The Prontosaurus is reimagined

[jqavins]

Looking good. I like the way the black nose cone makes the orange pop on #2.

For the heaviest one, how are the rod exit speeds? How dose it sim on a D22 or E26? The D22 has about 15% more impulse than the D12, which doesn't matter since you're planning the higher impulse E12 anyway. The E26 has virtually the same total impulse as the E12 (2.6% more). But both pack more of that impulse into the first 0.1 to 0.2 seconds, when you're accelerating up the rod.

 

[bjphoenix]

Actually the number that is commonly thrown around on this forum is *3* times the rocket length.

What bothers me about this is should a big bertha had a much longer cord than a baby bertha? I think what is the average length of a rocket with similar weight to mine and then I use that length times 3 (or more). With parachute in LPR I've been using a 10' kevlar cord, but it seems that half the time the cord tangles and doesn't extend the full 10'. I use a cord more like 5' for us with streamers, that length is probably still excessive.

 

[Dotini]

Looking good. I like the way the black nose cone makes the orange pop on #2.

For the heaviest one, how are the rod exit speeds? How dose it sim on a D22 or E26? The D22 has about 15% more impulse than the D12, which doesn't matter since you're planning the higher impulse E12 anyway. The E26 has virtually the same total impulse as the E12 (2.6% more). But both pack more of that impulse into the first 0.1 to 0.2 seconds, when you're accelerating up the rod.

View attachment 501809 View attachment 501811

Thanks, I too am pleased with the colors on #2. I've found some fluorescent yellow, and will give that a whirl on #3.

Unfortunately, I have no sim. Is one available for an older Mac?

But fortunately, I was able to hold the weight of the ready-to-launch #1 rocket to well under 12 ounces, and Estes allow me 14.0 for the D12-3. Since I'm using a 6' long 1/4" launch rod, I'm confident it will leave the rod safely.

 

[neil_w]

Unfortunately, I have no sim. Is one available for an older Mac?

Depending on the definition of "older", this should work: https://www.rocketryforum.com/threa...d-mac-to-solve-all-your-java-problems.143540/

 

[Raco123]

Nice !

 

[Dotini]

Prontosaurus 3 is almost ready for launch. Only the spin tabs remain.

After building 3 dozen rockets in the past year, I'm ready to stop building and resume testing. I have 9 scratch builds, 2 kits and a kitbashed CHAD to test. I will start at nearby Dahl field - but have joined the club that uses the vast 60 Acres facility and will do the higher altitude launches there.

 

[boatgeek]

60 Acres is a truly wonderful LPR/MPR field. If you have higher altititude flights, you can go over there pretty much any time soccer isn't in season and do private launches. If you're over there next Sunday, I'll be with one of the TARC groups off to the side.

 

[Dotini]

Spin tabs are attached. These are polystyrene angles from Evergreen Scale Models, are 3/4" wide and project 1/8" above the fin.


Complete with 0.4 oz ballast, altimeter, 24" Xform parachute and D12-3 motor, this model weighs only 9.2 ounces.
I'm counting on its wide BT-70 tube, 6 fins and spin tabs to keep the altitude reasonably low.

 

[lakeroadster]

Spin tabs are attached. These are polystyrene angles from Evergreen Scale Models, are 3/4" wide and project 1/8" above the fin.
View attachment 503957
View attachment 503958
Complete with 0.4 oz ballast, altimeter, 24" Xform parachute and D12-3 motor, this model weighs only 9.2 ounces.
I'm counting on its wide BT-70 tube, 6 fins and spin tabs to keep the altitude reasonably low.

Slick!

What's the overall length?

 

[Dotini]

Slick!

What's the overall length?

For the sake of simplicity and lightness, I went with a single 18" tube. With the 7" balsa cone, that gives 25". The fins are 2" x 2" x 3/32" basswood. The motor mount will accept an E14 if/when desired. Spirals are filled and edges mostly rounded.

 

[jqavins]

Since you want drag to keep the altitude down, I think you've got great spin tab. I can hardly think of a draggier way to induce spin.

 

[Dotini]

Since you want drag to keep the altitude down, I think you've got great spin tab. I can hardly think of a draggier way to induce spin.

I could have still induced spin but minimized drag by keeping the height of the Gurney flaps to under 2% of the fin chord. But, typically, I deliberately chose to maximize the brute force available to me.

 

[lakeroadster]

FWIW...

 

[jqavins]

I could have still induced spin but minimized drag by keeping the height of the Gurney flaps to under 2% of the fin chord. But, typically, I deliberately chose to maximize the brute force available to me.

As long as the result meets your goal, which it certainly seems to do, you've done your job well. I never mean to suggest that the draggy method is a bad method; you've used a method that is well suited to the project's requirements.

 

[Dotini]

FWIW...

View attachment 503961

Nice - thank you!
note: the mass with D motor is 9.2 oz, and the CG with E14 measures to 16.5".


Nosecone detail. Prior to launch, the Alt2 is retained with tape. Four very small holes ventilate the cavity.
The base of the nosecone is filled, smoothed and painted to promote adhesion of the tape.

 

[lakeroadster]

Nice - thank you!
note: the mass with D motor is 9.2 oz, and the CG with E14 measures to 16.5".

View attachment 503970
Nosecone detail. Prior to launch, the Alt2 is retained with tape. Four very small holes ventilate the cavity.
The base of the nosecone is filled, smoothed and painted to promote adhesion of the tape.

