Quest D16 vs Estes D12?

[billdz]

Is it possible there is some error in the data for these two motors? Rocket Reviews and Open Rocket state that the Quest has a total impulse of 12.68 and a peak thrust of 22.275, see https://www.rocketreviews.com/q-d16.html, while the Estes has a total impulse of 16.84 and a peak thrust of 29.73, see https://www.rocketreviews.com/estes-d12-5112.html. Accordingly, my Open Rocket sims show that my rockets will fly about 25% higher with the Estes D12. But that's not so, at least not for me, my rockets consistently fly substantially higher with the D16.

What am I missing?
Thanks,
Bill

 

[BEC]

Model? Altimeter data?

In other words, tell us more with some data, please.

A spent D16 would be a little lighter than a D12 but probably not enough to make much difference.

 

[BRS Hobbies]

Do you know if the sim takes into account the motor size and the difference in the weight between the two motors? The D12 is about twice the weight of the D16.

 

[jadebox]

https://www.rocketreviews.com/compare-motors-508946.html

The D16 has a higher average thrust and a progressive burn and weighs less. But, with half the duration of a D12, it doesn't seem that the D16 would propel a rocket to a higher altitude than the D12 unless the rocket was really heavy or draggy.

 

[billdz]

Here's the sim. There was no altimeter but it sure seemed to fly significantly higher with the D16.

 

[Wallace]

Velly interesing. We obviously need some real world data.

 

[shreadvector]

The sim shows the model with 2 x D12 flies higher than the 2 x D16.

He reports the real world flights look to him like the opposite.

What was the flight profile like? Was the model so heavy that the D12 version used up lots of total impulse sitting on the pad and slowly lumbering up the rod or rail?
Did the D12 version weathercock or fly in a feeble arcing trajectory?
Did the D16 version ZOOM off the rod or rail and fly laser beam straight upwards?

And how about selecting delay times that do not eject before apogee? Ejecting before apogee will reduce your peak altitude in the real world.

 

[BEC]

Wow - 476g with motors.

I agree with Fred about flight profiles.

Per the sims, he's using delays that are just after apogee (optimum delays just under 4s) so theoretically that's not a factor here.

But actual flight data would be better.

I have only one model I've flown on both a Q-Jet D and and Estes D - an Estes Eliminator. It's much lighter than the OP's design.

It flew last December 18th to 625 feet on a D16-4 (but the AltimeterThree aboard reported that it ejected 1.1s early). It flew to 738 and 813 feet on a D12-5 on April 1st.

In case anyone is wondering, the rapid descents are because instead of the usual 'chute this model has a thin-mil streamer in it.

I'll try to remember to put it up on a D16-6 the next time I'm out flying and get data for that.

 

[rharshberger]

Was optimum weight figured in? Drag being the same a heavier model could fly higher than a lighter model, due to the extra inertia.

 

[jadebox]

Bill, have you weighed the actual rocket as prepared for flight?

If it is actually heavier than the simulated rocket, that may help explain why it might fly higher on the D16s.

Look at the difference in the thrust curves for the two motors:

https://www.rocketreviews.com/compare-motors-508946.html

The D12 has a higher initial thrust that drops to 10 Newtons for most of its duration. The D16 is a progressive burn that starts at about 12 Newtons and builds to about 22 Newtons.

A heavier, somewhat draggy, might slow down after the initial boost from the D12 while benefiting more from the progressive thrust of the D16.

If the rocket does weigh more in real life, you might try overriding the weight in OpenRocket and see if that changes the simulation results. (Also try setting the finish settings so that the rocket is a bit more draggy.)

Edit: I am not very confident of my analysis because 10 Newtons should be enough to continue to accelerate a .5 Kg rocket (and the design actually shows two motors) and the D12 thrust duration is longer.

 

[neil_w]

I flew my first D16 last weekend and I must say it went higher than I expected from the sims. No altimeter, though, just my uncalibrated eyeballs.

 

[Scott_650]

I’ve flown the following Estes rockets on both an Estes D12 and a QJet D16 - Vagabond, Top Shot, and Hi-Flier XL. They all worked well on the QJet and my Mark 1 eyeball agrees with my sims that the QJet is faster off the pad but lower apogee. Haven’t used my altimeter - it’s a simple “beep out the altitude” type - but next time I fly I’ll use it and confirm the sims. Interesting question...

