McCutchen Machine Trimming

[Bill Mixon]

Hi, All

I have been trying to build a flyable McCutchen wing or "Charibdis" for the past year or so, and now have a design that will fly. However, I have run into a problem with stability and really need some help.

I've built dozens of these wings of various sizes and means of power, and late last year built one with electric power. Motor is a GWS fan motor with a 3X2 prop, running on 3 or 4 110 mah Sanyo cells. Provides the power needed to fly the model well.
Here's the problem.

Shortly after release it will start to wander in a circular path leaning in the direction of travel. Eventually it leans over enough that it can no longer climb and hits the ground I've tried different dihedral settings on the outer portion of the rotor, changed Cof G, etc.. but have not been able to get the thing to fly like it should.
I don't expect it to stay perfectly straight, but it should climb to altitude staying upright.

Sometime, I will post a picture of the latest design for reference, and for those who have no idea what I'm talking about.;)

Thanks,
Bill

[Bill Mixon]

Here is a picture.
You can see a 3 cell battery pack on top of the inner part of the wing or rotor. GWS motor mounted at the end of the arm, not wired up now. Model launches by pivot located at the inside leading edge of the rotor. Some (I think) prefer to launch these by holding on to it and giving it a quick spin with the wrist. I use a pole with a wire rod to pivot on, and hold it above my head to launch it.
In the pic you can see that out on the outer portion of the rotor dihedral has been added to try to stabilize it. this rotor was originally flat. I don't know that the dihedral made any difference in stability.
Any input appreciated.

Bill

[Tony Oliver]

Hiya Bill.

Interesting problem, and here are my thoughts, but without any current practical experience of that problem, or any confidence in the solution.

I think the dihedral is the causing the difficulty. The path the tips make is now slightly offset - higher on the 'wing' side than the motor side. If the overall balance is back in equilibrium (how's that for a word on Saturday night!) once rotation has stabilised, there is a wobble due to the balance pod at right angles to this (lower than the rotation disk). As far as I know, I think that for stability, all three need to be in the same plane - no pun intended.

Perhaps some increase in height of the counterweight would help? These things are so fascinating, yet few play around with them so there's little real experience to draw on.

Tony

[Bill Mixon]

Thanks, Tony

That is something that I need to look at, since adding the dihedral didn't seem to help any.
When flying, the blur (viewed from the side) is in a cone or shallow V shape. With the motor arm being lowest due to all the lift being created on the other side. The rpm's would have to be relatively high to get it rotating in a more flat path.
I had this same problem with a Norvel .061 CL powered version. I quit with the glow powered ones because of the large size, unpredictable run times, and danger of being hit by it or the parts it slings when it hits the ground.
I don't really see any way to get one to rotate in a flat plane without having the motor arm side lifting. However I'm sure that there would be difficulties with it setup like this also.

Bill

[mlbco]

I was looking through some old posts on this list when I came across this thread, a topic I actually have some experience in! I've built many McCutchen variants including gas powered, rubber, and electric ones. I even built some one channel RC jobs where I could change the collective pitch setting for climb and descent by rotating a padle on the stabilizer boom. These models are tricky to adjust because their asymmetry produces many effects from simple design changes.

The McCutchen wing is stabilized be a balance of both aerodynamic and gyroscopic forces, the same as a helicopter rotor. The aircraft is most similar to a helicopter rotor with only one blade and one half of the flybar.

The easiest way to increase hover stability is to add weight to the boom that is oriented 90 deg to the wing. This is the same as increasing the flybar weight on a model helicopter and increases the stabilizing gyroscopic effect of the boom. You may have to readjust the wing/tail incidence for proper climb. You can also place a 'paddle' on the end of the boom for climb adjustment. If you can come up with a way to cyclically vary the incidence of the paddle in flight, you can steer the model too (the easiest way to do this is to add a fuselage, swashplate, etc.. and you'll end with a little one-bladed helicopter).


Steve Morris

P.S.
I met Charles McCutchen 8 years ago and he is still an active inventor with an unbelievably creative mind.

[Bill Mixon]

Thanks for your reply, Steve!

I'm glad to know that someone else out there flies these.
Thanks for the valuable tips. I'll give it a try.
I have to say that this is the most challenging and interesting thing I have ever worked on in the model hobby/sport.
I have almost given up several times, but I keep thinking that one day I'll come up with one that works and be able to reap the rewards.:)

Do you have any pictures of your models that you could post on here?

Thanks again,
Bill

[KnifeEdge51]

Are there any plans available for these things? I'm rather interested, and I've got a small collection of 50mah batteries and various motors to mess with (Thanks, Dylan!). I would like to see how I fair at making one. It would sure be an interesting thing to go fly at the park! Thanks!

Nick R.

