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Author Topic: Chrysalis F3-RES, DJAerotech I'll be improving it until it doesn't work  (Read 431 times)
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Konrad
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« on: November 09, 2017, 04:29:12 PM »

In this thread I asked, what were some of the HIP Hive mind impressions of the new F3-RES 2 meter class? After going through most if not all links I selected the DJAerotech Chrysalis F3-RES.
http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=22606.0
http://www.djaerotech.com/news-updates/tag/3+channel
Thanks to all that contributed to that thread

Well, the kit arrived in two days after placing the order. As luck would have it, it was also subjected to its first stress test. The box was badly damaged by USPS crushed end to end. But the way Joe had packaged the kit there were no broken parts. Most of the laser cut parts had fallen out of the sheets but no damage.

Something I’ve yet to come to grips with is that laser cut balsa stinks! The wife wouldn't allow open laser cut kits in the kitchen. In this case I have to agree with her. The smell of burned balsa destroys any culinary experience you would expect to find in the kitchen.

This is going to be my usual build review where I show how I improve the product until it doesn’t work! And then hopefully come back from disaster

The first thing I’ll look into is tapering the trailing edge (green line). This means I’ll have to recut 8 rib, I know why buy a kit! Then I’ll try to laminate with 5 maybe 4  0.5mm basswood strips (red) a new wing tip hoop. This should more than make up for the loss of the sheet wing tip. I plane to add some stability with a large gusset (yellow). The aim in all this is to take weight out of the wing tips to help the Chrysalis F3-RES signal lift.

I have to admit I don’t like to use fiberglass as shown to reinforce the tip break at the leading edge. I’d like to see a blade (brown)added to the break rather than a glass patch. I know it is possible to model with 3D CAD. But I’m not sure a 2D laser can cut the slots in the rib and maintain a tight fit.

The bad news is that this kit arrived so early I haven’t cleared off enough space on my bench. I was expecting the package no earlier than Friday. I’m already behind the 8 ball.

All the best,
Konrad
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dosco
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« Reply #1 on: November 10, 2017, 08:37:25 AM »

Konrad:
I'm interested to learn of your results. Do you have any prior experience with the Chrysalis that indicates the wingtips are too heavy?

I ask because Don Stackhouse posts prolifically on RCG and the impression I get is that Don and Joe spent quite a bit of time ensuring the design is good.

Regardless, I'm interested. Will pay attention!

Regards-
Dave
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Konrad
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« Reply #2 on: November 10, 2017, 10:22:06 AM »

The last DJAerotech glider I had was the Monarch in the mid 90’s ( right before the discus launch).

I’m not implying that there is any fault in the design. In fact it is the best that I saw in my initial search, that is why I purchased it.

As this is a competition ship I’m looking to see if I can add (take away) anything to the structure for any advantage to overcome my piloting ability. As I see a structural member that has the same cross section across the whole span. I have concerns that it might be too heavy out at the tips.

The reason the TE is as it is, is to try to control the buckling of the ribs from the covering. This force is the same regardless of where the rib is placed. So the TE has a constant cross section along the whole span. 

As I have major issue with the  management  of RCG  and their lack of transparency, I avoid it if at all possible. ( I just learned that there has been a management change).

I did ask Don for his input on the design changes. He came back with a detailed explanation of why he didn’t like it.
Don had a lot of other issue with my design proposal many are valid. I'll see if I can address these and will add it here on HIP.

I have to say I’m impressed with that kind of customer support. As I know their profit margins does not support the time it took to reply to my request for information.

All the best,
Konrad
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dosco
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« Reply #3 on: November 10, 2017, 10:39:37 AM »

As this is a competition ship I’m looking to see if I can add (take away) anything to the structure for any advantage to overcome my piloting ability. As I see a structural member that has the same cross section across the whole span. I have concerns that it might be too heavy out at the tips.

Got it. I tend to concur with your assessment on this.

Quote
I did ask Don for his input on the design changes. He came back with a detailed explanation of why he didn’t like it.
Don had a lot of other issue with my design proposal many are valid. I'll see if I can address these and will add it here on HIP.

