Difuminar: 9500 feet and Mach 1.5 on a CTI G150

TRFfan2 · Postby **TRFfan2** » Fri Feb 10, 2017 9:36 am

Hi all,

This is a build thread for my 24 mm MD (called "difuminar" spanish for blur). It is essentially designed to get the most possible altitude out of a non-HPR motor. It consists of a Polystyrene 6:1 Von Karman nose cone resting on top of a fiberglass body tube with 4 CF fins.

The design of this rocket depended heavily on the reduction of drag which was a key factor in gaining altitude. Openrocket was used mostly to test out different configurations.

Nose Cone

As the body tube was designed to be as short as possible, most of the electronics were transferred to the nose cone as to cut down on unnecessary length. The electronics are mounted on top of a 3D printed sled and secured inside the nose cone with another 3D printed bulkhead. Stability was ensured throughout the rocket by implanting 35 grams of tungsten powder with epoxy in the tip of the nose cone.

3D printed polystyrene was chosen for the material for the nose cone due to its low price and easy machinability. Fiberglass and Carbon Fiber were originally considered as materials for the nose cone due to their high strength to weight ratio but they were more expensive and not as easy to machine.

For the Nose cone, a Von Karman shape was optimum for the speeds achieved by the rocket. A number of different lengths were experimented with and in the end a 6:1 ratio was ideal for achieving maximum altitude.

Body Tube

The material chosen for the nose cone was Carbon fiber. Fiberglass is cheaper but due to the small size of the rocket the cost was not substantial.

The main source of the drag was the body tube which caused more than 50% of the drag on the rocket. Compressing the components in the payload section and storing the parachute and shock cord inside the nose cone’s hollow shoulder allowed the length to be shortened a good deal and therefore cut down on the drag.

Fins

Carbon fiber was found to be the best material for the fins due to its high strength to weight ratio. Most other materials were found to either be too heavy or too weak. Fiberglass possesses similar characteristics to carbon fiber but carbon fiber has an edge over fiberglass in strength and weight and so CF was chosen to be the final material.

The design of the fins was also crucial to get the maximum possible altitude out of the rocket and went through over 50 different configurations before the final design was implemented. From the start, it was obvious that a three-pointed fin had a significant advantage over a delta fin performance-wise. For the three-pointed fin, three different designs were considered. Swept fins are more efficient when tilted back a long distance but they become structurally weak after and prone to fin flutter after a certain extent. They also do not offer an advantage over a short distance and so were disregarded as an option. Clipped fins cause too much drag and although they are more structurally sound, the 1mm thick CF plate provides more than enough structural integrity. A balance was found between the two by making fin halfway between clipped and swept (a 90-degree triangle). This provided a good deal of strength while also keeping drag to a minimum.

Another challenge was finding the perfect balance between the Tungsten weight in the nose cone and the size of the fins. Increasing the weight in the nose cone and decreasing the fin size ultimately ended up with a higher altitude in the simulation but in real life an insufficient fin size would have resulted in weather cocking soon after leaving the rail. To lessen this effect, the fin size was increased to a sufficient amount (enough to ward off the effects of weather cocking) and the weight in the nose was lowered to 35 grams.

Avionics

The model will be tracked with a Telemini altimeter, which also will enable deployment and measurement of the rocket’s final altitude. A buzzer was also added in the nose cone to aid tracking.

So anyway, there is the introduction. build should start in a month or so while i get the parts.

SpaceManMat · Postby **SpaceManMat** » Fri Feb 10, 2017 12:32 pm

Sounds like a great build, will watch with interest.

TRFfan2 · Postby **TRFfan2** » Fri Feb 10, 2017 12:36 pm

SpaceManMat wrote:Sounds like a great build, will watch with interest.

Thanks. Do you know how to upload a ORK file? I cant seem to find the attach button. And i also cant edit my original post.

kopius · Postby **kopius** » Fri Feb 10, 2017 3:08 pm

TRFfan2 wrote:
SpaceManMat wrote:Sounds like a great build, will watch with interest.
Thanks. Do you know how to upload a ORK file? I cant seem to find the attach button. And i also cant edit my original post.

You can't edit posts after 30min. This was to stop certain users modifying posts that then took the whole thread out of context.

Try and compress your file (zip it up) and upload it

Sent from my iPhone using Tapatalk

CATO · Postby **CATO** » Fri Feb 10, 2017 6:17 pm

SpaceManMat wrote:Sounds like a great build, will watch with interest.

+1 Good luck with the build.

TRFfan2 · Postby **TRFfan2** » Sat Feb 11, 2017 12:48 am

Ok here is the openrocket file.

