|May 24, 2011, 03:29 AM|
Grumman Albatross Twin Engine
Finally, she's ready for maiden flight!
Original plans (intended for paper) are from http://www.bobscardmodels.net76.net/ .
The plane is made of Epp (3mm), Depron (mostly 3mm, some 6mm) and the wing has a balsa spar.
- Winspan aprox.: 52cm
- Length aprox.. 39cm
- estimated weigth : 50g
- AR6400 just rudder and elevator
- 2 x PZ J-3 Cub motor/gearbox/prop in parallel (Amp reading with cold motors, full throtle : 1,91amp at most)
I haven't maidened it yet, but glidetests are good. CG seems correct and it doesn't look like all these cables in the wing sets it to high vertically either.
During glidetests, she also showed her ability to auto-stabilize her flight. I might have got that dihedral and the V right this time!
Additionnal landinggear is under constrution
|May 24, 2011, 05:43 AM|
The upper part of the fuselage is made out of 3mm Epp sheets, while the bottom is made of 3mm Depron. The Plan's drawing gives the fuselage it's form naturally (more or less:-)).
I first made, seperately, the bottom of the fuselage (in 3 main pieces). The upper section from the nose to just behind the cabin. The upper main fuselage, from behind the cabin to and with the tail. Allready then form was taking. Then, with two bulkheads, I assembled the upper main and the two lower main fuselages. Same for the nose/cabin section...
Look at these plans, they're more or less exacly what I did : http://www.bobscardmodels.net76.net/
Of course it requires a lot of cutting, sanding, bending and adjusting!... But it's great fun
Wingspan is aprox. 52cm and length aprox. 39cm
|May 25, 2011, 07:28 PM|
Finaly maidened her! And she flew!
I started with some glidetests to verify CG and trims. Sure she isn't a glider, but CG was confirmed suitable and no trim were needed. She didn't show any signs of disymmetry or bad behaviour. Made a few turns, just good. So far so good!
Next step: Simple gentle trow, with engines on, just flying straight. I was quiet scared of this flight-test-step. Would the motors have the right angels, what would they induce on the planes flight? ... Well, she just flew staight! Yupi!
Only thing thing left to do was to perform her first powered flight with turns. Maiden flight ! : Facing the wind, throtle at approx. 50%, a very gentle throw and there she went. The trust/weight ratio is good, she is climbing decently to the sky. Pitch control is soft but precise, no stall in sight. Throtle does affect the pitch just enough, but not to much (like on a real one). Getting to the first turn, I started pulling on the rudder... she started banking slowly and very softly, I barely had to correct the pitch. No noticeable loss in altitude while turnigng (without pitch correction) and the nose didn't want to point out of the turn, but followed it better than I did expect. She did turn better to one side than the other, I must correct those angels on the motors. Getting out of a turn needs quite some opposite rudder and the shifts are very slow. It does need anticipation.
My very first general impression of the Grumman Albatross's flight is astonnishingly good and it is satisfying for me how well she flies. Controls are respondant and precise, even if induced banking is slow. It makes it look relly realistic, massive, imposing! Thrust is there and the motor angels are allmost good. Speed is low, comparable to a UM T-28. It looks like she can handle some wind.
WHAT A GREAT SUCCESS !!
I'll try to get somebody to film soon, so I can post a/some flightvideo(s).
|May 25, 2011, 07:38 PM|
I think I might want to build another one, but this time with ailerons maybe also with separate flaps?... I still have to finish the landinggear (dismountable) for this one...
