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Slider Glider! My take on a home design sloper


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CTR

Hi fellow frustrated flyers!

Thought I would give you something to ponder, poke at or muse over during this time of lockdown.

Last Easter the weather was totally different, strong winds and cold. Four of us had previously determined to have a week at the slope. Mam Tor was the designated location. However, I didn’t have much in the way of suitable slope models, and even less experience, but what the heck! Who could turn down the chance of a week of congenial company and flying to boot.

Anyway; I was stirred to create a slope glider of my own design which, as it happened, was not too shabby in the flying arena. Being stirred with this modicum of success prompted me to build Rev1 of the model, implementing advice from the seasoned flyers who formed the party last Easter.

The result is the model in the photos:

The main reason for sharing this is the fuselage design & build method. Perhaps it will be of interest to somebody as it results in a jigless but accurate fuselage which proved to be very stiff, reasonable weight whilst keeping to my desire to make something which looked pleasing (to me anyway) and takes a second look to realise it is a trad, built up affair.

More to follow....

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Finished fuselage photos: Easy fit for the servos, RX and SBEC (alongside where the battery fits. The white Velcro in the 3rd photo is where the 500g of ballast sits. There’s a couple of dowels e

Hi fellow frustrated flyers! Thought I would give you something to ponder, poke at or muse over during this time of lockdown. Last Easter the weather was totally different, strong winds and

Thanks Mike. Maybe a trip to your neck of the woods for a day flying once social isolation is lifted. Do you allow visitors to your slopes? Next stage is to work more on the wing. This is a built

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CTR

Before going into details, I must confess that I am extremely fortunate to have some serious 3D cad, and access to laser cutting 😁

This makes a big difference in the design philosophy in as much as the capability of cut parts accurately to fit like a jigsaw but without needing the necessary dexterity.

The first & second photos show the jigsaw parts which make up the nose and wing seat skeletons. These are then slid together (photo 3) and the result shown in photo 4.

You can see in the second photo, the rudder & elevator servo cutouts and the battery cutout the other side of the former.  I chose to use an ‘Airsoft’ battery, thinking the shape would be available in volume manufacture for some time to come. The battery is only 18 x 20mm and 124mm long. This means it fits right up to the nose block in a small section fus’. Its capacity is 2S 2000mAh so long hours of flying on a single charge. Bonus!

Sorry, photo 4 is upside down.

The nature of the slot-together design is that it is straight & true, without stresses at this stage.

The glider spec is:

Wing span: 1750

Fuselage length: 1035

Wing area: 33.5dm2

Fuselage AU weight: 520g

Wing AU weight: 606g

Wing loading: 33.6g/sq dm (11oz/sq.ft)

Ballast capability: 500g

Ballasted AUW: 16oz.sq.ft.

Dinners ready! 🤗 more later.

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SilentPilot

Good work!

Looks like something Chris Foss could have come up with, that’s a complement by the way :) 

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CTR

Thanks SilentPilot. I must admit, when it was finished I momentarily thought about calling it ‘Phase Shift’ but thought it might be a bit pretentious!

Not had any of the Foss gliders but recognise that they are well respected. Hope mine is half as good when I get to fly it later in the year.

The design was tempered with my instinct to be a miser when it comes to material usage. The whole fuselage  is made from 1/3rd sheet  2mm birch ply, 1 sq.ft.   3mm lite ply. 4 lengths of 3/8 triangular stock and 2 sheets of 100x915x3mm C grain balsa. There was also some balsa block for the nose and hatch cover. Both these items have a central lite ply former to help with more accurate shaping of the parts.

The first version had wings held with rubber bands which were treated with total distrust by Paul, the test pilot at Mam Tor 🤔

This time, bolt-on wings. Less crash resistant in my opinion, but apparently the way to go (according to Paul) for high G manoeuvres which he was afraid to do. I was pleased that the model survived in one piece in the 30+ MPH winds during the week last Easter.

This photo shows the multi-part ply and balsa sides jointed up and ready to apply to the skeleton. Note the small doublers of ply over the joints which also back up the former at the wing LE where the dowels fit.

The 3mm balsa sides were made in three pieces for two reasons: 1/ to align the grain of the front section to the direction of compression and the boom grain in line with the rear section. 2/ to fit the length and other balsa parts into the minimum of sheets.

Photo 2 shows the first 2mm ply side added to the skeleton. Note the hatch formers made up in the background. The 2mm ply is flexible enough not to stress the skeleton.

Photo 3 shows the full sheet layouts for the complete model; not much waste there 😉

 

 

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SilentPilot

It’s funny because I prefer throwing my MiddlePhase about with its elastic band retained wing, my Phase6 on the other hand uses a nylon shear bolt to retain the wings (and a weak link plate). I’m terrified of this setup shearing under Aerobatic G forces.

