Ornithopter or ni- thop ter. The “ornith” part means it has characteristics of a bird and may or may not fly by flapping the wings.

That’s a pretty good definition of Jerky Herky, sort of resembles an ancient bird and may or may not fly. But,….. Jerky Herky’s flying ability depends entirely on how well you follow these instructions. Past experience has shown that some of you big kids don’t follow instructions very well.

While it is possible you may know more about building ornithopters than I do, remember that I built my first ornithopter before you were even born. My youngest son still holds a National Ornithopter record he set way back in the 1970’s. Follow the instructions and you will succeed. When you can build an ornithopter that’s flies, you know that you can build anything you set your mind to, Period. No exceptions.

Building a super lightweight model like this is going to require some special tools and supplies.

The first tool you will need is a new double edge razor blade. You will need about two of these double edge blades per model you build.

Next you will need a new single edge razor blade; one is generally sufficient for several models. Normal model building knifes are not suitable as the blades are so thick that they destroy the tiny pieces of wood while slicing them off the sheet. Also they are not very sharp.

You will need something like a pocketknife for cutting the tubing to size.

Two pair of small pliers are required, one needs to have round jaws to bend the round wire hooks. And of course you will need a pair of small wire cutters for trimming those wire hooks.

Also needed is a cutting board, something hard and smooth but not too hard or it will ruin the razor blades. A wooden board doesn’t work because it has a wood grain to it that will cause your razor blade to wander off line. Plastic is nice, and high pressure laminates are fine, both of these will work until the cutting area gets badly cut up.

You will need to purchase two kinds of glue; the first is old fashion model cement. This should be a cellulose type of model cement such as the hardware store type known as “DUCO CEMENT” or from the hobby shop use “SIG CEMENT “ or “AMBROID”. The DUCO has long been used by many of the world’s top indoor flyers. You must apply these glues with a small stick such as a toothpick.

The other glue you will need is from 3M and comes in a spray can and there are at least two different can sizes available. This glue is commonly known as 3M Super 77 contact cement. We probably need about 3 cents worth on each model. If you don’t already have some of this around the house you will be amazed at how handy this stuff is, you need a can anyway. All we are going to use it for is to attach the Mylar covering to the framework. Nothing else works as well for this task.

A bit of fine sandpaper is needed to smooth out the cut off end of the brass tubing used for the trust bearing. #400 wet or dry paper is excellent.

You are also going to need some waxed paper or Saran wrap from the kitchen to keep from gluing the parts down to the plans.

You will need one (1) straight pin. This is to push holes in the connecting rods. NOTE that at no other time will you ever need to stick any pins in the balsa wood. Pins destroy balsa wood. Don’t use pins to hold the wood in place. For holding the pieces down while the glue dries you will need some small weights. Small fishing sinkers work fine but guess what? Dominos work really good, so we have finally found something dominos are good for.

In order to cut nice straight strips of wood you will need a metal straight edge. I use an 18” metal ruler that cost $1.39 at the local drug store. Plastic drafting triangles are not good enough for this critical task. This is the first tool you are going use.

Now that you have the supplies you need to go with your Herky Jerky kit all you need is three evenings with no TV and no serious interruptions. That is about two hours on three different days. This is not a 15-minute project and you can not do it in one 6-hour session because the glue needs to dry properly.

Although your kit contains materials to build 3, 4, 5, or 6 models, you should build only one model at a time. Build one model and learn from that model. Build each one better than the last one. Learn from your own mistakes.

I can sort out the well build models by looking at the glue joints. Good models have good glue joints with very small gaps. Perfect models will have absolutely perfect joints with no visible gaps and the miter work with the razor blade is perfect in all directions.

Such perfect models fly better, usually because the builder does pay attention to the details. When you pay attention to the details the big items always seem to go well for you.

Don’t do stupid sloppy little things.

DAY ONE CONSTRUCTION SCHEDULE
The first step is always to spread out the plans and stare at them until you can understand what it is and how you are going to build it. Note the simple pivots and the connecting rods, did you also notice that the only thing holding the wings in place is a small piece of tape?

