Largest motor for a PML Endeavor?

[brettkeller]

(This may overlap somewhat with Conan's Motor Comparison thread)

My PML Endeavor (named Lunch Money) has flown on I's and a J350 to date. I have Aerotech 38mm hardware, 54mm hardware up to the 54/1706, and the Loki 54/2800 motor.

My Endeavor has Quantum tubing, and the only major non-stock modification was fiberglassing the G10 fins to the motor mount (fin can construction photos here).

Normally I fiberglass cardboard of phenolic tubing for my rockets, but I hadn't built a rocket with QT before so I wanted to try it out at least once. Now I want to know how far I can take Lunch Money, and am hoping for more specific answers based on real-world flights with QT, rather than rules of thumb (like 0.85 Mach).

So, a couple questions:

• What's the largest motor you've flown a PML Endeavor (preferably with Quantum tubing) or a similar 4" rocket with Quantum tubing on?
• What's the largest motor you've flown an Endeavor or similar rocket on if you reinforce the body (drogue bay and main parachute bay) with phenolic couplers?

I'm most interested in flying on a K185, or possibly a K550 or Loki K270.

And here's some data to help the discussion out (took a little while to format). I ran a number of Rocksim simulations, and have ordered here by velocity, with mach numbers calculated by dividing the velocity by the speed of sound, in this case 1,125 feet/sec:

Motor--|-Altitude (ft)-|-Velocity (ft/sec)-|-Mach #--|-Accel (ft/sec2)
L1400--|--8837---------|-1503--------------|-1.34----|-1148
K700---|--8601---------|-1206--------------|-1.07----|--729
K1100--|--6949---------|-1193--------------|-1.06----|-1290
K550---|--7401---------|-1040--------------|-0.92----|--654
K350---|-10965---------|-1035--------------|-0.92----|--817
J800---|--6120---------|-1021--------------|-0.91----|-1069
K270---|-10048---------|--926--------------|-0.82----|--266
J570---|--5284---------|--840--------------|-0.75----|-1052
J415---|--5979---------|--830--------------|-0.74----|--443
K185---|--6889---------|--726--------------|-0.65----|--249
J460---|--4190---------|--689--------------|-0.61----|--524
J135---|--5608---------|--652--------------|-0.58----|--198
J275---|--4189---------|--634--------------|-0.56----|--299
J350---|--3690---------|--619--------------|-0.55----|--675
I435---|--2914---------|--530--------------|-0.47----|--785​

Thanks!

 

[JDcluster]

What thickness are the fins; 1/16 ( 0.063") or 3/32" ( 0.093")?
You could have slotted a couple & slid it into the fin can.

Allot of it depends on the weight of the rocket & fin thickness.
I've flown an Aurora on a K 185, it was a little over weight for that motor at 13lbs. The only motor that may give you problems would be the K 550.


JD

 

[hartlch]

I assume you also modified it to use something other than the standard kwik switch motormount? I didn't, so can only use up to the 54/1280 case. I've flown the J415 and J540 with no problems.

 

[brettkeller]

Thanks JD. My fins (stock) are 0.0625" G10.

Not sure what you mean by "You could have slotted a couple & slid it into the fin can." I did extend the fin slots to the rear of the body tube and fiberglass the fins to the motor mount first (as pictured in the constructions pics I linked to).

Your Aurora on a K185 (assuming it was stock with QT and 0.093" fins) makes me feel good a/b the tubing but doesn't tell me much about the fins. Anyone else?

 

[brettkeller]

Right - I forgot that was even a modification from the kit. I just have a 54mm phenolic tube for the motor mount, so I can put as long a motor in there as the airframe will handle.

J415 max velocity and acceleration in the sims above are both higher than the K185, so that's another vote in favor of a safe K185 flight.

 

[cjl]

Stock 0.0625" G10?

Definitely stay under 0.75 mach or so. The quantum tubing will be fine, but those fins will flutter like crazy if you push the speed too much.

 

[Sailorbill]

Stock fins, one wrap of CF over Phenolic, Slimline 3.9" to 54mm tailcone, PRO 54 L730 flown to over 9000 ft. at Argonia, KS.

 

[brettkeller]

Thanks cjl and sailorbill. So far the consensus seems to be that the J415 and K185 should be fine, and that faster flights are more iffy (with more concern being voiced about the stock fins than the Quantum Tube).

I'm sure there are other rocketeers with relatively stock (QT) Endeavors out there... Don't be shy - I'd love to hear if any of you have flown on larger 54mm motors.

