Well that didn't go as planned...

The Rocketry Forum

Help Support The Rocketry Forum:

FlyingMonkey

Well-Known Member
Joined
Jun 19, 2016
Messages
78
Reaction score
20
The Bertha has been our favorite rocket so far. So I started with that but tried my hand at a few new things. Probably too many at one time.
TTW basswood to a 29mm mount
Clear payload section
Apogee strap on boosters
At the last minute I threw on a nose cone that matched the boosters.
Nomex chute protector.

I Sim'd this thing with a Bertha nose cone when I had a working pc about a year ago. The rest I just winged.

First launch was on a C6-5. That's a great motor for a standard Bertha but it turns out I added way more weight than I anticipated per the sim. It launched ok but the delay was too long. It lawn darted.
I quickly cut the visibly damaged section off (about 1.5"), removed the payload section, and strapped the boosters on.
C6-5, A8, A8.

Jumped off the rod quick! But 1 booster out performed. The rocket took a turn, boosters peeled away correctly, but rocket was once again too low for a proper recovery. The ejection charge clearly lit but it didn't pop the nose cone. This time it landed like a plane. With FAR more damage.
No wind on either launch.

I should have started with more motor in the main. I probably should have larger fins for stability in case of uneven power distribution. I can't help but wonder if the nomex was used wrong and caused the lack of ejection. I should have weighed it.

Love to hear your thoughts. Feel free to tell me what else I did wrong and what I should change next time around.

Sim is currently not an option.
20191103_150359.jpg
20191116_141036.jpg
20191116_141105.jpg
 

FlyingMonkey

Well-Known Member
Joined
Jun 19, 2016
Messages
78
Reaction score
20
I think there is enough good tube to cut and couple, saving the fins and mount. My hands don't want to cut that basswood again lol.
 

Lugnut56

What, me worry?
Joined
Apr 7, 2015
Messages
631
Reaction score
53
Can you download and use OpenRocket? I use Rocksim, but from reading the posts on the TRF, a lot of folks use and have good results using OR. I was going to get a set of the strap-on boosters on my last order from Apogee, but they were out-of-stock at the time.
 

Rex R

LV2
Joined
Apr 21, 2010
Messages
6,086
Reaction score
140
I believe that you're going to need a bigger motor, something like a D12.
Rex
 

FlyingMonkey

Well-Known Member
Joined
Jun 19, 2016
Messages
78
Reaction score
20
Can you download and use OpenRocket? I use Rocksim, but from reading the posts on the TRF, a lot of folks use and have good results using OR. I was going to get a set of the strap-on boosters on my last order from Apogee, but they were out-of-stock at the time.
With the exception of final built weight I did sim it. It sim'd great. Either the sim is wrong in regards to weight or drag because it didn't fly the same.

The uneven propulsion is a risk with this type of cluster. If the rocket didn't turn off the rod it may have got high enough for good recovery. Not sure though. I ordered a scale and I'm going to weigh the pieces.

Also I found video I'll try to post.
 
Last edited:

John Taylor

Well-Known Member
TRF Supporter
Joined
Aug 22, 2019
Messages
684
Reaction score
228
Location
Fort Worth TX
Way bigger/ more powerful motor, give it more altitude to recover stability and deployment early enough for recovery.
 

FlyingMonkey

Well-Known Member
Joined
Jun 19, 2016
Messages
78
Reaction score
20
Ok so my thought about more motor seems valid. What about more fin?
The RSO suggested that I lose the swept back look and move that fin area out away from the rocket and pods. It will definitely shift the weight but will the fins themselves offer any more stability?
 

David Schwantz

Well-Known Member
Joined
Jul 23, 2018
Messages
1,361
Reaction score
484
Location
MN
How did you line up the grain of the basswood? Basswood is NOT strong if the grain runs straight along the air frame tube. On the second flight, with more power, could you have had flutter to cause the drift in the vertical line of flight? Also,if it landed like an airplane, on its belly, then when you cut off the bad section you may have changed the CG enough to cause erratic flight. With no ejection, she should have come down nose first.
 