LOL. I'm not surprised. If you're so inclined, it would be interested to see what you suggested and his response. If not, that's fine.

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As I have major issue with the  management  of RCG  and their lack of transparency, I avoid it if at all possible. ( I just learned that there has been a management change).

Err. I admit ignorance. Maybe you could provide insight (if you'd prefer not to air the laundry in public, feel free to send a PM).

Regards-
Dave


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Konrad
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« Reply #4 on: November 10, 2017, 11:27:54 AM »

Ok, since I brought it up I should mention why the design is as it is.

The wing tip sheet needs to be thought of as a large gusset. It with the large glue line is trying to keep the leading and trailing edge in parallel. Removing the tip plate increases the risk of flutter as it is easy for the LE and TE to come out of parallel. This will allow flutter to develop that will destroy the wing.
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« Reply #5 on: November 10, 2017, 11:40:33 AM »

What I suggested, is what I posted in the opening post of this thread.
The major issue was detailed in the above post.

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As I have major issue with the  management  of RCG  and their lack of transparency, I avoid it if at all possible. ( I just learned that there has been a management change).

Err. I admit ignorance. Maybe you could provide insight (if you'd prefer not to air the laundry in public, feel free to send a PM).

Regards-
Dave
I see no reason to protect inept and despicable management, so I'd love to air the practices of RCG publicly. And I love to be able to give the management of RCG the ability to respond to defend their indefensible actions. But the management of HIP has asked that I don't. I can see their point in that this is a site to discuss aeronautics as it applies to our toys.

Please be aware that there has been a slight change in the management of RCG since I last participated in that site.

Poor management, be it in the political arena of even in the field of toy airplanes is not in the scope of this site.

I do mention that I don't visit RCG as a way to indicate that I often don't know what is going on over there. This is the extent of what I think I can say and still respect the wishes of the management of this site.

All the best,
Konrad
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Konrad
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« Reply #6 on: November 10, 2017, 03:41:52 PM »

Something else that Don mentioned was that it is a good idea to condition the TE of the wing with the covering before shrinking the rest of the wing.

This conditioning of the TE is done by sealing the covering film, both the top and bottom, to the TE with the iron  before shrinking the rest of the open structure. The tension on both the top and bottom will act much like case hardening or shot peening a metal bar. Work the film on the TE first and get it straight. Once the trailing edge is straight shrink the open areas a little at a time. You don’t want to shrink one panel or one side of the panel tight and then move to the other. You want to gently  shrink the film on all panels slowly and at about the same time. You want to use the minimum heat possible. Think of iron on film like a metal if you heat it too much the temper is lost. Not an accurate description but I hope you get the idea. Don’t over heat the covering.

All the best,
Konrad
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Konrad
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« Reply #7 on: November 14, 2017, 12:09:20 PM »

I know this is putting the cart in front of the horse. But one can make an argument that the reason we have all that structure is to give the covering shape. When covering the trailing edge of the wing it’s a matter of leverage when it comes to distorting the thin trailing edge. Here are some thought from the designer. (Please note he is not endorsing that one go against the recommendations of the film's manufacture.)

 ”If the covering is stuck only to the trailing edge itself, then as the covering tenses up on the top surface, it will tend to lift the trailing edge stock, and as the trailing edge gets higher, the covering material gets a longer effective lever arm above the top of the aft upper edge of the rib to pull on it. The result is a trailing edge stock getting bent upwards. By sticking the covering to the entire upper surface of the trailing edge stock, the pull point is now fixed to the forward edge of the trailing edge stock, so it does not have any leverage.

Shrinking the bottom surface first also helps.

As far as ribs buckling, there's a couple conflicting factors involved. If you stick the covering to the ribs first, then shrink it, any unevenness in the covering can pull the rib to one side, setting it up for buckling as the covering tension increases to max. However, if you don't stick the covering to he rib, then the only lateral support the rib has is itself.

