Mefisto build (BLEJZYK)

[Glenn Beer]

Depends on construction. Keep the loops tight, and make that last twist just right, and putting it on and off will be tighter than your current plastic clip. Did I mention it should be music wire.

Edit: the sample in the post is actually quite tight. I had to use a pair of needle nose pliers to slip the second loop in place after the horn.

 

[Konrad]

Bedding the wing, I've seen on the web that this has caused some angst. That is folks are reluctant to bed the wing to the fuselage, thinking that it is an indication of some kind of incidence mismatch. I like to bed my wings as it adds stability to the fuselage and wing connection. It also adds efficiency as there is less of a "pressure leak" from under the wing into the fuselage (read less drag).

Of note my wing overhangs the factory wing mount by about 8mm. The manual says to overhang the wing the amount of the leading edge. I just slid the wing forward until the bottom of my wing made contact with the front of the OEM wing bed.

All the best,
Konrad

 

[Konrad]

Spent four hours flying the Mefisto at Mussel Rock in 10mph to 14mph winds. I have to say that I still can't wipe off the grin! She flew best fully ballasted! Today the whole flight envelope was better with ballast. Stalls are looking a lot better than at Sunset Beach. But I think I over corrected, as the right wing sometimes let's go first. I still have a problem with the V tail mix ratio. (I just hate going into programs to straighten things out). I also need to add some color to the bottom of the wing.

Guys when they are back "In Stock" and you are looking for a light to moderate lift ship that won't break your budget this is the model to get!

 

[Konrad]

Flew the Mefisto again for a few hours. It really is eerie how quiet the model has become with the wing bedded to the fuselage. It has lost a lot of that swoosh we love to hear so much in our high performance gliders. But on the upside it is an indication that there is less drag.

I’ve removed most of the aileron differential and now have an acceptable roll rate. Other than at low speeds I don’t see much if any adverse yaw. Yes, at low speeds it is there but that is why we have a rudder.

I made a dozen or so landing at Mussel Rock over the ice plant carpets. In the 16mph winds I could park the Mefisto. In crow I could do the classic stair step landing moving forward to loose height fly backwards to regain some ground and repeat until I’ve landed. Some might say this is dangerous as the ship is flirting with ground turbulence for a lot longer than the lawn dart style of landing.

This is true, as I did catch a wing tip in the sand and cartwheeled on one landing. I’m happy to say that the one piece wing with the "fiberglass spring” center section held up fine. And much to my surprise there was no damage to those sexy wing tips! It needs to be said that I was carrying full ballast when she cartwheeled. I’m ashamed to admit it that I lawn darted into my backpack (this is actually a tackle box). I hit the Mefisto right on the wing root leading edge and fuselage junction. This brought the Mefisto to an abrupt stop! Again the Mefisto showed how strong she is as there was no damage.

To give you an idea of how capable the Mefisto is. I had three of my moldies (carbon slippers) and never pulled them out of their wing bags! To be clear the $180 Mefisto can’t fly as well as some $600 carbon ship, but she comes real close in these light to moderate winds. Then there is the comfort of flying a $280 all up model as opposed to the $800 all up carbon ship!

I really need to get Wayne to bring out his light Mefisto and have a fly off at Tic Point!

All the best,
Konrad

 

[Konrad]

I just got back from flying my Mefisto, love it! Make sure you keep track of the number and placement of slugs. On one flight I miscounted the number of slugs and spacers I had installed. When I threw her off the cliff I felt the slugs slam into the back of the ballast tube. Much to my surprise the tail-heavy Mefisto did not snap. I never let her slow down or fly backwards. I also made the best landing of the whole day in that trim condition, to my surprise. It is amazing what fear can do for one's flying skills!

The S6063 airfoil really showed how great it is. I had installed 7 of the 9 ballast slugs, so I was effectively flying tail heavy with 2 slugs missing from the front of the ballast tube. I need to mark the nose with a "9" to remind me that the slugs and spacer need to add up to 9. For some unknown reason I thought the ballast tube was limited to 7 slugs. When I felt those slugs slide aft I realized how wrong I was!

