Soaring USA gift certificate (Strega purchase?)

[Konrad]

Ok, Hank here is what I’ve done to repair the wing. I opened up the seam with tooth picks. I then forced an epoxy Cab-O-Sil mixture into the seam with a broken APC prop blade. Clean up the overage with an alcohol soaked rag. Tape the seam shut. Place the wing with the seam down so that anything in the wing flow to the seam, and hope the epoxy cures! I’ve included a photo to show that the process is not neat, it is messy!

All the best,
Konrad

 

[Konrad]

I’m trying to show how different the two ways to hold the Multiplex connector look. The yellow fuse is of the Strega and the white is on the Sanda Mach II. You can see how much of the connector is outside the fuselage of the Strega. This isn’t a good of bad thing, just different.

I’m also trying to show how the servo tray might look inside the fuselage. I’m also showing that I like to use some glass cording saturated with epoxy to aid in bonding the servo tray to the fuselage. I also hope you can see that I’ve filled the space between the ballast opening and the fuselage with epoxy and Cab-O-Sil. This was a process discussed by Doc in this thread. It really did help stiffen the fuselage on the Mefisto!

Mefisto build (BLEJZYK)

Yes, that was an error I made, no key for the back of the slip on nose cone. I had to adjust with some tape. Lesson learned. Looks super nice, glad you got the glue to cure. I remember gluing on the nose on mine, that is a big step!

forum.alofthobbies.com

So it looks like all I have left to do is make up a set of push rods. Find the mass needed to get the CofG to 115mm aft of the LE and then fit this into the nose of the fuselage. Write the model program, flight test redo what ever the flight test shows to be a problem. Should only take a few hours. NOPE I know better!

We all know that the last 3% of a job takes 25% of the time!

All the best,
Konrad

 

[Konrad]

I’m happy to say that all the epoxy mixed today has set. Now I'm waiting to see if it reaches full cure by tomorrow morning.

Now I’m about to venture into areas I know nothing about: airfoils!

As I recall 20 to 30 years ago that the focus on computer generated airfoil was on minimizing the drag from the separation bubble at higher Cl values. Now in the last 10 to 15 years I think the focus has been on minimizing the drag at low/ very low Cl and letting the snap flap (variable camber ) add the need camber at higher Cl values.

Assuming this is true, what was the philosophy for the airfoils used on the Strega? I ask as I’m writing the radio program. I generally like to have my snap flaps (camber TE) set to have very little movement for most of the elevator stick movement. This is to try to keep the ship dampened and not twitchy as I make small elevator correction. As I add more elevator like in the turn I want the TE to drop allowing the airfoil to develop the much needed camber. I think the guys call this a High Exponential on the snap flap (dead near the center of the elevator stick with it coming in late and fast as the elevator is pulled. I’m thinking of allowing the TE to flap to drop about 3mm for the flaps and 2.5mm for the ailerons/ 0.5mm rigging washout to help keep from snapping out of the turn.

I’m open to suggestion as this will be my first F3F radio set up.

All the best,
Konrad

 

[Hank GB Z]

Konrad,


The repair looks good. Hope you can still make the races but don’t rush it.

Hank

 

[Konrad]

It is bad form to let racing interfere with one's test flight program. I should know I do it all the time!

All the best,
Konrad

 

[jvaliensi]

I bought 3 different kits from RCRCM over the past two years and had friend that got one in the same period. We did not experience the quality issues that you unfortunately did.
I would recommend get their airplanes in carbon and ordering a color that is not in stock so they have to make it for you.
Issues:
Weak fuselages - I broke them all except my pure sailor Tomcat fuselage.
I broke my E-Tomcat fuselage twice! One time from a tail-whip landing, and the repair job was crap and it broke again.
Tomcat EVO - top of the wing was not smooth, mine had a very fine crease along the spar. I destroyed the air plane in an F3F race. It was put back together, but the repair job is so aweful that it is going in the bin after I strip it. It was a good flyer. The same hack that repaired my E-Tomcat fuselage.
RCRCM 300 - this is a real bastard of a sailplane. It is huge, the wing cord is +12" It needs about 5lbs of ballast to go fast. My surfaces flutter due to loose linkages. I cracked the fuselage in front of the wing from a series of lawn-dart landings. I fixed it, so it is good.

