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Post by thevon on Apr 11, 2007 20:35:05 GMT 10
This thread is about the new Drongo plank I first flew at Easter. Here are the first few lines of the article - if you want to read more, please click on the link below, or go to the "Reviews" section and find it there:This is a story about my first “Plank” which is a Drongo, made by Glenn Dorrenboom in Sydney (aka “Zipper” on RCGroups.com). I wanted a tough fast energy-retaining EPP plane to start learning dynamic soaring, got talking to Glenn about the Drongo, (a modified copy of the Bluto) and decided to buy one. So if you’re a seasoned plank flyer and DS’er, stop here - this article is probably a bit too basic for you. I was impressed when Glenn said he’d supply a full kit with all the hardware for $110, plus an optional ballast tube and slugs for $30. I said yes, then didn’t hear from Glenn for a while, and got the impression that he wasn’t coming up with the goods, so I phoned to cancel out of the deal. He was most apologetic as he’d had been flat out with work plus we worked out that he’s more contactable thru R/C groups than email. The kit was together but he said he’d do some of the assembling to help me out. We got talking for ages and I learnt a lot. Glenn is very experienced and really has the modellers spirit of learning to make all sort of things. I mentioned that I wanted to put in a model alarm and a “blackjack” plug/switch and he said that he makes them himself, and he would put a freebie of each in for me! Now I have to say that Glenn’s only just getting into selling kits, and mine was an introductory price offer! I’m sure he didn’t make any money. So if you want one, it will cost more – ask him! Without my asking he performed a lot of the building … rounding the wingtips, installing the full length carbon spar, ballast tube, joining the wings, spruce subtrailing edges, balance weights either side of the nose. Then he spackled and sanded it and covered the entire thing with crossfilament tape! He also marked the positions for the servos, battery and receiver. Plus, he completely made and sanded the balsa tail ready for covering (with 3 carbon rods that slot into a corflute mount under the wing, which he also installed). My glider obsession already dominates my family life and even without building new gliders I spend far too long fiddling with my planes and bits! This compulsion needs to be curtailed where possible, so I really appreciated the huge amount of work Glenn did. I told him he didn’t have to do it, but he reckons he enjoys building, and it was easier to just do it than to write out extensive instructions (which I’d been asking for!) So with the wing all in one piece, it had to be couriered up because at 1.7m long, the package couldn’t go by Aust Post! (max 1.1m length). They chose to make the wingspan of this one a bit bigger than his previous versions – 159cm or 62.5” span. Bigger than a Moth 60”! I was really very impressed when I unwrapped it. The wing and the other bits were packed very professionally and the wing looked … well, long, thin, planky and sort of scary really! Could a klutz like me ever fly a thing like that?? I started to wonder if I was crazy. They had packed all the ballast (8 big slugs weighing total 550gm!) into the tube so the thing was really heavy! I removed them and cut some matching bits of dowel to substitute for the slugs. The fibre tape had been laid lengthways .... For more ... go to the link to the full article ... www.frogmedia.com.au/windsock/review.htm
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Post by Drongo on Apr 11, 2007 23:13:49 GMT 10
Thanks for posting such a great build and review!! The Drongo really is a ballistic plane. Swoopdown (from RCGroups) maidened his drongo down here at Byron, a while back. It certainly is very fast and eats up alot of sky. Apparently ds'es well too. His is the 59 inch version and has an all up weight of about 1.5 kgs! Unballasted!! I am sure this larger version is even more impressive. Can't wait to hear how it goes on the darkside. ;D Eric P.S. Let me know if you are going ds'ing. Always keen.
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Post by ezza on Apr 11, 2007 23:16:35 GMT 10
Sorry, I wasn't logged in when I posted that reply....wooops.
