Technical Talk (Aerodynamics, structures and such)

[hank jarrett]

There was a suggestion to start a technical thread here to discuss the technology in WW-I. Sounds like a pretty good idea to me. There are several Aero Engineers on the forum and a technical thread might be a lot of fun. Everyone needs to understand that the aerodynamics world evolved PAST what they were doing in WW-I (for a LOT of good reasons) and really good technical data may be hard to come by. This thread may have some "interesting" opinions with little solid data to back them up.

NACA gathered data on some WW-I planes early on and there was some testing but not much was focused on aerodynamics. I know I saw a LOT of info on props, engines and cooling systems in the NASA libraries as well as a lot of tests on different landing gear configurations. Unfortunately it was a lot of REALLY OLD information and no one had ever cataloged it (I tend to crawl around in places no one else ever looks and I find things everyone else thinks is trash. Sometimes THEY are right, sometimes I strike GOLD). I'm retired from NASA now so I will need to find out if they will still let me crawl through the archives. Why not? No one else seems to!

Hank

[j ferguson]

Hank,
Although I now fly a swivel chair, and my construction is limited to boat appliances, i think this would be a very useful thread.

Brisfitworks spent a lot of time in personal messages helping me to understand the relative aerodynamics of thin winged planes with a lot of wires (think Spad) vs cleaner, thicker chord planes like the D7. My thoughts were directed to the question of the possibility of equivalent performance due to possibly equivalent draq, the one case being from all the wire, and the second due to airfoil.

He seems to have left the fold here, but his thoughts seemed sound. Besides, one of the real problems in these discussions is not knowing what you don't know.

good luck with this idea.

john

[1eyedpilot]

Unfortunately it was a lot of REALLY OLD information and no one had ever cataloged it

Oh, for shame! These things need to be catalogued if only for the sake of the historical record. Someone could put together a nice expensive book with obscure subject matter! Yes, I know that it requires work, so this is mainly just a lament. However, the engineers among us should be able to provide some good insight as to what design elements are important for the very thin sharp nosed airfoils usually used in the early designs, just based on accurate lift/drag/moment data if such data exists. Important would be stall/spin entry and recovery. One member here frequents the other airplane forum I am a member of and posed a question about one such "primitive" airfoil to which the chorus (of which I'm a member, I'm afraid) all began chanting "Don't do it, don't do it, don't...." ! There is a sort of logic there, i.e., to "stay on the beaten path", which is a poor substitute for "stay on the well understood path", but, lacking understanding, what else can you do?

As for structures, as long as the loads are understood well, I see nothing wrong with the old wood and wire type structures; structures were well understood and had been for some time and some relatively modern aircraft were built this way into the late thirties and even into the fifties, I think, such as the Stampe and the Avia-Lombardi Fl.3.

I'm very interested in this old technology and wish to learn more, sorry I can't contribute more. Some of the old planes had reasonable handling, from what I understand. As an opinion, I think that it should be possible to design, say, a Rover v8 powered Se5 replica built in the same way as the original and with a similar airfoil that had nice (and safe) handling. Auto conversions are a whole other can of worms, though.

I would like to have some insight on how and when and by whom, the stability and control equations were made increasingly important in aero engineering and if they were used much during the war. I know that they were derived fairly early on.

[paolomiana]

Originally Posted by hank jarrett

(I tend to crawl around in places no one else ever looks and I find things everyone else thinks is trash. Sometimes THEY are right, sometimes I strike GOLD).Hank

Hi Hank,

I know the feeling - just spent last holydays digging in the alenia archive for WWI stuff; I wish to use it in a book about WWI italian aviation technology development.

A good starting point to approach such a topic is flight archive, on line for free here

Aviation History - Browse the History of Flight from 1909

or a search on Internet Archive: Digital Library of Free Books, Movies, Music & Wayback Machine thta host a LOT of related books

all the best

Paolo

[TSJohnson]

It would be interesting to discuss the evolution of airfoils and their design.
What is the process for airfoil selection for a particular design, rules of thumb etc.

In the meantime, here are some links to whet your appetite.

