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Author Topic: Chrysalis F3-RES, DJAerotech I'll be improving it until it doesn't work  (Read 9965 times)
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Konrad
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« Reply #225 on: January 24, 2021, 06:48:19 PM »

I tend to believe that 3° of 4° was more that adequate. This would be for dihedral ships (I first start with 2°).But for polyhedral ships it appears that with the wider distance between the center of lift and the thrust line dictates more down thrust.

Most of my time under power will be in the vertical. ( I indicate that I'll have 2.4 time the thrust as weight).

Do you favor mixing over thrust line adjustment to control the pitch up and possible stall?


I have to admit that 7° of down thrust looks excessive!
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Kevin M
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« Reply #226 on: January 25, 2021, 02:10:47 AM »

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Do you favor mixing over thrust line adjustment to control the pitch up and possible stall?

I don't, or rather only for fine-tuning. When you increase throttle on the Tx there is a delay before the motor/prop spins up to achieve the new demand whereas the elevator input from the mixer is effectively instant, makes the transitions a bit untidy. But if all you do is vertical climbs from launch, then glide I suppose it isn't that important.
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Konrad
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« Reply #227 on: January 25, 2021, 08:48:01 AM »

Kevin thank you.

I whole heartedly agree with trying to get the best possible mechanical rig prior to using programing solutions.

I'm concerned about your statement that mixes are effectively instant. I've been using the Multiplex Profi 4000 and OpenTX programs for the last 3 decades. These programs allow the rate (speed) of the mix to be adjusted. Not servo speed but the actually the mix function. Is this not a basic function found in most radios? Otherwise it is very easy for a mix value to over run the control function, such as flaps, motor, spoiler.  For example a 25% elevator comp for spoiler could easily be full implemented while the spoiler is only 25% deployed (assuming the servos have the same speed). This can get real ugly if the compensation curve is not linear! (See reply #150 page 7) I like to try to slow down the mix as a function of the percentage of correction and the servo speed.


As I was using the wrong prop, I didn't speed too much time testing the thrust line.  
As the thrust line doesn't go through the center of drag I have down thrust to keep the model from performing a "Figure 9" as we power up for a go around. I also don't want too much down thrust pulling the nose into the ground, again on a go around. Then there is the elevator trim as a function of nose weight. I'm sorry to say that I'm a bit impatient having violated the #1 rule of trimming and have changed two things at once. I took the opportunity to change the thrust line at the same time I shortened the nose. I really should have waited for a new set of prop blades and waited for good weather to test.
« Last Edit: January 25, 2021, 09:09:35 AM by Konrad » Logged

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Kevin M
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« Reply #228 on: January 25, 2021, 09:46:16 AM »

Konrad,

My old Tx wouldn't allow mix speed to be set. I've just got a new one, though not as capable as yours. I haven't had time to learn it yet, and I suspect it might have that ability. If so, thanks for the heads up, it will be useful.
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OZPAF
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« Reply #229 on: January 25, 2021, 06:24:23 PM »

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Do you favor mixing over thrust line adjustment to control the pitch up and possible stall?

While i don't have the same ratio of thrust/weight with the "Inside" F5J I have found that the combination of a small amount of down thrust and  elevator mixing works well. I have the throttle on a slide (not originally by choice) and this enables me to control the transition to the glide much better.

I had a far more potent - for it's time, 7 cell ( old Australian rules) which would climb on rails using this approach. I never measured the thrust but it pulled around 65A on 7 cells(nicads) on a direct drive 10x6 prop.

John
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Konrad
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« Reply #230 on: February 01, 2021, 06:16:58 PM »

I too have an old 25 to 30 years old 7 cell 2 meter monster. Today she is sporting 2 cell lipo and drawing 120 amp!  Thrust numbers loose all meaning when I get over 2:1 thrust. This ship is not a gas bag. While I don't think of her as a hotliner (open wings). She does fly nice and level at full power and will rotate into the vertical on my command. Slow high speed rolls are a joy to see, when I do them right! You might be able to see that there is very little down thrust, 3° at most.
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« Reply #231 on: February 01, 2021, 06:30:05 PM »

I still have the remains of the 7 cell and was thinking of refurbishing it with a 2s Lipo driving it's original Plattenberg brushed motor. it's definitely not a hot or even warm liner though but the old rules required high speed climbs(30sec max.) and this 1.85m model did this very well.

Your model sounds fun.

John
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Konrad
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« Reply #232 on: February 01, 2021, 06:32:11 PM »

Back the Chrysalis Lite F5-RESt. Here I cut off another 12mm after the first test flight. Added another 0.7° down thrust  and remover 4 of the 5 grams of tail weight.

I have to say wacking off the nose is getting a bit old. I think my nose length is 195mm from the LE to the spinner back plate. I think I've reached neutron star density in the nose. In that to make the nose any shorter I'll have to move my radio installation.
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dosco
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« Reply #233 on: February 01, 2021, 06:49:20 PM »

I think I've reached neutron star density in the nose.