Next you examine the materials and wonder why the kit cost so much. (But remember that MRL looses money on every kit). You can’t start building until you know what all the materials are used for. Also take a good look at the balsa wood. In this model you must use very light straight grained balsa. When you go to buy similar balsa for future Herkys, here are the magic weights; 1/16 x 3 x 36 inch sheet shall weight between 9 grams and 12 grams. The 1/8 x 3 x 36 sheet shall weigh between 16 grams and 20 grams. Expert model builders never pass a balsa rack in the store with out looking for good wood, which they store for future projects.

Next thing is to decide that you are going take real good care of these plans. Your plans will eventually become collector’s items and worth a lot of money since the production of this kit will be strictly limited by the demand. Also someday you may want to build another Herky just to prove you can make a flapping wing model fly, the plans are all you really need.

Thou shall not cut on thy plans… Thou shall not get glue on thy plans… Thou shall not cause thy plans to become torn and ragged… Thou shall not allow insects or other animals to eat thy plans…

If you are unable to accept the terms of the above agreement, return the unopened package to the store where you purchased the product for a full refund.

The first thing we have to do is learn to strip sticks off the sheet just like an expert modeler.

Get your cutting board out and your straight edge ready. Take a fresh new double edge razor blade and hold it between the thumb and the first finger, do not place a finger on top of the sharp edge. Hold the razor blade so the cutting edge is at an angle of about 30 degrees to the horizon. That’s the easy part, the difficult part is holding it so the sides of the razor blade are 90 degrees to the cutting board. You must learn to hold the blade at 90 degrees or all the wood you strip off will have a trapezoid cross section and not be very strong. This is damn difficult to do for most people, you gotta pay attention. Even the experts forget sometimes.

Place the sheet of 1/16 balsa on the cutting board and put the metal straight edge on the wood and slide it up to the very top of the sheet, move it down about 1/16 inch and take a slow careful cut from end to end. You don’t need to press down very hard with the razor blade but you should cut all the way through with one cut. It is very important that you keep the metal straight edge pressed down on the balsa firmly, as the straight edge tends to slip down at the right end of the sheet.

What you have done is trim the edge and clean it up, removing the crooked damaged strip along the edge. The saw that cut the big boards damages the wood by pulling on the fibers, so we cut that off. The flat surfaces of the sheet have been sandpapered which is a little bit better.

Cut off a few more strips that are as wide as the sheet is thick. Look at the strips and make sure that you were truly holding the blade at 90 degrees and not cutting trapezoids. Do save all the pieces, they will come in handy later. You now need to cut off five perfect strips for the stabilizer or front wing.

LETS BUILD THE STABILIZER RIGHT NOW.

Spread the plans out on a nice flat, hard surface, a glass tabletop works fine for this and we are not going to damage mom’s table. Cover the stabilizer portion of the plans with waxed paper or saran wrap and tape things down so there is no movement. Now proceed to cut the five strips for a perfect fit at the four corners of the stabilizer. Get the dominos out, get the glue ready, and get a toothpick out; we’re ready to glue.

Using a couple of dominos, place the center rib piece in its place, slide the leading and trailing edges up close to their places and get the glue out.

Open the glue tube and place a drop of glue on the waxed paper a few inches above the stabilizer so its out of the way. Now using a small piece of strong wood such as a toothpick, dab some glue on the front edge of that center rib. Place the two leading edges in their correct location while adding another small drop of glue between the two leading edges. Get the dominos in place to hold things down.

Repeat this same procedure for the two trailing edges, but this time put the leading and trailing edges apart a bit at the tips and apply a small drop of glue in the tip joint. By now you should have about 12-15 dominos working for you. These joints will need to dry for more than five hours so leave this part alone.

Back to striping wood like an expert. This time its wood for the connecting rods, just a tiny bit more advanced. You will need to strip off a piece that is 1/16 thick x 3/32 wide. This is one and one half times as wide as it is thick, you know, half way between 1/16 and 1/8 wide. A piece 1/16 square would be strong enough for the connecting rods but its too difficult to get the pin holes in the center of a piece that narrow. So I went the easy way and made the wood a bit wider for ease of construction. You need to strip off two pieces like this and just put them safely away until we need them. Note that we did not put any holes in them yet.

LET’S BUILD TWO WINGS.

You start the wings by making up the wire attach points. Cut the four little wire pieces to their correct lengths; glue these pieces of wire onto some pieces of 1/16 wood. It will be a lot easier to do this if you leave the wood pieces plenty long until the parts are finished.

Set these pieces aside to dry, when they have dried for about an hour or so, you will want to apply a second coat of glue to each joint.

