RES-Eagle Glider RCME March 2018

[Andy Botyle]

Hi Guys,

I got this kit as a Christmas present and can't wait to get started on building it.... It's been 20+ years since I have built a glider and hopefully, the techniques all come back to me. Lots of my questions have already been asked and answered by members on here, so that's a great start for me, but I do have some other questions that I hope you can help with.

I seem to have been given short steering cables, I believe is for the elec version when the servos are located closer to the CG and thus less distance to the elevator and rudder. Should I get longer cables in one piece or should I extend, if so how would I go about this?

For the vertical and horizontal stabilizers are these fixed to the fuselage?

Thanks in advance

[buster prop]

Hi Andy I'm building an RES Eagle as well, from the S M C kit. I'm hoping to get on with it now Xmas is over. Yes the wire rods are too short for the tow line version. I soldered lengths of piano wire onto them and covered the join with heat shrink tube. We shouldn't have to do this, I assume that a standard 36" wire was all that S M C stock. The fin fits into two angled balsa blocks on the upper side of the tail plane which is then glued onto the fuselage. It's a straightforward build but there are one or two things to think about. If you have any more questions please ask.

[buster prop]

This wing centre view shows that I fitted small blocks of balsa to support the covering where the wing fixing bolts go through. The spoiler will be hinged by the covering. I've planed and sanded the trailing edge to match the rib profile. The two balsa pieces attached to the W01 ribs weren't in my kit, they came from my balsa offcuts box.The outer wing tip trailing edge looks too short against the plan that comes with the kit although it does match the magazine free plan from March 2018. Luckily I have a copy which I am using to build from. Everything else seems to be ok so I think it must be a drawing error.

[Sussex Pete]

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

[Sussex Pete]

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.

[buster prop]

Hi Pete. W01 and W02 ribs are recessed by about 2mm to allow the spoiler to drop into the frame. With the 2mm frame thickness they should be flush with the upper surface of the wing when retracted. The spoiler should be sanded slightly to blend in with the aero foil. It isn’t very clear on my earlier post unless you expand the picture. I’ve covered the centre section now and am trying to get the spoiler to extend and retract fully. I’ll take a picture and explain.

[Sussex Pete]

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?

[buster prop]

Ah yes, the spoiler. Getting it to work took some time. I made a pushrod from paper clip wire so that it could be bent to a length and shape that would completely open and shut the spoiler. At first I used a servo tester with the servo wedged between the W01 wing ribs at the centre, as in Ton’s picture and temporarily hinged the spoiler with Sellotape. Trying to get enough ‘up’ movement as well as closing the spoiler completely didn’t work so I used a longer horn on the servo. Better, but the pushrod was binding against the spar and lifting the front edge of the spoiler when closed. There’s very little room in there so I bent the wire to raise it away from the spar. Then it was binding at fully open, against the spoiler frame. Filing a small notch and moving the servo fixed that but it was buzzing at fully closed. After that I used the radio instead of a servo tester so that the servo’s movement can be adjusted for each direction at the Tx and finally got the spoiler opening and closing completely with no binding or servo-buzzing. I’m working it from the throttle stick on the Tx rather than a switch because it might be useful to have proportional control. A small Alturn servo from the spares box fits. Getting the spoiler right has probably been the most difficult part of building the RES-Eagle. It works now, closes completely and just about enough ‘up’. Flight tests will tell. You can see the completed fuselage. Getting there!

[Sussex Pete]

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?

[Sussex Pete]

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

[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.

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-)

[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

[buster prop]

Hi Pete, work on my RES-Eagle is on hold at the moment because we have the builders in and my workshop is being used for storage. What I did though was put the wing centre section flat on a table and plugged the wingtips in to measure the dihedrals. At the tips I have 140mm and at the dihedral break 35mm. The model is basically finished, all covered, servos are in and working. The cg is too far back, so I must get that sorted. Can’t fly at the moment anyway. I haven’t fitted the towhook either, the plan doesn’t show how but I thought of glueing a hardwood block inside to screw the tow hook into. Might reinforce the fuselage floor at that point with 3mm ply..

[PatMc]

I used to fly in a few glider comps in the past & found that the plastic tow hooks are useless. They tend to twist & bend too easily allowing the ring to slip off prematurely.
Simple & effective alternative is a common or garden small cup hook straightened out then re-bent to "L" shape. Glue an oblong of 3/16" - 1/4" birch ply onto the inside fuselage floor, drill a small (1.5mm - 2mm) pilot hole, partially screw the hook in place then unscrew a couple of turns, apply a drop or two of cyano & screw the hook in all the way. Job done.

