Mirage Build

[erich]

It's Thursday, great day to start building a new glider. Had a Mirage kit from the 80's, from which I built the wings, about a year ago. Either the kit was badly made or time had warped some of the balsa, at any rate nothing seemed to fit well. Was going to straighten it all out with sandpaper. Recently looking at the semi finished wings, realized it would take a lot of aggressive sanding to clean them up. And these wings are pretty fragile to begin with. So scrapped them. Found Isthmus had a short kit, and got one. Comes with ribs, and all the wing joiner pieces, plus main fuselage parts. The plans I had were pretty old and yellow, got a new set from one of the plans vendors (RCM, or Flying Models). Anyway the short kit came in a carton, that would make a perfect flight box (been using a plastic grocery bag???). Sooo had to build plane to empty the box, besides it's a great plane (not to be confused with company of same name).

From what I remember of my first attempt at this plane, it's not a simple build, as would appear at first glance. The airfoil is definitely not a flat bottomed one. Certain places need to be supported, during wing construction. Part of this is taken care of in short kit. The kit has tabs at TE of each rib to keep them at right height, and helps set the washout also. Soooo come Friday will start plane.

erich

[slozuke]

Looking forward to your build posts! I am a big fan of the Mirage having built 2 of them some years back. Mark @ Isthmus is working on a full kit for the Mirage that should be ready sometime soon.
I am curious to see what you do for the main spar to beef it up some and the wing joiners. One of my last planes was lost due to a wing tip coming off in flight. Although the plane flies remarkably well with a missing wing tip , just no turns with full opposite rudder!! My other plane was lost due to the main spar breaking during a tapping launch on a winch.
I thought about using CF in place of the spar caps top and bottom but last time I tried to get the correct size CF I couldn't get any. Once Mark has the full kit ready I plan to get one of them and address the spar issue at that point.
I hope you plan on posting pics of your build.
Thanks,
Brian

[tw126a]

You know we all enjoy your builds, Erich. I have a Mirage kit waiting to be built although I won't tackle it anytime soon, this will be great for reference.
Tom

[Mark Miller]

The prototype laser cut parts are done and I should have htem next week. I can then check them against the new CAD drawn plans and make sure things fit. Once that is verified I can start putting together the stock materials and put the kit on the market. I am very excited about this one guys. I will keep selling the short kit along with the full kit for those folks who like a more scratch built experience.

The Mirage is a great design and can fly well in a wide range of conditions. My old buddy Augie McKibben finished a short kit last winter with a single blade spoiler in the center panel that weighed 37 oz. RTF. You can fit 20 oz. or so of ballast in the fuselage under the wing which makes it fly very well in windy conditions. The semi symetrical airfoil sure works well. Part of the trick to making a nice Mirage is to not over build it and add weight in the wrong places. Build the tips stock and they will be light and help the plane turn and respond easily. I can't wait to see this thread as it progresses.

Mark Miller
Isthmus Models

[cynjon]

I'm looking forward to this build as well...I debated for quite a while between the Mirage, the 3m Scooter (which erich recently completed) and the Isthmus Models Mistral (which I ended up buying). I had planned to build the Mistral as a winter project, but it looks like I'll be spending a few months in Iraq instead. If Isthmus Models has a Mirage kit by the time I get back, I'll definitely be interested in picking one of them up as well. I doubt I'll be able to follow the build thread closely, but I'll definitely be checking it out when I get back. I'll be in touch, Mark!

Keep 'em coming erich!

[oracle_9]

I am also eager to watch the progress of this thread too.

Erich built a 3m Gnome? Is there a build thread for that too, because I cannot find it. That is probably interesting as well.

Merry Christmas, Happy Holidays.

[erich]

cynjon

What I do when I can't make up my mind between two different planes is: I get them both. Course then you got the problem which to build first. Can tell you that building 3M Scooter fuselage is more complex than Mirage. While Mirage has the more complex wing (IMO).

PS: believe cynjon meant 3M Scooter not 3M Gnome, a very similar, and from what I've heard, a good plane also.


semper fi
erich

[cynjon]

PS: believe cynjon meant 3M Scooter not 3M Gnome, a very similar, and from what I've heard, a good plane also.


semper fi
erich

Oops, sorry! Yes, I meant the Scooter build, not Gnome...

BTW, technically it's Friday now...shouldn't you be building? :p

[erich]

cynjon

You're absolutely right. So here is the first step. The plans call for an optional scalloping of the TE edges. This looked like a lot of work. It would however save some weight, and looked cool. So since I got all this time on my hands, got out the whittling knife and went to work. Made a paper template of the scalloping effect. Transferred to TE. The slightly tricky part is: the wood removed gets slightly larger towards the tips. Between each rib the shape of scallop remains the same but is made deeper, the closer to tip. Scallop effect is used on main panel as well as 2 tip panels. Went for the tips first. Couldn't believe it, this process cut the weight of TE in half. Since I had the old plans (all yellow and icky) used them instead of new ones (I checked, both are same). So plans are taped down and TE is made. All before 3:00 AM on Friday. Thank-you cynjon.

erich

[Mirage1]

Erich,

When I built my Mirage I waited until the wing was completed , marked the scallops and then used my oscillating drum sander. I picked the appropriate size drum, dropped the wing over it , turned it on and sanded to the line.