FlyingMonkey

Well-Known Member
Joined
Jun 19, 2016
Messages
78
Reaction score
20
How did you line up the grain of the basswood? Basswood is NOT strong if the grain runs straight along the air frame tube. On the second flight, with more power, could you have had flutter to cause the drift in the vertical line of flight? Also,if it landed like an airplane, on its belly, then when you cut off the bad section you may have changed the CG enough to cause erratic flight. With no ejection, she should have come down nose first.
Wood grain is probably close to 90°.
I cant load the video yet, gonna try again today. But it came off the rod and turned. It's flight was very horizontal and low altitude. I think if it was up higher it would have lawn darted like it did the first time. I'll try to get the vid up as it will probably help
 

FlyingMonkey

Well-Known Member
Joined
Jun 19, 2016
Messages
78
Reaction score
20

Ok let's try again.

First flight is c6-5 empty payload tube.
2nd flight is sans payload tube and 1.5" of body tube that was damaged.
Boosters in place with A8's
 

neil_w

Hunkered down and slowly going crazy
TRF Supporter
Joined
Jul 14, 2015
Messages
8,825
Reaction score
2,234
Location
Northern NJ
Top 2 mistakes:
1) Adding a bunch of stuff to a rocket and not weighing it before flight, to confirm motor has sufficient thrust to lift it safely. That's a big no-no.
2) Not checking center of gravity on modified rocket to confirm stability. You added a lot of weight to the rear of that rocket, and a more powerful motor to add even more. If you don't sim it, you should at least swing-test it.
 

FlyingMonkey

Well-Known Member
Joined
Jun 19, 2016
Messages
78
Reaction score
20
Top 2 mistakes:
1) Adding a bunch of stuff to a rocket and not weighing it before flight, to confirm motor has sufficient thrust to lift it safely. That's a big no-no.
2) Not checking center of gravity on modified rocket to confirm stability. You added a lot of weight to the rear of that rocket, and a more powerful motor to add even more. If you don't sim it, you should at least swing-test it.
I did sim it. The apogee boosters have a file so I simply added them. I selected basswood, 29mm (paper rings), etc, etc.

I even played around with different payload weights. In the sim it flew fine. Now, I understand that the sim can only guess how heavy I applied glue and paint but without a scale I hoped it would be close. Guess it wasn't close enough.

I can't sim anymore but I did order a scale so in the future I can at least use old school methods.
 

FlyingMonkey

Well-Known Member
Joined
Jun 19, 2016
Messages
78
Reaction score
20
20191201_121437.jpg
20191130_121832.jpg
BTW: the fin area survived. Once I get ahold of some BT60 I'll rebuild it and try again.

Scale arrived...
Rocket (including payload section) is 186g w/recovery gear
Boosters are 50g w/recovery gear
That's 236 grams combined.

A8 is 13 grams each x2
C65 is 24g
Combined that's 50 grams

286 grams all together.
 
Last edited:

FlyingMonkey

Well-Known Member
Joined
Jun 19, 2016
Messages
78
Reaction score
20
I can't find max lift weight for A8 but if 2 A's make a B, they list the B6 and the c6-5 at 113g. Giving about 226 grams of max lift. Clearly I was under powered.

By the chart I should have used a D12 in the rocket and the boosters could have been A,B, or C.
 

Steve Shannon

Well-Known Member
TRF Supporter
Joined
Jul 23, 2011
Messages
6,237
Reaction score
2,752
Location
Butte, Montana
If you didn’t run the simulation with the final loaded weight and with the correct center of gravity, you really didn’t sim it.
 

FlyingMonkey

Well-Known Member
Joined
Jun 19, 2016
Messages
78
Reaction score
20
If you didn’t run the simulation with the final loaded weight and with the correct center of gravity, you really didn’t sim it.
Fair enough, but I didn't have that capability until today. When the simulator had weights available for these added items I hoped that whoever made the files were accurate. The string test looked fine.
 
Top