Helice Normale

[pmdec]

Hi,

@ Dennis : great pictures, thanks!

@ Pete : there is no standard thickness for laminations before 1916 in France. An often used thickness is 20mm, but one, or both, "last" laminations were often thinner, so you can't deduce lamination thickness from hub size.

"2m08" is 2.08 meters. "WmXY" is a common writting for W,XYm, that is W.XY (in France, the coma is used in place of the dot to mark decimal). "2m08" writting is not "official", but easier to read: you don't tell "two coma zero eight meters" in current language, but "two meter zero eight". And strictly speaking, 2m08 is 2.08 meter, or 208 centimeters, but not 2080 millimeters, as if there are only 2 digits after the dot, it implies you don't know the measure with a millimeter accuracy, while 2080 millimeters "tells" it is not 2081 or 2079.

Regards,
PM

[drrivah]

Helice

If I understand, then the pitch "0m76" would be 760 mm, or 76 cm? I understand your point about significant digits and metrology.

From an engineering point of view this apparent 76 cm pitch for a Ratmanoff prop doesn't make sense for a 208 cm prop. Should be minimum of 100 cm.

I would disagree on the board thicknesses: all sawmills cut boards to a standard thickness, even a century before 1910. Ask anyone who has done carpentry. The one thinner board in front or back is a means of saving material on a part of the hub that is not full prop length, not a result of having random board thicknesses.

Let me see if a 20 mm thickness fits with other photos of European props.

Thanks.

-pete

[pmdec]

Hi,

.../...
I would disagree on the board thicknesses: all sawmills cut boards to a standard thickness, even a century before 1910. Ask anyone who has done carpentry. The one thinner board in front or back is a means of saving material on a part of the hub that is not full prop length, not a result of having random board thicknesses.

Let me see if a 20 mm thickness fits with other photos of European props.

Thanks.

-pete

I was not speaking about boards, but about laminations. There was, during WW1, and probably before, a kind of standard thickness for boards use to make laminations: 27mm. It was NOT 1 1/16, because metric system was in use for a long time, and before it, there were some different "archaic" measurement units in different France areas.

And I didn't tell there was random thickness for lamination, but use of different thickness in the same prop, all planned (same for all props made from a particular blue print: prop blue prints include laminations thiskness, even in 1910 (I have no blue print example before)).

During WW1, some standards appeared, for example hub thickness: they were 95mm, 100mm, 103mm, 150mm and 180mm. As you can see, the "greater common divisor" is one millimeter... Even if yoo look only for 100, 150 and 180mm hubs (95 and 103 are discontinued for new designs after about 1915), the "greater common divisor" is only 10mm. And props were not made with 10mm laminations (but there were some built from 5mm, even less: it is another story).

Perhaps, if you clarify why you are looking for, and which data do you need, I may (or not) write what I know (or believe to know), without handing in all directions!

Regards,
PM

[drrivah]

Ratmanoff Helice Normale

Dave:

I have used a calculation to estimate sections and helical angles at the labeled radii for the Ratmanoff Helice Normale prop from the photos. Now to test how good the fit is, if you will indulge me.

Dave, if the sections below were scaled to the bottom width at the radii indicated, are they close to the actual sections on the Ratmanoff prop?

Are the section bases (the surface closest to pilot) flat as shown here, or concave?

-pete

[pmdec]

Hi Pete,

Intrados side (the surface closest to the pilot of tractive props) is flat on Ratmanoff Normale props.

If you want to understand how those props are computed and made, and why they are like they are, you have to read two books from Stefan Drzewiecki, who was the man who computed the Ratmanoff props (Normale Ratmanoff props were "Drzewiecki patented":
- Des Hélices Aériennes, Théorie Générale des Propulseurs Hélicoïdaux (About air Propellers, Global Theory of Helicoid Propellants), published in 1909,
- and Théorie générale de l'Hélice (General Air Screw Theory), published in 1920.
I can't make copies, because they have too many pages, and all had to be read. Pretty fun: the back cover of the first one is a Chauvière advertisement You may find the second one in Google Books.

About your sections. IMHO, I think you take it the other way round. Sections are deduced from propeller full size drawings, and used to make templates to control the work in progress. Sections have to show the different laminations, because workers use the shape of the glue lines to make the prop right. Except if you use a numeric cutting machine, but then you will never have a credible replica, because softwares are not designed to make "old fashion" propellers...

