SailplaneDave

I just got a Sterling Diamant new sailplane kit in off of E-Bay. For whatever reason it came with an extra canopy. Man is it going to be fun building it, but I am debating putting 2 or 3 channel micro system in it. Suggestions?

As to turning, I am debating putting ailerons in it, as dihedral planes just suck when it comes to turning. As to modifications, it uses two piece leading and trailing edges with reinforcements at the junction of the straight and tapered tips. I will go with full length pieces here. It also uses wood dowels for wing spars, I ought to go with carbon fiber rods and tubes if I can find that company that produces all sizes of that.

As to the spar, it is a two piece spar and I think it is a balsa spar with balsa sheer webs glued onto the face of the spar. If I can find that company that makes precut carbon with thin foam laminated in between, or carbon laminated to balsa, that way the balsa will face upwards so it can be profiled to match the airfoil.

As to the airfoil, the undercupped or reflexed undersurface looks like a nightmare to monokote. I would think that the second I hit it with the heat gun the material will shrink and since the glue is now warm it will release off the undercambered airfoil underside. Micafilm seems stronger, and I do hear there has been a version with the glue already on the Micafilm.

I would love to have plans scanned into CAD and have some laser cut sheets done up maybe 50% or 100% larger. I would have to get some guys to go in on it with me to defray the costs. Can you imagine, a Diamant with a 117" or 156" wingspan built up?

BMatthews

Just switch the two main spars to spruce and use 1/8 x 1/4 tapering to 1/8 sq at the tips with the webbing glued to the front face. I'd also double up on the webbing with a second set on the other side of the spars for the first 1/3 of the wing out from the fuselage. There's no real need for carbon in a model of this size where something else would fail long before the carbon spars would even feel any real strain. If the stock design does not have the main spars located one above the other so you can use webbing then modify it so it does. The original kit was really not intended for serious flying and truthfully was more intended for hanging from a string attached to a plant hook on the cieling so don't be afraid to modify it so it can withstand a light duty high start.

Dihedral models don't all turn badly. Only the badly designed ones. But you're right in thinking the Diamant would look VERY odd with polyhedral. SO ailerons it is. Use lots of differential throw with the up travel much larger than the down travel. Better yet arrange to have the rudder operate as well and either drive it off the aileron servo or off a small parkflyer servo to keep things light. With that narrow wing it does not have a lot of wing area and what it does have is hamstrung by the design being scale and having a very short chord. So light is VERY right with this design.

Good luck with the project.

SailplaneDave

Well keeping it light is why I thought carbon rather than spruce spars, especially if I go with the added weight of ailerons. Carbon is cheap. The balsa shear webs are glued to the faces of the spars, in a C configurration rather than an I configuration. I have to figure out how to have one microservo for both ailerons as the wing may be too thin for a servo for each aileron, not to mention that added weight. This is why a 50-100% larger model would be the ticket.

BMatthews

There's not much load on the surfaces of something this light. Use plug on wings with a carbon rod instead of steel wire for the plug on or make it a one piece with a hatch. 1/8 balsa pushrods out to custom made light bellcranks in the wings that then have very short rods to the aileron horns will be as light as you can ask for but still be nice and slop free. Use 1/32 wire for all control rods or rod ends. The micro servos are set up for that size wire anyway. The aileron servo in the fuslelage under or between the wings could then also drive the rudder as well.

And I suppose of you use carbon caps then hard balsa to support it and provide a nice glueing face for the webbing would work just as well. Or that carbon and foam sandwhich.

Either way you need to keep this thing light. It's only got.. what.... maybe 200 sq inches of area? That's not much. To make a decent glider with that small an area you need to keep the weight down to probably no more than 12 oz. And 10 would be even better.

SoCal GliderGuider

Personally I would never try to build and fly one of the older Sterling sailplane kits. Their wing joiner system is OK for moderate slope flying but their adherence to scale airfoils and making rudder onlys out of what should be an aileron controlled sailplane is nuts.

I would redesign the wing to have a decent airfoil such as the Selig 3021 and change the wing joiner to one rod in the center. The outer wing is way too thin for a decent metal geared servo so you would have use a bell crank and control rod arrangement with the servo at the root of the wing or even in the fuse. If you are only going to do slope flying then you could use a semi symmetrical airfoil along the lines of the Eppler 374. The airfoils have to be buildable in wood. The higher performance airfoils require hot wired foam and epoxy fiberglass/carbon cloth lay ups.

Build up TE's are sometimes necessary to get the airfoil "right". One can never find TE stock that matches a constant cord wing let alone one that tapers.

SailplaneDave

Well I've taken the Sterling Diamant kit apart and wasn't paying a whole lot of attention as I spent hours cutting out all the die cut parts. Now I know what the seller meant when he mentioned he would throw in some parts for a second kit. I have pretty much two entire kits with two canopies to boot.

It is listed as a 270 square inch wing. The manufacturer states that 5 clear coats and two white coats of dope will yield about a 10 ounce model. Cirrus ultra micro servos are listed as 4.5 grams each. If I put one in each wing, and two in the fuselage cockpit area, that is 18 grams, about 2/3rds of an ounce. The wing uses two 1/8' wood dowels for wing joiners I will swap that for carbon dowels and tubes. For such a relatively slower flying ship, I don't know if metal gears are going to be necessary. I wanted to see if I can use the servos in the wings so I can use them as flaperons/spoilerons.

