Bob Llewellyn

CS-VLA allows use of a sheltered intake for carbys that are "inherently resistant to ice formation", whatever they might be...

mmf, it's been a long time since I read the book... but I still find the idea of mishandling the engine in order to stay aloft, mildly horrifying. Wasn't it actually ice forming on a gauze stone filter or something? I have had icing in a Thruster, and I was pretty disgusted at that... flying along a bit of low-altitude wave, and a wisp of cloud started to form around me, out of the blue... then the trusty ring-a-ding began to splutter. Sawed the throttle and left the cloud...

Earnest K Gann, richening up to get a backfire to clear the ice before it stopped the engine... every few minutes...

....and here's the one I wasn't going to put up today... the sub-helical twist with tapered tips and a tad more advance... shows that efficiency and thrust don't go hand-in-hand... Prop #1-5.pdf Prop #1-5.pdf Prop #1-5.pdf

No worries... That's because you're not mad enough ... it rots your brain... makes you think politicians are silly and the media is shallow...

The certification requirement is that an energy input sufficient to raise the air temperature 50C, is sufficient to control icing. It's not actually a function of energy input; it's a function of lifting the temp out of the zone in which icing can occur. If you fly in marginal icing in VFR conditions (been there), holding an electric cigarette lighter under the slide often helps. But if you're ever caught in serious icing, the Rotax electric system is useless. The Merlin - which normally fought day VFR - used a water-heated butterfly... with a 1,200hp heater...

Getting back to the constant chord versions, here's what happens when you reduce the root advance and increase the tip advance... it's getting a lot more useable, although the first part of the takeoff will still be pretty lethargic. This is probably it for today, but we still have to look at effects of spinner size, tapered tips on the reduced-twist form, changing the thickness distribution, optimising the twist distribution, fine-tuning the chord distribution, and fine-tuning the taper (or planform).... Prop #1-4.pdf Prop #1-4.pdf Prop #1-4.pdf

Now find attached, the effects of tapering the outboard 1/3 of the blade, from 4" to 3"... Prop #1-3.pdf Prop #1-3.pdf Prop #1-3.pdf

wonder if it's varnish or coking on top piston rings? If so, too hot... good case for silicon based oil!

Because most of the information on modern cylinder bore treatments is proprietary (and secret!), it's hard to justify the reliability; and doing it in the backyard does not garauntee good results. Lycoming brought out a "cheap" training donk with steel bores and chromed rings, which has the same prob. as Jabiru (some model of O-320, from memory...). The lesson is, don't stop flying for more than a weekend. Ever...

Find attached the effects of increasing the advance by 10", with no other change. Stay tuned... Prop #1&2.pdf Prop #1&2.pdf Prop #1&2.pdf

It adds bending moment. It adds a lot of root bending moment. Any effective tip device does. The winglets on one of the Cessna twins - 421 mebbe? - drop the fatigue life to ~1/4 of the life without winglets. The Hoerner tip produces less bending moment than a winglet, and less benefit than a winglet; if you want the benefit of higher aspect ratio, build a bigger wing. There are far better places to improve most aeroplanes than the structurally arduous wingspan extension. Airliners use winglets for hangarage reasons, not because they're better than a span increase.

They're fair cows... the physics is NOT as simple as it looks. I've spent a lot of time developing prop analysis tools (and, I'm pleased to say, I've won an argument with Hartzell about the performance of one of their own props!)... Anyway, once you've got a set of charts showing the effects of various geometry changes, you'll have a better idea of how to pick one, at least..

Sorry I was distracted, and only ran one prop - I normally start with a constant-chord helical twist, and it's in the attachment. I should be able to run a couple more tomorrow, and a couple more the next day - by which time you may be shopping for a variable pitch prop that'll hold its blades!! Cheers, Bob. Prop #1.pdf Prop #1.pdf Prop #1.pdf

Next time you get into a dogfight, you might be sorry... 3~4% can be the difference between victory and defeat!

Good question. At a guess - and it's just a guess - the spat is far enough below the cowl outlet for the effect to be small. For reference, the DC-3 fuselage was found to increase the nacelle (engine) drag by ~11% or so... and those engines weren't terribly close to the fuselage!

sure thing - I'll have a go later tonight, after I've welded myself to the scenery (or set fire to my overalls!) and convinced the kid to sleep :o)

The deal with fixed pitch props is that they have a pretty limited speed range; it can be extended by having the inboard part of the blades stalled at low fowards speed, but this requires either a bigger donk (Spitfire 1 is an example) or a very long takeoff roll! Even the humble Piper Cherokee, which barely manages twice its stall speed at high cruise, was offered with a "climb" and a "cruise" prop. Because of the thick shank, most wooden props are stalled near the blade roots at low speed, which contributes to the perceived vibrations and poor cooling flow; but the reduced anti-rotational "lift" of the blades allows the engine to develop more power early in the TO run. The classic helical twist prop shape - c.f. Fred Weick - is very much of the "extend the speed range by stalling the shank" school. From this aspect, use of a smaller diameter prop gives a higher static speed through the prop, so for the same speed ratio, the smaller prop has a higher top speed. If you let me know the prop RPM at the engine's full power, I can run you a couple of performance curve estimates (they will vary with twist distribution and planform, but not hugely).