The trick here is to leave the ribs free from the covering, shrink all the "slack" out of the covering, but do not take it up to full tension yet. Now, stick the lower surface covering to the rib edges and shrink the upper surface. The partially tightened lower surface covering will provide lateral support to the ribs and help prevent them from buckling when you shrink the upper surface. After that, you can go back and finish shrinking the lower surface. Finally, clamp the wing down on a flat surface and re-shrink the top to set the washout, then re-shrink the bottom.”

Again please refer to the films instruction for how they recommend using their covering, such as overlap amount and temperature ranges, etc.

You might note that I like to cover the bottom last. This makes it a bit easier to maintain the wing as I can peal off the bottom covering with little disturbance to the top covering. As the bottom covering often shows wear much faster than the top I find this an advantage.

All the best,
Konrad
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« Reply #8 on: November 16, 2017, 08:29:00 AM »

Ok, since I brought it up I should mention why the design is as it is.

The wing tip sheet needs to be thought of as a large gusset. It with the large glue line is trying to keep the leading and trailing edge in parallel. Removing the tip plate increases the risk of flutter as it is easy for the LE and TE to come out of parallel. This will allow flutter to develop that will destroy the wing.
Hum, nobody is going to call me on this? Ok, I'll call out myself.

For the sake of clarity the term parallel is incorrect. I should have used the geometry term plane. The gusset is trying to keep the LE &TE in plane. Not to be confused with trying to keep them on the plane (aircraft) Grin

In case some missed it the upper spar is also forming a tripod like structure anchored on the wing tip plate. This is key to the rigidity of the wing tip panel.


All the best,
Konrad
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dosco
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« Reply #9 on: November 17, 2017, 07:24:58 AM »

I understand the drawing you presented ... the verbiage is a bit difficult for me to visualize.

Thus, waiting for your as-built result.

<:popcorn:>

Regards-
Dave
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« Reply #10 on: November 18, 2017, 10:15:01 PM »

I was glad to learn that Don and I agree that the “pull/spring setups” are rather poor control systems. He sent me this description.

Quote from Don:
“I am NOT a fan of pull-springs for tail linkages, they are simply not as stiff for their weight. They also use the torque of the servo inefficiently. To get the same control linkage stiffness you will need a very stiff spring and a bigger servo. And yes, the loads on the hinges and the loads on the tail structure could be a problem. The stress concentrations to the tail boom structure where you anchor the springs could also be a major problem. The weight difference, if there is one (by the time you finish dealing with the other issues involved) is not worth the risk, uncertainty and hassle. Particularly on this model, with its wide control surfaces (and wide for a reason)!, you’re asking for trouble, or at least a protracted development program.”

I’ll be a bit more blunt, I hate them!

There is a way to save some weight in the tail by getting rid of the balsa triangle stock.  I have a slightly different approach in that I’m trying to use the yellow tubes to support themselves. I use a 3 hour epoxy micro-balloon  mixture  to secure the ends and then I’ll run CA down the tail boom. Both Don and I are using metal wires and magnets to hold the yellow wires in place while the glues cure. As I think the micro-balloons will make the epoxy less brittle I will not be adding the bass wood shelf Don recommends in his set of instruction. Just my triangle stock weighs 2.1 grams. Multiply that by the tail to nose ratio and this could save 6 to 8 grams of weight!


I’ve included his instructions below. Again from Don;

“You can eliminate the triangle stock, and that does save a significant amount of weight. Slip some 1/32" music wire into the yellow tubes to hold them straight when you install them in the tail boom. Tape them together for about an inch at the aft end, with about a 3/32" to 1/8" thick shim between them (so the brass tube rod end fittings on the pushrods at the aft end do not snag or rub on each other). do the same at the other end at a location that will be clear of the forward end of the boom, with about an inch sticking out of the aft end of the boom. Clean the tubes with acetone or other degreasing solvent that does not leave a residue. Wipe 15-minute epoxy on the tubes and insert them into the tail boom and use magnets on the outside to pull on the music wire to hold the yellow tubes against the inside of the boom.