All the best,
Konrad

 

[Konrad]

I have said that each flight is a chance to improve on the trim of a model. Even after many hours of flight time I’m still trimming the Mefisto. The latest trim has been lateral balance. To get both wings balanced I had to add 4 brads to the LE of the left wing. That actually means that the wings by Blejzyk were well balanced. This weight will tell me which wing to add paint to achieve an asymmetric look. This is to help me tell left from right in flight. It also tells me which wing to sand more to get my desired finish.

I’d also like to show how strong the light fuselage of a Blejzyk kit is. I hit a concrete drainage ditch hidden under a lot of ice plants. I hit this concrete fully ballasted at 1.1Kg. The damage really was slight. I know that a lot of the strength came the properly glued in ballast tube. But it still needed to absorb the force from 470 grams of ballast lead. Now I need to make it clear that the fuselage never was intended to deal with this kind of force. So if adding ballast tubes make sure they are properly supported. In any future ballasted Blejzyk fuselages I will be adding carbon tow to fill out the wing fillet radius. This is how I repaired the damage.

All the best,
Konrad

 

[Konrad]

Reading this thread I see I omitted a very important process step. Now I’ve been building toy airplanes since the late 60’s, OK 1969. With the Blejzyk kit I just learned a new to me process. With thin veneer wood sheeting Blejzyk has you under cut the veneer by crushing the foam for a few millimeters as shown on the top wing panel. What this allows is the formation of an epoxy bead under the veneer that spans the joint. This makes for a much stronger joint! If making a face (butt) joint with the wing prepped like the bottom panel there would be little glue actually bonding the panels together. (Note; any glue on the white styrofoam adds NO strength to the joint). After the joint cures a follow up fiberglass bandage will be applied on top of the veneer. This wing is of a stress skin design, there are no spars. So all skin joints need to be well fitted and have some fiber running across the joints. Here Blejzyk is using fiberglass. I’ve seen some guys omit this glass as it interferes with the staining of the wood. DO NOT OMIT THIS FIBERGLASS!

All the best,
Konrad

 

[Wayne]

Just thought I would add this..
I have the Blejzyk Fen, a 60" thermal rudder elevator ship. It arrived with a little shipping damage, so I brought it home. I have glued the butt joint as described above and am not planning to add any outside glass as my goal is to keep the plane super light. I am pleased with the wing strength as is.

Just thought I would add that thought. I have not flown it, so it may be a horrible ideal.

 

[Konrad]

Hum, well I understand wanting to save weight. But the main wing joints Isn't where I'd omit strength (sorry save weight). I'm sure for most thermal flying a good bead of epoxy on the inner skins will be fine. What I have concerns about is the loose nut on the sticks. I know I would be doing loops and rolls so I'm not sure how the wing would hold up at the higher "G" loads. Also I know what my landing often look like! Grabbing a wing tip and ground looping would surely break any of my non-reinforced dihedral joints.

I don't think the omission of 2 or 3 layers of 1 inch wide 0.6 oz glass is worth taking on the added risk. Even with a free model I'd add the glass.

 

[Wayne]

Yeah, after I hit send I started to think I may add a circle of glass on the bottom where it is harder to see. Would give me the positive G strength needed for almost no weight. LOL

This will be a very light weight plane with a tiny lipo for power. Goal is a plane that will fly in very light slope lift, and that is it. Wind picks up other planes get flown.

You know me, I'll probably never get it done. On the plus side, I did start cleaning out my garage this weekend. I really want to be able to build out there again, it is been pretty bad for about 6 months. I have multiple gliders mid-build, a half built utility trailer, and a mid-built International Harvester Scout II all taking up space in a 2 car garage.

 

[Konrad]

Yep, I too would concentrate on the tension failures (bottom of the wing).

