Monday, May 16, 2016

HobbyKing Aether 3.7 Review Part 6

Weight and Balance

The manual indicates that the CG should be at 115mm from the leading edge of the wing.
Like on the previous version of the Aether, even moving both the RX and Motor battery all the way forward I still had to add weight to the nose (21 g)

I secured the ballast externally using electrical tape so that I can move it easily. Once the CG is in the sweet spot I can mark the CG spot and re-balance the model internally.

I used velcro to secure the ESC and batteries. This allows me to move the battery back if I want to use a bigger battery.

Be careful checking the CG. This plane can weigh as much as 2500 g (5 pounds).
You have hold the plane up by resting the whole weight of the aircraft on two points under the wings. The sheeting there is very thing you can easily poke a whole through it if your CG testing hardware has small points.
I just used my index fingers (trimmed nails). No way I can use two pencils as we used to with our small free flight models.

Plan on having to adjust the CG as you gain experience on this plane. In my opinion the CG is way to forward. It makes the plane easier to handle but you can definitely see the plane settling in a fast descending glide as soon as the power is off. Moving the CG back makes the plane more difficult to handle but it will glide better. How much back you should move it depends on your flying skills and willingness to sacrifice stability for performance.

First Flight Test

Let me start by saying that after the maiden flight I was pleased.

The day of the first flight was not ideal. Winds were 8 MPH gusting to 12 MPH and Temperature was upper 70s. Our field in Florida is close to sea level.

Adding to the stress I test flew this model on the same day we were having our monthly competition. The good side of this is that plenty of experience glider pilots got to see the plane and give out their opinions about it.

Flight tests started with a simple hand launch. Followed by powered climb and glide tests. I will not use the motor in this plane except for competition-like climbs.

Unpowered Glide Test

Flight tests started with a simple hand launch glide.
  1. Verified the CG was 115mm from the leading edge of the wing.
  2. Verified that all the surfaces were in the neutral position. 
  3. Headed into the wind
  4. Started to run holding the plane level. Gently moved my arm forward but didn't toss the aircraft, I simply opened my hand and let it go.
  5. The model settled into a gentle glide straight ahead. No major inputs were needed to keep the glide path.  
This first test clearly indicated me that the CG was within acceptable limits and that the incidence angle between the horizontal stab and the wing were also within reasonable limits.

When I was holding the aircraft for launch I noticed how thin the fuselage walls really feel. You can easily feel the walls giving in a little as you hold the aircraft. While I've never heard of anybody squeezing the plane too much and breaking the fuselage, I wish there was a bulkhead in the area where you hold the plane for launch.

Another thing to be alert is that the surface of the fuselage can be very slippery. Sweaty hands and gusting winds can end up in a mishap. Be careful. 

No other surprises here.

Powered Climb Tests 

First Flight
  1. Plugged the motor battery.
  2. Did a very fast  (3-seconds) motor test.
  3. Facing into the wind, flipped the switch that puts my radio in "Launch condition". The flaps go a few degrees down, the motor comes to life to full power. Rudder stays at zero at this point. But I expect to set it a few degrees to compensate for any turning tendencies.
  4. The propeller literally ripped the plane from my hand. This was a surprise I had hoped to be able to hold the plane but I couldn't. The trust of the power drive and the slippery  fuselage made it imposible to hold on to the plane. Plan for that!
  5. Without inputs, the plane settled in a steep climb without any mayor tendency to turn. I guess I won't have to make the turn compensate during "launch condition".
  6. I controlled the climb with gentle down input. Mainly because I didn't want to let the nose raise to much in fear of any unusual behavior with the an extreme nose up attitude. (Plus just because the nose is pointing way up doesn't mean our vertical speed will be big).
  7. After a 20-second climb, I changed the radio to "cruise condition. The motor turns off and all surfaces go to zero. The expectation is that the plane should settle in this best best glide attitude. 
  8. Unfortunately the plane immediately showed a tendency to lower the nose too much and gain speed. I controlled the glide but kept on compensating for a nose down attitude.  
  9. Noticed that the plane slowed down significantly when flying against the wind (10 MPH). Penetration is not this plane forte. Keep in mind that I didn't attempt to use reflex at all on this flight.
  10. I didn't exercise the flaps at all. 
  11. As gently as I could flew the plane around our flying area and setup for a landing against the wind.
  12. Landing was predictable and uneventful. No flaps were used for landing.
I noticed that aileron performance was way slower than on my Xplorer. That big wing requires us to use rudder as well. I am used to more aileron authority. I have a lot of work to do on the differential aileron setup on my radio.
I concluded that the nose down attitude was due to too much nose weight. I proceded to remove 7g of weight from the nose. and prepared for a second flight.

