Wednesday, July 29, 2009


In the U.S. general aviation community, that one word cannot be confused with the name of the town in Wisconsin, or the brand of clothing that bears the same name.

Oshkosh is the name of the biggest airshow in the country, held every year during the last week of July. More formally named Airventure, the event is located adjacent to the EAA campus at Whitman Airfield in Oshkosh, Wisconsin.

Tens of thousands of pilots and enthusiasts come to see thousands of aircraft that fly in annually.

This onlooker is admiring an L39 beautifully painted and restored, flown to the show.

Old aircraft and new aircraft fly in different airshow segments on a daily basis. At this years event, several associates flew to Oshkosh as they have in the past. Although attendance was down,

Phil made a number of contacts with other museums and enthusiasts who recognized his Cold War Air Museum shirt and made arrangements for future visits and events.

Tuesday, July 28, 2009

Mike's Mic

Microphones should be simple.

Of course, in the best of all possible worlds, everything should be simple. As a former radioman might tell you though, nothing is ever as simple as it seems, and not all microphones are the same.

The M1-DC headset mic shown above has a built in amplifier. The small screw visible in the picture is a gain adjustment screw. Turning the screw "up" makes the wearer "louder". A better use for this adjustment is to balance the microphone output to match other microphones or systems requirements. A technician can match A radio to A microphone, or in the case of the microphone above, A microphone to A radio. When you start mixing a bunch of different mics with a bunch of different radios, you don't always get good results. That is where standardization becomes necessary.

The recent installation of a new radio/intercom system in the Mi-2 brought attention to cabin noise levels and balancing different microphone inputs. One pilot's mic (Mike's mic) had significantly more gain than the others and background (turbine) noise was strongly amplified during the flight.

Recent experience with piston helicopters at the Cold War Air Museum has been at much lower ambient noise levels and hot mikes or voice activated intercoms have given good performance. Because of high noise levels, most military helicopters have push to talk intercoms. But we are still working towards the convenience of voice activated systems in the Mi-2, at least for the pilots.

Although a subjective evaluation can be made during flight tests, it is expensive to experiment with different settings and equipment while burning 2-3 liters of Jet-A per minute. So evaluation and testing is done on the ground when possible.

Although classic shop equipment is available, testing has been made easier by the availability of plug in analyzers for laptops computers. After a series of ground tests, we can focus further in-flight tests on specific noise issues associated with the Mi-2.

This gaggle of headsets represents some of the headsets used by our associates. ANR's from Bose and Lightspeed as well as passives from Peltor and David Clark, including the 10-46, 10-56 and 10-66 are shown. Each has a different microphone.

Although all are "GA Helicopter" headsets, microphone outputs varied by 3:1 across the group. While the human ear can easily compensate for this kind of difference, an automatic squelch or background noise adjusting circuit has a much more difficult time.

Saturday, July 25, 2009

Hot Wash Sprayer

Prop wash, Jet wash, Hot Section Wash. Only one has something to do with a bath. In a previous maintenance post, Jon talked about his work chasing rising temperature indications in our Cold War Air Museum, L-39, Bord 107.

Another step in the maintenance process involves washing the engine with a special cleaning solution while it is running. Essentially this gives the guts of the engine a bath, helping to clean out any accumulated gunk interfering with the combustion process.

After receiving diagrams and information from a former Eastern Bloc specialist, Jon fabricated a high volume, high pressure spray unit to inject the cleaning solution into an intermediate stage of the engine at high power. With the help of our local network of scroungers and specialists (not to be confused with scoundrels and speculators), Jon created this unit to deliver the pressure and volume specified.

To test the unit we timed the required delivery of the required volume of fluid. The test went exceedingly well.

Jon demonstrates the cleaning solution delivery system by a emulating a boy in a European fountain (well, he sorta kinda had that Greek/Roman statue look anyway).

Before the wash procedure, copious quantities of distilled water were acquired to mix with the cleaning solution.

Monday, July 20, 2009

Mi24 on display at "Warbirds on Parade"

Previous posts about the Mi-24, "Gate Guardian" have shown it outside, next to the Commemorative Air Force (CAF), DFW wing hanger.

From an event planning standpoint, this years "Warbirds on Parade" event (September 5th) is fast approaching. One of the target action items left in the event planning is relocating and completing the CAF's Mi-24 static display.

Bruce and Jim discuss logistics over some of the parts left to be moved from the Cold War Air Museum hangar as the CAF volunteers rig the transmission for transport.

In order to finish the work, the CAF crew moved the aircraft inside their hangar to get it out from under the hot Texas sun.

Before moving the transmission inside, the bent blade attach fittings were heated and restored to shape so the rotor blades could be remounted. Charlie, the Wing commander gives his signature smile of approval as he checks the work.

