CL-84 scratch build; OpenAero VTOL; Constant Velocity Props - RC Groups
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Feb 06, 2017, 09:41 PM
Nicholas Jacobs
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CL-84 scratch build; OpenAero VTOL; Constant Velocity Props

In the air museum at Ottawa there sits a beautiful CL-84, #402, the one shown in all the propaganda and clips in all its glory.

I'm a scratch builder from when I was 14 designing and flying C/L, and to me, there is only one way to have one of these birds - build it myself.

Enter OpenAero VTOL - a present to us VTOL enthusiasts from Happy Sunday (David Thompson), and the equally talented Ran D St. Clair. If you don't know already, Happy wrote the code, and Ran tested and documented it and continues to provide great support and enthusiasm to us all.

I have scavenged lots of documents including an operational manual, but have no blue prints or other technical documentation. I have a "3D view" drawing which looks like a plan from a plastic model. There are some errors based on the photos I have of the real thing - anyway its plenty good enough for my 1/12 semi-scale prototype.

Having visited the Ottawa Air Museum a couple of summers back, I have a lot of pics. I contacted the curator and they have manuals which I'm free to copy or take pictures of - the catch - get back to Ottawa on a Monday or Thursday ! Well, before I attempt any kind of large scale ... I'll build a 1/12 scale first

My plan
- Use OpenAeroVTOL (KK2) for the flight controller
- Basic foam sheet construction
- Use constant velocity (variable pitch) main rotors and rear rotor
- Tilting wing with coordinated tilting stabilizer (using documented curves)
- Working rudder and elevators
- Working flaperons; coordinated deflection with wing tilt (using documented curves)
- Main motor assisted yaw; coordinated with wing tilt deflection (guided by documented curves)
- Retractable gear
- Lights

Although the real CL-84 has leading edge slats (also coordinated with wing tilt) I won't be putting them on this model. I'm also using hinged flaperons, not slotted flaps like the real model.

I'm using a Taranis Tx with Frsky 8XR RX, mode D4 - CH9-16 with telemetry on PWM, and s.bus to KK2 CH1-8. I'll use CH9-16 for Wing Tilt, and other things, while using s.bus for the KK2 inputs of ELE, THR, AIL, RUD & AUX

OAV has an AUX input which controls its mode from P1 through P1.x to P2. Where P1 is Hover mode, P1.x is some form of Slow Forward flight (depending on Wing Tilt angle) and P2 is Fast Forward flight. One can setup a 3 pos switch to fix those three postions (which will also control the wing tilt angle). Instead I've setup my RS slider (Taranis) with a 5 point step curve to take advantage of the two end positions, middle point "click" and between. This easily gives me a way to select 5 points between P1 and P2. My initial thoughts are 0, 20, 40, 75 and 90 degrees to give me some reasonable tilt positions to start with.

The real CL-84 also has a 10 degree REAR tilt, which I will eventually like to try out. However, I think flaperon tilting may yield ample slow rearward flight.

The stabilizer tilt angle is basically a bell-curve based on the Wing Tilt angle (P1.x), where the angle ranges from 1 to 40 degrees where its maxed out at about 50 degree wing tilt angle and zero at both 0 and 90 degree wing tilt angle.

I have two ( home-made, variable pitch, from 600 Heli tail rotors, direct driven) main motors and a variable pitch tail motor (direct driven 450 heli tail rotor). (I cannot do the contra-rotating CV tail prop :< )

These motors all run on governor mode. Using a THR cut feature on the TX I can get away with a flat line pitch curve to get the desired 6000 R.P.M. and have it spin up once THR hold is released (after arming the KK2 of course ! ).

I plan to add optional steerable retracting landing gear and lights. Also the Cl-84 has a centre LE flap which sticks tight to the fuselage until 24 degrees of Wing tilt where it hangs in that position. That may just be a spring-loaded setup with a stop, or a KK2 curve and servo. The CL-84 also has LE flaps which deploy between 10 and 70 degrees wing tilt. A bit much on this 1/12 scale model. That will have to wait for a bigger bird.

I still have one spare KK2 output at the moment.

I'm at the point now where I have power tested the main motor units and tail rotor assembly and have a very base body constructed. Ready for the wing tilt frame to be installed. The wing is ready for the motor mounts and tilt bearings to be installed and then top-covered after the tilt assembly frame (sides, bottom inside fuselage) is assembled. I have a 10kg digital servo I will use for controlling the wing tilt.

I'm designing as I go. Dry fitting, refining and onto the next puzzle. I have the wing tilt/servo design in my head and am thinking about the tail tilt..

So here goes..

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Feb 06, 2017, 09:50 PM
Nicholas Jacobs
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Layout on the "plans"

Like I said, no plans. Just a really nice drawing, likely from a plastic model. There are 3 views with section shapes. I've build planes from scratch from far less detail. There is some discrepancies, especially around the tilting stabilizer, as the drawing clearly does not show the same bottom mounting that my photos show. I'll have to "wing-it".
Feb 06, 2017, 10:33 PM
Nicholas Jacobs
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Power testing the CV motors

The rear propeller is a tail boom directly driven 450 Heli tail rotor. I mounted it on a paint stir-stick. I'm using a motor with 4mm shaft coupled to the torque rod via a universal drive from an electric boat.