Alternatively, you can put the tubes in position dry and hold in place with the magnets, then hold the tail boom vertical and drip CA down the length of the tail boom to lock the yellow tubes in place (note, I have not tried the CA method myself, it was recommended by a builder).

Once everything is dry, remove the music wires, and glue a small piece of basswood strip across the inside of the tail boom at both ends with epoxy, so they act like a "shelf" to lock the tubes in place. Do not completely plug the tail boom, it needs to be a vent for the inside of the pod to prevent air leaks and airflow separation around the edges of the wing saddle. Finally, trim the extra 1" off the aft ends of the yellow tubes so they are flush (or nearly flush) with the aft end of the tail boom.

We don’t put that method on the plans because it can be trickier for beginning builders, but an experienced builder should be able to do it without much trouble.”

I think this should be in the manual as this is NOT a beginners model. It is a competition glider for the F3-RES class. Now I too would keep this out of their other sport boom and pod models

All the best,
Konrad
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« Reply #11 on: November 20, 2017, 08:02:45 AM »

“Slip some 1/32" music wire into the yellow tubes to hold them straight when you install them in the tail boom. Tape them together for about an inch at the aft end, with about a 3/32" to 1/8" thick shim between them (so the brass tube rod end fittings on the pushrods at the aft end do not snag or rub on each other). do the same at the other end at a location that will be clear of the forward end of the boom, with about an inch sticking out of the aft end of the boom. Clean the tubes with acetone or other degreasing solvent that does not leave a residue. Wipe 15-minute epoxy on the tubes and insert them into the tail boom and use magnets on the outside to pull on the music wire to hold the yellow tubes against the inside of the boom.

Konrad:
I presume you're familiar with the method used by the DLG folks?

Put wire in the tube, fish it into the boom, and use magnets on the outside of the fuselage to hold everything in place. Wick CA down the sheath until it drips out the other side. Done.

You'll obviously need a wire that can be held with a magnet, and something under the tail end of the fuse to catch the CA drippings.

-Dave
 
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« Reply #12 on: November 20, 2017, 09:05:22 AM »

Isn't this the method Don describes, just that he said he hasn't performed it himself?
But actually, no I didn't know about this method. Most of my models have been so small that I haven't even needed a bowden tube to guide/support the carbon rods.

I tried to not allow the CA to drip off the ends of the tubes. I feared that the CA could, through capillary action, wick into the tubes. Has this been a problem for others?

I hope my method (description) adds some support by making a triangulation with the tubes and the tail boom.

I fear I was a bit too enthusiastic about my weight loss predictions. I used the nose to tail ratio as my multiplier. But since all the mass (2.1 grams) removed is not at the tip of the tail boom but rather distributed along its full length. I should have used the average 1/2 of the tail boom as part of my multiplier.  So the short of all this is that I'm sure I saved 2.1 grams and maybe 4 grams total when looking at trim weight.

This isn't a night and day type improvement put it should be noticeable, if nowhere other than the gram scale.
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« Reply #13 on: November 20, 2017, 11:20:54 AM »

Konrad, I have to (respectfully) question your aim of reducing weight in a model of this type? While it's a useful preoccupation in other areas of modelling, in F3-RES the benefits will be minimal but at some potential cost.

You will gain a percent or two of thermal climb performance in the very lightest wind conditions but there is a definite lower weight limit on these models where penetration will suffer. You'll just end up adding ballast most days anyway.

In making these mods there is a very real danger of losing airframe stiffness which is already hard enough to achieve under the limited carbon specified in the F3-RES rules. Reduced stiffness means worse handling, more drag and lower launches.

Don is one of the better glider designers out there and the aerodynamics of the wing design will match the all up weight. The weight is used thoughtfully to provide stiffness. He also does plenty of testing to fine tune handling. I would suggest following his design Smiley

(That doesn't mean I agree with him on pull-controls however Wink they have definite advantages on smaller models IMHO)
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« Reply #14 on: November 20, 2017, 12:08:38 PM »

The "New F3-RES" class glider is much cleaner than the comparable 2 meter woodie, so ballasting isn't going to be needed. If it is needed I can add it under the wing in the fuselage.  Heck, the slight weight loss that I think is possible can be negated with using steel wing joiner rods

That is the design exercise, trying to "improve" what Don and Joe have brought to market. I am making an assumption that there were compromises made to bring the kit to market.  And yes, I'm fully aware of the difficulty that is why I said; I'll be improving it until it doesn't work.

