AT H73J under-performance - anyone else?

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afadeev

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Quick question about Aerotech H73J-10A 38mm motors - has anyone else experienced thrust defficiency from that motor?

I bought three (3) of them during last year's Xmas sale, and burned the first one last weekend.
Instead of the OpenRocket simulated 1568 ft with my 2.5 lbs rocket, it barely climbed to ~300 feet. Altimeter 3 recorded 318 feet, exactly, but onboard RRC3 never triggered 300 ft arming lock-out (confirmed after emails with Jim A), and rocket core-sampled ~3 feet deep into moist farmland.
FireFlier on H73.png
Luckily, fiberglass rocket came out of the ground without any damage, so it will fly again.
But I'm a little antsy about flying the other 2 (out of 3) H73's that came out from the same batch. FWIW, the next H73 motor from my stash has the with serial # of: 05191705.

Based on Altimeter 3's data, the motor burned for 2.55 seconds, which is right inline with H73's spec, and all grains burned fully in the motor casing. No blow by, all closures in place, with no signs of anything not working properly. Except that the motor did not generate nearly as much thrust as expected.

Thus, the question - has anyone had a similar experience with H73's severely under-performing?
Or is it a one-off bad motor SNAFU?

TIA,
a
 
Could have been the wrong size nozzle included in the reload. Check your unused ones, see if correct or not.
 
I burned one in my Little John at last launch a few months ago, took it to 2500 or so, forget exact numbers. Great flight, well the up part anyway.
That isn't a punchy motor so it needs to be in a light rocket. But thrustcurve is showing 44ft/s off the rail which is good enough and you have close to 15 lbs of thrust right toward the beginning so I'm voting improper nozzle or grease in the wrong spot inhibiting the burn somehow.
 
H73 and a vulconite (loc paper rocket) is a winning combination. A fiberglass rocket is a bad choice for this very tame motor. Gotta wonder if you weren't the victim of a binding rail due to dirt or rail button misalignment.
If i were gonna fly a glass rocket on this motor tube, I'd do the H180.
 
Wimp motor , only for very light rocket & small diam. [as far as I'm concerned]
Has 13.2 lbs of thrust/ by 5 =2.64 total weight of rocket and motor..... in IDEAL low wind conditions.

I lost one years ago on flight that barely made 100 ft. Didn't have light enough rocket to fly other one safely so I gave it away.
 
As Jim pointed out, this is a really poor choice. A rocket that weighs 2.5 pounds is too heavy for this motor. Probably the motor you should have chosen for that case is the H123 or the H242.

44’/sec is questionable off the rail. Velocity off the rail is your friend- more is better.
 
What does the rocket weigh loaded on the pad?

2.6" MadCow Fire Flyer, 2.5 lbs with this particular motor.

Gotta wonder if you weren't the victim of a binding rail due to dirt or rail button misalignment.

Interesting thought on rail binding.
It was the very end of the day, with the eight foot long 1010 rod getting exercise throughout. I did not observe any binding sliding on, but then again, I was getting tired by then.
Which is why I picked a tame motor to fly, for easily visible black-smoke trail, and minimal recovery walk.


Wimp motor , only for very light rocket & small diam. [as far as I'm concerned]
Has 13.2 lbs of thrust/ by 5 =2.64 total weight of rocket and motor..... in IDEAL low wind conditions.

As Jim pointed out, this is a really poor choice. A rocket that weighs 2.5 pounds is too heavy for this motor.

Agreed on the motor observations: my 2.5 lbs rocket is at the edge of desirable weight range. I am not flying that rocket on that motor again. I am trying to validate if the motor performed as advertised, or not.

I don't have time to build a rocket flight simulation from scratch, and simple parabolas don't begin to account for drag and weather cocking. Thus I have to rely on OpenRocket.
For my exact model size and H73 motor, I get OR project total velocity of 228 mph at motor burnout.
Even if the rocket has weather-cocked 45-90 degrees, it should accelerate to somewhere north of 200+mph.
I observed Alt 3 recorded 85 mph.

Therein lies the puzzle, and the motivation for this thread.
 
The H180 is a 29mm motor, wrong case. I agree that the H123 would've been great. Nice motor.

Binding on the rail may be a possibility too.

I prefer slow(ish) off the rail and I've gone as low as 41, it depends on conditions and rocket of course. I had my H73 for over a year before I had ideal conditions and a light enough flight proven rocket to fly it in.
 
The H180 is a 29mm motor, wrong case. I agree that the H123 would've been great. Nice motor.

Binding on the rail may be a possibility too.

I prefer slow(ish) off the rail and I've gone as low as 41, it depends on conditions and rocket of course. I had my H73 for over a year before I had ideal conditions and a light enough flight proven rocket to fly it in.

If you have essentially zero wind that might work. I personally would not do less that a 5:1 unless there is no wind. Most of my flying is closer to 7:1 thrust to weight or higher ratio. Get the rocket moving.
 
If you have essentially zero wind that might work. I personally would not do less that a 5:1 unless there is no wind. Most of my flying is closer to 7:1 thrust to weight or higher ratio. Get the rocket moving.
Not arguing with ya Mark. If I'm looking at rail speed I will shoot for 50+ but if it comes in slower I'll fly it if conditions are right and it hits somewhere around 5:1. Tripoli requires only 3:1 IIRC.

But either way, may have just been a gummed up rail. I recently does one and it performed perfectly, though I'm not sure on my rocket weight.
 
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