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Sep 11, 2013, 09:34 PM
Koo
Koo
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RVjet to be dropped from 100,000 feet. Planning needed


EDIT( 9/18):
Looks like the RVjet is going to be the best choice for our mission. 90% sure that we will use ardupilot mega +minimOSD+RDF900 data radios.
So the questions are as follow:
1)Do we need to fabricated the RVjet (or part of it) in S-glass or carbon fiber?
2)Any possible problems with dragonlink v2, 1.5w 1.258ghz vtx, and 1W 900mhz data radios? We will use yagis for 900mhz and 433mhz, gatlin for video.
3)FAA really doesn't like the idea of having a motor. To my understanding, they were fine with us calling the plane "experiment aircraft" so we shouldn't have an issue with a 8lb RVjet.
4)Free fall or parachute initially? We could let the rvjet drop to 20,000-40,000 feet with a parachute before staring to fly but free fall would be cooler.
We have all the video gear already and got about 50 mile range on one of our missions. We are expecting to have a succesful mission by the end of this semester. We also have radio tracker which allows to follow the balloon in real time. It sends the GPS coordinates to a GSM tower every few minutes so we can tell which way the winds are blowing at different altitudes and our altitude.


Original post.
Quote:
Hey guys, I'm part of undergraduate research group called Project High Flight at Miami University and we are dropping a RC glider/plane from one of our weather balloons this year. The airframe we are planning on getting is skywalker x8 because of the payload it can handle.
We are planning on fiberglassing (or carbon fiber) the airframe so it can handle the stress and high winds.

I have couple questions I can hopefully get answers to.
If we use carbon fiber, will it impact 433mhz LRS or 1.258ghz video system? We would have the antennas outside but we don't want to have them sticking out too far.

Would there be a better airframe than the x8? We need to be able to carry decent payload of around 3-4lbs not including the power system so zeph and rvjet won't work.

And finally, would Eagle tree osd work fine or do we need APM? We couldn't get ublox neo-6m gps work above 35K feet with ET even though its not a GPS limit and ET is just very limited.
Thanks!
Last edited by Koo; Sep 18, 2013 at 09:12 AM.
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Sep 11, 2013, 10:11 PM
Registered User
Cheese5's Avatar
You may be interested in this video:
Space Glider - FPV to Space and Back! (6 min 1 sec)
Another weather balloon assisted space flight, though the aircraft was not powered. Make sure you have a good recovery plan!

IMHO a flying wing or something more aerodynamic than the skywalker would work better at high altitudes (where the wind speed can vary drastically), since you aren't going to get much thrust at that high altitude, mostly just gliding.
Sep 12, 2013, 02:53 AM
Crash....Fix......repeat.
kokopropelli's Avatar
Check out these guys. https://www.rcgroups.com/forums/show....php?t=1744541
Sep 12, 2013, 11:25 AM
Koo
Koo
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@ Cheese5 I've seen that video and the fact that he did all that without an OSD or autopilot is really cool. And the skywalker x8 is actually a flying wing :P
Sep 12, 2013, 11:35 AM
Registered User
Quote:
Originally Posted by Koo
We are planning on fiberglassing (or carbon fiber) the airframe so it can handle the stress and high winds.

I have couple questions I can hopefully get answers to.
If we use carbon fiber, will it impact 433mhz LRS or 1.258ghz video system? We would have the antennas outside but we don't want to have them sticking out too far.
I will let others with more experience with the X-series airframes answer those questions, but I can address the questions above.

First, long-tow carbon fiber, like that used in cf fabrics is only a weak rf absorber. Engineered cf microwave absorbers use special resins saturated with ferrite particles and short-strand cf (a few millimeters long) to achieve maximum absorption, and even then are only effective from about 2 GHz - 18 GHz, so if your system is operating at 1.258 GHz and below, you should be fine. If you need absolute certainty, S-glass is nearly as strong as cf, about the same price, and is completely rf transparent.

Good luck...it sounds like a fun project!
Sep 12, 2013, 11:40 AM
Koo
Koo
Registered User
Thread OP
Quote:
Originally Posted by Dauntless Stan
I will let others with more experience with the X-series airframes answer those questions, but I can address the questions above.

First, long-tow carbon fiber, like that used in cf fabrics is only a weak rf absorber. Engineered cf microwave absorbers use special resins saturated with ferrite particles and short-strand cf (a few millimeters long) to achieve maximum absorption, and even then are only effective from about 2 GHz - 18 GHz, so if your system is operating at 1.258 GHz and below, you should be fine. If you need absolute certainty, S-glass is nearly as strong as cf, about the same price, and is completely rf transparent.

