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Yokosuka 'Ohka' RC Rocket Glider
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g_boxwood



Anmeldungsdatum: 08.06.2006
Beiträge: 172

BeitragVerfasst am: Do 05 Jun 2008, 19:49    Titel: Antworten mit Zitat

The cockpit on the plans (black outline) is really off-scale and I re-drew it according to 3 views of the aircraft (red line):



Next I made a lite-ply frame...



... and filled it with foam (I hate foam, did you get it?):







I'm now in the process to give this 'thing' a decent shape before glassing and finishing it to become a vacuum-forming plug.

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g_boxwood



Anmeldungsdatum: 08.06.2006
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BeitragVerfasst am: Do 05 Jun 2008, 20:09    Titel: Antworten mit Zitat

Juerg hat folgendes geschrieben:
Hi Giacomo

"Long time no see"! Wink

I know, but I didn't quit, just turned to airplanes for a while.

Juergh hat folgendes geschrieben:
What motors are planned? A G12 is on the low side for take-off, unless you use two motors in sequence like on the test glider...


That is THE point. Actually the real and only difference with the featured article is that WE'd like to launch it on the pad (60 to 45° above hor, 45° being already off rules).

The G12 and almost all the RC 32 mm reloads are rather weak in thrust so this is what I came up with:

[1] single 29 mm G38

[3] D12P in a cluster and/or

[3] D12-0 to [3] D12P or [3]E9P

Juerg hat folgendes geschrieben:
Why a 60mm motor mount?
Sounds like a very weird selection?!

This is why I made my own 60 mm ID MMT so I can switch between motor configurations (from left to right, single 32 mm, 24 mm cluster and single 29 mm):



Both configurations sport out around 36 N avg. thrust which gives a 3:1 thrust-to-weight ratio with rather short burntimes... only the time will tell...

I'm building it to be towed so I can test-fly it before attempting more hazardous methods of getting it airborne.

I'll get you updated and this is why I posted.

BTW, this is how I molded my MMT:

. mandrel + mylar + first glass hose layer



. 1 mm balsa core





. second glass hose layer



. finished tube, mandrel and mylar


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Andy



Anmeldungsdatum: 05.03.2005
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BeitragVerfasst am: Do 05 Jun 2008, 21:22    Titel: Antworten mit Zitat

Hi Giacomo

Shocked
Wow, this is a really great construction!
You better don't tell us how much time you invested to design and build this rocket glider, but it's worth each second.

Which software did you use for designing?
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Juerg
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BeitragVerfasst am: Do 05 Jun 2008, 21:56    Titel: Antworten mit Zitat

g_boxwood hat folgendes geschrieben:
Juerg hat folgendes geschrieben:
What motors are planned? A G12 is on the low side for take-off, unless you use two motors in sequence like on the test glider...


That is THE point. Actually the real and only difference with the featured article is that WE'd like to launch it on the pad (60 to 45° above hor, 45° being already off rules).

The G12 and almost all the RC 32 mm reloads are rather weak in thrust


Hi Giacomo

Well, have you ever considered one G12 plus some "booster" for launch.
This could be either a ring of 18mm Blackpowder motors around the G12 (I don't think there is enough space) or some "drop-off" booster staging to the G12, like seen on Tomahawk cruise missiles.
You also could use a "drop-off" booster under the belly like it was used on Matador.
Booster recovery released after it was dropped, to stay safety-code compliant.
Once launched the G12 will be great for a scale-like flight.
Or a catapult of course.
Unfortunately the 60mm mount doesn't leave space for two G12's...
Another option: G12 and F39 one above the other, the F39 beeing a booster for Liftoff...

Cheers

Juerg



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g_boxwood



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BeitragVerfasst am: Do 05 Jun 2008, 22:12    Titel: Antworten mit Zitat

Andy hat folgendes geschrieben:
Hi Giacomo

Shocked
Wow, this is a really great construction!
You better don't tell us how much time you invested to design and build this rocket glider, but it's worth each second.

Which software did you use for designing?

Hi Andy and thank you for stopping by.

I usually draw in Rhinoceros and render in Penguin (non-photorealistic renderer sold as a plug-in for both Rhinoceros and AutoCAD): Rhino isn't the best available but it is fast-learning and complete.

http://www.rhino3d.com/

http://www.penguin3d.com/

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TRA#9986 L2


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g_boxwood



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BeitragVerfasst am: Do 05 Jun 2008, 22:15    Titel: Antworten mit Zitat

Juerg hat folgendes geschrieben:
Hi Giacomo

Well, have you ever considered one G12 plus some "booster" for launch.
This could be either a ring of 18mm Blackpowder motors around the G12 (I don't think there is enough space) or some "drop-off" booster staging to the G12, like seen on Tomahawk cruise missiles.
You also could use a "drop-off" booster under the belly like it was used on Matador.
Booster recovery released after it was dropped, to stay safety-code compliant.
Once launched the G12 will be great for a scale-like flight.
Or a catapult of course.
Unfortunately the 60mm mount doesn't leave space for two G12's...
Another option: G12 and F39 one above the other, the F39 beeing a booster for Liftoff...

Many useful hints, I'll consider each of them!

What about the single G38: do you think it is too much or not scale enough (due to the rshort burntime)? Single=simpler=more reliable=safer, this is why I preferred it.

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Juerg
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BeitragVerfasst am: Do 05 Jun 2008, 22:28    Titel: Antworten mit Zitat

g_boxwood hat folgendes geschrieben:
What about the single G38: do you think it is too much or not scale enough (due to the rshort burntime)? Single=simpler=more reliable=safer, this is why I preferred it.

