Hi!
I am looking at converti-planes or combo-copters as models.

Seeing as they use full rotor head/swashplate units, this may be a good forum.

The plan is to start with a 450 class electric heli, and build up to a Kaman-style intemeshing rotor setup, with a pusher prop.
I also want to use a wing, but this is limited by loss of lift capacity of at least 10% for a half sized wing.
Maybe a tilting wing would be good?

Are there any existing threads that come into this area?

I would need to build up a complete second rotor drive, blades, control mechanical set.
Is it economical to do this, or do I need to but two complete kits?

I was think of using a setup of plastic pinions and crown-wheels on 1/8" axles as a synchroniser system.
The pinions can be slanted enough relative to the crown-wheels, mounted on a cross-shaft.

I think belt-drive is the usual reduction method?- I would use twin motors and belt sets.

Having effectively a 4-blade system made from two, two blade systems, should give me enough lift capacity.
It should be about as efficient as a stacked-rotor setup.

I am presently working on designing and building a string of fixed-wing ,fixed motor planes,
but I would like to try a rotorcraft after that.

An advantage of a combo-copter is that it can function as an gyrocopter for level flight, using half the power at the same speed,
or longer duration for the same battery.
It is also an opportunity to make a really swoopy-looking aircraft!

I am currently looking at a VTOL/STOL plane that would not be practical as full-size aircraft-too much
"Roller-coaster ride from hell" - with a stalling, prop-hanger-gyro-assisted take-off and landing.
a copter-type launch is easier on any passengers or freight.

I also need to learn how to control the flight modes so the rotor tend to auto-rotate a bit.

The autogyro people think that takes a rotor angle of attack of 20 degrees-a lot!, so rotor unloading may be the
best I can expect.

Another interesting aspect is that a forward tilt is not needed to fly forward, which basically needs
2 sets of controls, or an interesting control intermix, or automation of several flight control features.

Anyone wish to discuss this project?

More notes:
1) The tilt-wing can have feathering capability, and load-sensing on it axis,
to see if it has a reasonable lift-drag ratio.
We can use a free-floating paddle as a windsock, for a reference.

This would require an add-on processing module. Outputs and monitor inputs can be routed through a flight controller.
2) The main rotors and motors need an optimising routine to control collective pitch, main pitch, and rpm
to optimise lift and drag along with the horizontal drive motor and wing.

This means rotor rpm monitoring.

3) Pilot inputs are "fly by wire", and mixed in with computed interpretation,
along with gyro stabilisation.
The pilot can have more direct control over the horizontal drive power/ revs regulator.

https://www.helifreak.com/showthread.php?t=255613

Originally Posted by rotorist

https://www.helifreak.com/showthread.php?t=255613

I don't really fancy tilt-rotors.
I thought combi-copters was something interesting and different, and I like the "Eggbeater" setup.
Kaman are still selling their Heavy Lifter version.

The problem with combi-copters is that they need a lot of control-twiddling to optimise flight.

I thought a little electronic measurement and feedback control would be good, though the rotor/wing trim looks like it would need a "learning" system, as you don't know in advance what the correct settings are.
You need to search the operating envelope, and measure results.

A pitot system and an accurate altitude barometer or gyro altitude tracker would be handy.
Then again, it doesn't need to be all that optimised for a model!

I thought monitoring wing performance and ambient airflow direction would be a good start.
You do need a tracking control loop to move the wing.
You also need some micro load cells and associated electronics.

It is a bit like a biplane where you can trim the attack angle of one of the wings.

This is a lot less critical than with a tilt-rotor, which will plummet if you do it wrong.

The wing also needs to be long with a narrow chord, to fit under the rotors. Maybe a slatted wing?
Possibly an intermeshing rotor system does not allow enough room for the wing?
-I will draw it up.
<Edit>
Here are some load cell units.
This adds up the results from 4 units.
I need to find out how to look at that as a data stream, and to read values into a program.

- a bit of research required on how a telemetry network functions, and coms between a flight controller and a
supplementary board, and picking a board that I can learn easily. Arduino, raspberry pi?
I don't want to get deeply into C+++ - high learning curve there.
Arduino may be simpler.

This looks interesting!

They don't provide detail, though, so you can figure out what it does.

The price seems suspiciously low, when you compare it with ready-to-fly 450-sized helis.

This is the price of one you can stand on your hand- maybe 250mm blade diameter.

The 80cm size sounds good.

Re: trimmable wing/rotor set.

There is probably a way of determining whether a wing angle is producing more lift than drag.
4-5 degrees is known as a good angle of attack for relatively flat-bottomed wing sections.
the no-lift line is around -2.5 degrees.
This is for aircraft, and I suppose it applies to rotor-blades as well.
for ground vehicles, 7 degrees is known as the angle where negative lift surpasses drag reduction.
assume this applies to the aircraft travel axis- which you can work out from
the 6-axis gyro outputs. then, if the angle of attack relative to the travel axis passes 12 degrees, you can be pretty sure
that is far enough to apply positive wing trim, and can feather the wing.
What do you think?
The wing angle of attack relative to the "ambient" air flow can be set relative to the indicator paddle.
set at , say, 5 degrees, to allow unloading of the rotor lift.

