Monnet Experimental Aircraft, Inc Newsletter Reprints

For back issues of the Sonerai Newsletter as published by Ed Sterba, and now Fred Keip, contact Fred at 11428 Six Mile Road, Franksville, WI 53126

July/August 1983

Monnett Engine Conversion - As with many opposed engines that have intake manifolds of unequal length, the two cylinders on one side of the engine tend to run leaner than the two cylinders on the opposite side. The difference in the two sides can be seen by the color of the exhaust stain. Usually the right side of the Sonerai cowl has more soot on it than the left side. One thing that can be done to help the problem is to add a crossover tube between the intake manifold head castings. The tube helps by equalizing the pressure between the two sides. The results seem to be more even fuel mixture to all cylinders and a little smoother idle.

To make a fitting for each end of the tube the head castings can be drilled in the center just above the flange and a short aluminum tube bent in a 90 deg elbow can be welded in place, otherwise the hole can be tapped (pipe thread) for a 90 Deg fitting such as an Airborne #1 K1-6- 10. On our installations, the elbows point towards the firewall and the crossover tube passes from one manifold back around the rear of the engine (above the magneto) and to the other manifold. The tube can be made of 5052 aluminum and sizes ranging from 3/8" to 5/8" have been used. For connecting everything together we have just used a hose and hose clamps over the tubing and manifold fitting. All of the connections should be air tight just as all the connections in your intake manifold. A loose fitting connection or head casting could cause a lean mixture and possibly serious engine damage.

Nov /Dec 1983


On October 20, 1983, Monnett Experimental Aircraft, Inc. issued a service bulletin, #002, effecting all Sonerai II aircraft models. Service bulletin #001 was relative to Monerai aircraft and did not apply to Sonerai.

The bulletin was issued to enforce temporary flight envelope restrictions on the aircraft.


History: During the past 10 years of flight service history of the Sonerai II, there have been a total of 4 fatal crashes.

Fact: All four accidents were a result of acrobatic related flight. (By F.A.A. definition.)
Fact: One accident involved a spin or spiral in/after a series of acrobatic maneuvers. It was determined the pilot suffered incapacitation prior to the aircraft striking the ground.
Fact: Another accident occurred when a wing folded during a high "G", low level turn on a high turbulence day.
Fact: Two of the four accidents were a result of high speed and/or sharp, high "G" pull ups which caused a wing to yield and ultimately fail.
Fact: Of the four accidents, only one involved the builder/pilot. Two were at least the third owners. The remaining one was a pilot who "borrowed" the aircraft.
Fact: None of the pilots had purchased or read the Sonerai flight manual. Maneuvering speed and gross acrobatic weight were evidently disregarded.
Fact: Of the three failures due to overload, all involved modifications or deviation from the plans, or excessive weights that were contributory to the wing failures. No two wings failed in the same manor.

The list of contributory facts is much longer, but the point should be clear. An airplane, especially a "clean one" like the Sonerai II or RV-3 (I refer to a very parallel article in Sport Aviation, January 1983) can be easily taken to its structural limits if its flight envelope limitations are not respected!

The most recent accident brought this problem into clear focus. As a precaution, the service bulletin was issued while we sorted out the circumstances and probable cause. Here are just a few of our findings relative to that accident.

1. The aircraft was being flown by the third owner.
2. The operation limitations were not amended to permit acrobatic flight.
3. The permanent airworthiness certificate was never issued. Total airframe time was about 90 hours.
4. The aircraft was technically out of license for two years.
5. An entry in the log book indicated a number of acrobatic maneuvers had been performed including "snap rolls" which are strictly against the operation limitations of the Sonerai II as defined in the flight manual.
6. The aircraft weighed 600 pounds empty. A total of 80 pounds overweight compared to the "average" Sonerai II and 94 pounds heavier than the prototype! With a 150 pound pilot and no fuel, the plane was at the acrobatic gross weight of 750 pounds.
7. The airplane appeared externally to be well made and "clean" yet with a 1834 cc engine at 3800 R.P.M., the reported top speed was only 135 M.P.H. The airspeed indicator was previously checked by a shop for accuracy, but flight test comparisons were not performed to determine static error. It appears a seriously low airspeed reading could have had the pilot working at speeds much higher than the published maneuvering and entry speeds.