A sailplane buddy recently got a E-Tomcat in carbon. He stuck the servos in the tail. (I have 1-2 ounces of lead in my tail) So, far he has had good success with it and likes the way it flies. It's a Dr JH design and RCRCM didn't F- it up.

I wouldn't get any that are in stock at Soaring USA, they are too old and there are potential quality issues. HobbyKing is stocking the Tomcat now, I bet these are okay.

 

[Konrad]

I'm happy you have gotten at least one usable ship.

While my two are from 2012 or earlier I can say that giving a cursory looking over of the new products, I still see much the same issues. The lay up of the fuselage is very poor. There is inadequate material aft of the wing TE. The part lines are mismatched, the fibers that does go across the part line often don't lay down properly with the mating side.

I don't like the geometry of the canopy openings. If using a non-flanged opening there should be stiffening materials in the lay up (carbon) around the opening.

That 60mm wooden servo tray supplied in the kit is again a bad joke! As you can see I've tried to use my servo tray and ballast tube to stiffen the nose. As supplied the nose will not survive much past the flight testing stage. And other than a perfect landing I don't think the fuse will survive even if ballasted to only 60g/ square decimeter.

The beauty of a molded ship is in the fidelity of the airfoil. And here RCRCM has fallen real short! Again every set of wings I've seen I can see/ feel the sub-structure in the skin surface. I also haven't seen a smooth hinge line. Now these were from models I've seen at the slope. I don't really know their history in detail. But looking at Vladimer's, Sanda, Samba models and just about any other manufacture's models one can see the quality deficiency in the RCRCM product line, even of those made today.

Now I hope RCRCM has improved their materials like the use of higher quality epoxy that is much more stable. That spoiler action form the shrinking epoxy really did suck the enthusiasm from this product.

The lack of a LE epoxy bead was just more fuel on the fire. Yes, there was a very very small indication of an impact point on the LE, but to have 1/3 the wing separate at the LE really was shocking! I'm glad this LE failed before I flew my Strega.

These are not meant to be competition ships or even good sport ships but I would expect them to be safe ships. Of the quality issue I can see and test for RCRCM falls way short in this regard. I have reservation that the spar and support structure really are adequately manufactured. I will need to do some sandbag testing prior to loading her up for racing. I'll also have to flight stress her clear of any bystanders.

I really have lost all confidence in the RCRCM product.

Yes I was warned about RCRCM and my demands for quality. So I entered these projects having a vague idea of what I was up against. But it was in the actual details and working with the products that all hope was lost.

For that sandbag test does anybody have any data as to the "G" loads we see in F3F? I'm assuming it is about 15Gs.

All the best,
Konrad

P.S.
What am I not seeing?
A RCRCM 2.5 meter Tomcat for $500 and the 2.4 meter Sanda Mach II for $500. Ok, the Mach II costs 10% more.
https://hobbyking.com/en_us/tomcat-...kbW0VXuxlWD5MFwRs5CgIFYgsCn3C-VwaAkAsEALw_wcB

https://alofthobbies.com/mach-2-fiberglass.html

 

[Konrad]

The poor performance of the RCRCM nose is why I go through all the effort to try to have the servo tray offer as much support as possible. Take a look at what RCRCM supplies with the Strega model, what a joke and a poor one at that! Then look at what I've done to stiffen the front end of the ship to survive the landing that these ships are subjected too. RCRCM does not understand how to integrate structure to do more than one thing. Here I'm using the servo tray as ballast stop, side support for the fuselage just ahead of the wing, as a stiffener for the canopy opening, and yes even as a servo tray.

I try to build my ships to last. Not be an excuse to buy another one! Planned obsolescence or product failures is not what I think of as exemplary engineering.

All the best,
Konrad

 

[jvaliensi]

It sure sucks to spend money on poor quality. I'm putting together a Shinto and it is the nicest sailplane I've ever seen. It took about a 1/2-hr to install the wing servos, the IDS was in place and ready for the the servos.

I think you will have success with your project.

I don't think F3F will get to 15g's. I see the fast guys down here and their wings are not flexing that much in the turns. But I'm sure my landings are above 300g!

 

[Konrad]

A wiseman once told me; “Quality pays it does not cost"! Whenever I come across a product so poor as these Stregas his words ring true in my ears.

