a very entertaining flight for reasons you might not want.

Looks cool though, I'm interested to see how the spin tabs perform. I kinda like spin stabilization.

 

[Dotini]

Unless you need the nose weight for cp/cg reasons I might think again about adding it if it's just to get closer to your intended motor's max lift-off weight. Closer to max lift-off weight is closer to "not gonna work" weight. Add in a little variance in motor performance and the planned optimized flight could become a very entertaining flight for reasons you might not want.

Looks cool though, I'm interested to see how the spin tabs perform. I kinda like spin stabilization.

Thanks for your thoughtful reply. I don't think I need the nose weight for CG/CP reasons as the rocket is 36" and has 4 big fins and extra base drag. But I do want to hold down the altitude as much as possible. The motor is rated for 14 oz max lift, so I thought maybe 11 or even 12 oz. would be a reasonable figure for my situation. In the deep past I've launched a Maxi Alpha Three at 11 oz and it leaped skyward like a raped ape.

 

[Aslansmonkey]

You probably won't need nose weight unless the fins are made of something heavy.

There's every reason to believe that rocket will fly just fine on an E motor, providing it swing tests ok (or sims ok).

And I've had no problem with E motors, which I use pretty often. Never one cato or issue. A10-4Ts on the other hand, tend to blow up almost every time.

 

[BABAR]

You are going to have three motors ejecting into one stuffer tube. Very do-able. Issues you may have already addressed but just in case.

Good motor retention is a MUST, preferably motor hook or other mechanical holder, and even WITH a motor hook I might put a piece of tape around the motor and the hook (I have had at least two and I think three failures WITH motor hooks.) The reason here is that with the stuffer it is possible the back pressure may blow your motors out the back WITHOUT deploying the laundry out the front.

Maybe I am wrong or you just don't have it in the picture, but I think your stuffer tube will need both a forward AND a rear centering ring. The rear ring as well as the tail end of the stuffer tube is gonna get a heck of a lot of heat from those three motors, whether they eject simultaneously or not (reality is, no matter what you do they will never be EXACTLY simultaneous, the only question is will the variance [e.g. 1 millisecond verse 2 full seconds] make a difference.) Options here, put a piece of aluminum can over the rear end of the rear ring and around the first 3 inches of the stuffer tube, or smear the area with JB Weld. There are probably other options. I CAN say from experience (not with clusters but with staged rockets where I used a stuffer that was SMALLER in diameter than the motor---e.g. an 18 mm motor with a BT-5 stuffer, and the stuffer was JUST in front of the motor mount) that without something inside the first vew inches of the stuffer, I got burn through of the stuffer just forward of the motor with just a few flights.

Don't overdo the length of the stuffer, make sure you leave enough forward room to LOOSELY pack the chute and the wadding or chute protector, and make sure the nose cone is snug but not tight. With three motors, if they ARE nearly simultaneously you are going to have a lot of pressure which is great if your gear is loosely packed and clears the tube promptly, NOT so great if things are so tight the pressure blows out the stuffer and/or the body tube.

Finally, I remember you saying you have a fairly small field. Three Ds is a good bit of motor. Yeah, you are intentionally making it kind of draggy, which is fine, but my Tank Killer is a REEEEEEAAAALLLLLY draggy rocket (Toilet Ball floats aren't very aerodynamic. Who knew?) and on a single D it scoots up easily to probably 300 feet. I assume you've simmed this, so you should have a feel for how high it is going to go. Options for first flights include going with 24mm Cs, or go with three adapters and go with 18 mm motors.

Get some good video on this one, with three motors and your spin tabs, you're gonna blaze a unique trail! Then again, that's nothing new for you!

Best wishes.

Tom

 

[Dotini]

You are going to have three motors ejecting into one stuffer tube. Very do-able. Issues you may have already addressed but just in case.

Good motor retention is a MUST, preferably motor hook or other mechanical holder, and even WITH a motor hook I might put a piece of tape around the motor and the hook (I have had at least two and I think three failures WITH motor hooks.) The reason here is that with the stuffer it is possible the back pressure may blow your motors out the back WITHOUT deploying the laundry out the front.