Good luck...it sounds like a fun project!
Thank you! I just knew that CF isn't friends with 2.4ghz
I found few places that also sell kevlar fabric but I imagine it wouldn't be fun cutting it and its not going to be as good for our purposes than CF. I'll look into the S glass as well.
Sep 12, 2013, 12:43 PM
Registered User
Correct, Kevlar is neither fun to cut (we use specialized, expensive and exclusive-to-Kevlar cutting tools) nor well suited to your project. On the scale of stiffness and strength for common reinforcements, Kevlar is softest.

Carbon fiber > S-glass > E-glass > Kevlar
Sep 12, 2013, 05:27 PM
Registered User
Cheese5's Avatar
Quote:
Originally Posted by Koo
@ Cheese5 I've seen that video and the fact that he did all that without an OSD or autopilot is really cool. And the skywalker x8 is actually a flying wing :P
Ah I thought you meant this one http://www.fpvhobby.com/24-168-cm-wi...-airplane.html which is another wildly popular FPV airplane. How will you make sure all the electronics will be working at minus some Fahrenheit degrees? Lipo batteries don't like to be in the cold .
Sep 12, 2013, 09:22 PM
Koo
Koo
Registered User
Thread OP
Quote:
Originally Posted by Cheese5
Ah I thought you meant this one http://www.fpvhobby.com/24-168-cm-wi...-airplane.html which is another wildly popular FPV airplane. How will you make sure all the electronics will be working at minus some Fahrenheit degrees? Lipo batteries don't like to be in the cold .
Haha no problem, I actually have that exact same plane. We will most likely use fibergrass insulation and have couple handwarms in as well. Foam is also a great insulator so I don't think this will be a problem.
Sep 13, 2013, 05:20 AM
On a holiday?
boopidoo's Avatar
Quote:
Originally Posted by Koo
Would there be a better airframe than the x8? We need to be able to carry decent payload of around 3-4lbs not including the power system so zeph and rvjet won't work.
The RVJET can handle 2kg payload but it might not be able to handle the volume.
Sep 15, 2013, 12:29 PM
On a holiday?
boopidoo's Avatar
Update, just learned of a guy flying the RVJET with its short wing configuration and a AUW of 8lb. That's more payload then what you need. Also the RVJET in its short wing config can handle very high speeds without mods.

Also I would use either APM or maybe RVOSD but the former might have, as of now, more advanced GS options.
Sep 16, 2013, 06:25 PM
Registered User
Ramz Innovations's Avatar
Very cool project! You might consider reinforcing the wing by inserting a carbon graphite rod, as well as vacuum forming a strip of carbon fiber fabric across the leading edge.
Sep 16, 2013, 07:02 PM
Registered User
Daemon's Avatar
Yes, carbon cloth will mess with your Rf signals. Carbon joiners, spars, and other
reinforcing rods and ribbons have little effect, bu any solid expanse of cloth
will cause problems.


Quote:
Originally Posted by Dauntless Stan
Correct, Kevlar is neither fun to cut (we use specialized, expensive and exclusive-to-Kevlar cutting tools) nor well suited to your project. On the scale of stiffness and strength for common reinforcements, Kevlar is softest.

Carbon fiber > S-glass > E-glass > Kevlar
Actually, Kevlar is quite easy to cut.
The trick is to take any set of scissors (expensive or cheap as you like) and "ruin" the edges
by either filing or grinding em briefly at exactly 90 degrees. Basically you're putting
micro-teeth in the edges that grab the individual Kevlar fibers as it cuts. After that treatment
it cuts Kevlar cloth like butter. The edge will last through a project or two, then must re-apply,
but the technique is very fast, and works incredibly well.

Kevlar works quite well as a strengthener of EPO foam (common to all these
airframes) because it will not crack like glass or carbon cloth on moderate
impacts. It's also light and pretty easy to apply, although again it takes a trick.
You spray a dusting of Super 77 spray adhesive over one side, stick it down to the foam
and spread it out with a card till it's smooth, then hit it with thin CA (with lots of ventilation,
because the fumes are pretty intense). I spread the CA out using a thin piece of flexible
plastic, or just smooth side of some thick clear packing tape stuck to my fingers. The result
is a smooth, light, rigid surface, with excellent bonding to the foam. Thin CA
saturates the Kevlar fibers better than almost anything else, and it bonds
to the EPO chemically.

Another way to strengthen the X8 wings is with the use of iron-on laminating film,
3 or 5 mil thick. Just have to be aware that most of the wing is behind the CG, so if you
cover the whole thing with a thick laminate (or any epoxy impregnated cloth),
it will be tail-heavy with a normal payload. If you need a heavier
than normal payload, then it'll probably balance fine with the whole wing covered,
although your payload may be competing for space with the batteries in the nose.