[Bill Mixon]

Nick,
I'll be working on mine for some time I'm sure. I don't know of any plans specifically for an electric version. If I did I would probably be building by them instead of working on my own.

Here is a link to a site that has a lot of information.
http://home.att.net/~dannysoar2/Whirlygig.htm
They even show pictures of a full scale version. I wonder if they found anyone brave enough to fly it.

Bill

[mlbco]

Here is my McCutchen type model. It has a symmetric 'flybar', a wing which can rotate 360 deg about the pitch axis (feathering axis) on a wire and brass tube hinge, and a boom weight on the wing. There is a one channel on/off RC system installed and the propulsion is from an old Cox electric model. This was all built around 1996, so the components are older. It flies for a coup[le of minutes and is very stable. The feathering hinge was used to get a better autorotation glide, and I have thermalled it on rare occasions. The overal span is 54 inches and it weighs 6.7 ounces.


Steve

[mlbco]

Here is another photo taken during flight. I'm sorry it is so blurry. The model is stable enough to fly indoors using the onn/off RC to avoid the celing and floor.


Steve

[mlbco]

This model is a actually a boom powered helicopter and was derived during my experments with McCutchen wings. It is 24 inches in diameter and weighs 3 ounces. It flies over a minute and has the one channel on/off control. I've built lighter versions that fly 2 minutes on 5 x 50 mah nicads. This one is heavier and was a prototype that a toy company considered for production, but they eventually backed out.


Steve Morris

[mlbco]

Here is the boom powered helicopter in very blurry flight.


Steve Morris

[Bill Mixon]

Wow!
Thanks so much for those pictures, Steve.
I like the hinged wing idea. Seems to make more sense than the fixed construction. I assume that the blade is balanced a good bit forward of it's rotation axis. So that it hangs down in a negative AOA until the speed gets high enough for the tail to put possitive pitch in it.
Is the motor angled upward to provide some lift on the motor arm side?

The boom powered helicopter looks like a more simple and practical design.

Huummm..
I need to get to my building board now.:D

Bill

[Bill Mixon]

I now have something that will fly, well somewhat anyway.
Span tip to tip of rotor is about 58". Pixie 7P control, (4) 370mah NIMH cells and a 610 receiver to cut motors on and off. Two GWS IPS ducted fan motors turning 3030 props.

Longest flight so far has been around 45 seconds.
When flying with full power one rotor drops below the flight path of the other causing it to loose lift. You can pull the power off and it gets back in track. This problem is at just over the power it take to hover it. So, if it's in a steady hover and you increase power it gets out of whack and goes down. Sometimes I can cut the power let it get stable and put the power back to it.
Still haven't figured out what is causing this.
Everything seems to be even and balanced, so it must be a difference between the two motors or something is happening to the structure that I can't see at higher RPM's.

Still this is by far the most successul of all my attempts.


Steve, I sent you a PM a while back however your e-mail notification isn't turned on. Have a look at it sometime.

[Alfredo Rubio]

Guys....how do you take off this....planes???

[Bill Mixon]

I used a piece of wire in the end of a dowel rod, which goes in a hole it the bottom of the machine.
I hold it above my head until it has the lift to "take off"

I also lanched them by a twist of the wrist. Sometimes you have to get out of the way of it if things go awry.:D

For an update on my progress..
There has not been any. I never figured out the problem I mentioned in my last post. The model also crashed after it started into forward flight. It was in a hover about 10 ft high and it started to drift of in one direction. I pulled some of the power off, but it had quickly built up speed and started climbing. With the power off it continued on until the RPM's got to low to keep it gyroscopically stable, so it tumbled into the ground. Damage wasn't too bad but I needed the motors for something else I was working on so it's on the back burner for now.

One of these days I'll get it.. I hope:)

Bill

[mlbco]

I got bored today and tried to build a small version of this weird machine. The photo shows a 12 inch size version that flies well using the motor from a KP-00 drive and a cut-down GWS prop with some extra pitch twisted into it. The battery is a Kokam 135 mah Li-Po. It flies great indoors, smacks the ceiling a lot, and is very stable. I'll try it outside in calm air soon and hope I don't loose it. The weight is 12.4 grams.


Steve Morris

[mlbco]

Oops.., my picture was too many bytes and did not attach. Here it is reduced in size.

[Bill Mixon]

Thanks for posting the picture, Steve.

I have a programmable timer to use with some of the small lipo cells so it should make things a lot easier.

Looks like you have some + in that "paddle" on the balance boom. Did you have to do anything else special to get it stable?

Bill

[mlbco]

Bill,

I did add a small amount of lead under the paddle to eliminate "orbiting" motion. The boom that the paddle is on is angled about 10 deg down from the bottom of the wing. The idea is that the paddle is like a hiller-flybar and will rotate in a plane 90 deg to the spin axis (when viewed from the side), so the blade must be set with the correct positive incidence. The Li-Po battery is mounted under the main blade about 2" outboard from the joint of the 2 sticks, so that the "spanwise" CG is near the joint.