NACA Technical Reports
NASA Technical Reports Server

NACA-TR-93 Aerodynamic characteristics of aerofoils I
http://hdl.handle.net/2060/19930091156

NACA-TR-124 Aerodynamic characteristics of aerofoils II : continuation of report no. 93
http://hdl.handle.net/2060/19930091187

NACA-TR-182 Aerodynamic characteristics of airfoils III : continuation of reports nos. 93 and 124
http://hdl.handle.net/2060/19930091247

NACA-TR-244 Aerodynamic characteristics of airfoils IV : continuation of reports nos. 93, 124, and 182
http://hdl.handle.net/2060/19930091311

NACA-TR-286 Aerodynamic characteristics of airfoils V : continuation of reports nos. 93, 124, 182, and 244
http://hdl.handle.net/2060/19930091355

NACA-TR-18 Aerofoils and aerofoil structural combinations
http://hdl.handle.net/2060/19930091046

NACA-TR-309 Joint report on standardization tests on N.P.L. R.A.F 15 airfoil model
http://hdl.handle.net/2060/19930091378

[drrivah]

Hank:
Your idea is an excellent forum for those of us whose curiosity exceeds our
technical/engineering training.

OK, here is a structural flaw in the N28C.1 (underside of starboard upper wing facing) that did not appear in prior Nieuport designs, the N27 for example. Can we reverse engineer why this occurred pulling out of a power dive, what the essenital structural design flaw was, and ask what role materials and aerodynamic forces interacted to cause near fatal results.

In this case, sharp pull up near Vne rapidly changed airfoil angle of attack. Junction between lower rib and riblet attachment to forward face of main wingspar was stressed beyond its strength: loss of riblets, loss of ribs fwd of main spar, loss of compression ribs fwd of main spar, shredding of wing doped fabric, loss of fwd ~12% of airfoil along entire fwd margin of upper wing.

It is of interest why such a series of events resulted in such little damage:
Meissner was still able to nurse the 28 safely back, and walked away, although he was not a happy camper as a result. Lucky the ailerons are on the lower, not upper wings.

Why did this happen in the N28, but not the N27?

-pete

[1eyedpilot]

In this case, sharp pull up near Vne rapidly changed airfoil angle of attack.

One piece of the puzzle would have to be in the sketch below. It is a mathematical approximation of the chordwise lift distribution from thin airfoil theory. The real lift distribution is smoother and more flowing but this approximation is good enough to do the actual structural design of the wing rib, etc. according to Hiscocks. As you can see, while there is lift over the entire chord, it is most pronounced at the leading edge and at high angles of attack the lift would be very strong (at its strongest) at the leading edge placing a large moment on the front part of the ribs. Why these ribs failed when others don't, I don't know:

[jumpinjan]

Originally Posted by drrivah

...forward face of main wingspar was stressed beyond its strength: loss of riblets, loss of ribs fwd of main spar, loss of compression ribs fwd of main spar, shredding of wing doped fabric, loss of fwd ~12% of airfoil along entire fwd margin of upper wing.

It's just a bad design, that didn't appear with the lighter Nieuports, but did fail with the larger & heavier Nieuport 28 and/or poor construction quality with the N28.
The CP will move forward at high AoA, so yes, the forces will be much greater in the structures just forward of the front spar.
Jan

[drrivah]

OK, I like the explanation. Lift unsustainable by wing structure at high angle of attack. Probable excess compression where rib capstrip met upper front face of main spar as well as excess tension where rib/capstrip met lower front face of spar. Wooden structures under stress not supported by seam of doped fabric. One fix is pilotage: do not pull out so abruptly (maneuvering speed caution issue?).

My colleagues say the engineers "fixed it" (no detail).

How would you have addressed the "poor design" to make it serviceable with minimal weight penalty added?

Now some comparisons:

Parameter N27: N28
Gross Weight 1290 : 1539
Capstrip 5/32 ash : ?
Ply 5/64 poplar : ?
Rib web 4 mm poplar : ?
Spar 39/64 x 1 25/32 : ?
Width
Comp rib 1 1/4 : ?
Normal Rib 5/8 : ?
Noseriblet spacing
2/bay : ?
Wing back sweep ~4 deg : None
HP 120 : 160


Diagram from B. Hardesty's N24/27 Blueprint (1956). Don't have comparison of N28 dimensioned structure with materials identified.

[jumpinjan]

I would suggest make a "D-box" front spar, by applying plywood sheeting around the leading edge and secured to the existing front spar. An aerodynamically benefit is from the smoothing of the leading edge.
Jan