Pultrusion carbon rarely has any fibers interwoven between the main fibers. As a result it is rather easy to split pultruded carbon shapes. The push rods in the RCRCM Strega as pultrusions. To keep the threaded rods from splitting the rods I’ve added an aluminum collar to both ends of the push rod. Prior to inserting the threaded rods I did grind some notches along the length of the rod to hold the epoxy.

I’m a bit perplexed as to why RCRCM didn’t use longer control arms (horns) on the V tail. This would help alleviate any flutter and allow for a higher resolution from the servos. I think I’ll make a 3mm or 4mm longer set and try them out on my second red and white Strega.

The good news is that I’m now finished with the manufacturings of system parts. All I have left to do is add the nose weight to reach the 115mm balance point. Fit in a receiver and train the wires where I want them to go. I think I’ll be able to test fly her at the Slot on Sunday. But I don’t think I’ll be racing this Strega on Sunday.

One Strega down one more to go!

All the best,
Konrad

 

[Doc James Hammond]

Well this put another nail in the coffin of Strega! While cleaning off my epoxy finger prints I noticed something didn’t feel or sound correct with this wing. Yep, the top and bottom of the wing had separated. This was because there wasn’t much if any glue bead at the LE bonding the top and bottom together!

This is a different failure mode than what we saw with the Sanda mini Mach. In that failure we had a localized shock induced de-lamination of the top composite skin. Here with the RCRCM Strega we have to top and bottom of the wing separating!

mini Mach (Sanda Models)

One of the benefits (or curses) of having Aloft Hobbies as my local hobby shop is that I get to go through customer returns. I went in to Aloft Hobbies looking for a 60” racer other than a Sunbird and walked out with a customer returned Sanda Mini Mach. I’m still in need of a good value 60”...

forum.alofthobbies.com

I fear that this has put an end to any hope of getting this model ready for Sunday’s F3F race at the Slot!

If you guys take anything away from this thread it is DON’T BUY AN RCRCM PRODUCT! It just isn’t worth the cost or the time to correct the issues. The issues are systemic to the build. There is no point in trying to make a silk purse out of a sow’s ear!

Pissed off,
Konrad

P.S.
Full discloser time!
While prepping the wing for repair, I did find an ever so small an indication that there was impact damage to the LE. Still RCRCM should have provided a sufficient LE bead, as is there are spots where this bead is less than 1 mm thick. The impact damage doesn't show up on the camera, just yet. After the glue cures the impact point might show after I block sand the area.
View attachment 2364

The two things that pissed ME off - as the designer are that 1) they modified the design by adding incidence - without telling me "After all a model can't fly without incidence" Unquote - they said.

And 2) It honestly takes the same time to make a moulded model well, as it does to make a crap one. "But if we make weak models the flyers will break them and then buy new ones" Unquote - they said.

You can see why I said sayonara.

Yaaaahhh!

 

[Doc James Hammond]

A wiseman once told me; “Quality pays it does not cost"! Whenever I come across a product so poor as these Stregas his words ring true in my ears.

Pultrusion carbon rarely has any fibers interwoven between the main fibers. As a result it is rather easy to split pultruded carbon shapes. The push rods in the RCRCM Strega as pultrusions. To keep the threaded rods from splitting the rods I’ve added an aluminum collar to both ends of the push rod. Prior to inserting the threaded rods I did grind some notches along the length of the rod to hold the epoxy.

I’m a bit perplexed as to why RCRCM didn’t use longer control arms (horns) on the V tail. This would help alleviate any flutter and allow for a higher resolution from the servos. I think I’ll make a 3mm or 4mm longer set and try them out on my second red and white Strega.

The good news is that I’m now finished with the manufacturings of system parts. All I have left to do is add the nose weight to reach the 115mm balance point. Fit in a receiver and train the wires where I want them to go. I think I’ll be able to test fly her at the Slot on Sunday. But I don’t think I’ll be racing this Strega on Sunday.

One Strega down one more to go!

All the best,
Konrad
View attachment 2370

View attachment 2371

The inside of that fuselage looks really sketchy.

Doc.

 

[Konrad]

I think I've address the deviation from design. The fairing looks bad, but it is all about how the plane flies. So I'll take the esthetic hit.

