A throw back

[Konrad]

I’m starting to get back into hand launch gliders actually just small gliders. I was up in the attic and noticed some glider parts scattered all over the place. This was as a result of neglect on my part. I was lucky in that I was able to find all the sub assemblies. It now looks like I have Larry Jolly Flinger that I scratch built from a set of Model builder plans. I built this around the time frame of 1985 as an upgrade to the Bridi Tercel 50” grenade launch gliders. While it was an improvement it quickly became apparent that the Finger was never going to be a high performance 1.5m (60 inch) glider. The best weight I could get at the time was 13+ oz. Also somebody was using a rubber ruler if they thought that 57” equated to 1.5 meter. It also was an open wing with the Eppler 205 airfoil. I flew this until the late 80’s when I got a DJAerotech Monarch. Wow, that was a night and day difference in performance. The performance was so great that it looks like I just put the Flinger away even though it looks like she was in flying shape. Just my luck the DLG came along at the same time as I got the Monarch!

Somewhere along the way I “upgraded” the stab to a full flying stab. I think I got the idea that this was a lower drag set up and that it would help on the launch. I think I copied the setup as found in the Top Flite Wristcrat. (I also found a NIB kit of the Wristocat and the .035 Phasoar).

Covering looks to be a mix of 21st Century and CoverLite. Oh, and now some orange tape! While far from being pristine I think I’ll try to set up a radio and see if I can throw out my shoulder.

All the best,

Konrad

 

[Hank GB Z]

Konrad,


It looks awesome.

Last year my friend gave me a new in box Tercel just like he gave me back in high school. I recently found a new in box Skeeter like I gave him in high school. We are hoping to do parallel builds this summer.

I like javelin launch style gliders. I think they’re a different set of challenges from DLG and less pressure on your knees. Do warm up your shoulder though.

Hank

 

[Konrad]

A problem I recall with the Bridi Tercel and Flipper was that the first bulkhead (front wing hold down, AKA #2) didn't go down the full depth of the fuselage. The wings kept tearing out this bulkhead any time the wing tips touched the ground. Extend the bulkhead all the way to the bottom sheeting and add some 3/32 triangle stock on both sides of the bulkhead for added glue area. Also one of the two models had the horrible counter balanced rudder. Change the fin and rudder to eliminate the counter balance. And don't add the lightening holes to the tail feathers. If you need to loose weight think about doing a stick build up of the tail feathers.

 

[Wayne]

I recall the Tercel was a good flying plane. I never owned one, but a buddy did. Don't think it lived long, probably a mid air.

 

[Hank GB Z]

I really enjoyed my Tercel. I looked at the plans and see the issue you discuss about the bulk head. Agree it needs to be stronger. I’ll probably do built up tail feathers. I never had that bulk head break from what I remember. I did have the wing fold (build error) but that was after lots of fatigue and my friend who gave me the kit gave it a really hard throw. He was on varsity baseball at the time.

Anyway, back to your flinger. I’ll be interested to see how much weight you save going over to modern equipment.

Hank

 

[Konrad]

How did we ever fly these things? Thermals must have been a lot stronger in the old days!
I see that my Flinger has 2 17 gram servo under the wing. I suspect I placed them there to make room for the RX and 4 cell 250 NiCad battery in the nose. Today I bet I can fit 2 6 gram servos an RX and a 2 cell lipo in the nose. But with the short nose I'm sure I'll still need nose weight.

 

[Konrad]

With the short nose not sure what benefit there is to using lighter electronics. So it might be best to just keep to simple mechanics. Here I've cut off the nose to allow me to hollow it out. As I found 21 grams of lead in the front compartment I assume I need at least this much for balance. I'll try to add as much of this weight in the way of Woodsmetal poured into the nose cavity.

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[Konrad]

Sometimes I can't see the forest for the trees. This time the trees where the plethora of servos I have in my micro servo drawer.

I was able to cast 25 grams of lead into the nose cone. I also found a set of high voltage metal geared 5 gram servos. These should run fine native on the 2 cell Lipo I have.

On my scale the old servos weighed 37 grams the and the new set weighs 10 grams. That's a savings of an ounce! (Don't you just hate mixed units)! I can also move these smaller servos into the nose to aid in the leverage of the mass. As it sits now with a large 700 mAh Life I get the balance close to what I think I had when I retired this ship.

So with the servo weight, battery weight and RX weight saving combined with getting more mass further out into the nose I should actually remove over an ounce of weight from what I recall was a 13 oz glider.

Now that I have a damaged wing tip I think this will allow me to add some inches to the span to reach 60". Big deal you say, but remember induced drag drops as a function of the added span squared.

 

[Hank GB Z]

Looking good Konrad. Have you given any thought to re covering the tail feathers in lighter material? Doculam or if the last bits of Solite would probably help save a few more grams in the tail.