 

[Konrad]

I suffered an in-flight radio failure after hitting myself in the chest. (I think the battery came loose or an antenna pulled out). My Mefisto took a 150 foot nose dive into the wet sand. I'm impressed at how well the light glass work, that is the fuselage, is holding up. The damage was actually a lot less than what she suffered hitting the concrete drainage ditch. Actually only one of the repaired breaks opened up in the wing opening area. The nose and tail boom held up fine.

The wing is also holding up well. I'd have thought that those tips would be toast by now. But they are holding up fine, even against my cartwheel landings!

The composite leaf spring I added to the center section is working fine. But I don't think it really did what I wanted. That is allow the Mefisto to be a high wind ship. I've flown her in 40 mph wing at the "Slot" and can say she is real fun fully ballasted. But at those speeds and weight the wings often looked like a sine wave!

I think Wayne is correct to leave the Mefisto as a light wind ship. She responds to ballast just fine. But maybe limit it to about 200 grams of ballast. If one needs much more than this it might be time to bring out your heaver wind ships. She flies fine with the full ballast of 470 grams. But that is about the upper limit. I do think it was worth the effort to add the ballast tube, as I do love the versatility and I think it adds a lot of strength to the fuselage.

So far the only hit I have against the Mefisto is that my trailing edges do distort a bit in the sunshine (not too much of an issue as I often fly in fog). Easy enough to straighten out with an iron set at low temp. On my next Blejzyk kit I might think about glassing the ailerons and flaps with .7 oz glass just for some stability. I don't know how well that would work.

I love the wood look when she is next to all that carbon we see on the slopes!

All the best,
Konrad

 

[Konrad]

I’m hearing that some folks are freaking out about having to place the wing on the fuselage bed. This is not a problem as long as one makes a decision and sticks with it. The airfoils used are basically flat bottom airfoils with Philips entry leading edges. So just moving the airfoil (wing) fore and aft will have no effect of the incidence.

As Artur said he encourages his customer to experiment. With my ship I wanted to know where the wing would rest so that I could place the ballast tube properly relative to the CofG.

As this was going to be a “Fast Slope” ship I wanted as much control authority as I could get from the tail. So I narrowed the “V” tail angle to match the high aspect ratio of the Mefisto’s wing much better than the Beechcraft 110° we see far too often! I also lengthened the tail boom 4mm to 6mm by pushing the wing as far forward as I could with an 8mm overhang*. Just eyeballing the setup I feared that the incidence was set up for thermal flying. As I expected to be flying in a very wide speed range, I decided to lower the decalage angle by raising the LE of the Vtail. I figured if I made a mistake the trim correction needed with “UP Trim” would actually be good. As the resulting camber would be assisting the stab in keeping the tail down at speed.

Decalage - Wikipedia

en.wikipedia.org

In the end the Mefisto has turned out to be a great light to moderate lift ship. And much to my surprise rather strong. I feel the only real mistake I made was in the dying of the bottom of the wings.

Your friendly engineering type,
Konrad

* This could be an issue (shorter nose) if one didn't want to add nose weight. As I was using a 5 cell 1300 mAh battery I didn't think I'd have to add much if any nose weight. Flight testing proved this correct.

 

[Konrad]

Elsewhere I’ve been accused of going overboard. ? Maybe so, but in my threads I not only try to show what I do but explain why I did what I did. If the thread is a build thread I then try to show what worked or didn’t. I also try to show any issues I may have overlooked.

To the “V” tail angle I changed it to 99° as I wanted a ship that could track well through a loop or a pylon turn. Historically “V” tail have lacked directional control. When I see 110° I think the designer may not have given this angle much thought. I know the "V”-tail angle is highly dependent on the aspect ratio of the wing. I also know that there is an inverse relationship for the need of vertical fin area and dihedral when looking for directional stability.

