Scale Soaring UK

Many years ago (when Pat Teakle was selling his short kits), John Hall (who made Pat's fuselages) had his own range of models which included the 100" Diamond plus others such as the Prelude, Albion etc.
John still has his fuselage moulds and is interested in making some of his old models available again via Laser Cut Sailplanes (LCS).

As a result, I have recently designed new built-up flying surfaces to go onto John's Diamond fuselage to upgrade it to a 3 metre electric soarer, albeit using the same root wing profile, but transitioning to S3021 along the inner panel.
The wing is designed as a 4 piece affair, with zero dihedral on the centre sections to make it easy to use a single carbon joiner tube. The outer panels have 4 degrees dihedral & are plugged on using 3mm carbon rod joiners, with the end sections of these cranked up by a further 4 degrees.
The wing panels can be left joined to ease rigging.
No spoilers are fitted as separate flaps & ailerons give pretty much full span control.
The wings have a sheeted D box and rear open structure, whilst the AMT has been enlarged for the increased span and is fully built-up, as is the rudder.

John told me that when he retooled the Diamond a few years ago, he made the fuselage nose section circular, so blending in the motor mount and spinner should be easier

Anyway, I made a start on the tail feathers last week, making these up as simple structures from 1/4" Sq. balsa & 1/8" balsa strip ribs, LE & TE, plus brass tubes to suit an available AMT crank. The rudder has also been enlarged a little.
I received a set of laser cut ribs from Cliff Evans at lunchtime today, so by teatime had the basic RH wing structure largely glued up using Aliphatic glue as shown in the pics. Once this has fully set, I will add the joiner tubes & then the top spar pieces.

With main & panel joiners in place, we now have a complete RH wing structure less the rounded tip shaping.

Interesting Peter! I remember these models from back in the day. I will watch this build with interest. My only thought at the moment is with regard to the fuselage installation. Looking at the fuselage picture, fitting a motor,esc,lipo,2 servos and an rx in front of the wing will be a tight squeeze. Will it bring the CG too far forward?
What is the profile on the wing root? Will it be a problem to blend it to S3021 on the inner sections?
Brian.

Hi Brian,
The fuselage moulded wing root section is E193 which thus defines the wing root section.
However, it’s easy these days to progressively transition the section to S3021 using a CAD program such as DevWing
This is what I have done over the length if the inner panel & the proof of the pudding will be in the wing build currently well on the way.
(I have now got the 2nd wing basic structure nearly assembled & even managed put the inner panel upper D box balsa skin on the RH wing this afternoon)
Note that another reason to split the wing at the flap/aileron break is that apart from wanting to define an airfoil section at this point, it also allows me to easily modify the rest of the wing planform/section without affecting the inner section/joiner part.

Tomorrow, I plan to sort out the fuselage joiner tube installation as this will then allow me to check the wing fit & get a feel for the overall model weight/motor sizing.
I can’t remember what the original 100” Diamond weighed in at, but I’m hoping for an overall weight between 4 & 5lbs to allow something like a 3548 motor running on a 3S Lipo for relaxed climb & soaring.
The plan is for ESC & battery forward/in the front part of the hatch area, with Rx & 2 small servos in front of the wing joiner.
Time will tell if this can be achieved.

Fuselage wing roots drilled for joiners and Uniloc placement, so dry fit of the various bits tried.
Apologies for the rather cramped pics, but it was bit wet outside
Pics of the Habicht version (inner wing panels only, plus one with outer panels also. (Tips will be fitted after outer panel D box has been skinned.)

An initial weight check looks good for <5lb AUW.

That is looking very presentable Peter and the proportions look about right. Can you tell me what is the tail volume ratio to the wing?
Why all the questions? I was thinking of designing a 3 metre electric soarer to replace my ageing Graphite and this may be a possible alternative.
Brian.

Brian,
The tail volume comes out at 9.7% which is pretty close to the 10% I was aiming at.
The total wing area is 6.44 sq ft according to my calcs, so with an AUW weight of <5lbs, the wing loading should be <12.5oz/sq ft.
It looks as if it should soar well

Moving on to the tailplane installation, I have thickened up the fin sides by fitting 1.5mm ply root plates each side - thus increasing the AMT crank pivot tube fixing area.