Now we need to strip some tapered wing spars, this is not as hard as it looks. Notice on the sheet wood layout drawing how we alternate large ends of the spar. We do this to keep the grain straight on the spars. But just as important, we always cut two sets at a time and this will help provide spars that are matched in strength and flexibility. Very important when you are going to be flapping these things to fly. You must use a set of spars that both had their 1/8-inch wide ends at the same end of the sheet. The easy way to keep these spars as matched sets is to put a magic marker mark on the ends of one set of spars. I do this by marking the end of the sheet of wood before even cutting the spars off

Spread the waxed paper or Saran wrap over the wing drawings and tape it in place. The first thing to do is cut that little short piece that fits between the leading edge and the center rib. You should try to cut this correctly in order to get a good lightweight glue joint later on. Next cut the 1/16 center rib pieces and note the angle on the front end. Put these first pieces down with dominos and using a fresh drop of glue and another toothpick, glue them in place. Place the spars up on their edges and glue them in place using the approved glue procedure and six more dominos. Trim the spar tips to the correct length. Please allow 5-6 hours for the glue to dry.

TIME TO MAKE THE FUSELAGE.

For the fuselage you must use the 1/8 thick balsa sheet. Note that both ends are saw cut nice and square. You should preserve the square ends so you can get a good glue joint to the wing mount piece.

To strip this 1/8 balsa you will want to get out your new single edge razor blade as its too hard to strip with a double edge blade. Strip off two pieces that are ¼ inch wide, that is twice as wide as it is thick. Simple.

Well not that simple, you must keep the razor blade at a 90 degree angle to the cutting board to avoid those crazy trapezoid pieces of wood. This wood is thick enough so that it really matters.

Cut a piece to the correct length for the wing mount and using the double edge razor blade, put the “V” notches in each end. Do not glue any tubing bearings in place yet.

Spread the waxed paper or Saran wrap over the fuselage portion and tape it in place. Glue the wing mount to the fuselage and domino the assembly down.

Go ahead and add the thrust transfer post pieces. It is best to cut the bottom piece first and then the long top piece and then add in the little cross brace. This will require another 5 or 6 dominos. You are still cutting carefully and gluing with the drop of glue and toothpick skill. All the thrust produced by the wildly flapping wings is transferred to the fuselage by these three flimsy little pieces of 1/16 square balsa so do it right.

Add in that little gusset at the fuselage and wing mount joint. Note that the wood grain must be parallel to the long side of the triangle or the gusset is worthless. Cut this part to fit properly or it will waste a lot of heavy glue for you.

Whether or not Herky will fly is largely a function of how good, straight and true you build your Herky. How long Herky will fly is a function of weight, or rather the lack of weight, and how good your rubber motor is at storing energy.

We are just about done for the first session. First lets go back to the wing construction process, remember those four little pieces with the wires glued on them? Trim these four pieces to their correct length and carefully glue them on the wing at their exact correct locations. The locations you glue these determine the total stroke of the wings.

BUILDING SESSION NUMBER TWO.
Progress. Start by removing the fuselage assembly from the building board. You will need to use your single edge razor blade to part the glue loose from the waxed paper, you can do this by slipping the blade under the wood somewhere near each glue joint and carefully sliding the blade between the glue joint and the waxed paper.

The first thing is to glue on the aluminum tubing for the wing pivot. Start by using sandpaper to rough up the outside of this tubing. Cut off a piece about ¼ inch long. The way we all cut tubing is using a knife such as a pocket knife or butcher knife, any large knife that has a smooth edge will work just fine. Lay the tubing on a smooth hard surface, place the knife across the tubing at the ¼ inch mark, press down on the tubing with a force of about 2-3 pounds and roll the tubing back and forth. After 10 or 15 rolls the tubing will just pop apart for you.

Trail fit this piece of tubing in the “V” notch on the wing mount and if necessary trim the notch until the tubing points straight ahead, parallel to the motor stick. Glue it in place with about 6 drops of glue.

The brass tubing thrust bearing is next. Sort of the same thing except this time you also must first sandpaper the very end of the tubing smooth so the wire crankshaft has a smooth surface to rub on as it rotates. Rough it up just like the other tube and mark the correct length. Cutting brass tubing is a bit more difficult that the aluminum tube as you must press down a bit harder and it takes more rolls with the knife. You should clean up the new cut edge before you glue it in place.

