denverdoc

Some interesting parts present, for example the graphite cone, the filament wound CF coupler, and the "quasi-isotropic fins material." Curious about the last material--are these stacked plies of CF cloth at various fiber orientations which would minimize in-plane differences at various angles but not address the out of plane vs in-plane strength differences or something altogether different?

Just Jerry

The motor section is long enough to accept a 38mm full K.

Just Jerry

denverdoc

Hee, hee. I noticed that too which I don't think is any accident. Otherwise why the high temp epoxy and aluminum tipped NC. Question is will the 1/8 CF fins hold up to such a rip-snorting flight.

Steve_Shannon

It looks like it would be just right for a hybrid also.

denverdoc

Steve, That reminds me how are your hybrid projects coming along?

Steve_Shannon

Oh, God, you had to ask. I haven't done a thing lately. I bought a tank, valves, O2 regulator, and set of fill stems for the club, but have done nothing more. I still need to buy one more valve (a BFV from Doug Pratt) and then wire them up to my controller box and test the plumbing. Then, I need to go shopping in our state for nitrous.

denverdoc

Not to worry--still have a few months before you guy kick off your season, or are you guys like the brave souls at NCR and CRASH who fly year round? Me I'm a fair weather flier.
J

Steve_Shannon

We'll have our first launch sometime in late March so TARC flyers can come and qualify. Our summer flying has been interrupted with fire restrictions, so we have to brave cooler weather in the spring and fall to make up for it. So now we have two crashing seasons and two rebuilding seasons

Just Jerry

That airframe tube looks sufficient to BE a hybrid or solid motor casing.

Just Jerry

bobshultz

Here is a link that I ran across today with more info on the kit.

http://www.performancerocketry.com/mongoose38.htm

Bob-

deandome

I saw these kits a few weeks ago...they are sweet, for those who are into the min-diam thing (I'm not in that group).

That nosecone is amazing, but I kid you not; in a lawn dart situation, that rocket would literally pierce a car clean through.

Lesson #1: DON'T LET A LAWN DART HAPPEN!!

denverdoc

Bob, Thanks for the link--it shows a balanced and symmetric ply orientation using pre-preg CF for the plate fins. My understanding is the really good CF usu gets gobbled up by the pre-preg suppliers--that is aerospace grade with the higher modulus--so no skimping here or anywhere else. Looks like an interesting alternative to the re-released Shadow Composites 38mm bird. Dare I ask what one of these beauties costs?

Steve_Shannon

They are listed on the Wildman site for $260.

denverdoc

Hey thats almost affordable and about 1/2 of what I was thinking. Would only need the 38mm compatible GPS's from Big Red Bee, one of those fine young BSD 16 grain 38mm cases....And you got an 800 dollar project that would turn heads, and snap a few necks.

Steve_Shannon

Let me know when you are going to launch it. I'll try to come visit my daughter and watch your launch.

denverdoc

Shucks, I can't afford the kit. But I do have have some graphite blanks for engine nozzles long enough, and some good CF plate I bought from the other composites man, Mick Kelly. Need an AF and a motor is all.

Didn't Mike Binder say that he had to go to Al tubing on those K4000's or whatever they were--kind of relates to the strength of materials thread where we were discussing the one achilles heel of CF esp at higher L/D ratios--brittleness. If this thing flexes much at a 2 # dry weight, it may be all over in a real hurry.

Steve_Shannon

All over pretty much describes the location of the pieces as they come down also.

Interesting that this kit uses a graphite nosecone with an aluminum tip (presumably to prevent damage to the graphite because graphite would be better at temperature) but the new ShadowAero kit, the Phoenix, uses aluminized urethane for a rocket that looks like it is made for the same kind of performance.

H_rocket

Real men fly in ankle deep icy slush...

denverdoc

Yea, Well I came too close to a coronary hauling a 50 lb rocket in three inches of snow at 8800' to test my real man credentials again. Took me a full 20 minutes before I could smoke again

Steve_Shannon

Icy slush would be about 70° warmer than it was here on Monday. Today it has warmed up considerably and is up around 10°F, but Monday was -37°F. Real men stay inside and watch TV on those days.

denverdoc

Steve,
Good grief--I think -30 is about as cold as I have been--this in Steamboat Springs, Colorado. Much to my delight, my Mustang GT fired right up that morning, while all the Volvos and Subarus went click or barely turned over.

Steve_Shannon

Yeah, our brass monkey made a "click, click" sound.

H_rocket

No, SMART Men stay inside and watch TV, Us knucke dragging Pyro-whores will brave damn near anything for an AP fix, As an example I present the Lake Champlain Ice Launch in February. When I asked why anyone would do something so stupid, I got two rational reasons.

1 - big skidmarks wit no chance of fire
2 - snowmobiles used to fetch rockets

Somehow that all made sense.

Steve_Shannon

It made perfect sense to me too. However, I have seen what can happen to plastic (and even pot metal car door handles on -40 days) and I bet you have too.
Edmonton Rocketry Association has their annual "Fire and Ice" launch in mid February:

markkoelsch

A Big red Bee, or anything else will not work unless you can figure a way to get the antennas outside the body. Considering a close to maximal motor for this I would think that cutting a hole in it for a gps receiver/transmitter might have a bad effect on the strength of the airframe. It could be a tricky thing.