[erich]

Mirage1

Sounds like a good solution. Wish I had one of those. Did it the old fashioned way (read hard), out of necessity.

erich

[erich]

The airfoil used here, tapers toward the TE, on bottom as well as the top. So the ribs all have a positioning tab at the TE to raise rib (tab will be cut off after wing is all framed up and unpinned). This means the TE needs to be shimmed up to meet the ribs properly. Got first 4 ribs, and TE, along with a forward stringer, all pinned down. Glued ribs to TE. Added two 1/8" balsa shear webs using Titebond. Left 1st bay open, as that will take tip joiner box, which will be made after top spar cap is in place.

erich

[Mark Miller]

Where is the Scooter build thread? I remember seeing it but can't find it now. I just put the Scooter in my line up and wanted to see the insides.

Thanks,

Mark

[erich]

Mark

Posted to Scooter thread, it should now be near top.

feliz navidad

erich

[cynjon]

Scalloped TE looks really cool--are you planning to cover the wing with transparent covering to show it off?

I don't have an oscillating spindle sander either, but it almost seems like one of those spindles you chuck up in a drill press would work, as well. I may go that route when the time comes.

[erich]

cynjon

Transparent, absolutely. Probably go with yellow, and maybe orange (never used orange before). Doing it by hand isn't so bad, was able to get all 4 TE pieces done in about
6 hrs. The problem with using a power tool on something as fragile as these wings, one wrong move and you end up making firewood.

erich

[Mark Miller]

For those of you lusting for the full kit I thought I'd post some small copies of the new updated plans for the Mirage. There have been some slight detail changes such as the thickness of the shearwebbing and a bolt on wing using a dowel in front and a nylon screw in the back. I hope the quality of these files are ok.

Mark

[SoCalGliderFlyr]

Get rid of the canopy. That was added by Bill Mueller of Hi-Flight models because he thought all planes should have a canopy. Yes I and Blaine did argue with him.

[Mark Miller]

One of my favorite details of the Mirage is the curve from the nose over the canopy and down the airfoil. Next is the kick up of the bottom surface of the fuselage aft of the wing. Then of course is the offset vertical stabilizer and one sided elevator. There are cool things to look at all over this plane. Changing any of this stuff also makes it not conform to the Nostalgia class rules. Early on I had the rudder without the balance tab but was told it would make it ineligable for the class.

Mark

[SoCalGliderFlyr]

Canopies are made to be looked out of not into. The original Blaine Rawdon plans I have has no plastic canopy. Clearly dated before 1980.

[Mark Miller]

But since they were not published or kitted that way they are not usable as a legal Nostalgia class sailplane. I know, it's not right but that is what is used.

Mark

[Joe Minton]

Hey, SoCalGliderFlyr:

Wanna part with a set of those original plans of the Mirage?? Huh, huh -- Pretty Please??!!

Joe Minton

[erich]

Gentlemen, and I use that word loosely, I will be making a wood canopy, as I hate plastic ones. Don't care about no nostalgic rules, so will have a straight rudder, no balance. The reason, it works better. Other than that will make it as planned, single elevator and all.

Merry Christmas
erich

[SoCalGliderFlyr]

Joe, Plans are cut up. Guess I could try to paste them back together some how. All a bit faded. Think I posted a scan of the title block a while back. Kind of had it in mind to do this with the Mirage as well as the original BoT plans that Dave sold with his hand cut kits.

Guess Bill Muellers canopy will live on longer than Bill did.

[Mark Miller]

Thats one of the great things about this hobby. Like McDonalds you can have it your way. I tried to stay true to the original kit so those who want Nostalgis can have it and those that don't can do their own thing. Erich, It's been about 8 hours since your last build post. Are you slacking? See what happens when you dawdle? We start talking about miscelaneous info.

Cheers,

Mark

[schrederman]

Mark,

I'd like to have a Mirage... I'll be flying in West Texas and Eastern New Mexico, where the wind always blows... When will the kit be ready? I like the canopy... I vote keep it!

Jack Womack

[SoCalGliderFlyr]

He didn't mention the rivits that hold it on...

[erich]

Mark

Too busy reading this stuff. Mark, it's a wonderful canopy, I just prefer working with wood, if possible. Will try and keep that favorite detail of yours, and make the wood to conform to outline of plastic. By the way I now have two plastic canopies, if anyone wants one, speak up. You know what it really is I don't like about the plastic canopy....just to darn hard to get the monokote to stick to it. Now with wood.....

erich

[erich]

Finished the shear webs. Bay 2 & 3 have 1/8" shears, 1/16" for bay 3 & 4, and 1/32" in 5 & 6. No webs in rest of bays. Put T-pins under, LE bottom stringer (they act as spacers), to raise stringer to meet the upward curve of forward ribs. Used thin CA on stringer / rib joints. Used top spar cap to get proper height of webs.

erich

[SoCalGliderFlyr]

You shouldn't pin through the spars.

[erich]

I wouldn't and didn't.

erich

[erich]

Cut slot in tip root rib, for the joiner. Glued in ply, tip joiner, using epoxy. Used a small triangle to make sure joiner was square to table. Added top spar cap with Titebond (epoxy in area of joiner), which means I had to be real fast (Titebond sets up pretty quick). Used my patented, rubber band / t-pin method, to hold cap tight while drying. Building the tip takes a somewhat delicate touch. Everything is light and small, spar 1/8" wide, shear webs down to 1/32". Can't wait to unpin this tip and see what it weighs.

erich

[erich]

Added 1/32" ply shear webs to tip root. These form the box around joiner. So used 30 min epoxy here. Will also wrap this with kevlar, later.

erich

[Mark Miller]

All,

I am not sure if it is mentioned in any of the Mirage building articles but, I'd reccomend using 1/8" square Basswood for the turbulators in the center panel. It adds a tad more weight but sure increases the durability of them. Balsa ones tend to get cracked easily with a thumb or rough landing. Use balsa in the tips. It doesn't have the same issues and needs to be kept light. Also, the pre cut sticks tend to be made out of harder balsa. If you find some light 1/8" sheets and cut your own you can get lighter material and save some weight.