Place a piece of the wire inside the tubing and trail fit it in the “V” notch. This tube needs to be aligned with the motor stick to the best of your abilities. Glue it in place, note that it overhangs the wood at the rear to provide clearance for the connecting rods. Come back to this joint in about 30 minutes and apply a good second coat of glue to this joint.

Using the single edge razor blade, carefully remove the stabilizer from the building board and examine the glue joints. If necessary apply a second coat of glue to any poor joints and set aside for now.

Using your single edge razor blade, remove the wings from the building board and repair any poor glue joints. Also apply a second coat of glue to the four wires making certain that every wire is covered with a thin layer of glue for its full length. It is very bad news when a connecting rod wire comes off up in the air.

Now for the wire bending. Start with the front motor hook. With your round nose pliers grip a nice long piece of wire bout ½ inch from the end and with a good strong grip on the wire and the pliers, proceed to wrap about ¾ of a turn around the pliers.

With your flat nose pliers, looking at the plans, bend the wire to fit the fuselage. Do not cut it off yet, this long piece makes a good handle.

With the flat nose pliers, bend the short straight section that enables us to get the rubber onto the hook. Now lay the piece down on the plans and try to reform it so it matches the plans. Also, the short straight section that serves to get the rubber away from the fuselage a tiny bit. When satisfied with the hook, cut off the little piece that extends from the round loop area. Holding the round loop in your flat pliers, sandpaper or use a small file to remove any sharp edges or burrs from the end of the hook. The rubber we are using cuts about like jello and can not stand any sharp edges.

When you are convinced the hook is good, cut it off from the long piece of wire and glue it in place on the fuselage. Now is the time to examine all glue joints on the fuselage and re-glue any poor joints.

Being as how you are now a good wire bender, lets go ahead and bend the crankshaft. The crankshaft is a lot easier. Again start about a ½ inch from the end of a long piece of the wire, with the round pliers bend a complete circle. While still holding the wire with the round pliers, use the flat pliers to bend that little short straight part that helps us get the rubber on the hook. Also bend the long straight section that will extend through the brass thrust bearing. Note that you can not bend the two 90 degree bends yet. Measure on the plans and cut the wire off to the correct length at both ends. Deburr and smooth the rubber hook end. Save that crankshaft, we will now make the two connecting rods from those pieces of 1/16 x 3/32 that you stripped off a long time ago and saved for this.

Using the straight pin punch a hole about a 1/16-inch from the end of one of the 1/16 x 3/32 strips. Enlarge that hole by pressing the pin way far into the wood. Measure 3.00 inches on the strip and punch another hole and enlarge it also. Then if all looks well, cut the connecting rod off the strip and make another one just like it. To toughen the bearing areas we must spread glue on the holes and then press and smear it into the wood around the holes. Wait about 10 minutes and once again press the straight pin way deep into the wood to clean out and enlarge the holes. About 30 minutes later you should do this same thing again. We cannot stand to have the connecting rods fit too tight and bind on the wire shafts. Make sure the fit is nice and loose even after the glue is dry.

DAY THREE, COMPLETETION
Time to cover and assemble Herky. Insert the crankshaft in the brass trust bearing and using the flat nose pliers, make a nice sharp 90-degree bend at the thrust bearing. This bend needs to be out away from the thrust bearing about ¼”, so you will be able to get the rubber on and off the hook. Make the second 90-degree bend out exactly ½ inch. This determines the power stroke delivered to the wings. Increasing this ½ inch is like increasing the pitch in a propeller. Decreasing this ½ inch is like reducing the pitch in a propeller. A shorter stroke allows the rubber motor to flap the wings faster. Set the fuselage aside for now.

Time to cover the stabilizer and wings. We will need a smooth surface about 24 inches square. You will need to cut on this surface and it will damage the surface, choose according. Get the plans out of the way so you don’t ruin them by trying to cut on them.

Cut off about 18 inches of the .0005 Mylar and tape it down to the smooth surface. Tape it down nice and tight using at least eight pieces of tape. Lay the stabilizer and the two wings on the Mylar so you know right where they will fit. Get the can of 3M 77 cement and shake it up real good. Hold the stabilizer by the center rib piece and from about two feet away spray a light coat of cement on one side of the stabilizer. Holding the stabilizer by the tips about two inches above the Mylar, get it lined up where you want it and then just drop it on the Mylar. Press it down to the Mylar with a tender finger. This is all a lot easier that it sounds but there is one other major thing that you must know and never forget; this spray cement is highly flammable, a cigarette is deadly.

