Sussex Pete

Posted by buster prop on 09/11/2019 13:04:57: Thanks for replying Ton. I’ll make positions for the tow hook to be fitted at either location then. Front 63mm for windy conditions and rear at 73mm if it’s calm. I was surprised that the present plan includes details to fit a motor, if I wanted another 2M E-Glider I’d have bought the Red Eagle kit instead. Meant to add, I'd be very interested in seeing some pics of your tow-hook installation, BP - or anyone elses! I'm trying to be F3-RES rules compliant and my go-to standard nylon SLEC item is too big so I guess I'll have to fabricate one. Edited By Sussex Pete on 11/02/2020 15:58:52 Edited By Sussex Pete on 11/02/2020 15:59:08

Posted by buster prop on 09/11/2019 13:04:57: Thanks for replying Ton. I’ll make positions for the tow hook to be fitted at either location then. Front 63mm for windy conditions and rear at 73mm if it’s calm. I was surprised that the present plan includes details to fit a motor, if I wanted another 2M E-Glider I’d have bought the Red Eagle kit instead. Not the only discrepancy on the RCM&E plan I suspect. I used the short-kit's dihedral template to set the w06 and W14 ribs and came out with a slightly larger dihedral (about 5 deg more) than implied by the dihedral angles line on the plan and more than the 140mm dimension shown as total tip lift. The first break at the centre section is dead right but the second break is a bit steeper with the template than shown on the plan as "Second Dihedral Angle". The dimension "70.00" in the angles line is also not the distance shown (which is about 57mm) but is approximately the distance of second tip lift as-built if measured at right angles to the first dihedral line. Anyway, I don't think any of that will make much difference: the wing jigged very nicely to equal angles on both sides and the increase is unlikely to be so much as to induce Dutch roll on the bungee. So I am happy! 8-)

Thanks for the data, Phil - given my servos together weigh about 20g more than yours, with luck I'll not need any lead at all!

Quick update: My own RES-Eagle build is well under way - wing about done and should be ready to fly this month. A fellow ESSA club member is ahead of me and we will be entering the 2020 BARCS postal as soon as we can get them finished and airborne (from a flat field, not the South Downs!). Rumours of a "proper" F3-RES comp this year on BARCS sound good - hope to see you at one!

Posted by Piers Bowlan on 01/02/2020 12:20:30: Out of interest Pete, do you know how much the battery and any extra ballast in the nose weighed? I wondered how that compared with the weight of a suitable motor and LiPo. Hi Piers, no, not yet - my RES-Eagle is still on the building board - but I hope to need minimal ballast. The nose lever length looks reasonable on the plans for hardware to balance the tail. I'm using a 4xAAA square 1000mAh NiMH (50g), 2 x Hitec HS85-MG servos (total 44g) and a 4ch Rx (7g) installed front to back in that order and as far forward as possible. So the radio kit will weigh about 115g with bearers, a switch, etc. I will leave final installation late in the build so I can shuffle weight if needed. There are lighter servos but I just love the HS85-MG for great torque and metal output gears that don't strip when a control surface or horn snags on landing (that's what disposable plastic clevises are for!). I have used loads in slope soarers and none have failed me even in heavy "arrivals" 8-) I also aiming to build the tail-end lighter where possible - a failing on an earlier 100" soarer I built where I went for tail strength over weight but needed 7oz (200g!) of lead to balance it! Edited By Sussex Pete on 03/02/2020 08:53:02

Sorry, typos! Should read "So flutter occurs when the effective centre of mass of the wing is behind the twist "hinge" line"