Mark

[erich]

Used spruce for some of the turbulators, on main panel.

erich

[histarter]

All,

I am not sure if it is mentioned in any of the Mirage building articles but, I'd reccomend using 1/8" square Basswood for the turbulators in the center panel. It adds a tad more weight but sure increases the durability of them. Balsa ones tend to get cracked easily with a thumb or rough landing. Use balsa in the tips. It doesn't have the same issues and needs to be kept light. Also, the pre cut sticks tend to be made out of harder balsa. If you find some light 1/8" sheets and cut your own you can get lighter material and save some weight.

Mark
I built my Mirage wing totally stock right out of the kit (all the balsa supplied was about 10 lb+ stock). ;)
I made the tail surfaces conventional, because of needed deflection activity pursuing low lift and tight spiralling. :)
After a couple of years of (sport) winching, the plug in boxes started to unbond. :(
Since the machine was cartwheeled breaking the fuse at the time, I simply shortened the tail boom and added a dorsal fin to rudder and stab to improve CLA relationship and damping. I then made a wrap of nylon and epoxy to correct the wing box problem and the machine, now 20 years old, is still flying (With main spars of each center secion spliced due to lamp post and tree arguments). It is currently being club gorilla winched (carefully). My Mirage was flown in 20 mph+ winds with 20 ounces of ballast (I was leary of adding more ballast into such a light structure, when needed). With your loving care Mark, I would have been able to stuff another 10 ounces, and be able to have used it for some sloping. :eek: :D

[erich]

Have added two stringers, and LE, using Titebond. Did some preliminary sanding. Will shape LE when all three wing sections are done, in an attempt to get all three shaped alike. Also put in the 4 corner braces, with Titebond. Gotta say the ribs in this short kit really lined up well with LE, one of the best I've seen. Didn't have to retouch anything, to get all ribs mated equally, with LE piece.

erich

[erich]

Histarter

Do you have two center sections?

erich

[Mark Miller]

Erich,

You are doing a great job. I can tell it's going to be a nice one.

I thought I'd post a photo of the Mirage from Bill Mueller who owned Hi Flight Models and did the original kit. This was taken back in 78 or 79 above Palm Desert for the RCM construction article. I may just use it for the label on the full kit. I kind of like the old school look for an old school design.

Mark Miller

[erich]

Mark

Only thing comes to mind is.... Wow!! Two beauties.

erich

[erich]

Installed last stringer. Did some further sanding on the TE scallops, to have them blend in with corner braces. With stringers in place wing is starting to look good. Unpinned tip, and tossed it on scale, 1.9 oz. Not sure, but that seems pretty light to me. The monokote will probably weigh more than the structure.

erich

[erich]

Built other wing. Was sorta the same as first, but kinda backwards. These gotta be, relatively, the longest tips I've ever made. Each tip is 3/4 as long as entire, main panel. Next, on to the main event.

erich

[histarter]

Histarter

Do you have two center sections?

erich

Nope, one long spar from tip box to tip box! Spliced 3/4 way from center to the tip left hand side, and 1/2 way from center to other plug in tip. Fractures occured about a year apart! And both were a suprise failure of depth perception!! :censored:

My bob-tailed Mirage took a second place in the first HAM postal contest, beaten by an F3J flown in SA.
It was also used for control in my evaluations of an Elipse with RG-15. (When turnaround was greater than 400 ft away, the ballasted Mirage just couldn't compete - whereas less than 400 ft the Elipse gave out). ;)

[erich]

Started work on spar for main panel. The main wing panel, on this plane, is built as one completely flat section. Held down by either rubber bands or dowel/bolt, method. At first glance wing appears to be a cinch to make. There are however a few areas that need a little more than casual attention. Wooden joiner boxes need to be fitted on either end. From past experience with a Paragon, these boxes can be easily over-stressed. Will need to build these well and with some added reinforcement. A 4" center section that needs to be completely sheeted in and fiber-glassed. Finally the spar will have, unbroken (my addition), full width webs for a span of about 9" in the middle, which will be wrapped with kevlar, as will the joiner boxes.

Have bottom 3/8" spruce cap in place with pins alongside (not through) cap. Made one continuous web for the middle, 9". Had planned on using 3/8" balsa and then 1/32" ply outer webs. But this, wheather a good or bad idea is what I did: Had some nice looking hardwood, so decided to laminate hardwood and balsa to make a stronger full width, center web (and skip the ply outer web). Later on, to reinforce this area, will wrap entire 9" section with kevlar and finally 4 oz glass cloth (as compared to 2 oz recomeded) over 4" of the middle sheeted area. At this point have bottom cap and 9" web in place using Titebond.

erich

[SoCalGliderFlyr]

Ribs should go through the spars. This keeps the LE and TE straight. The shears are designed to butt against the ribs. Laminating a hard center into the shears does little to add strength. Better to cut the ribs back after the LE and TE assemby and add 3/32" hard ply front and back of the spars. Stagger the ends to avoid a hard structural transition. Take one out to the second rib the other to the third or fourth.

I would add 0.014" carbon to the top and 0.007" to the bottom of the main spars. Cut the ribs and shear webs down accordingly.

[slozuke]

I like the idea of adding CF to the top and bottom caps but what about just replacing the caps with CF entirely? If the shear webs were also made thicker as it sounds like Mark is planning with his kits, wouldn't this combination be the strongest? The only problem I can see with this combination is a possible bonding issue with the CF caps and the wood shear webs. Anyone care to elaborate?

