Wow you weren't kidding when you said they overlaped :y: but what niche do the D's fill? Isn't the D13W reload comparable to a D12?
Well, first of all, the Estes D12 really should be called a D10, because that number more accurately reflects its average thrust. The D13 uses composite propellant while the D12 uses black powder. Composite propellant has a higher specific impulse than BP (IOW, it is more "efficient). Due to that fact, the D13 can deliver the same general level of power (D class) in a much smaller, more lightweight package.
The thrust profiles of the
D12 and the
D13 are quite different, too. They have similar burn durations, but the D12 has a classic BP motor profile: initial thrust spike, followed by a long, steady low thrust tail. The composite D13 starts out with a high thrust that climbs a bit and than stays up there for a significantly longer length of time. Notice also that the D13 reaches a high level of thrust nearly instantly, whereas the D12 takes a "pokey" 0.25 seconds to build up to its peak thrust. (A machine can tell the difference, but on the field, you or I probably could not.) From these two things you can therefore see that the average thrust of the D13 is higher than the average for the D12. The D13 has a higher total impulse, but the D12 actually has a higher peak thrust. (Impulse and thrust, of course, are not the same thing.) So although they are similar in nomenclature, the two motors are actually quite different.
Although D motors are considered to be mid-power motors, they really straddle the line between LP and MP. (BTW, low-power and mid-power are strictly informal groupings that are commonly recognized in our hobby but nowhere else. The only power grouping that has any formal status is high power. There are also groupings based on propellant mass, but that is a different matter. The notion of "mid-power" is a fairly recent development.) The niche that 18mm D motors from Aerotech and Apogee fill is providing D power for models with that size of mount. These are usually, but not always, low power-style designs that can handle the increased thrust or that are a bit overweight or have a fair amount of drag. The niche that 24mm D motors from Estes and Aerotech fill is providing D power to rockets that have that size of mount. Typically, but not always, these have larger, longer airframes that are built very light. Such motors also power a lot of very draggy saucer-style and pyramid-style rocket designs. Finally, 24mm black powder D motors are also great for clustering.
The new 20mm D5 motors from Quest don't straddle the line between LP and MP; they sit right on top of it. These motors may be the ultimate expression of "one foot in each category." Another word that comes to mind is "ambidextrous."
MarkII
) I shudder to think of the hassles that must be involved with installing liners, O-rings, fuel grains, delay elements, etc. into Green Monkey's 13mm hardware. :bang:
