Is it really that much lower in thrust than an A3T? I wonder if the big advantage of the Delta motors has something to do with their smaller diameter and lower mass? That 5-second delay would really come in handy in some situations, too, I'm sure.
Yes, the thrust is lower. I do not have the thrust curve info, but it is lower. Slightly higher than the old Apogee micros. I had a prototype S4B (B powered) boost Glider that held up to an Apogee B2 fine but shredded on a Delta B2...but just barely shredded, as the B2 boosted a little bit faster and that bird was on edge (fortunately I found a good light way to beef it up just enough). That same model would definitely shred on a B4, and even if it did not (it would), it would not boost as high either.
I mention B’s when some others have mentioned A’s, since years ago some of the events like copter (S9) and B/G (S4) were B power and more recent years those old B events dropped to A power. But effectively the main difference from the Delta (or old Apogee) B2’s were casing length, and propellant length. The thrust curves were much the same shape except the B burns longer than the A (just like the B6 and C6 have the same thrust curve shape, the C6 just burns longer than the B6).
Anyway, multiple benefits of those motors, DO keep in mind that the models they power weigh grams, not ounces. A model over an ounce liftoff mass is rare, maybe some copter models and even those few are not over 28.3 grams by much.
The lower thrust gives a more efficient boost compared to a higher thrust boost.
The lower thrust means less boost stress, so the model can be designed and built lighter, structurally.
The lower engine casing mass helps in the events like Parachute, Streamer, and Helicopter. My original 2002 S9B copter models, which could fly for FIVE MINUTES dead air on a Delta B2 motor, cannot get two minutes dead air on an Estes 18mm B engine, they are really dogged-down by way excess engine mass of an 18mm B and of course do not go quite as high either.
Also, those engines are made VERY close to the Newton-second limit. Such as 2.4 to 2.45, maybe even 2.49 n-sec. By contrast, a “hot” Estes 13mm A tends to be more like 2.3 n-sec, and thru the years I think they have dipped under 2.0 at times.
As for the 5 second delay, yes, that can be useful. So can a 6 second delay, or 3 second delay, or 7 second delay, or 2 second delay, depending on the needs of the models. The thing is, Delta will make them to order for whatever time delay that a team or group wants to order. Of course, long ago, Estes used to have A3-2 and A3-6 engines, plus of course A3-0 and A10-0 booster engines, to only mention 13mm A’s.
As for the Deltas, it seems they are hand--pressed, not made by machines. They use some sort of high energy propellant that is something above Black Powder, but below composites as we think of them (someone once called them a “pressed composite”. But I do not think that means there is APCP in it, but I do not know what is in it). Whatever is in them, would make it extra-difficult to get them an explosives EX number to import for sale here. The casing, whatever it is, is just sufficient for doing its job. Part of it burns away so there is apparently less casing mass after bring than before burning, but I do not recall if anyone has dissected an unfired one to see just what the masses are for the casing, and nozzle, and then the propellant/delay/ejection. While with an Estes or Quest BP engine there is very little erosion of the casing by comparison. Perhaps it is that the casing wall is thinner by proportion than for BP motors, so that also helps make the motor especially light, that is it not just the propellant.
The closest thing to those that were in the US, was from 1995 (or 96) to 2001(?) when Apogee made 11mm micro engines. And then literally overnight stopped making them. They were heavier and longer than the Deltas, and a hair bigger in diameter, but they were definitely the next best thing. Available from 1/4A thru B power. And yes, those were an attempt to copy the Delta motors, but the Apogee micros used BP propellant and conventional casing material.
- George Gassaway