Thanks again for the details Buster. My club-mate and I have decided to put the spoiler servo behind the spar to get a bit more room. Here's a sketch of my plan: With a "9g" servo glued to one centre rib I can just get a 9mm arm on it between the ribs which gives about 10-12mm of linear throw. A 14mm horn hooked round the spar a bit should give me 45 deg of spoiler angle which should be plenty to stall that part of the wing. The compromise is the servo hangs a bit further into the fuselage than the forward position but I couldn't see how to fully bury it in the wing without entirely redesigning the centre section! I am also concerned about two risks of high-speed flight on bungee: spoiler suck-up and flutter. Following an idea from my fellow builder, I laminated the spoiler blade from 2.5mm balsa with the grain span-wise over 1.5mm with the grain fore-aft. This is nice and stiff but I still might add (also from my friend's ideas!) torsion springs to keep the ends down. Several people mentioned flutter so I reached for my trusty copy of Martin Simons' "Model Aircraft Aerodynamics" which has this to say (in section 13.9 Flutter). He says the general solution is to stiffen the wing against twisting, then goes on in detail: "If the torsional axis of the wing, i.e. the line around which the outer panels twist, lies ahead of the wing's centre of gravity, flutter is sure to occur at some speed. The stiffening should be added to the leading edge, usually in the form of sheet balsa covering and vertical spar webbing, to produce a 'D' shaped torsion tube. The extra weight added near the leading edge also helps to bring the centre of gravity nearer to the torsional 'hinge' line. This is in effect a partial mass balance. Other forms of stiffening, such as diagonal ribs, or (as in some older types of wooden full-sized aircraft) by twin spars with diagonal strutting internally between the spars, is less effective because it does not move the centre of gravity of the structural members forward. " So flutter occurs when the effective mass of the wing is being the twist "hinge" line and the solution is to stiffen the structure and move the component's centre of mass forward. Twisting the RES-Eagle main wing section by hand puts the hinge line pretty dead on the main spar, and it's clear the wing alone balances behind the spar. Stiffening the spar itself (i.e. with the 6mm CF tube) therefore only partly helps. I will be adding some webbing between spare and the leading edge for the ply rib pairs that carry the wing-joining tubes on the main section and the tips to try to further stiffen the panel ends. Separately, has anyone added any wash-out on the outer tip sections?

Hi David great to know more are on the building board 8) There's a separate build thread at RES-Eagle Glider RCME March 2018 where a few of us are sharing ideas. Someone somewhere suggested building one wing and both Red and RES Eagle fuselages. The glider fuselage will weigh a lot less without motor and Lipo. Also the BARCS 2020 postal competition is off a 60m bungee to fit smaller fields which might work for you? Edited By Sussex Pete on 01/02/2020 08:24:04

Thanks Buster. This is clearly my Doh! moment on the meaning of "Short Kit" - time to hit my balsa logpile for the other bits 8-) I like your tip about supporting the covering around the bolt holes. Have you managed to get the spoiler servo linkage sorted?

Tony-- A question: just started on my wing centre section. The plans show the spoiler outline from 2mm and the spoiler from 4mm. There was no precut wood for either (and no 2mm wood at all, in the short kits we ordered. Should there be? Lovely stuff so far otherwise! Thanks.

Seems quite a few RES-Eagles are on building boards - great news for own-built 2m competitions this year! May I put a word in for BARCS in case anyone interested is not already a member? There's a good chance of another "postal" comp using 60m bungee+line this year and rumours of a full F3-RES comp. See the BARCS forum thread "F3-RES UK Competition Interest." I really like the own-build aspect of F3-RES in general and RES-Eagle is a great way in. Edited By Sussex Pete on 14/01/2020 12:54:18

Thanks to all for this log and discussion. Two of us in the East Sussex Soaring Association have RES-Eagle short kits for the coming flying season. My pile of nicely CNCed wood is just on the workbench so it's time to read all the build logs! I'll post my own on a separate thread but it's good to see several are coming along. I like the look of F3-RES as well as the "postal" 2-m comp that BARCS run (see eg the F3-RES UK Competition Interest thread). Must be a few builds in progress as all model shops seem to be short of 6mm x 4mm carbon tube! BTW, I've flown a 38oz 100" Kamco Kloudrider off a European-standard F3-RES bungee and it is really good fun, especially into some knots of wind when I can kite the tubing off the ground and re-stretch it on the way up 8-) Launching a much-lighter Eagle with the same energy should be quite exciting...

Andy, Martyn-- Thanks for the feedback guys. I'm certainly putting an F3-Res glider on my to-do list (bit of a kits backlog to get through first 8-) and I'll mention this thread at the East Sussex Soaring Association AGM to see who else can be tempted towards F3-RES. We all fly slope but many of us also fly off bungees for fun. Could be opportune for a bit more club-level competition at least! Cheers --Pete