CTI Spacers with 4gr case

[northbendbob]

I got my first HP kit to get my level one.... it's a Madcow Phoenix... Mike at madcow says use a 2-4 gr motor... has anybody used 2 spacers in a 4gr case?? the video on Apogee says 2 spacers can be used, but I was wondering if anybody ever had a problem with ejection or anything doing that... thanks in advance for any replies!!

 

[bytesiz]

I got my first HP kit to get my level one.... it's a Madcow Phoenix... Mike at madcow says use a 2-4 gr motor... has anybody used 2 spacers in a 4gr case?? the video on Apogee says 2 spacers can be used, but I was wondering if anybody ever had a problem with ejection or anything doing that... thanks in advance for any replies!!

I've used 2 spacers in a 3G case without any issues. I don't see why you would have any issues with your 4G case. The only case that is "special" is the 6XL cases.

 

[bobkrech]

I got my first HP kit to get my level one.... it's a Madcow Phoenix... Mike at madcow says use a 2-4 gr motor... has anybody used 2 spacers in a 4gr case?? the video on Apogee says 2 spacers can be used, but I was wondering if anybody ever had a problem with ejection or anything doing that... thanks in advance for any replies!!

CAR, NAR and TRA allow for the use of not more than 2 spacers with any reload kit.

The assembled motor weight of a longer motor casing and the weight of the spacers is greater than the optimal lenght casing, the thrust to weight ratio of a reload in a longer casing with a spacer or two is lower than the optimum length casing without a spacer. For example, a single space and a 1 g longer Pro38 casing weighs 50 grams more than the optimally designed casing. 2 spacers add an additional 50 g, for a total additional weight of 100 g. https://pro38.com/pdfs/Pro38_Case_Spacer.pdf

This extra weight will lower the apogee compared with the optimally designed spacer and may require a 2 second shorter delay so you need to run a sim with a 100 g addition rocket weight for 2 spacers with a Pro38 reload with 2 spacers, but otherwise will not change the reload performance significantly.

Bob

 

[G2Rockets]

I used 2 spacers in a 38 just this past weekend. I have a couple times. You won't have any problems using 2 spacers, but don't use more than that. The only time I worried about ejection was when I had a Long 4 inch airframe and I needed more charge to make sure it worked.

Good luck on L1

John

 

[COrocket]

I usually get a 3 grain and 6 grain case, so i can fly anything 1-6. You could also get a 4 and a 6XL if you wanted to sacrifice the ability to fly 1 grain loads to get the use of the 6XL stuff

 

[Handeman]

CAR, NAR and TRA allow for the use of not more than 2 spacers with any reload kit.

The assembled motor weight of a longer motor casing and the weight of the spacers is greater than the optimal lenght casing, the thrust to weight ratio of a reload in a longer casing with a spacer or two is lower than the optimum length casing without a spacer. For example, a single space and a 1 g longer Pro38 casing weighs 50 grams more than the optimally designed casing. 2 spacers add an additional 50 g, for a total additional weight of 100 g. https://pro38.com/pdfs/Pro38_Case_Spacer.pdf

This extra weight will lower the apogee compared with the optimally designed spacer and may require a 2 second shorter delay so you need to run a sim with a 100 g addition rocket weight for 2 spacers with a Pro38 reload with 2 spacers, but otherwise will not change the reload performance significantly.

Bob

2 second shorter delay??? We're talking a 100g or 3.5 oz. 2 - 4 grain CTI motors are large H through I size. Do you really think 100g is going to make a 2 second difference in time to apogee? I would guess the difference would be more like 0.2 sec.

 

[bobkrech]

Don't disagree. It all depends on the weight of the rocket with a standard motor and a motor with spacers. A lightweigh, minimum diameter rocket would be the most sensitive. The point is do a quick simulation to see if you have to shorten the delay.

Bob

 

[Handeman]

Yes, the light MD would be the most effected. I suspect that most of those probably don't have enough delay available already and could probably use lengthening, even with a spacer.

Your right, always do a sim.

 

[cbrarick]

a 2 grain 29 is a G so I doubt that 100 grams is 2 seconds as well, but sims are where it's at....I'd love to see what the difference is in the pheonix. I certainly wouldn't cut down the delay for 3 ounces on a G motor..but hey, I could be wrong, it's happened before. The most sensitive would be that min diameter screamer, but hey, the delay's too short so you're using electronics anyhow!