BTW for best tow results we positioned the hook on the cg or slightly behind.

Here's a couple of pics of a typical hook in my 100", 5lb (2.4mtr, 2.25kg) Diamond glider & one pic the glider itself.
We ​​​​​used exactly the same type of hook on wood fuselage gliders.

[Sussex Pete]

I'm ahead of you on cup hooks 8-).

But the SLEC Large Tow Hook Hook **LINK**

works fine on my 100" 3lb Kloudrider

even off an S100 competition winch! Tough as old boots but too wide for F3-RES rules.

As for CG and hooks, I might write later on all the fallacies one can trip on. Full-size practice for winch or aerotow puts the "hook" at the front way way ahead of CG... Suffice to say it matters nuch less than in free flight.

[buster prop]

George Stringwell’s book about thermal soaring recommends that the towhook should be placed just ahead of the CG. If you drop a vertical line from the point on the wing where the CG is, then another line sloping at 30 degrees in front the towhook position should be where that line crosses the bottom of the fuselage. I wonder about this method because it depends how deep the fuselage is? GS says that it can be fine tuned to get a steep but stable climb. I will make sure my glider is trimmed by hand launches first before risking the bungee, don’t want three months work converted to matchwood in seconds! The hook in the kit is an L shaped wire with a woodscew thread at one end but the plan doesn’t show any fitting details. I’m sure a straightened out cup hook would do the job.

[Sussex Pete]

BP, the 30deg-ahead-of-Cog rule of thumb was what I was taught as a kid. And it generally works too for most any model glider, FF or RC, although probably not very efficiently.

However! What really matters is where exactly the centre of mass is, usually somewhere in the middle of the fuselage, not the point directly above the CoG (or below for a low-winger) where we hold the wing to check angle of attack when "balanced". So you have to be careful where that 30-deg line starts...

Simons' book discusses the pitching torque the towline applies and the need for down-elevator (and consequent speed increase) needed to compensate. He also discusses stability on tow (generlly, worse than on glide) but not efficiency and only says a too-far forward hook with respect to CoG can lead to weaving on tow but down elevator again fixes it by reducing the wing angle of attack.

PatMc, can I ask how you were towing? Running, pulleys, bungee or winch? The change of direction of pull during launch, the total energy that can be transmitted to the model and the rate of energy transfer (i.e. power) differ for and during each method, so any 'optimum' hook position for one will likely not be optimal for other methods or in other conditions.

For bungee/Hi-start (however it's spelled!) I see the big issue as total energy available in the stretched line (in still air, wind changes everything!). So getting most of that energy into speed (and hence lift and hence height) and not wasting it dragging the glider towards the ground seems to me to be the right aim.

I would expect a rearward hook to cause more nose-up pitching torque than a forward hook, needing more down elevator. Too far forward will need up elevator to get any climb. But _any_ elevator increases drag, wasting energy. I don't know where the compromises lie, but my guess is (a) somewhere in between and (b) it won't matter too much except in high-level competition in still air.

So, after all that, and in order to get on with finishing this kit (and actually flying it in this year's BARCS postal comp!), I'm going to just follow Ton's advice and put the hook about 63mm behind the l/e, secure enough to hold 8kg, double the F3-RES bungee limit. 8-)

[Sussex Pete]

Posted by buster prop on 12/02/2020 10:28:21:

...I will make sure my glider is trimmed by hand launches first before risking the bungee, don’t want three months work converted to matchwood in seconds!

Meant to add I think you're dead right to be cautious! Bungee energy can be quite excting, and once you've launched, you're committed to using it! But that's why the carbon spars.

The reported flutter problem, because the wing centre of mass is behind the stiff main spar, is scarier for me. I have yet to add stiffening gussets but I wonder if Ton could add a third 4mm CF member between the main spar and the l.e. but offset up a bit, to add a little mass forward and increase the torsional stiffness? I thought about drilling the ribs myself but didnt think I could be accurate enough on pre-cut ribs. I will also be building up speed carefully on bungee tests to avoid shaking the wing to pieces as well avoiding as folding it

[PatMc]

Posted by Sussex Pete on 12/02/2020 18:03:53:

 

PatMc, can I ask how you were towing? Running, pulleys, bungee or winch? The change of direction of pull during launch, the total energy that can be transmitted to the model and the rate of energy transfer (i.e. power) differ for and during each method, so any 'optimum' hook position for one will likely not be optimal for other methods or in other conditions.