The removal of the aft triangle stock is done with the blessing of Don. The triangle stock was included as a nod to ease of assembly (keep the tubes straight while glueing them into the tail boom). Not sure what other mods I've made. I wanted to remove the large tip plate. But I hope I explained why Don said this isn't a good idea.

I've requested and got Don's design consideration (this is great customer support) for my planed "upgrades". For example I asked Don why the TE wasn't tapered and he effectively said that covering was dictating the need for the large TE, and that he had designed the airfoil with it being there. He also told me how to deal with the thin TE of the ribs while covering. I tried to convey this information in the simple cartoons I've drawn.

Now to be honest there are very few upgrades that I can think of for this ship. That is why I chose this DJAerotech F3-RES design over the others.
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« Reply #15 on: November 20, 2017, 12:15:29 PM »

(That doesn't mean I agree with him on pull-controls however Wink they have definite advantages on smaller models IMHO)
I see none.  Can you go into specifics or give me a link.

I see the spring as placing a continuous strain of the servo. This alone gives me reason to reject their use. I've burned up far too many amps and motors in the micro and nano servos without the load of the spring fighting the servo around center.
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« Reply #16 on: November 20, 2017, 06:55:55 PM »

Over the years I have worn many hats, at one time I was a manufacturing and process engineer*.

This post will be about changing the lamination process called out in the manual. The manual says that medium CA works well for this. I find medium CA messy, heavy and often times problematic for laminating wood. I like to use what I call the iron on Aliphatic-resin (PVA-Polyvinyl acetate) method. Using yellow carpenter’s glue, spread a very thin layer on the plywood to be laminated to the balsa part. Make sure the notches are clear of any glue.  On the matting balsa part I also apply the glue very lightly where there are bulkheads on the off chance that there is a dry area on the plywood. Let dry for about 3 hours.

Then take your time to align the parts. With a covering iron set at mid temp iron down the plywood to the balsa wood.  Hold the iron down for about 5 seconds. The heat will reactivate the  resin making a permanent bond.

If there is any bowing of the laminated parts iron the other side as the bow is most likely from uneven moisture in the assembly from the uneven heating (one sided).

The benefit of this is that there is no rush to align the parts. All the contact area is bonded to the plywood and balsa wood. There is no excess soak up of glue. The joint is as strong as the wood without being brittle like that with CA. And last you can move on the next assembly step without your finger being covered in CA.

*I’m going to have to work on how growing turbine blades has anything to do with balsa wood construction.
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« Reply #17 on: November 21, 2017, 07:35:28 AM »

I like to use what I call the iron on Aliphatic-resin (PVA-Polyvinyl acetate) method. Using yellow carpenter’s glue, spread a very thin layer on the plywood to be laminated to the balsa part. Make sure the notches are clear of any glue.  On the matting balsa part I also apply the glue very lightly where there are bulkheads on the off chance that there is a dry area on the plywood. Let dry for about 3 hours.

Then take your time to align the parts. With a covering iron set at mid temp iron down the plywood to the balsa wood.  Hold the iron down for about 5 seconds. The heat will reactivate the  resin making a permanent bond.

Ah yes. I enjoy this method as well. I first learned about it around 1987 or so, and used the approach to laminate the wing leading edge sheeting on my Sig Riser.

When I first learned of the method (I was a teenager back then) I was shocked. I'd given up the Elmers stuff after many irritating experiences (mostly with model rockets) and had moved on to CA, cellulose glues, and epoxy.

Quote
Over the years I have worn many hats, at one time I was a manufacturing and process engineer*.

Me too. I was a manufacturing engineer at my last employer, focusing on sheet metal welding of nickel alloys and titanium. We made aerospace pneumatic components (think bleed air systems).

