Trans-Sonic Rocket - F-13TS

[evildave42]

Hi All,
I'm still a rocket amateur but I'm building most from scratch. I have two other rockets to finish first, but one of my future projects is to create a very simple trans-sonic (Mach 0.8-1.0) or super-sonic (Mach 1.2) rocket powered by the Estes G motor (which I can get at my local Hobby Lobby).

So, questions:
1. What is the best nose cone shape for trans-sonic or super-sonic speed?

2. I plan to use a BT-55 (the heavy duty version) paper tube for minimum diameter with 3 small fiberglass reinforced balsa fins going through the tube and epoxied to the motor tube.
Now I know that at trans-sonic and sonic speeds the CP moves upward negating the already small fins. How do I combat this without adding too much drag?

3. Also, is there a well proven fin shape for this?

 

[UncleVanya]

Look here: https://en.wikipedia.org/wiki/Nose_cone_design

Scroll down to the section labled: Nose cone drag characteristics. Depending on the speed expected a Power Series X 1/2 looks to be the best fit for lowest drag over a range of speeds at or near mach but the Von Karmen gives it a run for the money also. The good thing about the Power Series is that it is a fairly straightforward math problem to generate the pattern. Lastly the Aerospike is another option but this really only is useful for very high sustained speeds over mach.

 

[MasonH]

1) Von-Karmen shape is typically the best, I believe

2)Noseweight, move the fins back, make them thicker

3)Ask Crazy Jim or Troj. They will probably have that answer.

I THINK these are right. Not 100% sure though

 

[evildave42]

2)Noseweight, move the fins back, make them thicker

I want to keep weight to a minimum, would it add saficient drag to make the tube longer insted? Or would this not be as effective?

Also, what exactly do you mean by thicker fins? Something like the wedge rudder on the X-15?

 

[T-Rex]

OOP Estes WAC Corporal, upscaled, sims at Mach 1.03 with the G80. Will it survive? Probably not, but it would be fun to watch.
OOP Estes Black Brant II is similar.

Get a copy of RockSim or Open Rocket then make / play with some designs. Never know what you will come up with.

 

[evildave42]

I just played with the Proline's Formula design in Open Rocket. If you change the materials to polystyrene, kraft phenolic and 1/8" plywood, add 50gm of nose weight and it sims to Mach 1.37 on a G-80. I don't have a warm-fuzzy that it would survive the flight, but it is a place to start.
OOP Estes WAC Corporal upscaled sims at Mach 1.03 with the G80. Again will it survive? Probably not, but it would be fun to watch.

Survivability would be nice but not a top priority, cheap rocket after all. You mentioned polystyrene, kraft phenolic and 1/8" plywood, is that all in the fins? I'm only really familiar with low power construction methods. Would plywood fins reinforced with medium-weight fiberglass not suffice?

I’ve been using the Rocketry Handbook a lot up to now, but it is not very clear on the aerodynamics at transonic speeds, does the tube length suddenly play a serious role in drag or just strength? (I haven’t chosen a length yet)

Hmmm... Maybe I should invest in Open Rocket after all.

 

[T-Rex]

Open Rocket is beyond worth the investment... it's a freebie!

https://openrocket.sourceforge.net/

No, my list of materials is based on your description of basically a low power rocket that you want to send supersonic. Plastic nose, cardboard tube, and plywood (at the least) fins.

The only thing I know about going supersonic is that it generally considered that a cardboard rocket wont survive. If the rocket does not survive, then 1) it is not a successful flight 2) becomes a lot of litter that needs to be picked up. In keeping with the intent of the safety codes and laws associated with hobby rocketry, you need to have a reasonable belief that you will be getting it back safely.

 

[evildave42]

Hmmm.. I've heard some of the dubious reports on cardboard tube, I was planning to use one from the heavy duty line Semroc carries and just build it like a very serious low power rocket. If that’s not enough, what material would you suggest (that is also cheap)? I could also glass such a tube, I've been getting better at that.

As you pointed out, while I dont really care if the rocket is damaged, I am not keen on having a rocket disintegrate during lift-off and sending a rouge motor into my face. Or more likely into a stroller or bus full of orphans.

That would not be cool.

 

[UncleVanya]

There have been plenty of cardboard rockets that flew > mach 1.0 but they were built correctly and appropriately. Fiberglassing the cardboard tube may be worthwhile but it will add weight which drops the changes of reaching the velocity you want. Very light thin Carbon is the best choice if money is not considered due to the twin pillars of stiffness and low weight. However, there are other factors that need consideration including cost, ease of working with the material, etc.

 

[evildave42]

Well, it looks like Semroc does not sell the BT-55 in a heavy duty version, and I don't trust regular 55 at anything approaching mach. Any specific ideas for a cheap alternative in the BT-55 diameter (specifically where to get one), or would I be better off with a light coat of fiberglass?

I downloaded Open Rocket and made a quick model in it (see attached file). It shows just breaking Mach 1, but this is probably missing the heaver body tube and some other miscellaneous weight. Never used Open Rocket before so let me know if I really messed anything up! Thanks!

View attachment F-13-TS.ork

 

[Chuck]

Take a look at this:
https://www.apogeerockets.com/Rocke.../Take_Your_Apogee_Aspire_to_Supersonic_Speeds

The Apogee Aspire kit is about 20 bucks plus shipping.

~Chuck G.

 

[bill_s]

BT-55? Use 29 mm (1.14" I.D.) tubing (Semroc: under "large body tubes" and/or "Series").

You will not see the rocket again. I have seen one made using the Estes Black Brandt, it didn't shred (best could tell). Press the button and the rocket dissappears and is replaced by a smoke trail going up as high as can see, awesome but that was about it. Pretty much identical to a min. dia. A10 powered rocket except for the noise and smoke amounts.