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CTR

There’s always a weak point! Make it stronger and you’re just relocating it to the next weakness.

For me as a novice slope pilot, landings are the tricky part especially in strong wind flying fast, hence adding flaps to this rev1. Rubber sounds good for tip strikes, but not so good for radical flying like my mates are used to!

I chose to use 2 x M5 nylon bolts TE and 2 x 6mm dowels at the LE this time. The nuts are square and captive in the ‘block’ of 3 laminates of ply in the middle photo in the previous post. Major repairs in the pipeline 🥴

However, the fuselage only takes a day to build and is fairly low cost in materials. Finishing is the slower part. It’s covered with 25gsm glass cloth on the bias and painted. So 3 days and a new one rolls off the production line! Great to be retired.

The built up wing takes longer than the fuselage.

Back to the build: Once the other side of 2mm ply is added, then add the balsa sides. This way, there is much less stress in the sides compared to gluing the ply and balsa in the flat then bending them to the fus’ curve.

After the Balsa sides are glued on, I then fitted the balsa 3/8” triangular fillets from wing TE to tail, and along the bottom edges. After that, the top and bottom cross-grain planking was added. The nose is very strong with its keel made from 2 Layers of 2mm birch ply. This extends below the planking creating a belly skid. It also forms a vertical rib up to the battery base plate.

Razor plane the rear fuselage to a round section and put generous rad’s on the belly up to the nose. The ply former in the middle of the nose block helps with the profiling. I also added the hatch blocks before the final shaping as sanding it all as one piece with the fus’ body results in smooth transitions.

 

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CTR

Finished fuselage photos:

Easy fit for the servos, RX and SBEC (alongside where the battery fits. The white Velcro in the 3rd photo is where the 500g of ballast sits. There’s a couple of dowels each side of the ballast position. These are used for a rubber band to go over the ballast block, under the dowels and back through t slot in the former. The band ends then hook over a couple of hooks at the ends of the side rails each side of the ballast. Belt and braces to keep the ballast in position tight against the Velcro (photo 4) You can also see the 2mm carbon pushrods for the rudder/elevator each side of the ballast area. These go through a series of holes in the formers which provides ample support. There is need for a short length of PTFE tube at the tail end. This is from the last former of the skeleton, after which the rudder pushrod curves up to exit the top of the fuselage.

Max fuselage width under the wing is 52mm. Still fairly narrow but ample for an easy install! Totally different and a joy after the DLGs I normally fly.

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isoaritfirst

Super job .

some very nice detail.

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CTR

Thanks Mike. Maybe a trip to your neck of the woods for a day flying once social isolation is lifted. Do you allow visitors to your slopes?

Next stage is to work more on the wing. This is a built up job on Rev1 as opposed to a blue foam core on the first model, kindly cut for me by John H . It's very stiff with two full length 1/4 x 1/8 spruce spars and two central half length spars, fully sheeted with 1/16 balsa and glass cloth. Heat shrink over that.

The first had full length strip ailerons. This time I added flaps and increased the cord of the ailerons a bit to compensate for the reduced length. The wing span has also been increased from 1550 to 1750mm. Interestingly, the AUW of the Rev1 four servo wing is 605g @ 33.5dm2 (18g/dm2) and the 1550 span blue foam wing is 458g @ 29.1dm2 (15.74g/dm2) so significant increase in weight per dm2 with the  built up job even if you subtract the weight of the two additional servos (30g including wiring). 

I used AG40 airfoil for both these versions. Inverted flight on the first was acceptable according to Paul, my test pilot, so kept it for the rev1 too.

I increased the AOA from 0 to 2deg. this time to offset the elevator trim needed on the first model. I did this by raising the LE which helped increase the fuselage front side area which I'm hoping will be enough to attempt knife edges. (not realistic with the first one). However, I'm concerned that the 2deg. increase will have an adverse effect on inverted 🤔

The fuselage will be my test bed for wings as it is very stiff and the first version proved to be strong enough at the Orme last year.

Leaning towards a wing with AG40 root and MG05 tips.

Looking for any views on my ideas and also input on the percentage of cord for typical ailerons on sports slope soarers?

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tonym

Hi Neil

Did Linux have any input in cutting the wood?

I like a trip out to Shropshire most years - https://www.lmsa.org.uk/ - sometimes I even join 🙂

Super looking model

Tony

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CTR

Thanks for the complements guys. 🙂 I hope it flies as well as it looks.

Tony, no Linux used on this one because my CAD & graphics software isn't supported; but got it up and running on the dedicated PC with your help, thanks.

I'm in the process of designing a combined CNC machine as a router and hot wire cutter. That's the project for Linux. Probably another month to 6 weeks away from mechanical completion. Will give me a 1220 mm x 610 mm router and HW capability. Can't see me building anything that can't be done on that! Trying to keep the machine footprint within reasonable range to help with workshop space. Currently it's working out at about 1550 x 800. However, when parked, everything protruding above the bed is at one end so it makes a reasonable 1220 mm build surface too.

