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Part 103 Max Speed vs. Climb Power

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BTCrenshaw

Well-Known Member
Joined
Dec 13, 2020
Messages
76
Location
Dallas, TX
Starting a new thread based on some ideas/comments made about Part 103 as it pertains to maximum speed of an ultralight. The comments were that Part 103 covers maximum speed at 1000 feet (adjusted for sea level if needed), with a 170Lbs pilot and what that means when it comes to climbing and descending. Descending is obvious, we can descend at faster than 55 knots. There also doesn't seem to be a reference to how fast we can climb or how to get more power so we have a better climb capability. Discussion was on how this could be done. One member made the below comment. I think this could be done using electronics and I explain (high level) on how. I thought this would be an interesting topic so I pulled it out of the original post for separate discussion.

Interesting approach! For sure it would be easier to employ this idea for an electric UL which will have an electronic controller. Seems complicated for a gas engine which typically has mechanical linkage.

Actually I've been looking into this. It's very do-able on an ICE powered plane. At first I thought it would be complex, but some research found that all the needed hardware is available. First is to get rid of the cable, links or whatever is presently controlling the throttle position. We're going fly by wire for the throttle now.

The throttle lever would be a simple rheostat. This would allow a resistance device to determine position of the throttle lever.

On the carburetor or fuel injection, the actual throttle control whichever method of fuel delivery is used (carb or FI) is a servo motor. This would control how much fuel is delivered to the engine via the carb or FI.

The brains between the two devices (rheostat and servo motor) would be an Ardunio, Raspberry-PI, or possibly even a Basic STAMP or other micro-computer. I've only researched the Ardunio so far (the other's may or may not work depending on available peripherals or options).

What would be needed on the micro-computer? The speed of the processor would be important. We don't want any delay when the throttle lever is moved to when the servo motor reacts. The micro-computer would need to have GPS built in or as an add on. The GPS is used to calculate speed, ensuring that with level flight we don't exceed 55 knots. There also would need to be an analog input measuring capability to measure the resistance for the throttle position. I was thinking of using digital instead of analog but analog is simpler and being such would require less work to design/build. The micro-computer would also need the capability to drive a servo motor, again either on board the micro-computer or as an add on piece of electronic hardware.

We'll skip redundancy (which I highly recommend) at this point since this is just the first steps to getting something working.

Programming - Here's where the difficulty starts - The code would have to be setup to recognize altitude, descent, ascent, speed, and throttle position. Most likely a few more things I haven't thought of yet.

Let's say the plane is at level flight at 1000 feet. Here the micro-computer is adjusting for minor changes but in general it knows were at 1000 feet. It then knows how to calculate our speed, ensuring the servo-motor does not provide more fuel to the engine than what's needed to maintain 55 knots. This is all simpled down, there are several ways to build this in the code. If the micro-computer detects that we are climbing, it would allow the servo-motor to advance the throttle for more power, enhancing our climb rate. This could be balanced out to ensure that we still don't exceed 55 knots but we now have the power to climb at 55 knots where before we didn't. A table could also be created to adjust for altitude variation, meaning our Part 103 plane can fly faster than 55 knots at 6000 feet because of lower air density. This would be based on GPS. I was thinking that a barometric measurement could also be made by the micro-computer, but that's simply no accurate enough. It would be better in my opinion to use a set standard accepted pressure at altitude increments.

I was thinking that there would need to be something to prevent the engine from being able to be spooled up to a high RPM while descending, but that's not correct. If the plane is headed down and the pilot has the throttle wide open, well he/she's an idiot anyway, this can be done on current Part 103 planes now and it would ultimately end up destroying the plane when it flies apart at its VNE. So, simply, going down doesn't matter. If the micro-computer detects the plane is descending, the throttle can be wide open.

There would be the need for code that would detect if something went wrong with the GPS, servo-motor, or throttle rheostat. If the GPS goes out or is providing bad data, the micro-computer would need to default to a specific mode, still allowing throttle control but not able to exceed a set speed. You may ask, how's that done without the GPS. It would need to be a calibrated setting or table in the code. That's not difficult to set up and the micro-computer could actually build the table itself over several flights. If the throttle rheostat or servo-motor failed then the same would be setup for them. A set speed would need to be locked in - enough to keep the plane flying and give the pilot time for options. At final descent the engine would most likely be shut off just before final and a glide in touch down would be made. In most cases a non-event. However, with a redundant servo-motor, double throttle rheostat, and double micro-computer These issue may never happen. We just do the same for the ultralight.

Again this is a very basic overview of how this could be done. I was very surprised at number of options/features the Arduino micro-computer has available. There may be concern over the use of electronics to control an engine like this, but my bet most of us are driving cars that do just this. I know my 2002 Chevy Avalanche throttle body is controlled by a servo-motor. There is no linkage between the throttle peddle and the throttle body. Under the dash where the throttle peddle is located is a rheostat. The computer measures how far I have the peddle pressed and translates that into how much the servo-motor opens the throttle body. Granted this is a commercially built control, but I've got over 220,000 miles on the truck without a glitch out of the rheostat controlled throttle and servo-motor controlled throttle body, and I'm sure that something similar could be built for use in ultralights as well. In fact I've had my truck up to its maximum speed - which is 98 mph. That appears to be controlled by the computer. The engine is not being shut down, it's still running very smooth. The truck simply won't go any faster, and that's not because of the lack of capability. The engine in my Avalanche is a 496cid Chevy Big Block. It has more than enough power to push the truck faster, it simply doesn't. This is because the computer knows the truck is in high gear, what speed it's traveling at, and controls the throttle body servo-motor to not open the throttle any more, thus limiting the top speed, without shutting down spark to the engines cylinders. This allows the engine to continue running smooth, but limits the trucks top end speed.
 
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