Second Flight
  1. Climb was exactly as before. The prop ripped the plane of my hands. The pitch up attitude during the motor run was still there. Will have to figure out a good attitude for climb and preset that on the "launch condition".
  2. Upon motor shutdown, the plane settled in a glide. 
  3. The nose down tendency was still there but not as much as the first time.
  4. I found the plane easy to handle in the air even with the CG moved back. But turns require both aileron and rudder inputs. Considering my radio is programmed to already give some rudder with aileron inputs I found this surprising. The wings move slowly in reaction to the aileron input.
  5. Rudder authority was not enough in my opinion. I will increase the rudder travel.
  6. Again I landed the plane upwind without using any flaps. Landing was again predictable although the slow aileron responses made me fearful of a sudden gust of wind putting the plane  in an unusual attitude close to the ground.
I didn't want to remove any more weight from the nose at this point. But I believe I could handle another 7grams less on the nose.

After two 20 second climbs with my first motor battery I changed the motor battery.

Third Flight:
  1. Take off was as before. The plane surges forward tracking straight.
  2. This time I ran the motor for 30 seconds easily getting to the same altitude the winch glider pilots release at. Once the CAM device is installed, the motor will automatically turn off at 150 meters.
  3. I did a number of glide passes to test stability. The plane flies well without any major trim changes. 
  4. Again I chose not to exercise the flaps.
  5. The wind had diminished below 10 MPH and since I was already close to the ground decided to land downwind over our large grassy field.
  6. Landing was attempted downwind.
  7. This proved to be a mistake as the plane got in the ground effect and glided the whole length of the field a few inches from the ground.
  8. The plane settled down near the end of the field sliding sideways and ending up with the nose pointing at me. No damage just too much ground speed on touchdown.
On none of the flights I noticed any flutter on any of the surfaces.

The wind whistling on low passes was nice. Not as intense as in the Xplorer but definitely there!

More Observations

The 1300 mAh battery is taxed heavily by this plane ... it demands over 50Amps on the ground! My 1300 mAh motor battery is enough for 2 ALES launches and no more!. (run motor for 30 seconds or until 150 meters is reached)

Note on battery: 2-launches with a 1300 mAh battery may be even a stretch. On my last flight, using a fresh battery I climbed once and upon landing the charger indicated I was already at "storage level capacity" 3.8 V per cell. The batteries are brand new so they may not giving full performance yet.

Word of caution: While testing the power drive on the ground I killed a 25C-rated battery. This was totally my fault. eCalc indicated the motor was going to pull over 40C and the 25C battery could not handle that. My new batteries are rated at 70C continuous. This plane will test the battery limits. Some of those "cheap" batteries may not handle the stated C-rating. I was very nervous about the power drive so I made sure the RX and servos had an alternate power source.

The battery setup described here is more than adequate in a competition environment. (Where you switch motor batteries every flight). Naturally if you are flying for other reasons you may want to get a significantly bigger battery. Also running the motor at full trust may not be indicated in other situations.

Word of caution: My prop-combination makes the motor, ESC and battery very hot. I do not have a temperature sensor mounted on this aircraft so I cannot tell you how much. But let me say this. You CANNOT touch the motor after my on-ground motor test.