Mmmm. Neutronium.

(lol)

-Dave
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Konrad
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« Reply #234 on: February 01, 2021, 09:53:38 PM »

Not sure I ever showed the amount of down thrust I'm using. This is about 7.5° to 8° of down thrust.
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Konrad
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« Reply #235 on: February 02, 2021, 12:20:12 PM »

I'm now recalling that a lot of 2 meter glider from my yoof  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.
https://outerzone.co.uk/plan_details.asp?ID=11286

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
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Konrad
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« Reply #236 on: February 02, 2021, 02:42:12 PM »

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 posted 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 so, to tame the power off stall, then bring the elevator back to cruise setting.

Then again that stall might be more of an effect from being out of trim on a maiden flight.
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dephela
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« Reply #237 on: February 02, 2021, 05:30:08 PM »

Down elevator mixed into motor, I've done that in both my eplanes and it works very well. Motor shuts off from ALES and trim pulls plane into level flight. My motor is on a separate switch so if I have shut it off it's still in launch mode. Then I switch out of launch mode and into cruise with normal trim. It looks beautiful and it's easy to tell if/when motor stops.

Dennis
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Konrad
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« Reply #238 on: February 02, 2021, 05:56:42 PM »

Let me see if I'm reading this right.

You have a launch mode. I assume this is a bit of down and maybe a bit of right rudder to correct for P-factor. Along with this launch mode you have a switched (On Off) motor? So to climb you have to manipulate two switches, mode and throttle? At top of climb you switch off the motor but still have the down in the elevator from the launch mode, to keep out of the stall? At some point in the push over from climb into horizontal cruise flight you switch normal flight taking out this down elevator motor compensation?

If so may I ask what program you are running on your radio. Does it have the functions for timed mixes and virtual switches.

I guess I'm really asking which is the more efficient way to control the climb, with down thrust or elevator manipulation? I'm starting to lean towards elevator mixes as I think the down thrust is putting more load on the wing fighting the climb. But in the vertical I'm actually on the prop. Is there more of a penalty for the added elevator drag than down thrust vector?

All the best,

Konrad

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dephela
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« Reply #239 on: February 02, 2021, 06:16:23 PM »

You have it correct. I use a JR 9303 and simple mixes, nothing timed.
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Dennis
Konrad
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« Reply #240 on: February 06, 2021, 01:10:09 PM »

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 triangular 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 195mm 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 so 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 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.

As a side note, I've debranded the prop blades as they have been radically reworked.

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Kevin M
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« Reply #241 on: February 06, 2021, 01:43:25 PM »

Quote
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.

Have you tried rolling on about 45+ degrees of bank as you close the throttle (leading slightly with the bank)?
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Konrad
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« Reply #242 on: February 06, 2021, 02:31:37 PM »

It's and RES ship.  One does not get the classic roll in the vertical with rudder inputs.

The down command (bunt) does bring the tail up to arrest the stall. The issue I have, is that if I have to use an onboard altitude limiter (As proposed by some F5-RESt rules) how does one time the motor cut off with the control surface command to control the stall?
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Kevin M
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« Reply #243 on: February 06, 2021, 02:49:45 PM »

Oh, O.K., I find I can do this with RES up to about 60 degrees climb angle, but I don't have anything with the thrust/weight ratio you have on this.
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« Reply #244 on: February 11, 2021, 07:25:53 PM »

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The issue I have, is that if I have to use an onboard altitude limiter (As proposed by some F5-RESt rules) how does one time the motor cut off with the control surface command to control the stall?

Altitude or motor run limiter?

I have my timer counting down the motor run time and usually cut just before the nominated time of 30s for F5J, when going for max. height. I also have my motor on a slide switch(not by choice) so I can ease it off and that also helps.

Other than doing some altitude/time check climbs on the day - I'm not sure how you could handle altitude limited motor runs.

Quote
I'm finding that it is best to push forward stick to get some speed prior to inducing a turn at very low speeds.
I found it beneficial to do this in my rudder elevator thermal contest days as it gives a far more positive and faster roll into the thermal. It also in my experience helps with aileron models that have long wings and are light.

John
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Konrad
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« Reply #245 on: February 11, 2021, 08:10:10 PM »

The tentative rules are altitude, right now set at 100m. The idea is to try to fly F3-RES and F5-RESt at the same time. So the idea is that they both start at the same height.

The slower I go the more I rely on the rudder.  I laugh at guys that think flying a glider is easy. As to skill I can say unequivocally that gliders take more skill than any F3D Pylon ship I've ever flown. Ok, things happen a lot fast with the pylon ship closer to the ground.

I like the slider throttle, but then I came from a single stick TX many many years ago.
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