Crossfire ISX vs Alpha- is there much difference?

[RocketJ2]

Good afternoon, everyone!

After a super LONG delay (roughly 10 years), I'm starting to get back into rocketry. I've narrowed my focus to older kits, and I think I'd like to build an Alpha.
My first rocket as an adult was a Crossfire, I think I built it in 2012. It was launched twice successfully by my oldest son. I was impressed on the first launch that it went up, but even more so that it landed back within about a foot of where he was standing at the launch pad! On the second launch, it was almost as good, but hit pavement and broke off a fin. I repaired it years ago, but haven't got around to launching it again.

For my next attempt, I was thinking of doing an Alpha. They appear to be somewhat similar, so I think I'm safe in assuming the launch and flight characteristics should be about the same? Looking for something somewhat painless to ease back into it. I like the older kits, and was thinking of building the 1975 line in order as that was the year I was born.

Does anyone recommend something different? The kids are gone (but I'm in school now at Embry-Riddle) so I have a little more free time to play with. Plus it's gray season here in Michigan, so I can see cabin fever setting in soon...

Thanks in advance!
v/r,
jason

 

[BEC]

The Crossfire ISX and the Alpha are similar in size. The Crossfire's fins, along with those little strakes, are quite a bit larger (so theoretically more drag). There's also a little weight and drag in that plastic nozzle at the aft end. The Crossfire also has that long nose cone that ends in a conical section, while the Alpha, especially post-1992 version, has a simple ogive-shaped nose cone. The earlier shape is broader towards the nose cone shoulder. The Alpha's fins are surface mounted rather than through-the-wall as in the Crossfire. Through-the-wall fins are kind of unusual on a model that small.

I haven't built a Crossfire ISX so I don't have any altimeter data for one, but I have LOTS of Alpha data, and have seen Crossfires at club launches. I would expect the Alpha to fly a little higher, but not significantly.

Now if you clone a 1970s Alpha using a two-ring motor mount assembly (as in the Crossfire) it will be lighter than the current ones with that big fat cylinder used as a "centering ring" and will perform better. I have one built from an early 1980s kit which is 0.2 ounce lighter than one built from a contemporary kit, which is a significant difference (20%) and this is enough to affect performance measurably.

 

[RocketJ2]

The Crossfire ISX and the Alpha are similar in size. The Crossfire's fins, along with those little strakes, are quite a bit larger (so theoretically more drag). There's also a little weight and drag in that plastic nozzle at the aft end. The Crossfire also has that long nose cone that ends in a conical section, while the Alpha, especially post-1992 version, has a simple ogive-shaped nose cone. The earlier shape is broader towards the nose cone shoulder. The Alpha's fins are surface mounted rather than through-the-wall as in the Crossfire. Through-the-wall fins are kind of unusual on a model that small.

I haven't built a Crossfire ISX so I don't have any altimeter data for one, but I have LOTS of Alpha data, and have seen Crossfires at club launches. I would expect the Alpha to fly a little higher, but not significantly.

Now if you clone a 1970s Alpha using a two-ring motor mount assembly (as in the Crossfire) it will be lighter than the current ones with that big fat cylinder used as a "centering ring" and will perform better. I have one built from an early 1980s kit which is 0.2 ounce lighter than one built from a contemporary kit, which is a significant difference (20%) and this is enough to affect performance measurably.

BEC,

Thank you for that information! I'm digging through files I've saved over the years and seeing if I have an older set of instructions/plans for an Alpha. So far, it looks like I just saved bigger stuff, but I'm going to keep looking.

The nose comparison is especially helpful, as I wasn't aware the design changed. Good stuff to know.

Again, thanks!

v/r,
jason

 

[Rex R]

I am gonna stay out of any discussions about changes to the alpha fins(the last one took 10 years to resolve)

 

[BEC]

I am gonna stay out of any discussions about changes to the alpha fins(the last one took 10 years to resolve)

Rex,

I wasn’t going to bring THAT up…..

But after supper I’ll get into the nose cone stuff a bit, with illustrations.

 

[Scott_650]

Biggest difference outside the shape is the Crossfire’s through the wall fin construction - I’ve built two of them - I found the pre-cut slots to be a little snug on one but nothing a little sandpaper couldn’t fix. I left the finlets/strakes off my second build just to make it a bit simpler.

I’ve never flown either my Alpha or Crossfire with an altimeter but I’d guess their performance will be very similar - just as BEC stated earlier.

 

[smstachwick]

Comparing the stats on the Estes website, the Alpha appears to be shorter, lighter, and simpler to assemble, and it has a larger number of recommended Estes motors. It also is equipped with a parachute, compared to the Crossfire ISX’s streamer. Interestingly, both recovery systems are 12”. The Alpha’s estimated max altitude is 150 ft lower, although Estes’ apogee predictions are known to be optimistic.