Equally important, there will be quite a bit of overspray and it is terrible. The cement overspray will just simply ruin any carpet it gets on. It will not come off any carpet and it makes the carpet sticky and collects dirt instantly. Normally you can remove the cement from tile or concrete surfaces using acetone or MEK but these will also remove any paint.

You should do the 3M77 cement spraying outside with no wind and do put some newspapers on the ground to protect the ground. It would be downright stupid to spray this stuff in the house.

Spray and drop the wings onto the Mylar just like you did the stabilizer except this time you can hold the wings by the two wires on each wing. When you doing the wings note that the covering goes on the side opposite the wires.

Trimming the Mylar is not easy but you can do it by just being careful and going slow. Take out another band new double edge razor blade and your straight edge. Cut the stabilizer out by placing the straight edge on the Mylar up close against the stabilizer and taking slow a precise cut along the edge. You should be cutting through the Mylar and well in to the surface of the surface under it. Watch carefully and make certain the Mylar does not start to tear instead of cutting. Repeat this cutting process for the wings. It is a good idea to do the loose trailing edge of the Mylar first and then center rib area followed by the leading edge. Cutting underneath the wire is difficult for us all but you will be able to do it by lifting the wing up a bit and cutting from the under side.

Turn the stabilizer upside down on the work area and glue on a scrap piece of 1/6” square as shown on the plans. This goes at the leading edge and gives Herky the angle to provide the necessary lift. This piece of wood is easier to glue on if you leave it a couple of inches long and then trim it to length after the glue dries. The length shown on the plans is probably longer than your Herky will require. But when you are out flying, it’s a lot easier to make a piece of wood shorter than to make a piece of wood longer.

The next thing is to install the wings on the fuselage. Trial fit the wings by inserting the wing pivot wires of both wings into the aluminum tubing on the wing mount. Note that the wings should move freely in both the up and down directions. Now also note that if the wings are pulled back just a tiny bit, no part of the wing wood comes in contact with the aluminum tubing, just the wires. This is the desired setup as it is an almost friction free bearing.

Next we are going to tape the wings in place.

Turn the assembly upside down on a flat surface. You will need to prop up the front end of the motor stick so that the wings will lay nice and flat on the work area. When you can get the wings flat with the wing mount nice and vertical, you can then line up the aft end of the two center ribs and the aft end of the thrust transfer post. You will have three pieces of 1/16” square and these pieces should be positioned with about 1/16” space between them. If you have a problem with this, look at the drawing.

Cut your self a couple of pieces of tape about ¼” wide and ½” long and store them where you can get to them with one hand. Carefully position the wings, thrust post and pivot wires so that there is a small space between the wing wood and the aluminum-tubing pivot. You do not want any contact between the wings and any thing else except the wire in the tube. When everything is right, apply a strip of the tape to the bottom surface of the wings and the thrust post. Turn the assembly over and apply a second piece of tape on the top surface of the wings and thrust post. Now make certain the tape is stuck down to the thrust post, as this is the connection that transfers all the thrust of the flapping wings to the rest of the model.

To attach the stabilizer we must prop Herky up in a nice straight position with the wing mount piece vertical. Support the stabilizer in a position so you can glue it to the fuselage with no tilt to either side. Remember birds do not have ailerons, birds turn by tilting their tails. Glue the stabilizer on straight, no tilt. Use several drops of glue, as stabilizers do tend to come loose in the air.

While that last glue joint is drying, lets tie up a motor. The rubber supplied in the kit is known as FAI TAN II. It is a custom made rubber for use on rubber powered contest models. This rubber is designed to store energy and it does it better than any other rubber in the world. This is a tremendous storage device, One pound of this rubber will store about 4,000 foot pounds of energy when it is handled properly. Take care of your rubber.

This rubber can not stand sunlight. Rubber can not stand heat, Rubber can not stand chaffing. Rubber can not stand cuts and nicks.

