M1297W Aerotech motor

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Apollo8

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Hi all,

we at LabSA (www.labsa.it) have a problem: due to permit issues, we cannot launch our Madcow DX3-XL on a M1297W Aerotech motor to the highest apogee altitude. Moreover, we can't have any other motors with lower total impulse (K or L).
Does anyone know a safe system to lower the tot impulse of our M motor?

Thank you in advance,
Livio
 
Unfortunately, I don't think there's any good news to be had here. Any modifications you make to the motor to lower the impulse will essentially make the motor an "experimental" motor, and I don't know what the rules are in Italy concerning EX motors. I suppose you could only use 2 of the 4 grains, but that would require cutting the liner to size with enough precision to truly square the cut end so that it engages with the washers correctly, and even then I'm not sure it would then fit in a smaller size casing. Bottom line is I doubt anyone here would recommend you do that.

The other bad news that I see is that if you cannot fly a K,L, or M motor, I'm not sure a J motor will be enough to fly the DX3 XL. It would definitely be a low altitude flight...

Sorry about that!
-Robert
 
rhildinger said:
Unfortunately, I don't think there's any good news to be had here. Any modifications you make to the motor to lower the impulse will essentially make the motor an "experimental" motor, and I don't know what the rules are in Italy concerning EX motors. I suppose you could only use 2 of the 4 grains, but that would require cutting the liner to size with enough precision to truly square the cut end so that it engages with the washers correctly, and even then I'm not sure it would then fit in a smaller size casing. Bottom line is I doubt anyone here would recommend you do that.

The other bad news that I see is that if you cannot fly a K,L, or M motor, I'm not sure a J motor will be enough to fly the DX3 XL. It would definitely be a low altitude flight...

Sorry about that!
-Robert
Click to expand...
IIRC the K560 is two of the four grains used in an M1297, by contacting Aerotech you could purchase two liners and two of the correct nozzle for the K560 then use the fuel grains you already have, it would also require either a shorter motor case 75/2560 or the 75mm Reload Adapter System aka 75mm RAS.

However not being able use a K or L impulse invalidates that suggestion.
 
Last edited:
Is the issue the altitude or the motor, or both?

Can you buy any other motors, or is that the issue? If you're only barely over your limit on altitude, the M1500G has slightly less total impulse in the same hardware.
 
How much reduction in altitude do you need? Can you add some ballast to keep the rocket lower?

Edit: I see that sierrafoxhobbies currently doesn't have any K and L motors in stock - was that what you were referring to? There is still a J460 in stock. The DX3 won't fly high on that motor, but it is enough for a safe flight to about 500m/1500ft, assuming your rocket isn't much heavier than the 14lbs listed on Madcows homepage.

Reinhard
 
Last edited:
I believe, if I am reading correctly:
- your m1297 would exceed your waiver
- you can't obtain any k's or L's

If that is indeed the case, I'd recommend adding drag to your airframe e.g. with a plate behind the fins.
 
dhbarr said:
I believe, if I am reading correctly:
- your m1297 would exceed your waiver
- you can't obtain any k's or L's

If that is indeed the case, I'd recommend adding drag to your airframe e.g. with a plate behind the fins.
Click to expand...

Many thanks, dhbarr, interesting tip! In which way do you think to place the plate to the three fins of the DX3?
 
Apollo8 said:
Many thanks, dhbarr, interesting tip! In which way do you think to place the plate to the three fins of the DX3?
Click to expand...
How are you currently planning motor retention? Are there any pictures?

Many of the standard retention methods should allow a centering ring affixed to the aft and sandwiched by the motor thrust ring.
 
dhbarr said:
How are you currently planning motor retention? Are there any pictures?

Many of the standard retention methods should allow a centering ring affixed to the aft and sandwiched by the motor thrust ring.
Click to expand...
Below how we have planned to make the motor retention:

9k=
 
So that looks about like an RA75 on a 75-to-98mm CR?

You'd want to discuss with your team ( and simulate! ) of course, but affixing something like a 75-to-120 mm fiberglass ring at an appropriate thickness by replacing half the hex cap screws with longer ones should work.

By adding a fairly small amount of area at the very aft end, we should dramatically increase the drag coefficient without introducing angle-of-attack problems.
 
dhbarr said:
So that looks about like an RA75 on a 75-to-98mm CR?

You'd want to discuss with your team ( and simulate! ) of course, but affixing something like a 75-to-120 mm fiberglass ring at an appropriate thickness by replacing half the hex cap screws with longer ones should work.

By adding a fairly small amount of area at the very aft end, we should dramatically increase the drag coefficient without introducing angle-of-attack problems.
Click to expand...

They may even be able to hold the ring in place with the retainer cap without changing the screws.
 
dhbarr said:
So that looks about like an RA75 on a 75-to-98mm CR?

You'd want to discuss with your team ( and simulate! ) of course, but affixing something like a 75-to-120 mm fiberglass ring at an appropriate thickness by replacing half the hex cap screws with longer ones should work.

By adding a fairly small amount of area at the very aft end, we should dramatically increase the drag coefficient without introducing angle-of-attack problems.
Click to expand...

That should work, but it would require standoffs for the rail buttons as well, if I am imagining things correctly.
 
Apollo8 , can you explain to us exactly what your issue with this motor rocket combo is ? Can you tell us why you cannot fly any motor any smaller then a 75mm 4 grain motor ?
 

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