Hamilcar - a complete rework!

[quorneng]

Over 2 years ago I built a Hamilcar X out of Depron

It proved to be by far my most unsuccessful plane yet! All 3 flights latested less than 10 seconds and all ended in disaster with a spiral (always to the left) into the ground.
After its third rebuild I was not happy that I had addressed its ills so for the last 18 months it has been 'parked'.

So the time has come to do something about it by giving it a complete rework.

With 3 servo right at the tail (1 rudder + 2 elevator) it was always a struggle to get a suitable CofG so these servos will be repositioned forward just behind the wing with pull/pull cables for each surface.
The servos cut out.

Moving the servo forward also saves the not inconsiderable weight of long servo wires running all the way down the fuselage.
The servos reinstalled.

A short video of the rudder pull/pull cables in action.
https://vimeo.com/56690071

So far so good but there is still a lot to do.
The flap system need to simplified and the linkages strengthened.
The ESCs need to be repositioned to reduce the long (18") battery leads. This will require the engine nacelles to be cut off and rebuilt.

Overall the 3 previous crashes have not been kind to the structure with the load bearing skin becoming unglued in places.

[xmech2k]

Nice! Good luck with it. I love to see the rare birds done!

[baz49exe]

"It proved to be by far my most unsuccessful plane yet! All 3 flights lasted less than 10 seconds and all ended in disaster with a spiral (always to the left) into the ground."

Really interested to see how you resolve this problem.
I have a model from about 4 years ago which has developed this problem and just wants to tip stall out of every turn.
I've tried everything from C of G manipulation to aileron mods without much luck. When I get time I'm going to build a totally new wing with a new airfoil section and plenty of tip washout. If that doesn't work I'll burn it!!!

[quorneng]

baz49exe
I must admit it was only my hurt pride that stopped me scrapping this, I hate to be beaten!

It has huge scale flaps. As originally built it had 4 flap servos with rather long and flexible links. The revised system will use just 2 servos but placed close to the wing trailing edge with short direct links.
Removing the old servos and wiring requires a lot of wing cut outs for access!

The repositioned servo. As the two flaps sections have slightly different hinge lines it requires a double link.

A short video of the flaps on one wing being cycled.
https://vimeo.com/56777857
As it is quite light, and just like the full size, the flaps will only used to achieve a very steep speed controlled approach and landing.

[quorneng]

The RH nacelle rebuilt and the motor installed with its 9x4.5 LH prop.

With temporary electrics in place it is ready to be tested. With a fully built in installation such as this everything has to be tested at each stage of construction!

The next major change is to move the battery forward nearly 2" into the nose area.

The nose itself will no longer be hinged but held in place with magnets.
A bit drastic but it will bring the CofG to about 30% of the root chord. As the outer wing panels have a distinct sweep back the CofG will actually be about 28% of the aerodynamic mean chord, which should be safe enough.

[quorneng]

A 'surface' mounted component?

The MOSFET side of the ESC heat sink is flush with the wing top surface!

I truth I doubt any cooling is really required as even at WOT the ESC is only running at half capacity.

[CHELLIE]

Originally Posted by quorneng

The RH nacelle rebuilt and the motor installed with its 9x4.5 LH prop.
Attachment 165428
With temporary electrics in place it is ready to be tested. With a fully built in installation such as this everything has to be tested at each stage of construction!

The next major change is to move the battery forward nearly 2" into the nose area.
Attachment 165429
The nose itself will no longer be hinged but held in place with magnets.
A bit drastic but it will bring the CofG to about 30% of the root chord. As the outer wing panels have a distinct sweep back the CofG will actually be about 28% of the aerodynamic mean chord, which should be safe enough.

Hi what motors are you using ? i think you might have a low thrust problem, how much thrust are you getting out of your motors, measure it with a digital fishing scale tied on the back of the plane at WOT,

here is a suggestion that may help, use 2 -1800kv motors with 2- 7x6 APC props, and differential throttle, give the motors 3 degrees of down thrust, no right or left thrust, set the CG at 25% of the wings cord, make sure the wing and elevator/stabilizer are set at 0-0 incidence, Hope that helps, Chellie
AX 2308N 1800kv Brushless Micro Motor

http://www.hobbyking.com/hobbyking/s...idProduct=5430

http://www.speedwing.net/minitwin_25...structions.pdf

differential thrust at bottom of page.

[CHELLIE]

I run these 1800kv micro motors at 20 amp they love it, the motor has thick windings, these little motors are a power house.

from what i can see, is that you dont have very much prop wash over the ailerons if any, I would make the ailerons full length and add flap mixing into them, that way you have better aileron control at slow speed, Also give the rudder more throw, from the video you have very little rudder throw. just my 2 cents worth.

http://vimeo.com/56690071

[quorneng]

Hi Chellie
I am using Emax 2212s. In its original form it used 9x3.8 props and the thrust was very close to its weight - held vertical it was virtually prop hanging - so I don't think the static thrust was a problem although there was a very significant torque reaction. The motors were drawing 15A.

In the rebuild I will be using 9x4.5 counter rotating. I did wonder if the thrust from the fine 3.8 pitch props was actually falling away before a 'safe' flying speed had been reached. The 4.5 pitch should help in this respect.

[eye4wings]

I think you have a fair bit of your answer right there - the greater pitch will allow a greater airspeed which will alow you more margin above the stall.

The other major factor is the amount of washout you have in the wings. With a high aspect ratio wing this is more critical because of the difference in airspeed and therefore lift of the wingtips in a turn.
My suggestion would be for the inclusion of about 3 degrees washout in the aileron section of the wing. Perhaps a slit cut in the vertical face of the aileron bay at rear of the wing, the wing twisted and re-glued, would do the job if you don't already have washout in the wing.