About lamination thickness: have you find something? I have looked at some props and found different thiickness, from 16 to 22 mm., but 20 mm. seems to be the most common. I have two Levasseur WW1 props of the same serial, one made by Levasseur and the other by a subcontractor. All measurements are identical, but one have 8 laminations and the other have 9 for a 180 mm. thick hub: look at the pictures...

And I do not understand what you want to do. Prop replica? Airworthy ones? Or to sell them on eBay ?

Regards,
PM

[Dave]

Actually, the laminations on the Normale prop are unusual. The front and rear thicknesses are 30 mm and the two central boards are 17 mm. The total is 94 mm.

The approximate pitch could be determined using the angle of the blade at the tip, knowing that the distance from the center bore is half the diameter of the propeller. Both of the attached photos are first leveled to the horizontal then the angle at the tip and another one at 40 mm from the center are shown. The rear of the blade is flat throughout - neither convex nor concave in cross section. (Note that the blue template tool remains flat along that surface.)

[drrivah]

Helice prop math

Hi Pierre-Michel:
The point is to understand prop design theory (historical and modern), how it has evolved and how to design props for new (2012) engines.

I am curious to know where, in the inventor's mind, ideas and technical innovation come from.

Regarding lumber, in the U. S. the rough-cut board is labeled and graded in quarters of an inch.

4/4 (26mm)
5/4 (32mm)
6/4 (40mm)
8/4 (51mm)
10/4 (64mm)
12/4 (77mm)

Nominal 1" lumber is sold as 1", if planed and smooth sided, has a final thickness of 3/4" (0.750). Note that a rough cut 26mm board planed to 20mm would be 0.78", close to the 3/4". So, 20mm seems reasonable for stock European lumber planed both sides. My guess is that in 1909, a small inventor would just go over to the 1909 equivalent of Home Depot, and buy a few boards (without wood flaws) off the shelf for his experiments. In the US, they would have been 3/4", in France likely 20mm.

Your measurement on the Levasseur examples is consistent with the idea that prop makers used 26mm lumber planed to 20mm finished thickness.

BTW, investigating old props is like synthetic analytical chemistry: you make some measurements about structure, take a few guesses, come up with a likely structure. To confirm your deductions and experimental guesses, you have to synthesize according to your hypothesis and see if the final design is "right". This may lead the experimeter to understanding structure, at which point he may be tempted to make a "better one".

Thanks.

-@pete

PS: My first experiment is here:
http://s290.photobucket.com/albums/l...ops/?start=all
It is not a copy of a prior historical design: it is new, based on study of prop math and old props, for use possible on a C85 engine. It is pine, and a first model, not meant to be used on an engine. If warranted, a test model would be constructed of walnut, properly balanced and certified.

[pmdec]

Hi Dave,

Actually, the laminations on the Normale prop are unusual.
.../...

All is unusual about Normale props: Drzewiecki had very special theories. His main one was to make prop with a constant Angle of Attack along the blade of about 2°. Angle has to be computed taking into account the displacement at the expected speed and the direction of the air stream when flying. Very interesting, but those shapes have been quickly discontinued, probably because they were not truly efficient.

Regards,
PM

@drrivah: I will be out for a while, so don't expect answers before end of the next week. I have already seen some of your pictures by looking at the address of the one you posted (right click and "picture properties" gives the PhotoBucket address of your albums. Beware of that ). Nice job!

[drrivah]

Helice

Hi Dave:

"Whoa: way cool".

More on helix math, face angles and what goes in to figuring that, shortly...

-@pete

[Dave]

Hi Dave:

"Whoa: way cool".

More on helix math, face angles and what goes in to figuring that, shortly...

-@pete

I realized that the two angles I showed above might not match up. The first photo is taken end on and the yellow line is probably close to the chord. The 40mm one is showing the rear face, so the angle of the chord line might be slightly different. (Although I think it would be the rear surface that would be used to estimate pitch.)

[D.Hicklin]

Magnificent obsession!

I along with Bob Gardner wish to say how much this particular thread is truly fascinating. It is greatly appreciated that this site exists, its like a pack of would be sherlock holmes types that are on the hunt for all of the clues, it just gets better and better with each passing day.

