modify images

Author: RCmags

collections/projects/Airplanes/_posts/2019-09-19-stabilized_airplane.md

@@ -87,7 +87,6 @@ __Iteration 1:__
 
 The first version of the aircraft was designed to have _passive stability_. The idea was to enhance its stability electronically and use this _excess_ stability to move the center of mass aft. This stability would make it easy to progressively move the mass and observe the behavior of the aircraft. Eventually, the mass would move aft enough to cause the aircraft to depend on the active stabilization. As a consequence, the flaps would deflect downwards to maintain equilibrium. 
 
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 The aircraft was also equipped with a motor and a propeller to fly under its own power. However, this made it difficult to place the angle of attack sensor. The local airflow felt by the sensor is greatly affected by its location on the aircraft. Any regions behind the wing are disturbed by the large [downwash](https://www.grc.nasa.gov/www/k-12/airplane/downwash.html), and the [powerful slipstream](https://web.mit.edu/16.unified/www/FALL/thermodynamics/notes/node86.html) affects anything behind the propeller. A simple solution was to place the sensor atop a long vertical stabilizer. If it were tall enough, the sensor would lie outside the propeller's slipstream. Likewise, any lift caused by the fin would be perpendicular to the rotation of the sensor. This would minimize any effects it had on the measured angle.
 
 ![image](/img/figures/sensor_airstream.png)
@@ -125,7 +124,6 @@ Unlike the previous terms that increased the resistance to pitch disturbances, t
 
 Having obtained a level of excess stability, it was possible _destabilize_ the aircraft by moving the weight aft. This was done by taping a coin to the tail. Test flights showed it was only possible to shift the center of mass by a moderate amount. Beyond this point, the servos were _incapable of reacting quickly enough_ to stabilize the aircraft. It was evident the aircraft still depended on passive stability as the flaps still had _reflex_ while in flight.  
 
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 Given this limitation, the aircraft will need to employ faster servos to eliminate its dependency on passive stability. An alternative solution is to slow down the dynamics by increasing the [moment of inertia](http://hyperphysics.phy-astr.gsu.edu/hbase/mi.html) of the pitch axis. This would allow the servos slowly at the cost of a sluggish pitch response.
 
 # Arduino Code

collections/projects/Autogyros/_posts/2017-09-07-tailless_autogyro.md

@@ -1,6 +1,6 @@
 ---
 layout: post
-title: "Autogyro stabilized by an offset hinge without a horizontal stabilizer"
+title: "Review | Autogyro stabilized by an offset hinge without a horizontal stabilizer"
 
 # image sliders:
 slider1:
@@ -24,15 +24,11 @@ slider4:
 
 # Introduction to concept
 
-An autogyro is an aircraft kept aloft by a rotor that spins by moving through the air. The aircraft is powered by a propeller that pushes it to maintain airspeed. The rotor does not suffer from an abrupt stall like a wing and allows the aircraft to descent vertically like a parachute. However, the rotor needs motion between itself and the air to generate lift so an autogyro cannot hover in the air like a helicopter.
-
-One can think of an autogyro as a machine with a pneumatic transmission. Instead of the engine powering the rotor directly like in a helicopter, the engine imparts relative energy to the air that in turn drives the rotor. In this sence, air acts as a kind of working fluid that transfers power from the engine to the rotor.
+An autogyro is an aircraft kept aloft by a rotor that spins by moving through the air. The aircraft is powered by a propeller that pushes it to maintain airspeed. The rotor does not suffer from an abrupt stall like a wing and allows the aircraft to descent vertically like a parachute. However, the rotor needs motion between itself and the air to generate lift so an autogyro cannot hover in the air like a helicopter. One can think of an autogyro as a machine with a pneumatic transmission. Instead of the engine powering the rotor directly like in a helicopter, the engine imparts relative energy to the air that in turn drives the rotor. In this sence, air acts as a kind of working fluid that transfers power from the engine to the rotor.
 
