My First S8E Bird

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TheAviator

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I've just finished my first (acceptable) S8E wing and am working on the design for the full glider. I have some Allegro tailbooms from Goodwinds Kites and put an order in for some ASK/RCBuilder.com all flying stabilizer mounts. Next on the agenda is to work up a CNC mould for the pod and sand some balsa tail surfaces. I'm really looking forward to getting this thing done and getting some true RC sailplane action.

Wing Specs:
Construction: Standard DOW blue foam, 1.4oz E-glass 45* bias (one layer, 2" root doubler), .25"x.007" spars, top and bottom
Airfoil: Drela AG16 (root), Thinned AG16 (tip)
Root Chord: 5.75"
Tip Chord: 4.5"
Span (flat): 47"
Wing Area: 241 sq. in.
Dihedral: 12.5* per side
Mass: 65g

EDIT: I almost forgot: a huge thank you to Bob F. from the MTMA club for getting me this far. He helped to get me past the "scare factor" of doing foam/FG wings and let me use his vac-bagging equipment.

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I've just finished my first (acceptable) S8E wing and am working on the design for the full glider. I have some Allegro tailbooms from Goodwinds Kites and put an order in for some ASK/RCBuilder.com all flying stabilizer mounts. Next on the agenda is to work up a CNC mould for the pod and sand some balsa tail surfaces. I'm really looking forward to getting this thing done and getting some true RC sailplane action.

Wing Specs:
Construction: Standard DOW blue foam, 1.4oz E-glass 45* bias (one layer, 2" root doubler), .25"x.007" spars, top and bottom
Airfoil: Drela AG16 (root), Thinned AG16 (tip)
Root Chord: 5.75"
Tip Chord: 4.5"
Span (flat): 47"
Wing Area: 241 sq. in.
Dihedral: 12.5* per side
Mass: 65g

EDIT: I almost forgot: a huge thank you to Bob F. from the MTMA club for getting me this far. He helped to get me past the "scare factor" of doing foam/FG wings and let me use his vac-bagging equipment.

Brian,

25 degrees of total dihedral is excessive. Usually, 15 degrees total is used on gliders without ailerons.

Dave Fitch
 
Hey Brian,

Looks good. I am in a similar boat. I have two Raven 9 wing cores, CF booms, flying stab mounts. The wing is the same area but slightly lower aspect ratio (44" span), Drela AG16 blended with to AG18 at the tip. I'll also be going 2 channel.

Keep the details coming. I plan to do a thread on my build as well.

Don
 
Keep the landing task in the back of your mind while building. A glider this size in the weight you are planning (slightly over half the allowed mass) should be able to make the time barring sink. You won't be able to grease every landing and you don't want to sacrifice strength in the model to meet a super light target mass.

Going to have it done for the Capitol Cup next weekend? :)

kj
 
Keep the landing task in the back of your mind while building. A glider this size in the weight you are planning (slightly over half the allowed mass) should be able to make the time barring sink. You won't be able to grease every landing and you don't want to sacrifice strength in the model to meet a super light target mass.

Going to have it done for the Capitol Cup next weekend? :)

kj

I'm going to try to have it done for the Capitol Cup. My two biggest hurdles are the wing mount and the fuse pod. If I run out of time, I will just do a balsa pod, but I would like to try my hand at an FG pod. How many layers of what type of glass do you use for yours, Kevin? I can do structural analysis of wings built like this, but I honestly have no idea how to model impact forces on such a pod. I do plan on having an 1/8" ply crutch as I've seen in some of the later Raven designs by Bob Parks.

Also, I know I can't "grease the landings," but honestly, I'll be happy to make time and get within 10m of the spot. I have very little experience with sailplanes and no experience with anything that I (or anyone else, for that matter) would consider a performance sailplane. I have pretty thorough RC experience though, and have flown trainers, pattern planes, sport planes, high speed craft, and flying wings.

Also, what do you use for your Rx battery? I think I'm going to use an E-Flite 120mAh 2S battery from the 180-size brushless micro aircraft.
 
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Very nice. Looking forward to a flight report!

Ari.
 
Minor update: I'm planning on doing a SuperGee style wing mount. See https://www.charlesriverrc.org/articles/supergee/SuperGeeI.htm for more info. I'm using a standard piece of .210OD .132ID carbon tube from Midwest as the wing pylons and wrapping fiberglass around it to make the mating tubes that go in the wing. To give a little slip fit tolerance, I wrapped the carbon with a layer of waxed paper. To this, for insurance, I applied a mist coat of Crown mold release. I cut a strip of 1.4oz FG cloth on the bias at 6"x3" and wet it out on a piece of drafting mylar. I then lifted the edge of the fiberglass and stuck it to the wax paper with a little excess epoxy. Finally, I wrapped the FG around the tube and pulled it tight. By pulling on the ends of the wrap, I could make it tighten and get a perfect fit. I'll let it cure overnight then pull it off and see if I have a good wing tube!