Further Testing: Monnett Experimental Aircraft, Inc. has taken a conservative approach to help prevent these kinds of accidents in the future. The service bulletin was the first step towards that end. It does not appreciably restrict flying Sonerai lI's except in the area of aerobatics or with whose examples that have been built, modified or equipped to the extent where they are greatly overweight (above 520 pounds empty). Continued confidence in the Sonerai's design and performance is our utmost goal.

A relative simple modification to the main spar and root ribs has been tested and proven to give a full one "G" margin in yield above the published yield limit loads on the wing. It must be installed to amend the operations limitation back to the original published figures. The F.A.A. has been informed about this requirement.

A survey card was enclosed with each service bulletin issued. Please return your card immediately if you have not already done so! The returns have shown that there are a considerable number of Sonerai builders who do not have the flight manual. They should be familiar with it prior to any further flight. We are presently making some update changes relative to the operation speeds in the manual and will forward those to the builders.

Although the service bulletin does not affect the Sonerai I, this mod would significantly strengthen the Sonerai I wing and should be considered.


Know the airplane. Keep it light. Respect its limitations as you should respect yours. We'll all be safer for it!

John T. Monnett, Jr.

This Sonerai II wing Static Testing <photo didn't scan well from newsletter- RRY> is demonstrating the 6 G acrobatic loading (4.4G utility category loading). At this point the wing was deflected 4" and skin rippling was evident but the wind did not have any permanent deformation. Further tests with 25# increments showed yield to be 7 G's with the modification.

January/February 1984

SONERAI, CONTROL SURFACES - The rudder and elevator surfaces use a welded type of hinge, which, in the plans, is shown as lengths of bushing stock welded directly onto the spars of the stabilizer and control surface. There is another method that can be used that makes the process of alignment a little easier, and it automatically spaces the hinge away from the spar tube a sufficient amount for fabric clearance. As can be seen in figure 1, a long length of the hinge stock can be made up ahead of

time, by welding the desired size of bushing stock (1/4 inch for Sonerai) to a piece of 4130 tubing. The tubing must have the same l.D. as the O.D. of the spar tube (example, 1 1/8 inch spar tube, use 1 1/4 x .058 tubing for the hinge). The hinge stock is then made by welding down the entire length of the bushing stock/tube, cutting the tube down the middle, and then just cutting off the hinges to the desired lengths and welding them to the structures (the bushings will have to be drilled out to size after welding). Using this method will make alignment of all the hinges a little easier, easing access for welding, and easier removal of the hinge pins after welding.

SONERAI, MAGNETO TIMING, The Monnett Aero Vee conversion uses a stock 4216 Slick Magneto with a lag angle of 25 degrees. For engines of 2020 c.c. or smaller we have always set the mag/engine timing at 28 degrees B.T.C., however with the larger engines we use 25 degrees B.T.C.. The difference is not much, but does seem to make the starting a little easier for the larger engines.

For those of you building your own engine you'll have to set the initial mag timing. As a part of regular maintenance the timing should also be checked every 100 hrs., or on a yearly basis.

There are two problems you'll have to overcome for doing this.

1. You'll need a magneto timing light. The light will indicate (glow) when the breaker points in the mag are opening and when spark would be occuring. If a mag timing light cannot be found then an ohm meter can also be used.

2. You will need to accurately determine the position of the crankshaft at 25 or 28 degrees B.T.C. To help you do this we've made a full size drawing of the front of the propeller hub flange<not included in this reprint, get one from GPASC>. Simply cut it out and slip it onto the hub, aligning the hub keyway with the key position shown on the drawing (see next page). On the outside diameter of the flange use a stamp or punch and small hammer to make a mark adjacent to the proper timing position. When this mark is in line with the crank case split line on the top of the engine, it is in the proper position to find the firing position of no. 1 cylinder, remove the spark plug from that cyl. and place your finger over the hole, turn the prop hub thru in the normal direction of rotation until you feel air pressure forcing your finger from the hole. Now you keep rotating until the timing mark on your hub is lined up with the split line. The piston is now in the proper position for firing.

The mag is roughly timed by using the pin and directions that come with the unit. The mag is assembled to the engine, and then final timing can take place. For this the spark plug leads should all be disconnected and the p-lead terminal must not be grounded to the engine or airframe. The mag timing light is connected to the p-lead terminal and a grounding point on the engine.

