Samuel Falvo Performance Report 

April 29, 2002

Following are test results from Samuel Falvo in his efforts to compare Tesla designs to bladed designs. His efforts demonstrate that excellent tests can be run on very limited resources -- it puts to shame any excuses for not making an effort. We have to remember that technical excellence comes from individuals, not big biz with inaccessible big budgets.

From: Samuel Falvo SFalvo@hifn.com 
To: "'krieli@up.net'" krieli@up.net 
Subject: (UPDATED) Tesla Turbine Performance Comparison Results
Date: Wed, 24 Apr 2002 18:40:52 -0700

1. Introduction

A test was designed so as to measure the power output of each of my turbine designs. Several turbines were used: my PT-45A-8 paper Tesla turbine, my 5.5cm diameter, 16-blade axial turbine, and my 6.3cm diameter, 16-bucket radial turbine. I also added a 10cm diameter radial turbine, using the same buckets as the 6.3cm radial turbine since the initial report was published. In all cases, the turbines were made using paper products.

The test relies on measuring the change of potential energy of a known mass through time. As much as possible, lacking suitable equipment to perform the test, a consistent breath pressure was used to supply the compressed air to operate these machines. Each breath consumed two seconds of time, and exhausted my entire lung capacity. In all cases, a 3/8" (9.5mm) air inlet was used to deliver the pressurized air.

The suspended mass was measured using a digital scale to be 1.4oz, or 0.1925kg (1.4oz * 1 lb/16 oz * 2.2kg/1 lb).

2. Tesla Turbine Performance

Without the rotor housing, the PT-45A-8 (formerly PT-3A) didn't even lift
the weight more than 5cm off the ground in the 2 seconds I exhaled with. Thus, the maximum demonstrated power was 47mW.

With the rotor housing (standard octagonal housing described in other
Tesla-turbine list archives), the PT-45A-8 raised the mass through a
distance of 0.6m (the height of my cubicle counter top) in 2 to 3 seconds. I attribute variations to breath pressure differences. Only one breath was used to raise the mass through this distance. Average power (taken as 2.5s lift time) is 452.8mW -- approximately 10x improvement over the unhoused turbine.

It's interesting to note that the Tesla turbine had only one inlet nozzle.
Using two nozzles, the turbine would have produced double the power. Since the diameter of the inlet nozzle is only 9.5mm, and the circumference of the turbine is 319.6mm, it follows that one could, at least in theory, make the PT-45A-8 (319.6/9.5) up to 33 times more powerful (up to 14.9W), assuming all the air flows into the engine can be suitably directed, and have equal pressures.

The turbine exhibited reasonable spool-up, but more importantly, it also exhibited quite a bit of moment of inertia, due to its relatively high mass. This is what enabled me to lift the mass with a single breath -- after I had exhausted my lung capacity, the mass kept lifting for about 0.75 to 1.0 seconds after.

I discovered that, with the mass suspended on the shaft, I could easily
counter-act the desire to unspool the string using relatively little amount of breath. Without that breath, however, the mass unspooled the engine rapidly, taking about 2 seconds to reach the floor again.

The Tesla turbine was completely silent.

3. Bladed Axial Turbine Performance

This turbine is about 14cm in diameter total. The 16 blades are 3.5cm in length, and angled at 45 degrees (purely impulse driven). The air inlet was positioned for best performance. It raised the mass through 0.4m in roughly 3 seconds or so; by extrapolation, it would have moved the mass 0.6m in 4.5s. The power thus produced is 251.5mW.

THIS DOES NOT NECESSARILY MEAN THAT THE BLADED TURBINE IS NOT MORE EFFICIENT THAN THE TESLA TURBINE. The active surface area for the bladed turbine is 0.0032 square meters, of which I'm effectively only using 0.00005675m^2, or only 1.75% of the power-producing surface area for the turbine. It follows that with a full-on flow of gas, the bladed turbine can be up to 56x more powerful, for 14W of shaft power.

The bladed turbine had more difficulty in maintaining the mass at equilibrium than the Tesla turbine. When the mass was released, it took approximately 5 to 7 seconds for the mass to fully unspool. During the unspooling process, a *LOT* of air was blown from the turbine.

Noise levels were moderate, sounding like a can of compressed air being blown through a running floor fan.

4. Bladed Radial Turbine, 6cm diameter

Next, I tried using the 6.35cm diameter bladed radial turbine. This is the first bladed turbine I've ever made. It lifted the mass in 1 to 2 seconds, for a demonstrated shaft power of about 0.755W. However, it was easily brought to a complete stop with any amount of friction on the shaft.

Note that the average circumference of the turbine is 199.5mm; thus, with a 9.5mm inlet nozzle like I was using, up to 20.99 (so, say, 21) nozzles can be ganged together to produce an incredibly powerful turbine, for a total predicted power output of 15.8W.

This is, bar none, the single loudest turbine of the three. It created a
whine that reminds one of air-wrenches used in automotive repair shops.

5. Bladed Radial Turbine, 10cm diameter

I recently re-finned the 14cm diameter turbine to use radial turbine
buckets, resulting in a smaller diameter. The performance of this turbine was similar to the Tesla turbine, except it was noisier. It raised the test mass in about 2 to 3 seconds, yielding a power close to 0.452mW. It's outer circumference is also 319.2mm, so the same 33x improvement in power can be had by using its entire circumference for air flow purposes. It's maximum power, therefore, is also 14.9W.

6. Conclusions

The three turbine types have demonstrated some pretty interesting behaviors, which when compared against one another, avail themselves of their applications. For silent operation and extremely simple construction, you cannot beat the Tesla turbine. If you want high power output, but don't care much for noise, and low moments of inertia are required, the bladed radial turbine is the best choice. Finally, if the size of the radial turbine doesn't suit the application, but high power is still needed, the bladed axial turbine should be used.

It is interesting to note that employing cross-flow heat exchangers for the purpose of recuperation is made substantially easier by both Tesla and bladed radial turbine engine designs, since gas flow is external to the engine's shaft.

With respect to my own ambitions and goals, namely the design of at least one go-kart suitable for use with SCCA Solo-II Autocross racing, I feel that a Tesla turbine would be the ideal because:

1. High moment of inertia makes for drastically reduced input pressures for maintaining a constant speed. This makes for *far* better average fuel economy, though it necessarily means higher fuel consumption during initial spool up.

2. They are significantly easier to make than any competing turbine type.

3. Their reasonably high moments of inertia are ideal for applications requiring high degrees of control. This makes the Tesla turbine-powered vehicle easier to control for the power it's designed to deliver, as acceleration and deceleration will be smoother.

4. Their power levels are adequate. Thus, while power to weight ratio isn't the best it could be, it's certainly not the worst either.

5. Trivial shaft reversibility allows any equipped transmission to be simpler. It also enables substantially more powerful and more controllable engine braking, allowing the vehicle to slow down substantially, without relying on friction material devices, like disc brakes.

6. Completely silent operation. The only noise heard is the rush of air flowing through the turbine's rotor housing.

Note that this does not answer the question of which of the turbine types makes the best air compressor.

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