Soon, the rotor head and blades will be securely remounted for static display (Not for flight!) and the Mi-24 will be moved back outside to a new display pad between the CAF hangar and the road.

Sunday, July 19, 2009

Sopwith Camel?

Back at the turn of the century, (20th) in the cold gray skies over Europe, the Red Baron dueled with intrepid English airmen in their Sopwith Camels.

Well, this is not exactly a Sopwith Camel, and this is not the cold gray skies of Germany, but it's an interesting image to share.

The Cold War Air Museum is always looking for interesting aircraft and artifacts to add to our growing physical collection and interesting stories to tell our visitors in person and on the web. We admit that this one may be well beyond our normal scope. It may be odd, it may be unusual and it may beg the question , "What has this got to do with aviation?" But I think Snoopy would probably understand, and hoist a brew in salute.

Thursday, July 16, 2009

A little radio goes a long way

A lot of pilots equate size with performance.
The Soviet era radios in the back of the Mi-2 are plenty big (and heavy), but they don't give us the performance or full range of channels we need to communicate in US airspace. Although the Mi-2 is big by most standards, the range of options for easily putting radios within useful reach of the pilot is frustratingly limited. Fortunately we came across a very small but powerful radio that we are evaluating for the Mi-2 at the Cold War Air Museum.

The MGL Avionics, V10 mounts in a standard 3 1/8" instrument cutout and takes up only about 2 inches of depth behind the panel. The entire radio, not just the control head, is shown in the picture above. With modern technology, this small box should equal the range and performance of older boxes many times its size.

The radio essentially "dropped-in" to the panel in place of the inop radar altimeter directly in front of the pilot's station.

The radio specs are very promising and hangar tests of the radio and its built-in intercom showed good performance. This weekend we hope to get a chance to do an in-flight evaluation of the unit (and its built-in intercom) in a real-life, noisy, operating environment. Radio troubles are often caused by poor installation of the radio or antenna, so we will be paying special attention to identifying and correcting any problems in those areas as well. Tune in later for updates.

Monday, July 13, 2009

Hot, Hot, Hot

One of the museum's L-39s, Bord 107, has been running high EGT (exhaust gas temperature) for some time. The L-39 has an EGT limiting circuit that illuminates a warning light at 700°C... and should the EGT reach 730°C in flight, the engine will automatically be shut down when the nose-wheel touches the ground. (No go-arounds possible!)

A "730" event is very serious in nature and requires an inspection to be performed before the secret reset button (location not divulged to pilots) is pressed and the engine can be started again.

Bord 107 was regularly seeing the 700°C light flash on take-off and the situation was mitigated by pulling the throttle back a bit. But too much of that and the turbine will start spitting blades out the back.

Soot buildup in the combustion chambers eventually disturbs the flame pattern, causing the combustion to continue as it moves further back. Flames licking at the EGT probes behind the engine gets the warning light to start screaming, "Ow! You're hurting me!"

Over time the ventilation holes in the inner jacket get, as our very German adviser says, "stuffed like little bratwurst". Lack of good air flow prevents a good clean burning of the fuel.

The problem initially manifested itself as a drop in the HPC (high pressure compressor) RPM. Our Czech mechanic had adjusted the fuel controller to put a little more fuel in to bring the RPM back up. That brought the RPM back up, but the EGT came up with it... in effect, it only made the problem worse since extra fuel burned even longer and even farther back in the compressor area.

One indication of this problem is flames in the exhaust at high power. Our adviser, Bernd of Aero Contact, sent these graphics to illustrate what to look for:

Taking a look at Bord 107, that's what we saw — and Brad has a whole new respect for jet exhaust! Fortunately, there is a solution, although not a simple one.

The first step was to send all the instruments to Bernd in Germany to have them inspected and calibrated; it simply wouldn't be possible to get to a "correct" solution without accurate readings on the instruments.

So out they came...

And off they went...

After Aero Contact's analysis, the instruments were judged to be in tolerance, although the front and rear RPM indicators need to be swapped so that the more accurate one would be in the front cockpit.

Historically there have been a number of ways to deal with soot buildup in jet engines. One of the simplest ways to clean an engine is to fly through heavy rain. The scrubbing effect of the water and steam will do wonders for a mildly dirty engine. Rain water has the added benefit of having a very low mineral content, so it's much better for the engine than tap water. Another simple method was to bring the engine up to speed and throw a small amount of ground Walnut shells (yes, WALNUT SHELLS) into the engine. While this worked reasonably well for centrifical flow engines, it doesn't work quite as well for axial flow engines... and a hard chunk of walnut shell can do more harm than good.

The more modern method is to spray a solvent into the engine in one of two methods, either OFF-LINE or ON-LINE. Off-line (or "crank washing") an engine consists of "cold" rotating the engine at 20-25% RPM and soaking it down with solvent. On-line washing injects the solvent while the engine is actually running at about 90%. Using both methods together generally results in a good cleaning.