Meanwhile at the forward end of the fuselage, a removeable ply tray has been fitted at the rear of the hatch area to carry the AMT & rudder servos. The forward hatch area is for the power train battery, where a 3S Lipo fits with ease.
There is still 6” forward of the battery to accommodate spinner, motor & ESC, plus ballast if needed.
The Rx can probably go just behind the servos, but if a FrSky G8 series or similar it can go almost anywhere.

The rudder pull-pull wire exits are currently being fitted prior to making up the AMT pushrod & then fitting the AMT crank.

Most of the skinning compete now, plus flappy bits made and the tips attached.
Soooo... time for a quick assembly to give a better idea of what the finished shape will be - even if not covered.

Although I have designed the outer wing sections to be detachable from the flat inner wing panel, I think that in retrospect it will be prudent to glue the joint to give a 2 piece wing for flight. (The 3mm carbon rod joiners do not give a 'solid' enough attachment for my liking, although no doubt this could be improved with larger/tighter fitting joiner items).

I will start on the motor installation once the airframe is otherwise complete.

Looking at the power train at present before I cut the nose off to fit an epoxy motor mount
With overall weight coming in at around 4.5lbs, I am looking at having say 350w available from a 2200mAH 3S Lipo.
So am currently looking at an Overlander Thumper 3548/05 motor driving a 13x5 ish Aeronaut folding prop.

Stan Yeo does epoxy motor mounts for 35 size motors at 37.8mm & 41.8mm diameters & my fuselage moulding thickness is approx. 1.5mm, so am looking at using the 41.8mm ring together with a 45mm cool nose spinner & appropriate yoke/folding blades. A 60A ESC is recommended for this motor.
Cutting the nose back to 45mm diameter will remove approx. 50mm in nose length, which I would imagine is fairly close to the spinner length.

I know that a 3548 motor is probably a bit of overkill, but would rather have some scope for extra power if I need it - at least on this beta build.
A 28 size motor doesn’t appear to be powerful enough, so it may be possible to reduce the 35 series motor length.
With the simple (free) electric flight calculator readily available to me, it looks as if the above power train arrangement should do the job (I cannot input exact components), but wondered if anyone out there had any better info/thoughts?

Well, I bit the bullet & ordered some parts from Stan Yeo at Phoenix Model Products on Thursday evening & these arrived today.
First up, was to cut 60mm off the front of the fuselage (in 2 bites - just in case) & slide the 41.8mm Glass Fibre 35 size motor mount in from the canopy opening.
I fitted a long M6 bolt into the central hole of the mount, both to help pull it forward & also to check alignment of the motor axis, before fixing in position with polyester resin, leaving a resin fillet on both sides.

The 45mm cool nose spinner fits nicely once the fuselage cut has been cleaned off parallel to the spinner backplate.
The rest of the airframe is now ready for covering, so can also complete that using transparent Oracover.
Photos to follow tomorrow when daylight improves chance of clear images.

Pics of the installed motor mount plus view with cool nose spinner in position.
Also a shot of the cockpit area with 3S Lipo & 60A ESC in position.
Can now get the model covered and make a pair of NACA duct style air outlets under the wing roots.
Also need to check the model balance to see how much lead is needed.

Model now covered & control surfaces hung so its time to do an overall weight & CoG check.
With just a couple of small items to finish off (canopy latch, Fuz. MPX connector cable to fit, Unilocs to fit, flight battery tray & wing servo links) the overall weight comes out at 1.82KG (4lbs) and the model balances 75mm back form the LE (33% of inner wing) complete with 3S Lipo, but no additional nose weight, so I am very pleased
Hopefully, everthing can be finished off, ready for a maiden next week, if the weather calms down

The eagle flew this morning at the Woodspring Wings field.
Pleased to report that after a clubmate gave a firm flat hand launch for a test glide, we had to walk 30m to collect her.

The subsequent hand launch under 50% power saw a 25-30 degree climb away with no need for any power trim.
Subsequent flying was gentle & the stall is a non-event. The only ballast fitted is approx 80gm taped to the forward part of the 3S Lipo. A gentle dive test gave a gentle hands off recovery.

