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Old Jun 10, 2007, 06:04 PM
Bernoulli+Newton=Lift
magic612's Avatar
Somewhere south of Chicago, IL
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Despretz J1-31 lives again...

Quote:
Originally Posted by Dereck
Anyway, not this week as I've gotten back to busy, but here's a cute little three view I picked up from an old RCM clipping someone gave me. All I know about the aircraft is that it's called the "Spretz Flash" - no idea of size, country of origin or even it ever got built, let alone flown.

But it sure is cute and different. Once I can find my workbench again, I intend to start in time honoured fashion with a free flying 'chuck glider' version around 18" span, to check out the CG. It'll have to have some dihedral, which my three view shows the full size to be completely lacking in. This will be used to figure a CG start point and the design's basic stability attributes (or lack thereof )

Depending on inclination and spare motors, I'd be looking at either a 36" or 48" RC version, with an imaginative colour scheme.
(Yes, this quote is from WAY back at post 78!!!)

Dereck, I don't know if you (or anyone else?) ever got around to building a J1-31 Despretz Flash or not, but I was intrigued by this model back when you posted the 3-view. I made a "chuck glider" with days of you posting the 3-view, and it's been sitting on a shelf in my kitchen for the last 5 months.

Well, I finally got around to building a full, fuselage R/C version.

Construction material is Dow blue Protection Board. I tried to keep modifications from the original to a minimum. I made the rudder a tad longer, since it seemed a bit small, and I figured I could always expo it or use EPA's on it. The wings are not semi-symmetrical as the original plane was - since this is just a 36" wingspan craft, I went with a 4-40 airfoil on both the canard and main wing. Canard incidence is +5 degrees, main wing is +3. Main wing is slightly lower than original plan, but that was necessary due to airfoil shape.

I originally thought of using a brushed 280 motor on this plane, which would probably have been okay if I'd had a GWS EDP150. Since mine was an EDP100, the thrust was about half the 150, and it wasn't enough "oomph" for a 10 ounce plane. So I swapped that for a 24 gram blue Hextronic brushless motor and a fairly paltry 8x3.8 APC propellor (which sips just 3.3A at WOT). Using a 7.4V 800mAh Lipo, I gave her a toss - here's the maiden flight with the brushless motor:

http://www.rcgroups.com/forums/showt...73#post7605583

Pictures are below - the first pics are with the planned 280 motor, which later was swapped for the brushless after I discovered the lack of thrust.

It flies quite nicely. Not particularly aerobatic, as the loop I pulled was quite large and not very straight, though in fairness it was the maiden flight. I'll try an 11.V pack later. It turns well with the rudder too, even with no dihedral built in.

I should note that I have the front canard flaps attached to the rear elevons, but in order to do this properly, I needed to have the left elevon be hooked to the front right canard flap, and vice versa. I realized this after mentally thinking how the plane would turn with the flaps done with the linkage on the same side, and concluded that I needed to do some fancier linkages. Fortunately, they work just fine, and are barely noticeable - note the picture on the picnic table showing the side view.

EDIT: spelling / grammar
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Old Jun 11, 2007, 12:09 AM
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Congratulations on your achievment,Magic. Post 90 and others show your great imagination. I know Dereck must be happy to see his thoughts come to pass. Charles
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Old Jun 11, 2007, 09:36 AM
Bernoulli+Newton=Lift
magic612's Avatar
Somewhere south of Chicago, IL
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Thanks for the congrats, Charles. I hope Dereck is excited about this. I wish I had a video camera that would zoom in - my digital camera in movie mode doesn't do this plane much justice.

I did try it yesterday evening with an 11.1V pack - BIG difference in performance. Loops with authority - inside AND outside loops! I'm not very good at rolls yet, so hard to say if they are nice or not. Inverted flight - no problem; very stable, even with an undercambered airfoil. And the really interesting thing it does is stopping on a dime when pulling out of a dive - must be the combination elevons / canard flaps working in tandem. It's quite the sight to see - high altitude, straight-down dive, full back on the stick - BAM! Snaps right into forward flight again. Very interesting to watch.