Maybe I am wrong or you just don't have it in the picture, but I think your stuffer tube will need both a forward AND a rear centering ring. The rear ring as well as the tail end of the stuffer tube is gonna get a heck of a lot of heat from those three motors, whether they eject simultaneously or not (reality is, no matter what you do they will never be EXACTLY simultaneous, the only question is will the variance [e.g. 1 millisecond verse 2 full seconds] make a difference.) Options here, put a piece of aluminum can over the rear end of the rear ring and around the first 3 inches of the stuffer tube, or smear the area with JB Weld. There are probably other options. I CAN say from experience (not with clusters but with staged rockets where I used a stuffer that was SMALLER in diameter than the motor---e.g. an 18 mm motor with a BT-5 stuffer, and the stuffer was JUST in front of the motor mount) that without something inside the first vew inches of the stuffer, I got burn through of the stuffer just forward of the motor with just a few flights.

Don't overdo the length of the stuffer, make sure you leave enough forward room to LOOSELY pack the chute and the wadding or chute protector, and make sure the nose cone is snug but not tight. With three motors, if they ARE nearly simultaneously you are going to have a lot of pressure which is great if your gear is loosely packed and clears the tube promptly, NOT so great if things are so tight the pressure blows out the stuffer and/or the body tube.

Finally, I remember you saying you have a fairly small field. Three Ds is a good bit of motor. Yeah, you are intentionally making it kind of draggy, which is fine, but my Tank Killer is a REEEEEEAAAALLLLLY draggy rocket (Toilet Ball floats aren't very aerodynamic. Who knew?) and on a single D it scoots up easily to probably 300 feet. I assume you've simmed this, so you should have a feel for how high it is going to go. Options for first flights include going with 24mm Cs, or go with three adapters and go with 18 mm motors.

Get some good video on this one, with three motors and your spin tabs, you're gonna blaze a unique trail! Then again, that's nothing new for you!

Best wishes.

Tom

To recap, the original Prontosaurus is the defective black model (foreground), carrying three 24mm motors in a BT-70 tube, which is decades old, never flew and never will. The Prontosaurus 2 is the new gray primer BT-80 model beside it which is ready for one D or one E.

I have a separate thread going on a fleet of three new clustered models - Big Spinning Cluster, Small Field.

 

[lakeroadster]

Hmm? Why not fly the original with just one D motor, and plug the other 2 motor tubes with used D motors? Apogee shouldn't be to high for your field, as big & heavy as the rocket is.

I'll be glad to simulate these in Open Rocket if you want.

 

[Dotini]

Hmm? Why not fly the original with just one D motor, and plug the other 2 motor tubes with used D motors? Apogee shouldn't be to high for your field, as big & heavy as the rocket is.

I'll be glad to simulate these in Open Rocket if you want.

Thank you, that's a very generous offer, but I genuinely want to leave the original in the past where it belongs. Over the decades, some of the parts have been damaged and no longer fit well together, and my confidence in the fin join is low. However, I'm at the point of being able to determine the CG of the new one later today. If it seems possibly too far aft, a sim may be called for.

 

[Dotini]

@lakeroadster
Current weight is a shockingly heavy 12.45 oz with altimeter and 24" Xform chute, ready to fly lacking only topcoat and launch lug(s).

Length, exclusive of motor mount and motor, is 35.5". End of motor is 7/8" behind end of tube.
CG is 23" from tip of nose cone.
1/8" fins are 3" wide by 3.25" high.
Fins are 32" from nose cone.
Spin tabs are 1/8" x 2.5" each.

Edit: I have ordered some E12-4 motors.

 

[boatgeek]

You might think about using composite E motors to get a little more oomph for liftoff. They also ship without hazmat if you're getting motors sent to you.

FWIW, 60 Acres is pretty safe to about 1500 feet if you're cautious about wind direction (send something to 800 or 1000 first!), and up to maybe 2000 feet on flat calm days. The morning is usually better over there. One weird thing is that it's in a bowl so there can be a wind shear at about 500-1000 feet with significantly higher winds above the shear line than below.

