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Steven88 said:
I’ll do what I can. I live in rural western Kansas and I don’t know of one solitary HPR guy out here! There probably is, but I’m not aware of any. Lol
Click to expand...
Well if your in Kansas, Airfest is a good option. Lots of folks from Nar and Tripoli. Plus at big events like that, there will be more than enough people willing to help out.
 
RS-V9-Screenshot-Qfactor.pngRS-V10-Screenshot-QFactor.png

Steven88, above are screenshots of the sims for your rocket - run on RS 9 and 10. I'm not getting the error you mentioned. The K560 may have your 15lb. rocket going very slow off the rail. The rail velocity in the table for V10 sims does not give you the complete Launch Guide Data. That can be found in the "Display details" by selecting one of your sims and then "right click" the mouse. So for sure have someone at Airfest confirm the motor selection.

Also - my max. altitudes come up "lower" then a standard sim, and that's because my Cd is set at 0.60. The RS program uses a progression of Cd's through the launch, and over the years I have found it to overestimate the altitudes on my builds. I adjust the Cd on my designs as I collect launch data so that I can dial in future motor selections & performances.
 
QFactor said:
View attachment 429291View attachment 429292

Steven88, above are screenshots of the sims for your rocket - run on RS 9 and 10. I'm not getting the error you mentioned. The K560 may have your 15lb. rocket going very slow off the rail. The rail velocity in the table for V10 sims does not give you the complete Launch Guide Data. That can be found in the "Display details" by selecting one of your sims and then "right click" the mouse. So for sure have someone at Airfest confirm the motor selection.

Also - my max. altitudes come up "lower" then a standard sim, and that's because my Cd is set at 0.60. The RS program uses a progression of Cd's through the launch, and over the years I have found it to overestimate the altitudes on my builds. I adjust the Cd on my designs as I collect launch data so that I can dial in future motor selections & performances.
Click to expand...

You know, a lot of times it is recommended to fly your smallest motor recommended for the first flight. I am learning, ok, but I purchased a large J and a K and an L reload for this rocket a couple months ago so that I’d have em in time for Airfest. The problem was, my rocket wasn’t run through a sim yet and I was still learning the ropes. Now it’s looking like maybe I should choose my largest motor instead of the smallest. I will have someone at Airfest or somebody from there confirm my choice before I fly it! I can also take 16” section off for first flight too if needed and then maybe the K would be ok. That takes 1lb 7oz off the rockets weight. Of course I should sim that first as well and get a lift off speed.

Does anyone here have a recommendation for me for my first flight with 75mm?

Should I take it easy on the first flight and fly smallest motor and shortest rocket length possible?
 
Steven88 said:
You know, a lot of times it is recommended to fly your smallest motor recommended for the first flight. I am learning, ok, but I purchased a large J and a K and an L reload for this rocket a couple months ago so that I’d have em in time for Airfest. The problem was, my rocket wasn’t run through a sim yet and I was still learning the ropes. Now it’s looking like maybe I should choose my largest motor instead of the smallest. I will have someone at Airfest or somebody from there confirm my choice before I fly it! I can also take 16” section off for first flight too if needed and then maybe the K would be ok. That takes 1lb 7oz off the rockets weight. Of course I should sim that first as well and get a lift off speed.

Does anyone here have a recommendation for me for my first flight with 75mm?

Should I take it easy on the first flight and fly smallest motor and shortest rocket length possible?
Click to expand...

Please list the motors you purchased so we all know exactly what you have for this rocket.
 
Steven88 said:
Aerotech 75mm J135W,
Aerotech 75mm K560W,
Aerotech 75mm L850W
Click to expand...
Thanks for confirming your motors. Just so you know, the K560 and the L850 are good high impulse motors but that's because of their long burn times. This is what helps push your rocket to the high altitudes. It's getting a heavy rocket off the rail that's the challenge. For me the L850 is the better choice for what will look like a stable launch off the rail. But with a 6,800 ft. simulation altitude - I would have a tracker in the rocket. If the Main comes out at a high altitude you could be in for a long walk. I think you said you planned to go to Airfest. I have never been to it, but I know a few Ohioans that say it's awesome. For me the K560 is on the edge for a stable liftoff. But the lower altitude would be a lot nicer for a first launch. There will be a whole lot of people at Airfest with way more experience than me who can go over the two motors with you. It may not be the clear cut answer you were looking for but that sometimes happens in this sport.
 
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That’s a good answer for now. Yes I do have a tracker in this rocket. I wish I could meet you at Airfest. Maybe one of these years...
 
Steven88 said:
That’s a good answer for now. Yes I do have a tracker in this rocket. I wish I could meet you at Airfest. Maybe one of these years...
Click to expand...
Some day I'll make it out to Kansas - and good luck on your launch. Let us know how the flight turns out, and what other comments & suggestions you come across on your motor challenge. Every launch is a learning experience for everyone around you . . .
 
I'm not aware of a AT J135 in 75mm... There's a 54/1280 J135W long burn... Which is in no way big enough for a 15lb rocket unless you have a super calm day.
The smallest AT 75mm motor I'm aware of is the K1499N. Please recheck what your J motor is.
 
jd2cylman said:
I'm not aware of a AT J135 in 75mm... There's a 54/1280 J135W long burn... Which is in no way big enough for a 15lb rocket unless you have a super calm day.
The smallest AT 75mm motor I'm aware of is the K1499N. Please recheck what your J motor is.
Click to expand...
I think he did mean to list it as a 54mm motor. He has an Aero Pack motor adapter for 54mm/75mm motors. And I think he saw in the simulations that the J135 will not work.
 
QFactor said:
I think he did mean to list it as a 54mm motor. He has an Aero Pack motor adapter for 54mm/75mm motors. And I think he saw in the simulations that the J135 will not work.
Click to expand...

OK, good. I'm late to the party and just catching up on my reading while recovering from @#$%^& Covid...
My comprehension might be a little off currently.
 

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