Mark

UncleVanya

Could you use the thin copper foil tape and just slightly notch the coupler fitting to allow it to pass to the outside? You could then run just the right length or transition to a standard antenna outside the airframe. I think the foil would work - but I may be completely confused.

denverdoc

I think its a splendid idea and have a 50 ft roll of self adhesive very thin copper foil for anyone who wants to try it. This can be clear coated over and looks very sexy IMO. Besides antennae, it can be used to conduct current down airframes for ejection and airstarts. This is especially handy if you forget the internal wires during the build.

Steve_Shannon

If you chamfer the edge of the coupler, I bet it'll slide past the tape without needing to cut a groove. You could cut a groove (in woodworking a dado; in electrical work a chase) if it was too tight.

Steve_Shannon

Hi John,
Does it come with any specs, such as equivalent wire gauge or cross sectional area that could be used to determine current carrying capacity (ampacity) at various lengths?

UncleVanya

You can also use flat speaker wire - 16 gauge flat wire is readily available. But what you have sounds better. Where did you get it and how do we obtain some?

Steve_Shannon

I googled for conductive tape and got too many hits, but then I googled for conductive alarm tape and got this.

denverdoc

Similar products likely do--if bought from say McMaster-Carr. This was purchased at McGuckens Hardware up in Boulder--no specs. If it were simple copper, we could determine that easily enough, but the adhesive is conductive paste as well. I know it measures 0.00 on my cheapo DVM in several foot lengths. But my cheapo DVM is cheapo, and whats more missing in action. If not I could figure something out.

I would say at least the equiv of 24 gauge wire as its a 1/4 inch wide. It may even be the equiv of 18/20 ga. If you have some decent test equipment I'll send you some. That stuff is a dead ringer.

Steve_Shannon

Probably the best way to test is to roll out a fairly long length and measure the resistance, but I could mike the thickness and calculate the resistivity.

With a conductive adhesive, do not put it on a carbon body rocket, unless you put down an insulating layer first.

heada

McMaster-Carr part number 76555A721




Tape is 0.0035" thick and consists of a 0.0014" thick foil with 0.0021" of acrylic adhesive.

-Aaron

denverdoc

Agreed, I should have measured the 50' but unrolling it--no rerolling it is the hassle, and with the paste it is potentially shunting in the rolled condition--tho there is a peel off section. Let me see if I can find some data on M-C.

Addendum: looks like surface resistivity for the M-C product is 0.0065 ohms/sq inch. If I'm figuring this right, then assuming a 20 inch run of 1/4" is 5 sq in. R=0.0325 ohms (thats half the circuit series resistance contribution for a pair) What it doesn't tell us if actual current carrying capacity. I'll pick up a 1/4 ohm resistor and try dumping a nicad packs worth to see if it becomes a fuse. I've just used them for e-matches where it is a non-issue. Thats about the length I measured 0 with my cheapo hand held so the stuff I have maybe is thicker than this M-C product. For whats its worth if you look at a copper head using similar stuff they don't melt under automotive battery apps, but thats a brief pulse (before finding another one and trying it again)

Steve_Shannon

I calculate that the resistance per meter of length should be about 0.0743 ohms. I saw that John posted a calculation also and I don't have great confidence in mine (I just threw it together based on the cross sectional area of the conductor times the conductance of copper and then inverted the result to get resistance. I'll be interested to see what it measures.
Also, the tapes that I saw were listed as the metric equivalent of an inch, based on 24mm/inch, which is wrong. An inch is defined as 25.4mm, so that can shift the resistivity even higher.

denverdoc

Actually Steve, I have no confidence in mine--these are weird units given at M-C. Yours is a conventional and perectly sound approach from physics. The units given seem to imply 2-D shape has no bearing--something that is completely counterintuitive--I'm assuming it assumes 1/4 " width or it makes nonsense, not no sense--I was just winging it and the number is higher than I measured. I would have guessed something much closer to what uou came up with.

markkoelsch

I like the idea, but have not tried it. I would think you would need to insulate the foil from the carbon fiber. I would also be worried about the airframe getting into the line of sight between the antennas, and obscuring the signal.

As far as the gps receinver in the rocket, I do not know how this could be done. The receiver antennas I have seen are kind of large, and will not work from the inside of a conductive airframe.

Is not just the resistance of the antenna, but the length...hence the frequency it is tuned to?

I have a Walston, and would be interested in trying the foil antenna on something using that.

Mark Koelsch

denverdoc

Mark,

Yea definitely insulate from a carbon fiber rocket--I would go beyond depending on the non-conducting adhesive found on some of the foils and use a clear coat of poly-u, otherwise you have just shunted your folded dipole antenna into a blob.

Steve_Shannon

I wonder if you could not just connect to the carbon fiber and use it as the antenna. It's a faraday cage if your antenna is inside it, but if you connect to it, and assuming it is the correct length (some even multiple or even fraction of the wavelength) then perhaps it would work well as an antenna. I can't think of why this would not work, but I am not a radio guy.

Mike Fisher