Do manufacturers inflate performance numbers?

I know in the world of Air guns there is always a lot of drama concerning manufacturer's claims of performance in relation to muzzle velocity. They claim 900fps but you will be lucky to get 800 out of it. They play little tricks like shooting ultra light pellets and such.

Today I was looking at the Estes Nike-X kit. On the bag it says 600ft.

In open rocket the simulation only gets 500ft (with a C6).

Not a big deal but I was wondering if my suspicions are validated.

Not really, those numbers may be based on a bare kit (no paint, etc). Variations in air pressure and density, motor variation, humidity etc can all play a hand, so 500' could easily be all it gets, or it could go 700'+.

Makes sense, I suppose since I am at only a dozen or so feet above sea level

Elevation of Penrose, Colorado is 2106 ft. Might be the difference.
If you launched that from Leadville, Colo. (elev. 10,430') you might get 700+.
But the air might be too thin for the fins to do their thing.

On a more philosophical note, from the ground looking up would 200' more make that much of a difference?

kuririn, no way Penrose is that low. Wikipedia (yeah, I know) puts it at 5338 feet. Also much test flying that John B. does is at the SCORE field in Colorado Springs which is just over 6000 feet.

To the OP: I have found most altitude estimates on Estes packaging to be a little optimistic....but not always. I fly a bunch of altimeters so have data on a number of models. These days I expect they are Rocksim estimates. I don't know where the numbers came from, say, 30 years ago.

Yup, wrong Penrose.

OP mentions Air Guns... You guys have to see air compressor ratings!!!

BEC said:

I fly a bunch of altimeters so have data on a number of models. These days I expect they are Rocksim estimates. I don't know where the numbers came from, say, 30 years ago.

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jlabrasca said:

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I know how optical tracking is done.

But I doubt they used to put the biggest motor in a model, used one (or better, two) of these to track a prototype model in flight and then put that data in the catalog. But then again maybe they did.....

The variability of the motors alone is enough to throw things off. Really, I've never felt 'cheated' because my rocket didn't go to the advertised altitude. Heck, sometimes I've actually exceeded it (verified with some Jolly Logic altimeters)! I mean, I can't tell the plus or minus 100 foot difference on the ground, so what am I losing?

See it for what it is, just like EVERY SINGLE OTHER PRODUCT THAT YOU BUY.....advertising.

After all, you accept gas mileage estimates, don't you?

BEC said:

I know how optical tracking is done.

But I doubt they used to put the biggest motor in a model, used one (or better, two) of these to track a prototype model in flight and then put that data in the catalog. But then again maybe they did.....

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In 1979*, when that Alitiscope catalog listing was published, a state-of-the-art flyable altimeter would have weighed enough to significantly affect the flight of the rocket.

https://patents.google.com/patent/US3715925A/en

In grad school, in 1988-ish, I taught a freshman physics lab where the students built some skill level 1 kit (not Alphas, but something similar). We had a program (running on Apple II computers) that took some dimensions from the rocket and the specs on the motor and plotted a flight profile. We launched the rockets and used genuine blue plastic Altitracks (tm) to measure the height at deployment. While there was some hope that the exercise would show them some things about about fluid drag, and help in getting them from conservation of momentum to the Tsiolkovsky equation, the lab was mostly meant to be an exercise in data reduction.

We launched as many as 15 rockets, collected one data point for each. Then we launched the three best performing rockets 3 times each. Finally, the students evaluated the prediction of the black-box computer program against the data. Lots of error propagation and uncertainty analysis went into that comparison. I cannot remember how closely the ideal flight predicted by the simulator came to the averages we got from the flight of the three best rockets. I do remember that our data from the field was very noisy. We had spreads of a hundred feet or more in the measured altitudes (on 1/2 A-6 motors).

*Is it weird that I spent 45 minutes trying to track down that NOT Data 70- typeface used for the "Predicted Altitude Computer" headline? I am guessing it was a rub-down face from some Letraset competitor. The oblique strokes on the A and M are weird for an E13B knock-off.

Banzai88 said:

After all, you accept gas mileage estimates, don't you?

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No, I don’t. I keep records. I can say that the EPA combined estimate and my actual experience with a 2013 Mazda3 hatchback match pretty well over about 70,000 miles so far....the EPA city figure is a touch pessimistic and the highway figure is a touch optimistic. But then I probably drove a little faster than the EPA highway cycle test across Idaho and Wyoming on the way to, say, NARAM-60.

to quote a line for the movie "How to get a head in advertising":

"It's either high in one thing, or low in something else!!

Things like fillets, fin bevels, launch lugs, and surface quality will effect Cd, something a simulation can only estimate until it is updated based on real data. Also, how close the rocket is to the optimal mass will change the altitude obtained.

Banzai88 said:

I mean, I can't tell the plus or minus 100 foot difference on the ground, so what am I losing?

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So true, and the higher it goes, the harder it is to get back. Especially for smaller fields, I don't want the rocket to go too high.