I hooked up the KK2 with OpenAeroVTOL and set it up to auto level.

As you can see from video, when I pressed (sometimes quite hard) in both directions, the rotor easily counter-acted. Plenty of power there to balance out my model.

450 rotor with KK2 attitude mode (1 min 2 sec)

The variable pitch drives are made from a hobby king 35 sized motor, a 4 to 5 mm coupler and a hacked up 650 metal heli rotor. I have detailed step-by-step pictures of how to make this, which I will post a little later on in the build.

Pitch is controlled by a digital servo. Throttle is controlled by a 40 A DLUX ESC from HK, running in governor mode. This thing is so smooth as you can see /hear in the video.

I hooked up a tach and watts-up to keep an eye on the R.P.M., Vmin, Amax and Wmax respectively. Good job too, because you can see the Amax went to 48 A - and the ESC is rated 40 with 50 for a burst. I could have pushed more, but it was already drawing near 450W. I'm waiting for a couple of 70A ESCs to be safe.

For testing right now I will have 800 to 900 W of power available. At 250 W/Kg required for lift, I'm going to be able to lift > 3kg model with ease. And I'm estimating this plane will not be more than 2Kg AUW.

I varied pitch with a dial between 0 and 25 degrees, while shifting throttle to get the R.P.M. I'm looking for lowest R.P.M. that will not sag under any pitch setting. At 6200 R.P.M. its almost there.

I won't need a throttle curve to run this. Since I know what my throttle setting is, the throttle curve would just be a flat line. So I'll set the channel output accordingly and drive both governed ESC's directly from the Rx, not through the KK2. Pitch, on the other hand will be driven by the Tx throttle stick and be fed into the KK2.

The rear motor will be similarly setup. Pitch will be driven by the KK2 in proportion to Wing Tilt angle, auto-leveling and pitch input on the ELE stick.

IMG 6553 CV power test (1 min 27 sec)
Feb 06, 2017, 10:50 PM
Nicholas Jacobs
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Tilt wing

NACA 63(3)-618 airfoil used by the CL-84 was first mocked up.

I'm building the top first, using the "flat" to keep it aligned.

Hinge is a carbon fibre rod and cut-up nose steering gear, drilled out to fit the rod. The nylong hinges will be anchored to a ply block which will be anchored to ply doublers.

The tilt servo will sit on a cross member between the ply doublers. (not installed yet)
Last edited by njacobs; Feb 06, 2017 at 11:23 PM.
Feb 06, 2017, 11:10 PM
Nicholas Jacobs
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Motor mounts

900 W + is a lot of power hanging off a tilt wing. I want the mount securely fastened to the wing. There is a birch spar and 4mm cf rod which they must be attached to for maximum strength.

Ok so the wing in the drawing is not "technically correct", I want the NACA 63(3) -618.

So I laid it out on graph paper! No high tech stuff here (just the plane and FC !). Photo-copied, cut out paper template and transferred to 1/8" ply.

Then dry the mounts and motor pods.

Next up - build the tilt wing fuselage doublers/frame and dry fit it all with a tilt servo in place before getting out the 30 minute epoxy.

Motor pods will need some corner bracing. Motor mounts will be braced
and pods will be screwed into the mounts for easy servicability.

FYI: last pic there's a
- Retired Tensor
- 5 flights on the Regal Bipe KF2 airfoil - first real bipe - real nice
- Dart made 5 years ago by my daughter, modelled after the base wind-up
- 1 m Reactor which needs some TLC rebuilding the front end
Feb 07, 2017, 04:47 AM
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chulian1819's Avatar
wow nice job!
Feb 07, 2017, 11:20 AM
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Ran D. St. Clair's Avatar
That's an impressive project you have going there.
Feb 08, 2017, 03:17 AM
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Very nice project! I'll be following ! I like the extra challenge of the variable pitch props. This should (theoretically) allow tuning of the rpm and prop blade pitch angle for maximum efficiency in both hover and forward flight. And all of the output offset curves in OAVTOL exist to do this (thanks HS and RD). It would be interesting to do some studies to see how energy use can be optimized by tuning of the prop angles and rpm.
Last edited by OwlCity; Feb 08, 2017 at 03:23 AM.
Feb 08, 2017, 06:48 AM
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v22chap's Avatar
cool ,, very nice building going on here ,,, will follow this ... best of luck .
Feb 08, 2017, 10:52 AM
Nicholas Jacobs
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Originally Posted by OwlCity
Very nice project! I'll be following ! I like the extra challenge of the variable pitch props. This should (theoretically) allow tuning of the rpm and prop blade pitch angle for maximum efficiency in both hover and forward flight. And all of the output offset curves in OAVTOL exist to do this (thanks HS and RD). It would be interesting to do some studies to see how energy use can be optimized by tuning of the prop angles and rpm.
Yes, this would be a very cool thing to do. Hmmm I'm looking for a thesis for a Master's degree which I want to do when I retire, or part-time start on. Always wanted to be an engineer (aeronautical), but an interest in computers blew it out of the water - in fact I used to walk past the wind tunnel at Univerisity of Western Ontario daily to get to Comp Sci classes!! So that might be a very good study.

