D12-3 vs D12-5 max lift weight ?
 

Thought I was starting to understand engines until I read the Estes chart.

It looks like all the specs are same between the 2 engines except for delay and initial weight - 1.49g vs 1.52g.

Max lift wt for the -3 = 396g. -5 = 283g

What am I missing?

The 5 second delay engine will lift the heavier rocket but the delay will be too long. The 3 second delay engine will lift the lighter rocket, but the delay will be too short. Anyway, that's my read on it, but I've been wrong before.

Both engines will lift the same because thrust and power-wise, they ARE the same. However, heavier weight rockets, obviously, will not coast as long, so the 3 second delay is more appropriate. Lighter weight rockets will coast longer with that same amount of power, so they will need the longer delay.

So, for a GIVEN engine ‘type’ (A8, B6, C6, D12, etc.), the variations in rocket weight (all other things equal) are what determines which DELAY to use for that rocket. Something like a small Alpha might use the A8-5, whereas the larger Big Bertha will definitely need the A8-3. In either case, the A8 motor will be producing the same exact amount of thrust for each flight.

I hope that helps. :o

Earl

Both answers help.

Maybe I don't understand the terminology.

I assumed "Max lift weight" meant the heaviest rocket it could lift?

Estes Engine Chart

I suppose what they mean by “max lift weight” is actually something closer to “max lift weight AND safely eject a recovery system BEFORE impacting the ground”.

Earl

That makes sense.

Thanks Earl