So I need to amend my prior statement about this plane not being particularly aerobatic. I said that when using a 7.4V pack, and in that set up, she's a very sedate, predictable flyer. With 11.1V, she'll still do that - even with the extra weight - but when desired, will take off and do some pretty fun stuff. And it just looks so different in the air, too. Quite the sight to see.
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Old Jun 11, 2007, 11:34 AM
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magic, have any plans for the j-31`? looks like a fun one to build. I finished my 36" LEZ and need to maiden
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Old Jun 11, 2007, 01:34 PM
Rhinebeck CD-99,00,01,02
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New Bern, NC
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I could be interested in building one of them too. Got plans ? ? ? ?
Kyle, I maidened my Horizon E Cub today. Put a 450 watt Hacker 30-10XL in the nose, and it flies great. It will take off at 1/2 throttle. What a sweet flyer. Wednesday my AXI powered Bird of Time goes out to the field with me, and Friday my Long EZ Voyager. Any word on Jeff's park jet rally.
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Old Jun 11, 2007, 01:49 PM
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Tom,great to hear about the Cub. Might have to do a .25 seaplane up soon to go along with my GP PBY and Formosa Twin I'm building. Think I'm taking the LEZ out soon.will try to get pics and maybe video.
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Old Jun 11, 2007, 03:15 PM
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Magic, Your model is interesting with the large amount of stagger or separation of the wings. I believe this is the reason for the quick change of pace from the dive. Changing to three cells was wise because amperage increases on a straight line with voltage but power increases with the square of the amperage. Two cell lipolys are OK for small indoor models. It is great to see the apparent increase of interest in canards and the fun we are having. I have been driven by you all to get back to work. I call my new design a double delta canard. The rear wing is low and the front wing is high. The wings are not true deltas but the top view will give the overall outline of a delta. I intend to show pictures as the build progresses. The chuck glider is stable and has a gradual recovery from stall when tossed upward. It required at least 3.5 degrees of incidence up front to glide well. Kyle, good luck with the maiden. Charles Edit: When starting to build wing, raise the hardwood landing gear mount 3/32 inch with shims to allow the 3/32" wire LG to be flush with bottom of wing.
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Old Jun 11, 2007, 04:16 PM
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Tom,heres the thread for the jet event. Sorry for the delay,hope to see you there http://www.rcgroups.com/forums/showthread.php?t=693004
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Old Jun 11, 2007, 05:55 PM
Bernoulli+Newton=Lift
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Quote:
Originally Posted by canard addict
amperage increases on a straight line with voltage but power increases with the square of the amperage.
I did not know that - learn something new every day. Thanks, Charles!


Quote:
Originally Posted by canard addict
I call my new design a double delta canard. The rear wing is low and the front wing is high. The wings are not true deltas but the top view will give the overall outline of a delta. I intend to show pictures as the build progresses. The chuck glider is stable and has a gradual recovery from stall when tossed upward. It required at least 3.5 degrees of incidence up front to glide well.
You might want to take a look at the Star Cobra thread in the Scratchbuilt Foamies section. Sounds like a similar design with a low wing and high canard. I know I learned some things by reading that thread which I applied to the J1-31 (notably, that a canard near the COG doesn't lift well, and works best with the linkages mixed with elevons).

Let us know how your work progresses!!
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Old Jun 11, 2007, 09:56 PM
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I'm in love with a LONG EZ

Well guys had the maiden and second flight. Only thing that could be better is the lack of aileron trim(bad radio) and having to use full up elevator trim to keep it almost straight and level. Flies great,rolls nice,inverted is great. Just a great plane overall and landings are a dream. Only got pre and post maiden pics no video yet but soon.
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Old Jun 11, 2007, 10:06 PM
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Thanks, Magic for the great string of threads. I can' t seem to keep up with all the canard threads and really thought I had a new style of model in the works. My Idea must have had it's start with the Firebat which has been flown as a delta or with canard. My design is 36" by 36" and the center of lift of the canard is 10.5" forward of the COG. I am considering elevons with elevator if that is possible without using linkages but I feel it may work OK with ailerons-elevator. Charles
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Old Jun 11, 2007, 10:17 PM
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Nice going with the EZ,Kyle!! You would love the ground handling with the 2.5" Maxx Products wheels. If the COG is right on,you may need to add a little UP reflex to the ailerons. Charles
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Old Jun 11, 2007, 10:36 PM
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Thanks Charles,the ground handlings pretty good with the stock wheels and I like the looks. I have a very nice Firebat to get going soon my friend built,covered and modified with twin rudder and fixed shock absorbing lg with a steerable nose wheel.Should be fun to,he flew it as a delta but I'm glassingthe canard back on.
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Old Jun 11, 2007, 11:15 PM
Rhinebeck CD-99,00,01,02
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Wish I still had my Firebat. It flew great.
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Old Jun 12, 2007, 02:48 PM
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Firebat

If my Firebat could return, It would be changed to elevons. Charles
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