The stock launch lug size, recommended launch controller, body tube diameter, and fin material are the same, so you can use the same launch equipment and many of the same repair supplies.

The main difference you’ll notice is recovery characteristics. The Alpha will drift farther under a parachute than the Crossfire ISX will with a streamer. If I were you I’d start on the recommended 1/2A6-2 (18x70mm casing, standard size) and work your way up from there. If you fly it on a C6-7 from a relatively small launch site, you might lose it, so it’s better to start small and get a handle on how the wind affects it.

 

[BEC]

BEC,

Thank you for that information! I'm digging through files I've saved over the years and seeing if I have an older set of instructions/plans for an Alpha. So far, it looks like I just saved bigger stuff, but I'm going to keep looking.

The nose comparison is especially helpful, as I wasn't aware the design changed. Good stuff to know.

Again, thanks!

v/r,
jason

OK - nose cones. Let’s see if I can tell this story without writing a full page. The original K-25 Alpha used the BNC-50K balsa nose cone that was in use at the time in several other Estes kits, and it first appeared in Model Rocket News in late 1965 (and first appeared in the Estes catalog in the 1967 edition). In approximately 1983, the balsa nose cone was replaced with a blow-molded plastic nose cone that was essentially the same shape. Then, about eight years later apparently something happened to the mold and for three years the Estes catalogs said you might get a red, white or blue nose cone in the kit. The white one could be the existing design or it could be the new pointier shape, both blow molded. If it was red (or vary rarely, blue) it was the injection molded nose cone introduced in the Alpha III. After about 1993, the narrower (more “pointy”) shape nose cone was the only one, and it has remained so to this day. When kit production was moved to China in the early 2000 time frame, apparently the nose cone mold was remade, but the shape on the Chinese-made blow molded nose cone is indistinguishable (to my eye, anyway) from the second blow molded nose cone shape that appeared circa. 1992.

Here’s a display I made for an Alpha 50th Anniversary event we had at the Museum of Flight, and one showing four Alphas.

On the right side of the display you can see the nose cones (Alpha III type not shown).

On the left side is the evolution of the motor mount. The second from top is the one you want to use if you clone the Alpha to be like an older one. You can see that heavy “centering cylinder” that was introduced with the “Beta Series” version of the Alpha in the early 1990s. That much heavier version of the motor mount is still with us today.





From left to right: An original BNC-50K, the first blow-molded shape (PNC-50KA) from an early 1980’s kit, the second blow molded shape, from a circa 2009 Chinese-made Alpha kit from a bulk pack (this model has been flown a lot and looks it), and a Semroc BNC-50K (which, as you can see, is not quite so sharply pointed). That last model is an Alpha (clone) my wife built and which is painted in the colors of our college alma mater, New Mexico State University.




I pulled a Crossfire ISX kit out of my stash and can also say that the body is 1 1/2 inches longer than the Alpha, which makes a difference when packing wadding and a ‘chute. The Crossfire nose cone is considerably longer as well, of course.

I’ll leave the fin shape discussion aside unless you really want to hear it. Very short version: when the Alpha’s production moved to China the fins went from die-cut (and faithful to the original template one used to hand-cut the fins back in the early days) to laser cut. When they did the cut files they took out (probably by accident) the tiny bit of outward rake at the tip, and changed the chord slightly as well.

RocketryWorks in Tucson has laser-cut fins of the original Alpha shape (in both balsa and basswood) if you don’t want to just print out a scanned SP-25 template sheet and cut your own, or just use the laser-cut ones from kits made in the last ~22 years.

Comparing the stats on the Estes website, the Alpha appears to be shorter, lighter, and simpler to assemble, and it has a larger number of recommended Estes motors. It also is equipped with a parachute, compared to the Crossfire ISX’s streamer. Interestingly, both recovery systems are 12”. The Alpha’s estimated max altitude is 150 ft lower, although Estes’ apogee predictions are known to be optimistic.

The stock launch lug size, recommended launch controller, body tube diameter, and fin material are the same, so you can use the same launch equipment and many of the same repair supplies.

The main difference you’ll notice is recovery characteristics. The Alpha will drift farther under a parachute than the Crossfire ISX will with a streamer. If I were you I’d start on the recommended 1/2A6-2 (18x70mm casing, standard size) and work your way up from there. If you fly it on a C6-7 from a relatively small launch site, you might lose it, so it’s better to start small and get a handle on how the wind affects it.

If the Estes site says that the Crossfire ISX has a streamer, there is an error there. The Crossfire kit I have to my left as I type this has the usual 12 inch Estes ‘chute in it, and all the ones I’ve seen flown at club lauches have had a 12 inch parachute.

