Estes recommended motors

[Bill]

Does anyone know the methodology Estes uses to make motor recommendations for their rockets?

Consider the following E2X kits:

0803 Bandito
Length: 11.2 in
Estimated weight: .60 oz
Projected altitude: 600 ft
Recommended Engines: 1/4A3-3T (First Flight), 1/2A3-2T, A3-4T, A10-3T

0804 Firehawk
Length: 11.2 in
Estimated weight: .65 oz
Projected altitude: 550 ft
Recommended Engines: 1/4A3-3T (First Flight), 1/2A3-2T, A3-4T, A10-3T

2434 Silver Streak
Length: 10 in
Estimated weight: .74 oz
Projected altitude: 575 ft
Recommended Engines: 1/2A3-4T (First Flight), A3-4T, A10-3T

The Firehawk looks like a slightly stretched Silver Streak (same plastic fin can?). The Bandito has different fins and only three of them (not a one-piece molded fin can.)

Why is the 1/4A3-3T recommended for the Firehawk but not the Silver Streak? Is that tenth or eighth of an ounce too much for the 1/4A3 (not according to the stated max liftoff weight of 1 oz)?

Why is the recommended delay for the 1/2A3 four seconds instead of two for the Silver Streak? Are the Bandito and Firehawk below the optimum mass for that motor?


Bill

[ghrocketman]

Estes motor reccomendations at times seem almost random.

The reason for their reccomending the 1/4A3-3T and 1/2A3-2T is due to the only delay available in 1/4A is 3 seconds.
Estes used to produce a 1/4A3-2 and a 1/4A3-4. Those were replaced with just the 3 second delay as a compromise motor for both single and upper stage use.

[Jerry Irvine]

I think the reason motor recommendations are slightly non-intuitive is actually product display inventory control. They probably only want one style each of 1/4A, 1/2A, A motors for mini-motor displays. So a nonsense recommendation is made on the packaging to conform with what a consumer is likely to see on a mass retailer's shelf.

That's what I think. Most mass-market Estes kits really need a long delay motor.

Jerry

[Rich Holmes]

Well, neither of the above two replies actually responded to the questions you asked.* Neither will this, really.

But I've seen Estes kits with recommended engines whose maximum liftoff weights, according to Estes, were lower than the weight of the kit, according to Estes.

And there was the Estes Tornado, weighing about 0.56 ounces, whose recommended motors were B4-2, B6-2, C5-3, C6-3. Mine flew fine on an A until I lost it and probably would have done okay on smaller motors; a C would have put it in the stratosphere.

Given these, I think the lack of a 1/4A for the Silver Streak and the -4 delay for the Silver Streak vs. the -2 for Bandito and Firehawk are not surprising. I don't believe there is any rigorous methodology at work.



* Alert the media.

[GregGleason]

I would write Estes and ask. It's not like it would be proprietary.

I'm thinking it is a mixed bag.

But since we are speculating, perhaps in the old days is was by empirical evidence. That is, launch the rocket on the motor and see how it did. Rockets that were of similar geometry of a known rocket had the results applied to it without testing. I doubt that they used "mind sim", but even if they did I bet they were close to reality.

Perhaps now they use simulation software.

Estes doesn't seem like a company that would play fast and loose with data. However, over time motors may change slightly and materials may, too. And even with that, the motor sigmas can have a big impact if you get a motor that performs at the lower end of the sigma.

The only thing that I might mention is that the build weights of the rockets may be "optimistic". That is to say, the rocket will wind up heavier from the user with little or no finishing skills than indicated on the hang tag.

So, I would think pinning it down on any one thing would start to numb the brain at some point.

Anyway, this is all conjecture on my part. I just think it is a reasonable one.

Greg

[ManofSteele]

I am not sure how John and the crew are currently making recommendations, but on the models I designed, I would use a mix of simulations and test flights to determine the suggested engines. If there were any questions as to which to use, it was more conservative to use the shorter of the two choices. That often helped with the variance in weight (wadding, glue, paint) you could expect to experience with a wide range of consumers building the product, and the wide range of weather and wind conditions.

In looking at the three models you listed, yes the third one was likely judged to be too heavy for the 1/4A3-3T, especially with the 3 second delay.

One of the tricky aspects of test flying models at Estes was the high altitude of Penrose. There were a couple of times where flying models at sea level caused issues that didn't show up at the rocket ranch.

Don't read too much into the max liftoff weight recommendations. There are a lot of factors that go into a safe flight (diameter, drag coefficient, wind, launch rod length) that make using just the max liftoff weight not much more then a suggestion. The max weights are set very conservatively, due to the very fact that there are other parameters that can influence a safe flight.

It did not have anything to do with inventory shaping.

Hope this helps. I still use the same approach for North Coast Rocketry kits.

Matt

[Royatl]

One of the tricky aspects of test flying models at Estes was the high altitude of Penrose. There were a couple of times where flying models at sea level caused issues that didn't show up at the rocket ranch.


Matt

I wondered if they took that into consideration. I also wonder if some stability anomalies (like the Estes SpaceShipOne or the Quest X15, where one flight would be perfect, the next flight would be tumbling coming off the launcher) could be masked by the thin air, or if they just didn't fly it enough.

[Bill]

And here is the kicker:

2445 Mini Max
Length: 8.8 in
Estimated weight: 1.3 oz
Projected altitude: 300 ft
Recommended Engines: 1/2A3-2T (First Flight), 1/2A3-4T, A3-4T, A10-3T

The same longer delay for a much draggier and heavier rocket...


The question originally came up because I had bought several 1/2A3-4T bulk packs on clearance about a year ago and discovered many rockets I thought could fly on them not being recommended. With such arbitrary and inconsistent listings, no wonder Hobby Lobby failed to sell enough of those bulk packs. On the bright side, they now carry the A8-3 bulk packs - a much better choice for outreach use.


Bill