-Dave
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« Reply #18 on: November 21, 2017, 10:48:14 AM »


Me too. I was a manufacturing engineer at my last employer, focusing on sheet metal welding of nickel alloys and titanium. We made aerospace pneumatic components (think bleed air systems).

-Dave

I always felt sorry for the guys that had the responsibility for the tube and ducts on the aircraft side

Another thing I like about Aliphatic-resin (PVA-Polyvinyl acetate) it that if the parts are small enough (like the stabs) you can put the parts in the microwave and force dry the parts. Don't use pins to hold the parts in place! Shocked I like use tape to hold the parts in place. I really like to use the microwave drying method when I'm laminating tip hoops. It's like using instant CA with none of the issues associated with CA.

All the best,
Konrad
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« Reply #19 on: November 21, 2017, 04:54:40 PM »

Working some more on the tongue depressor (fuselage pod to you Cheesy ). I have to say I really like working with well thought out laser cut parts.

When working with carbon tubes one needs to be aware that they are often thought of as being notch sensitive. That is any scratch can result in it becoming a stress riser (force concentrator). Stress riser cause material to fail much earlier than otherwise expected.  When working with glue it is usually recommended that the shine be removed from the bonding area to give the glue some bite. These are often conflicting requirements. On the tail boom I used very fine sandpaper 400 grit to knock off the shine. Try not to cut into the carbon underneath the shine. I also make sure that the 400 grit scratches are running parallel with the boom.

I used a two part adhesive called “Stabilit Express”. This adhesive really has a tenacious bond with most plastics (the epoxy in the boom is a plastic). You might see that I have made large fillets around the boom adjacent to the bulkheads and on both sides of the bulkheads. I may have made the fillets a bit too large.

Now I have run into an assembly issue. That is after I freed the fuselage from the work surface and in the free state the bottom of the tail boom is parallel with the bottom of the fuselage pod. The manual and plans state to use a fixture (F) to hold the boom at the proper angle which defines the tail plane incidence. Over the length of the tail boom the bottom of the tail boom is to rise 1.2 mm in the rear.

In my build this rise in the boom did not happen. I suspect that the issue is that the hole for the tail boom in bulkhead F4 is too low. I think it should be raised in the cut file about 0.1 mm to 0.2 mm. In my case I like to fly with a rather aft CofG, I’m hoping that this error will actually help lower my drag as the tail surfaces might be more in line with each other than they would be otherwise.

I’ll ask Don for his take on these rigging angle, manufacturing and build issues. I hope he doesn’t say; “You fool you didn’t follow the manual, in step XX do this”.
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Re: Chrysalis F3-RES, DJAerotech I'll be improving it until it doesn't work
Re: Chrysalis F3-RES, DJAerotech I'll be improving it until it doesn't work
« Last Edit: November 21, 2017, 05:23:07 PM by Konrad » Logged

Cut it twice and it's still too short!
Konrad
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« Reply #20 on: November 21, 2017, 10:36:01 PM »

Don got back to me on this.
 
By the numbers this is what he said.
That 1.2 mm discrepancy equates to 0.097 degrees, and a difference in tail lift coefficient of about 0.008 (allowing for tail planform effects).

And in terms of a vertical distance between F3 and F4 (which are about 2” apart), that 0.047” equates to the bores being out of alignment by 0.0034”.

Also, can you rig your tail surfaces, including thermal expansion effects, servo jitter and hysteresis, etc, within 0.2 degrees (which is about the amount of elevator deflection these numbers represent)? BTW, that number represents about 0.009 inches in deflection measured at the elevator trailing edge. This is not a significant problem, even if you don’t do anything about it and just leave things as-is.

I will be leaving well enough alone. BTW 0.009' is the equivalent thickness of three human hairs! I know I’m good but I’m not that good as the notice this error inflight! Roll Eyes

I’m impressed that Don did take this into account when he made the assembly fixture F5.

The take away is that in step 15 make sure that the tail boom is free to move inside the bores of F3 and F4 when the aft end of the boom is propped up on fixture F5.
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Cut it twice and it's still too short!
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