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CTR

Hoping for input about the wing ideas.

(Left handed shot on my phone! Is there a way to rotate photos here?)

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isoaritfirst

LMSA also has a facebook page.

listed as Long Mynd Soaring Association.

Joining LMSA will cost you a fiver, (we do pay the landowner) but happy for visitors to come along a few times a year without joining.

BMFA licence is required and no power is a stipulation.

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CTR
23 hours ago, CTR said:

Thanks Mike. Maybe a trip to your neck of the woods for a day flying once social isolation is lifted. Do you allow visitors to your slopes?

Next stage is to work more on the wing. This is a built up job on Rev1 as opposed to a blue foam core on the first model, kindly cut for me by John H . It's very stiff with two full length 1/4 x 1/8 spruce spars and two central half length spars, fully sheeted with 1/16 balsa and glass cloth. Heat shrink over that.

The first had full length strip ailerons. This time I added flaps and increased the cord of the ailerons a bit to compensate for the reduced length. The wing span has also been increased from 1550 to 1750mm. Interestingly, the AUW of the Rev1 four servo wing is 605g @ 33.5dm2 (18g/dm2) and the 1550 span blue foam wing is 458g @ 29.1dm2 (15.74g/dm2) so significant increase in weight per dm2 with the  built up job even if you subtract the weight of the two additional servos (30g including wiring). 

I used AG40 airfoil for both these versions. Inverted flight on the first was acceptable according to Paul, my test pilot, so kept it for the rev1 too.

I increased the AOA from 0 to 2deg. this time to offset the elevator trim needed on the first model. I did this by raising the LE which helped increase the fuselage front side area which I'm hoping will be enough to attempt knife edges. (not realistic with the first one). However, I'm concerned that the 2deg. increase will have an adverse effect on inverted 🤔

The fuselage will be my test bed for wings as it is very stiff and the first version proved to be strong enough at the Orme last year.

Leaning towards a wing with AG40 root and MG05 tips.

Looking for any views on my ideas and also input on the percentage of cord for typical ailerons on sports slope soarers?

I am hoping for some constructive ideas & guidance on the questions posted yesterday.specifically the red text above!

Any gurus reading this message please send your inspired thoughts. I need all the help I can get so as not to waste time & materials on too much trial & error.

Thanks in anticipation!

Neil P

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oipigface

I’m no guru, but I do believe you are right when you say that a positive angle of attack on the wing will not help inverted performance. When the plane is upside down it will be a negative angle of attack! If it were me, I’d change the tailplane’s angle of incidence rather than the wing’s. Is it an all-flying tailplane, or fixed? I can’t tell from the photos. 

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isoaritfirst

LIke John I'm no Guru either, but AOA are for gliders, floating about without input.

IMO what you want is performance. If the model needs to go up stick in some elevator.

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CTR

Thanks Mike, and John for the link. 75% recommended according to the table. Mine is at about 83% 🤔 More research needed next time .

I've only flown 'floaters' up till trying this one last year; so I was flying blind so to speak when it came to sport style gliders.

The first model had 0 deg.  AOA. Needed up elevator by about 2 to 3mm for normal slope flight in 12 mph or so at Ivinghoe, that was with the AG40 airfoil and no washout.

It's a fixed tail on the basic design. I'm not too sure about the mechanics of AMT, not the control side of things, but the rigidity. Whats the point of making a torsional stiff fuselage then adding a wobbly tail! The seat width under the tail is 26mm but depth is only 19mm. would be a bit tricky to fit the mechanics in there. I didn't want to use snakes so had the elevator pushrod straight out of the rear of the fuselage, direct to the elevator control horn. Any suggestions as to the length of an AMT horn to avoid flapping or deadband?

I could try raising the tail by making a stub fin thereby adding room for the control horn; but the seat width for the tail would be a lot narrower.

Could have a fixed narrow portion of stabilizer and AMT ends outboard of that but its not a clean aerodynamic solution. Not sure how important that is with a sports type glider.

I appreciate the input and ask you to excuse my ramblings and lack of experience in what is a new venture for me. Just wish I could get out and test fly the thing!

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oipigface
59 minutes ago, CTR said:

. I'm not too sure about the mechanics of AMT, not the control side of things, but the rigidity. Whats the point of making a torsional stiff fuselage then adding a wobbly tail!

You may be able to find a lot of guidance about this, and many other aspects of aerobatic slope soarer design and construction on Graham Woods’ site www.favonius.com. 
I can’t find the page at the moment, but there’s definitely a detailed description of how to fit a non wobbly all moving tail somewhere on Graham’s site.

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