When the prop hub is rotated backwards about 10-15 degrees and brought back into position, the light should just start to indicate as the timing mark comes into position. If the prop hub is backed off too much, the magneto impulse coupling will engage and the indication will not be correct. To disengage the coupling just rotate the hub past the timing marks and the impulse should snap somewhere around T.D.C., then return back past your timing mark and try it again. If you accidentally make a full rotation of the hub or are not sure of the position of no. 1 piston, repeat the process to determine that the piston is on the compression stroke. It is easy to become confused and the timing could get 360 degrees off, the result being that spark would be occurring on the exhaust stroke instead of compression.

March/April 1984

Sonerai, Tail Spar - The horizontal stabilizer spar is made up out of 3 layers of tubing. The outermost tube (1-1/8" x .035) is a part of each stabilizer surface which is removable. The primary part of the spar consists of a 48" x 1 " x .058 piece of tubing with a 12" x 7/8" x .065 piece of tubing stuck into it at the mid-way point. The 7/8" tube is retained in the 1 " tube by bleed-through from welding the 48 inch spar assembly to the fuselage structure. If desired, small rosette welds (1/4") can be added between the inner and outer tube approximately 5-1/2" out from fuselage C/L to help retain it. (Ed. Note: Shrinkage of the weld at the longerons is sufficient to hold the inner tube in place.)

The 1/8" wide weld beads, 1 " long and six places as shown Sh. 6 of the drawings, are primarily used to provide a snug fit between the 1- 1/8" stabilizer tube and the 1" spar.

Sonerai, Wing Spar - When building a new wing spar assembly, make a note in the drawings (Sh. 14, revised 11-1-83) stating that the upper spar cap reinforcing angle (1-1/4" x 1-1/4" x 1/8") should not be permanently riveted in place until the wing skin has been fitted and drilled to the structure and the spar flange dimpled. Temporarily fasten the angle to the spar with approximately a dozen 8-32 machine screws and. nuts. If the angle is riveted to the spar prior to dimpling the flange, then the dimple die set (as available from us) will not have sufficient clearance to fit between the angle and flange. A dimple die that would fit can be manufactured easily by you by just countersinking a piece of aluminum or steel bar stock that will fit snugly between the angle and flange and then use the male portion of our dimple die set and small hammer to set the dimple into the flange.

Sonerai, Cowling - Quite often we get reports of the top cowling interfering with the top longerons before the cowl will fit properly. It will probably be necessary to cut away the outer, top comer of the top longerons at the firewall station to provide the clearance desired. Close up the longeron comer by welding an .065 steel patch over the opening.

Sonerai, Fuselage and Fabric - As the fabric covering tightens, the longerons and stringers tend to be pulled in by the tension. If the longerons in the two large bays aft of the cockpit are bowed out approximately 1/2", the fabric will draw them back into a straight line. They can be bowed out by heating (normalizing) the cluster at each end of the bay while pushing out on the longeron (example, bumper jack between top left longeron and bottom right longeron). The bottom longerons are affected more from the fabric tension than are the top ones. The belly stringer should be bowed out approximately 3/4" to 1 " and the side stringer approximately 1/2". If the stringers are bowed out excessively for the fabric tension and do not pull in enough, then they can easily be pushed in by hand till straight

June 1984

Sonerai, Mounting Tabs - Throughout the fuselage, tabs are used to retain the cowling, access panels, etc. If you prefer to use machine screws and nut plates as fasteners the size of the tabs should be increased to 1 inch by 1 inch, as the original size tabs may not allow enough room for mounting the nut plate.

Sonerai, Axle Bolts - As specified in the plans the 3/4 inch axle bolt is shown to be 6-1/2 inches long. When the axle assembly finally gets bolted to the gear leg, the width from the wheel pant mounting plate to the axle end may exceed the width of the wheel pant. The axle can be trimmed off as required so that the pant can slide over the assembly without stretching the pant out of shape.

Sonerai, Fuel Strainer - Normally the fuel strainer, gascolator, on a Sonerai is mounted on the forward side of the firewall. The problem is that this location exposes the fuel to the engine heat as it passes through the cowling. It has been common practice for builders to insulate the gascolator and fuel lines that are in the engine compartment in an effort to prevent the fuel from over heating, bubbling and causing intermittent or long term fuel starvation.