As I knew I wanted to lower the dihedral to get a more neutral feel on the slope with the typical cross winds. I knew I’d want more fin area as a result of lowering the dihedral. This and the fact that I think 110° is too flat for the long wings and short fuselage, I increased the fin area by bringing the inclusive “V” tail angle down to 99°. Was this needed? NO, there are plenty of Mefistos flying just fine, even great at 110°.

I will say that my Mefisto has the strongest “V”-tail rudder response of any “V”-tail I own. Well, she is second only to the DJ Aerotech Chrysalis F3-RES. But the F3-RES class is a rudder elevator class, and one would want a very strong rudder response with that class of glider.

As to decalage, I would add a 0.7mm shim to the front of the LE of the “V”-tail mount with the S6063 airfoil. (Note; that the “V”-tail actually pivots mid span on the fuselage mount). This is because the S6063 airfoil at speed does not need much incidence. Because the tail boom will whip on hard landings this will place a lot of load on the “V” tail glue joint. I would add this shim during the build because one should glass the “V” tail with many layers to make a solid mount. With a glassed on “V”tail one really doesn’t get a good opportunity to try to re-shim the “V”-tail as part on one’s flight testing.

If one wants to experiment with the decalage a bolt on tail might be a nice option.

Your friendly engineering type,
Konrad

 

[Wayne]

LOL - I knew you would read that posting. Just being honest, I like your build and the details. I shared the link with the other person as he is an engineer type just like you. I figured he would enjoy it, and he did. That is the fun of building, you get to do what you want to do!

 

[Konrad]

I have no issue with what you posted.

Yes, I do have strong opinions. And I do try to incorporate my experience into my builds. This is why I often don't like ARFs as they are, often by their nature, aimed at the lowest common denominator (cost and the general expectation of the masses).

Not sure I read that he was an engineer. He did say he suffers from OCD. Engineering is the science of compromise. For an engineer with OCD that would be hell.

I too hope this thread has helped him and others.

All the best,
Konrad

 

[Wayne]

Engineer like.. LOL Technical writer I think he said. Usually means he worked with you engineers so much that his brain is now warped. ??

 

[Konrad]

Hum.

If he had to take my words and try to make a cohesive set of instruction, I think things would be more than warped.

 

[Konrad]

I’m impressed at how much strength the ballast tube adds to the fuselage. In my last 150' nose dive into the sand I failed to notice that the front of the ballast tube had come loose. I repaired what little damage I did notice and went back to flying my Mefisto. Well, I again had a less than graceful landing, but not too bad. I was stunned to see that the fuselage had torn! And this was with no ballast on board!

Giving the airframe a close examination I found that the front of the ballast tube had come loose. It was difficult to see this as all the parts still fit well. I noticed the de-bonding of the ballast tube as I was flexing the fuselage trying to realign the tear.

I can only assume that this de-bonding of the ballast tube happened with the 150’ dive she suffered earlier in the week.

Well I repaired the damage by grinding out my previous carbon lay up in the wing fillet. I then reapplied as much carbon tow as I could into the fillet spanning both wing hold downs. I then re-glued the ballast tube with low viscosity epoxy (heated up) to make sure all the cracks were filled.

I have to say I’m a bit surprised at how much weight my Mefisto has gained since her maiden. While carbon may be 10 times stronger than steel for the same weight, it is still heavy. With the repairs and trim weight added for lateral balance she now weighs 752 grams empty. The weight gain has NOT had any effect on the flight performance as it has all been very close to the center of gravity. At my slopes she is actually flying better and better with each outing.

All the best,
Konrad

 

[Konrad]

Developing a slight problem with the wing hinging. As a result of humidity and temprature the exposed wood of the aileron and flap pocket are warping. Easy enough to fit with an iron. But to keep the area a bit more stable I would recommend that the wiper pockets be sealed with water based urethane.

I'd like to report that the Mefisto is almost as good a light lift ship as the Dream Flight models. Earlier this morning I was flying my Mefisto in very light lift. Actually thermals rather than slope lift. She actually flew rather well! In fact she held her own against some of the foam DLG that we saw out on the slope.

All the best,
Konrad