Looking at the Crossfire ISX face card, I see a claimed max altitude of 1150 feet. I suspect that that’s a bit optimistic as most such Estes estimates are. A lightly built Alpha will almost get there on a C6-7 under ideal conditions, though. They currently quote a max altitude of 1000 feet for Alpha, and they WILL do that on an Estes C.

Also attached is rev. F of the Alpha instructions. This is the last one showing the two-ring motor mount.

 

[smstachwick]

OK - nose cones. Let’s see if I can tell this story without writing a full page. The original K-25 Alpha used the BNC-50K balsa nose cone that was in use at the time in several other Estes kits, and it first appeared in Model Rocket News in late 1965 (and first appeared in the Estes catalog in the 1967 edition). In approximately 1983, the balsa nose cone was replaced with a blow-molded plastic nose cone that was essentially the same shape. Then, about eight years later apparently something happened to the mold and for three years the Estes catalogs said you might get a red, white or blue nose cone in the kit. The white one could be the existing design or it could be the new pointier shape, both blow molded. If it was red (or vary rarely, blue) it was the injection molded nose cone introduced in the Alpha III. After about 1993, the narrower (more “pointy”) shape nose cone was the only one, and it has remained so to this day. When kit production was moved to China in the early 2000 time frame, apparently the nose cone mold was remade, but the shape on the Chinese-made blow molded nose cone is indistinguishable (to my eye, anyway) from the second blow molded nose cone shape that appeared circa. 1992.

Here’s a display I made for an Alpha 50th Anniversary event we had at the Museum of Flight, and one showing four Alphas.

On the right side of the display you can see the nose cones (Alpha III type not shown).

On the left side is the evolution of the motor mount. The second from top is the one you want to use if you clone the Alpha to be like an older one. You can see that heavy “centering cylinder” that was introduced with the “Beta Series” version of the Alpha in the early 1990s. That much heavier version of the motor mount is still with us today.

View attachment 552194



From left to right: An original BNC-50K, the first blow-molded shape (PNC-50KA) from an early 1980’s kit, the second blow molded shape, from a circa 2009 Chinese-made Alpha kit from a bulk pack (this model has been flown a lot and looks it), and a Semroc BNC-50K (which, as you can see, is not quite so sharply pointed). That last model is an Alpha (clone) my wife built and which is painted in the colors of our college alma mater, New Mexico State University.

View attachment 552195


I pulled a Crossfire ISX kit out of my stash and can also say that the body is 1 1/2 inches longer than the Alpha, which makes a difference when packing wadding and a ‘chute. The Crossfire nose cone is considerably longer as well, of course.

I’ll leave the fin shape discussion aside unless you really want to hear it. Very short version: when the Alpha’s production moved to China the fins went from die-cut (and faithful to the original template one used to hand-cut the fins back in the early days) to laser cut. When they did the cut files they took out (probably by accident) the tiny bit of outward rake at the tip, and changed the chord slightly as well.

RocketryWorks in Tucson has laser-cut fins of the original Alpha shape (in both balsa and basswood) if you don’t want to just print out a scanned SP-25 template sheet and cut your own, or just use the laser-cut ones from kits made in the last ~22 years.


If the Estes site says that the Crossfire ISX has a streamer, there is an error there. The Crossfire kit I have to my left as I type this has the usual 12 inch Estes ‘chute in it, and all the ones I’ve seen flown at club lauches have had a 12 inch parachute.

Looking at the Crossfire ISX face card, I see a claimed max altitude of 1150 feet. I suspect that that’s a bit optimistic as most such Estes estimates are. A lightly built Alpha will almost on a C6-7 under ideal conditions, though. They currently quote a max altitude of 1000 feet for Alpha, and they WILL do that on an Estes C.

Interesting. Thanks for the correction.

 

[BEC]

Interesting. Thanks for the correction.

It wouldn’t be the first typo on the Estes web site!

Instructions show a ‘chute as well: https://estesrockets.com/wp-content/uploads/Instructions/007220_CROSSFIRE_ISX.pdf

 

[RocketJ2]

Wow! I missed a lot while I was sleeping!

BEC, thank you for that wealth of information! My Crossfire ISX has a 12" chute as well. I'm thinking I'll have to replace it though, as when I unfurled it yesterday it had a couple holes I don't remember poked in it.

I don't remember if the fins were through the wall though, I thought that I had to mark the tube and glue them on? It was, as I recall, around 12 years ago, so my memory is a bit faded.

The nose cone info is spot on for what I was looking for. Thank you for that! I knew it was different from looking at the older catalogs vs what is at the hobby store now, so at least now I know where to start looking. And thanks to all for 'sparing the drama' about the fins, but the information is extremely helpful as well as to knowing what is correct and what isn't.

Thank you to everyone that contributed so far! It's an immense help!

v/r,
jason

 

[Mugs914]

I think overall the biggest difference is that, as we would have said when I was a kid, "The Crossfire looks more cooler."