That being said, as much as I am involved in the aviation industry on levels that most dont get to enjoy, the little kid in me that has the ability to also poke fun at the aviation world through graphic design and silkscreened textiles ( T-Shirts ) I will now post a photo of an image that I designed about 12 years ago.

Before the replys start as to what this machine is, here are the specs. The front engine is from a B-17, with a 3 bladed hamilton standard with an aero-matic hub. The main rotor is from an aerospatiale lama powered by a turbo mecca turbine. The cock pit is from an air tractor aerial applicator, and the tail rotor is from a bell jet ranger III. The tractor is the model "U" which stands for universal and it was manufactured by Minneapolis-Moline Co.

Each year when I bring these shirts back to the seaplane base at oshkosh, its amazing how many people just get a huge kick and a belly laugh when they see this mating of exotic interconnected mass of meshing gears.

Every circus gets quite when the trapeze act starts, especially when there is no net, think of this as the small clown car that comes out to offer a bit of humor to something so serious and sacred.

Sincerely,
Dennis Hicklin
Seattle Washington

[drrivah]

Helice Normale

Hi Dave:
...at the risk of throwing (more) gasoline on the fire...

OK, and at risk of exposing rank ignorance, time for some testable specifics. I made a few assumptions about the Ratmanoff form and prop sections and have run a few rough numbers to test whether model 1 or model 2 is closer to the real prop.

Ratmanoff D2080, Pitch Unknown.

RADIUS Predicted Face Angle Predicted Max Section Thickness
MODEL1 MODEL2

231mm 39 deg 33 deg 50mm
404mm 26.8 deg 18.5 deg 31mm
578mm 20.5 deg 9 deg 25mm
751mm 8.1 deg 3 deg 22mm
924mm 5.5 deg 1 deg 14mm
1040mm 0-5 deg 0-1 deg 10-14mm

Radius leading edge corner ~1040mm radius= 36mm
Radius training edge corner ~1040mm radius= 54mm

The nice thing about the models is that you have something to measure to say "yes" or "no" or "maybe". Or, back to the drawing board...

On working this exercise so far, I have to retract my skepticism above about how low the overall pitch is. Could actually be "0m76" (ie, 760 mm), which would be astonishing, but I have to bow to the authority of the data however it turns out.

The above was done from measurements and assumptions without assuming
anything about pitch.

Have fun.

Cheers

-@pete

[Dave]

I'm not sure how to process all those figures. I would think, however, that a single angle at a known distance from the center would give you a rough idea of pitch and that all measurements along the blade would be predictable based on that estimate.

In this case if you assume the angle of the chord is 6 degrees at a distance of 105 cm, then the pitch calculated on that basis would be extrapolated to any point along the length of the blade, as in this diagram:



Certainly just by looking at this Normale propeller in the picture at the tip I would consider it to be a very FLAT pitch compared to most others.

I've forgotten any trigonometry, but an angle of 6 degrees would "climb" a specific distance over the course of the circumference of a single turn, and that circumferential distance is a simple function of the radius of 105 cm. (PiXD, or 210 x 3.14 = 660 cm ). So how far "up" does a 6 degree angle go in a distance of about 660 cms?

[drrivah]

Prop Math

Dave:
I agree you can measure the angle at any radius and get a first guess of pitch.

The diagram you posted is very complicated (but complete in terms of engineering). It has three or four families of information going on: to define the form of a prop without a diagram you have to take one family of parameters at a time and nail the family down before proceeding.

Since the blade is relatively narrow (compared to Chauviere), the blade edges are nearly parallel and the "intrados" side is flat bottomed, the most likely airfoil family is as follows:



The family is mathematically defined, but don't worry about that yet.

To ask whether you have the right family of airfoils on a prop, you need only measure the thickest part of the airfoil at any radius (defined).

For example,

At radius 231mm, 50mm should be the thickest part of the airfoil. Easy to measure with a curved caliper and metric ruler.

If wrong, no need to do more (back to the drawing board). If right, look a little farther out at:

Radius 404mm: the fat part should be 31mm thick.

And so on.

-@pete

[drrivah]

Helice

Dave:

At D2080 P076 with typical airfoil sections I get:



Most of blade is P076 but there are some non-linear adjustments
that may be due to measurement error or intended design.

-@pete