Revised sim, and updated post #73

 

[Dotini]

FWIW...

View attachment 503975

I had the pleasure of launching Prontosaurus 2 and 3 today at 60 Acres. Both flew on D12-3. The weather was perfect! Both flights were nominal with plenty of spin evident. I received spontaneous compliments from other rocketeers on my parachute descent, of all things. The delay was perfect and the Xform performed remarkably. My parachute recovery skills have been a real weak point of my rocketry forever - but these days I'm trying seriously to get that phase right at last.

The sim calculations of @lakeroadster turned out to be about 10% optimistic - very close! I think the Prontosaurus family wants to fly on E power.

 

[Dotini]

The Prontosaurus family has had a baby!

This BT-50 model was conceived for the purpose of flying an A8-3 at a nearby park - walking distance!
It is very light and depends on a 3" x 30" streamer for recovery.

 

[BABAR]

The Prontosaurus family has had a baby!
View attachment 506654
This BT-50 model was conceived for the purpose of flying an A8-3 at a nearby park - walking distance!
It is very light and depends on a 3" x 30" streamer for recovery.

I’m suspicious of the mailman……

 

[Dotini]

Here are the latest completed members of the Prontosaurus tribe. Above, the BT-50/A8-3 for use at a small field. Below, a BT-55/E12-4 intended for 60 Acres next week. The bigger model weighs 5.2 oz complete with motor, 18" chute and altimeter. The spirals are filled and the edges rounded. What do you think, would E12-6 be the more prudent choice?

I may add spin tabs to both these models, as well as additional finishing.

 

[neil_w]

Why would you want the longer delay on the larger, heavier model? I would think you'd go the other way. 4 seconds seems too short for the small one. Have you simmed?

Spin tabs will change the calculus and shorten the delay requirements a bit.

 

[Dotini]

Why would you want the longer delay on the larger, heavier model? I would think you'd go the other way. 4 seconds seems too short for the small one. Have you simmed?

Spin tabs will change the calculus and shorten the delay requirements a bit.

No spin tabs will be added until the models are thoroughly tested as is. That way, I'll be able to precisely define the changes in altitude, etc. that the spin tabs will produce.

The larger E12-4 model has a motor rated for a 17 oz lift. But if the 4 second delay is correct for a model bordering on 17 oz as Estes recommends, it stands to reason that it would be insufficient for the 5 oz model we have here.

The smaller model weighs about 1.5 oz. Since it will launch initially on a very small field - 350' x 450', I want to use a smaller motor. If all goes well and the rocket goes straight up and down on the streamer, I may change the motor to maybe an A8-5 or B6-6.

 

[neil_w]

LOL, never mind, I completely misread your previous post. Sorry about that.

6 seconds might still be short for a 5 oz model on an E12. A quick sim would be worthwhile (even just throw it into Thrustcurve.org).

 

[Dotini]

LOL, never mind, I completely misread your previous post. Sorry about that.

6 seconds might still be short for a 5 oz model on an E12. A quick sim would be worthwhile (even just throw it into Thrustcurve.org).

Alas, I have only an ancient Mac and no sim, so I rely on other means for my designs. @lakeroadster has given me a helping hand on several occasions., which I greatly admire him for.

A D12-7 or an E12-8 might be good for this 5 oz model.

 

[jqavins]

Alas, I have only an ancient Mac and no sim, so I rely on other means for my designs.

(even just throw it into Thrustcurve.org)

That.

The only problem I personally have using ThrustCurve's sim is guessing the C_D. Others are probably better at that than I am, or know better rules of thumb.

 

[neil_w]

Alas, I have only an ancient Mac and no sim, so I rely on other means for my designs.

1) How old a Mac are we talking about? I would expect the packaged OpenRocket 15.03 to work on pretty old machines.
2) Thrustcurve.org is available to everyone, and excellent for a first approximation.

The only problem I personally have using ThrustCurve's sim is guessing the C_D. Others are probably better at that than I am, or know better rules of thumb.

Yeah, it's a bit of a guess. For a standard rocket such as this I just go with the default that Thrustcurve gives. For this rocket with Cd of "Average" (0.6) it estimated 7 seconds delay for an E12. So a 6 or 8 second delay would probably work.

 

[Dotini]

1) How old a Mac are we talking about? I would expect the packaged OpenRocket 15.03 to work on pretty old machines.
2) Thrustcurve.org is available to everyone, and excellent for a first approximation.


Yeah, it's a bit of a guess. For a standard rocket such as this I just go with the default that Thrustcurve gives. For this rocket with Cd of "Average" (0.6) it estimated 7 seconds delay for an E12. So a 6 or 8 second delay would probably work.

1) I bought it new several years ago. It's a 26" iMac which came with Safari, works well, and I have no desire change it.
2) Although I stubbornly stick to my dinosaur instincts, I may look into this.

I will need to order the 6 and 8 second delay E12's, so I will do the first launch on a D12-5. Many thanks for your assists!




The Prontosaurus family in their five sizes. All except for #4 are very suitable for small fields.

 

[neil_w]

1) I bought it new several years ago. It's a 26" iMac which came with Safari, works well, and I have no desire change it.

I can almost guarantee it will run OR 15.03 just fine, and the new beta would probably work fine as well.

 

[lakeroadster]

Here's the plot for Prontosaurus 3 on a D12-3 and a D12-5.

The D12-3 ejects just before apogee, the D12-5 ejects just after apogee. The D12-5 is actually a better choice, the rocket is traveling slower at deployment.