Eric
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Post by callun on Apr 12, 2007 18:42:40 GMT 10
Yeah, a good write up indeed! Thanks Andrew. The worry I have with big heavy planes like that (even Steve's Skua which isn't as big as the drongo) is I'd feel like I wouldn't get to use it enough, so it'd be a good bit of an investment for something that's not useable (to me) much, except for strong winds and in certain locations. Having said that, I'm enjoying reading up on other people's experiences
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zipper
> 50
Off The Edge Sailplanes
Posts: 88
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Post by zipper on Apr 12, 2007 19:41:39 GMT 10
The Drongo will fly in about 8 knots as long as you keep it moving. Mine is 2kg fully ballasted and will fly in 15 knots with all that ballast. I have had it up to 132mph on the front side and I think I can still get a bit more out of her yet. I had a unofficial race with a redback and just left it in my wash, there was no comparison on speed. The Drongo can be made light which dose make it a little more aerobatic and fun to fly, but it dose sacrifice the speed.
Glenn
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Post by thevon on Apr 12, 2007 22:18:11 GMT 10
Hey thanks for signing on Glenn! Yep Callun I do agree with both you and Glenn. I was surprised how well the Drongo went even when the wind dropped the other day - once it gets up to speed it seems to get lift efficiently even with some ballast in. It gained massive height like a sailplane. But I guess what you mean is that you almost only ever fly at Shorncliffe where it's a tiny rough area about 30 metres wide, and a narrow lift band just in front of the cliff. I think that you'd be working pretty hard to fly the Drongo there and it's so rocky that the fast landings would probably lead to damage. But I'll try it one day when there's plenty of lift.
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Post by thevon on Apr 12, 2007 22:20:48 GMT 10
Replying to Eric here too - thanks Eric. I'd love to have you around to give me some lessons! If you're coming to Maleny again let me know but I guess that's unlikely. Wouldn't mind seeing what it clocked on that radar gun of yours either ...
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Post by ezza on Apr 13, 2007 12:31:36 GMT 10
Replying to Eric here too - thanks Eric. I'd love to have you around to give me some lessons! If you're coming to Maleny again let me know but I guess that's unlikely. Wouldn't mind seeing what it clocked on that radar gun of yours either ... Yeah, I think you would be surprised how fast that Drongo will go in a big frontside dive. I'll bet it would pass 100mph quite easily. I managed 110mph in a dive at Beechmont, just before Easter, with my Reaper. The Drongo is bigger and heavier. I also managed 105mph while ds'ing up there......then I ploughed it into the ground at 104mph! Luckily the grass was pretty thick, the fuse seperated from the wing, and the tail snapped off. Happy to say that she is flying again, just a little heavier. ;D I will keep you posted, as I might be heading up to the Sunshine coast, probably next weekend or the weekend after. Eric
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Post by thevon on Apr 13, 2007 19:46:12 GMT 10
Geez, scary about your crash! I'll have to get myself to a DS spot. For me I think Maleny on the ridge would be best. Also there's another spot there to try too. But I think we need an Easterly day. Yes if you're heading up let us know. Check my previous emails to you Eric - should have my phone numbers at the bottom. If you're planning to do any DS, there are at least 3 of us who would plead with our wives to let us out for the day, so we can come and watch and get lessons!
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Post by thevon on Apr 13, 2007 20:16:37 GMT 10
Andrew here - update on Drongo fiddling. Last night I extended the ailerons on the Drongo to the recommended 45mm length (they were 35mm). I was hoping that would allow me to remove some of the 90 or so gms of lead I had taped to the nose.
Took it to Mt Mee to day. It was a moderate SE which was good lift but the Drongo would have been happier with another 10 knots, and/or a shift to Easterly. When the wind is a bit more E at Mt Mee, it really pumps.
I removed about 1/4 of the nose weight, then Sean had a test flight too and suggested that it needed less elevator throw, and that it was nosing down too much when it banked into a roll or turn. I removed the lead bit by bit, but it progressively got more up/down unstable ... if you gave it the slightest touch of down it would descend into an increasing dive, even with neutral stick. If it hit lift or if you fed in a tiny bit of up, it would nose up and start to float. Sean was helping me with the testing. We removed more lead (I guess back to 45 grams) and cut the elevator rates back dramatically but I was very uncomfortable with it. No matter how much I fiddled with the rates, EPA's or Exponential, I just didn't like the way it could suddenly nose down halfway through a flypass. Also removed the 2 slugs of ballast from the tube. I didn't like it at all - just felt scary.
