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Propeller Dynamics

Essential reading for model aircraft contest fliers. This is the only book on the market explaining propeller theory in non-mathematical terms. A rattling good read, I know, I wrote it.


Dead and gone to Heaven


It was Charles Lindbergh (born Detroit, 1902) who stated "A coward can sit in his house and criticise a pilot for flying into a mountain in fog, but I would rather, by far, die on a mountainside than in bed. What kind of man would live where there is no daring? And is life so dear that we should blame one for dying in adventure? Is there a better way to die?".

Well I don't know if flying Garuda Indonesia to Los Angeles via Denpasar, Jakarta and Honolulu quite counts as daring, but breathing the smoke from clove-scented Javanese cigarettes sure must! The delta flight from LA to San Francisco, and the drive in Alamo-rental Neon to Reno was tame, but the Corn-Dog poisoning at Stead field was pretty awful.

Certainly the pilots at Reno 1996 Air-Races weren't in any danger of hitting mountains, they were too dang close to the ground! The field is a natural ampitheatre, at a guess 20 miles across. Portions of the race course are below the finish line, so that airplanes would appear to pop up out of the ground as they hit the chequered flag. Classes flown were biplane, Formula 1, T6, T28 and Unlimited, with airshow items in the intervals. After 3 days of this fare, one was quite exhausted. Finals day would have been enough, especially as the airshow items were the same every day: you can handle just so much of the Canadian Snowbirds, Northern Lights and Rocky Hills' Extra-300, despite their non-stop action at very low levels. 

The heavy-metal Unlimiteds were the main attraction, my motivation in seeing them being a rumour that the world is short of WW2 fighters, so get there while ye may. As it turned out, there were heaps of everything, Sea-Furies, Mustangs, Yak-11's, Bearcats. One clipped-wing Sea-Fury, Critical Mass, was particularly attractive in its brilliant black and red livery with racing canopy, but it wasn't as fast as it was beautiful. 

The P51's Strega and Dago-Red were well turned out, but ever since the plastic-fantastic R/C version I have not been a fan of Dago-Red. As things turned out, I was badly mistaken in this irrational bias. Dago had a dose of the same Merlin-tuner as Strega: in the final the two aircraft were locked together for most of the race. When I say locked together, I mean within 50 feet of each other and the ground, at average airspeeds per lap in excess of 470 MPH. That is really extreme! Dago edged out Strega to win, and seeing Dago went all-out in the heats as well, that was some Merlin up front.

Poor old Rare Bear,the clipped-wing F8F-2 Bearcat that holds the World piston-engine speed record at 528 MPH (in hot air in Mexico), did not get to show its stuff, despite a $100,000 engine re-work. Apparently blanking plates were left in the oil-lines, or some similar misdemeanor, and the Bear may-dayed out with smoke streaming from the engine. I tell you it glided like an F3D, I half expected the guy to do some thermalling on the way down. He did at least 3 glide circles before safely dead-sticking on the main runway. It was a great disappointment to me, as the prop on the Bear was in contrast to Strega and Dago-Red.

The Bear, if I recall correctly, has a gear-reduction unit off a
Lockheed Constellation, and was wearing 3 Orion blades. All this to keep down the tip Mach number and hence keep up the profile efficiency. These blades have semi-circular tips, while the big Ham-Stan 4-bladers on the Mustangs were essentially square tipped, so it was hoped the debates about tip shape might have had an answer here: but it was not to be.

Later, I fortuitously met George Heaven at Van Nuys airport, just inside LA. George, it turns out, is not only the designer of the Rubber-Bandit (worlds-first man carrying rubber-powered airplane), but he also does the props for most of the heavy metal. I pumped him about this as hard as human dignity would allow, and it turned out he was not too happy about the round tips on the Bear. 
The argument is that the shock waves formed around the circular periphery of the orion blades produce more drag than those formed on the leading and trailing corners of the square tipped blades.

My own opinion, derived from reading Abbott and Von Doenhoff's "Theory of Wing Sections" and other material, is that the nature of shock formation at the tips is hard to know due to the strong 3-dimensional tip-flow effect on the pressure distribution. I guess it depends just how hard you're pushing the Mach number, especially as with the Unlimiteds you're at Mach .64 before the propeller even starts to rotate. 

The Rare Bear prop blades were interesting visually as well. They had P-51 style cuffs, while outboard of this was a matt shot-peened surface. From 50% to the tips they were very highly polished,like mirrors. The tip section(s) were very thin, probably less than 5%, but with a surprising amount of camber. If anything, they were a cambered flat plate. One of the Yaks was running a Ham Stan Tigerclaw prop, which is a composite prop very similar in blade shape to Ranjit's Rossi prop.