Other progress: I made a fuselage mold on my school's ShopBot CNC router. I took that over to Bob F.'s house to get his help with the mold. It should be curing right now, and though we had some problems with the first layup, I feel confident that I will get a usable fuse pod out of it. Hopefully, the next one should go more smoothly.

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How many layers of what type of glass do you use for yours, Kevin?

My current pod was made by Dimitre and is kevlar/glass for the doinks and doesn't have an internal structure. The servos are gooped right to the pod. If you are going to go the crutch/fairing route you can carve a shape for the fairing out of pink foam and lay up light glass- a couple of layers of .75 with doublers should work- and then once it's cured dissolve away the foam with acetone. It's not structural so it can be thin and light.

Also, I know I can't "grease the landings," but honestly, I'll be happy to make time and get within 10m of the spot. I have very little experience with sailplanes and no experience with anything that I (or anyone else, for that matter) would consider a performance sailplane. I have pretty thorough RC experience though, and have flown trainers, pattern planes, sport planes, high speed craft, and flying wings.

You can get pretty good with just 2 control surfaces, but what I meant was that there are times that you will want to nose in to make the spot. You don't want to be fixing stuff between rounds. You can build in failure points, but for someone competing for the first time I wouldn't prioritize lowest mass over survivability.

Also, what do you use for your Rx battery? I think I'm going to use an E-Flite 120mAh 2S battery from the 180-size brushless micro aircraft.

I have been using the EFLB2002S25 with a regulator that matches the connector cause the servos I used are not 7.2v safe. I have a mess of D47's for future builds.
 
I got the wing mount installed in the boom. I drilled two .210 holes at the proper locations in the boom, then installed balsa plugs that were carefully sized to the locations of the holes. I made a mark at the mid point of each plug, then slid them, one at a time, into the boom. When the first one was in and located, I wicked thin CA into the plug and the boom, firmly bonding the balsa to the boom. This should restore the strength that I removed by drilling the boom. I then drilled the plug with the same .210 drill bit. I used some of the FG tube that I made in the last post to put mating tubes in the wing. These mating tubes were slid over .210 carbon tube that was cut to size and used as an alignment jig to glue the posts into the fuselage. The result is shown in the pictures.

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Got the radio pod together today. My experiment with a fiberglass pod didn't pan out, so I cobbled together a balsa pod. First order of business was to make a transition plug out of more of that balsa chunk I used to make the pylon reinforcements. I then put balsa slab side on either side of this plug. Adding at top and a nose block for shaping gets most of the way there. The hatch is more of the same balsa, but with a small piece of 1/32" hard balsa on the bottom to center the hatch and give a lip to hold it down. Finally, I applied a little sandpaper and elbow grease and voila! pod.

The pod as it stands now weights 8.5g. I'm considering adding a wrap of 1.4oz glass for ding resistance and some bursting strength.

Also, I apologize for the odd camera angles. I cannot find my wide angle lens, so I'm stuck using a telephoto zoom at close range.

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I've got to get this thing ready for tomorrow, so it's the final rush to finish. I got the tail feathers and the pylon for the horizontal stab made. The pylon contains a piece of .210 carbon tube with threads for a 6-32 bolt on the inside and a .060 carbon rod for alignment. The tail feathers themselves are 3/16" 7# balsa. I probably could have gone lighter, but I have pretty good confidence that these feathers won't flutter apart on boost. They're covered with a layer of orange esaki tissue.

To glue the horizontal pylon on, I mounted it to the horizontal tail. I propped both wing tips up the same distance, then glued to pylon underneath the boom. Bags of granular material (a bag of chocolate chips, a bag of walnuts, and a bag of quinoa) were placed on the boom to weight it down while the epoxy cured. I will reinforce this joint with some 1.4oz cloth after the epoxy cures.

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Is your motor pod to be under the plane? If not I would build a few spare fins.


Richard
 
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Actually, the fin is mounted only temporarily in that photo. I slid it onto the boom just so I could get the spacing right on the horizontal stabilizer. It is now mounted on the bottom of the glider.

I've finished up the glider. Final orders of business were to glue the fin on, install the pushrods, and glue the pylon on. With this done, it balances just a little aft of where I ideally want it, but it comes in at a glide weight of 165g! This gives an empty weight of 143g. I am extremely happy with that.

These final pics before flight show the assembled glider and it disassembled for transport.

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Not to steal Brian's thunder, but he put in some really good flights with this glider on Sunday. After a hairy first boost on a D, his E flights were straight and high. Need to buy him a pack of wide black markers though.. blue wing against a blue sky was hard for me to pick out. :)

kj
 
Unfortunately, I have no pictures or usable video of the launch, but I do have a couple of cool shots. First is the glider on the pad. Second speaks for itself. I'll try to get some more video this weekend.