This is ok for me because the motor will run for only 20-30 secs and then it will stay off until landing. (ALES competition rules).

The turbo-spinner allows air into the motor. The build-in fan of the Glider Drive will help cool the motor. I expect the hot air to travel through the fuselage and exit on the back. The boom tuve is open on the back.

I used a separate 2C-900mAh LIPO to run the RX and the servos. My servos are high-voltage so I do not have to worry about regulators etc.

It should be possible to run the airplane from the ESC power source but I prefer the power redundancy. As a bonus the extra battery helps keep the CG where it needs to be.

The recommended CG is too forward in my opinion. I expect to move further back than it is now.

No terrible habits in the air. But I felt that I didn't have enough aileron authority at low speeds. This is most likely being caused by my aileron-flap mix not being optimized yet.

I felt I didn't have enough rudder authority either.

I need to play more with the control throws until I get more familiar with the airplane.

In the air not bad habits but this is not a beginner airplane either. All turns need to be coordinated to help move those big wings around.

I have a set of mixes that are supposed to help handle the plane:
  1. flaps move with the ailerons.
  2. rudder moves with the ailerons.
  3. flaps move with the elevator.
I am not happy with the current mix settings. I will have to experiment to get a workable "cruise condition". 

Adding flaps for thermal flight will change the needed compensations. No idea how much flaps will be needed to stay on a thermal.

Using reflex flaps for speed will also change the needed compensations. My reflex flap travel is limited.

I did not attempt to lower the flaps to 90 degrees yet.
  1. I do not know yet the speed at which this will safe.
  2. I do not know what degree of elevator compensation will be needed.
I'll try those settings at altitude next flight session

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HobbyKing Aether 3.7 Review Part 5

Power System

Power system information in the manual is very lean.

The expectation is that the modeler will pick the power drive of choice. Considering that plane is being marketed as an entry level ALES plane it would have been beneficial if they would have specified the power drive fully. (motor+esc+prop+battery).
I decided to use HobbyKing's motor recommendation: 

This is a relatively inexpensive "outrunner in a can" glider motor. It retails for about  $36.00.

My initial calculations on eCalc called for a 14x9 prop. However this proved to be problematic

Warning: eCalc does not explicitly tell how what size folding propeller "yoke" is using in its calculations. This lead me to believe I could use a 14x9 prop safely. This proved to be wrong. the 55mm turbo-spinner combination proved to be too much for my battery in real life.

After talking with the eCalc folks it was pointed out that they used 42mm for their calculations. I am using a 55mm turbo-spinner-yoke combination. Therefore I recomputed by power requirements by adding 13mm to prop size. 

This is the second set of calculations in eCalc using a 14x8 propeller and a 55mm folding prop yoke:

Follow this link for the actual eCalc worksheet .

Warning: This prop-motor combination will damage you battery if it cannot handle 40-50C continous discharge. 

Warning: This glider does not cool the motor properly for continuous operation beyond 30 secs at full throttle level.

On the maiden flight the motor at full throttle ripped the plane of my hands. Climbing to altitude per ALES rules should not be a problem.

This are the initial power components. The battery with the white tape was replaced because it could not handle the current load.

The ESC is rated to 70 Amps.

The small battery is my receiver and servo battery.

This battery has no problem handling the 50 Amp load that the prop and motor demand.

It is necessary to enlarge the center hole so that the motor fits correctly.

There are 8 pre-drilled holes on the fiberglass firewall. 4 are used to mount the motor. I enlarged the other 4 so that the motor would have some "air-intakes for ventilation"

After installing the motor. We can see that there is some space for air to squeeze into the motor. The built-in fan and the motion air coming through the "turbo spinner" should provide enough cooling for the 30-sec motor run.

There is plenty of space in the Aether to mount the motor.
The rear shows the Glider Drive built-in fan.
 I used a 55mm turbo spinner. This spinner allows air to penetrate the motor for cooling.