Another way to keep the fuel cool is to mount the gascolator on the rear side of the firewall, and have minimum length of fuel line exposed in the engine compartment. A standard, small gascolator will fit in the center of the firewall below the magneto box area, between the rudder pedals. The fuel quick drain can be remote mounted on the forward side of the firewall, accessible by reaching into the cowl outlet from the bottom, and fed by a flexible fuel line from the gascolator. The 1/4 inch l.D. aircraft fuel hose with the braided stainless steel external reinforcing (MiL-H-58089) is ideal for use between the gascolator and carburetor as it has high temperature limits and a small bending radius. The hose normally is used with MS style fittings; however, with the Sonerai fuel system the standard hose fitting and hose clamps work well.

Sonerai, Cable Guides - Nylon fairleads that are fitted into short, steel tubes are mounted in the fuselage at stations 73 3/8 and 154 3/8 to guide the rudder cables through the fuselage structure to the rudder horn. The two fairleads shown for station 73 3/8 can be mounted to the underside of the rear crosstube for the rear seat. This will raise the cables up a few inches and not allow them to rub on the diagonal and cross tubes back through the fuselage.

If your structure is already built, some sort of precaution should be taken to prevent the cable from chafing on any tubes. A piece of vinyl tubing with a 1/2 or 5/8 inch l.D., split down the center, and then tied to the tube works well.

Sonerai, Tri-Gear - The original method of mounting the nose wheel steering cable pulleys has worked fine on our own tri-gear. However, here is an alternate method that will allow the pulley to be self aligning and makes provision for tension adjustment on the steering cables.

The only welding required is when the attach bracket (see Fig. 1 ) is welded to the diagonal fuselage tube. The pulley bracket can be formed cold or hot around a piece of 3/8 inch rod stock in a bench vise. A 3/4" long piece of 3/8 inch steel rod stock is flattened slightly on one side for easier drilling. A #11 hole is drilled and then counter sunk with a 100 degree cutter for the head of the AN507-10-18 counter sunk structural machine screw. This acts as the pivoting point for the pulley bracket so the screw shank must have a 1/16 inch hole drilled through it so that a castle nut and cotter pin may be used. The pulley is assembled to the pulley bracket with the clevis pin, washer and cotter pin. A 3/32 inch cotter pin is used as a cable guard to prevent the cable from jumping off the pulley, if the cable should become slack. The steering cables can be adjusted by adding or removing washers from under the nut as required. The steering cable tension must be set up so that there is sufficient tension to prevent nose wheel shimmy, but not too much so as to cause excessive wear on the pulleys, cable fairleads and rudder hinges. The tension can be checked by measuring the cable deflection in the center of the cable length between the pulley and rudder pedal. It should require approximately 4 pounds of pull to deflect the cable 1 inch. The tension is correct for either the standard pulley arrangement or the previously described alternate method.

July/August 1984

Sonerai, Engine Mounting: Mount the engine to the airframe using the aluminum spacers as shown in the catalog. The rubber mounts are meant to be used with a 3/8 inch I.D. x 1/2 inch O.D. steel bushing 1 -3/4 inches long inside of them. A piece of 1/2 inch x .058 wall 4130 tubing works well. 3/8 inch diameter bolts are used for mounting. An AN960-6 washer should be used on each side of the rubber mount. Torque the mounting bolts/nuts to 175 inch/pounds. Check prop flange for squareness with the fuselage center line and use washers as spacers to correct misalignment as necessary. If the misalignment is severe, then the lengths of the aluminum spacers may have to be adjusted.

The 3/8 inch bushing stock that is used for the fuselage motor mount fittings should be shortened to 1 -1 /8 inches instead of the 1 - 1/2 inch length as shown in the drawings. If built as shown, the AN6-60A bolt furnished in the hardware kit will not be long enough. If the bushings are already welded in place and cannot be shortened, then AN6-63A bolts will have to be used. It is really an easy job to shorten the two top bushings but the bottom ones may be difficult.

General, Engine Temperature: Maintaining acceptable engine temperatures are very important factors when it comes to the reliability and usable lifetime of your engine.

