Nytrunner
Pop lugs, not drugs
A smaller diameter motor of the same impulse as a larger diameter motor will often have a longer core which can often translate to more thrust (abd shorter burn) than the larger diam motor
VERY NICE!!!!
if i may ask, what was your final weight (recovery and all) w/o motor?
After overriding the weight and CG in OR, the estimated stability is 1.35 cal, which sounds just right, and means that I will not add the weight in the nosecone. Further, I ran the simulations using multiple different sized motors, from a D to an F. I was getting somewhat low velocities off rod, so I edited the simulations to a 48” rod, which improved the VOR. Still, it looks like my plan to have first flight on Estes BP E16s or F15s might not be feasible, and that it looks like I’ll have to pick up some Aerotech F20s and F23s. If anyone has a minute, I would appreciate any insight into my Open Rocket results, and thoughts on my conclusions for nose weight and motor selection. Thank you!
Thank you! The final weight without motor is 358 g, or 12.6 oz. I have some composite motors on order for it which should work well based on Open Rocket simulations. You very well may see this rocket launch in person, as I've been looking for nearby club launches! Please let me know when you guys launch next, the drive shouldn't be too bad.
I would tend to agree that 8 seconds is too long for the F44. I'm always annoyed that they don't have anything between 4 and 8. Even 7 seconds for the E30 is very long. What does OR say?Thank you for the comments! I received the package I ordered with a pair of E30-7s and F44-8s, along with a pack of Estes 29mm to 24mm adapters. I test fit everything, and it all works fine. However, after looking at the performance specifications of the F44s, I'm concerned that I purchased the wrong delay. The specs say that the maximum recommended weight for the 8 second delay is 284 g, which is significantly lower than the 358 g my rocket actually weights (ready to launch, without motor). The minimum weight for the 4 second delay is much higher, at 453 g. I chose the delays based on the Open Rocket simulations I performed using these engines, and it seemed like the longer delay was the way to go, but now I have my doubts. I don't want this rocket to lawn dart due to a long ejection delay. I may just use the F44s in my Big Daddy, and the E30s in the Doorknob. This all seems a little counterintuitive, especially as I'm just beginning to learn the voodoo magic of motor/ejection delay selection. Any thoughts/reassurances from those with more experience with these motors is appreciated.
SEVRA has scrubbed tomorrow's launch at the Isle of Wight fairground. Keep an eye on sevra.org for the next launch. We're flying LP/MP currently and, if the waiver goes through, we'll be good for HP to 3,000'. We launch on the 1st & 3rd Sat of each month and hope to have Performance Hobbies in attendance on the former.
I would tend to agree that 8 seconds is too long for the F44. I'm always annoyed that they don't have anything between 4 and 8. Even 7 seconds for the E30 is very long. What does OR say?
Whoops sorry I didn't catch that on the earlier post. E30-7 looks OK; F44-8 is borderline but frankly looks OK to me if you're adequately protected against zippering. Sure would be nice to have a -6.Here are the results for the E30s and F44s with their respective delays, originally posted in Post #135 above. The optimum delay appears to be right in the middle of the available delay options for the motors, so I looked at velocity at deployment next. For both of the motors, the longer delay options had lower velocities at deployment, so I went with those. So I'm not exactly sure what to think. The manufacturers weight recommendations in a way contradict the motor choice found through the OR simulations. How accurate do the OR simulations tend to be? (Keeping in mind that these simulations are using the actual, measured rocket weight from my completed model). Should I follow these results, or the manufacturer guidelines?
View attachment 426483
Whoops sorry I didn't catch that on the earlier post. E30-7 looks OK; F44-8 is borderling but frankly looks OK to me if you're adequately protected against zippering. Sure would be nice to have a -6.
Thanks for the info! I had found SEVRA in my nearby club searches, but I thought I had seen that the launches occurred someplace south of the border in NC, so I discounted that. But the Isle of Wight fairground is a much more reasonable drive from me, so I will definitely keep an eye out for the next launch. I've gone ahead and requested to join the Facebook group to stay informed.
The NC field is our primary, but it's a working field, so we can't launch until crops are up. The fairground field is new - we've only had one launch there so far. As I said, the waiver is in the works. Depending on how things go, this may become our primary.
Your excellent build thread here prompted me to get going on an Estes Doorknob myself. I do see in the instructions where they have the launch lugs positioned at 1/2 in from the fin slot rather than at the midway point between the fins which I believe is 1 1/8 in. Never have run in to this before and have always positioned lugs at the midway point in all my other builds. Anyone know why Estes has instructed the lug positioning line to be drawn at 1/2 in from fin slot?Launch lug installation. I measured the half-way point between the fins, and made a mark. Using a length of aluminum angle stock, I drew a centerline for the lugs. Following the instructions, I marked up 0.5” and 10” from the bottom of the body. For a more secure bond, I used a file to carefully scrape away the primer and glassine on the body, and lightly sanded the lugs. To keep them aligned, I slid them onto a wooden dowel, applied some Titebond Quick & Thick, and placed the lugs on the body. Two small clamps on each end secured the lugs in place in a perfect line while the glue dried. I'll add fillets to the lugs a bit later.
*I recently noticed that the instructions have you mount the lugs 0.5” from one of the fins, instead of the midway point. Not sure if this matters, but I doubt it does. Oh well*
Your excellent build thread here prompted me to get going on an Estes Doorknob myself. I do see in the instructions where they have the launch lugs positioned at 1/2 in from the fin slot rather than at the midway point between the fins which I believe is 1 1/8 in. Never have run in to this before and have always positioned lugs at the midway point in all my other builds. Anyone know why Estes has instructed the lug positioning line to be drawn at 1/2 in from fin slot?
Thanks for the info! Not going to try and paint to scale as any ambition in that direction usually outweighs my talent. So, at the midway point my lugs will go!
I also used your rc airplane fuel tubing idea to prevent possible zippering and it appears to me to be a great idea. Thanks!View attachment 427373
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