# Altitude or Speed?

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## I told you soo

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#### Justy

##### Well-Known Member
At the last club launch, one of the members gave me an Aerotech D21-10, with the condition that it be launched at a club launch where he can watch.

So I'm building a fairly minimalist, disposable, minimum diameter rocket to fly it in. The risk is large... the chance of recovery is low, because it will be flying quite high, and I'm told the D21 had a bit of a CATO problem.

So here's the question. I can build this rocket as light as possible, and it should break mach somewhere around 300', on its way up to 2700'.

Or I can throw 3/4 oz of junk in the nose and shrink the fins, and I can hit about 3200'. It's 400' short of the NAR record for D impulse; it would be enough to set a Canadian record (largely because there is no record yet). But with that mass, it won't go supersonic.

What would you do? Go for speed, or set an altitude record?

Speed because you have no way of recording altitude.

Speed is sooo much cooler

Originally posted by DPatell
Speed because you have no way of recording altitude.

Speed is sooo much cooler

No way of recording speed either, unless there's a disposable altimeter and telemetry transmitter.

METHOD FOR PROVING ALTITUDE

Add powder paint wrapped in one square of recovery wadding to the recovery gear. Equip ground trackers (3) with incline-o-meters. Use that "math" thing to estimate altitude, then average the three results.
(use 2.0g of paint to keep things light if going for speed, 25.0g if going for altitude... it needs nose weight anyhow, might as well make a bigger puff)

METHOD FOR PROVING SPEED

Calculate altitude as above. If the ejection altitude matches the prediction from the RockSim simulation, it validates that simulation, so it's reasonable to assume the simulated max. velocity was at least close to accurate.

METHOD FOR DEALING WITH THE WHOLE PLAN GOING OFF WHEN THE MOTOR CATO'S

Collect debris so as not to anger landowner. Clear launch site. Arrange for safe transport home. Add 2.0 pints of Sleeman's Honey Brown to rocketeer. Add additional pints as required.

I agree speed is more cool, but a record...HOW COOL IS THAT!!
I say if you have a chance to set a record, go for the record!

Go High !!!

How about using video cameras on tripods to prove how high/fast it went? You could send up reference rockets with altimeters that are tracked optically to calibrate the cameras.

This would be useful for club contests--instead of spending a lot of time/effort on real time tracking you could just see which one did the best on video.

If I were you I would see about hitting that 3600 foot record altitude...

Just based on what you've provided here, rockets of this size have *gone* MACH, but have *not* gone 3601 feet...

now, that's cool

alt is cooler
add noseweight for maximum performance... make the fins as small as posible (its amazing what some nose weight can do!), take the bt/nc down to the smallest posible OD and build up the ID to keep the strength... and make everything glass like. put some powder in and let her rip!! (hopfully not RIP, tho)

good luck!

Go for the altitude record.
Post pictures.

Originally posted by Justy
METHOD FOR PROVING ALTITUDE

Add powder paint wrapped in one square of recovery wadding to the recovery gear. Equip ground trackers (3) with incline-o-meters. Use that "math" thing to estimate altitude, then average the three results.

Actually, you can use the 3 angle measurements together to get a proper altitude estimate. No averaging needed. See Stine's figure 17-9 for the 3-station tracking scheme.

Ken

The problem I've had with D21s is thrust misalignment, not CATOs. Two motors, probably from the same batch. The thrust vector seemed to be about 5 to 10 degrees off axis. The nozzle shows asymmetric erosion. I have an inflight photo that clearly shows the off axis exhaust jet.

BTW. I wrote an article for Sport Rocketry about a bigger version of a project like this -- a throwaway "carrier" for an Apogee F10 that would reach a mile altitude. I actually got the thing back, but to do a mile with an F10 you need a longer delay than is available so the recovery system (a streamer to minimize my investment) was pretty torn up.

Hmmm

Normally I would say go mach, but since you have an opportunity to make a record I say altitude.

Blue

It's odd - I find the most impressive launches (as an observer, anyway) to be directly related to velocity, not altitude.

Big, lumbering rockets on long burn motors that don't fly *fast*, but fly loud and a fair height with very clean (straight) flight charactaristics are my favorite. So, relatively slow and realistic.

A close second is the other end of the spectrum. The rockets that leave the pad like a shotgun blast at light speed are *mega cool.* The bigger and louder they are, the better.

Now, compare to altitude: No matter how fast it gets there, there's no question it's *way* up there. You can hardly see it, and it's a long walk/wait for it to come down. All the action was getting there. That's what most people notice - the "getting there" as opposed to where it ends up in the ionosphere.

I say go for speed.

slow and high.

I like the giggle factor. You see a little rocket with a HUGE motor in in...it launches and what do you do?

HEHEHEHEHEHEHEHEHEHEHE

Jason

Do both.

Build the rocket light enough to go supersonic on the D21, and if you go for altitude, just add the extra weight and go for for it.

BTW the NAR Adult D Alt record is 1214 m (3982 ft) set on 4/17/94 by M McCauley. You really want a long burn low thrust motor for an altitude record since the drag goes as the square of the velocity. An Apogee D3 motor was probably used for this record.

Right now, neither the D21 nor the D3 are NAR contest approved because they are not generally available due to the Aerotech fire and not yet back in production, so there is virtually no way a new Adult D Alt record will be set.

Unfortunately for you, the CAR altitude record rules appear to be very similar to NAR so I doubt you can set an official record at the present time with the D21, and most certainly not the D3, but you will be ready when they get back into production.

Bob Krech

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