Hello, this might sound crazy but I've got some old (around 15 year old) FSI
F7-6 motors laying around. I'm wondering if these would work in Apogee's
aspire. The model was built to make the most of their F10 engine, but I'm
wondering if the FSI motor might be close enough to work. What do you guys
think? I don't have the parameters of the FSI motor in front of me, so I'm
not sure if this combo is workable.
I used to fly both the old fsi f7 steam engines and the f100 thunder sticks
and the F7 was for very light weight rockets. Takes a good sized area to fly
them in, like the desert fields where I now live.
Without having thrust data and simming the flight, you can use the average
thrust to see if you have enough oomph to get it off the pad.
I've calculated the newtons to pounds to ounces and 5:1 thrust to weight and
the formula comes out:
Rocket weight (ounces) <= 1.4 * Average Thrust (newtons)
So for the F7, if your rocket weighs less than 5 ounces (7/1.4) you _should_
be safe. I'd say something about how much wind there is at launch time, but
if you are going to put an F in a light rocket, you're waiting for a very
light wind day anyway to keep it from drifting away.
Well, I think I answered my own question. I created a rocket profile
in WRASP, ran a check of the profile against predictions from Apogee
with other engines and then tried it with the F7. The F7-6 is the
desired engine, with ejection coming about 1 second before apogee
(rocket is traveling around 30 fps at the time, the F7-8 would allow
the rocket to arc over and eject when descending at around 33
fps...ideal predicted delay is 7 seconds). Max altitude is 3580
feet....a little less than the 5468 max design altitude using an F10-8
(the engine the rocket was built around, according to Apogee). This
looks like it might be doable and a way to use up my stock of those
Launch rod velocity is 27 fps...nice and slow...maybe too slow?
(By the way, the rocket is 29" long and weighs 1.85 ounces empty
according to Apogee.) Now to run out and buy the rocket! :-)
I once launched an FSI OSO with an F7, it rose up the launch rod and as it
cleared the rod, a very slight tradewind breeze came up, the rocket didn't
go up during the 2 or 3 seconds of the breeze, instead it went sideways and
burned the nesecones of 3 other birds on the pad before it got enough steam
up to get going upward again for the rest of the 9 second burn time.
In all probability, unless you are extremely lucky, your whole flight
with the F7 motor will be one big arc. Flights with F7's usually go up
about 50-100 feet and then start a really large arc until the parachute
/ streamer comes out.
A lot depends to where you are launching (high humidity areas are
worse) and how much of a breeze there is. Notice that I didn't type
By the way, an F10 will take the model up much straiter and higher than
These and the E5 were the most fun I ever had with FSI motors. Loved 'em
If you do things right they fly fine. Build light and lighter, and make sure
the ride up the rod/tower is stiction free, and get that launch elevation as
close to 90 degrees as you can. I flew many BT-60 3FT based rockets on
these, and had no problems. The only time I did was a light BT-55 based
thing I once built that had fairly small fins and I had the CG just a bit
too far back - someone has great video of it snaking around in the grass,
occasionally breaching a couple of feet up then back to slithering again.
Needed nose weight or more speed off the rod.
Whatever you do though, don't build any rocket for these like you are going
to fly it on F50's or the like. And use light weight fins and don't skimp
too much on the area due to the speed off the rod with these motors. It is
nothing like the F10 at all, which I have flown in very lightweight 2.6"
rockets. In fact it is not even an F7 if you look at the real cert data
versus FSI's data. I believe the real average thrust is between 5 and 6
That said, my biggest concern would be the reliability of these after 15
years - they were not the world's most reliable motors although I think I
saw more F100/E60 problems, likely simply due to more of them being flown.
All the examples I flew worked, but they were not old at the time. I believe
Don Carter could elaborate on the reliability issue, for those that remember
that incident in the late '80's IIRC.. ouch :-(
But you may as well fly them! Enjoy, wish I had some.
The D20/E60/F100s I flew were 100% reliable nce I learned to ignite them at
the nozzle end like a regular BP motor, instead of at the top of the core
like a composite motor. I burned a lot of them up the last couple years
before they lost certification. The neatest was a Tazmanian Devil that I got
to work on E5s. Never got the F7 version to work without shreading.
Bob Kaplow NAR # 18L >>> To reply, there's no internet on Mars (yet)! <<<
Kaplow Klips & Baffle: http://nira-rocketry.org/Document/MayJun00.pdf
My thanks to the group for a most interesting thread and for the
replies...I've ordered the rocket today and will let everyone know how it
turns out. Now for another question....how about FSI engines and the LOC
(No not the F7's ! :-)) I also have a bunch of E60-4s...according to wrasp
this should also be a good engine for that model. My question is, do you
think the Aerotech F14-4J is good for this rocket? I'm sitting on a dozen
of these with no rocket (at this time) to fly them in. I bought them about
12 years ago and lost the rocket that they were to fly in on it's second
flight. Wrasp predicts it to be okay, but again (and like the Aspire with
the F7) liftoff velocity is a touch slow. Predictions are listed below:
E60-4 374' apogee with launch rod velocity of 33 ft/sec ejection just 0.1
seconds before apogee
F14-4 984' apogee with launch rod velocity of 30 ft/sec ejection just 0.3
seconds before apogee
On paper these seem to be reasonable engines for this model with slower
realistec liftoffs and apogee's that are reasonable for launching in a local
On a related note, I also have 3 engines from Composite Dynamics. Are these
worth much as collector's items or should I go ahead and use them in a
rocket? I have 2 E20-7s and 1 E20-10. Both are date stamped from 1980!
(Even still have the original ignitors!) These are 24mm engines and on
paper they look like they might work okay in some of the lighter Estes
rockets. I also have one A10-0T left (did have 5, but burned the others a
couple nights ago launching my old Estes Mini Cobra It was great to be
flying again and it was my wife's first foray into rocketry and we had a
blast (pun intended)! Sure glad I painted that rocket flourescent orange or
we never would have recovered it! Wrasp listed the A10-0 and 1/2A3-4 set of
engines as pushing it up over 900'...way out of site for such a small
Craig (yet another BAR but one with a big box full of old engines :-)
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