How altitude effects thrust

I like many people live at a “high” altitude around 5000". Does anyone know how much thrust an electric paramotor looses at these altitudes?

if the speed on the propeller remains the same, the thrust drops by about 10 -12% per 1000 meters above sea level. but that is not so relevant. more relevant is the takeoffspeed which is only 2-3 km / h more per 1000 meters above sea level but for people who cannot run very fast it can be a problem. all of this applies to zero wind and average humidity and 15 degrees celsius.

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I’m really curious how it would effect electric paramotors because to an extent the electric motor will compensate for altitude with increased rpm.

I actually found that with the gas paramotors in changing altitudes the prop rpm stays the same because the engine looses power at the same rate that it gets easier to spin the prop… But electric is not the same :thinking:

Your question would be how the thrust changes. I have given you an answer. there is a change at the same speed. what do you want to know. how is it with cheap petrol engine and cheap e-ppg or how is it in the professional field?

You said that if the prop speed stays the same you loose 10-12% per 1k meters. But on an electric it won’t change that much because the motor doesn’t loose power with elevation. So as the elevation goes up the motor will spin the propeller faster because there is less resistance. So what I am looking for is the combination of the propeller losses and the propeller rpm increase.

I asked you if you would like an answer in the hobby area or professionally. you currently only speak from the hobby area because you have no experience about eppg. if you want to learn something you have to accept that there are people who can answer your questions. You already have answers even though you have never built, flown and tested hundreds of measurements before? it’s pointless …

I’m sorry I have frustrated you. I know how thrust changes with constant propeller rpm. But when your altitude increases the air becomes less dense. Because it is less dense the motor has less resistance so it spins faster. How much will the rpm change? And what will be the final results of the rpm change combined with the roughly 11% loss per 1000m. I hope you understand what I am trying to ask and how your answer was different from what I was looking for.

I have built an electric paramotor based on a falling apart open ppg paramotor. we did test a few things on it, but the thrust was so bad we at this point are planning to sell it and start fresh with a single propeller unit. I only got 80lb thrust with the open ppg based unit. based on your math provide at sea level it should get roughly 95lb thrust at sea level. But at sea level due to the higher air resistance the propeller won’t spin as fast. So what would the actual thrust at sea level be?

edit new in other posting

That’s not quite true with brushless motors and motor controllers. They tend to keep RPM pretty constant under load and will just draw more or less power depending on the load. You might see a slight increase in RPM, but probably not enough to actually compensate for the thrust reduction due to reduced air density. Play around on eCalc and you’ll see what I mean. Ideally you can compensate with a larger propeller and/or more pitch, but in the end you’ll still lose efficiency compared to a higher air density. If you give me a specific combination of batteries, motor controller, motor, and prop I can give you numbers from eCalc

edit: out of curiosity I ran the calculations using my own setup. At standard atmosphere (0’ PA, 15 degrees C) I calculate 38.3 kg of thrust at 8110W. At 5000’ (1524m) PA, 15 degrees C, I calculate 32.9 kg of thrust at 7041W. That’s 14% less thrust (or roughly 9% less per 1000m) and 13% less electrical power. RPM only increases by 1.7%.

Ok, thanks. The rpm change was a little bit less than I expected. I would have also thought efficiency would have been changed more. Interesting.

For propeller I was thinking a 125ch 4 blade eprop, Mad M40 motor (42kv) I don’t Know on motor controllers yet, and a 22 or 24cell li-ion battery pack rated at 6.7c and 45Ah. I don’t know if the eCalc could give answers for that but if it could that would be great.

Or the paramotor unit I messed with used 4 180kv dualsky ga6000.8, 4 hobby wing xrotor kv 80a ESCs. The props where 22x10 xoar, And it had 4 multistar 6s 16.0 batteries with 2 parallel and 2 series.

Here is the calculation from your existing unit. Looks like ~83 lbs of thrust at 5000’ PA and 15 degrees C with fully charged batteries, so that’s pretty close to the 80 lbs you measured. I think @bratwurst has determined that you lose about 20% thrust by putting the prop(s) in a typical PPG installation. eCalc is usually +/- 10%, so it’s all in the right ballpark. These numbers are per motor, except for the “Wattmeter readings”.

dualsky

As far as calculating thrust numbers for the Mad M40, it will really depend on the specifics of the prop (diameter, pitch, and efficiency). I have no doubt that you can make that M40 produce enough thrust to fly. The real question is will it overheat at that power level, and the only way to really answer that question is to build it and test it.

Ok thanks for running the math.

I saw the picture of your setup and those motors were never sold with OpenPPG kits. Where did you get those motors? Perhaps the motors sold with the kit would work better.

I recently talked to Paul and he told me that the motors and electronics I am using came from one of the original Open PPG prototypes. If you watch the second video that Paul made of his prototypes it has the same motors and throttle.