What are we testing?
We have developed new techniques to measure exact thrust that the propeller can achieve for static testing, on the engine, on the plane, on the ramp. Take a minute to look at what we are achieving.
First up, the video below shows a run with a standard propeller:
And then, the same propeller now modified by deltaBurn:
Our modifications reduce the amount of torque required to achieve the rated thrust. We are working towards (supplemental) certification for our modifications to be put on existing propellers. The theory behind what we do is aerodynamically similar to what we are do on the turbofan, without the complications of mass flow rate choking. Which, by the way, is also something that we solve for the turbofan – see elsewhere.
Our original research began with propellers, and many years later we are back at it again, this time however concentrating on certification rather than experimentation.
Original experiments were undertaken on piston-powered propeller aircraft, starting with a Piper Aztec, pictured below. This aircraft served us well for research on the propellers, but also wings, flaps and more areas of interest.
The propeller outcomes were remarkable in its effectiveness, but for sheer fascination, modifying the flap, flap cove and outer wing was quite breathtaking as well. The only twin aircraft we tested that came close to matching the modified performance of the Aztec was a Robertson STOL Cessna 337G, which could land and stop before the numbers and take off in the same distance. The stall speed of our modified Aztec dropped below the minimum reading of the ASI, and we saw fully attached flow over the full flap, approaching what took the place of the stall.
In our testing on propellers, apart from increasing thrust at all occasions, one notable change was an overal lower vibration. Always. This characteristic occurred even when modifying only one of the two blades, half a disc so to speak, and this has proven to hold true for turbofans as well – again, see elsewhere.
Our test aircraft today
For our first of a series of turbo-propeller STC’s, we are working with a timeless aircraft: Ed Swearingen’s Merlin III. As an aircraft, a Merlin evokes strong views from all those that have crossed paths with one:
- There is no doubt when a Merlin may be running an engine on a ramp, from any distance;
- It can fly long and far enough that both coffee and bathroom facilities are a planning consideration;
- The climb capability of heavier versions is reminiscent of an A340-300; an effective instrument to determine the curvature of the earth;
- The extended wing versions had ailerons that politely suggest any roll.
For the purposes of a propeller modification, the plane is perfect. The Garretts turn various versions of propellers, either Hartzells, McCauleys or Dowtys, and they can turn in either direction depending on what siren was fitted to the aircraft. The blades are, blades. Perfect.
As an aside, Merlins and Metros have nose-wheel steering that will be familiar to Learjet pilots, with some quirks. Early testing suggested we might need wider runways to be working with (a)symmetry testing of the power plants, and to avoid that quirk we invented a means to measure static thrust while parked. We developed a thrust plate was developed on which one can park the aircraft, with the produced thrust being used to ensure that the plate will not slide while the parking brakes are OFF.
This system will actually work for any size of aircraft, it’s just a matter of scaling correctly. A new version is under development, designed to accommodate a four-engined jet producing full power on 2 engines at a time, symmetrically.
Our technology alters the aerodynamics of the propeller, resulting in an increased amount of thrust produced by the propeller provides related to the amount of power that is needed to spin that propeller (torque).
We love squiggly lines, and color, so the above sample set of test results for the modified prop compared with the standard prop are colorful, and clear as mud.
Is this change consistent with the aerodynamic change that we are doing? Actually, it is, it’s very close to the analysis of what the changes in CL & CD are for the propeller modification. The CL/CD difference is on the money for what we see in the change of torque required. The static thrust chart shows clearly that we are getting greater thrust for the torque applied. Moreover, this is repeatable and is seen on every larger propeller that we have tested so far.
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