Dafydd became an aeronautical engineer about a century ago, and worked in aviation businesses, for DCA, and as a consultant... I've worked professionally in the design area for the last 12 years. In the CAR 35 game, one has to become an expert on the job(s) at hand, so I've learned fluid dynamics, FEA, metallurgy etc on the fly - doing a bit of electrical engineering back in 1988 and 1992 helped, but maths, physics, and materials science at high school has been fundamental. I recomment to you, very strongly, the NACA reports on the web (cranfield site); there's a lot of practical experimentation up to the end of WW2... there's a weakness in the airfoil data, as they were in love with their variable density tunnel, and a bit short on appreciating how much extra turbulence exaggerates the Clmax of laminar or otherwise poor low Reynold's Number sections; and the RAeS (Lock etc)had a much better grasp of propellors; but things like surface finish, wing planform effects, undercarriage drag, and practical stability are all there... and how to correctly baffle a Continental (ignored by Cessna!), etc etc

That's a big speed range - how much should it weigh, and what are you using for a prop?

I think it was a Hawker specialty - I believe they machined tricky multi-spigotted tube ends, which were rivetted into place. It avoided de-heat-treating the structure by welding, gave spaceframe structural efficiencies, and made them rather faster to repair from battle damage. Does anyone know how Shorts / Fairey fastened their polygonal stainless steel tube structures?

Sounds good - speaking as a speed freak (who flies Thrusters...), reducing the outlet area as a nozzle should give a bit of "thrust", provided you don't increase the positive pressure field around the inlet. Anyway, reducing the cooling flow certainly reduces the cooling drag.

Oh yes, GIGO always applies; but when an FEM of a thin-shelled circular tube under torsion loading produces a steadily increasing plate shear around 360 deg, with a step back to minimum, and claims that the solution is correct, and the inputs and reactions are appropriately distributed, the algorithm(s) are called into question... the same model worked well in bending, but not torsion... The ability to crunch numbers is certainly faster than, say, the Douglas design office; but the equations are no different - and for the proponents of "more complex is more accurate", chaos theory is hard to argue with. Certainly the graphics give a clear repesentation. I am averse to neither FEA, or modelling; I use FEA regularly, and have developed quite a few mathematical models in my time; but doing so has made me very cautious of the extrapolative ability of complex models, and acutely conscious of the shortcomings of FEA when applied to structures. As these same shortcomings are increased by at least 2 orders when applied to fluid modelling, even by the heat transferrance analogy, I don't trust aerodynamic FEM very far at all. For those who like it, feel free to use it. My understanding of an engineer is one who appreciates, and can compensate for, the uncertainties of reality. For me, fluid FEM (other than perhaps simple elemental models) introduces more uncertainty than it removes - just because it shows expected results does not mean that it is correct!

Well, yes, as them isobars are inextricably linked to local velocities and so - at high speeds - compressibility, yes. However, I was positing that the isobar distribution need not be so gradual if the flow speed is well below compressibility shock initiation.

djp, it was a hangar discussion during morning tea at a small Aus aircraft factory; the bloke was a (visiting) honours graduate in Eng. Aero from some major Aus university, and he'd been expanding his FEM / FEA experience whilst - I think - visiting the US. At the time he spoke, he said that there were a couple of prototypes entering construction, and the "real" reason was primarily to resolve the FEM issue. Bearing in mind that this probably represented the views of the FEM people he had been working with at the time, I can't say how big the FEM disagreement was in terms of the overall project, or how it was eventually resolved. From foggy memory, compressibility in the flap shroud had something to do with it... hrmmm... are you familiar with R&M 2375 (the "King Cobra" flight tests in pursuit of laminar flow?) Hoerner's world tour (so to speak) of sphere tests of major wind tunnels is also quite revealing. Perhaps it is simply my mathematical unsophistication, but I am as yet unaware of how to repeatedly solve large systems of simultaneous equations without "forcing". The concepts of fluid flow modelling that I have dabbled in, have all required either sweeping simpifying assumptions or VAST numbers of equations... even Brownian motion does not equate to the small scale turbulance found in nature, and the subject of turbulent vortex size range influence on local surface pressure gradients at the difficult Re of 3,000,000 ~ 7,000,000 makes too many unknowns for the variables.