 

[bobkrech]

I suggest you look at https://www.publicmissiles.com/images/pmlalti.pdf for PML's recommendations. It states that a stock Endevour will have problems with certain high thrust, full Js and and all larger motors except for the K185.

Based on PML's reommendations for the motors on your chart, the J570 and the motors below it are ok by PML, and the one's above it are not.
I believe the primary reason is that the 1/16" will flutter at the velocities above ~850 fps (>Mach 0.75) which is what you get with the non-recommended motors and in line with CJL's warning . The split fin design is particularly susceptable.

Sailor Bill has a phenolic kit with a single wrap of CF whiich will add significant stiffness which is why his Endevour survived on an L730. Your stock kit won't but it will make a good video if you try.

Bob

 

[Andy Hugh]

I flew a PML 4" Quantum tube Endeavour with the standard 0.062" fins (but converted for dual deployment) on an Aerotech J800.
It flew beautifully. Great motor for the rocket.
In a bid to test an altimeter by pushing a rocket to its limits, next up will be the Aerotech K1100 and then the Cesaroni K1200 (which doesn't really fit without a bit of help).
My feeling is that it might struggle a bit with the K1100. I'm not sure if it will cope with the K1200. I'll let you know if I still have the rocket after it's launch in March.


All the best
Andy

 

[DAllen]

Thus sayeth the PML web site:

When to use Quantum Tube:
With any rocket 2.1" through 3.9" that will use an internal motor mount tube and will not fly faster than 0.85 mach.
For any rocket 2.1" through 3.9" that may encounter rough handling or hard landings.

That can be found on PML's Spec page. I have heard from more than one source that going transonic or supersonic with QT is a very bad idea and is a big 'ol gamble with the rocket-gods. From what limited understanding I have and how the spec page is worded I suspect that this is not a flutter issue but an airframe problem. However, I have not seen failures of that kind first hand or have experienced it on any of my projects. Take this info for what it's worth...

-Dave

 

[bobkrech]

I flew a PML 4" Quantum tube Endeavor with the standard 0.062" fins (but converted for dual deployment) on an Aerotech J800.
It flew beautifully. Great motor for the rocket.
In a bid to test an altimeter by pushing a rocket to its limits, next up will be the Aerotech K1100 and then the Cesaroni K1200 (which doesn't really fit without a bit of help).
My feeling is that it might struggle a bit with the K1100. I'm not sure if it will cope with the K1200. I'll let you know if I still have the rocket after it's launch in March.


All the best
Andy

Andy

This is what happens to fins on a PM Quantum Leap with tip to tip 3 oz. fiberglass reinforcement to a thickness of 3/16" in the transonic range. These fins begin to flutter at 970 fps (295 M/S) M=0.87 and are violently flapping by 1050 fps (320 m/s) M=0.94. Stock unreinforced fins without tip to tip reinforcement would have ripped right off the rocket.

https://www.videorocketry.com/XPRS_2004/index.html

https://www.videorocketry.com/XPRS_2004/video/USS_Bakula_with_data.mov

You were lucky that your fins stayed on with the J800. My prediction is that they won't with the K.

Bob

 

[dixontj93060]

Bob,

Thanks for sharing this. The comments on the Videorocketry web page about the degradation of G10 especially caught my eye as I have seen this in at least two of my former designs--one did shread, one didn't, but in both cases microfractures in the G10 were evident.

-Tim

Andy

This is what happens to fins on a PM Quantum Leap with tip to tip 3 oz. fiberglass reinforcement to a thickness of 3/16" in the transonic range. These fins begin to flutter at 970 fps (295 M/S) M=0.87 and are violently flapping by 1050 fps (320 m/s) M=0.94. Stock unreinforced fins without tip to tip reinforcement would have ripped right off the rocket.

https://www.videorocketry.com/XPRS_2004/index.html

https://www.videorocketry.com/XPRS_2004/video/USS_Bakula_with_data.mov

You were lucky that your fins stayed on with the J800. My prediction is that they won't with the K.

Bob

 

[cjl]

Thus sayeth the PML web site:



That can be found on PML's Spec page. I have heard from more than one source that going transonic or supersonic with QT is a very bad idea and is a big 'ol gamble with the rocket-gods. From what limited understanding I have and how the spec page is worded I suspect that this is not a flutter issue but an airframe problem. However, I have not seen failures of that kind first hand or have experienced it on any of my projects. Take this info for what it's worth...

-Dave

The PML website may say that, but I have seen quantum successfully pass mach several times. I have almost never seen the stock 0.062 fins on most PML kits do the same though.