As has been said - nice to see one of the rare types being modelled.

[quorneng]

The wing panels complete and painted. The radio is mounted in the centre section.

For strength the centre section will be fully skinned although some access to the radio will be required to disconnect the rudder and elevator servos in order to actually install/remove the wing.

[CHELLIE]

Originally Posted by quorneng

The wing panels complete and painted. The radio is mounted in the centre section.
Attachment 165531
For strength the centre section will be fully skinned although some access to the radio will be required to disconnect the rudder and elevator servos in order to actually install/remove the wing.

I just noticed something Your Ailerons are not long enough, they should go all the way out to the end of the wing, if your trying to pattern your plane after the full scale plane, it wont work, Rc planes generally need some modifications to work right at lower speeds, your not getting any aileron control over the plane or very very little, Again, if you use full length ailerons, get rid of the flaps so that the prop wash is helping you, I dont think this plane will ever fly right, Just my 2 cents worth, Chellie

[quorneng]

Chellie
I do wonder sometimes if full length ailerons are almost more of a fashion than an absolute necessity, unless of course you want 3D aerobatics.

Both these wings (one bigger, one slightly smaller span) perform perfectly satisfactorily.

And they both have smaller ailerons in relation to their span and wing area than the Hamilcar.

They do both have differential movement, as does the Hamilcar, which certainly seems to prevent a wing drop from developing into any sort of a spin.

I am fairly certain (or perhaps it is more of a hope!) that the Hamilcar's problem was basically a CofG issue which this rework should address.

We shall see!

[CHELLIE]

Originally Posted by quorneng

Chellie
I do wonder sometimes if full length ailerons are almost more of a fashion than an absolute necessity, unless of course you want 3D aerobatics.

Both these wings (one bigger, one slightly smaller span) perform perfectly satisfactorily.
Attachment 165538
And they both have smaller ailerons in relation to their span and wing area than the Hamilcar.

They do both have differential movement, as does the Hamilcar, which certainly seems to prevent a wing drop from developing into any sort of a spin.

I am fairly certain (or perhaps it is more of a hope!) that the Hamilcar's problem was basically a CofG issue which this rework should address.

We shall see!

Hi the smaller Ailerons would work on those wings Because they are on the outside where they have much more leverage to work with, ailerons being mid wing, wont have the same leverage, and at slower speeds wont be affective, prop wash helps a lot at slow speeds to get air over the control surfaces to work with, I dont mean to be Critical of your design, But looking at it in Mechanical Terms, there are a lot Issues with it, that will not allow it to work right, 1. prop wash is not helping your Ailerons, 2. Ailerons are too small, mid wing, no leverage, they will need a lot of air speed to work, Just my 2 cents worth, Take care, Chellie

[CHELLIE]

These wings have the advantage of the Ailerons being on the outside which gives them the leverage they need to work with,

[stuart]

quorneng, i find this rebuild fascinating enough to have just spent a 1/2 hr or so searching for pictures of the Hamilcar with the twin engines.

how frustrating to see the same photos in all my searches of a tank unloading,side shots, being towed or towing,but never one picture to show the scale location of the ailerons. i tried real hard to see the scale location.

do you have the drawings your building off showing a top view? if the full scale had the ailerons located same as your building then i say go for the scale version whether it flys great or not. i must say the build you did in 2010 of the Hamilcar looked great!

if it were my plane,I'd bump the ailerons out cause handleing is always important to me ,but if scale of the modified glider to twin power is your goal then thats awesome. fly it like a 3 channel.......rudder/elev. looking forward to hearing a success story of her flying around an maybe get a vid of her to share. we all love videos... stu

[xmech2k]

How's this?



Looks like unless we can't see the ailerons in the picture of Quorneng's wing, there are only flaps on his wing.

[CHELLIE]

Originally Posted by xmech2k

How's this?



Looks like unless we can't see the ailerons in the picture of Quorneng's wing, there are only flaps on his wing.

Great Pic Mech

look at the pic at the bottom real close, you can see that the Ailerons are mid wing, and they have very little if any prop was over them, the flaps are getting all the prop wash,

[CHELLIE]

I dont see the ailerons going out to the end of the wing in this pic, they stop mid wing, the Drawing has the ailerons going out to the end of the wing, Thats what is needed to make this model plane fly right, and even better yet, full length ailerons to take advantage of the prop wash, and add flap mixing into the ailerons, the prop wash will aid the Ailerons and Flaps that way. Just my 2 cents worth, Chellie

[CHELLIE]

[BBCorvette18]

I could be wrong but it looks to me like the ailerons of the RC version is where the flaps would be of the real plane and the ailerons of the real plan go out to the edge of the wing. The place where the Flaps are on the RC version is a very weird spot for flaps to be. I would expect that just be stationary wing.


Looking at this picture I think it clearly shows the Ailerons are at the very outside of the plane and the flaps are HUGE

[xmech2k]

Ahem! Those are pics of the full scale plane. Our planes are real, too!

[BBCorvette18]

Originally Posted by xmech2k

Ahem! Those are pics of the full scale plane. Our planes are real, too!

No our planes are toys. anyone who says different are just kidding themselves trying to justify the amount of money that we spend

[quorneng]

My Hamilcar has scale aileron and flaps.
The ailerons are quite big although the tape top hinge and the camouflage paint does a good job of hiding them!
Aileron full up

Aileron full down showing the differential movement


In some respects the Hamilcar was not really 'disposable'.
I think this view does show just how complex and massive its construction was.

Not surprising that General Aircraft went on to design the GAL60 which became the Beverly when built by Blackburn.

[xmech2k]

LOL! Remember, I did throw in the qualifier, "Unless we can't see the ailerons in the picture"! They are well camouflaged!