[John Walter]

Take a look at the Bubble Dance spar construction. That's how I built my Grand Esprit. VERY STRONG.

http://www.charlesriverrc.org/articles/bubbledancer/markdrela-bubbledancer-3m.htm

Probably overkill for the Mirage. If you overbuild the center section you just change here the wing breaks!

[erich]

Here's my take on the Mirage. It's a very very lightly loaded plane. What makes it that way is NOT overdesigning or overbuilding it. No, one can't expect to do ANY kind of winch launch except with the lightest touch on peddle. I have planes that can do a great zoom launch (Camano to name one). This plane was meant to fly in the lightest of lift, however it does have some legs (slightly semi-semetrical airfoil). If one tries to reinforce the main wing, much, in hopes of doing harder launches, then tip joiner boxes will fail unless reinforced. At which point harder launches are attempted and new weaknessess are found which leads to more reinforcement, which leads to harder launches , etc, etc. and eventually what you have is a Houston Hawk, which although a great plane is not what I'm after. Besides already got one of those.
What I intend this plane for is: hi-start launches on days with very little wind. To be able to get out on the smallest of lift, or to slope soar a 5' drainage ditch. I think of this plane as a bigger and slightly better Gentle Lady. Sooo am looking to make it as LIGHT as possible, and have it get it's strength from being well built (good joints, good glue), with light, reasonable reinforcements (kevlar tow). Not a rant or rave, just an explaination of my view on the Mirage.

Green air
erich

[erich]

SoCalGliderFlyer

If adding a ply shear adds strength, what makes you believe a stronger web in the form of a laminated shear, would not make spar stronger? Isn't a web BETWEEN the caps, More effective than one glued to sides of caps? As far as keeping the LE and TE straight, that can be accomplished by other means (especially with the small number of ribs invovlved here (3)). Many kits have front and rear ribs, near the root area. Are you saying these kits are all designed badly? Adding CF to spars is a good idea, however I am not doing this, cause frankly, I won't need it. Actually I would rather just replace caps with CF strips of same size as caps (as Slozuke states).

erich

[SoCalGliderFlyr]

Carbon straps don't like to stay put on their own. Laminating them to spruce (real spruce not the five growth rings per inch some think is spruce) and then the spruce to the shear web structure is stronger than just the carbon alone. The spruce could be milled down the thickness of the carbon rather than the shears and rib notches.

Besides transferring the loads between the spars the shears stop a compression loaded spar from buckling inward. If the lamination (gluing) is not sufficient the spar will separate from the shears and buckle outward. The wrapping on the BD spar structure is there to stop the carbon spars from buckling outward. Shows concern for their lamination.

As to capping the center each side with ply; the ply is glued to the full width shear webs as well as the spars. Reason for 3/32" is for the five plus laminations. 1/16" is hard to find with five. Usually has three. Also it's one piece not broken by the ribs. I would rather cut the ribs away from the spar/shear webs and insert the ply than to cut the ribs and loose wing alignment.

I have broken a stock center section on an attempted zoom. Still have the wing tips. Built another center and fuse. This was in 1979. Broke the fuse behind the wings with a bad hand launch a few years ago. Need to build another fuse -- just a bit stronger. Don't have the holes in the tip joiners. I concure that building a stronger wing center will require stronger wing joiners.

The Mirage was designed using the materials available and with an understanding of the forces of the launching methods of the late 70's. Was designed to be a lightweight thermal machine with some reasonable legs for getting back from down wind.

Yes I'm saying that the kits with the "broken" ribs are not a good design for home building because of the misalignments that can occur. Laser cutting could mitigate this to some extent. Remember that the Mirage was designed with one piece ribs.

[SoCalGliderFlyr]

Take a look at the Bubble Dance spar construction. That's how I built my Grand Esprit. VERY STRONG.

http://www.charlesriverrc.org/articles/bubbledancer/markdrela-bubbledancer-3m.htm

Probably overkill for the Mirage. If you overbuild the center section you just change here the wing breaks!

Difference between 1979 and now. Also the BD has a much thinner wing.

[Ercoupe Ed]

You can some real nice high quality spruce from Aircraft Spruce and Specialty .
I'll look up their website.
I buy stuff from them every year at the Oshkosh air show.
You might just put their name in your browser and it should pull them up.

[erich]

SoCal

I still use the launch methods of the 70's. They worked then, they work now. I do not build planes for the launch, but for flying. I accomodate the launch to the plane as built.

Do not dispute your build methods, they seem sound, I dispute my needing them and their extra weight.

May all your zoom launches be good ones
erich

[erich]

Ed

Did the google thing and found them, thanks.

erich

[erich]

Added first two uncut ribs. Using Titebond for all web and rib work. Glued top cap strip to center shear and the 2 ribs. To facilitate working on spar, I prop up end of top cap with 6" wooden block. Won't be gluing remainder of top cap until all shears and ribs are in place. To get proper height of webs, will lower top cap down on webs and ribs.

erich

[Mark Miller]

Erich,

You are going down the right path. The Mirage is what it is and will not ever be what it isn't. If you change the design to much the qualities that make it a Mirage are lost. Augie has made two Mirages in the recent past. One was a stock wing with carbon caps, .007 on bottom and .014 on top as SoCal suggested. He wrapped the joiner box areas with Kevlar thread. This is the one in the Mirage build photos I had on my site. It can be winched as you can actually be gentler if you have the right touch than using a high start. if you get a gust of wind or go through a thermal just ease up on the switch tapping.

The second one he built used carbon caps but I forget the size. He used full width 60 PSI blue foam for the shear webs and it seems to work great.

The line you need to balance on is the strength to weight deal. In stock form it does a great job. You can do a few things to make it a bit better but go to far and you have more strength but also more weight. As JAWALTER mentiones you make it to strong in one place and it probably just will break in another.

