Altitude Expectations for a Minimum Diameter 54mm

Hello,

I have a 2.1" Wildman Jr that I plan on converting to minimum diameter the same way I did with the 1.5" Cardboard Mini-Tomach.

After measuring and weighing all the parts, I entered all the numbers into OpenRocket.

The numbers I'm seeing for altitude are not impressing me very much. I'm wondering if I'm doing something wrong?

For a CTI L935 the altitude OpenRocket gave was 13,428 feet.

With no motors, the rocket weights about 30.3 oz 1.89 lbs. Let's say I add electronics and other stuff, bump it up to 3 lbs.

Other minimum diameter 54's I've seen on TRF have gone at least 20K feet with the same motor.

Am I missing something?

View attachment 54mm_Min_Diam_Wildman_Jr.ork

I'm too lazy to download your file, but fin cross-section and overall surface finish makes a big difference in OR results. Square cross-section fins kill performance.

I've flown over 20K feet with a 54mm MD on a K300, so yeah, you should expect better.

Those are pretty thick fins for a start but my Mongoose only sims 16389' on same motor with 3/32" fins.

For a double-check, a quick run through Thrustcurve using average finish shows 18,230 ft.

You have square cross section fins, you have regular surface finish, and your rocket is very long, longer than it needs to be. When I airfoil the fins, set all the surfaces to polished, and shorten the BT, I get close to 20K feet on a K300.

Agree with everything stated above. If you really want to go high cut the booster down until you can just squeeze the parachute in. Get rid of the payload bay altogether. My 54mm minimum diameter rocket went to 24,626 on an L265 on a windy day.

I did not realize the extent to which these changes can impact a rockets performance.

Per Mike and Chris's suggestions, I changed fin cross section from square to airfoil and I also polished the finish.

I also experimented with a swept fin design, instead of the shape that comes with the Wildman Jr.

This is how the changes affected the max altitude on a CTI L935:

• New Shape of Fins = 15,933 ft
• Polished Airframe and Nose Cone = 19,179 ft
• Airfoil the Fins = 21,912 ft
• Shorten Body Tube Length to 88 cm = 24,425 ft
• Shorten Payload Tube Length to 20 cm = 25,632 ft

Regarding the shape of the fins, if I leave the height of the fins to 7.4 cm, I get the above numbers. But, the stability goes below 1 cal during the flight on the L935 for a brief period.

If I increase the fin height to 8cm, the max altitude goes down to 24,766 ft, and the stability never goes below 1 cal during flight on an L935.


Every time I post on here, I learn something from you guys. I'm very grateful for everyone's help!

View attachment 02_54mm_Min_Diam_Wildman_Jr.ork

One thing I am curious about is Cesaroni's tapered rear closure vs normal rear closure on a min dia rocket.

TheNewGuy said:

Hello,

I have a 2.1" Wildman Jr that I plan on converting to minimum diameter the same way I did with the 1.5" Cardboard Mini-Tomach.

After measuring and weighing all the parts, I entered all the numbers into OpenRocket.

The numbers I'm seeing for altitude are not impressing me very much. I'm wondering if I'm doing something wrong?

For a CTI L935 the altitude OpenRocket gave was 13,428 feet.

With no motors, the rocket weights about 30.3 oz 1.89 lbs. Let's say I add electronics and other stuff, bump it up to 3 lbs.

Other minimum diameter 54's I've seen on TRF have gone at least 20K feet with the same motor.

Am I missing something?

Click to expand...

If it helps as a point of reference, the student team I work with built a 3" rocket with tailcone, nice surface finish and reasonable fin beveling, and ~9 lbs dry. It just flew to 13,350 or so on the L935.

TheNewGuy said:

I did not realize the extent to which these changes can impact a rockets performance.

Per Mike and Chris's suggestions, I changed fin cross section from square to airfoil and I also polished the finish.

I also experimented with a swept fin design, instead of the shape that comes with the Wildman Jr.

This is how the changes affected the max altitude on a CTI L935:

• New Shape of Fins = 15,933 ft
• Polished Airframe and Nose Cone = 19,179 ft
• Airfoil the Fins = 21,912 ft
• Shorten Body Tube Length to 88 cm = 24,425 ft
• Shorten Payload Tube Length to 20 cm = 25,632 ft

Regarding the shape of the fins, if I leave the height of the fins to 7.4 cm, I get the above numbers. But, the stability goes below 1 cal during the flight on the L935 for a brief period.

If I increase the fin height to 8cm, the max altitude goes down to 24,766 ft, and the stability never goes below 1 cal during flight on an L935.

Every time I post on here, I learn something from you guys. I'm very grateful for everyone's help!

Click to expand...

Another lightweighting method is not to use an airframe but to attach the fins to the bare motor casing via a fin can, see for example this design for the fin can for the "Bare Necessities" rocket:


https://highpowerrocketry.blogspot.com/2012/09/bare-necessities-n5800-competition-entry.html

Bob Clark

Performance nut said:

One thing I am curious about is Cesaroni's tapered rear closure vs normal rear closure on a min dia rocket.

Click to expand...

The 54mm tapered rear closure by CTI is definitely worth it if you're looking for extra altitude. I'm in the process of building a L935 MD bird and by using the tapered rear closure in my sim I gain an extra 2,270 feet in altitude on the flight.

Make sure that it will actually fit your case. I bought one a couple years ago and it wouldn't screw on to any of the 6XL cases I could find (3-4).

Im doing something similar but I ditched the payload section and went with head end deploy. The nose cone is pretty much full with recovery gear and no room for my tracker so Im putting my tracker inside a 38mm tube and attach that to my shock cord in the booster section.
I get 23250' in mine and mine weighs in at 3.126lbs without motor. I'd post the Ork. file but cant seem to get it to go.

I built and flew a Mongoose CF MD rocket to 23,500' on a L935 at BALLS a couple of years ago. I did have the CTI tail cone and launched it from a tower. My OR sim showed 24,273, which is within 4% of actual altitude. Just an example of an actual flight.

Mass with motors shows 144oz.


Tony