Schwing Corsa 2.75m (secondary market purchase)

[Konrad]

Well I'm now the proud owner of a Schwing Corsa 2.75. I'm not the first owner of this model. Generally the build/assembly looks to be to a high standard. Now I'm noticing a few things that concern me. First is that the servos in the wing look to be KST 135. These are 6v servos. I can't find 2/3A NiMh cells any more. Nothing that throwing some money at can't solve. So I'm using 2 round cell lipos and a linear regulator to drop the 7.2v down to 6.5 volts.

But what concerns me is that I found what looks like an anomaly at the tip of the wings. That is there is a bulge in the LE as it comes around into the tip. This bulge is about 1.5mm thick and about 20mm long. This looks like an error in the mold as the part line shows this bulge. I assume this is an error in the CAD or CAM profiles as both wing show this bulge. Even a much older set of wings (Non-SWS) shows these bulges So I've seen 2 set of wing and all 4 wings show this.

I'd like to learn if this is a design feature and if so what does it do? If it is a manufacturing error I'd like to know so I can start to block sand it away.

 

[Konrad]

Damn!
With the new power system (battery and reg) It looks like I'll need to rework the balance. My understanding is that this plane balances at 100mm. As it is, there is no space to add nose weight. This build was done using lead shot. As spheres only fill the space to about 2/3 the available volume. I'm thinking of knocking out the shot and using woods metal lead as my nose weight. This brings up the problem of knocking out the shot. I'm thinking of cutting off the tip of the nose to gain access to the shot. Then using a drift to hammer out the shot. As I want to repair the damage found at the wing root this really isn't much of a concern for the finish as I will need to make a paint spot repair anyway.

Now If I want to use this for F3F racing I'll need to have a model with an F3F compliant nose radius ( R=7.5mm @90°). Anybody have pictures of a Corsa with an FAI nose? If my math is right I'll have to cut back the nose to where the fuselage is 11mm (10.6mm) wide in top view.

So before I start hacking away on this graceful fuselage is the CoG of 100mm a good point?

 

[Wayne]

Mine has a mark at 91mm. Would need to confirm that is where it it balanced.

 

[Konrad]

That sounds much better. I think my Redshifts balances at 96mm. But that means I need more space for nose weight.

 

[Doc James Hammond]

Well I'm now the proud owner of a Schwing Corsa 2.75. I'm not the first owner of this model. Generally the build/assembly looks to be to a high standard. Now I'm noticing a few things that concern me. First is that the servos in the wing look to be KST 125. These are 6v servos. I can't find 2/3A NiMh cells any more. Nothing that throwing some money at can't solve. So I'm using 2 round cell lipos and a linear regulator to drop the 7.2v down to 6.5 volts.

But what concerns me is that I found what looks like an anomaly at the tip of the wings. That is there is a bulge in the LE as it comes around into the tip. This bulge is about 1.5mm thik and about 20mm long. This looks like an error in the mold as the part line shows this bulge. I assume this is an error in the CAD or CAM profiles as both wing show this bulge. Even a much older set of wings (Non-SWS) shows these bulges So I've seen 2 set of wing and all 4 wings show this.

I'd like to learn if this is a design feature and if so what does it do? If it is a manufacturing error I'd like to know so I can start to block sand it away.

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Hi Konrad. Bad CAD on the original moulds. Just another of many many mistakes I have found since I changed manufacturer.

Sorted out with the new Corsa. I don't think it will have any discernible effect.

Just for info I put a small kid's plastic toy ball on the front of mine the one time I flew it in F3f. Caused a little comment and not a little mirth as you can imagine, but I actually did fairly well.

Doc.

 

[Konrad]

OK good to know I'll block sand the the bump if for no other reason than they aren't to spec.

As to the nose it should look just fine with an FAI nose. This will make it easier to knock out the lead shot to allow for the needed higher density nose weight. This should all be a win win upgrade for me.

Wow, I love the size! just look how small the Corsa is! This and the long high aspect ratio wing should show up as a lot of speed over the Alpha 2.8

 

[Konrad]

Just because the top view shows it so well, I thought I'd talk about why I like the Aeroic wing so much.

In the 80's Wil Schuemann showed with tuft yarn that there is strong lateral air flow at the TE. To minimize this drag the TE is placed 90° to the fuselage. (Or even swept aft). This lateral flow gets stronger as the Cl gets higher. You can see this in Schuemann's video as the wing stalls (all the TE yarn tails are pointing to the fuselage). This means that any wing area aft of the wing tip is dealing with this lateral TE airflow. This is why most small wing tipped wings have such a strong harsh stall. The stall at the TE of the tip disturbs so much wing area. (In the photo this is the white area of the TE). The yellow Aeroic wing has almost no area aft of the wing tip.