While the nose weight was cut back, I again tried to do an outside loop from a huge dive. It just got around but only just.
Anyway I finally taped most of the lead back on (75 gm) and was instantly really comfortable with it. It feels like a different plane - just cruises around fast, gets lift, holds its path with almost no control inputs at all. Fantastic. I was then happy racing the rest of the guys back and forth, in close.
So when I came home I've cut into the nose and shaped an 80gm V shaped bar of lead to fit in front of the existing (huge) pre-installed nose weights. I surrounded it with Shoo-goo and filled the space under the cut covering with Goo and the EPP beads I dug out, so it's pretty much back to original shape. Looking forward to getting it up there in a huge wind again!
By the way, the all up weight of the Drongo with no ballast is 1.40kg. It can hold an additional 550gm of ballast (8 slugs each approx 70gm) in the ballast tube as well.
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Post by ding on Apr 13, 2007 20:52:52 GMT 10
Andrew here - update on Drongo fiddling. Last night I extended the ailerons on the Drongo to the recommended 45mm length (they were 35mm). I was hoping that would allow me to remove some of the 90 or so gms of lead I had taped to the nose. Took it to Mt Mee to day. It was a moderate SE which was good lift but the Drongo would have been happier with another 10 knots, and/or a shift to Easterly. When the wind is a bit more E at Mt Mee, it really pumps. I removed about 1/4 of the nose weight, then Sean had a test flight too and suggested that it needed less elevator throw, and that it was nosing down too much when it banked into a roll or turn. I removed the lead bit by bit, but it progressively got more up/down unstable ... if you gave it the slightest touch of down it would descend into an increasing dive, even with neutral stick. If it hit lift or if you fed in a tiny bit of up, it would nose up and start to float. Sean was helping me with the testing. We removed more lead (I guess back to 45 grams) and cut the elevator rates back dramatically but I was very uncomfortable with it. No matter how much I fiddled with the rates, EPA's or Exponential, I just didn't like the way it could suddenly nose down halfway through a flypass. Also removed the 2 slugs of ballast from the tube. I didn't like it at all - just felt scary. While the nose weight was cut back, I again tried to do an outside loop from a huge dive. It just got around but only just. Anyway I finally taped most of the lead back on (75 gm) and was instantly really comfortable with it. It feels like a different plane - just cruises around fast, gets lift, holds its path with almost no control inputs at all. Fantastic. I was then happy racing the rest of the guys back and forth, in close. So when I came home I've cut into the nose and shaped an 80gm V shaped bar of lead to fit in front of the existing (huge) pre-installed nose weights. I surrounded it with Shoo-goo and filled the space under the cut covering with Goo and the EPP beads I dug out, so it's pretty much back to original shape. Looking forward to getting it up there in a huge wind again! By the way, the all up weight of the Drongo with no ballast is 1.40kg. It can hold an additional 550gm of ballast (8 slugs each approx 70gm) in the ballast tube as well. I can't wait to see it flying with the skua The handling you talk about is very typical for moving CG rearwad. When I first flew the skua it was rearward and it was nigh on unflyable. I then moved it to the recommended position and that's where it is now. It's quite good, but still hunts a little on elevator. I can handle it though What you do have to watch is it's stall behaviour which is just wicked (also typical for rearward cg). The trade of is the further forward you go the more you loose performance but the easier it is to fly. More rearward and you get better performance but the handling goes out the window.