I tested the whole affair on the ground using an inline power meter. this allowed me to double check eCalc.

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Friday, May 13, 2016

HobbyKing Aether 3.7 Review Part 4

Attaching the Pod and the Boom

Carefully separated all the jig parts from he plywood. Its important to make sure the edges are flat.

Make sure that you have an area big enough to place the plane flat on the floor ideally with the wings assembled. (or at least the center section of the wings). Must make sure that everything is aligned and the vertical stab is at right angles with the wing. The jig will make sure the incidence angles are correct.

There is only one part to glue but you must make sure that the bottom of the jig is straight. I used Gorilla Glue and clamped the parts

I sanded the boom because I wanted to make sure I was gluing the carbon fiber to the fiberglass and not to the paint.

Manual indicates to use 30 min Epoxy. I used Gorilla Glue.
After the jig dries you assemble it in a flat area. There is no need to glue the other parts but make sure that you assemble the jib properly. The parts fit in only one position.

Following the instructions i used rubber bands to secure the fuselage to the jig and then laid on the floor making sure that everything was aligned properly.
Gorilla glue needs to be clamped for 30 minutes and cures completely in 24 hours. I let the whole assembly sit there for 24 hours.

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HobbyKing Aether 3.7 Review Part 3

Tail Section

The tail section remains mainly unchanged from V1. The vertical and horizontal stab are secured to the carbon fiber boom. The boom comes predrilled for this purpose.
The tail servo gets wrapped and glued with a small amount of Gorilla Glue to to the vertical stab servo cover. Alignment is important here so take your time and make sure the servo horns can be removed easily.

The servo cables can be easily routed through thew bottom of the assembly.
At this point is important plan how to route the servo cables all the way to the front.
The linkages provided need to be installed aligned properly and making sure that the holes in the horns coincide with the hinge line. The linkages provided are adequate. Is important to verify there is no play in the linkage.

The horizontal stab servo is not glued in place but secured with screws.  The servo opening was too big for my servo so I had to add a small piece of hardwood on one side of the opening.
Again is a good idea to mock the installation and make sure that there is a good plan to route the servo cables to the front of the plane.
I attached the cradle to the horizontal stab using the hardware provided. Note that the screw holes are simple holes trough balsa. Some modelers may want to reinforce them with small carbon fiber tubes or at least soaking them in CA.

Is important to understand how the servo cables will make it inside the fuselage. My plan was to thread a string trough the pod openings and then pull the servo wires with it.

Here is where HobbyKing's provided hardware simply does not work. Given my servo the linkage is too long.
During this build I have tried to use the items provided exclusively but this is when I reached a stoping point. Given my servo I could not make this work. unless I moved the control horns way back. (which should have worked but I've always been told to keep the horn holes aligned with the hinge line)
Digging in my hardware left overs I found this linkage and it saved the day. The threaded rod provided by HobbyKing fits nicely into the linkage stopper.
It was a bit disappointed the provided hardware didn't directly work. But it was not a terrible thing. Those linkages are easily obtainable.

After the elevator linkage was acceptable I carefully removed it and went back to the task of mounting the horizontal stab cradle on the boom and routing the servo wires.
Initially I simply routed the cables to the back of the boom. Then moved on to gluing the horizontal stab craddle.

I used sandpaper to rough the carbon fiber tube in the area where the cradle would be glued.

The manual suggests using Epoxy but I used Gorilla Glue instead.

The Vertical stab screws and its concave cradle nicely align the Vertical stab. This is the reference to make the horizontal stab at right angles.

Since I'm using SBUS i attached both servo wires with a Y extension.
After the glue dried I inserted a piece of string with a small weight at the end through the tube (holding it vertically). And then used the string to pull out the extension through the tube to the front.
Once the servo wires were routed to the front of the plane I reattached all the linkages and tested the tail section controls.

At this point the boom is not yet permanently attached to the pod.

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