I test flew it outdoors today and I lost it. It climbed to about 150 feet and just went chugging along downwind, last seen drifting over the neighborhood, still at 150 feet after several minutes. I should have tested it in a bigger field with less wind!


Steve

Steve

[Bill Mixon]

Oh no..
Sorry to hear that you lost it.

I'll have to give it another go now at this smaller size with my timer and lipo cells.
I'm a bit surprised that it takes near 10 degrees of pitch for it to fly. I offset my boom downward but I never tried that much.

Bill

[gbarc]

Whoa!!! I'm impressed by these flying machines! I fly solely electric(indoor) models and i thought i've seen them all but this is a twist. So now i just gotta build me one. Steve are you willing to share more info on your smaller one blade heli? I already figuered out the "ufo" looking one(which by the way is way cool!) But that single bladed one hmmmm.... Any help would be greatly appreciated!

Greg

[CAFplanekid]

These are pretty cool! I have everything to build the small one single-blade one, Steve, so I too would like spme more info if you dont mind sharing. Thanks,
jonathan

[mlbco]

Since the original flew away I can't post more photos or draw accurate plans, but you can scale some plans from the photo I posted earlier. The main wing is 1/16" sheet with several ribs glued to the bottom, each rib is cambered. The paddle on the other boom is flat 1/16" balsa and I place lead weight under it to achieve stability. The paddle has 10-15 deg positive incidence. The booms are hard 1/4 x 1/8 balsa. The boom with the paddle is angled down about 10 deg. The battery is a 135 mah Kokam Li-Po and the motor is the same one that is used in the popular KP-00 electric motor drive. Attach a small GWS propeller (3"?) that is cut down about 5/16" from each tip. You will have to carefully bend more pitch into the propellor by twisting the blade at the root until the plastic takes a permanent set. It needs about 5 deg more blade incidence than stock. The battery is glued to the bottom of the main blade a few inches out from the joint of the 2 booms. This should put the CG close to the balsa reinforcing gusset. A very small micro switch is used to turn it on an off.

The rest of the recipe is to fly, adjust, repair (if necessary), repeat. The paddle incidence controls collecive pitch and the boom weight controls stability. This is not an overpowered model, so try to keep the weight under 12.5 grams.

Good Luck,

Steve

[Bill Mixon]

I came very close to making one fly today..

I started over with a formed balsa blade, 1/8X1/4 boom and a carbon rod boom for the paddle. I weighed my motor and battery and came up with about 11.5 grams for that itself. This did include the prop, wires, and the prog. timer which is less than a gram.
Total weight ended up at 19 grams.

I made the blade 11" long and the motor boom 6" long. (from root of blade to motor)

This is by far the best one of this type that I have made. After release it gets into a steady hover, even if it is moving in one direction to start with. I didn't realize how much difference the lead weight at the end of the "flybar" would make. On all of my previous models I tried to keep everything as light as possible. Now I see that the weight out there is a must for stability.
All it would do is hover or descend slowly though. A couple of times I got a little lift that took it up a few feet.
I think the next thing I'm going to try is moving the motor in a inch or so to see if it will up the RPM's a little and go up.

Bill

[Bill Mixon]

I got to thinking about the model I posted a picture of in post #2 later today. I still had it and thought, why not try it with a different boom arangement and more lead at the end.
So I tried it with a 4cell 110 bat charged to 25mah. It worked perfect. :) In fact I almost lost it to a tree after not guessing the run time and wind.
So I put a small RX and ESC on it so I could control it. Had to go up to 5 cells with the additional weight (which was only about 8 grams) to get it to climb.
So my whole problem from the start was not having enough weight on the boom. I simply never added enough. Thanks for the tips, Steve.

Anyway, here is a pic showing both of the models. The smaller one is the one I built earlier today with a single 130 lipo cell. The other has the low voltage GWS motor with 3X3 prop.

Bill

[mlbco]

Bill,

Congratulations on your success! Perserverance pays off! Now that you have the basic recipe, it should be easier to iterate and make improvements. The RC control is a necessity if you don't want to loose them. I've lost all of my free flight electric "helicopters" a few flights after I get them adjusted properly. I wonder why? :)


Steve

[Bill Mixon]

Thanks, Steve
It's been such a challenge to get this far. I feel like I have acomplished a great deal and I'm very happy. :) :)
Now that you have the basic recipe, it should be easier to iterate and make improvements.
Yeap, I'm going to get some measurements, weights, moments, etc from this model and try to come of with "standards" to build by. I'm also going to try 2 cell lipo packs when I get some smaller ones. Tried a 2s 830 this evening but it weighs about 15 grams more than 5 nicads which threw things off and made it not fly as stable.
I just got back in from flying it once more right at dark as the wind calmed down.
I put full power to it and watched it go nearly straight up to what I would guess is about 200' high (it was getting small and hard to see) and then pulled the power off and came back down. It never started to orbit around at any point. I found that the paddle keeps it from doing a autorotation which I expected and am not really concerned about as long as I can control throttle.
I haven't tried it yet but I think if you pulled the power all the way off at altitude it would slow down and drop in motor arm side down.

