Chute location for 38 mm min diameter

I’m finishing up a 38 mm minimum diameter build following an impulse buy from a recent mad cow sale. The problem is that the main chute I have is just a touch too large for the upper airframe where I would normally put it. But, there is plenty of room in the lower tube.

Am I going to have problems if I put the main in the lower and the drogue in the top? My concern would be premature separation of the lower tube caused by the drogue’s release. But, it’s a small rocket (less than 1.5 pounds loaded, and I’m using threaded 4mm headless bolts to keep the lower section connected to the av bay/coupler.

Worst case is that I get a new main, but for such a small project I’d hate to do that when the fix seems simple enough. Thoughts/advice?

Shear pins

Banzai88 said:

Shear pins

Click to expand...

I’ve drilled for three of the smaller nylon pins. Hoping that will be enough to counter the force of the drogue engaging. The drogue itself is just an 18” x form, so I’m not expecting a major change in velocity. Just hate breaking conventional wisdom.

As far as I know, the only reason for that conventional wisdom (drogue in lower section) is it allows for the use of motor ejection as an apogee backup. But if you're using a minimum diameter retainer that blocks the ejection charge, or a plugged motor, then that point is moot.

if it works and it's safe, that's all that matters. Seriously looking at my Go Devil pile of parts myself.

Not a deal-breaker, but drogue on top, as the OP suggests, does bring some other factors into play. First is the additional mass above the separation point that opens for the main. That mass combined with the acceleration (jerk) of the drogue opening (potentially tens of Gs) increases the vulnerability of having the main come out at apogee. So, some quick calculations should allow you to determine just how many shear pins are needed to keep that closed, and then how large a BP charge is required to break that number of shear pins.

Another factor is that the main will now open toward other airframe parts and recovery gear, which some might say increases the chance for fouling.

So, yes, there are good reasons for the traditional drogue in the middle, main on top, but you can minimize the risk with some care, especially with a rocket that's this light.