Anybody have a stable CG for a Blackstar Voyager?

[LithosphereRocketry]

The title says it all. Anyone know the CG/CP for a stock Blackstar Voyager? I'd run it through OpenRocket, but there really wouldn't be much point...

 

[ericm541]

I have a CP of 32.13" and a CG of 21.61" no engine, CG could be different depending how it was constructed. I've flown mine with just estes E9 so far and the couple times it was flown the rocket was wobbly. Fun rocket to fly though, rocsim sim shows it overstable with an E9.

 

[neil_w]

The couple of videos I've seen of BSVs flying were definitely wobbly. Regardless of the CP calculation, there is not a lot of fin area back there.

But it is beautiful.

 

[ericm541]

I planed on fixing the issue before flying it again, took awhile to build i would hate to loose it, just a matter of moving the CG.

 

[LithosphereRocketry]

OK, thanks all. I'll take 32" as a tentative CP and see how it balances, and launch in low wind to hopefully mitigate the wobble.

Now, to wait for my 24/40 & E11Js to arrive... Supposed to ship by January... *sigh*

 

[wighty44]

My BS Voyager's CP is 32.1". The no motor CG is 20.8" (I added 15g of nose weight - BBs & Epoxy). It's flown once on a CTI E22 and the launch pad CG with that motor was 24".

 

[rcktnut]

My BS Voyager's CP is 32.1". The no motor CG is 20.8" (I added 15g of nose weight - BBs & Epoxy). It's flown once on a CTI E22 and the launch pad CG with that motor was 24".

How did it fly? With your motor you still had + 4.8 calibers stability. You and ericm541 have stability margins of + 10-11 with out motors. If I were OP I would try to decrease the margin first flight and see how it performs. I have an Estes AIM 54 Phoenix that I over stabilized and it flew wobbly. Luckily I used clay in the nose cone and removed some, brought down the margin to +2.3 calibers w/o motor and it flew straight as an arrow ever since. I know big difference in design, but worth a try I guess.

 

[Nytrunner]

Can I ask how you determined the CP of 32"? That seems pretty far back by my calculations. I don't really trust Rocksim or Openrocket with this one.

When I built mine, I ran several airflow cases at various speeds and settled on a point of aerodynamic balance ~27" from the nose. Check out posts 31 and 32

For flight, I aim to keep the CG w/motor ~4" (10% of the length) ahead of that point and it's behaved well (the E20 was fun!). I set it up so I can add weight in the nose.

 

[ericm541]

It was determined from a rocsim file i found, someone elses work. Typically with estes kits i just build them and fly them unless i modify it. Taking a closer look at the rocsim design the fin structure isn't exactly how the kit is built. So yeah i bet the CP isn't exactly 32". So i went and set up my darkstar and checked the CG with an E9, which is how i previously flew it, and the CG was 25 5/8".

 

[LithosphereRocketry]

Can I ask how you determined the CP of 32"? That seems pretty far back by my calculations. I don't really trust Rocksim or Openrocket with this one.

When I built mine, I ran several airflow cases at various speeds and settled on a point of aerodynamic balance ~27" from the nose. Check out posts 31 and 32

For flight, I aim to keep the CG w/motor ~4" (10% of the length) ahead of that point and it's behaved well (the E20 was fun!). I set it up so I can add weight in the nose.

This sounds like a good conservative option, especially based on actual analysis rather than a simple approximation. I'll stick with a CG of 24" or forward for the time being.

Thanks all!

 

[Nytrunner]

With a caveat, mine was not stock lol

 

[wighty44]

How did it fly? With your motor you still had + 4.8 calibers stability. You and ericm541 have stability margins of + 10-11 with out motors.

First I should mention that the RockSim file I created is an as-built vs. a generic model. All my dimensions and weights are carefully measured and entered. Given that basis, my (no motor) margin is either 6.9 or 8.6 depending upon whether you select "Max frontal Dia." or "Nose Cone dia". Considering the Voyager's fin placements and design I suspect 6.9 is more realistic. Then the E22 loaded margin becomes 4.9 - still over stable.

My first flight was so low (est 500 ft.) that it's hard to evaluate it's flight performance. However, it went up, parachute opened, and landed without any damage.

I will always select a light / no wind, warm temperature, day to fly the BS Voyager.

Note: I should mention that I lengthened the MMT to over 6" so that I could use longer motors.

 

[rcktnut]

Given that basis, my (no motor) margin is either 6.9 or 8.6 depending upon whether you select "Max frontal Dia." or "Nose Cone dia"View attachment 335092

I would agree that 6.9 is correct. In my first post I mistakenly listed the difference between CP/CG relationship (10-11) rather than the figured stability margin. My bad.

 

[LithosphereRocketry]

Can I ask how you determined the CP of 32"? That seems pretty far back by my calculations. I don't really trust Rocksim or Openrocket with this one.

When I built mine, I ran several airflow cases at various speeds and settled on a point of aerodynamic balance ~27" from the nose. Check out posts 31 and 32

For flight, I aim to keep the CG w/motor ~4" (10% of the length) ahead of that point and it's behaved well (the E20 was fun!). I set it up so I can add weight in the nose.

Update- finally flew the Blackstar yesterday on a D12-3. CG was at ~24.5", at the aft edge of the first strakes. The flight was perfectly straight with very little wobble or coning. I didn't get a video but there might be one on my club's website soon.

Thanks everybody!

 

[Nytrunner]

Good show!