 

[jqavins]

I could use an Estes E, probably at 60 Acres, but I've heard worrisome comments about its reliability. Any truth to that?

You read it enough here to believe it. But lately I've been reading that the problems seem to have been worked out. But I se you've bought some already.

As for this:

Note: I do not plan on using an E in this model. I expect it might blow the fins off!

I guess you changed your mind, or are those E motors you bought intended for a different rocket? Second, the E engines won't expose the fins to very much more stress than the D12.

 

[Dotini]

You read it enough here to believe it. But lately I've been reading that the problems seem to have been worked out. But I se you've bought some already.

As for this:I guess you changed your mind, or are those E motors you bought intended for a different rocket? Second, the E engines won't expose the fins to very much more stress than the D12.
View attachment 494935

Thanks for your remarks and graphics, always appreciated. The Prontosaurus 2 is almost ready to launch with a D as planned, since it is under the max lift weight recommended by Estes. But it beats the limit only by fractions. So I expect the acceleration will not be terribly fierce. I've taken no extra measures to reinforce the fin joints. I'll be using my 6' 1/4" diameter launch rod, and keeping the E's in the box in reserve should the weight increase over the limit or the liftoff too sketchy. What with the big tube, heavy weight and spin tabs, I'm guessing an altitude well under 800', easily accommodated at my small field (500' x 500').

I know I'll build rockets capable of higher altitude, and when that happens I'll move my launch operations to 60 Acres. Right now I have a BT-80 with 2 D's in work, almost finished. A BT-70 with 2 D's, a BT-60 2 x 18mm and a BT-70 3 x 18mm are on the build list. All these cluster models will have reinforced fins.

 

[lakeroadster]

@lakeroadster
Current weight is a shockingly heavy 12.45 oz with altimeter and 24" Xform chute, ready to fly lacking only topcoat and launch lug(s).

Length, exclusive of motor mount and motor, is 35.5". End of motor is 7/8" behind end of tube.
CG is 23" from tip of nose cone.
1/8" fins are 3" wide by 3.25" high.
Fins are 32" from nose cone.
Spin tabs are 1/8" x 2.5" each.

Edit: I have ordered some E12-4 motors.

I ran a rough draft of your Prontosaurus 2 into Open Rocket. You'll want to fly it on something bigger than a D motor for sure....

 

[Dotini]

I ran a rough draft of your Prontosaurus 2 into Open Rocket. You'll want to fly it on something bigger than a D motor for sure....

View attachment 494970

Your work on my behalf is greatly appreciated! Thanks! I'm very relieved to see my rocket is indeed fit for a small field, so I will not hesitate to use the E motor.

 

[lakeroadster]

Your work on my behalf is greatly appreciated! Thanks! I'm very relieved to see my rocket is indeed fit for a small field, so I will not hesitate to use the E motor.

Glad I could help!

The "draggy" nature of the spin induced by the spin tabs are beyond the capacity of Open Rocket. My mind sim shows an apogee lower than what Open Rocket specifies.... but due to the wide variations in black powder motor thrust, who knows?

Looking forward to your flight report.

 

[jqavins]

Can you get altitude at deployment? With the delays being longer than optimum and the apogees being lower than predicted, I wonder if it will be high enough to unfurl a 'chute before hitting the ground. The E12 gives more altitude, but also more excess delay. :nailbite:

 

[Dotini]

Glad I could help!

The "draggy" nature of the spin induced by the spin tabs are beyond the capacity of Open Rocket. My mind sim shows an apogee lower than what Open Rocket specifies.... but due to the wide variations in black powder motor thrust, who knows?

Looking forward to your flight report.

We've had new records set for wind and rain all through the Fall season here. As a consequence, I have a backlog of new scratch build flights (and an Estes Savage) lined up pending weather:

Venturi Ring Fin BT-55 / 18mm
Venturi Ring Fin BT-60 / 24mm #1
Venturi Ring Fin BT-60 / 24mm #2 (smaller ring area)
Horizontal Recovery BT-60 / 24mm (Magnus X-5)
2 Stage Ring Fin BT-60 / 24 mm each stage
Prontosaurus 2, BT-80 / 24mm
Cluster BT-80 / 2 x 24mm

I expect January to be equally bad, but I'm hoping February will bring about weather favorable for rocketry here. At minimum, I'll have at least 2 or 3 additional cluster designs ready by then as well.

