TARC Team Has RMS Troubles

[sandman]

OK, my TARC team (well, the one I was observing for) had done some flight testing last weekend and wound up with some respectable times using F22-5 RMS motors from Aerotech.

There best time during flight tests last weekend were 38.4 sec and 749'. The rest of the test flights were very consistant and all resulted in less than a 10 or 15 point score. Very impressive!

Unfortunately I wasn't there so the those test flights weren't recorded so this information was basically hearsay.

Yesterday the winds were light (5 to 7mph) it was sunny and about 50 degrees. Perfect flying weather!

Here's the problem.

They made 5 flights using the same batch of F22-5 motors but honestly, I think something was wrong.

The flights all seemed to weather cock badly (two eggs in the nose is a lot of weight!) in fairly light winds. all flights arced over into the wind. Like they had weaker thrust than normal.

Maximum altitude out of 5 flights was 618' but most were in the 300 to 400" range.

The bad parts were the delays. The F22-5's all seem to have closer to 8 to 10sec delays. All heart stopping flights with deployment at close to terminal velocity and altitudes of 100 to 200'.

They tried a shorter 3 sec delay (that came with the reloads) and wound up with ejection at 8 seconds after burnout.

I can verify this because I had the stopwatch.

My question is, why all the bonus delays?

Any ideas?

They didn't appear to be doing anything differently when assembling the RMS motors.
__________________

[ghrocketman]

Not sure what the problem here is & I fly RMS 24mm in my backyard a lot.
What I have learned is that most of my older (5-8 yrs old) reloads exhibit the dreaded "bonus delay" and I almost always drill 2/32" (1/16") out of the delay to reduce all delays by about 2 secs.
They usually work out okay for me that way.

[sandman]

Not sure what the problem here is & I fly RMS 24mm in my backyard a lot.
What I have learned is that most of my older (5-8 yrs old) reloads exhibit the dreaded "bonus delay" and I almost always drill 2/32" (1/16") out of the delay to reduce all delays by about 2 secs.
They usually work out okay for me that way.

These were brand new from Commonwealth Display.

Still in the shipping box.

[tbzep]

Did a different person prep the motors?
Igniter all the way to the top?
Correct nozzle diameter to get correct chamber pressure and burn rate? (could be wrong nozzle dia. from factory).
Did everybody use correct body language and hold their tongues just right? :p

[ghrocketman]

Is the F22-5 a mandatory required motor for TARC ?
This seems quite low on average thrust for throwing two eggs into the air to me.
I would be selecting a much higher avg thrust F for lofting two eggs such as the F50T SU 29mm or F40W RMS29 or F52T RMS29.

Blackjack motors are actually LOUSY for lifting payloads; they are exactly the opposite for what you want for payload lifting; you WANT high-thrust spike/short thrust duration, not long-burn low-thrust motors.

If this is a mandatory motor for this challenge, the individual that wrote the criteria may have bumped his head on something prior to choosing the motor requirements.

[Shreadvector]

Is the F22-5 a mandatory required motor for TARC ?
This seems quite low on average thrust for throwing two eggs into the air to me.
I would be selecting a much higher avg thrust F for lofting two eggs such as the F50T SU 29mm or F40W RMS29 or F52T RMS29.

Blackjack motors are actually LOUSY for lifting payloads; they are exactly the opposite for what you want for payload lifting; you WANT high-thrust spike/short thrust duration, not long-burn low-thrust motors.

If this is a mandatory motor for this challenge, the individual that wrote the criteria may have bumped his head on something prior to choosing the motor requirements.

it is absolutely not the only motor allowed. A HUGE list of certified motors is published. I and others have answered this exact identical duplicate thread/question on The Rocketry Forum and your suggestions/advice is absolutely correct.

[Royatl]

Delays are VERY dependent on proper ignition, and Black Jack motors can be very finicky about ignition.

Did someone different put together the motors on the first day vs the second?

As was said, an F22 lifting two eggs is not the best idea unless you get perfect ignition. The flights you describe sound like usual poor Black Jack ignitions to me (i.e. slow, weathercocking even in light wind, bonus delays).

[sandman]

Delays are VERY dependent on proper ignition, and Black Jack motors can be very finicky about ignition.

Did someone different put together the motors on the first day vs the second?

As was said, an F22 lifting two eggs is not the best idea unless you get perfect ignition. The flights you describe sound like usual poor Black Jack ignitions to me (i.e. slow, weathercocking even in light wind, bonus delays).

The same person prepped the motors. Actually the motor person was the Principal. These are sorta "special needs" student. They all seem to be ADD but good kids and the Principal thought he should prep all of the motors.

Yes the exhaust seemed like Black jack motors.

I would have used an F40-4 but that's me.

[poke44]

For my tarc team i am a teacher for they used for 24mm rms f24w and f39t's

24 was to low and the 39 overshot wich seemed odd as both had the same impulse. We probably wont get in an official flight as they are kinda apathetic but the 24 shot us to aorund 650 and the 39 was around 850.
with times of 40 and 54 sec.

We also built a 29mm rms hobby and put in a f52t for our first rms launch and boy it was loud... but it went way up, 1200 or so... We had a fin can that we could exchange to a the same payload bay.

[Shreadvector]

For my tarc team i am a teacher for they used for 24mm rms f24w and f39t's

24 was to low and the 39 overshot wich seemed odd as both had the same impulse. We probably wont get in an official flight as they are kinda apathetic but the 24 shot us to aorund 650 and the 39 was around 850.
with times of 40 and 54 sec.

We also built a 29mm rms hobby and put in a f52t for our first rms launch and boy it was loud... but it went way up, 1200 or so... We had a fin can that we could exchange to a the same payload bay.

Your F39 soounds like it will get you EXTREMELY close to the desired altitude and duration with the addition of ballast. You must be able to vary something for flights in suboptimal conditions (like wind), so add ballast for perfect results in no wind and remove the ballast for perfect flights in wind.

I saw a team get a darned good boost with a F42-4 Econojet in wind that was between 15 and 20 mph. They wanted to use an F20-7 but I vetoed that on safety grounds and I explained why in detail.

[artpays]

We had 3 teams in TARC this year and between them they launched 90 times. Only one is going to finals. The lack of RMS consistency was astounding. Delays in the same batch of motors varied from 6 seconds to 14 seconds. One team had two CATOs on official certification flights. The second one was a complete failure to ignite the ejection charge, resulting in the loss of $200 worth of equipment. The team tried EFCs because the delays were so bad. The EFCs failed three times in 20 flights even though they were cleaned and tested before each flight. The EFC in each of those three flights indicated that the glow plug had fired.

One motor just sat on the pad and chuffed.

On one flight a team hit a good qualifying score, next flight (official qualification flight) with same motor, same batch, same person prepping, same weight, same rocket the motor was just a plain dud. It only achieved 433 feet. The next day another team used the same motor, same batch, similar basic rocket design, same weight and qualified for finals midpack.

One Aerotech SU motor blew up on the pad.

So our teams are using different motors next year. They may even revert to (gasp) black powder.

Jeff Lane

[sandman]

Sorry, I never got back to this.

It turned out that the principal wasn't there for the final flying day so another student prepped the motor this tim.

It seemed that (I forgot what) was being installed upside down. (by the principal) The senior who prepped the motor on that last Saturday of flights started assembling the reloads correctly and we were having consistant delay times.

Unfortunately not good enough I guess.

They wound up with a scor of 32 with wasn't good enough for the finals.