Fixed Wing 101 – Lift, Angle Of Attack and Stall

With this short article I would like to initiate new series: Fixed Wing 101 where I will describe some basic concepts connected with fixed wing airplanes that should help beginners to enter the hobby. Today: why airplanes fly and why, from time to time, they fall down from the sky…

Lift

Airplanes fly thanks to the lift. It is a force generated by wings (by the way, propeller thrust and wing lift are the same force. After all, propeller is a rotating wing) thanks to pressure difference. When air pressure below the wing is higher than above it, lift appears. To archive level flight, lift has to be big enough to counteract mass and gravity.

The most important condition for a wing to generate lift is: wing has to move though the air (or air has to move around the wing). If there is no movement, there is no lift.

When there is air movement, there are two factors responsible for lift:

Bernoulli’s principle

Bernoulli’s principle states:

when gas or liquid is moving faster, it has lower pressure.

Simple. To obtain lower pressure above the wing, we have to make air move faster over there. This is why wing has a shape (airfoil) it has: top side (above chord) of a wing is longer than the lower side. Wing splits air into 2 stream. Upper one has longer way to travel than lower one, so it has to move faster. If it moves faster, it has lower pressure. If it has lower pressure, lift appears.

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Review: BuildTak Printing Surface

For last few months I’ve been happily 3D printing PLA on glass. Prints were repeatable, initial adhesion was just fine, ready print was easy to remove after glass cooled down. But I wouldn’t be me if I did not wanted to try something new. So I tried “the ideal 3D printing surface” BuiltTak.

My initial impressions were very positive. Nice mate surface a little similar to fine grain sanding paper. I was a little afraid that adhesion will be even too good and it will be hard to remove the print. But hey, they had to think of it, right? After all, BuildTak is quite expensive after all. Continue reading “Review: BuildTak Printing Surface” »

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How to print with elastic filament

Elastic filaments opened brand new areas for 3D printing. We are finally able to print something that bends, compresses and stretches. While TPE (ThermoPlastic Elastomer) filaments like NinjaFlex or FlexiSmart are still about 4 times more expensive than plain old PLA, they are not so expensive not to give them a try.

Unfortunately, due to the fact that they are elastic even before melted and extruded, they require special printing conditions. During my experiments with FlexiSmart I've came down to following conclusions:

  1. Because TPE is elastic, flow through the nozzle has to be as smooth as possible. If not, it will coil inside extruder
  2. Bowden extruder system greatly increases chance of failure. Friction of bowden, while small enough for ABS or PLA, is too big for TPE. Filament will coil. Direct extruder gives less chance of failure
  3. One has to pay big attention to the distance between extruder nozzle and bed. Usually it has to be a litter bigger that for PLA or ABS. In all the cases when I was switching from PLA to TPE, I had to raise nozzle a little. If not, TPE coiled. TPE has better initial adhesion than PLA, so rising a nozzle does not have side effects
  4. Filament retraction is a huge NO NO. Disable retraction since it will increase the chance of coiling significantly
  5. With no retraction it is a good idea to enable Combing. Nozzle, instead of taking the shortest route to travel, dripping TPE everywhere, will move above already printed layer. This greatly improves print quality
  6. Top printing speed is 30mm/s, but I recommend slower speeds. I have best results when printing at 15mm/s. On 25mm/s quality is still acceptable, but degradation starts to be visible
  7. I had best results of TPE printing on glass with 220deg nozzle temperature and 60deg bed temperature
  8. Not everything can be printed with elastic filament. Any thin vertical structure will come deformed. After all, it will move during printing due to a friction with extruder nozzle

While I was printing with FlexiSmart, almost all points from the above list will be true for other TPE (NinjaFlex). Temperatures might be slightly different, but general rules applies.

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Mechanical Bat: Bat Bot B2

Nature gave ability to fly to birds, insects and some mammals quite some time ago. We, as a species, learned how to fly only very recently. And let's be honest here. We are not very good at it. We need machines to fly. Any our machines are not very efficient at that task. They require huge amounts of energy to do it, need maintenance and make a lot of noise. Look at birds and bats. They fly for longer using less energy. And they do it with grace.

This is project that caught my attention only today: mechanical bat from University of Illinois called Bat Bot B2.


Bat Bot, from Caltech von PopSci

Take a look at that video. Maybe it's not stable or capable of longer flights yet, but I'm really, really impressed. One day I would really like to have an UAV like that!

Via Hackaday

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Relaxing Winter FPV Session

Winter is not the best time for FPV. Day is short, it is cold, it snows or rains most of the time. But sometimes, when sun is shining, there is a slim window ofopportunity to just go outside and fly. You will get cold, batteries will last shorter, but it will be worth it.

Some people will say it is boring. For me it's not boring. It's 100% relaxing…

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ESP8266 and DS18B20 – wireless ThingSpeak sensor

Here is another small project of mine: battery operated ESP8266 ESP-01 WiFi thermometer using DS18B20 and ThingSpeak API to collect data.

Before we proceed, you should:

esp8266 ds18b20 thingspeak sensor

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ESP8266 ESP-01 Low Power Mode – run it for months

Amazing ESP8266 ESP-01 WiFi boards have pretty irritating problem: theirs power consumption is pretty high. Minimal power consumption of about 70mA when doing nothing and above 100mA when when transferring data makes it rather impossible to use it on battery power for a longer period of time. Set of 2 AA batteries would be drained in less than a day. Not good.

There is a way to make ESP-01 work for months using something called deep sleep mode. When in deep sleep, ESP8266 disables almost all of its functions and reboots after specified period of time. There is one catch: ESP-01 is capable to enter deep sleep, but unable to restart and resume operation. XPD_DCDC MCU pin in not connected to RESET pin. To fix it, you would have to solder thin wire between XPD_DCDC and RESET pin just like on a picture below:

ESP8266 ESP-01 Deep Sleep hack

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INAV 1.6: Fixed Wing PIFF Controller

Another new feature of upcoming INAV 1.6 (BTW, INAV 1.6 ALPHA-1 has just been released) is brand new PID controller for fixed wings. I repeat: this new controller is used only on fixed wings, multirotors are not affected.

So, what is new about this new PID controller? First of all, it is no longer a PID (Proportional, Integral, Derivative). It is a PIFF (Proportional, Integral, Feed Forward) controller. What is the difference?

Traditional PID controller computes error between setpoint and measurement and feeds it to 3 modules: P, I and D.

PID controller

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