 

[Alan15578]

I think it would be impossible for a D12 to compete with the QJet D16 in a BT-20 rocket.

But on a more practical issue, what is the useful shelf life of a QJet? Composit propellant motors don't seem to age as well as PB motors.

 

[BABAR]

I think it would be impossible for a D12 to compete with the QJet D16 in a BT-20 rocket.

True, if for no other reason than the D12 wouldn’t fit.

 

[billdz]

Thanks for the replies. Yes, the sim is based on actual weight. Both flights were normal, no weathercocking, no slow lift off, the D16 did seem to jump off the pad a bit more quickly. I thought perhaps there was an error in the manufacturer's reported data, but that seems unlikely. Maybe just my bad eyes and the D12 did go higher, but I don't think so, and I've seen several flights. Next time I'll use an altimeter.

 

[jadebox]

Ahoy Matey,

You need to build a second rocket t' drag race 'em!

 

[neil_w]

Ahoy Matey,

You need to build a second rocket t' drag race 'em!

That’s actually a great idea, someone should totally do this and get a good video. Would also like to see a drag race between an Estes C11 and a QJ C12.

 

[jqavins]

There are two issues, assuming the report of greater altitude on the D16s is accurate. One is why it should be so when the D12 offers more impulse. The other is why the simulation gets it wrong. That is, the simulation agrees with what one would expect, and both are wrong compared to actual performance.

Or, it's the reported performance, measured by eyeball that's in error. Occam prefers this explanation.

The rocket is remarkably heavy. One should keep in mind that the impulse delivered to a rocket by the motor is offset by the negative impulse delivered by gravity over the same time period. You can think of it if gravity steals some impulse from the motor, in an amount equal to the rocket's weight (not mass) times the burn time.

D12:

• Motors impulse = 33.6 Ns (2 motors)
• Burn time: 1.7 s
• Weight: 0.476 kg × 9.81 m/s² = 4.7 N
• Stolen impulse = 1.7 s × 4.7 N = 7.9 Ns
• Net impulse = 25.7 Ns

D16:

• Motors impulse = 24.8 Ns (2 motors)
• Burn time: 0.8 s
• Weight: 0.476 kg × 9.81 m/s² = 4.7 N
• Stolen impulse = 0.8 s × 4.7 N = 3.7 Ns
• Net impulse = 21.0 Ns

This does not take into account the difference in mass between the motors; the 476 gram mass includes one of these, but I don't see which. The D16's shorter burn and consequent lower loss to gravity brings the two pretty close together, and the difference in motor mass will bring them even closer by a little.

But the D12 should still win.

 

[BABAR]

Ahoy Matey,

You need to build a second rocket t' drag race 'em!

Drag racing “identical” rockets would have a minor disadvantage to the 18 mm Quest D motor, you’d need an adapter to fit it to the 24mm mount for the Estes D, which would cost a small amount of mass. May be negligible. Certainly if the Quest “won” you’d have your answer.

 

[BABAR]

There are two issues, assuming the report of greater altitude on the D16s is accurate. One is why it should be so when the D12 offers more impulse. The other is why the simulation gets it wrong. That is, the simulation agrees with what one would expect, and both are wrong compared to actual performance.

Or, it's the reported performance, measured by eyeball that's in error. Occam prefers this explanation.

The rocket is remarkably heavy. One should keep in mind that the impulse delivered to a rocket by the motor is offset by the negative impulse delivered by gravity over the same time period. You can think of it if gravity steals some impulse from the motor, in an amount equal to the rocket's weight (not mass) times the burn time.

D12:

• Motors impulse = 33.6 Ns (2 motors)
• Burn time: 1.7 s
• Weight: 0.476 kg × 9.81 m/s² = 4.7 N
• Stolen impulse = 1.7 s × 4.7 N = 7.9 Ns
• Net impulse = 25.7 Ns

D16:

• Motors impulse = 24.8 Ns (2 motors)
• Burn time: 0.8 s
• Weight: 0.476 kg × 9.81 m/s² = 4.7 N
• Stolen impulse = 0.8 s × 4.7 N = 3.7 Ns
• Net impulse = 21.0 Ns

This does not take into account the difference in mass between the motors; the 476 gram mass includes one of these, but I don't see which. The D16's shorter burn and consequent lower loss to gravity brings the two pretty close together, and the difference in motor mass will bring them even closer by a little.

But the D12 should still win.

Will the Quest D have a higher max velocity and therefore more drag?