...then, do I want to make it floatable ? ...
|Aug 22, 2011, 06:13 AM|
Chrizz that one slick lil plane. I do want to build this, I would live to see how you have the RX, ESC and the motors wired and set up. I was thinking about using my old PZ Cub guts and a second PZ Cub motor wired in parallel but i wasnt sure if the esc would handle the extra amps. Whats your take on this. Thanks for sharing your link with me.
|Aug 22, 2011, 10:11 AM|
Using two UM Cub J-3's motor/gear/prop setups in parallel is a nice idea, but I'm not sure that the 3-channel brick from a UM Cub J-3 will handle the necesary amps. I do know, that it works fine with i.e. a AR6400, since the two motor/gearbox/prop setups will draw around 1,91 amp (max reading with new, cold, motors at imediate maximum throttle) and that a AR6400 allows 2 amps. Check out if the Cub's brick also will handle 2 amps or not and do keep in mind that the motors will draw more amps while aging. You'll need to check amp-readings regularly to be sure.
If you look towards the end of the first video, you'll see the inside of the fuselage with some of the (only) two cables going up to the wing and the connecter I've installed to ease the acces for amp readings.
If the UM Cub J-3's brick isn't enough and you then get i.e. an AR6400, you could consider adding ailerons to the build (single servo with bellcrank or double servos with flap/spoiler programming option?). Or Ailerons and flaps!? I'm sure weight would not be that a big issue with the twin UM Cub J-3 setup.
It would of course add some building to the project. On my Grumman Albatross there are no ailerons or flaps... Its wing is made like on Bobscardmodels plan: two wing formed sheets, extrados and intrados (for each half wing). The extrados is a bit larger than the intrados, so that when glued together, the larger extrados (made of flexible 3mm EPP) forms a curve while the intrados (3mm Depron, stiff) remains flat. To obtain a look-alike Clark Y profile, the intrados leading and trailing edges has been cut to angles that leads the extrados to a correct curve. At the same time the angles helps reducing the edges thicknesses.
I think it would be farely easy to cut out the ailerons of both intra- and extrados. Then not cut an angle in the intrados where the ailerons are located, but only along the rest of the trailing edge. Glue it together giving the wing its profile and then sand down some ailerons out of 6mm Depron. The same thing could then also be done for flaps.
Whether build with one or two servos for ailerons, an interesting question is, if the servo(s) should be mounted inside the fuselage with torsion bars connecting it (them) to the ailerons. It would look prettier that two servos mounted under the wind for a dirrect attack on the ailerons. Another solution could also be to try to place them in the motor nacels, or even in the thickness of the wing. ???
|Aug 29, 2011, 11:06 AM|
Some good ideas in there, I will keep you posted on how it goes, I will likely have to send it to Kwinters to test fly it for me, I ahve already been warned that anyting I try to fly here will be taken. Being im so close the LZ i wont be allowed to fly. Bummer.
I figured out the building board situation, Amazon had some laptop boads that look like they will work well. Made of EPP like my kayaks so warping shouldnt be a problem.
|Aug 29, 2011, 05:00 PM|
|Aug 31, 2011, 04:02 AM|
I like it very much! Good work!
This could be a nice project for me, as i was planning to build a seaplane (there is a little lake nearby).
I would make a 24" ws version with EPP.
|Dec 30, 2012, 02:37 PM|
Starting a second build, but with ailerons and flaps!
I've been wanting to build another version of a Grumman Albartoss, but this time with ailerons and flaps.
The precedent build was a simple RET with dihedral. It flew great, almost like a trainer, but was slow to react on yaw-input, with its relatively small rudder and the twin-engine setup. Still it flew great, but needed quite some anticipation.
After a lot of thinking, I've decided to setup both ailerons for a single servo and to link the two flaps to one single servo too.
I've considered having a servo per aileron (more precise control, stronger, mixing possibilities: fine tuning- differential- flap/spoileron), but the challenge of building a single servo system with hidden linkages and bellcranks inside the wing, while hopefully saving some weight and maybe even some electrons (?), is too tempting!
The flaps will use the same setup as seen on HH's UM T-28's ailerons, mounted beneath the wing (the wing is 6mm thick where the scotch-tape-hinges are located, which will give the flaps a nice movement downward). Both flaps will be linked to a single AR2000l inside the fuselage.
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