Can you get altitude at deployment? With the delays being longer than optimum and the apogees being lower than predicted, I wonder if it will be high enough to unfurl a 'chute before hitting the ground. The E12 gives more altitude, but also more excess delay. :nailbite:

Great question. I was wondering about that too. I have accepted that building with larger rockets and motors was going to have issues and setbacks. If Prontosaurus 2 proves to be impracticable,I have plenty of other designs to try.

 

[lakeroadster]

Can you get altitude at deployment? With the delays being longer than optimum and the apogees being lower than predicted, I wonder if it will be high enough to unfurl a 'chute before hitting the ground. The E12 gives more altitude, but also more excess delay. :nailbite:

Great question. I was wondering about that too. I have accepted that building with larger rockets and motors was going to have issues and setbacks. If Prontosaurus 2 proves to be impracticable,I have plenty of other designs to try.

Here are the flight plot(s) for the 2 engines selected.

The D12-3 reaches apogee in 4 seconds
The E12-4 reaches Apogee in a little over 5 seconds

​

So the E motor burns longer (that's good) and it will attain a higher altitude (that's good).

The only thing that bothers me is... I don't trust E-motors especially for a scratch build. If it were my rocket... I'd fly it on a composite motor, like an Aerotek E15-4 or E30T-4.

Here are the flight plot(s) for the 2 composite engines

The E15-4 reaches apogee in about 5-1/2 seconds
The E30-4 reaches Apogee in a little 4-3/4 seconds

​

With the 1/8" thick rugged construction of the fins, your rocket should handle these composite motors just fine.

 

[jqavins]

The altitude at deployment for the E12 doesn't look bad, I just worry about its accuracy with the high drag of those fins. Lake, does the sim use an amped up C_D?

E30 looks like the winner to me. It's got the best speed off the rod and the nearest to optimum delay, which results in the lowest speed at deployment. Add better altitude and better reliability than the E12 and I think it's the engine of choice here.

 

[lakeroadster]

The altitude at deployment for the E12 doesn't look bad, I just worry about its accuracy with the high drag of those fins. Lake, does the sim use an amped up C_D?

E30 looks like the winner to me. It's got the best speed off the rod and the nearest to optimum delay, which results in the lowest speed at deployment. Add better altitude and better reliability than the E12 and I think it's the engine of choice here.

Just regular paint (not smoothed & not polished) on all the components and square edged fins. If you look at the fins, see Post 17, you will see I added a wide flat fin surface on the trailing edge of the main fins to add drag. As I stated previously the spinning effect will likely hurt apogee also.

 

[Dotini]

Just regular paint (not smoothed & not polished) on all the components and square edged fins. If you look at the fins, see Post 17, you will see I added a wide flat fin surface on the trailing edge of the main fins to add drag. As I stated previously the spinning effect will likely hurt apogee also.

View attachment 495014

I recall reading somewhere that merely rounding the edges of square edge rocket fins will reduce its drag by an astonishing percentage, ~ 60%?

FWIW, Prontosaurus 2 has all rounded fin edges, and all spirals filled. The final coat of paint is intended to be wet sanded with 600 and done. It will have two 1/4" lugs.

Although I absolutely adore your simwork and graphics of my humble model, I woulds note that there is a full 3" Qualman baffle located 16" back from the tip of the nose cone. Also I have omitted the stuffer tube.

So, is there any difference in the strength of the ejection charge amongst any of the motors that have been mentioned above? My nosecone has a very light fit and carries no added weight other than the altimeter.

I really appreciate your contribution to my project, and also that of @jqavins

 

[neil_w]

Don’t forget the Q-jet E26 as another option. A bit less punch and total impulse than the E30.

 

[Dotini]

Don’t forget the Q-jet E26 as another option. A bit less punch and total impulse than the E30.