 

[evildave42]

The Series 115 tubes are just about right, and I had not noticed before but they have a similar wall thickness to the heavy duty tubes, thanks for pointing that out! I can also get a matching cone for around $5.50, I already have the mount and fin material.

I was planning to use flat fins with rounded leading edges as they are easier to make than airfoils, do you guys think this will be a problem?

The Apogee Aspire kit looked inticing to build as an introduction. I'll be considering that.

 

[Chuck]

You are going to want the fins to come to a point on the leading and trailing edge.

 

[evildave42]

Looks like the 1.22" Series 115 is slightly too small for a 29mm motor, so I think I'll use the more roomy 1.5" Series 150, also heavy duty with matching 7" ogive nose cone.

That should provide enough room for the engine mount I already have. Since ther does not seem to be an exact centering ring for this, I plan to fit it by soaking two 1/2 inch strips of paper in a water/elmers glue solution and tightly winding it around the mount, creating a custom centering ring and then sanding it down to fit. Then the homemade centering rings get soaked in 30 minute epoxy and placed inside the tube to cure nice and good.

The basic arrangement will be unchanged from the OpenRocket file above, I'll update it when I get back home.
I can try making tapered edge fins from balsa, covered in medium or light fiberglass, unless you think paper laminating will do. Is there an easy way to get them sanded uniformly?

Anything I'm missing?

 

[bill_s]

^-- I checked that and you're right that 29 mm>1.14" ... but look at the specs for 29 mm motors, 1.13 and 1.125", and other 29 mm tubes, 1.14".

 

[evildave42]

^-- I checked that and you're right that 29 mm>1.14" ... but look at the specs for 29 mm motors, 1.13 and 1.125", and other 29 mm tubes, 1.14".

Yes I noticed, but that doesn't leave much room for the any securing hardware and the fins will not have the support of a through the wall tab. I did notice that the 1.5 inch tube failed the simulations in Open Rocket, I changed it to 1.25 inches and (even though those tubes are on back order) and got better results. Still had enough room for the mount too.

Attached is the updated Open Rocket model, I got it to top out at 350 m/s, just over Mach 1
Do you guys see any problems I missed? What do you think of the fin shape.

View attachment F-13-TS.ork

 

[evildave42]

The rocket guy at my local hobby shop described going supersonic on an F motor.
With my inexperiance in mid-power and the Estes motors avalable at my local Hobby Lobby, do you think it is worth my time to redesign this to use an F motor insted of a G80?

 

[awseiger]

You're going to have serious trouble breaking Mach, even with a G80. It's been done... But it's not easy.

And breaking Mach with a Black Powder motor is, from as far as I can tell, Actually impossible (Although someone... please prove me wrong or back me up with Le Mathematicas)

CTI makes an F240 that WILL send a light enough rocket past mach. I actually built a 24mm MD who's motor block was positioned to fit an F240. Problem is, I know I'll never see it again, as I loose it on Estes C11's. When you go to a project like this, the biggest concern moves quickly from "will it stay together?" to "If it stays together... Will I ever see it again?"

Go with the G80. And Good Luck!

 

[evildave42]

Thats what I was thinking. Even if it has been done before, my mid-power construction skills are probably not up to that yet and I would like to get it back too.
I've thought a lot about trying the Apogee Aspire first, but I really wanna see if I can do it myself.
I'm teaching myself the construction on a much larger/heaver G powered rocket, I'm not building it for speed just awesomness so I can make/coverup my mistakes. Also tying to build a D-E power rocket built with mid-power techniques on the side.
Once done, I should have the skills to bring the F-13SS to life!

 

[evildave42]

Okay, hammered out the designs much more and ordered some of the parts. Simulations put it around 350-352 m/s.

Problem: Launch Lug
The bigest rockets I've done so far are E size. At the moment I am simulating the F-13SS with a 1/4 inch regular old launch lug mounted in a fin root.
1) Is it safe to use a regular launch lug on such a powerful rocket?
2) what would be a better answer?
3) and how does that change my launch procedure/equipment?

 

[mwtoelle]

Ditch the launch lugs and use a tower launcher. A tower launcher uses three or four rigid rails (depends on the number of fins) that slide along the body tube between the fins. Another plus with a tower launcher is that you don't have to deal with rod whip. Launch lugs will add unnecessary drag to the model, although I have used them on my LOC Vulcanite with HPR motors.

 

[evildave42]

Ditch the launch lugs and use a tower launcher. A tower launcher uses three or four rigid rails (depends on the number of fins) that slide along the body tube between the fins. Another plus with a tower launcher is that you don't have to deal with rod whip. Launch lugs will add unnecessary drag to the model, although I have used them on my LOC Vulcanite with HPR motors.

Hmmm... I thought that would be the case. Ditching the lugs will give me some extra speed too. Is that sort of launch system something my local club (SOAR) would have? Or is that something I should just build/buy myself? (the only times I'm going to be anywhere where I can launch such a rocket are with the club anyway)

Also, any such launch pads you'd specifically recommend?

 

[evildave42]

I found some "Conformal Launch Guides" for rails on
https://giantleaprocketry.com/products/components_launch_systems.aspx (halfway down the page)
They seem to have a very small forward profile. They look pretty good for an entry level.

I've never seen a rail launch before, it is only attached to one rail (at least on a small rocket like this) correct?

 

[CarVac]

I found some "Conformal Launch Guides" for rails on
https://giantleaprocketry.com/products/components_launch_systems.aspx (halfway down the page)
They seem to have a very small forward profile. They look pretty good for an entry level.

I've never seen a rail launch before, it is only attached to one rail (at least on a small rocket like this) correct?

The smallest conformal rail guides are for 38mm, but you can bend them a little to fit 29mm tubing just fine.