DJ Aerotech Chrysalis F3-RES to F5-RESt

[Konrad]

Just playing with some numbers. As I've said before, I don't put too much faith in the power prediction programs. But this time with my set up the numbers came in right on the money. Using E-Calc with the CN 25mm "Z" hub I had to drop down 1/2 inch in diameter. So I used a value of 12.5" x 10" Aeronaut prop and got 105 watts. With voltage suppression in the real world I got a voltage reading of 10.5V and a current draw of 10 amps after running for 5 seconds, for a real world reading of 105watts!

 

[Konrad]

More playing with numbers, I see that the DJ Aerotech's follow up to this Chrysalis lite the Monarch-E Ascension is coming in at around 475 grams. My Chrysalis Lite F5-RESt is coming in at 427 grams AUW ready for test flight #2. (OEM Chrysalis electric is coming in at 450g with balsa tail) So where is the 50 grams coming from for a smaller model?

I was thinking of getting an Ascension. But I'm now thinking I should build my back up kit, but to what configuration, F3-RES or F5-RESt? I'd like to try the F3-RES again but this time add a proper nose to get out the lead. With the lighter diagonal balsa V tail and 20mm longer nose I should easily get under 400 grams in F3-RES trim. I'm thinking 375 grams is within my reach. But I so love electric gliders as opposed to gummy band launch models.

I already have an F3-RES spec'd high start.

 

[Konrad]

Reaching neutron star density in the nose! Now I have to wait for nice weather for the second test flight.

Lot going on with the second test flight. Shorter nose (12mm) more down thrust (0.7°) less weight (4 grams) lighter load prop (13x10 Aeronaut) (0.5 amps less load) and new spoiler control action and compensation curves.

 

[Hank GB Z]

More playing with numbers, I see that the DJ Aerotech's follow up to this Chrysalis lite the Monarch-E Ascension is coming in at around 475 grams. My Chrysalis Lite F5-RESt is coming in at 422 grams AUW ready for test flight #2. So where is the 50 grams coming from for a smaller model?

I was thinking of getting an Ascension. But I'm now thinking I should build my back up kit, but to what configuration, F3-RES or F5-RESt? I'd like to try the F3-RES again but this time add a proper nose to get out the lead. With the lighter diagonal balsa V tail and 20mm longer nose I should easily get under 400 grams in F3-RES trim. I'm thinking 375 grams is within my reach. But I so love electric gliders as opposed to gummy band launch models.

I already have an F3-RES spec'd high start.

Hey Konrad,


I've thought about buying the new Monarch assencision too but I really don't need any more models. As to your question on weight difference, as both are 2M gliders i'm not sure one is smaller than the other. Also the Monarch is balsa fuse and has a sheeted leading edge.

Also i'd say if you build the second one make it F3RES you already have an electric one.


Hank

 

[Konrad]

Smaller as in wing area. Chrysalis Lite 583, Ascension 507.
(The Ascension in F3-RES trim is advertised as being so much lighter that the Chrysalis Lite F3-RES).

Yep, but I so much prefer electric gliders.

 

[Hank GB Z]

Ok, that makes sense. I didn't check the wing area.

Sell the back up kit and buy the Ascension electrick kit?

Hank

 

[Konrad]

But it looks like the Ascension electric is coming out 50 grams heavier than my Chrysalis F5-RESt. I don't like the idea of more weight and less wing on a RES type model. I think with proper sized batteries I could get the Ascension Electric close to the same weight as my Chrysalis. So far so good, but I think the Ascension has about 75 square inches less area.

 

[Konrad]

I have to admit that carrying all that down thrust (7.5° to 8°) has been bothering me. But now, I'm recalling that a lot of the 2 meter gliders from my youth had a lot of down thrust when converted to 0.049 Cox power. I'm thinking of models like the Craft Air, Piece of Cake.

Oz : Piece O Cake plan - free download

outerzone.co.uk

Heck, even the great Astro Flight Challenger had a lot of down thrust. So I'm starting to think, what I'm carrying in the Chrysalis lite F5-RESt isn't so unusual in a polyhedral glider with an underslung thrust line.

All the best,

Konrad

 

[Hank GB Z]

Konrad,


I wonder if the down thrust is due to the drag of the wing. The piece o cake has a 72" ws where as a normal 0.49 model would have 30-40" ws. Just that much more drag wanting to pull the nose up hence the extra down thrust. Also a normal sport model with the motor you're using on your Chrysalis would have a shorter span and less area. I can across a similar problem with an autogyro but that ended up needing about 12 degree down thrust due to the really high drag of a rotor wing and the rotor wing being up so high on the pylon.