The biggest source of variability in apogee is trajectory, and the figure I use is 40%. That's the difference between a straight up flight and one that weather vanes into the wind. Yeah, it's that much. Much of your impulse can be spent going sideways, and fighting wind, rather than being put into altitude.

I think motor variability is 5-20% (I recently read 10%). I used to say 20%, but at least one recent study showed that my figure is probably outdated. Motors have gotten pretty uniform.

Weight is another significant one. It's not hard to put many extra ounces of paint on a rocket.

And then there's weather (in the form of air density slowing down the rocket and affecting the reading on the altimeter, which doesn't correct for weather).

I try not to discourage students from doing fin and nosecone shape studies, but in reality they are testing the above more than they are testing those...

jlabrasca said:

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The Estes Altitude Computer, despite its name and slide rule appearance, is just a simple look up table. I don't know what the tabulations are based on, possibly just the advertising BS published in their catalog and kit packaging.

The Altiscope is at least educational. You would need to use four of them expertly and be able to solve the 4E problem to get results on par with NAR two station tracking (e.g. with one pair of Centuri Skytracks).

Estes also published TR-10 on Altitude prediction, by Douglas Malewicki. It is still useful, but it is based on the bogus catalog motor data; for example, it assumes the C6 delivers exactly 10.00 N-s. The Centuri version is easier to use and includes the old Mini-Max motors, but does not include burnout velocity, and of course it uses the bogus catalog motor performance numbers. To get any reasonable prediction of altitude performance you need to use representative motor data, such as that independently measured by NAR S&T.

Shortly after I arrived at Iowa State University in 1974 I discovered that they had a nice drum plotter, and I produced a complete set of altitude charts for all of the NAR Certified motors, including the AVI Gold Series, using the S&T certification data. Around this time Mike Bergenski(?) was promoting AVI Astroport as a one stop shopping center to buy products from all manufacturers. I tried to interest him in buying or publishing my altitude charts. He reasoned that since he had a computer he could just produce his own charts. He never did, but he did send some of my charts that I left with him as sample pages to other rocketeers.

As a general rule, the marketing department always inflates the performance of of their products. One should never blindly trust manufacturers data. Furthermore, motors may substantially deviate from NAR S&T certification test data. Rocket kits can also vary substantially in mass, Cd and performance based on builder skill and other factors.

One area where performance claims are often inflated is hybrid motors. Their performance is very sensitive to the fill and NO₂ tank temperature. The manufacturer can get it perfect, but the average hobbyist cannot especially out in the desert on a hot afternoon.

Do manufacturer's inflate performance? Here's a fun one -
The first picture is the copy block from the Centuri Payloader II kit from 1971 claiming 2,000' with a C engine.
The second picture is from the Centuri catalog in 1976. The same Payloader II lost 1,000' of altitude in only five years time.

That's funny, Chris. I haven't flown the reissue Estes version of this enough to have lots of data....but 1000 feet on a C6 is probably on the upper side of reasonable. The slightly larger Nova Payloader when pristine and new will do 750 on a C6. Even an Alpha just gets to 1000 feet upon a C6 (carrying 3g of FireFly for the altitude data).

They would, of course, all go higher when flown out of Phoenix (or better Penrose) given the altitudes of the launch sites.

jlabrasca said:

In 1979*, when that Alitiscope catalog listing was published, a state-of-the-art flyable altimeter would have weighed enough to significantly affect the flight of the rocket.

https://patents.google.com/patent/US3715925A/en

In grad school, in 1988-ish, I taught a freshman physics lab where the students built some skill level 1 kit (not Alphas, but something similar). We had a program (running on Apple II computers) that took some dimensions from the rocket and the specs on the motor and plotted a flight profile. We launched the rockets and used genuine blue plastic Altitracks (tm) to measure the height at deployment. While there was some hope that the exercise would show them some things about about fluid drag, and help in getting them from conservation of momentum to the Tsiolkovsky equation, the lab was mostly meant to be an exercise in data reduction.

We launched as many as 15 rockets, collected one data point for each. Then we launched the three best performing rockets 3 times each. Finally, the students evaluated the prediction of the black-box computer program against the data. Lots of error propagation and uncertainty analysis went into that comparison. I cannot remember how closely the ideal flight predicted by the simulator came to the averages we got from the flight of the three best rockets. I do remember that our data from the field was very noisy. We had spreads of a hundred feet or more in the measured altitudes (on 1/2 A-6 motors).

Click to expand...

Nowadays, of course, one can get a very precise electronic altimeter for $25 and it weighs about 3g including a protective pouch (FireFly in a fleece pouch my wife made for some of mine).

I have tried to use those Altitracks with students (rather younger than freshmen) as well and the two I purchased for this are so finicky in use that I don't think we ever got data we could trust.

Even an Alpha on a 1/2A6-2 only goes to around 100 feet...so even a slightly dirty launch rod or a puff of breeze could confound data based on using those.