One other gem from George is that the early 50's XF84H Thunderscreech which was a gate guardian at Bakersfield airport (current location unknown!). Damn, I drove past there without knowing! The XF84H is a most dramatic turboprop (Allison XT-40) fighter, featuring a fully supersonic propeller: it is also the fastest propeller driven aircraft ever. According to "The Thunder Factory", it did 670 MPH:

George informed me it did 623 MPH in Air Force tests. That is a must see! 
After seeing the Rubber Bandit (I'm lost for an adjective), we popped into a hangar next door and there was the green Yak-11 from Reno. This aircraft had more power than the propeller could absorb, even with 4 clipped blades. The problem was ground clearance, you just couldn't run enough diameter or get wide enough blades. The blades were Aeroproducts hollow-steel,with the end welded-up after clipping. This revealed a fairly odd airfoil section, not unlike those seen on some ducted-fan blades: quite thick at the tips.

I didn't understand this but couldn't bring myself to pump George further; he had already been far more generous with his time than I ever would be. 
The Unlimited races were conducted in most spectacular fashion. First off were T33 and Mig 17 jets. The race planes took off as quickly as they could after this and chased after the Mig, doing a large circuit around the basin while they formated on the Soviet jet. The Mig then lead them in a dive across the start line, so they were all screaming from the very start. I stand in awe of the skill of pilots who could get just this far.

In the course, they just went flat out, no more than 300' above the deck. As they approached the spectator stands from the left, the noise was spine tingling: something like a swarm of angry bees, the whine rising to a crescendo as they passed by. From the rear, the scream of the props gave way to the clatter of the piston engine, in something of a catharsis. Waiting above them was the T-33, ready to act the Guardian Angel in case of a Mayday. A number of ships got a good once-over from this aircraft, especially the poor old Bear. The Bear is also the symbol on the flag of the Californian Republic (brown-bear, not Rare Bear).

After Reno, we (daughter Remy and myself) visited Yosemite, Death Valley, Las Vegas, Orlando (inadvertently) and New Orleans. Then on to Madera for the Giant Scale pylon racing.

We set up our stall in 90 degree heat, but otherwise beautiful weather, managing to sell all my books and Formula 1 18X20's over the 3 days of racing. We tented on the rock-hard ground, rolling over as each part of the body became numb. Eventually totally numb, we were then able to sleep, despite the noise from the freeway nearby (Exit 17 left for Madera airport). Madera didn't seem to be much of a town, maybe we looked in the wrong place.

The T-6's were fairly boring, the F1's better. Just as in Reno, it was the Unlimiteds that shone. In point of fact, they were better than the Reno heavy metal. With 5 aircraft howling up and down the straight line course, they were spectacular, visible and entertaining. With Herbrandson engine delivering in excess of 35 HP, the top ship, Vendetta, was doing 220 MPH down the straight. On the turns it seemed to lose about 80 MPH, then about 1/3 down the course it accelerated madly, leaving the other aircraft like they were stopped dead. Most spectacular was a P-38 with twin 2-cylinder Husky engines. Quite competitive, this ship was really hauled around the pylons. 

Most impressive on the turns were the Lancairs. With their tiny high aspect ratio wings, they made mincemeat of the turns. The structure of these aircraft were really high tech, with glass/honeycomb fuselage construction. I saw one fold a wing at the pylon and then roll around the fuselage until it disintegrated on the ground.

On the subject of prangs, one T-6 seemed to get full down elevator and dived straight into the bitumen: nothing left. Another lost a wing and rolled in too, making a huge dust cloud. A Team Extra Nemesis F1 got hit square-on in the turn; there was nothing left to hit the ground.

Unfortunately the finals had still not started at 5:30 pm on the final day. We were too tired to last any longer and headed back to LA. One good thing about LA: you can see the air you breathe. But we were left with many impressions. Not least, this has to be the ultimate in model pylon racing.

F3D is great, but its just not in the same class as Unlimited.

Mind you, despite what we call expensive, F3D is cheap compared to any of this. If $20 for a prop bothers you, try US$260 for a 26X26 RacePro. Airframes go about US$7000, I hate to think for engines, but a 3W twin F1 is about $1500. As a result of this expense and the labour involved, you don't see too many individual efforts. Mostly the entrants are teams, which are owned.
The boss guy flies in on his Learjet and visits his 10-man team with their semi-trailer/hanger, plane-towing ride-on tractors and 40X40 tent. The team services maybe 10 aircraft, mainly Unlimiteds and F1's.

I was hoping to meet an owner who wanted to buy me. I'm definitely one prop man who's up for sale! No such luck. Biggest problem I found was getting to know what's going on.

My thanks to Keith Harvey for getting the dates right for me. It seems Reno is mid-September every year. There are at least 3 outfits organising Giant Scale Racing, including Endless Horizons, the Race Marketing Group and Lone Star Unlimited. 

Oh, by the way, Lindbergh died of cancer in 1974, on Maui.

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