 

[neil_w]

Drag racing “identical” rockets would have a minor disadvantage to the 18 mm Quest D motor, you’d need an adapter to fit it to the 24mm mount for the Estes D, which would cost a small amount of mass. May be negligible. Certainly if the Quest “won” you’d have your answer.

In any application where both motors are an option, you'll be using the D16 with an adapter, so it seems far. The Estes plastic adapters are very light, although obviously non-zero.

Will the Quest D have a higher max velocity and therefore more drag?

One sim I just pulled up quickly shows both D12 and D16 achieving similar max velocity.

 

[jqavins]

That’s actually a great idea, someone should totally do this and get a good video. Would also like to see a drag race between an Estes C11 and a QJ C12.

More impulse, lower mass, faster build-up followed by a progressive burn. I'd give 10 to 1 on the Q-Jet.

 

[cerving]

This is an apples and oranges comparison, because the QJet is an 18mm motor and the Estes is a 24mm motor. That's why the QJet has a lower total impulse... there's half the volume in the case for propellant, even though the propellant has a higher Isp. If you really want a "fair" comparison size-wise, compare an Estes D12 with an AT 24/40 F12... not much debate on which one would win out.

 

[neil_w]

This is an apples and oranges comparison, because the QJet is an 18mm motor and the Estes is a 24mm motor.

Respectfully disagree. The Qjets are excellent alternatives to C11 and D12 for smaller 24mm rockets. Further, I sometimes seem to find myself trying to decide on whether a rocket could live with an 18mmm mount, and that decision rests largely on how Qjet performance would compare to C11 or D12.

The idea of drag racing C11vs C12, or D12 vs D16, would be to get a visual feel for how the motor performance compares. Sims give the numbers but there’s no substitute for direct eyeball input.

 

[BEC]

A few seconds with a scale just told me that a Q-Jet D16 in an Estes 18/24mm motor adapter is 14g lighter than an Estes D12 at liftoff. After they are spent, the Q-Jet/adapter is 4g heavier than the D12.

I'm headed up to Sixty Acres to do a little flying right now. I have that Eliminator with me and will fly it on a D12-5 and a D16-6 with an altimeter aboard (probably an AltimeterThree) to get same-day data.

Of course this model is MUCH lighter than half of the OP's design.

This does not take into account the difference in mass between the motors; the 476 gram mass includes one of these, but I don't see which. The D16's shorter burn and consequent lower loss to gravity brings the two pretty close together, and the difference in motor mass will bring them even closer by a little.

But the D12 should still win.

The Open Rocket screen shot says that the motor configuration is 2xD16, so this is the lighter liftoff mass case.

 

[BABAR]

One sim I just pulled up quickly shows both D12 and D16 achieving similar max velocity.

A few seconds with a scale just told me that a Q-Jet D16 in an Estes 18/24mm motor adapter is 14g lighter than an Estes D12 at liftoff. After they are spent, the Q-Jet/adapter is 4g heavier than the D12.

I'm headed up to Sixty Acres to do a little flying right now. I have that Eliminator with me and will fly it on a D12-5 and a D16-6 with an altimeter aboard (probably an AltimeterThree) to get same-day data.

Of course this model is MUCH lighter than half of the OP's design.

there you go, spoiling all the theoretical arguments with factual data. Party pooper!

(Hope you have clear skies and light winds and straight trails!)

 

[jqavins]

I'm headed up to Sixty Acres to do a little flying right now. I have that Eliminator with me and will fly it on a D12-5 and a D16-6 with an altimeter aboard (probably an AltimeterThree) to get same-day data.

Oooh, science!

 

[BEC]

I don't really expect any significant difference from the data posted further up (post #8) from the same model but on two different days. That said, with a six second delay it shouldn't be deploying before ejection this time.

The skies aren't clear (this is the Seattle area in September, after all) but the rain chance is very low and the winds are light, so off I go.

 

[Scott_650]

What all this discussion is really pushing me to do is order an altimeter with more capabilities. I’m on the stock watch notice list for Flight Sketch so soon as their revised, Android capable, Bluetooth altimeter is available I’m certainly getting one or two.

 

[Nytrunner]

As we proceed further into the weeds......

A loaded D16 w/ adapter is lighter during boost -> Less gravity loss
An empty D16 w/ adapter is heavier during coast -> higher momentum in the draggy atmosphere

Little things add up sometimes