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Oct 26, 2018, 08:24 PM
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mdickey's Avatar
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Hi-Flight Mirage Build


Build season is upon us in New Hampshire, and I have had the pleasure of finding an original Hi-Flight Mirage kit. The wood is in great shape and Iím excited to put it together.

Some specs on the plane for those who arenít a familiar with it:

Wingspan: 112.5Ē/2.85M
AUW: 33oz/935g (dream on)
RES control surfaces

The plan:

Build mostly to stock specifications EXCEPT

1) laminate spar with carbon and wrap with Kevlar
2) laminate lite-ply joiners
3) install carbon pushrods

This plane is unique in that only one half of the elevator works. According to the designer Blaine and several other pilots, it has plenty of authority this way.
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Oct 26, 2018, 08:31 PM
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mdickey's Avatar
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Day one of the build:

We just moved from Cincinnati to New Hampshire, so the first item of business was to get my materials back together. After a lengthy process of setting up a build table, I was finally able to roll out the plans and start getting to work.

My initial impressions after unboxing were good. The ribs are pre cut and punched out of balsa, there wonít be much work here. There are turbulators instead of a D box for the wing, so the construction will be quick and simple. The fuselage halves are single pieces, which eliminates joining pieces together. This also saves a step. I have a feeling this build will roll right along after the initial planning stages.

The plans call for stab pieces to be cut out of 1/4Ē balsa, so I started with that. After copying the pieces to another sheet, I used 3M spray to affix my templates to the 1/4Ē balsa sheet and cut them out. Then, they will be sanded to their final shapes before gluing up the stabs. Modern laser cutting would have saved me a few hours of cutting and sanding, but I have until April to get this plane finished.
Oct 27, 2018, 04:15 AM
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whacker's Avatar
Cool

Always liked those Hi Flight Mirages

There's likely lots of these out there, wonder how others did the TE inside scallops

Watching on baited breath the Trailing Edge shaping

Dream on yes, Box Top weight, Don't know how anyone builds that under 1 kg.

Great Flying Plane, nice silhouette

whacker
Last edited by whacker; Oct 27, 2018 at 08:55 AM.
Oct 27, 2018, 07:47 AM
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abieex's Avatar
OK, I'm watching
Oct 27, 2018, 08:43 AM
Sonoran Laser Art
I'll follow to Matt. It would be fun to fly with some Mirages and scratch built BOT's all under 40 oz.
Oct 27, 2018, 11:41 AM
Registered User
The way I scalloped my TE's was I drew a light pencil line about .5" along the span of the TE. Then I used a dremel sanding drum to sand in a half circle by the ribs. Then, I used a balsa stripper and stripped away the wood between the bottom of the radius and the next readius.

I also added carbon to the spars and thread wrapped with Kevlar. Damn wing still fluttered. OH, and I made it a 5 panel. handled great.

For all that, it is still a great floater. Climbed out from about shoulder ht. more than once.

JDK
Oct 27, 2018, 12:00 PM
Registered User

Scalloped TE


They say a pict us worth a thousand words. This is a pict of a 3 panel Mirage wing. It fluttered. I scalloped the TE and removed every other rib behind the spar. Hasn't fluttered since.

JDK
Oct 27, 2018, 12:01 PM
Registered User
Actually, It is not a Mirage wing, but an early F3RES wing I built.

JDK
Oct 27, 2018, 12:02 PM
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craigrrr's Avatar
Quote:
Originally Posted by mdickey View Post
Build season is upon us in New Hampshire, and I have had the pleasure of finding an original Hi-Flight Mirage kit. The wood is in great shape and Iím excited to put it together.

Some specs on the plane for those who arenít a familiar with it:

Wingspan: 112.5Ē/2.85M
AUW: 33oz/935g (dream on)
RES control surfaces

The plan:

Build mostly to stock specifications EXCEPT

1) laminate spar with carbon and wrap with Kevlar
2) laminate lite-ply joiners
3) install carbon pushrods

This plane is unique in that only one half of the elevator works. According to the designer Blaine and several other pilots, it has plenty of authority this way.
HI, mdickey:

I built my Mirage from Mark Miller's Isthmus Hobby kit. The Mirage is still my all time favorite woody thermal machine.

Mark's kit varies somewhat from the Hi-Flight kit.

He holds the wing down with a single wooden dowel protruding horizontally from center leading edge of wing. This dowel slips through a hole in the plywood bulkhead (at leading edge of wing). The rear of wing is held down with a single nylon screw, 1/4-20. This works very well.

I do not know if the Hi-flight kit uses a "one half length elevator" but the half length elevator is all you need for control.

I used a rudder that has a straight hinge line the complete length of rudder; better strength, simpler, and works fine.

I used the stock wooden push rods; they are fairly light weight and simple. You don't have to worry about building the tail extremely light (like a TopModel sailplane). And the push rods exiting from directly behind the fuselage is very nice.

The spoilers should be 4 rib bays long. I started with 3, but went to 4; the Mirage does not want to come down.

I also laminated the spar (of the center panel) with .007" thick carbon, did a light wrap of spar with kevlar thread, and a tight kevlar wrap at the ends of the center panel to support the wing joiner.

As for the wing joiner, I made my own out of multi-ply pieces. Strong plywood is a good idea.

