C-4 "Centenario" Autogiro project

[Arco]

Hi,
I would like to introduce you our project: making a replica of the Autogiro C- 4 and flying it ( https://centenarioautogiro.com/en/ ) to commemorate the first flight of a rotary wing in the world.
This historical event happened on January 17, 1923 when a C-4 autogiro flew in Getafe, Madrid Spain. Today, the aerodrome exists and it is an aerodrome used by the Spanish Air Force and Airbus Spain. https://goo.gl/maps/S3TQFuiXE9Mn8oedA
Our goal is to fly the replica of the C-4, in the same place and on the same day, 100 years later.
Later on, in the spring 2023, we are going to prepare an autogiro and helicopters meeting to which you are all invited. We have the collaboration of the Spanish Air Force that will open the aerodrome and will bring its helicopters for this purpose.
The project began in February 2022, and our goal is to have it ready in September/October, to do the flight tests on fall.
There are no original drawings at all, we started the design phase based on photos and some old books, quite a challenge, both technically and financially, since it is a project financed by ourselves.
We have already made the airframe and we are assembling the systems: control, engine, rotor, fuel, instruments...
In this forum there are at least three participants, Fernando Rosello https://www.rotaryforum.com/members/ferranrosello.1799/, Javier Susaeta https://www.rotaryforum.com/members/xxavier.2654/ and myself.
I encourage you to see the following web site where we will be exposing the progress of the project: https://centenarioautogiro.com/

Please, we would like you to give it as much publicity as possible and of course if you can help financially better than better. We will be very grateful.
I hope you like it.
I will post some pictures, enjoy!!

 

[Arco]

 

[WaspAir]

Very exciting - wish I could visit!

 

[Mayfield]

Absolutely gorgeous!

 

[Jean Claude]

I hope that a modern rotor on this beautiful project will not be too obvious an anachronism.

 

[Arco]

The rotor was a big issue when we stared the project.
From one side we want to do a replica as close as possible to the real autogiro.
From the other side we know that the C4 rotor design was defective, it has only one articulation, the flapping, but not the lag articulation and will be a matter of time to have a catastrophic failure.
We could use a rotor based on the C- 7 ( the one with the two articulations) or any other design form de la Cierva.
So in any case from rotor point of view, we are not going to be stick to the C-4 because safety, but we want to use at least a Cierva design rotor or based on his patents.
Doing a search in his patent list we discovered that he patented the semirigid rotor, so we found the solution to use a Cierva design but a safe design.
See the document attached, patent dated December 6 1926 page 69-71. The document is a very nice technical document, sorry in Spanish, enjoy it.

https://www.oepm.es/export/sites/oe...aciones/monografias/juan_de_la_cierva_esp.pdf Very nie doc

For us was a surprise discover this patent, and we was very happy because we solved our problem to use a safe rotor based on Cierva deisng and patents.

As you can see the anachronism is not obvious or even looks a real a anachronism.

 

[Jean Claude]

I am very surprised to see that Juan de La Cierva had already thought to a seesaw rotor in this patent (fig 1,2,3,4) of 1926. I thought it was Arthur Young, later.


In any case, fig 5 and 6 seem to me to be forbidden because of the lack of articulation of the drag when the centers of the flapping do not cross the axis of rotation. Moreover, they seem to me to be marred by a geometric rigidity of the flapping, despite this hinge.
The biggest challenge will be the design of your rotor

 

[Arco]

Yes, this was our surprise too. For this project the time is very critical, we started less than year in advance of the centenary date, so we don't have too much spare time and we are going to use a conventional seesaw autogiro rotor. Just to design and make the airframe, test it and to learn how to fly a gyro without cyclic control is enough challenge.
The effort to design a new multiblade rotor it is more than 10 times complex than to do a complete new airframe autogiro, in fact, since the Bensen rotor design, all the new projects are focus in the airframe but none is focus to create a new rotor, that it is the key component of a gyro.