A 2nd flight was done using a self launch, which proved to be no problem with another steady climb out
I will probably try removing the small ballast weight for the next flight but all looking very promising.

These initial flights were conducted with flaps disconnected as the RH one didn’t want to work for some reason
(Wiring checked at home & everything works ok now)
So maybe able to try some thermal flap during the next outing.

Just for Brian, here are a couple of shots of the electrics. I am using a small G-RX8 FrSky Rx ((with built-in altimeter/vario) which is velcroed to the side of the Fuz just behind the Elev servo.

Nice to hear that the maiden went well Peter. There appears to be plenty of room in there for all the sparky bits.
Brian.

Flying pics now obtained, so that brings the build thread to a conclusion.

That looks superb. A beautiful looking glider

Hello Peter

I have sourced the redesigned wing kit/plan for E-Diamond from Cliff. I have the previous (old) fuselage from Chris Hall Models, which is slightly shorter and has smaller tail fin/rudder.

May I request your views on a few clarifications:
- This is my first polyester fuselage build. I assume I will epoxy in ply double/cuppings inside the fuselage into the wing seats where the connecting tubs/rods ill go through?
- I will go with a 3536 motor (400w, 3S 2200 MAH LIPO) with a 41.8 mm firewall from Stan. I think this is more than adequate. What is your view on this as you used a much more powerful motor?
- Rather than enlarging the tail fin, I will increase the rudder size to give an equivalent rudder/tail area. Do you see issues with this in terms of stability/flutter etc?
Thank you in advance. Regards.

Hi Murat,
If you have one of the original fuselages from Clive/John Hall (Clive is John’s father) then I understand that the nose length is a bit shorter as well as the tail moment/fin being a bit smaller, so you may well need a bit more nose weight than I used. The nose cross section also wasn’t as circular, but you may be able to ‘persuade’ it once the extreme nose has been removed.
I fitted my motor mount from the rear, leaving as small lip at the front to take a fillet of polyester resin, followed by carefully forming a small fillet at the rear afterwards.
I also used a threaded rod temporarily fitted in the motor shaft hole to align the mount. I didn’t use any side or downthrust - it’s far easier to try to install & align centrally with a rod protruding back inside the fuselage.
(Try it all without any resin to start with, then fix with a little resin on the disc edges, then add fillets from & rear. The resin is very runny so hold fuselage vertical when waiting for resin to cure, otherwise it will tend to run to the lowest point).

You will probably be fine with the smaller motor as I made sure I would have enough, not knowing what the total weight of the new design would be.

When glueing items into a Polyester resin fuselage, I tend to first abrade the surface to ensure good clean surface, then bond using a Polyester resin (David’s Isopon or similar, easily available from car accessory type shops) rather than Epoxy resin. People say that epoxy resin will bond ok is the surface is clean & roughed up, but I like to use the same type of resin. (Polyester resin cures much faster than epoxy, especially if you overdo the catalyst).

I would think that increasing the rudder area would work, at least for the vertical tail surface.

Please note that although I designed the wing to allow the tip sections to be removeable (taped on), I ended up glueing mine on as the tape fixing wasn’t rigid enough for me.

Good luck with the build & remember to firmly secure any nose weight to stop it going into the rear of the motor in the event of a sudden stop.
Peter

Thank you Peter. I appreciate your feedback.
I am planning to use Pattex Stabilit Express as the glue.
I am also going to fix the wing tips as you did.
I will keep you updated as and when I make progress by adding to your existing blog if that is ok with you.
Best regards Murat

Hi Murat,
I’ve not used Stabilit Express before, so cannot comment on its compatibility/bond adhesion to Polyester resin, but it’s usually a good idea to rough up the surfaces with any bond.
When I said David’s Isopon, I meant Isopon Fastglas which was originally intended for fibreglassing repairs on car bodywork.

I don’t mind you adding to my build thread, but you may be better starting your own thread to avoid any possible confusion with the updated fuselage build version.
Just go back to the Non Scale Topics home & start a new topic thread by entering a title in the Create New Topic box.
Peter