Scale Soaring UK

With winter a'commin-in, I am considering having a go at a 25% Lo 100 build, probably using the the plan available on this site as a
guide.

I am hoping it will be fully aerobatic model, but still flyable/thermalable on lighter airs (say from 8-10 Kts). I was wondering if anyone that has a Lo100 could comment on its general flyability, AU flying weight or wing loading, nasty habits etc, I would be grateful.

My main fear is to end up with a too heavily loaded aircraft that will only fly in 40 Knt winds. Would prefer to build light and use a ballast tube in the wing for lively days if needed.

Also looking at the site plan, it appears to indicate zero incidence on the wing, whereas on most of the three views available on the web, the incidence looks to be anywhere from 3 to 5 degrees. I would have thought about 2 to 3 degrees would be OK (for Clark Y, maybe different for SD6060).

Probably prefer to use a Clark Y wing although SD6060 looks appealing for cleaner manoeuvers and inverted, however I think the reduced cL compared to Clark may restrict the model to high wind days.

Thinking that a 15mm round CF wing joiner on the spar, or 10mm + 6mm (front and rear spar) would be sufficient to handle plenty of G.

All advice and hints etc, gratefully received.

Martin, there is an SSUK member who has done a LO100 (and the extended 150) so I'll bring your post to his attention.

One thing, if you really want it to have a good aerobatic performance Clark Y is not really a good choice to say the least.

Martin,
I maybe wrong here, but I think you may be confusing wing incidence with decalage (the latter being angle between wing & tailplane).
The wing angle to fuselage longitudinal datum defines the ‘sit’ of the fuselage when the wing is at its normal flying angle of attack, usually set to minimise fuselage drag.
The angle between wing & tailplane gets efficient flight & is often in the range 2-3 degrees ‘ish’.
If this is all rubbish then others will soon chip in

Thanks to all,
Peter, I was actually thinking of the sit of the wing to the imaginary datum through the mid point of the fus - in most of the 3 views and pics I have seen, there appears to be a marked wing angle to this datum, but I could be wrong. The horizontal stab always appears as parallel to such an imaginary datum, which would be logical, as this would be close to a suitable flight decalage, as you say.

Very difficult to tell from the selection of grainy pictures and 3 views from the web, so was hoping someone would know.

Robbie, If I thought I could build it to an AUW of 6 lbs or so I would use SD6040, recognising that Clark is far from ideal for slope and aerobatics (although we are not talking about competition here!).

I don't need to fly inverted all the time, so there may be a compromise using Ritz-3 or S3021, which both have a much flatter and more stable moment coefficient/AoA and are better suited to slope flying than Clark. I use a 2.0m non scale with S3021 and that has an acceptable aerobatic performance for my purposes (and a very flat glide), but the loading is only 12oz/ft - my fear is a scale 100 built by me may end up at twice that.

As you say, building 2 wings may be a solution, but I think I can only manage 1 per winter!

Martin

I have a 1/4 scale Lo100 from the Charlesworth plan, it has the Clarke Y aerofoil as far as I can tell and it is lousy at inverted flying without 90% of the down elevator in and a fus angle of about 20% nose up (inverted nose up). However if you use the flaps when inverted to a fixed position reflexed (ie. down now its inverted) it does fly better, but loses altitude at a rapid rate so it is very draggy. You do need a good blow for the flying to be any good and that means it stays on the ground in less than 10 mph. It's very nice having said all that and will loop and roll with the best of them, but mine is fairly light (you will need lots of noseweight so I use double 5 cell NiMh 3700mAh batteries and it will only thermal in strong ones, it is not a light day type of model even with the 150 wings John Slater built, they have the same wing area as the chord is narrower and his is not as efficient as something like a skylark or minimoa if my memory serves etc.

Its a nice model to have in the hangar, but only comes out on suitable days. Don't let that put you off as I really like mine.

John M

John,
Thanks for that - useful info. 'Tis as I feared - the inevitable high-ish wing load means performance in light to moderate conditions is expecting too much, when added to that bulbous, porky, uber draggy fuselage. I imagine they come out at 8 to 9 lbs.

If Clarke cant provide enough power in modest conditions, then there is not much else available. I will then focus on the aerobatic qualities, use an aerobatic profile and be resigned to flying in grim conditions.