One more story to make this post even longer is the connection between the Mirage and Bubble Dancer. Mark Drela built a Mirage awhile back and liked how it flew so much he decided to make a modern equivalent. The result was the Bubble Dancer. The other cool connection is that both Dr. Mark and Blaine Rawdon were involved in the human powered flight area. Mark with MIT and their efforts (look at any of Mark's designs and the Daedelous and you see the family ties) and Blaine who worked for Dr. Paul McCready. He did work as builder and crew on the Gossamer Albatross and Gossamer Condor. He did the design work on the Solar Challenger. Then he went on to McDonnel Douglass. He is now a Boeing Technical Fellow in the field of aircraft configuration. His key accomplishments include configuration work on the Blended Wing Body and the Pelican Ultra Large Transport Aircraft. Bottom line is he knew what he was trying to accomplish and succeeded.

http://mrcss.org/pdf/articles/mirage.pdf

Mark Miller

[erich]

Added another web on each side. Wrapped section with kevlar TOW. Used thin CA to hold kevlar in place. While gluing up this section of spar, MADE SURE, with squares, triangles, and a transit, THAT bottom and top spar caps were perfectly parallel to each other. In other words square to building board. Spar is pinned to plans and ready for rest of ribs.

Thanks for the words Mark. By the way I have an unbuilt kit of your Sensor 117. Only problem, can't find the glass fuselage that came with it.

erich

[Mark Miller]

Erich,

I may have an extra fuselage around here. I need one to make a new mold from.

Mark

[histarter]

Here's my take on the Mirage. It's a very very lightly loaded plane. What makes it that way is NOT overdesigning or overbuilding it. No, one can't expect to do ANY kind of winch launch except with the lightest touch on peddle. I have planes that can do a great zoom launch (Camano to name one). This plane was meant to fly in the lightest of lift, however it does have some legs (slightly semi-semetrical airfoil). If one tries to reinforce the main wing, much, in hopes of doing harder launches, then tip joiner boxes will fail unless reinforced. At which point harder launches are attempted and new weaknessess are found which leads to more reinforcement, which leads to harder launches , etc, etc. and eventually what you have is a Houston Hawk, which although a great plane is not what I'm after. Besides already got one of those.
What I intend this plane for is: hi-start launches on days with very little wind. To be able to get out on the smallest of lift, or to slope soar a 5' drainage ditch. I think of this plane as a bigger and slightly better Gentle Lady. Sooo am looking to make it as LIGHT as possible, and have it get it's strength from being well built (good joints, good glue), with light, reasonable reinforcements (kevlar tow). Not a rant or rave, just an explaination of my view on the Mirage.

Green air
erich
Great comments. I built my Mirage primarily for HL (a new trend at the time) and was very successful with it. It did everything better than my GL I carried about 4 oz of ballast most of the time for best results, even though the kit wood was better than 10 lb stock for all balsa. Great thermalling machine! :D :D

[erich]

Mark

Thanks Mark, may take you up on that fuselage.

erich

[erich]

Histarter

Instead of ballasting up when wind kicks in, have usually changed planes instead. Gives all the planes, an equal chance at getting in air. Only plane I ever did much ballasting with, was the Sagitta 900. When I got the Dodgson stuff (Windsong, Pixy, Pivot) I would just use these planes when wind kicked up. They didn't seem to need ballast even in 30 mph winds. That's not to say ballast wouldn't have helped, am sure it would. Would relex the TE on the Windsong in heavy wind and just, handle it, sans ballast. While ballast for contest flying is almost a must, in all the years I flew, have only entered 1 contest. Found it hard to sit and wait for my slot, when great lift was everywhere.

Green air
erich

[erich]

Added most of lower center sheeting (center gets totally sheeted for 5"). Then glued in 3 more full width ribs plus 2 more shears (both the 3/8" full width) on each side. With 8 ribs in place, now have a reference to put in 3, cut center ribs. To align the TE portion of these 3 ribs is easy, just pinned the TE to plans (near the spacer tab) with the spar end butting into spar and tight against bottom sheeting. To align the forward portion of these ribs, spar end is simply butted up against spar and tight against bottom sheet. To align LE end of cut ribs, I used a 5/16' by 2' long brass tube (any kind of straight rod or tube will work). Slid this tube under the 8 ribs already in place, till it touched all ribs equally (this will only work if ribs are well made). Taped tube down. Then just aligned front of partial ribs with tube. Glued up with Titebond, using thin CA to spot glue the 3 center ribs in place, allowing Titebond to dry. Once all glue was dry, wedged up bottom sheet tight against ribs and thin CA'd in place. Slid in, bottom forward stringer, glued in with thin CA. This stringer (turbulator) also needs to be raised off of board slightly to allow for Phillips type entry on lower LE of ribs.

erich

[erich]

Have finished adding rest of ribs, except two ends ones. Will get to those, when making up tip joiner boxes. Varied the thickness of shear webs, 4 at 3/8", next 1 at 1/4" then next 2 at 3/16" and last 1 at 1/8". Once all ribs and shears were in place. Checked and rechecked to make sure top spar cap fitted tight agianst all webs and ribs. When satisfied used Titebond and glued in top cap, then added weights.

erich

[erich]

Had added some full length gussetts to 3 center ribs. Decided to put gussetts (think that's what they're called) on both sides of center rib. On the gussetts used 5 min epoxy, mainly for better adhesion with the kevlar tow.

erich

[histarter]

Histarter

Instead of ballasting up when wind kicks in, have usually changed planes instead. Gives all the planes, an equal chance at getting in air. Only plane I ever did much ballasting with, was the Sagitta 900. When I got the Dodgson stuff (Windsong, Pixy, Pivot) I would just use these planes when wind kicked up. They didn't seem to need ballast even in 30 mph winds. That's not to say ballast wouldn't have helped, am sure it would. Would relex the TE on the Windsong in heavy wind and just, handle it, sans ballast. While ballast for contest flying is almost a must, in all the years I flew, have only entered 1 contest. Found it hard to sit and wait for my slot, when great lift was everywhere.