For bungee/Hi-start (however it's spelled!) I see the big issue as total energy available in the stretched line (in still air, wind changes everything!). So getting most of that energy into speed (and hence lift and hence height) and not wasting it dragging the glider towards the ground seems to me to be the right aim.

I would expect a rearward hook to cause more nose-up pitching torque than a forward hook, needing more down elevator. Too far forward will need up elevator to get any climb. But _any_ elevator increases drag, wasting energy. I don't know where the compromises lie, but my guess is (a) somewhere in between and (b) it won't matter too much except in high-level competition in still air.

 

I used hand tows & electric winch in comps, bungee & winch in practice/trimming flights, never used the hand tow pulley system.

We applied a lot of up (more or less full up) elevator during tows until close to the top on all methods of launch. Exception being practice flying bungee launches in light/zero wind but in those conditions we would use an electric winch or, on very rare occasions, hand tow or give up on gliders & fly a power model.
Bungee launching in decent (strong) winds we would maintain the up elevator at the top in order to keep tension on the line & try to detect any lift whilst still attached. If the bungee re-stretched it was usually possible to get a "ping" launch by diving to release then climbing for the extra altitude, then try to detect and using the thermal that had caused the re-stretch.

Hand tows - full up all the way then ping release & extra altitude.

Winch tows - similar except that we would pulse the power as necessary to maintain tension but wind in as little line as possible until near the top. For the last few seconds - power on & ping release.

PS I always tried to make initial trimming flights at a slope site in light to moderate wind conditions, failing that flat field with a few gentle hand tow launches. IMO you don't really learn much from flat field hand launches.  

 

 

Edited By PatMc on 13/02/2020 23:53:41

[Sussex Pete]

Thanks PatMc - all good knowledge!

I've found a nice adjustable tow hook from Hyperflight, maybe a tad too large (metalwork weight 16g) but fits the fuselage and is nicer than I could make myself

Edited By Sussex Pete on 17/02/2020 11:51:21

[Sussex Pete]

Posted by buster prop on 12/02/2020 10:28:21:

George Stringwell’s book about thermal soaring ...

Thanks for the lead on that, BP, I didn't know the book before but Amazon just delivered a used copy. Very informative from a first scan through, I think my evening reading is sorted for a while! 8-)

[Ton van Munsteren]

Fun with the Res-Eagle and a quad with video.

https://www.youtube.com/watch?v=zL1T6QBE_08&fbclid=IwAR2t8DPYFn-bfdBUVjq_fcvykgs0KQA9XJvswr1Kq5FKBoDBybATOXcCJIY

 

Edited By Ton van Munsteren on 16/08/2020 23:14:59

[Steve Newman]

I originally posted this on Phil Murrell's thread from 10/10/2019 but with no replies and having origainlly meant to post it here I hope no one minds me repeating it here.

Having just finished the wing assembly I'm trying to work out the installation of the rc and electric motor etc in the fuselage before I start cutting/gluing.

David Hall 9, did you complete your build? I'd be interested to know what you've used and where it's installed and how the weight distribution worked out. I'm planning on an Overlander 2826 motor with 3S 1000mAh LiPo. I have a 10x6 folding prop but am unsure if this is actually a good choice for this motor/battery/model combination.

My initial thought on layout is shown below (note, Rx sitting with ESC):

Some pictures below of my complete though uncovered wing. This is my first build since the late 70s/early 80s and certainly my first electric build so all advice comments welcomed.

[David Hall 9]

It's looking good! Sadly my RES Eagle is still in the box.

I used much of my time repairing/upgrading several planes and have only just come round to considering what my next plane will be. I have fancied the RES DART as it's different and could be fun. I started the build only yesterday.

I think that it will have a similar power requirement to the Eagle. It will be powered by a 1350kv 2826 motor on 450mAh 3s. For initial flights, I will use a 7.5x4 prop.

For your 2826 motor (you didn't say what the kv rating is) on 3s, I'd suggest that a 10x6 will be too much unless the motor is around 850-900 Kv, which might then be underpowered (for my liking). For a 2826 motor around 1200-1400Kv, a 10x6 might be a good starting point if running a 2s system.

 

Edited By David Hall 9 on 22/01/2021 15:39:59

[Steve Newman]

Ah, sorry I should have added that the motor is 1000kV rated.