New Compressed (zipped) Folder.zip: (17.03 KiB) Downloaded 87 times

dhbarr · Postby **dhbarr** » Sat Feb 11, 2017 11:15 am

Any chance of extracting an image?

TRFfan2 · Postby **TRFfan2** » Sun Feb 12, 2017 12:16 am

dhbarr wrote:Any chance of extracting an image?

TRFfan2 · Postby **TRFfan2** » Thu Apr 20, 2017 9:51 pm

Got some progess on the MD. Will get some pics up later today.

TRFfan2 · Postby **TRFfan2** » Fri Apr 21, 2017 4:16 am

TRFfan2 wrote:Got some progess on the MD. Will get some pics up later today.

Viking · Postby **Viking** » Fri Apr 21, 2017 12:56 pm

Looking good!

drew · Postby **drew** » Fri Apr 21, 2017 2:38 pm

Hi TRFfan2. I've had a look at your sim file and I've got to say I'm pretty impressed! Especially considering I've been working on a similar rocket and I'll be lucky to get 6k feet on a G150 (which is what I'm planning to fly it on as I've got one "in stock"). That said mine's a chopped down BlackHawk 24 with a TeleMini in the nose for tracking and a Raven in a 24mm av bay for flight data and deployment duties. It definitely appears that you're definitely squeezing ever bit of performance out of it that you can, well done. All that said I do have a couple comments.

1. IF you use a G65 motor instead of the G150 you'll have a lower G forces (89G vs 55G) and squeeze another 50 meters / 150 feet out of your apogee. Remember MaxV and Max Altitude rarely match up with motor combinations. If you're looking for Max Alt a G65 is your best bet.
2. I'm not sure how you're going to leverage a Telemini in the nose without bending the antenna back "over itself" and thus lessening the effeciency and output of the transmitter. 1/4 wave whip antennas work best when the wire is extended in a completely straight manner. When combined with the fact that you'll be approaching 10k ft apogee I'd want to do a bit of field testing to ensure you can RDF the Telemini with it in its flight necessary "folded" configuration.

Good luck!

OverTheTop · Postby **OverTheTop** » Sat Apr 22, 2017 1:01 am

Looking good. Remember to treat the GPS unit to some glue on the antenna (epoxy to the PCB) so it doesn't come off during the savage boost. The ceramic patch antenna is only held on with double-sided tape and one solder joint normally.

TRFfan2 · Postby **TRFfan2** » Sat Apr 22, 2017 8:37 am

drew wrote:Hi TRFfan2. I've had a look at your sim file and I've got to say I'm pretty impressed! Especially considering I've been working on a similar rocket and I'll be lucky to get 6k feet on a G150 (which is what I'm planning to fly it on as I've got one "in stock"). That said mine's a chopped down BlackHawk 24 with a TeleMini in the nose for tracking and a Raven in a 24mm av bay for flight data and deployment duties. It definitely appears that you're definitely squeezing ever bit of performance out of it that you can, well done. All that said I do have a couple comments.

1. IF you use a G65 motor instead of the G150 you'll have a lower G forces (89G vs 55G) and squeeze another 50 meters / 150 feet out of your apogee. Remember MaxV and Max Altitude rarely match up with motor combinations. If you're looking for Max Alt a G65 is your best bet.
2. I'm not sure how you're going to leverage a Telemini in the nose without bending the antenna back "over itself" and thus lessening the effeciency and output of the transmitter. 1/4 wave whip antennas work best when the wire is extended in a completely straight manner. When combined with the fact that you'll be approaching 10k ft apogee I'd want to do a bit of field testing to ensure you can RDF the Telemini with it in its flight necessary "folded" configuration.

Good luck!

Well honestly the G65 has an offset core which will result in corkscrewing.So i dont think ill try it since other people with optimized MD rocketshave had issues with the offset core.

I didnt know about the antenna before and thats why my nose cone is a bit short. But I made a new file with an extra-long nose cone and so i can fit the antenna and have a little extra squeeze space.

And yea i will be testing the telemini on the ground and with a test flight with an AT D composite motor (altitude should be about 2000 ft).

TRFfan2 · Postby **TRFfan2** » Sat Apr 22, 2017 8:39 am

OverTheTop wrote:Looking good. Remember to treat the GPS unit to some glue on the antenna (epoxy to the PCB) so it doesn't come off during the savage boost. The ceramic patch antenna is only held on with double-sided tape and one solder joint normally.

Yes i will reenfource it. But it is not a GPS unit, it is radio tracking (im using a telemini).