Level 1Recommendations

[boatgeek]

I really hope so, otherwise I'm not sure what we will do. What would happen if I flew the H100? Would the rocket leave the rail and get angled by the wind?

Best to worst case:
You can get on a longer rail (like 12') and get enough rail exit velocity that everything works
You have a slow liftoff but not enough wind to disturb the flight and everything goes nominally
The rocket weathercocks significantly off of the pad, leading to a longer walk
The RSO doesn't let you fly (this is highly likely if your initial thrust to weight <5 and/or you don't have enough speed off the rail)
The rocket weathercocks more, leading to a low flight, too-long delay, and a zipper
The rocket is entirely unstable off of the pad and crashes with significant damage

See how long a rail you need to get ~50 ft/s off the rail. If you can get a rail that long, then that's your best case. It's also possible that a club member will trade a higher thrust equivalent motor for the H100. Or sell you a higher thrust motor from their inventory. I'm not sure how to deal with a too-small chute, short of adding another chute, with attendant risks of fouling and partial inflation. At least your fins are swept forward enough that in light winds you'll be landing on the motor mount.

 

[1Matthew]

I talked with our mentor who says we should be fine with an H100 because open rocket doesn’t pick up an initial spike in thrust and that’s why it says our velocity off the rod is slow?

 

[jmasterj]

open rocket doesn’t pick up an initial spike in thrust and that’s why it says our velocity off the rod is slow

That's definitely not true, and doesn't give me a whole lot of confidence in your mentor. Also, there isn't an initial spike in the H100s thrust curve:



Having looked at one of my sims for a similar rocket (4", ~4lbs) the H100 should probably be getting you more than 35fps with 6 feet of guidance. An 8 foot rail will probably get you 6 feet of guidance, so if you can find a 10-12 foot rail you should be good to go. But you should update your sim with your measured weight and CG, as well as the rail length available, so you can make that determination yourself.

 

[1Matthew]

That’s just odd, I haven’t checked thrust curve yet but definitely should have, that ain’t right. When I get home I have to mess with the sim. Something’s off.

 

[-Slick-Ice]

H130W reload or the H135W (29MM DMS) would be a better choice.

 

[-Slick-Ice]

If it really weighs 56oz that is not correct for a 8ft rod. I would expect something more like this which is a 5.5" IROC

 

[-Slick-Ice]

Did you change the rod length in the openrocket configuration or edit the simulation itself?

 

[kjhambrick]

@1Matthew --

I got ahold of a Binder-Excel-38mm.rkt file and imported it into OpenRocket.

I added mass to the empty rocket CG so the rocket mass matches your reported mass.

The mass object is the dashed line in the coupler.

Then I set the Site Altitude to 2500 ft and the rail to 8-ft and ran some sims.

The .ORK is attached.

This is a screen shot:


I checked the ROC website and they recommend rail buttons but they don't specify the length of their rails.

It might matter in this case.

HTH and GOOD LUCK !

-- kjh

 

[1Matthew]

You are a life saver! I just went onto the open rocket website and the issue was that my rail guide default kept unsaving itself for some reason, so it would revert back to 3 feet instead of 8 feet, The rocket is fine!!

 

[kjhambrick]

You are a life saver! I just went onto the open rocket website and the issue was that my rail guide default kept unsaving itself for some reason, so it would revert back to 3 feet instead of 8 feet, The rocket is fine!!

No worries, @1Matthew !

Remember that the off-the-rail speed depends on the length of the rail and the speeds in the sims I posted were for an 8-foot rail.

The off-the-rail speeds in your original sims were for a 3-foot rail.

These speeds are for a 6-foot rail:

The off-the-rail speed for your Excel with an H100 from a 6-foot rail is about as low as I would go if it was my rocket.

And I would only do that on a calm day.

Please let us know how it goes and post pictures if you can !

Good Luck !

-- kjh

 

[1Matthew]

Just did all my test runs and I think I got it down where I want to set the motor delay to 8 seconds for tomorrow. Does that sound about right?

 

[kjhambrick]

To quote @Rschub, TLAR

Good luck today, @1Matthew !

Please post pictures

-- kjh

 

[1Matthew]

Will do

 

[1Matthew]

Well just launched my level 1 and now have my certification! Overall it went okay, the winds were higher than expected and my rocket did not go to the expected altitude as a result. Thus, the motor delay which I set was at 8 seconds but probably should have been set to 6 or 7. My rocket did zipper but it was not a massive zipper down the whole tube. On Monday, I’m going to fill the zipper in with epoxy, the automotive filler, sand it down and repaint to make it seamless. I’ll use the nosecone to hold the shape of the body tube together so I don’t widen the diameter of the bt.

 

[thzero]

Congratulations. And open the wallet!

 

[-Slick-Ice]

Maybe I counted wrong but that looked like more than 8 seconds. It burned out around 20 seconds and ejected around 31?

 

[kjhambrick]

Congratulations @1Matthew !

And thanks for the video !

Yikes ! That must have been a real butt-clencher, waiting for your ejection charge to fire

I agree with @-Slick-Ice on the timing of the events ...

When I viewed the video in VLC, I noted the following events in the playback control dialog ( I've got to find and install a millisecond timer plugin ):

Ignition: 16 sec
Burnout: 19 sec
Apogee: 23 sec
Ejection: 31 sec

This makes the actual delay after burnout about 12-sec and the optimal delay was more like 4 -or- 5 sec ...

Did you notice anything odd when you shortened the delay ?

How long was your launch rail ( or was it a rod ) ?

It looked shorter than 8-feet long ...

Finally, it sounded a little windy.

That rocket does need more thrust ...

An H219T should work well and then a J350W might be a decent motor for a Level 2 attempt in the same rocket ...

Anyhow, enough Sunday-Morning comments from the arm-chair ... Congratulations @1Matthew !

-- kjh

 

[1Matthew]

Nothing was odd about setting motor delay, my whole group used the same batch of motors, maybe something wrong with them because most of the delays that were set were around 7-10 seconds but opened late similar to mine.

 

[1Matthew]

Maybe I counted wrong but that looked like more than 8 seconds. It burned out around 20 seconds and ejected around 31?

Well I did name it “One Way Ticket” for a reason