For weight savings as long as it balances out I can go with a lithium ion battery pack. The horizontal stab is set up fixed, so I am going to have to fiddle with it and make it all flying.

Between cutting out the parts for the fuselage and vertical stab, I spent just 1.5 hours putting 90% of the fuselage together. What I wouldn't have given to have had superglue as a kid. What a pain it was gluing on a few parts with aliphatic resin glue,, pinning them, and having to wait overnight.

Who is that manufacturer that makes prefabbed carbon skins over thin foam, both in sheets and strips?

SoCal GliderGuider

I just went over a set of plans and I think the 74" wing span is going to be a challenge. As this is rudder only design there are a lot of changes that need to be made to make it flyable -- if at all. The ailerons are too large for the wing. You can use half their length and still have a decent roll rate. If ailerons are incorporated you will need to flatten the dihedral. About 2 degrees is acceptable. Also the aileron throw is three times more up than down -- differential.

The elevator could be made all flying or you can just make about the last third a true elevator. Either way you are going to play heck with getting a control cable to it.

Covering the wing is going to be a challenge as the structure is marginal for plastic films.

I wouldn't have even tried to build this kit. It's worth more intact and sitting on a collectors shelf.

SailplaneDave

Well, if someone else made a scale sailplane that was built up, which is half the fun, I would buy and build it, but all others are foam wings..and all the two meter kit stuff is all non-scale and not particularly scale aesthetic looking.

SoCal GliderGuider

www.tmrcsailplanes.com

jetpack

My Feedback: (1)

I just bought one also from eBay. This kit i remember way back as a teenager in an old Hobby Shack catalog, and ever since that point, i was hooked on it.
I have since learned to fly RC 2M (Sig Riser, HOB T-Tail, and Bob Martin's BobCat) and when I seen this one come up for sale, I thought it would be a great project.
Not knowing anything about the kit, other than the picture on the box, im kinda suprised its not considered much of a flyer....seems to have all the right proportions and an underchambered profile would suggest "state of the art" performance.
I also would like to make this a good flyer, the small radio gear of today is fantastic for this i would think. I have a standard hi-start already, but yes....this one seems too light to take the strain. Good thinking on the spar ideas. About the covering, probably the old fashion silkspan and dope might be the way to go on this. Sure its a little bit more labor intensive than iron-ons, but the undercamber and such, almost cant get away from using it. Besides its nice to see the framework I think, especially on this one.
I'm anxious to hear more building reports and such before i dive into mine. I kinda want to make this one the jewel.

jetpack

My Feedback: (1)

What type of performance would a simple rudder only ship have, instead of trying to add ailerons and stabilizer...more or less going free-flight with it, all in efforts to save the weight and building complications? Would it be possible to stay over the field with something like that? What type of changes would be made in order to help make the rudder work better then? (if any)

What about going with just two channels, ailerons and stabilizer?

I wouldn't mind giving up "airobatic abilities" in order to have a really nice floater, and something that could be launched with a standard hi-start.

Speaking of hi-starts here, what size tubing, and assembled lengths should I use if I were to custom make one?

BMatthews

Aileron and elevator only works fine for a thermal ship. I did one that way after seeing another local modeler with the same setup. Both of our models were 2 meter designs and both used lots of differential. No issues with high starting or winching. Just steer as normal on the way up.

Vertical fin area size may become an issue though. If the model want's to "fall" into the turn strongly make the fin area smaller. If it seems to hang tail low in the turns and shows some signs of adverse yaw then make it bigger. It's all about finding the sweet spot for the spiral stability factor. I know this doesn't help much for a scale project but there ya go.

jetpack

My Feedback: (1)

Thanks Bruce that does help a bit. I wasn't really aware of the vertical area characteristics. I suppose if you want to have "full control" over a thermal ship the best way is two-channel operation, one being ailerons to control the roll and the other being the elevator for pitch. I have flown three-axis before and the rudder only seems to "smooth out" the turn - almost unnoticable if not even used.

jetpack

My Feedback: (1)

Looking at the plans, isnt there a better way to make a towhook other than the wire skid plus the two others set in back of it? If I would like to use a hi-start I would think this would need to be a little more robust. Only other planes ive built have a flat plywood bottom to them where a hardwood block gets glued and the towhook gets fastened to that.

BMatthews

If you can scan that area of the plan and post it perhaps there's some decent alternatives.

A very useful mod to the Sterling kit would be to modify the fin so that it uses a thicker symetrical airfoil and then sheet it with 1/32 balsa so it better supports the T tail stabilizer. T tails put a LOT of stress into the fin even during softer landings so a bit of beefing up would help a lot. The thicker airfoil and sheeting would be a big help. The rudder itself can still be built up to the same airfoil shape but left open framed and tissue covered for light weight.

Wayne22

My Feedback: (2)

I have a Sterling 1-34 and wonder how different this particular model is? The undercamber was no problem to cover..the center section is attached to the fuse and is sheeted, then covered with rhino covering, the outer panels are open bay , again covered with rhino....

This one was suppose to come out just a hair over 2 lbs, but it was more like 5 lbs when finished, including a ton of lead in the nose to balance it. In spite of that, it flies very nicely. My son and I aerotow it, and it will stay up in a decent thermal.....