That quote is real obvious!!! I was trying to hook up the control rods only to have control horn drop out of the stabilizer. There was only one or two square mm of glue contact area! Also there was no etching of the aluminum to aid the epoxy in bonding to the aluminum. This was a crash in the making. The OEM RCRCM's making! Guys please pease don't buy products from RCRCM if you value your hobby dollars, your hobby time and your flying partners. They are very dangerous products. Really what does RCRCM think they are doing. Making crap will only destroy ones reputation in the long run. (I'm truly shocked that they are still in business 6 years later)!

Doc, I don't know what your are seeing in that fuzzy photo (above). But yes the fibers joining the fuselage sides are not laying well across the part line. Nor is the fiber holding the joiner receptacles. But what I think you are seeing is my attempt to add material (white gray) to give the alignment pins more purchase. It does look like crap as my skills at building a boat in a bottle are what they should be.

I was doing the final set up making the balance nose weight. My ship needed 112 grams of mass to bring the CofG to 110mm from the leading edge.
Because of the poor layup at the part line I could not make an aluminum foil mold of the inside of the nose. This forced me to try to cast the lead directly into the nose.

I knew of this low melt material, Woods Metal, but I had told myself I'd never pay that much for lead. Well it is expensive for lead but as a solution to a casting problem it is worth its weight in gold. Ok, I'm pushing it a bit!

I put the nose in cold water (to protect the epoxy matrix) and poured the Woods Metal directly into the nose. It looks like there has been no damage to the epoxy matrix. I'm actually surprised and pleased.

All the best,
Konrad

 

[Doc James Hammond]

Konrad - I get a paper cup, put some paster of Paris in - you can also use wall spackle - then put a bit of vaseline on the nose of the plane and suspend it in the plaster. When its dry, lift the model out and you will have a perfect nose shaped cavity.

Get lead shot or whatever you are going to use, and tape it to the assembled model, adding or subtracting until you get it balanced just short of the ideal place. You will have to add a small mount of lead to bring it perfect, but that will leave you a little bit of leeway if you want to put the CG back a little more.

Melt that amount of lead only.

Before you pour molten lead into it PLEASE PLEASE MAKE SURE THE MOULD IS 100% DRY.

If not you will get a lead shower. NOT recommended.

Cheers,

Doc.

 

[Konrad]

My issue is that the inside of most nose cones have no resemblance to the outside. If I use the outside of the nose to make my casting the lead ballast will NOT fit the inside. This is more so when there are large blobs of epoxy and Cab-o-sil all over the inside. Then there is the issue of the fibers that goes across the seams often don't lay flat. This is why I make an aluminum foil master of the inside of the nose cone. It more closely matches what the inside looks like, allowing for a better fit with the balance lead. Now if the OEM used an internal bladder, things would be a lot better and the outside profile would more closely match the inside profile. But that is a technology far beyond the capabilities of RCRCM!

 

[Doc James Hammond]

My issue is that the inside of most nose cones have no resemblance to the inside. If I use the outside of the nose to make my casting the lead ballast will NOT fit the inside. This is more so when there are large blobs of epoxy and Cab-o-sil all over the inside. Then there is the issue of the fibers that go across the seams often don't lay flat. This is why I make an aluminum foil master of the inside of the nose cone. It more closely matches what the inside looks like allowing for a better fit with the balance lead. Now if the OEM used an internal bladder, things would be a lot better and the outside profile would more closely match the inside profile. But that is a technology far beyond the capabilities of RCRCM!

Aha! OK works well on my planes...hehehe.

Doc.

 

[Hank GB Z]

Konrad,


To expand on Docs idea about making a mold. Make a wax positive of the inside of the nose, then use that positive to make the plaster mold of the inside nose like James suggested. Use mold release everywhere.


Hank

 

[Konrad]

Another issue with making molds is that one needs to be cognizant of the draft angles. With all the surface discontinuities in these RCRCM products, any rigid/stiff mold plug will be permanently held captive in the nose.

 

[Konrad]

More detail of the tail cone clearance for the control horns.

Not sure one wouldn't needed to have done this even if the stab incidence was left as delivered from the OEM (RCRCM).

All the best,
Konrad

 

[Doc James Hammond]

More detail of the tail cone clearance for the control horns.

Not sure one wouldn't need to have done this even if the stab incidence was left as delivered from the OEM (RCRCM).

All the best,
Konrad

View attachment 2375
View attachment 2376

The first ones were not like that Konrad - they were quite an elegant snd small machined design similar to the ones I will be using on the Redshift II.

Doc.