As Kevin said, the first boost was a little hairy. I had too much down trimmed in and only just enough elevator authority to negate the down pitch. Fortunately, after the D7 burned out, I had full control over the glider. Also the perfect stress test. If it survived a 10* climb under thrust, it would certainly stand up to the E6 boost. I ran out of time to get a second test flight in, so I went into the first round with a guess as to how much boost trim I needed. Fortunately, I was close enough that I could control the pitch down tendency on the way up. I had it dialed in by the final round.

I've made a few changes since I got back. The motor pod flew off during a "doink" landing in the final round. It was an easy fix, but to help avoid it happening again, I've installed a shorter nose cone. The radio pod will now contact the ground first in all but the steepest dives. I also had some issues with the elevator being sloppy. The linkage was pretty much slop free, but the short control horn allowed the elevator to bend around the horn. While I think glide aerodynamic loads were low enough for this not to be a problem, the control mushiness I experienced on boost seems to indicate that this was a problem. I've installed a longer control horn and moved the linkage out on the servo horn. I have about the same amount of throw, but there is much less slop in the elevator. I think this will help with boost authority greatly.

A big, huge thank you needs to go out to a whole lot of people. To Bob Ferrante for helping me bag these wings (my second set ever!) To Mike Nowak for the ride to the Cup, as my car was in for repairs at the time. To Keith Vinyard for helping me tune the boost and glide before installing an engine. To Kevin Johnson for loaning me some E6 motors when the local vendor didn't have the ones I pre-ordered; also for taking pictures and video. To Jim Filler, who loaned me an extra casing so that I didn't need to reload in the 5 minutes between rounds. To Trip Barber for hosting an amazing meet and for putting up with my ineptitude, especially during S8 and S2/P.

Most importantly, however, to my brother, Sean, who was my slightly annoying, but extremely capable ground crew for all four rounds. He put up with my nerves and occasional shouting to swap batteries and motors between rounds. Somehow between being my spotter/timer, he managed to get my batteries recharged and the motors reloaded. In the Air Force, they say that the airplane is only the pilot's when it is in the air. It isn't any less true in this case.

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The video from the quad is pretty wide angle, but here is your 3rd boost:

[video=youtube_share;6io9qh63xk0]https://youtu.be/6io9qh63xk0[/video]

kj
 
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Wow. You don't really realize just how fast these things get up and move when you're flying them. The adrenaline kinda slows everything down.
 
Well, got another flight in this past weekend. I had a couple of D7 reloads left over from my one practice flight at the Capitol Cup. As far as the modifications go, the elevator change has made a HUGE difference. Boost was completely locked in and I didn't need to hold full up (boost dual rate) to keep it from pitching over. Small commands gave an equally precise change in boost path. I made the flight in the evening (~6:15) in very low wind conditions, ~2-3MPH if that. Despite the normal thought that lift dies in the early afternoon, I was able to work the small remaining bubbles for a 5:35 flight. Still no video as my camera (or the operator) malfunctioned.
 
I've flown this glider 6 times over the past week and it never gets old. All E6 boosts, all 410+ points per flight, and four flights 450/460 or better (perfect landing, slightly off time). I did nail one flight dead on 6 minutes and a <1 meter landing. Here's a boost graciously filmed by Michala Alexander at the PSC Weber Farm field.

[video=youtube_share;BNqVdAXfy1I]https://youtu.be/BNqVdAXfy1I[/video]

My father gets a little enthusiastic.
 
For future videos, boosts and landings. No one cares about the in between stuff. :)
You're getting good. I really need to finish my next plane and get practicing.

kj
 
About a month ago, I flew this glider for the (sorta) last time. A previous hard landing had knocked the servos loose, but the repair merely required re-seating them and repairing a servo rail. Unfortunately, this did change the pitch trim.

At last month's MTMA launch, I attempted to fly this glider for another practice flight on another E6/RCT motor. Right out of the tower it started a slow pitch up. I fed in a small amount of down elevator to compensate when the right wing folded under from the negative gees. The glider proceeded to cruise uncontrollably around the sky for another 6 seconds, somehow remaining aloft. The rocket was in a relatively level orientation when the motor burned out; it proceeded to lose speed and slowly arced into the ground behind a house across the street. Fortunately for me, it landed in a soft bush; the only damage beside the wing was a cracked motor pylon.

Anyways, so much for a good flying glider. I've got an aileron wing that I've been sitting on because I didn't want to build another fuselage. That wing will now be mounted to this fuselage. The wiring will be a little hack-y, but it will fly. The old wing is still usable for about 80% of the span. It will be used to prototype a C-RG for NARAM next year.

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