This ambient flow is mainly due the the rotor flow, and the aircraft vortex envelope.
(as per fixed wings-air intersects the wing as if it was a horizontal vortex, rotating back at the top.)

With a delta, the lift=drag point is at 20 degrees.
A straight wing will stall before it reaches this point.
Is this relevant?

More notes on combo-copter.
A ring-tail rear prop looks good.
This can be used on a single-rotor aircraft as well, with internal deflector vanes.
I was thinking 180mm (7 inches).
That would be a good size for a 450-type rotor set. (710mm)
underwater ROVs have these housings.- I can't find them in parts, though.
I will look for large bore PVC pipes.
<edit>
nothing less than 6M lengths.

Maybe a fabrication method, using made-up formers?- rings of epoxy-balsa.

Something like this?

Originally Posted by abenn

Something like this?

That was a jet-tip rotor.
They have been abandoned due to being too noisy.
The horizontal motors and wing are similar.

Question?
How would I obtain or make a custom nose-bubble?
This one I an working on has a flat top, sides, bottom, transition from spherical.
It would be nice to put the FPV camera under there, and not have a lot of seams.
I suppose I could get a Bauble clear ball, and glue flat sides on it, but I thought I would ask.

I may bump this rotorcraft up the list, and do some build work on it.
I have a 450 copter kit on order, and will track down the parts for a dual rotor axis.
-Just drawn up a pretty design.

In bare images, the frame seems pretty crowded. Not much spare room.
This one is rated at about 520 g takeoff, but with two motors, it should lift a lot more.
- I can always rev it up a bit.
These rotors should be good for 4500 rpm?

Originally Posted by Owen_bern

I thought combi-copters was something interesting and different, and I like the "Eggbeater" setup.
Kaman are still selling their Heavy Lifter version.

This was so good the Air Force decided that the Army should not have it and they complained loud and long enough to get it cancelled.

The Lockheed Cheyenne Helicopter 1/4 (13 min 36 sec)

When the army came back for a second go at an advanced attack helicopter the spec was dumbed down (top speed not to exceed 180mph) so as not to trigger the USAF and we got the AH-64 out of that.

The constant rate feathering prop on a helicopter concept seems to have made a return on the Sikorsky S-97 and Sikorsky-Boeing SD-1 though. It allows the helicopter to rapidly accelerate and decelerate and to cruise with the majority of forward propulsion coming from the prop rather than cyclic pitch which reduces drag and increases top speed by allowing a nose level attitude in forward flight. It sounds weird at first but when you think about it a bit it's actually a really good idea. It makes a better helicopter unlike tiltrotors which are a poor helicopter than turns in to a poor airplane because the proprotors have to compromise between disk loading and prop drag.

Originally Posted by Atomic Skull

This was so good the Air Force decided that the Army should not have it and they complained loud and long enough to get it cancelled.

https://www.youtube.com/watch?v=eDo04Lw_vbA&t=138s

When the army came back for a second go at an advanced attack helicopter the spec was dumbed down (top speed not to exceed 180mph) so as not to trigger the USAF and we got the AH-64 out of that.

The constant rate feathering prop on a helicopter concept seems to have made a return on the Sikorsky S-97 and Sikorsky-Boeing SD-1 though. It allows the helicopter to rapidly accelerate and decelerate and to cruise with the majority of forward propulsion coming from the prop rather than cyclic pitch which reduces drag and increases top speed by allowing a nose level attitude in forward flight. It sounds weird at first but when you think about it a bit it's actually a really good idea. It makes a better helicopter unlike tiltrotors which are a poor helicopter than turns in to a poor airplane because the proprotors have to compromise between disk loading and prop drag.

This video was about a rigid rotor concept, and is part 1 of 4. The other parts didn't come up.

I was thinking about autorotation, and you get a version of it if the rotor is tilted forward with positive pitch.
this would come into play with extra horizontal thrust propellers.
I bet it doesn't take a rotor angle of 20 degrees, either, like the gyrocopter people say.
it should still produce extra lift without much input torque.

This is likely why you see compound helicopters with an angle between the wings and the rotor, with the rotor angled down a bit.
The tailplane angle matches the wing.
<edit>
I found the other bits through search.

The competing copter produced by Bell did the job, and was much cheaper, if slower. (Bell AH-1 Cobra).
- victim of specification drift?

That may have had a big influence on the Cheyenne cancellation.

Here is my preliminary layout.
I am informed that these are also referred to as Combi-copters.
the ambient light is low, so there is some background patterning.

the file size is a little high.
the default motors seem to be 3500KV, 3S, massively geared down.
38,000 rpm to 4500 rpm is 8.4 to 1.
Seeing as power is largely independent of KV, they could have gone with a lesser gear ratio.
Based on a full sized copter, 30ft = 440rpm, so 28" = 5600 rpm.
If you look at a 14 inch prop at 9500 rpm, a 28 inch prop should do 4750 rpm.
I will check that. = 125,000/ ins = 8928rpm?
150,000/14 = 10,714- what does APC say?
You want very strong and secure blade ends to push up to 5600 rpm!