I did not glue the wing joiners into the wing. I just worked the joiners for a nice snug slip fit. If you find that you have slop in the joiner, just apply a thin coat of epoxy to top and/or bottom of joiner surface, let it set, then sand to a snug fit.
I like this set up just in case you were to break a joiner during a crash.

I had two very bad landings over a period of over 600 flying hours of my Mirage.
One was due to a rudder servo failure. The other was because I over sped (flew it way too fast while at spec altitude) and blew off a wing tip at altitude. Interesting that it was controllable and came home with only one wing tip.

I modified my wing center panel with a Mark Drela mod where you modify the center wing panel by building a D-box from the leading edge to the spar with 1/16" thick balsa strips, BUT NOT ELIMINATING THE ORIGINAL SHAPE OF THE UPPER SURFACE TURBULATORS (SHOULD NOT BE a continuous curve). This is an easy mod, especially if during the original build, and only adds a few grams of weight. Leave the outer wing panels as is.

I did this mod because I often over-speed my sailplanes and flutter the wing. This mod will prevent wing flutter at very high speed. But I think Mark Miller is correct in saying that flutter only occurs at around 60 miles per hour.

If you are interested in this mod (or just want to look at this great thread), go to Aircraft Sailplanes/thermal/Isthmus Models Mirage 112.5" RES, Report#223.

I wish you luck with your Mirage - an easy fun build and a GREAT thermal woodie. Hopefully Isthmusmodels.com will be back in business soon with his high quality kit because "no serious thermal woodie builder should croak before building/flying a Mirage".

Craig
Oct 27, 2018, 12:33 PM
B for Bruce
BMatthews's Avatar
Quote:
I used a rudder that has a straight hinge line the complete length of rudder; better strength, simpler, and works fine.
That was a popular mod at the time. Almost all the gliders at and before the time of the Mirage used large aerodynamic balance portions ahead of the hinge line. And it was learned by many at around that time that making the hinge run all the way up and making the front tab portion part of the fixed fin not only made the build a little more simple but also INCREASED the rudder's power. Seems that the ability to add camber to the fin/rudder was more effective than altering the angle of the whole flat upper portion. Also the drag and air mixup at the big open joint half way up the forward part was avoided. So less drag, better rudder response and easier building. What's NOT to like, eh?
Oct 27, 2018, 12:56 PM
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mdickey's Avatar
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Quote:
Originally Posted by BMatthews View Post
That was a popular mod at the time. Almost all the gliders at and before the time of the Mirage used large aerodynamic balance portions ahead of the hinge line. And it was learned by many at around that time that making the hinge run all the way up and making the front tab portion part of the fixed fin not only made the build a little more simple but also INCREASED the rudder's power. Seems that the ability to add camber to the fin/rudder was more effective than altering the angle of the whole flat upper portion. Also the drag and air mixup at the big open joint half way up the forward part was avoided. So less drag, better rudder response and easier building. What's NOT to like, eh?
That was something I have been considering as well. Iíll have to look at the plan, but it should be pretty easy to do.
Oct 27, 2018, 12:58 PM
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whacker's Avatar

I've got Popcorn


Build your Mirages,

mdickey got the Plan
Straight, strengthen those joiner boxes , keep the tips light.

there must be some stashed somewhere or even Scratch one If you have to

It's 40 Degrees here today, Absolute cloudy sky.

What a chance to fly the Mirage

and anchor the Hi Start

Didn't look good as I headed out, 3 seagulls went thru and they were paddling south into the hills

Looked for Eagles , no sign of them, maybe they hooked a thermal and are circling down over Halifax.

Who knows.

Hi start anchored on the south end, stretched out to perhaps 18 lbs or so.


4 Launches Later I decided to probe east, well what do you know.

Landed almost 15 minutes later. woo hoo

The first flite was close to 5 minutes, not to shabby for an Old design, scratched from a set of plans, and weighing over 40 OZ

Bring on those lite weight 2 M birds

Dumb Seagulls, did they find the Eagles

whacker
in Cloudy Tatamagouche
Oct 27, 2018, 01:00 PM
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mdickey's Avatar
Thread OP
Craigrr, I’m likely going to laminate the center panel only as well. Just that extra bit should make easy pedaling on the winch a lot more secure.

I have considered laminating the original joiners with a bit of fiberglass, carbon or just using nicer plywood. This one will likely come down to price and availability of materials.

Does the other thread contain Drela’s d box mod?
Oct 27, 2018, 05:44 PM
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craigrrr's Avatar
Quote:
Originally Posted by mdickey View Post
Craigrr, Iím likely going to laminate the center panel only as well. Just that extra bit should make easy pedaling on the winch a lot more secure.

I have considered laminating the original joiners with a bit of fiberglass, carbon or just using nicer plywood. This one will likely come down to price and availability of materials.

Does the other thread contain Drelaís d box mod?
mdickey:

Drela's posts on mods to the Mirage to avoid spar caps are located in the thermal section. Do a search called "The Lazy Method - Carbon Spar Caps".
Mark Drela descibes alternatives to spar caps in Reports 10, 23,24,and 29. He describes slight mods to a spar to avoid spar caps. But he also describes the mod I made to mine, building a D-tube to make center panel stiff.

To see photos of my D-tube mod, search "Isthmus Models Mirage 112.5" R.E.S.", go to Reports 223 and 224.

Craig
Oct 27, 2018, 09:12 PM
Registered User

Mirage type


This is my Mirage based model from about 2006. 37OZ flying weight. Lots of flutter with the wing moded as noted.

JDK


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