Hank

 

[Konrad]

It is covered in the same stuff we covered our Lady Bugs. I think that was pretty light stuff.

 

[Konrad]

I need to learn to do a damage assessment before I do any mods. After I stripped the covering I see what is typical, my competition ships tend to lead a hard life. The repairs are solid but I'm a bit shocked at just how often I broke the fuselage on this Flinger.

 

[Hank GB Z]

What prompted pulling the covering off?

 

[Konrad]

I hate patches!

Well to start with I cut off the nose to get the mass as far forward as I could. I thought I could bring out some dents in the balsa tail boom with the use of water. I repositioned the rudder pushrod so that I could get more throw to port. And I thought I could sand the fin to fuselage fillet a bit to save a few milligrams.

Also I had to recover the bottom anyway. So if I have the iron and covering out anyway I thought I'd try to do the job right.

 

[Hank GB Z]

Ok. That makes sense. It’s looking good.
Hank

 

[Konrad]

I'm having to laugh at myself for being so concerned with weight way back when. I see where I didn't carry the glass reinforcement back to support the rear wing hold down. That was just dumb! Now I have to pay for this as the rear of the fuselage is showing a lot of stress cracks around the wing hold down. OK, the whole fuselage is showing stress!

Here I'm using a layer of 0.5 oz glass cloth and Tap Plastic Hard 4:1 Epoxy. Normally this works great. But this time in my cold shop the viscosity was a bit thick so it didn't flow out as well as in normally does. You can see this in some of the glossy sections. Really not an issue, just not as nice as it could have been. I now have the fuselage in the oven doing my post cure heat treat. (Not needed it just makes it a bit easier to trim and sand).

 

[Konrad]

Well I'm surprising myself as to the weight saving. But first back to some structural concerns. I decided to add another layer of 0.5 oz cloth to support the rear wing mount. I really didn't see this as adding much weight but it sure added a lot of strength to the stressed structure. I also added a second layer to the nose part line as the nose is the first thing to hit the ground.

Now the surprise, the weight! With the 700 mAh 2 cell Life, two 5 gram HV servos an Archer 4ch RX all this in the nose. And the 25 grams of woodsmetal lead in the nose cone it looks like I can reach a weight of 290 grams at balance. I could have sworn that in the late 80's I had a great deal of issues reaching 360 grams.

While I don't see it now, I thought I had a finger hole cover (trap door) to help cut down on drag. I'll need to see it I can add a spring loaded finger hole cover.

 

[Konrad]

I never understood from a structures point of view, cross grain top and bottom sheeting. It always split on me if the boom whipped the slightest!

 

[Glenn Beer]

Short of a wreck I’ve not seen it fail. I would think that cross grain would help resist crushing by the ham handed.

 

[Konrad]

A wreck might be a good description of my landings. But every time I strip the covering off a fuselage with cross grain I find the cross grain has split and that at points the bond has also failed. More often than not it is the covering that it holding things together.

As to the fingers going through the sheeting I find that the internal bulk heads will help support the sheeting across the grain. If the fuselage is rather wide some 1/16 square supports across the grain can stop that. Oh, then there is the idea of not sticking one's fingers into the sheeting.

 

[Konrad]

Well, last year this poor model suffered a major set back! After doing a fantastic, if I do say so myself, restoration of the fuselage. I allowed it to be crushed by dropping a 2x4 piece of lumber on the tail boom. Let me tell you I was fit to be tied!!! All the more so as I am coming to the end of my supply of 21st Century metallic blue covering. I had accomplished one of my goals with the restoration in that I didn't need to patch the fuselage. This is no longer the case!

The 2x4 had crushed all the sheeting 360° around the boom. But luck would have it that the longerons and Bowden tubes were not damaged. As the wood was crushed there was still wood fibers going across the failed area. So I soaked the wood with water to expand the wood fibers while I repositioned the boom. After the wood dried everything was still in alignment and the control rods still moved freely. (This can be a problem with Bowden tubes AKA; snake push rods).
I saturated the crushed fibers with CA to finish off the structural repair.

Part of the restoration was to move the servos to the front to aid with balance. This meant that I had to add some extensions to the Bowden tubes to run the push rods to the front.

Note some issues with the new servo placement. First I had to keep the servos a bit further aft than optimal as I needed allow the heavy 2 cell battery to pass into the nose. This limited the use of hardware to adjust the push rod length as they would bind against the wing hold down bulkhead. I will need to rely on the radio trim off set to trim the control surfaces along with making the push rod wire a bit long to allow a kink adjustment.

Also note the piss poor engineering in that I made the servo tray with corners that cause stress risers in the fuselage sides. I did this as I used too small a scrap piece of plywood. I should have used radiused corners to blend into the fuselage sides. ( The fuse has 4 or so layers of glass cloth, so I'm not too concerned. But it is a poor practice to use sharp corners on a servo tray)!