Caustic solvents were originally the preferred detergent for cleaning engines, but they were an EPA nightmare. A lot of chemical engineering has gone into producing water-based solvents such as TurboTect 2020 that are almost as effective as the old solvents and the effluent doesn't have to be carted off in a HazMat truck. The water-based solvents do a little better job on hardened salts but not quite as good a job on small (35 micron or smaller) particulates. A number of patents have been issued in recent years for solutions to this problem.

Bernd is sending a special injection tool to do crank washing deep within the compressor section. A few cycles of this kind of cleaning will reportedly bring the EGT down as much as 40°C and improve the power output by several percent.

The instruments, injection tool and a 55 gallon drum of solvent should all be here this week... and none too soon, it's hot enough in Texas!

Sunday, July 12, 2009

What's in a name?

Despite the best efforts of officials, an aircraft takes on a name and identity given to it by those who fly it and use it, not by those who design it or pay for it.

The U.S. Army has an official policy of naming helicopters after Native American (Indian) tribes. Despite the best efforts of publicists, no one calls this an Iroquois, everyone calls it a Huey.

The T-37, featured in the preceding post, is one of a handful of U.S. aircraft that were not officially named when they were "born". Another was the F-111.

Never officially named during its service career, the F-111 was always known by its unofficial nickname. At its decommissioning ceremony, the F-111 finally received an official name, the name those who had flown it and worked on it all its life knew it by, the Aardvark. The "Tweet" may receive similar recognition on its official retirement.

The A-10 "Thunderbolt" follows a modern pattern of naming aircraft after a successful predecessor, in this case, the P-47 "Thunderbolt" of WWII fame. Like the P-47, the A-10 fulfills a close support role and can absorb a lot of punishment. The troops and those who fly it however know it more intimately by its nickname, the "Warthog" or simply the "Hog.”

Now officially retired, the F-117 was named the Nighthawk. But it was called by its nickname, the Wobblin Goblin, Wobbly Goblin or simply the Goblin. The F117 was the first of the current generation of stealth aircraft. Designed more for stealth than stability, early prototypes were described as "wobbly" because of their unstable flight performance (but later versions were reported to have improved handling). Its "spooky" ability to disappear on radar and its strange appearance easily justify the Goblin moniker.

Despite the best efforts of Generals, Admirals and Vice-Presidents of Marketing, the best value judgments and names that "stick" come from the field.

Friday, July 10, 2009

Bye, Bye Birdie

The T-37 was affectionately known as the "Tweet" or "Tweety-Bird".

Over a period of fifty years, more than 78,000 U. S. Air Force pilots received their initial training in the T-37. Now being replaced by the T-6A (Texan II), the T-37 will be officially retired from service on the 31st of this month.

Responding to a USAF request in 1952 for a lightweight basic trainer, Cessna offered this twin-jet with side-by-side seating. The Air Force liked what they saw and the first prototype was flying in 1954.

The wide track and a steerable nose wheel made it easy to handle on the ground, and the short landing gear eliminated the need for access ladders and service stands. The aircraft was designed for simple maintenance and had more than a hundred service panels and doors. Experienced ground crews could change an engine in half an hour.

The twin Continental-Teledyne J69-T-9 turbojet engines used were license built copies of the French Turbomeca Marboré engine (the same engine as in the Cold War Air Museum's Fouga). Since the short landing gear placed the engine close to the ground, screens pivoted over the intakes from underneath when the landing gear was extended, to prevent foreign object damage.

The A-37 was an armed variant of the Tweet. Developed as a light attack or Counter Insurgency (COIN) design in 1963, the "Dragonfly" had bigger engines, more hard points and more range (or loiter time).

The dual controls were retained, so it could still be used as an operational trainer and the second seat was available for an observer when used in the Forward Air Control (FAC) role.

The A-37 saw extensive use in Vietnam. This aircraft, on display at the Military History Museum in Ho Chi Minh City (Saigon), is a veteran of that conflict.

Twenty countries flew or operated the T-37 and fourteen flew or operated the A-37, making it one of the more widely used and longer lived military light jet designs.

Thursday, July 9, 2009


Jay is an associate of the Cold War Air Museum and one of two father-son pilot teams in the extended group.

He favors the CJ when he is in town (which lately isn't often). Currently in St. Petersburg, Russia, Jay is an ardent student of history, languages and economics. On his return to Washington, D.C. where he works and studies, he will be receiving a Masters Degree from George Washington University. His undergrad degree was from Michigan (Go Blue!).

With his love for history, Jay gathers contacts and pictures during his travels. This picture from Vietnam shows a montage of aircraft from that conflict on outdoor display. As time moves on and younger generations take over from the older generations, museums such as ours or even unattended outdoor displays like this one are a meeting point for the past and the future.