An aircraft builder usually keeps a close eye on his engine temperatures, especially during the first few flights. Unfortunately, the opinion that you form of your engine's performance is only as good as the information you receive. It is important that you know the difference between what your instruments are indicating and what is actually happening.

To start with, check your instruments for accuracy. The oil temperature can be easily checked by placing the bulb in a pan of boiling water. The temperature indicated should stabilize at 212 degrees F. The same check can be used to check the low end of your cylinder head temperature gauge.

To check the high end of your CHT, there are several common liquids which are known to boil at a specific temperature. A few of these are: ethylene glycol (386 degree F), glycerin (550 degree F), and linseed oil (600 degree F).

If the gauge does indicate off slightly, it does not mean that the instrument cannot still be used, but only that a correction card should be placed near the instrument.

Another problem with CHT indications is the spark plug gasket type of thermocouple. Some brands of thermocouples are made with a thin aluminum or steel washer which can be prone to fatigue or tearing during installation or poor sealing under the spark plug base. A failure of the washer can allow blow-by of combustion gases, and heat the thermocouple sufficiently to give a faulty indication. An aircraft grade of copper thermocouple may be less prone to this type of malfunction; however, because of their bulk, they are difficult to fit under the plug on a VW head and may not set properly. This again would allow blow-by and a high temperature indication. The only fix is to inspect your thermocouple for wear, etc. and to insure that the spark plug is tightened sufficiently to provide a good seal and prevent loosening of the plug.

Another convenient way to check your engine temperatures is to use temperature indicating crayons. These crayons are available from most welding supply outfits and are available in 25 degree increments. Each one is made of a substance that is known to melt at a specific temperature. When applied, the crayon will leave a mark similar to a chalk mark, but when the indicated temperature is reached the mark will melt and usually turn black or disappear. They are not too expensive (about $5.00 each) and are very accurate ( ~ 1 %).

A series of marks placed at the base of the cylinder head fins near the spark plug will give a good indication of cylinder head temperatures. One nice thing about the crayons is that marks can be placed anywhere on the engine to give you indications on total engine or cylinder cooling, and whether some areas are running hotter than others.

As far as engine temperature limits are concerned, I have not found an official VW limit prescribed. We can, however, compare it to other aircraft engines. For a Lycoming IO-360, the maximum CHT is 498 degree F with a Bayonet style thermocouple. According to a Lycoming service representative approximately 50 degrees should be added to this figure if a gasket type of thermocouple is being used, as a gasket type will indicate a hotter temperature than a bayonet type. Lycoming normally wants to see a cruise temperature of 400-420 degree F (Bayonet) and a cruise oil temperature of 210 degree F.

For a Continental 0-200 the maximum CHT is 525 degree F taken with a gasket type thermocouple on the bottom, rear spark plug. The bottom or downstream location will give an indication which better represents the actual CHT. Unfortunately, with a VW we have no choice.

For a Franklin 165, the Maximum CHT is 520 degree F taken with a gasket type thermocouple. Remember, the baffling must work well enough to provide adequate cooling to the entire cylinder and head assembly and not just blowing air at the front or top of your cylinders.

With this information, you can perhaps form a better or more secure opinion of your engines operating conditions.

September/October 1984

Sonerai II Gross Weight Clarification - With a modified wing or a "B" wing, all Sonerai are approved for the Standard Category at 1150 Lbs. gross weight. Operations at this weight however should be limited to those Sonerai equipped with a 2180 cc engine and a climb prop (less pitch - 54" dia.) Sonerai with unmodified wings (not upgraded or modified per Sonerai Open Letter of Nov. 10th, 1983) must still operate within the maximum 925 lb. gross weight. (All Sonerai plans sold after Nov. 1983 automatically included the B wing.)

Homebuilts and Night Flying

At the EAA fly-in this year, quite a few builders noticed the position and landing lights on our stretch Sonerai.

Consequently, alot of questions were asked concerning the possibility of equipping their own aircraft for night flying. Normally it is easier to install a standard set of Whelen or Grimes position lights. The tip lights come with their own brackets and are just screwed or riveted to your wing tip. The tail light will most likely require some modification of your rudder trailing edge. For landing lights you could install the standard G.E. 4509 lamp or an automotive type. For anti-collision lights, there is a considerable variety of sizes and styles of beams or strobes to choose from. As for making your own lights, we'll touch on that later.