 {% include youtube.html id='_25H9ZPE2So' %}   
 
-Because the air drives the motion, the rotor does not create a reaction torque like a helicopter. The drawback is that a pneumatic transmission is not as efficient as a mechanical transmission. The rotor is a kind of an axial wind turbine and operates an angle to the airflow. Like all wind turbines, the rotor cannot absorb all of the power in the incoming air. Add to this the inefficiency in the propeller and the overall efficiency is poor compared to a gearbox. If properly lubricated, a gearbox can achieve an efficiency in excess of 90%.
-
-Nonetheless, the air-driven rotor has a significant advantage when it comes to stability. As the air flows through the bottom of the rotor, the rotor induces a force parallel to the plane of the disk that tends to stabilize the autogyro. By comparison, a helicopter has a top-to-bottom airflow that reverses the planar force and destabilizes the aircraft. Hence, one faces the compromise between stability versus efficiency when comparing an autogyro with a helicopter.
+Because the air drives the motion, the rotor does not create a reaction torque like a helicopter. The drawback is that a pneumatic transmission is not as efficient as a mechanical transmission. The rotor is a kind of an axial wind turbine and operates an angle to the airflow. Like all wind turbines, the rotor cannot absorb all of the power in the incoming air. Add to this the inefficiency in the propeller and the overall efficiency is poor compared to a gearbox. If properly lubricated, a gearbox can achieve an efficiency in excess of 90%. Nonetheless, the air-driven rotor has a significant advantage when it comes to stability. As the air flows through the bottom of the rotor, the rotor induces a force parallel to the plane of the disk that tends to stabilize the autogyro. By comparison, a helicopter has a top-to-bottom airflow that reverses the planar force and destabilizes the aircraft. Hence, one faces the compromise between stability versus efficiency when comparing an autogyro with a helicopter.
 
 {% include image.html src="/img/autogyro/airflow-types.jpg" maxwidth="400px" %}
 
@@ -99,3 +95,4 @@ Should this happen, the aircraft will suddenly pitch forward in an unrecoverable
 {% include youtube.html id='b1p8pCHiuWo' %}     
 <p align="center"> Video 2. Flight of 2nd iteration </p>
 
+After some minor adjustments, this iteration of the autogyro flew quite well and was acceptably stable. It was not as easy to fly as a model with a horizontal stabilizer, but it proved that tail-less pitch stabilization is very possible. Despite this fact, it’s not clear whether a tail-less configuration is __worth__ pursuing. A horizontal stabilizer adds very little weight to the aircraft and is greatly beneficial for stability under all flight conditions. Therefore, while this project serves as an interesting proof of concept, the method of tail-less stability cannot be recommended as a general solution over simply installing a [horizontal stabilizer](https://en.wikipedia.org/wiki/Tailplane) on an autogyro. 

collections/projects/Helicopters/_posts/2016-08-06-heli_torque_rotor.md

@@ -1,6 +1,6 @@
 ---
 layout: post
-title: "Torque-compliant rotor for collective control"
+title: "Review | Torque-compliant rotor for collective control"
 ---
 
 # Introduction to concept
@@ -12,12 +12,12 @@ These changes in pitch can be accomplished automatically by using the torque act
 
 It must be mentioned that much of this project is inspired by the simplicity of the rotor of a radio-controlled autogyro. It is nothing more than a strap bolted onto a bearing housing in its simplest case. The blades attach to the strap, and [cyclic pitch](https://www.youtube.com/watch?v=04tJmP2aqcw) is accomplished by bending the strap. For part of the cycle the strap bends, and for the remaining half, it pitches the blades. 
 
-![image](http://www.bartonhewsons.uk/home/modelflying/helicopters/Resources/IMG_0793.jpg)
+![image](/img/torque_rotor/autogyro-rotor.jpg)
 [See: RC Autogyro - Panther build diary](http://www.bartonhewsons.uk/home/modelflying/helicopters/pantherbuilddiar.html)
 
 While an autogyro does not need collective pitch to fly, a helicopter greatly benefits from this ability. It allows the helicopter to rapidly change  lift and allows the rotor to transition from powered (positive pitch) and unpowered (little or negative pitch) flight. This is generally accomplished through a swashplate controlling the blades. 
 
-![image](https://www.rchelicopterfun.com/images/BellHead500pics.gif)
+![image](/img/torque_rotor/flybarless-rotor.jpg)
 [See: Flybarless helicopter](https://www.rchelicopterfun.com/flybarless.html)
 
 As can be inferred, a helicopter rotor with cyclic and collective is far more complex than the flexplate used by an autogyro. Evidently, it is very appealing to modify the flexplate design to include collective control while maintaining its simplicity.