A straight technical approach to IAR 80, Mytha and reality

RR-56 was also called Hiduminium- an aluminium alloy with Cu, Ni, Mg, Fe,Ti and Si.

My understanding of the dynamic pressure is a slight increase in power by increasing the aircraft speed (the air speed dynamic pressure becomes static pressure in a diffuser/carburetor and helps boosting) If the take-off power is 1150 hp at zero speed, probably in a low altitude flight the engine power can reach close to 1200 hp. Therefore I don’t see how the control stick can influence this effect. However, the fact that I can not see it, doesn’t means that is not true. Any explanation is welcome.

This post has been edited by Glijinski on March 05, 2008 02:34 pm

Well, boosting is a very tricky issue. The general acceptation of boosting is an overpressure in top of the atmospheric pressure. However is not clear if the atmospheric pressure is the local functioning value or the standard sea level value – Marine, automotive and aviation engineers will argue for ever on this issue… I’ll go for your data which are saying 850 mm Hg at 3200 m as “homologation” value (most probably measured in flight with an instrument by a test pilot). Now, if a charger in a given engine/carburetor/rpm combination can develop 850 mm Hg at 3200 m is very possible that at 3600 m the manifold pressure to be 760 mm Hg. In some regards this means means no boost (relative to sea level). So both sets of data might be correct, respectively 850 mm Hg at 3200 m and 760 mm Hg (no boost relative to sea level) at 3600 m. In the mean time any charger known today, driven with a fix ratio can NOT hold a constant pressure when the altitude varies. To regulate pressure the charger should be controlled in some way(s) vs altitude, e.g. varying speed, alternating number of stages, changing fix blades geometry, throttling or combination of the above. My understanding (so far) about IAR engine is a fix ratio compressor driven from the engine shaft. Might had (or not) an altitude regulator acting on the throttle but nothing fancier. Anyways, the throttle compensator is very unlike to correct at high altitude, but mainly at take-off. For a good simulation we’ll need to know several info about the charging system, e.g. compressor map

A single stage compressor is not necessary something wrong if in combination with an adequate control system can hold the same manifold pressure regardless of altitude. Actually is preferred to a two stage compressor because better efficiency and possible simplification in after/inter coolers configurations. Our exercise will try to investigate these aspects too.

The climbing rate is quite a complex and laborious issue. The engine loss of power with altitude definitely affects the climbing rate but also the lift and the induced drag are varying with the altitude. All three might have major influences

Thank you much for your help and interest.
CGlijinski

This post has been edited by Glijinski on March 05, 2008 02:38 pm

Cantacuzino

I got Zinner’s book and doesn’t have anything about the Gnome-Rhone engine (not too much information in general) - quite disappointing! So, the timing is still an important missing information.


I wonder if you can find the cam timing on the drawings. On the IAR engine the camshafts should look like rings (quite different then a conventional camshaft). On the drawings the cams angles might be annotated. Please confirm or not. Thank you in advance,
CG

Below is the distribution ( timing cams) drawing, if it help you.

Mr. Glijinski,

Welcome to the board!
In relation to the first post in the thread, I never heard about an Hurricane airframe retrofitted with a DB 605 in Romania, but I do know about the LVT-1, a Zmaj-built Hurricane fitted with a DB 601a engine in 1941 (just a few weeks before the German invasion of Yugoslavia). Acording to the little information available, the conversion performed very well.
Cheers,
Ruy

This is a great drawing! I tried to upload back the picture with some measurement made on it but something didn’t work. The 3 big lobs are (if it is a view from the prop) exhaust cams and the cam angle is about 28.5 degrees - equivalent with 171 crankshaft angle (the exhaust valve opens for almost half turn of the crank). The other small lobs are the inlet cams. Most probably the inlet cams are machined on a smaller radius and only the top of the lob can be seen. I’ll need a drawing from the opposite direction to fully reveal the other cams and a confirmation (or not) that the view is from the prop. Hope you have one. I’ll need also a detail with the cam followers, or any drawings in which the angle between the pushrods can be measured. Anyway, we are doing progress (which is more important) and I have to say, it’s a nice, challenging and hopefully rewarding exercise. Thank you in advance.
CG

P.S. Can someone produce an explanation (for an anti-talent like myself) about uploading pictures?


This post has been edited by Glijinski on March 10, 2008 10:45 pm

Thank you for clarification. Although it is understandable, I am still amazed (and amused) about how the information can fly. Anyway, is looking like the historians will never be jobless…
All my best,
CG

http://www.worldwar2.ro/forum/index.php?showtopic=2093

With some help (thank you) finally worked.

In reality the angle of cam actuation is slightly bigger than what the drawing reveal (will be further tuned). Anyway, the phase is more important and the drawing is quite accurate. I am pleased with the quality – especially for a hand made drawing 60 years ago. For your (and mine) amusement, I checked also the gears pressure angle and is quite a consistent 20.38 degrees (most probably 20 degrees in reality). I am impressed!

We still need the same measurement for the other 3 lobs (at the root) and the distance between the cam followers.
Thank you in advance!
CG




This post has been edited by Glijinski on March 12, 2008 02:16 pm

I checked once again all the drawings/pictures I have so far. Is looking like the cam followers are very close one to each other and a detailed drawing will be need. In the mean time I noticed in the cams-ring drawing a smaller hole (solo) between the top lobs. Very likely that hole is the top dead center mark for cylinder 1 and does not have any mounting/fitting role. Mr. Cantacuzino, can you confirm/infirm my supposition?
CG

Below more drawings it should help you.

I used D3UNSp for analysys. I can use several methods to calculate the flux: Scalar Upwind Pressure Gradient, ROE, Bhatnagar-Gross-Krook, Van Leer, Rusanov, Centred Scheme. The solver is bi/tri-dimensional and uses non-structurated grids (finit volume - median dual cell) for compressible Navier-Stokes with RANS turbulence modeling (k-epsilon model).
If I remember corectly, last time I used it (some 2+ years ago) I had a 3d grid with 64.000 nodes (part of a plane + the ejection seat). Will have to check with those who used it last to get some updated infos.

Wonderful drawings! At the first view the engine is quite advanced from a mechanical point of view e.g. multiple valve springs, needle bearing rockers, elastic cups bearings and many other features which are still not broadly available in present time engines. Well, I intend to take a closer look sometime in future.

So far all my presumptions were correct. I still need an opposite view for the cam-ring (the pushrod issue is solved) to calculate the inlet valve timing. I hope you have one. Thank you in advance,
CG

This might be enough for some analysis but if we want to see drag/lift issues we need to run 2 orders of magnitude more nodes (few millions). Let me know if you can do it (I can) and let’s try to synchronize our efforts.

In the mean time we have a major problem with the compressor. Normally I’ll need the compressor map but this is really unlikely to get. I am not sure if someone from IAR or G-R bothered to pick up this plots and we might look for something which never existed.
Now, if Mr. Cantacuzino has the compressor drawings and based on the accuracy I saw so far, make sense to try a compressor model. I can built quite fast a 3D model for simulation step, igs, etc (Mr. Cantacuzino, please confirm/infirm the availability of compressor drawings). My question to you is if you can run a transient analysis for a turbo-machinery.
Unfortunately this is a centrifugal compressor and for that size the similitude rules are not working (as you might be used for big size axial compressors).
Please let me know.
CG

This post has been edited by Glijinski on March 14, 2008 10:06 pm