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Post by sean on Apr 14, 2007 9:22:44 GMT 10
Hi Andrew, Thanks for giving me a go on the Drongo yesterday! I was thinking about the Drongo's yaw instability on the way home... it could have been that the lead you had taped over the nose was creating turbulent airflow over the fin, causing it to not work effectively. If that was the case, the mods you've done to the nose now should fix that. The other possibility is as we discussed, the increased span over the original Drongo means the current fin is too small to do the job. My feeling is that it needs a bigger fin. The centre of pressure on the high span wing is a long way out from the CG, giving any unsettling forces a greater leverage, meaning the fin has much more work to do. The current fin would be ideal for all high speed flying where the fin becomes more effective and the small size means less drag, but in the less than ideal conditions we flew in yesterday, I reckon a bigger fin would make it feel much more comfortable to fly. The downside here of course is a bigger fin means more weight behind the CG, but I reckon that's worth it for a plane that tracks straight. One thing I found a little unnerving was the pitch down with roll. If you roll 45 degrees left or right you can see a sharp pitch down. My Bat's the opposite here, it has quite a sharp pitch up with roll. I fixed that by simply mixing a small amount of down elevator with left and right aileron. The Drongo would require a small amount of up elevator mix with aileron. You know you've got it right when the aircraft rolls perfectly around it's center line (it doesn't 'barrel roll' at all). My Bat's still a bit off in this respect, but a pitch up with roll feels quite natural whereas a pitch down with roll is very off-putting (every time you turn it heads for the scrub!). I reckon with these things sorted the Drongo will be a blast, and unbeatable in a dive!
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Post by sean on Apr 14, 2007 9:38:30 GMT 10
Hi Ding,
It'd be cool to see you up at Mt Mee with the Skua... it's the perfect site for a plane like that, the speed you can get is unreal :-)
Andrew, further to what Ding says above about CG, it's important to match the elevator throw to the CG. I reckon if you can't use full elevator without something nasty happening, then you have too much elevator throw. The Drongo and Bat will both spin if you give them too much back stick. Obviously all this is ever going to do is get you in trouble so my opinion is it's worth reducing up elevator until this doesn't happen. You can also mix more down than up so you still have enough control for inverted flight. If reducing the elevator throw makes it feel a bit insensitive in pitch for your taste, then you could try reducing or removing exponential.
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Post by thevon on Apr 14, 2007 10:56:14 GMT 10
Sean yep thanks for that. I will just change one thing at a time and take it slowly . My main aim is to use it to learn DS, so I'm happier having it stable and predictable, as long as it maintains the ability to retain speed and energy. I'll try to get more time on it to get to know it better.
Another thing to throw in the pot wrt the pitch change with roll, is aileron differential. I'm no expert but it can make a big difference. The theory is that when you bank, the down aileron causes more drag than the up aileron. For example if you bank/turn right, the left aileron goes down and if both have the same throws, the left one causes more drag, and pulls the left wing back so the plane yaws to the left ... opposite of where you want it to go. This is called adverse yaw. So with sailplanes, you fix it by having Aileron Differential (AD) which means having the ailerons set to travel further up than down (eg about 3:2 ratio).
But Glenn reckons that you need the opposite with the Drongo, and with many other flying wings (ie more down than up). Certainly when I tried putting normal AD on my Duck, it totally stuffed it up (snap rolled out of slower turns, terribly, hard to fly). So I'll try that next, and I wonder if that will reduce the nose down effect as well? Due to more "uplifting' effect rather than "wingdropping" effect? We'll see!
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Post by sean on Apr 14, 2007 11:30:42 GMT 10
Hi Andrew,
Traditional aileron differential values are best avoided on a flying wing, the reason being that the ailerons are also the elevators. So if you were to use a typical sailplane differential value (eg 3:2 as you say) then it's just like mixing in lots of up elevator with aileron. What you'd then get is lots of pitch up with roll. A standard sailplane has a separate tail to control pitch, so aileron differential doesn't affect pitch in this way.
Having said that, your Drongo does actually need some up elev with aileron. So, a very small differential value would achieve the same thing as mixing in some up elev with aileron.
It's interesting that Glenn uses a little negative differential on his Drongo. My Bat is setup the same. The only difference is my radio doesn't allow negative differential, so I mix a bit of down in with aileron, which achieves exactly the same thing. I'm curious as to why your Drongo needs positive differential but Glenn's needs negative, it could be that the ailerons on your Drongo are already moving down further than up.
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