The G38 will be a good motor to start with, to trim the aerodynamics. But the burn is only 2 seconds, compared to the 7 seconds of a G12...

Cheers

Juerg

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Guido



Anmeldungsdatum: 06.03.2005
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BeitragVerfasst am: Fr 06 Jun 2008, 8:29    Titel: Antworten mit Zitat

Ciao Giacomo

Cant talk at the moment, still searching for my jaw, which droped somewhere below the table... Just great what you're building...!

Regards

Guido

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BeitragVerfasst am: Fr 06 Jun 2008, 9:08    Titel: Antworten mit Zitat

Juerg hat folgendes geschrieben:
The G38 will be a good motor to start with, to trim the aerodynamics. But the burn is only 2 seconds, compared to the 7 seconds of a G12...

I was a bit more optimistic about the burntime, I was thinking about 3-4 seconds... dunno why!? It's 2.1 as you said and it is way too short...

The G40 is around 3 seconds and may be better but still short.

Fact is G38/G40 are no more available, next options in the 29 mm SU are the F Econojets... with a max burntime of around 3 seconds and much less thrust...

In case of an air-start: is there any commercial unit that could fire the igniter safely and reliably via servo input (mechanical) or via the receiver (interpreting the servo impulse of the assigned channel, PPM or PCM or both, as the 'fire' instruction)? Is there any?

In case not, what do I have to consider to design one that meets safety and common-sense requirements? I'm not that good in electronics but some friends are.

It could be a useful unit in the end.

Thank you Guido!



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BeitragVerfasst am: Fr 06 Jun 2008, 12:44    Titel: Antworten mit Zitat

g_boxwood hat folgendes geschrieben:
Juerg hat folgendes geschrieben:
The G38 will be a good motor to start with, to trim the aerodynamics. But the burn is only 2 seconds, compared to the 7 seconds of a G12...

I was a bit more optimistic about the burntime, I was thinking about 3-4 seconds... dunno why!? It's 2.1 as you said and it is way too short...


I can tell you why: In the printed catalog there is a misprint of the G38 thrust curve, scale on the time axis is wrong.

As far as ignition is concerned, G-Wiz can handle this. You may need an external Relay Board to switch a high-current (12v) battery, but assuming you will need nose weight anyway, this shouldn't be a problem.
Or some own electronics... as you don't really need more than launch detect and timing.

Cheers

Juerg

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alessio



Anmeldungsdatum: 05.09.2007
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BeitragVerfasst am: Fr 06 Jun 2008, 14:48    Titel: Antworten mit Zitat

g_boxwood hat folgendes geschrieben:


In case of an air-start: is there any commercial unit that could fire the igniter safely and reliably via servo input (mechanical) or via the receiver (interpreting the servo impulse of the assigned channel, PPM or PCM or both, as the 'fire' instruction)? Is there any?


Thank you Guido!


looks like stefano may have something....

http://www.sierrafoxhobbies.com/catalog/product_info.php/products_id/875

or you can try to use a "old"regulator for brused motors..
they can handle a lot of current..

alessio

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BeitragVerfasst am: Fr 06 Jun 2008, 17:06    Titel: Antworten mit Zitat

ti-flyer hat folgendes geschrieben:
looks like stefano may have something....

http://www.sierrafoxhobbies.com/catalog/product_info.php/products_id/875

Unfortunately this unit won't do it (as is). It is designed for e-matches but Giacomo needs Magnelites.
So lots of current for considerable time and specially: 12V!
But Stefano's unit could drive a relay...

Also, strictly speaking an RC Control is not needed and adding a point ud uncertaincy (hitting the right moment).
All what is needed is launch detect (trip wire in parallel to arming switch) triggering a 1-2 second timer triggering a 1second duration high current relay for ignition. (Ignition circuit again with safety switch)
A simple NE556 and some external elements can do this.
The difficult part is the battery: 12V, lightweight, high current.

But as there is only one motor to ignite one or two 9V Alkaline blocks may work. This needs to be tested, as a fast and predictable ignition is required.
If there is not enough current, the magnelite may take a second or two to light.
If there is too much voltage (tricky point with 2 9V blocks) the igniter may spit away its pyrogen instead of lighting it.

Cheers

Juerg

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BeitragVerfasst am: Fr 06 Jun 2008, 19:14    Titel: Antworten mit Zitat

Alessio: that's exactly what I meant! Thank you 'cause I never noticed it!

Juergh: what about the above unit with e.matches as igniters?

I used them twice to light some J135Ws I had no luck with Magnelites but I was not the one who made them: they belonged to J. L. Sanchez and they worked pretty fine.

I regret using a 12V battery on board... a Li-Po @ 11.1 V may work but I don't have any. Again, e.matches as igniters and a single or double 9V may do the job.

I'm talking about air-starting after a regular tow to height (less critical) or after a bungee-launch (more critical).

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BeitragVerfasst am: Fr 06 Jun 2008, 20:24    Titel: Antworten mit Zitat

Giacomo

E-Matches to light J135?
But not the e-match alone then! The don't generate enough heat.
The problem ist that a J135 has a rather large nozzle, hwoever you will not even be able to insert an e-match into a "G" motors nozzle.

Cheers

Juerg

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BeitragVerfasst am: Fr 06 Jun 2008, 20:29    Titel: Antworten mit Zitat

Hi Giacomo

Great Plane that you're building!

In my glider I used a normal controller for R/C electrical powerd models. 8 cells of a NiCd or NiMH battery are enough for a first fire or Magnlight igniter. Maybe that could fit for your needs?

Andi

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