Green air
erich
Let me explain: Mark Smith was a hero of mine. His flying on demand for slope activities encouraged me to attempt the same thing with flat land machines. For almost 10 years I flew over 3 sessions per week (5 years of living next to my flying feilds). My database demonstrated a need for scoring that was contrary to flying using chaotic conditions supporting almost accidental, long flights. This meant I was flying before and after thunderstorms, in winds to 25 mph, dead calm, and occassional upper air high launchings. The statistic plots employed was simplified by using a upper control limit, and charting the probability of making the task (a max). This was quite workable, however the charting clearly demonstrated that to use airspeed wisely, one had to better match state of affairs.

1. Windspeed almost doubles at 2,000 ft AGL. Increasing mass 4X is ludicrous, so Alpha has to be compensated and/or MCL. Compromise is to ballast up to retain performance characteristics of the profile within the limits of its loading.
2. When seeking lower CL by less alpha for soaring without ballast, one runs into a upper surface bubble (Drela's profiles included) that creates high drag on top of the lower LD because of the steeper glide slope needed. (Mass is the motor).

Conclusion: Delta mass is better than lower alpha within the limits of speed range needed. Obviously doubling mass only increases airspeed by 40% - whereas going to CL 0.2 airspeed increases 200%, but is less efficient (even with improved re).

At first I used Legionairs that had 3 wingsets. 100 inch for high launching with wind, 120 inch with Shuttle fuse that could carry lots of ballast - and was my competition machine, and my 140 inch wing set used for light air low launch soaring (was rarely used).
Note: To improve low alpha performance, I discovered tripping to be very effective, and now wind tunnel tests from England demonstrates that open bubble drag can be reduced by more than 20% by tripping.

Actually, you are reciting my feelings! I prefer the short launch contests that have a realistic soaring factor over the present following of the competition crowd. Tasks that have soaring challenges, rather than evaluate hand eye coordination. AMA tasks typically have a SF (soaring factor) 0.6; whereas FAI is 1.2, conciderably more challenging.

[erich]

Histarter

Don't take offense at this, cause I admire folks who are able to weave their way around the science of flight. As for me, I would rather fly better than try to squeeze the last juice out of the aerodynamic science involved. Doing that would give me a tremendous headache, while trying to fly better only gives me a little headache.

erich

[erich]

Started work on joiner box for the tips, by adding one of the 1/8" ply shear webs, which form the sides of the box. Used pre-cut angle on web to cut and sand same angle on top and bottom spar caps. Made absolutely sure outside of ply web was perfectly flush with sides of spar caps.

erich

[SoCalGliderFlyr]

If you glue the 1/8" ply to the 1/16" outer ply then glue the assembly to the spars it's self gauging.

[histarter]

Histarter

Don't take offense at this, cause I admire folks who are able to weave their way around the science of flight. As for me, I would rather fly better than try to squeeze the last juice out of the aerodynamic science involved. Doing that would give me a tremendous headache, while trying to fly better only gives me a little headache.

erich
No offense at all. My whole effort was to simplify soaring, and make it enjoyable for all facets - so I would have a few guys for company flying evening 'contests' (attempting to knock off old FF goals) with a controllable craft, that was lots of un-serious fun. To bad they all got old on me!! :confused:

I just try to reduce the technibabble and go for the gusto now that I know what I am looking for! :D

[erich]

SoCal

Good tip. Will give that a try on other side.

Thanks

erich

[erich]

Histarter

Guess that's the way of people, we either get older or younger. Not sure which is better.
As for me, am headed for infancy, or close to it. Well back to the building. One good thing, when spring finally does come, will have plenty of new planes to fly. If the present rate of building keeps up, I'll have at least 3 more by then. That'll be a total of 5 new planes, yahoooo.

erich

[erich]

Cut slot, for joiner blade, in 3/16" end rib. Slid end rib onto tip joiner blade, then pushed tip panel into partial built joiner box, keeping main panel end rib flush against tip end rib. In this way, was able to check for fit of main panel end rib against spar and TE. Sanded TE slightly to get good fit. Glued on end rib, with Titebond. Drilled hole for a TE, alignment pin. Reinforced, alignment hole, in main rib with 1/64" ply.

erich

[erich]

Time to close up joiner box. Did a little sanding to get tip joiner blade to fit snugly between spar caps. Used 30 min epoxy to install 2nd ply shear web. To keep from gluing blade into joiner box, have usually used vaseline. Looked all over house, nothing. So used cooking oil. For you technically minded, it was Safflower oil. Was a little worried about the odor, but my worries were groundless. No odor. After sliding in tip, made sure tip root rib was aligned with main panel, end rib. Added epoxy to web sparingly, to keep from having to much glue ooze into box. Will add some glue to outside of box later. Clamped up, making sure NOT to use to much pressure. Want to be able to pull tip out after glue sets up. Must have done something right, tip pulled out, with a little force. Fit is very tight. Which is good, can always do a little light sanding to loosen it up, if necessary.

erich

[Mark Miller]

Grape Seed oil works better and adds a broad spectrum of flavor to your joiner blade.

Sorry, Couldn't resist. :)

I have a customer who shall remain nameless, who wanted to tighten up their joiner box. He waxed the blade and used some epoxy. He now has a two piece Mirage wing.