Generally speaking rubber should be stored in a light tight container in the refrigerator at a temp under 50 degrees F. One week of bright light exposure will pretty much ruin your rubber and it will break very easily. High temperatures will cause your rubber to over cure and become hard and brittle. The chaffing is a problem we can deal with by using a good lubricant on the rubber every time it is wound up. Recently the contest modelers have been using a wide range of lubricants. The most common one you are likely to have around the house is castor oil or mineral oil, even vegetable oil will work in a pinch. The thicker the oil is the better it will work but some contest modelers are experimenting with odd spray can oils such as Armor-All and Pam.

Your kit contains ten feet of good fresh rubber. Cut off a 24-inch piece and rinse off the protective powder; tie it into about a 10-inch loop following the tying instructions on the plans. This is one of the few knots that does not slip out very often when it is nicely lubricated. Make up that one motor and place it into a small plastic bag along with about a teaspoon of castor oil or other available rubber lubricant.

BACK TO THE AIRFRAME
The stabilizer must be dry by now so lets install the connecting rods. Test the bearing hole fits by placing each connecting rod on the wire shaft and make sure it is still a nice free fit with no binding allowed. Install the connecting rods and turn the crank slowly and make sure everything clears and runs smoothly.

Don’t force things, find out if anything is binding and fix it if necessary. Check that when the two wings are in the full “down” position that their center ribs are not being compressed together. Make sure the wings really do not rub on the aluminum tubing wing pivot. Most of the time you can fix these interference problems with a sharp double edge razor blade but do be careful.

The basic design has an inherent problem in that there is slight “catch” at the top of each stroke and a lesser “catch” at the bottom of each stroke. This is because the wings do not actually flap simultaneously; one wing is always a little bit behind the other. Interesting quirk and it does cause the models to always want to circle to the right. When I build in the offset bearings to fix this problem then I loose the safe dependable right turn. My point is, don’t try to fix the “catch” in the stroke, its an inbred characteristic of Herky’s family.

Now that you are sure the flapping is going up and down like it should, proceed to install the little connecting rod retainers. These are made from scrap 1/16” square wood. Just push a pinhole near the end and then cut off the little piece with the hole from the 1/16 scrap. Put a drop of glue on the wood-wire joint and it will retain the rod and still allow you to remove it to replace a connecting rod. When flying I break lots of connecting rods, usually with a dumb finger.

JERKY HERKY IS READY TO FLY !
First we need to break-in the motor. FAI Tan II rubber should be broken in by stretching with no winding. The first stretch should be to about five times the normal length of the motor: a 10-inch motor should be stretched to 50-inches. Anchor one end to something smooth that won’t cut the rubber and pull it out to the 50-inch mark, hold it there for about three minutes. Relax the rubber and allow it rest for at least 15 minutes. The second stretch should be to six times the normal length of the motor or 60-inches this time. Pull it out to the 60-inch mark and hold it for about three minutes. Let it rest 15 minutes and you are ready to fly.

Herky is an easy flying model that seldom has any problems, usually just flying off to the right in about a 10-20 foot diameter circle. Herky can not fly in the wind, NO WAY.

Herky will fly a little bit inside a large room in your house, or in the street after dusk, just plan on a right turn. And beware of cats. I have lost several to the neighborhood cats. The best place to fly is in the gym with about a 30-50 foot ceiling. Bigger buildings and higher ceilings are even better. Locate the best available site, close all the doors and windows to stop the drafts and lets wind it up.

A fully wound 10” motor will hold about 1000 turns, but only if done properly. We will work up to this slowly. The winder you use should be a fairly sturdy one with a gear ratio of at least 5:1, any winder that has a ratio greater that about 16:1 is very difficult to use on this size motor. The winders sold by MRL are a 5:1 ratio, are imported by Peck-Polymer and are plenty sturdy.

Wipe enough of the lubricant off the motor so it’s not dripping on the floor. Install the motor with the knot you tied at the front motor hook. No other place will work.

The only way to wind the motor is to have your assistant hold the rubber at the rear motor hook on the crankshaft. Do not hold the model itself because these next steps would pull the model apart. Now with your assistant gripping the motor tightly, hook the knotted end of the motor on the winder. Grip the winder in you left hand and stretch the motor out to a length of 30” to 40”. For this first test flight we are only going to put in 150 actual turns in the motor, if you are using a 5:1 winder this translates to 30 cranks on the winder. The way to do this safety is to put half of the cranks in while the motor is fully extended, and then put the other half in while slowly moving in to the correct length for the motor hook. When winding motors you must always pace yourself so that you arrive at the motor hook at the same time you arrive at the desired number of turns.

