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Old Jul 20, 2010, 02:45 AM
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I don't know why they chose it, the wing folding mechanism is a clever suggestion, but to my knowledge, the Airfish doesn't actually have this mechanism, the wings can only be pulled of and reattached completely.

The other thing could be that they tried to increase the efficiency of the wings, by making a sort of combo between a square and a lippisch ram wing. I don't know, it just made the model a lit more twitchy.

At the moment I am playing around more with the tandem concept, the positive stability in GE & in higher altitude flight really opened up another book on these crafts.

Marijn
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Old Jul 20, 2010, 03:41 PM
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did the airfish with the flat center have the same aspect ratio as your little one did?
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Old Jul 20, 2010, 04:10 PM
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It is as good as the same, I have three different plans of the Airfish and they all differ just a small bit. The angle of attack of the centre part(and thus the anhedral) is a bit larger than one the actual thing, I guess.

Ahwell, the model works, just not better than the other model. Are you building another model lately Derk? You said something about electronics trouble

Marijn
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Old Jul 20, 2010, 06:14 PM
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ah yeah i figured out that the esc i was using couldnt handle the 3 servos i had in it. it was weird because it acted like the receiver was going out, 2 servos still worked but it lost esc control and it was getting hot. i tested the receiver with a different esc and it still works so i need to swap out the one i have in it.
it may all be for nothing since it didnt fly well without power

i have a large supply of depron and have been thinking of making a larger lippisch with a thick wing for slow speed. big and light should make it easier to turn around in smaller spaces.

too many projects, not enough effort to go around lol
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Old Jul 21, 2010, 02:46 AM
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Haha nice, I am building a old Robbe Commander next to these WIG's, I glassed it and am now installing two brushless outrunners(power!), so the WIG's sometimes get shoved of the building table to continue on other stuff.

I did however work out the Tandem concept further, I am still amazed by the fact that I managed to get it to be really reliable. The current angle/CG distribution looks like this and works great:


I found some old documents, written by Gunther Jörg, the designer of the Tandem Flairboat(TAF) series, where it was actually described thet the front wing is the one which really lifts, the rear one is there to provide stability and should be much more offloaded, which actually confirmes the CG positions and profiles I have found to work the best.

That the real TAF boats had aproximately the same CG positions can actually be seen on pictures and drawings:

The craft has 2 hull steps, one is located at the trailing edge of the front wing, the second one located in front of the other one, zo the CG should be somewhere at that position.


You can even see, how they designed it in such a fashion, that the hull stays out of the water as much as possible further behind the CG, otherwise, you wouldn't have enough floatation in front of the CG, compared too behind it, and it would be harder to get it aquaplaning.


Or just look at these drawings, on both drawings the hull is the widest at, or in front of the CG of my model.



Maybe it's time to think of an RC version..

Marijn
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Old Jul 21, 2010, 04:21 AM
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Marijn, it looks like there is a smaller step in the center of the front wing on the hull. (see pictures)
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Old Jul 21, 2010, 05:09 AM
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Quote:
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The craft has 2 hull steps, one is located at the trailing edge of the front wing, the second one located in front of the other one, zo the CG should be somewhere at that position.
haha actually, that is what I meant, I just didn't describe it very clearly

Anyway, I think this confirms that my so far forward CG isn't as rediculous as it looks, and the real TAF boats used it similarly, right? I placed the CG even further forward this morning, which still seemed to improve the recovery handling. I started making drawings for an RC version, I am just worried how to design this thing that it's actually able to reach Take Off speed, without buying a very expensive high performance propulsion unit. On the other side, the Airfish was way overpowered, so I should be able to get a lot more speed out of that engine.