 

[Aerofoam]

I designed a small radio control autogyro in 1995 that had a teeter bar with the "Delta 3" hinge line.
It had a fixed head and small winglets with polyhedral wing tips, no ailerons.
All control was rudder, elevator and throttle.
It flew better than any of the conventional semi articulated head designs I have flown since....
Go figure....
It would seem like a control problem at low air speeds, but that problem never happened.

 

[XXavier]

I enclose one page of the Cierva patent related to what we know today as a semi-rigid rotor, with a translation of the relevant lines.





(…) diverse construction forms according to the present invention, showing:

Figures 1 y 2, respectively, in plan and elevation, a construction form that includes a pair of wings built as a single element.

Figure 3, a detail in elevation, in part as a section across the hinge joint.

(…)

In figures 1, 2 and 3 two wings A and B are shown, mounted as single element on one or several common longitudinal beams, with a vertical angle -x- between them, this angle being –in the general case– the same angle as that formed by the wings during a complete revolution, were they independently hinged.

These wings are fixed with hinges in the center C as if they were a single element, on a practically vertical element D, that rotates w.r.t. the structure of the flying machine, being mounted on it by any of the known and appropriate ways.

 

[XXavier]

I designed a small radio control autogyro in 1995 that had a teeter bar with the "Delta 3" hinge line.
It had a fixed head and small winglets with polyhedral wing tips, no ailerons.
All control was rudder, elevator and throttle.
It flew better than any of the conventional semi articulated head designs I have flown since....
Go figure....
It would seem like a control problem at low air speeds, but that problem never happened.

Very interesting...

It could be that the zero delta-three of the teetering rotor head used in most gyros is not optimal. Perhaps a moderate amount of delta-three might improve its efficiency. In his patent of 1926, Cierva states that it (then not yet known as delta-3) would improve the efficiency of a rotor, due to the reduction of the interval between the extreme values of the incidence of the advancing and retreating blade...

 

[Arco]

From aerodynamic and aeroelasticity point of view, a small autogiro and real size autogiro doesn’t fit too much.
Among other factors the Reynolds number is quite different, as consequence the autorotation angle range is totally different.
The conclusions from one to the other in terms of stability or control needs to double check carefully.

Follow the project: www.facebook.com/centenarioautogiro
Support the project: www.centenarioautogiro.com/en

 

[Aerofoam]

From aerodynamic and aeroelasticity point of view, a small autogiro and real size autogiro doesn’t fit too much.
Among other factors the Reynolds number is quite different, as consequence the autorotation angle range is totally different.
The conclusions from one to the other in terms of stability or control needs to double check carefully.

Air foils definitely do NOT scale down well, in general things scale up much easier.
The lack of steady state flow at very small Re. # make laminar flow foils almost useless for small wings.
Older basic airfoils tend to scale down much better. Flat bottoms come into play and as things get smaller (below 50k), air deflection becomes dominant
and Bernoulli becomes irrelevant. The curvature of a wing's foil becomes a matter of delaying separation of flow at AOA, not so much about lift.
This is a sliding scale that keeps moving away from the curved upper and lower surfaces and becomes a flat plane as wing spans get below 8"
Aspect ratio usually needs to be reduced as wings get shorter.
For the small gyro, I used a Clark Y at about 10% and the lower surface was 1/2deg. neg. incidence.
The chord was exaggerated a bit and the rotors were designed to be slower than what one would expect
from that size blade.
They were designed to self start. (they did, even in flight) and the thicker foil was for higher lift at lower speed.
It was only operating at about 250rpm. Most model heli's in that size range are between 350 and 500rpm.
The power to weight ratio and size to weigh ratios are drastically different for models, but aerodynamic efficiency is much lower.
In general, it is harder to make the smaller aircraft fly well. Even harder yet to make it fly like a large aircraft.
You can still learn a lot by building a smaller version before committing to a full size.
You just need to take the scaling issues into account.
Generally, if a small version flies well, the larger version will fly better.
I prefer crashing without pilots aboard....

 

[Jean Claude]

@Arco
If the project airframe maintains exactly the same appearance as the C4, replacing its 120 kg Rhone 9C engine with a 70 kg Verner engine will significantly change the pitching moment. Do you plan to use 50 kg of ballast?