Thanks for your suggestion. I'm thinking about it.

So far in my brief life of born again rocketry - under a year - I've used only Estes motors. I have wanted to continue doing that unless the need is compelling. My basic goal has been to build inexpensive rockets that attempt/fulfill a mission or purpose within a set of constraints. Right now my goal is build large, loud and smokey rockets suitable for a small, conveniently nearby field. Do these composite motors fit in my 24mm mount/clip? Are they as loud and smokey as an Estes motor? Is their ejection charge the same, or stronger/weaker, than an Estes motor? If I have built a rocket that must have an expensive composite motor in order to function correctly, I may decide to simply discard the model and build another which corrects the defect(s).

 

[lakeroadster]

I recall reading somewhere that merely rounding the edges of square edge rocket fins will reduce its drag by an astonishing percentage, ~ 60%?

FWIW, Prontosaurus 2 has all rounded fin edges, and all spirals filled. The final coat of paint is intended to be wet sanded with 600 and done. It will have two 1/4" lugs.

Although I absolutely adore your simwork and graphics of my humble model, I woulds note that there is a full 3" Qualman baffle located 16" back from the tip of the nose cone. Also I have omitted the stuffer tube.

So, is there any difference in the strength of the ejection charge amongst any of the motors that have been mentioned above? My nosecone has a very light fit and carries no added weight other than the altimeter.

I really appreciate your contribution to my project, and also that of @jqavins

If you look at the model, it has the baffle. That's the three bulkheads that are down near the motor tube. You state it is 16" back rom the tip of the nose cone. How is it restrained, such that it doesn't slide all the way back to the motor when the motor ignites? Regardless, if the CG and weight of the rocket is similar to the as built configuration of your bird, it's location doesn't affect the simulation.

It's my understanding that all the D motor ejection charges carry the same punch. Timing the charge to be near the apogee is ideal in regard to popping of the nose cone. See the simulation column "velocity at deployment".

As to the 60% drag reduction... I changed the paint to "polished" and rounded the fin edges, see simulations below:

If I have built a rocket that must have an expensive composite motor in order to function correctly, I may decide to simply discard the model and build another which corrects the defect(s).

No worries in regard to the motors listed above fitting into your 24 mm motor mount.

Don't throw the baby out with the bath water just because of a simulation. Your Prontosaurus is a stable rocket and will fly great.

Life is short.. Kick the tires and light the fire.

 

[Dotini]

If you look at the model, it has the baffle. That's the three bulkheads that are down near the motor tube. You state it is 16" back rom the tip of the nose cone. How is it restrained, such that it doesn't slide all the way back to the motor when the motor ignites? Regardless, if the CG and weight of the rocket is similar to the as built configuration of your bird, it's location doesn't affect the simulation.

It's my understanding that all the D motor ejection charges carry the same punch. Timing the charge to be near the apogee is ideal in regard to popping of the nose cone. See the simulation column "velocity at deployment".

As to the 60% drag reduction... I changed the paint to "polished" and rounded the fin edges, see simulations below:

View attachment 495186

Thanks for your elucidation and emendation of the data. It is very interesting.

As for my baffle installations, all my conventional recovery models have either a full baffle or a simpler "laundry shelf" version to which my cord is anchored. I've used them in all sizes of tubes, and none have failed. I've even disassembled a used model to inspect the baffle. The installation is always the same. After the baffle is complete*, dry and clean, I fully coat (with wood glue) the inside of the tube precisely where the baffle is to fit. The baffle is pushed up the tube until all its outer edges are in the glue zone. I inspect the upper end to ensure adequate squeeze-out of glue above the upper end, adding more if necessary. Often I make the main tube in two sections to facilitate perfect glueing of both the motor mount and the baffle. Sometimes I absorb the weight of an extra coupler to make this happen.
* I always coat the bottom of the baffle with a layer or two of epoxy or glue to protect it from the burning ejection particles.

 

[lakeroadster]

FWIW: I changed the chute and baffle location, and changed the finish to "smooth paint".

Also changed the E30 from a 4 second to a 7 second delay to lower the velocity at deployment.