The stock X8 wing joiner/spar is way too small. The wings (even stiffened) will flap
at speed, because of it. I enlarged mine to 1/2" OD, which takes some
work to drill out the the holes. I cut teeth into the end of my larger joiner tube
and then slid it in over the top of the stock joiner while turning to drill into the foam.
Takes a while, and plenty of sweat, but it's needed for a fast X8.

The stock foam elevons need to be replaced with stiff balsa and hinged well.
Servo linkage run on top of the wing rather than bottom.

Even with these mods and more, I'd be real leery of trying to push this plane over 100mph,
which it will surely experience being dropped from the edge of space. It is just
so big, and the aerodynamic forces so great, that I would expect it to flutter.
It's really hard to keep a large swept wing from twisting.
You might be able to avoid it if you permanently attach the wing halves
to the fuse, and span the fuse and wing with your covering of choice. Maybe.

The Funjet (used in the vid above), works great as a space-plane because it's
so small and light. Aerodynamic forces are smaller, it slows down faster as the air thickens,
and the rigidity is greater with smaller dimensions. Not to mention the straight wing
will tend to twist less at high speeds.
Sep 17, 2013, 08:39 AM
Suspended Account
Quote:
Originally Posted by Daemon
Yes, carbon cloth will mess with your Rf signals. Carbon joiners, spars, and other
reinforcing rods and ribbons have little effect, bu any solid expanse of cloth
will cause problems.




Actually, Kevlar is quite easy to cut.
The trick is to take any set of scissors (expensive or cheap as you like) and "ruin" the edges
by either filing or grinding em briefly at exactly 90 degrees. Basically you're putting
micro-teeth in the edges that grab the individual Kevlar fibers as it cuts. After that treatment
it cuts Kevlar cloth like butter. The edge will last through a project or two, then must re-apply,
but the technique is very fast, and works incredibly well.

Kevlar works quite well as a strengthener of EPO foam (common to all these
airframes) because it will not crack like glass or carbon cloth on moderate
impacts. It's also light and pretty easy to apply, although again it takes a trick.
You spray a dusting of Super 77 spray adhesive over one side, stick it down to the foam
and spread it out with a card till it's smooth, then hit it with thin CA (with lots of ventilation,
because the fumes are pretty intense). I spread the CA out using a thin piece of flexible
plastic, or just smooth side of some thick clear packing tape stuck to my fingers. The result
is a smooth, light, rigid surface, with excellent bonding to the foam. Thin CA
saturates the Kevlar fibers better than almost anything else, and it bonds
to the EPO chemically.

Another way to strengthen the X8 wings is with the use of iron-on laminating film,
3 or 5 mil thick. Just have to be aware that most of the wing is behind the CG, so if you
cover the whole thing with a thick laminate (or any epoxy impregnated cloth),
it will be tail-heavy with a normal payload. If you need a heavier
than normal payload, then it'll probably balance fine with the whole wing covered,
although your payload may be competing for space with the batteries in the nose.

The stock X8 wing joiner/spar is way too small. The wings (even stiffened) will flap
at speed, because of it. I enlarged mine to 1/2" OD, which takes some
work to drill out the the holes. I cut teeth into the end of my larger joiner tube
and then slid it in over the top of the stock joiner while turning to drill into the foam.
Takes a while, and plenty of sweat, but it's needed for a fast X8.

The stock foam elevons need to be replaced with stiff balsa and hinged well.
Servo linkage run on top of the wing rather than bottom.

Even with these mods and more, I'd be real leery of trying to push this plane over 100mph,
which it will surely experience being dropped from the edge of space. It is just
so big, and the aerodynamic forces so great, that I would expect it to flutter.
It's really hard to keep a large swept wing from twisting.
You might be able to avoid it if you permanently attach the wing halves
to the fuse, and span the fuse and wing with your covering of choice. Maybe.

The Funjet (used in the vid above), works great as a space-plane because it's
so small and light. Aerodynamic forces are smaller, it slows down faster as the air thickens,
and the rigidity is greater with smaller dimensions. Not to mention the straight wing
will tend to twist less at high speeds.

Cutting kevlar is even easier if you put masking tape on both sides of it
Sep 17, 2013, 08:51 AM
Registered User
Ramz Innovations's Avatar
Quote:
Originally Posted by David22
Cutting kevlar is even easier if you put masking tape on both sides of it
Lol, that was my though exactly. I do the same for CF fabric. I'm gonna say it again, at last do the leading edge of the wing with CF so it wraps from the top surface to the bottom. I've seen it done on actual aircraft when i worked for Cambata aviation at Starport. This will not only strengthen the wing in multiple directions as well as protect the leading edge with minimal added weight. A carbon graphite rod running through the wing will help too but may not be necessary. Best of luck on your project, can't wait to see how it goes!
Last edited by Ramz Innovations; Sep 17, 2013 at 10:05 AM.


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