Hank

 

[Konrad]

That is what I'm thinking, the center of drag is way up from the thrust line in under slung power with polyhedral design wings.

 

[Konrad]

Now I'm thinking that down thrust might have been the only practical way to address this phenomenon in the 70's and 80's. But with today's radio a programming fix might actually be the best option. In that video I post you can see the stall at top of climb. I'm wondering if with programs as powerful as OpenTX I can add down (elevator comp) on power up, nothing new here. But when I pull back on the power that I add even more down for a 1/2 a second or more, to tame the power off stall, then bring the elevator back to cruise setting.

 

[Haoyang Wang]

If you want the thrust line to run through the center of drag, the dropped nose lowers the motor, and increases the down-thrust angle needed.

 

[Konrad]

Good point. My set up drops the thrust line less than 6mm. Now as the side area (height) of the nose for the F3-RES is less than the diameter of the motor I actually had no room (as seen in a side view) without actually increasing the side area of the nose. (I do have a spinner bulge for most of the length of the added nose block). As you know this added side area ahead of the cg adds to instability. Grafting the motor on to the existing nose with the minimum of added side area resulted in a drooped nose as I had to take into account the downward tilt of the motor. Now as we know a glider is falling through the air. I decided to use the droop nose rather than add side area as the droop is aimed towards the up flowing air from the falling glider.

Now I admit this is nowhere near the 6° of nose droop I have.

P.S.
The side area ahead of the CG with my motor mod is actually less than the original F3-RES configuration. Assuming the blades fold against the sides. I shortened the nose about 30mm. Also the coefficient of drag in yaw is lower (most of the nose block is round).

 

[Konrad]

In side area the original F3-RES nose is a few mm narrower than the motor diameter. I chose to add the needed dimension to the bottom of the nose block. This gives the drooped nose and allows for down thrust. You can see this added material in the form of a spinner bulge.

Now I'd like to point out that I haven't as of yet polished the blades to remove the rework scratches. These scratches may be stress riser and need to be removed to add some safety to the blades.

 

[Glenn Beer]

On the power off stall issue. Instead of chopping the throttle, I’ve just been feathering it off.

That’s not going to work for ALES competitions, but it does deliver the plane into stable forward flight at the end of the climb.

 

[Konrad]

LOL

Moderation? That's a concept I'm not comfortable with.

 

[Konrad]

WOW! WOW! Can a ship be too light?

Just got back from another day of flight testing. This report is going to be a bit long, so you might as well get a cup of tea before we go on.

First the Chrysalis Lite F5-RESt is everything I hoped it would be. This came about from a reworked Chrysalis Lite in F3-RES trim with a diagonally braced balsa V tail. Weight as measured is 426 grams. Down thrust is 7.5° maybe 8° as measure with the stab as a datum. CG is at 90mm, nose length is 190mm from the leading edge to the spinner back plate. Spinner is a CN 25mm, blades are reworked Aeronaut 13x10. Power comes from a 3 cell 350 mAh 70c Thunder Power battery. Motor is a Hacker A10-7 4.4:1 gearbox, ESC is a 20 amp Hobby Wing. That is the hardware report.

Now to the flight report. Even after cutting off another 12mm from the nose I still needed 2 grams of lead to the tail to tame the dive test. I'm not 100% happy with the trim as there are some oddities in the flight profile. In the dive test I still get a bit more pull up than I like. But I don't think I want to go any more tail heavy. In very slow flight I can't get the ship into a deep stall. I can get her almost to stop in the air and drop flat. That is the tail doesn't drop faster than the wings forcing the ship into a deep stall. In this flat stall I can get the nose down and fly out of the stall. The only other time I've seen this is with canard set ups. At this CG 90mm the elevators are flat with the top surface.

As to flight characteristic this has meant that in slow flight the yaw induced drag can appear to stop the forward motion of the aircraft, allowing the aircraft to just fall in a flat horizontal attitude. I'm finding that it is best to push forward stick to get some speed prior to inducing a turn at very low speeds. This feels a bit odd, having to push forward then yaw the plane followed by pulling back on the stick to make the turn. In this trim I was able to work the lift coming off a car van.