Also different types of propellers. I did quite some scrounging for props. So I'm starting with the 110mm cf blades which are flat and have lots of power. Starting with governed mode fixed R.P.M. across the board and can go from there. Also ordered some wooden 450 blades (at the advice of one scale heli guys in the club). These can be cut to different lengths. Perhaps they can be modified to have some curvature.

There are various "large" cf props (15") for quads with a bit of twist which could be cut in half and mounted on the existing motor mounts.

Not sure if 3D printing blades is an option. Don't have a printer yet. Tom Stanton may be able to comment on this.

This is a 1m (32") wingspan. The props are almost scale for that size, just a tad short.

I eventually want to make a 1/4 scale (8' ) model. The real challenge will be the variable pitch propulsion system. Heli main rotor/tail rotor/blades etc.

Then there is that contra-rotating tail feather. Looks like 4 concentric shafts to make that happen. I have just bought a Tag metal lathe / mill from Leevalley tools

Long way to go... Thanks for the support.
Feb 08, 2017, 12:16 PM
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My little bit of tinkering doesn't amount to a hill of beans compared to the awesomeness of your undertakings. Bravo!!
Feb 08, 2017, 12:49 PM
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v22chap's Avatar
Glad you are looking in to different props ... as I have been down the heli bladed road a ways and they seem to hit a brick wall at about the mph that you need to become wing borne .Although that said Rotormast did it with their v-22 by using an amp draw monitor in the FC so that it automatically runs the pitch of the blades so that you don't stall out the motor , as it is kind of hard to hear the motors lug down at the distances we fly at .But their bird is light enough to do it also ... just barely .. he can carry another 2 lbs of weight and then it becomes trouble if still on the flat blades .
The hovering and up to about 40 percent conversion will work fine with symmetrical heli blades ...but from there on out it needs the governor on collective or twisted blades to make it go on into airplane mode and not crash ...especially as the size and weight of the bird grows .Not sure how the gov with work with larger weights of the larger bird though .

I did a v-22 with 3 bladed rotors and cut down wood props and it didn't work worth a darn ,, but it might have been my drive train as I had changed everything at once on that bird and after the crash I never rebuild that setup again .

Good luck and I am looking forward to your larger version .... take your time and have a lot of fun with your project
Feb 11, 2017, 11:13 AM
Nicholas Jacobs
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Originally Posted by PlumbBob
My little bit of tinkering doesn't amount to a hill of beans compared to the awesomeness of your undertakings. Bravo!!
I disagree. Your testbed is a very good learning tool for all of us and I eagerly follow you thought process and methods of madness to success.
Feb 11, 2017, 11:57 AM
Registered User
Thanks, Nicholas. I feel better now!
Feb 11, 2017, 10:07 PM
Nicholas Jacobs
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Tilt Wing Mechanics - mock-up

Before gluing together I need to figure out how to tilt the wing. I have a 10kg HK bb metal gear digital servo, metal arm and ball joint from a defunct Funtana 120. (I had considered using electric landing gear servo, however they have only two positions - up and down and have an integrated controller, so there is no way to make it work. Too bad because an electric motor driving a threaded shaft would be perfect for this application. Servo city has some linear actuators, which are a bit over-kill for this model. For a 1/4 scale though ... )

I put the wing hinge together and tacked it to the fuselage. Seems to tilt nicely by hand.

Tried a couple of locations for the pivot point on the wing and settled for where it is now. Its bolted with a 4-40 into the main spar. Later I will put a rib or two of ply around it back to the cf so that there is no flexing on the foam. I don't want foam to take any mechanical stress at all. Its just "balsa" after all

IMG 6853 (0 min 29 sec)

What I've got after experimenting seems to be the right mechanics. However you can hear it binding on the hinges. I think the bolts were distorting the nylon so it binds. May just try opening the hole a tad. I have a full set of numbered drills so I could do a few thou at a time. If not I'll try a brass bushing insert or some ball bearings.

Now that I know where everything goes, I'll build up the cage around the fuselage sides and front bulkhead to mount the servo on. A few cross braces to keep the stress 100% off the foam should do it. Then I'll epoxy the whole lot together and motor mounts.

I'm using a 5 step "curve" on the RS slider on the Taranis to get 5 settings, and have it call out the angle set. There is a delay set on both up and down movement to make it more realistic.

Technical details will follow on the KK2 and Taranis configuration later. I want to work out the kinks first.

Last edited by njacobs; Feb 11, 2017 at 10:21 PM.

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