Now for manufacturing reasons Schuemann used a faceted wing LE to have the wing area fit the elliptical lift distribution theory. This is a very good approximation.
airplanes like the P-47 and Spitfire tried to achive this with their wings but because of mechnical, structural and manufacturing constraints these wing were built along a straight spar. (You will note the high forward swept TE (not good)). Now with composite wings designers can make wings that comply with the elliptical lift distribution and actual air flow. Full size gliders are doing this and so are the wings from Aeroic models.

 

[Konrad]

This is working out great!

With the lipo battery my CoG came out at 110mm. Way too far aft!

I was able to knock out the lead shot nose weight after cutting off the nose to allow my drift direct contact with the shot.
I filled the inside of the nose with fiber and epoxy to allow me to maintain the FAI nose radius.

I was able to file down the wing tip bulge with a file. This really was only a 1mm to 2mm bump on the bottom of the wing at the tip.

I did notice a few other issues. One was that the aileron was free. It looked like the arm broke where it was thinned to clear the servo cover (hanger rash). I also found that there wasn't enough upward flap motion, heck I didn't see enough downward flap. This brings me to ask why Aeroic didn't provide jelly bean servo covers. I can't see how one was to get proper control surface motion with the control horns provided without jelly bean covers. I think the original builder was trying to build the model with the components supplied. This lead to the traps we see.

If the rebuild keeps going this good I might upgrade the KST 135 to X10 mini to allow the use of 7.2v (native). This was to be a sport ship. But it might become another F3F racer!

 

[Doc James Hammond]

This is working out great!

With the lipo battery my CoG came out at 110mm. Way too far aft!

I was able to knock out the lead shot nose weight after cutting off the nose to allow my drift direct contact with the shot.
I filled the inside of the nose with fiber and epoxy to allow me to maintain the FAI nose radius.

I was able to file down the wing tip bulge with a file. This really was only a 1/2mm bump on the bottom of the wing at the tip.

I did notice a few other issues. One was that the aileron was free. It looked like the arm broke where it was thinned to clear the servo cover (hanger rash). I also found that there wasn't enough upward flap motion, heck I didn't see enough downward flap. This brings me to ask why Aeroic didn't provide jelly bean servo covers. I can't see how one was to get proper control surface motion with the control horns provided without jelly bean covers. I think the original builder was trying to build the model with the components supplied. This lead to the traps we see.

If the rebuild keeps going this good I might upgrade the KST 135 to X10 mini to allow the use of 7.4v (native). This was to be a sport ship. But it might become another F3F racer!

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Jelly bean AND flat servo covers now included as standard.

As to the flap - Konrad I have told you before about landing inverted...Not Recommended.

Seriously though, all models are now fully assembled, tested and 'tweaked' if needed before shipping.

Doc.

 

[Konrad]

Roll Roll to get those long thin sexy wings up on knife edge!

Doc, what is the recommended CoG for this model? (I see where Jonathan Wells set his CoG at 100mm and said it still pulled up out of a dive)

To be clear this is a dated product and not what we see today from Aeroic

 

[Doc James Hammond]

99 mm in the manual was on the conservative side.
I used 95mm for a more responsive setup.

Doc.

 

[Konrad]

From the LE?

 

[Doc James Hammond]

From the LE?

 

[Konrad]

Am I reading that right? You start at 99mm and agree that neutral trim is a bit aft. But for a more responsive ship you like to place the C0G a bit forward at 95mm.
Generally I find that as I move the CoG aft the more responsive the elevator is. I do notice that ailerons start to act weird if tail heavy (this is a stall thing).

 

[Konrad]

Maybe it wasn't as clear as I thought. I stuffed the nose with fiber and epoxy to allow me to sand to the FAI nose requirements. That epoxy blob does not meet the FAI nose radius!

 

[Doc James Hammond]

Am I reading that right? You start at 99mm and agree that neutral trim is a bit aft. But for a more responsive ship you like to place the C0G a bit forward at 95mm.
Generally I find that as I move the CoG aft the more responsive the elevator is. I do notice that ailerons start to act weird if tail heavy (this is a stall thing).

Sorry Konrad - I'm arse about face, as my dad used to say.

Start at 99 then go back. I'm pretty sure I had mine between 105 and 110mm

Doohhhhh.

Doc.

 

[Konrad]

Ok, I'll place the initial balance with Woods metal at 105mm. I'll then add loose weight to place the maiden CoG at 99mm

 

[Konrad]

Anybody, @Chris ,know what size ballast slugs the ballast tube is to use?

 

[Chris]

I have no idea. Maybe half inch Copper pipe?

 

[Konrad]

Now that’s an FAI nose! In top view the radius is to spec+ a bit. In side view you can see a bit of a gap indicating that the radius is larger than spec.