Mark

[erich]

Mark

I believe you made that up. Grape seed oil? What would that be..........wine??

Probably could have resisted, but didn't.

Got a confession to make, before epoxy completely set up, moved tip a little, just to make sure. If I hadn't done that, I also, would have a two piece wing.

erich

[erich]

Added the 1/16" ply outer shears. Used 5 min epoxy. While this was curing added the TE alignment pin. You'd think with all the wood I got, I'd find a small dowel, no such luck. Had to use a square peg and make a round hole...er....dowel. Glued this to tip root rib using Titebond.

Did other side of main panel same way, except glued inner and outer webs together before gluing to spar (as per SoCalGliderFlyr). This worked out well. Just had to be careful in lining up the two webs, the 1/8" border needs to be equal on both sides.

erich

[SoCalGliderFlyr]

Used over size ply caps and just trimmed off the extra. Why do you need an alignment pin with a rectangular joiner?

[erich]

It's not absolutely needed, but it helps to keep TE from fluttering and to maintain alignment better. Although not positive about this; I believe it relieves some of the pressure on main joiner. The ply caps I used came pre-cut in short kit, as did all ply webs.

erich

[erich]

Glued in the rest of the stringers (turbulators). Added all the gussets. Plugged tips into main, sat back and admired. IMO what makes this wing look so good is all the stringers. A stray thought: would be kinda cool to make a wing with stringers for the entire span, bottom and top. With them spaced 1/2" apart, would be almost like a fully sheeted wing. A lot of work to be sure, but imagine how great it would look in the air (clear yellow covering, of course). Believe the Mirage or Oly II would be great candidates for this. Now, if only, I could get someone to laser cut the ribs, with ALL those little notches? Oh well, kinda of a nutty idea..... huh? Then again...

erich

[SoCalGliderFlyr]

It's not absolutely needed, but it helps to keep TE from fluttering and to maintain alignment better. Although not positive about this; I believe it relieves some of the pressure on main joiner. The ply caps I used came pre-cut in short kit, as did all ply webs.

erich


Tape.

[slozuke]

Good idea using the alignment pins! If you've ever had a Mirage you know the wings tend to twist and flex. With the friction fit of the wood wing joiner it sometimes works it way out. The additional alignment pin helps to correct this problem, and tape doesn't hurt either, I've used both.
If you just float around it may be overkill. However, if you do loops (I like to do wingovers) or any other aerobatics with your Mirage you will need whatever you can get to help keep those wings aligned.
I know, I know, there will be posts that the Mirage is not built for that kind of flying. It is if you build it and fly it correctly, it flies gracefully and is HIGHLY maneuverable for a plane of its size.
Ever done a barrel role in a Cessna 172?

[cynjon]

Looking good erich! Can't wait to see it with some covering on it...What's left for the wing? Just holddown blocks/dowel for mounting?

[erich]

cynjon

Will probably get some flak for this. Am going with the OLD but true, rubber banded wing hold down. My reason, believe it to be a simple, elegant, and an easier to fix if something goes wrong, setup. If done right it can also be fairly aerodynamic. On the Mirage it was and is done right. One of the things i really liked about the GL was this same rubber band hold down method. Had a v-tail called Icarus, which had the dowel in front and nylon bolt in back. I much preferred the GL and her rubber bands. It just plain works. So go ahead and hang me, I deserve it. Especially when you see what I'm using for pushrods.

erich

[SoCalGliderFlyr]

Push rods: 1/4" square medium grain balsa. Don't forget the supports half way down the tail boom.

[erich]

Finished the kevlar additions. Wrapped tip joiner boxes in main and tip panels. Made tighter wraps near either ends of joiners and boxes. Believe I saw a build photo of Mark Millers Mirage, and he had done it that way. So I did too.

erich

[Mark Miller]

Rubber bands will work great. It worked in 1978 and it will work now. I agree with using the alignment pin. One thing that can happen with the Mirage is when it starts to go fast the tip will act as a big lever and start to twist the inner panel and induce flutter. From what Blaine has told me at about 70 MPH it will flutter to distruction. I don't know a soul that is willing to fly a Mirage to 70 MPH but there it is. I would rather have the wing solidly aligned so that there is no undue stress put into the joiner blade. Think about it. If you wanted to break the blade would you think it was easier to bend it vertically or twist it? Twist of course.

BTW...You might want to make a ply doubler on the inside of the rib to help strengthen the alignment hole and pin. I could see the hole and pin getting worn from use. Soaking it with CA might work too.

I do remember 3 years ago at the NATS Stew Swanson blew both tips off of his Mirage at the same time on launch. It still completed the flight and made a reasonable time. Oh, It was an original kit built one. That Mirage is still flying with a set of tip panels from my laser cut parts. Post mortem concluded that 20 years of stress finally took their toll on the blade and caused the ply to start delaminating.

Mark

[erich]

Added the rest of top center sheeting. But first made sure I didn't leave any T-pins in lower sheeting. Unpinned panel from board. By golly it's almost straight. Finished up the bottom sheeting. Plans called for 2 oz glass cloth around center section. All I had was 3/4 and 4 oz stuff, so I used the 4 oz cloth. Used epoxy resin on the glass. Rounded all the LE's, to an attempted 1/8" dia. Added the 1/16" x 2" music wire at TE, protection against rubber bands.