I will definetely be using some type of cut off for these from now on.

Regards,
Bill

[gbarc]

VERY COOL!! I still haven't had much success with these BUT i'll keep pressing on until i do. My main focus is the "UFO" for right now. I think the people at the local flying club would get a kick out of these! Also as a suggestion, you really should consider moving this thread to indoor and micro model forum. Those guys would eat this up as well as providing a wealth of info on batteries and micro gear.

Greg

[Bill Mixon]

I got the little one to fly today.
I had been using a cut down 3x2 prop that I kept playing with trying to get the pitch right, but it seemed that it never turned as much as I expected. So I put a little GWS 2.5X1 prop on it to try. Didn't check it but the rpm went up a lot. Still wouldn't lift it so I tweaked a little more pitch in the blades and it worked.
It's no rocket ship but it will go up now.
After a few 5 sec test hops, I programed the timer for 25 sec and let it go. Perfect flight. I'll have to play with this one indoor now. ;)
Also as a suggestion, you really should consider moving this thread to indoor and micro model forum.
I thought about that as well, but couldn't figure out where such a model fit best and when it comes right down to it, it's still a free flight model.

Bill

[steelhead]

Undead Thread.

I've been doing some research on these things lately and I'm still amazed they work.

Dean

[rchopper56]

Bill Mixon
I just noticed this post today. I am responding to your inital problem in which as your machine picked up speed, it eventually pitched itself too much to maintain altitude then hit the ground. I had a simular problem with rubber powered coax helicopters. I resolved it by adding area above the CG. In doing so, the models would always upright themselfs even in a heavy wind. I am enclosing a PDF file that has an illustration of what I am talking about. Please pay attention to figure 2. The key is to have the center of drag above the CG.
Gene

[rchopper56]

Hi,

I want to clarify that the area for drag is to be mounted at and above the center of rotation. You need to experiment as to how much you need. I mounted mine on a pivot so that it was free to rotate as it wanted. A simple X looking down from the top and about 9 square inches each plate. Mine was mounted about 6" above the upper 24" diameter rotor. I think that this was overkill but it did the job.

I checked my files this morning and I do have the plans for the Charybdis, a very simple McCutchen machine. Hope that this will bring back memories.

Gene

[mlbco]

I put a video on YouTube of some experiments from around 1994 which show several McCutchen style models:

http://www.youtube.com/watch?v=QrY5tTIluKM

Steve

[Bill Mixon]

Thanks for that video link Steve. Interesting stuff as usual.
I especially liked the "seed" and auto gyro folder that you towed up. I've tried some single blade designs like that, but have yet to come up with a blade design that will always "flatten-out" after the drop and have a low descent rate.

[steelhead]

I'm going to revive this thread- there are some good videos

Dean

[TheNightowl]

Thanks for reviving it, Dean. That is a good video compilation. Very interesting stuff.
I feel like a dweeb now, after saying in the other thread on this how they reminded me of a one-bladed helicopter, and come to find out that is how they are classified!
Nightowl

[Petem]

I have been fiddling with these things for several years, and finally got one to fly reliably - so, is it Free-Flight, RC, Helicopter, Scratchbuilt Foamie?
Most previous tries seemed to be stable, but would not go up. The advent of LiPo batteries and small brushless motors made the difference. This one does display the spiral wandering instability noted early in the thread, but it is very gentle and can be settled by increasing or decreasing the power.
The slightly different features on this one are the 45 deg upthrust on the motor, stabiliser aligned with centre of rotation, and the small pyramid under the centre to allow spin for ROG and landing.
Lots of fun, good for discussions at indoor sessions, and totally pointless! :D
Cheers,
PeteM

[Bob Blackburn]

I have had this working for a couple of years now.

Uses my fftimer and a 140ma cell.

[Petem]

Excellent, Bob - does it autorotate when the noise stops?
And does it have the spiral funnies?
Peter

[Bob Blackburn]

The wing works great

My timer turns the power down slowly but the rotation does not decay as the wing descends, So yes it does autorotate.

The "funnies" do not occur the flight is very stable take off and landing are almost the same spot on the floor.

The wing flies with quite a bit of dihedral.
The curved motor mounts are required so that rog is possible as the point of contact with the floor moves along them during take off.
Relative to the floor the wing flies at approx 20 to 30 degrees.
The rpm approx 150 to 200

bobsworkshop.co.uk explains more about the timers