Are you still continuing to build a Lippisch with aileron controll? I really wonder if Aileron controll improves the turn handling, or that it just makes the model crash faster

Marijn
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Old Jul 21, 2010, 06:48 AM
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hey, some time ago I found this videohttp://www.youtube.com/watch?v=0cARt...rom=PL&index=0, I'm thinking two options for rc, the
aircat or tandem.
what do you say?
tandem or aircat?
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Old Jul 21, 2010, 08:44 AM
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Marijn, i still want to do that yeah, just haven't gotten started on anything for it yet. i did try and make some wings from 2mm depron and just base ribs but the foam wont stay straight on the t.e. without some kind of reinforcement so next one will have built up wings.

jjjasesino, the craft in that vid is cool, but i think it may be more of a hovercraft as its using blown air under the wings to make it lift off. thats why the motor is pointed up so far.
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Old Jul 21, 2010, 08:58 AM
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Hey Jorge,

I know the video, I think this guy was inspired by the Tandem WIG of Universal hovercraft:
http://www.hovercraft.com/content/in...x&cPath=30_174

The model in the video is just a crude hovercraft, take a look at the center of gravity(he has the lipo allthe way on the rear), so there is no way it will fly stable like this. Now I don't say that the tandem of Universal hovercraft doesn't really fly, it does, but I think that for a first RC Tandem model it is easier to focus on aerodynamic stability, and not mix in a PAR engine aswell, blowing air under all the wings.

And I would definately go for the aircat! No doupt, build correctly you won't be able to flip it in any way, you can easily use an elevator to reduce the Take off distance, it doesn't rely on the angles of the wings as much of the tandem etc. It is just an easier craft to build and operate Look at Gabriels Bixel model, it's as simple as it can get and performs very well.

@ Derk, havy you tried cutting foam? I never really had the motivation to build a cutter, till someday I connected a small piece of "Konstantaandraad"(Resistance Wire?) to a DC 12V adapter and was able to cut through all the foam blocks I had lying around. Haha I just build a frame of some tubes I had lying around and now I have a ready to go cutter and use it for everything

One of those tools you won't miss if you never had them, but if you ever used them you'll use it for anything.

Marijn
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Old Jul 21, 2010, 09:05 AM
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yeah i have a small cutter i built (cheap) but have not learned the art of wing cutting yet. i have made many thin sheets for indoor rc stuff though. i dont have a shop or workroom for a large building table so i cant use the weighted drawing bow style, it all has to be done by hand (templates and such) so its not so easy for me. i may pull it out again and try with some foam i have on hand and see what happens

i am a big fan of depron foam though, i can make things quickly with it and it needs no finishing on the outside too!
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Old Jul 21, 2010, 12:41 PM
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I have to admit that I don't actually cut wings as professional as others either, most of the times it's just sticking two triplex wing profiles to the siedes of a foam block with double sided tape, and pulling the wire over it with both my hands, a paint pot standing ontop of the block so it won't move.

But Depron is a great material, no doubt. It also results in much lighter constructions, than those cut from pure Styrodur.

@ Jorge, I am waiting for a reply from someone who has bought Aircat plans a long time ago, if he manages to pass them on(i don't think so), I'll upload the plans.

Marijn
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Old Jul 21, 2010, 12:54 PM
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Quote:
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@ Jorge, I am waiting for a reply from someone who has bought Aircat plans a long time ago, if he manages to pass them on(i don't think so), I'll upload the plans.

Marijn
I have much polystyrene. do not care that take much to send the planes, I'll have enough material for a second aircat.

thanks

jorge
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Old Jul 21, 2010, 01:25 PM
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I found some nice pictures of what I believe to be windtunnel or test models of the Jörg company. The White model seems to be an older model, the hydrodynamics seem to bee simpler and less worked out. The other model looks like a scale version of the TAF 4, the largest one with a turboprop.









Marijn
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Old Jul 21, 2010, 08:27 PM
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interesting, looks like they added a small triangle to the front wing roots. perhaps to keep water from coming up off the hull? couldnt be enough aerodynamic significance to be altering airflow really.
the yellow one looks like its built up wood and film covering. looks like the rudder was connected internally, maybe it was controlled testing?

cool find nonetheless
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