The Rhone 9C could drive a 2.8 m propeller, because of its slow rotation (<1300 rpm). This probably gave it more than 2500 N of thrust at takeoff. The Verner engine has a much faster rpm which does not allow such a large propeller, and therefore its thrust would be much less.
Are you thinking of fitting it with a gearbox?

 

[Aerofoam]

This brings up a point I have been wondering about since the first post.
Is this going to be an accurate scale reproduction?, Or a modernized reproduction that is scale in appearance only?
The weight reduction of modern materials would bring the power requirements way down and get you on the
"Less is More" side of the development curve....

 

[Jean Claude]

The wood and canvas structures keep as light as the aluminum alloy or glass/epoxy composite structures.


The great improvement came from the high aspect ratio of the rotor blades. Not only for the same reason as a glider wing, but also because their faster rotation allows to flatten them with a smaller mass.

Unfortunately the choice of a modern two-blade rotor would seriously distort the retro look.
But I suppose that the team has thought about these issues

 

[Arco]

@Arco
If the project airframe maintains exactly the same appearance as the C4, replacing its 120 kg Rhone 9C engine with a 70 kg Verner engine will significantly change the pitching moment. Do you plan to use 50 kg of ballast?

The Rhone 9C could drive a 2.8 m propeller, because of its slow rotation (<1300 rpm). This probably gave it more than 2500 N of thrust at takeoff. The Verner engine has a much faster rpm which does not allow such a large propeller, and therefore its thrust would be much less.
Are you thinking of fitting it with a gearbox?

From weight point of view the C4 replica will be different.
The original C4 had a MTOW around 500-600 kg and the replica estimated weight is 350 kg.
The airplane size is the same, so the airframe material: wood and fabric will be weight around the same. We think the main weight changes will came from the rotor, the rotor support and the engine.
But the 350 kg is an estimation, but look feasible because as today we are on track.
We are not thinking to use a gearbox, we will made a 2.2 m diameter wood propeller and we will adjust the propeller pitch to the engine performances

This brings up a point I have been wondering about since the first post.
Is this going to be an accurate scale reproduction?, Or a modernized reproduction that is scale in appearance only?
The weight reduction of modern materials would bring the power requirements way down and get you on the
"Less is More" side of the development curve....

No drawings from that time, so we are doing the more accurate replica based on the information we have.
The wood is a very light material. The cabane and rotor post are done in aluminum in the replica, we guess in the original could be done in steel, but no data to confirm.

Follow the project: www.facebook.com/centenarioautogiro
Support the project: www.centenarioautogiro.com/en

 

[Aerofoam]

Yes, there is no real weight advantage between a stick/cloth fuselage and a carbon sandwich other than aerodynamics which are
not really important for a slow autogyro. I figured you would end up at least 300lbs lighter just due to engine, rotors and landing gear.
I was wondering if the engine and landing gear and pilot was going to end up slightly forward of the original position to maintain the CG.

 

[Arco]

This a very good question, but with no a good answer.
We don't know where the cg was in the original autogiro so no way to do any comparison with the replica one.
We are not going to move the pilot seat, we will move the engine to the right position whatever will be.
We will do the calculation of the cg range, we will weight the autogiro all included, ( we will use a dummy engine mounts) and based on the data we will design the real engine mounts length.
It is a very experimental design with many challenges on the way.


Follow the project: www.facebook.com/centenarioautogiro
Support the project: www.centenarioautogiro.com/en

 

[Aerofoam]

This a very good question, but with no a good answer.
We don't know where the cg was in the original autogiro so no way to do any comparison with the replica one.
We are not going to move the pilot seat, we will move the engine to the right position whatever will be.
We will do the calculation of the cg range, we will weight the autogiro all included, ( we will use a dummy engine mounts) and based on the data we will design the real engine mounts length.
It is a very experimental design with many challenges on the way.


Follow the project: www.facebook.com/centenarioautogiro
Support the project: www.centenarioautogiro.com/en

That's a good answer!
Almost all of my projects end up that way.
Many of my larger aircraft have adjustable wing position to account for CG and payload issues.
I suppose you could even do that with the tower and put it on rails that give it a range of fore and aft position....