It is generally better to fudge on the number of turns rather than arrive to soon or too late at the motor hook. This may sound complicated but its really simple: stretch the motor out, put in ½ the turns and then put in the other ½ the turns while coming in slowly. And this works.

When the motor is wound up and you are ready to transfer your end to the motor hook, simply get a tight grip on the wound motor just in front of the winder with your right hand and allow the motor to unwind a few turns. Slip the winder off the rubber and put the winder in your pocket, and now using both hands slip the rubber motor on the motor hook. As your assistant carefully and slowly releases the motor at the rear motor hook, you get a grip at the crankshaft so that you can raise the model to eye level.

Release the model with no push; just hold it nice and level and let it go. Herky will fly in a large circle to the right and descend slowly to the floor. At this point you know why its called Jerky Herky.

On the second flight you should be able to put about 250 turns in Herky and it will climb a few feet before settling to the floor. This is where you can get an idea of how the circle diameter looks. If the model does not circle or circles real tight and does not climb you may need to add a small rudder at the front edge of the stabilizer. Very seldom is a rudder required and it indicates you built something crooked so don’t get in a hurry to add the rudder. If needed the rudder should be a triangle shape and sort of like a flag attached at the stabilizer post. Generally, it is better to add dihedral in the stabilizer and only on the right hand side. This will normally correct minor turn problems.

If the model goes out about 6-8 feet and then as the nose comes up it makes an abrupt turn to the right, that is a stall. You correct a stall by reducing the positive angle of the stabilizer. Simply cut that little post in ½ and glue it back together with some overlap. Adjustments are all pretty much trail and error.

On each flight you can increase the turns by about 100 turns until you are getting too close to the ceiling or other obstructions.

From now on you will need to wind in a more skilled manner. Before you even start winding, you must decide how many turns you are going to put in the motor. Stretch the motor out to about five to six times the normal length of the motor, (that’s 50 or 60 inches). You quit stretching when it gets tight. Wind about 10% of the total expected winds, the motor should not feel as tight as it did. You can now proceed with wining the first ½ of the turns. The motor will tighten up considerable more as you come in while winding the second half of the turns, and you will sometimes find it necessary to come in faster than desired and end up with fewer turns than planned. Very Tight, Hard motors break almost every time.

Anytime you are going to be putting lots of turns in the motor you must keep it well lubricated and give it some rest between flights or it will break. Between flights I like to take it off the model and put it back in the bag with the lubricant for perhaps 30 minutes. It is a good idea to have several good motors available but don’t make up additional motors until you have done some test flying.

You can adjust the power delivered by the rubber motor by changing the length of the motor. A shorter motor will deliver more of a burst of power at the beginning of the flight but holds less total turns. Conversely, a longer motor will deliver less power burst but have more turns to deliver over a longer time period.

Basically, if the model climbs too fast and is reaching the ceiling you should try using a longer motor, perhaps 11” or 12” long. A longer motor will, climb slower, not hit the ceiling, hold more turns and fly for a longer time. That means you built a good lightweight model. If you shorten the motor you will have more of a power burst to climb with, but a shorter total flight under most conditions.

FAI tan II rubber of 1/8” size should hold about 100 turns per inch of loop length. I would not recommend winding beyond about 80% of the maximum turns. Herky will fly for about 1 minute on 800 turns and close to 2 minutes on 1000 turns.

A motors life is very short when wound to its maximum.

Motors are very easy to break so you must be careful at all times. Look at the motor before you put it away after each flight, you can not stand cut or nicks in the rubber. Fuzzy chaffed edges means you wound it too tight too many times for the amount and quality of lubricant on the motor. That motor is getting old and will fail soon.

You are going to break motors, it’s a fact of life. Additional, fresh rubber in good condition can be purchased from us here at MRL or you can go to the source where we buy our rubber:

FAI Supply, Post Office Box 366 Say, PA 18840-0366

The very fact that you got this far and are flying an Ornithopter you built says a lot about your personality and abilities I’m convinced that you are capable of completing just about anything you start. You have an uncommon passion for the difficult. You can succeed at anything you attempt because you hang in there and finish the job. Don’t limit yourself to toy airplanes. There is a big world out there.

Big 44 inch wingspan

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Model Research Labs
25108 Marguerite #160

Mission Viejo, CA 92692