Mark, in re to your BTW....check out post #72. Is that what have in mind? Usually also add some thin CA to alignment holes than lightly resand to regain the fit.


erich

[erich]

Ok....on to the fun-ner stuff. For the wing hold down, have gone with, ye olde rubber bande methode. I may be loosing it. Too many month breathing all these glue & resin fumes. But to get on with it, built the cool looking bent metal rod hold downs. Really like the simple, yet seemingly strong method of (the glued in laces) fastening down the rubber band retainers (wire rods). Made only a small change, used kevlar string, instead of wire. Then covered area of threads with 5 min epoxy. To make these 2 bulkheads just used Mr. Blaine Rawdon's, easily understood, drawings.

erich

[histarter]

Note: If you are going to short hi start your Mirage, you may think about using a full elevator instead of the 1/2 blade designed.
The 1/2 blade worked great for the upper air where this 'almost a FF' design, needed small changes in pressure for control of large smooth spirals.

[erich]

Plans call for glassing the front half of fuselage. Will be doing this in a slightly different way than called for. The front part of fuselage is two pieces of 1/16" balsa sandwiched together. Am going to sandwich glass BETWEEN balsa sides. Will loose the anti-scuff of having glass on outside, but the places I fly all have lotsa grass, so it's not a major concern. Have a number of reasons for doing this, one of which is, just want to see how it works out. To late to talk me out of this as, have already done it. Used epoxy resin and some light glass. Did up both sides then piled on lots of weights, and let it cure for a day. The most difficult part was in neatly trimming the excess glass and epoxy. Used several exacto blades and emory boards to clean up the overflow. In addition, as the resin that would have been used to glass the outside, now also holds fuselage sides together, there is a good saving of weight.

erich

[erich]

histarter

One of the things that attracted me to this design, IS the single elevator blade, and the offset rudder. My figuring (is that a word) is: anyone who had the guts to put out a design like that, Must Know Something. So am building and hopefully flying it, to find out what he knew. Some people enjoy refining one thing to near perfection (and I admire them). As for myself, prefer to try many things, with the hope of every now and then, finding something really GREAT. And I have, more often then seems likely.

erich

[kostuk]

I really like my Mirage that I built from Mark Miller's short kit. Added 0.014 carbon on the spar caps and increased the shear webs. Also made a bolt on wing and a ballast box to add an additional 14 oz and a central spoiler like on the Bubble Dancer. Unballasted flying weight is 32 oz.
There is a picture of it on another Mirage thread in this forum.
I've launched it on several winches and I can get a very high launch without zooming. I also made my 1 hour LSF IV flights with it.
Ray

[erich]

The back half of fuselage gets butted to front, with a 3" or so overlapping doubler. Made this joint using glass and resin. Added the 1/4" longerons with Titebond except used resin in area where they come in contact with doubler. Than added the 3/32" x 3/16" crossbraces to both sides of fuselage. Used the plans to accurately place these, as they will form a square that gives fuselage it's shape and support.

erich

[erich]

Ray

Would love to see photo of your Mirage, here. That 32 oz is great, especially since it's with spoiler. Hope mine comes out that well. Would also like to see how you made you spoiler operate.

green air
erich

[erich]

The Mirage fuselage has two main formers, which have the wing hold down wires on them. Used the rear one to glue sides together. Fuselage has a bend in it just behind this former. Area to front and area to back of this bend are both straight. Since will be working on installing rear cross-braces, pinned down rear portion of fuselage over plans. Propped up front with some balsa stock. Made sure area from former to the rear was perfectly aligned with plans, and sides were square to board. Also that fuselage was evenly aligned front to back. All this is very easy to check with a small triangle. Since the front half is raised above board (couldn't use pins) used some weights here, to keep fuselage aligned to plans. Glued in this rear former with 5 min epoxy. Then went about adding the cross-braces, using a heavy grade balsa near front and medium balsa near rear of fuselage. This is the area where a little extra time and careful cutting pays off. The braces have a lot more strength if joints are as close to perfect as possible. Ended up tossing out a lot of braces that were over cut. Made sure that the vertical braces matched the horizontal ones to form an aligned square. Used Titebond here. Glued one brace, checked sides for squareness, waited 2 hrs, did another. Result, start of a really nice looking fuselage.

erich

[SoCalGliderFlyr]

The "little round holes" in the bulk head are for balsa push rods. The antenna was just dropped down the middle and tied off at the tail hole. Don't add any more weight in the tail than is necessary such as a tube for the antenna.

[erich]

SoCal

Did you really think, I didn't know what the 2 large holes in the bulkheads were for? The holes I am referring to are the 2 little balsa additions located on bottom cross braces, if you look carefully you'll see them in right bottom of fuselage. The little balsa squares are thin CA'd (use very little) in place, the hole is tight enough around tube so no glue is necessary for tube. I have weighed tube and little balsa holders, they come to .08 oz. with glue maybe .09 oz even you have to admit that's not much. The reason I put antannae tubes in my planes is I don't have enough money to buy a reciever for all the planes. So I move the recievers from plane to plane (I have 2 recievers). Not the preferred solution but an economical one. And I can't stand to see an antannae hanging off the outside of a plane. So therefore antannae tubes.

Love and Joy
erich

[SoCalGliderFlyr]

How are you going to get the anttenna wire down those "little holes"? Just tie a length of carpet thread to the antenna and pull it out the back. If the antenna is too short CA the thread to the fuse and cut it off. Why add the weight of a plastic tube?

[erich]

The holes are there to hold tube in place, the antanae goes INTO the tube. I have done this on 22 planes now, and have never had a problem sliding antennae into tube, I just push it in. The reciever antannae does have to be fairly straight. Photo shows what I do, to straighten a curly antannae. The reson for the tube, have found it very hard to snake an antannae wire into a completed fuselage, even using a string (still have to snake string through fuselage), the tube makes it a cinch and as I have already stated the weight is very very little.

Peace and Joy
erich

[SoCalGliderFlyr]

When is a Mirage Not A Mirage.