Down thrust was a pleasant surprise. In slow level flight I could slam open the throttle as the Chrysalis lite lurched forward as if it was shot from a cannon. There was no pitch change for about 20 meters until the speed started to gently pull the ship into the vertical. On the subject of vertical the 13 x 10 is a much better match as I have positive thrust at zero airspeed with a vertical acceleration until 20 meter. Then the Chrysalis climbs at a very good clip until it goes out of sight. At top of climb I do need to add full down at the same time I close the throttle to control the top of climb stall we usually see. I don't know if I can mix this full down and still have a safe ship for the other parts of the flight profile. With the faster climb I'm finding that I can actually climb to altitude using a lot less power. This has meant that I can get 7 or more climbs per battery charge.

The 800 lb gorilla in the room has been flutter. Well, I tried very thing I could with dives loops spins and full throttle speed runs and found no flutter!

The spoiler was another nice surprise. I had to add 48% up to the spoiler elevator comp. I also had to slow down this comp curve to 0.8 seconds. Now with this curve and reduced speed of the compensation I can bring out the spoiler and see no pitch change, only the speed changes. This really helps hitting the mark on landing.

So while I was hoping to loose more that 15 grams with the modification from F3-RES to F5_RESt I'm actually very happy with how the Chrysalis Lite F5-RESt flies. It wasn't just me but the guys I was flying with where keen to see a classic gas bag playing with so many light thermals. Penetration, covering ground was still a typical problem for an RES ship. But if one found oneself risking an off field landing you could just power back up.

This is both a great sport and RES competition ship. So much so that I've started on my second DJ Aerotech Chrysalis lite. Not sure in what trim but as the V-tail and the wings are the same I won't have to make up my mind for a while.

In the mean time I'll get back to my smaller 1.5 Stika, I'm sure I'll love the added control from a set of ailerons. https://forum.alofthobbies.com/index.php?threads/stika-f5k.1738/

All the best,

Konrad


P.S.
This is the first time I'm using my new X lite-S game console. I have a bit over an hour of actual stick time on this TX. I have to admit I'm not 100% happy with the ergonomics but with the slow flight of the Chrysalis Lite this hasn't been an issue. I was able to manipulate all three flight controls rather well. I only once missed finding the throttle for a go around.

Now I love having all the power on OpenTX in this little TX! I love all the fine tuning with the curves and speed settings.

Oh, I should also say that the Archer RX performed flawlessly!

 

[Konrad]

I've sanded the blade root with 400 grit sandpaper to minimize any stress risers from the rework process. I've also debranded the blades, as they have been radically reworked. I didn't want Aeronaut to get a bad rep. should my blades fail. I also want to cut down on the confusion should somebody in passing see my set up and keep bothering the resellers for Aeronaunt props that fit the 25mm CN spinner (there are none).

 

[Wayne]

Love it!!

P.S. Looks like Ed will be buying the remaining Stika. We will be the three Stika amigos.

 

[Konrad]

Some details.
The Chrysalis Lite has some engineering compromises particularly in the tail.
With the lift vector of a tail being downward we would normally want the hinge to be on the pressure side of the airfoil (stab top). Putting the tape on the low pressure side does little to help drag as the airflow over stab airfoil is likely already turbulent. I don't like to see all this clutter with the pushrods and linkages in the junction of the V-tail. Now there are good reasons for these issues as there is an over riding need to survive the landing. Stab linkages make horrible landing gear. (You might have noticed in my video that the stab hit the ground first)!. Also because of the fuselage boom the tape was put as far away from the pushrods as possible to effectively add length to the control arms.

I see that there is still some concerns about ESC and wire length. I cut the ESC motor leads to fit the fuselage space. Do not cut the motor leads as these are often just the motor field windings. These are hard to clean and make a nice solder joint for the connector. Also most ESC OEMs don't want you soldering on to the PCB for fear you will over heat and damage it. As you can see I left about 10mm of wire between the ESC and connector.

(In the old days (72mHz)we tried to keep these motor leads as short as possible to keep down radio noise. Today this hasn't been much of an issue. Also in the old days of sensored ESC this motor lead length (resistance)could effect the inductive phase (motor) timing. With modern ESC the back EMF is used to time the motor current lead so motor wire length isn't an issue).

What is an issue is the battery leads. Try to use as short a battery lead as possible. This is done to minimize the voltage ripple on the lead. This ripple can heat up the power MOSFETs and cause early failure. Try to maintain a ripple voltage of less than 10% of Vss.

I can't for the life of me understand why my 70C battery came with a 2 pin JST connector. At best these are rated for 10 amps. I find that the Deans micro connector is good for 15 amps and see no temp (voltage drop) at 11 amps.

And as this is a balsa fuse I kept the antennas in side but still a 90° to each other.