Tuesday, July 7, 2009

Who Broke My Helicopter?

At the Cold War Air Museum, some of our associates like to fly aircraft, some of our associates like to fix them, some of our associates like to talk about them and some do all three.

Summer in Texas brings daytime temperatures around 40C (over 100 degrees Fahrenheit). A recent mild "cold" front passed through and the temperature "only" reached about 34C (around 93F). Although our aircraft are in hangars and out of the direct sun, working on them in the heat is still uncomfortable. With the realization that there will probably not be any cooler days left this summer, we jumped in to do some avionics work in the Mi-2.

We are fortunate to have translated factory manuals, but even so, it can be challenging to read schematics and technical documents originated in a different language with different drawing conventions. Previous experience and perseverance helps. While the main DC buses are below the instrument panel, the breaker panels they feed are in the overhead with power running from there to the soviet style avionics boxes located in a compartment at the rear. Our more modern equipment will be up front, so some wiring has to be changed. The wires dangling in this picture will assist in adding modern radios to the panel while maintaining as much of the original look and feel of the aircraft as possible.

Of course the day would not be complete if someone didn't want to fly the aircraft when the radio guy left some panel open. Fortunately crew chief Phil knows the drill and helps to co-ordinate the program, buttoning things up and checking things as necessary. The normal shop schedule is to work around flying events and to leave each aircraft in flying status as much as possible. At the end of this day, Bord 211 was back in flight status with power going to a new radio box.

Sunday, July 5, 2009


We have fun whenever we can at the Cold War Air Museum and fortunately most of us maintain a sense of humor, most of the time.

Phil completed a project this weekend to attach the Mig21 wing so that Charles can finish fabricating the replacement short spar in the right wing leading edge.

Jon arrived just in time to help with setting the wing attach pins in place and to demonstrate a Victory Dance on top of the wing (we like airplanes we can walk on - or dance on, none of this wimpy Cessna stuff, thank you).

We had a delay from our earlier work bringing the Mig-21 together when we discovered some damage on one of the pieces of the wing. Our airframe consultant recommended replacing the piece and fortunately one of our volunteers was capable of fabricating a replacement.

The replacement piece is shown with the damaged piece above. The person fabricating this piece has made many "one of a kind" pieces for special U.S. aircraft and he was surprised at the techniques and technology embodied in the part (bearing in mind our belief about what we thought their capabilities were at the time).

The temporary attachment allows the replacement piece to be positioned so that rivet holes joining it to the wing skin and leading edge spar can be drilled in place, ensuring that the new piece perfectly replaces the old. After these holes are drilled, the replacement piece will be removed and a surface treatment applied before final attachment.

The wing will be removed and re-attached at least once more before final attachment. The lessons learned in each experience are incorporated as we go along.

Here, the wing dance floor and the wing attach bolts are shown prepped and ready for Jon's arrival.

Saturday, July 4, 2009

4th of July - Independence Day

Fireworks have been used for celebrations ever since the invention
of gunpowder.

It is the tradition in the United States to celebrate the independence of our country every July 4th. It is a Federal and local Holiday and many families attend parades, picnics, fireworks shows and patriotic events.

One of the most enduring myths about America's Independence Day is that the U. S. Congress signed the Declaration of Independence on July 4, 1776. The legal separation of the American colonies from Great Britain occurred on July 2, 1776, when the Second Continental Congress voted to approve a resolution of independence that had been proposed in June. At the time, John Adams wrote that July 2nd would be the day celebrated thereafter as the day of independence.

After voting for independence, Congress drafted the Declaration of Independence as a statement to explain their action. After debate and revision, the resulting declaration was passed on July 4, however most scholars agree that the 56 signers were never together as a group and the version generally referred to as THE Declaration of Independence, the one on display at the National Archives, was effectively signed on August 2nd, of that year.

In a remarkable series of coincidences, both John Adams and Thomas Jefferson, two of the founding fathers of the United States and the only two men who signed the Declaration of Independence to become president, died on the same day: July 4, 1826, which was the United States' 50th anniversary. President James Monroe died five years later, on July 4, 1831, but he was not a signatory to the Declaration of Independence.

Wednesday, July 1, 2009

More Emblomology

Red Stars have been used on more than just Sino-Soviet Aircraft.

The emblem on the left belonged to the XII corp of the Union Army (U.S. Civil War, 1862). Reconstituted as the XX corps in 1863, the unit's emblem was simplified (shown on the right).

The Chinese Air Force (The Peoples Liberation Army Air Force) has used a star alone and a star with bars extending to the sides. The symbols in the star refer to the date of the Long March.

In a somewhat similar manner, the U.S. has used a star in a roundel and a roundel with a star and bars extending to the side.

The graphic above, steps through a series of the emblems used over the years by U. S. Forces.