Also, to get one set to run in reverse, the pivots have to be cut off one end and grafted on the other, if blank blade stock cannot be obtained.
This is also carbon composite.
this can possibly done with a scarf joint, if a length of the blade is reshaped to plain elliptical.
- It should still work.
The other blade set would need to be adjusted to match.
<edit>
APC limits:
thin electric = 150,000
folding electric = 120,000
<edit>
No blank blade stock, but I can get woven carbon composite bars, and sand to shape.
Would random-fibre pull-truded be better than woven for sanding?- you are not cutting through the carbon laminations.

Actual vs possible tip speeds, rotor RPM:
I looked this up.

Normally a 450 model will run around 3000 rpm, out of a possible 6000 rpm.
This drops power usage by x8 times, and reduces gyroscopic effect.
at 3500KV, 3S = 11.1 V , 38,850 x 0.8 = 31,000 fully loaded approx.
to drop to 3,000 rpm = 10.3:1
The motor may be specced to load it up to 70 % rpm??
this changes motor rpm to 27,200, and ratio to 9:1, but the rotor will speed up when flying.

Many motors are designed to run continuously at 65-70% rpm.- This corresponds to
static loading on an aeroplane.
The gearing and structure is not rated for the extra torque required, as well.
the higher revs put a lot of load on the blade rotational bearings, and the blade pins.
I thought the blade pin diameter was a bit small.
You also want a bearing sleeve inside the blade end "hole".
Presumably pivot bolts are step-shanked and ground, shafting grade?

To make a rotor head run backwards, just flip the arms over.
everything is parallel.
The motor and drive should run in reverse just as well.

possibly we can benefit from going from 3S to 4S, and changing motors to suit.
This just limits amps. About 30A continuous for each motor sounds good.
The pusher motor needs about 250w, or around 10A at 4S, 1500KV?
I will check the reduction ratio.
looking at pinion sizes, if there are 13 teeth, with pitch of 3mm, perimeter = 39mm, diameter =
12.4, big wheel x 9 = 111 mm - they are smaller than that!
if pitch = 2mm, small wheel = 8.3mm, large wheel = 74mm, or 3 inches.
This is close to the fuselage width of maybe 95 mm.
Getting 2 spindles into this space is a problem.
If the drive wheels are at roof height, center clearance = 90 mm.
74/2 = 37, so it will fit, with a little outer projection.
All the swashplate mech can be fitted into the rotor pylons.
The synch gearing will fit below the main reduction wheels, as it only needs small pinions.
To use the same reduction gears, a 4s motor would be 2625 KV, same revs.
eCalc has rotorcraft simulators, so I can check there.
Launch weight is going to be well over 520g. Maybe 2000g? - size motors and battery to suit.
A little more rotor RPM would help.

Permanent rigging angle of rotor vs tail, wings:

-maybe 5 degrees down at the front for the rotor?

The wing works best at 5 degrees up angle of attack, and you usually want the tailplane
up a little more than that.

This is one reason why I want an adjustable wing angle-you don't know in advance what the net effect will be, rather like with a biplane.

The front upwash and rear downwash is likely to be more severe with a rotorcraft, do you think?
The upwash probably occurs well forward of the lower wing leading edge,
and the ambient flow around the lower wing is likely to be more downward than
with a conventional monoplane.

The wing is also half the size of a conventional wing, and maybe 1/4 of the area.
Most of the time, it must work in concert with the rotor to provide lift.

Originally Posted by Owen_bern

The competing copter produced by Bell did the job, and was much cheaper, if slower. (Bell AH-1 Cobra).
- victim of specification drift?

That may have had a big influence on the Cheyenne cancellation.

It was the Air Force's opposition to it that really put the nail in the coffin. They lobbied very very hard against it to congress.

This is likely why you see compound helicopters with an angle between the wings and the rotor, with the rotor angled down a bit.
The tailplane angle matches the wing.
<edit>
I found the other bits through search.

Look at the footage of the AH-56 (and the S-97 and SB-1 as well) in fast forward flight, they don't fly with the nose as far down as a traditional helicopter. That's because there is little forward cyclic pitch in that mode the forward propulsion comes mostly from the pusher. Of course in loiter they can fly forward with cyclic like a normal helicopter.

The CH-47 uses the same trick to reduce drag in forward flight though in that case they use longitudinal cyclic trim on the two rotor disks to pull the nose up while propulsion is from collective difference between the front and rear rotors (tandems don't really have "elevator" cyclic as such the elevator axis on the stick cause the collective to increase on one disk and decrease on the other. This is because elevator cyclic won't actually propel a tandem forward/backwards just cause it to drift in that direction and pull the nose up or down)