I wonder if you could confirm if the wing is set at an angle or is level to a datum defined by the main horizontal stringer on the Charlesworth model? Only asking because the free plan shows the wing and Horizontal stab as both horizontal, which surely cant be right.

In any case, I expect that if I do use SD6060 it will need to be set at a min of 3 degrees, otherwise in level flying trim the fus is likely to be nose up and look rather odd.

Martin,
If its any consolation, the Lo100 3 view in Sailplanes 1945-1965 by Martin Simons, shows the tailplane set at, or very close to, 0 degrees with reference to the fuselage longitudinal datum line, whilst the wing is set at a small positive angle to this datum.
This will give the expected +ve angle between wing & tailplane (decalage), whilst probably causing the fuselage to be at a small nose down angle in flight.
Peter

Martin

Just to satisfy my own curiosity, I weighed my Lo100 and the auw is 4.372kg or 9.635lbs. Most of that is in the fuselage and as noseweight, so I will be impressed if someone can build one very much lighter (I did not build this one - picked it up S/H ).
The flat bottom of the wing is at zero* and parallel to the fuselage datum (by eyeball) so the Clarke Y incidence through the LE radius will be about 3* and the tailplane seat looks to be at zreo as well. Decalage about 3* therefore.
HTH.

John M

Morning Martin,
As people have said, I built the Cliff Charlsworth LO100, which is a bit heavy, because thats the way I build but it will do every manoeuvre I can manage, it does have the section Robbie mentions.
Because I wanted a more sedate model I then decided to build wings to match the same fuselage for the LO150 version, and it is more of a floater, it has the same wing area as the 100 but obviously 50% more span.
I will be honest I have not flown either very much, because I do have a few other models and plus with this KOVID thing I have not been out a lot.
Lots to contemplate for you and the best of luck, its a nice size model and very enjoyable.
John

Thanks to all and John M, in my excitement completely forgot that it is the chord line that defines the AoA, Doh!

But 4.4Kg AUW Eeek! that is 20oz ft2. Beginning to wonder if this is a good idea after all!

Still, the 100 version is a relatively small / simple model so there might be some chance of completing it in 6 months.

Clearly there is beneficial reduction of drag on a wing with the same area but higher aspect ratio. However, I think if I was ever tempted to build the 150 wing, I might take a 'judgement' as to what constituted a 'scale' cord in order to deliver a satisfactory flying experience!

Just to be clear here, I plotted the aerofoils in Compufoil for John's LO100 and the main section is a Quabeck - HQ3014 only transitioning to a Clark Y (modified) from the start of the eliptical section out to the tip. Just looked at the file again to be sure.

.............and 16 - 20oz/ft², is not a bad loading for an aerobatic scalie.

'.......HQ3014 only transitioning to a Clark Y (modified) from the start of the eliptical....'

Interesting Robbie...What was the thinking behind the thickened centre section? Structural considerations or some aerodynamic reason?

I am leaning to S3021 root to tip and setting it out in Dev-Wing shows it will be fairly slim, but I can just get a pair of 12 tapering to 9mm x 4mm spruce strips in for the main spar which should be sufficient with the webbing and sheeting etc. If necessary for aesthetics the first few ribs can always be thickened up.

Martin Dee wrote: ↑09 Sep 2020, 09:46 '.......HQ3014 only transitioning to a Clark Y (modified) from the start of the eliptical....'

Interesting Robbie...What was the thinking behind the thickened centre section? Structural considerations or some aerodynamic reason?........

Well both to some degree.

I seem to remember (it was a while ago now) John wanted a more up to date section than the Clark Y that would be a compromise (isn't most flying machine considerations) between a reasonable aerobatic and soaring performance - although the LO 100 would be pretty far down the list as an efficient soarer.

The Quabeck HQ series has a great pedigree for use in large scale sailplanes and is now generally used full span without washout to great success - just thinned a little at the tip.

At the time I was still old school whereby in keeping with the common full size practice of increasing the camber of the tip section but washing it out by the difference in the zero lift angle of the two aerofoils. Doing it this way the tip stall is very effectively controlled and both root and tip reach their respective stall angles at the same time and there is no negative load on the tips at speed, Clark Y being a very good tip section for this.