First off, your homebuilt aircraft is not automatically approved for night flight, even though you may have the required lighting. F.A.R. 91.42 (d) (2) states "each person operating an aircraft that has an experimental certificate shall operate under VFR day only, unless otherwise specifically authorized by the administrator."

Now before you think about writing a letter to Washington, D.C. to get approval, note that "administrator means the Federal Aviation Administrator or any person to whom he has delegated his authority in the matter concerned." This is what your local FAA office is for, they have this authority.

When your airplane is approved for night flight, they will amend your aircraft operating limitations to indicate it.

Now to get this approval, you will have to have the required equipment. In order to fly your airplane between local sunset and sunrise the aircraft must have lighted position lights (F.A.R. 91.73).

According to F.A.R.91.33 to conduct VFR night flight, the required equipment is:

1. Standard VFR equipment 2. Approved position lights
3. Approved aviation red or white anti-collision light system
4. Adequate source of electrical energy
5. Spare set of fuses, though not more than three of each kind is required

Notice that landing lights or instrument panel lighting is not required, but certainly would be beneficial. About here the difference between part 91.73 and 91.33 should be pointed out, the main difference being that 91.33 is for night flying. Night means "the time between the end of evening civil twilight and the beginning of morning civil twilight, as published in the American Air Almanac, converted to local time, "or approximately one hour after sunset and one hour before sunrise."

From all this we know that position lights are required for any flying after sunset, and that the other equipment is not required until an hour after sunset. So if all you have is position lights, you can still fly for an hour after sunset, or before sunrise.

Notice that the required equipment listed in 91.33 calls for approved position lights and anti-collision lights. If you install the standard Whelen or Grimes units, this presents no problem as these are already approved. If you build your own strobe or position lights, you must have these approved and approved means approved by the administrator. (That again!) They may or may not require your homebuilt lights to meet the same specifications as production units. If you would like more information on lighting and installation, you can refer to Advisory Circular 43.13-2A, Advisory Circular 20-30B, and Advisory Circular 20-74. These may be available from your local FAA office, or they can send you information on ordering them.

January/February 1985

Q - Do I need an oil cooler on the Sonerai and where do I install it?

A - Most Sonerai II's fitted with an EV Cowling do not require an oil cooler. We do fit an oil pan baffle to the bottom of the engine which brings air from the inlet below the Spinner across the bottom of the Engine and out the air dump. Some Sonerai I's may require an oil cooler. We found in our prototype when one was used the best position is on the bottom of the engine just ahead of the carb, built into the oil pan cover mentioned above. <Note: the proceeding advice has found to be less than adequate, and most Sonerai use an oil cooler mounted on top of the engine using GPASC's special Sonerai adapter plate.>

Q - Is the Instrument panel bow required for a Sonerai II as shown on the plans?

A - No. The instrument panel bow is not necessary since the cowlings have a molded-in bulkhead and joggle for the canopy. Therefore. the only formed bows in the cockpit area are front and rear canopy bow and the turtledeck bow. The front canopy bow should be made to match the cowling. Since the cowling will fit slightly differently due to differences in fuselages it is impossible to give exact dimensions for this area. It is simply a build-to-fit item and of course is best done with the cowling fitted in place. We usually leave the canopy frame as one of the last things to finish prior to covering the airplane. The instrument panel is held by two vertical pieces of tubing placed between the instruments at that station. The panel will actually rest against the rear surface of the cowling joggle.

March/April 1986

Distributor Drive Gear Adjustment - For those who want to install the distributor ignition in their Sonerai or any VW we have changed the position of the distributor drive gear so the spark plug leads will face aft when leaving the 90 degree distributor cap. This helps make a smoother cowl and allows the distributor to fit under our fiberglass fairing (beauty bump). This drawing will show you what we have done.

November/December 1986

Sonerai Plans Correction - Page 11 Standard Sonerai and Page 13 Stretched Sonerai. The horizontal stabilizer spar (stab. hinge tube) should be 1-1/8" x .035 4130 not 1-1/8" x .059.

Main Gear Attach - Builders can directly bolt the main gear to the fuselage longerons instead of using gear retaining straps. We have used this method (as shown in drawing) on our original low wing and all of our tri- gear models. All that is required is to change the mount bushing location on the fuselage and drill the gear to match.

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