The Quabeck used is only a little thicker than the Clark Y and the same camber but like most modern aerofoils has a higher entry point at the nose; and thickness is not the ultimate arbiter of maximum top speed, camber plays a much bigger part in that. It's also important to understand you have to compare like with like - it's not as simple as just comparing camber and thickness between different aerofoils. It makes a significant difference where the maximum value of both of those parameters lie on the aerofoil. Modern model sections tend to have them further back on the aerofoil than older ones.

I'm a fan of thick aerofoils (within reason), they are much more forgiving, have a wider speed range and also a wider low drag range.

Hope all of this hasn't confused you even more...............

That makes sense..

Have made a start on the easy bit as per pic below. when I get to a point where I have some bits to glue together, I will post a build log as there doesn't seem to be one for Lo100.

I don't have a building jig, so will use the crutch method of construction with formers split vertically. The main challenge for me is to find my Mach3 license code, I hope they have kept a record of my license purchase made a few years ago now!

Martin & Robbie,
I am currently looking at updating the original Charlesworth wing plan design for Cliff & have come across this oldish thread.
My initial look at the original Charlesworth plan shows a fairly flat bottomed wing section throughout the wing & with little or no apparent washout. (The inverted wing build seems to be intended to result in a flat upper wing surface with no twist).
I had thought of using an HQ section & would be interested to hear whether the HQ/modified Clark Y choice as Robbie mentioned is a good one.
Also of interest was the ‘hard’ wing mounting & retention methods, which seem to be either intended to fail in the event of an ‘arrival’ (protecting the wing) or is likely to result in significant damage if not.

Martin, did you ever build the LO100 & if so then what sections did you use & how did she fly?

Peter

Peter,
Never did progress the Lo100 in the end. Prevaricated due to its barge like girth and general lack of aerodynamic pretensions, then hit by the balsa drought, then the doubling of balsa prices made it prohibitively expensive to build. Had to content myself with a Teakle Dart, now grinding to its conclusion 6 months behind schedule. Even the balsa for that was an eyewatering cost, I mean £2.50 for a sheet of 16th! - how do these people sleep at night. Not convinced it is going to be a good flier either, except possibly as a high wind pylon racer.

Now only considering scale projects that are feasible using only light ply, B&Q spruce (almost as light as balsa!), foam, brown paper and 50 gsm tent fabric!

The Pat Teakle Dart is a very good model, and flies very well.

The Price of balsa is beyond the control of the suppliers her in the UK. China purchased most of the balsa stock available throughout the world to make wind turbine blades, which caused a worldwide shortage. Now we have the cost of living crisis on top!

Martin,
If you built the built-up wing version (sounds as if you did from comments about balsa costs) plus use a built-up tail & rudder then it comes out pretty light & with the HQ section flies very well.
I built the prototype to prove the new built up plan & I think Brian Sharp also built one.
There should be a build thread for my build somewhere in the scale build threads section.

The wings (with 1/4x1/8” spruce spars) are fine for normal scale flying, but I think Brian found that the wings flexed a bit when flown a lot more enthusiastically.
Peter

Brians build of the Dart can be found here: viewtopic.php?t=2664

Ta,
I'm sure the Dart will be great, just mid-build defeatism!

It seems I am afflicted by a sort of inverse Midas touch when building flying models - they gradually seem to have turned to lead by the end of the build process. I try, really really try not to let it happen, but somehow it just does!

Opting to fully sheet the wing added to the general weight gain, but given more likely than not it will be landed in a gorse bush, on sharply gnashing rocks, on the horns of a cow etc, a robust solution was called for, for which I will pay a price (probably in the form of a non scale wing eventually).

While thinking about the sheeting problem and how difficult it is to find a good substitute for balsa, I experimented with a craft paper/20 gsm glass cloth PVA bonded sandwich. Not completely successful. Doesn't have the anisotropic stiffness of balsa, but is quite strong. Might be ok for non critical areas of fuselage skinning. The material resists tearing in one direction very well but is weak 90 degrees to the strong axis. Perhaps with 2 layers of glass cloth biased and squeezed together at very high pressure it might be better and a possible substitute for 64th ply, but would be twice the weight of balsa. It is also a pita to make!