Cold War Air Museum Mi-24D "Hind" gets U.S. Airworthiness Certificate

The second Mi-24D associated with the Cold War Air Museum received its U.S. Airworthiness Certificate today!

Licensed in the Experimental Exhibition category, bord 120, will soon join her sister ship, bord 118, flying to airshows and events.

Museum President, Bruce Stringfellow smiles as he shows off this all important part of our flying machine. Standing beside him is Museum Director Jon Boede and two smiling officials from the F.A.A.

This project truly was a team effort and we want to thank everyone who contributed their time, talent and labor. We also want to thank the F.A.A. for their help and guidance with the project. Look for more blog posts about the story of bord 120 soon.

Congratulations All!

Aircraft Registration Marks

Part of the process of getting an aircraft at the Cold War Air Museum ready for certification is complying with the external marking requirements of the Federal Aviation Administration (FAA).

FAR 45.22 provides a few things that are unique to Experimental Exhibition aircraft:

1) "N numbers" can be as little as 2 inches tall and;

2) Instead of the word "EXPERIMENTAL" on the outside of the aircraft, an X can be placed in the second digit of the "N number" to identify the aircraft in the experimental category.

These concessions allow an aircraft to be displayed close to its original military markings, without as many visual distractions. After going through this ordeal with his own plane, one of the museum benefactors bought a stencil machine to help us with this process and Jon has provided some pictures and a description from one of the current projects, below.

First, the stencil must be designed using the vinyl cutting program. Stencil material can be up to 15 inches wide and the image can either be "positive" (blocking paint from the surface), or "negative" (the stencil is painted over and then removed, leaving a painted image behind).

Here, a "negative" is applied to the aircraft.

Then masking is added to limit over-spray on the rest of the aircraft and the floor.

And paint is applied.

Finally, the stencil is removed. Some experience is helpful at this step, as the paint must be dry enough to leave clean edges but not so dry that it pulls up with the stencil.

The result is a very nice "N number" of precisely the desired size and style.

Watch for more updates on this aircraft in the near future!

Mi24 Bord 120, moving toward flight status

We never seem to be at a loss for projects around the Cold War Air Museum. Among other aircraft receiving attention last weekend was Mi-24 Bord 120. The second, soon to be flying, large Russian (former Bulgarian actually) helicopter based in Texas was scheduled to receive a new set of main rotor blades.

This project started with the new blades on the ground and the volunteers full of enthusiasm. The unique experience that these volunteers get working with associates on their aircraft attracts such aircraft enthusiasts.

The blades have to be hoisted about 5 meters up and aligned to the main rotor hub before they can be attached.

Don't let the look of scepticism fool you, Larry's seen this done before. I think he's just mugging for the camera. We are looking forward to doing articles on each of these associates new aircraft soon.

With a "Yo heave ho", a blade is brought over to the scissor lift that will be used to simplify and expedite the process. Improvising is no stranger to this crew.

Placed on padded saddles, each blade will be carefully raised and moved up to the hub for mating.

On approach, the crew holds her steady.

On short final, they are at the proper height and in the groove.

With minor adjustment, each blade slides easily into place. 

Hey Bruce, I've got cyclic and collective here, a blade on top and we're going up and down and back and forth. We are logging this as flight time aren't we?

Between helping and watching (with amusement), Johnny takes care of routine maintenance on Mi-2 Bord 211, cleaning the transmission filter. Johnny's motto of "Get 'er done, let's get 'em flying" is well applied here.

Mi-24 shake and bake (3 of 3)

How do you get an Mi-24 out of its shipping container? - Plan B

Answer: Pick up the box, tilt and pour, shake gently as necessary. Repeat until done.


One of the problems with successful shipment is constructing good fixtures and securing them in the container so parts don't shift and get damaged. The tails and rotor blades were packed tightly into two standard containers. Unloading these containers was a challenge and some damage occurred in shipment. With all the ingredients out of the box, we could finally begin to "bake the cake".

Putting the ships up on their gear made them portable. Bord 122 looks on sadly as her sister passes by.


A temporary ramp allowed the helicopters to move inside the newly completed building. Congratulations are exchanged as the sister ships, Bords 118 and 120, find their new home.

Mi-24 - Engine up - Right

In previous videos, we showed stop motion composites of the museums 2nd Mi-24, Bord 120 being topped off with the repaired transmission and the left engine being re-installed. After another full days work preparing the right engine bay, we re-installed the right engine. Here is a composite for that day.



One frame was taken every 30 seconds... so each second of video is about 15 minutes. George can be seen in the foreground meticulously checking (and chasing) all the details that needed attention.

Mi-24 - Engine up - Left

In a previous Mi-24 post, we showed a stop motion composite of Bord 120 being topped off with the repaired transmission. After another full day of preparation we were ready to re-install the left engine. Here is a composite for that day.



One frame was taken every 30 seconds... so each second of video is about 15 minutes.

Mi-24 Work Day - another view

In a previous Mi-24 story, we showed Bord 120 being topped off with the repaired transmission. The video below is a composite of still frames taken from start to finish on that work day. Enjoy!



One frame was taken every 30 seconds... so each second of video is about 15 minutes.

Taking Bord 120 out for the day

We are still working on the logistics of arranging the aircraft both for display and easy access in and out of the hangers for flight. Our Mi-24, Bord 120 is shown leaving the hanger before engine and transmission run-up testing. We know from experience with Bord 118 that this will be more challenging once we reinstall the main rotor and tail rotor blades. The following video makes it look easy (with no blades and everything else out of the way).

Bord 120, Engine Reinstallation

After the transmission repair on Mi-24 Bord 118, it was necessary to put everything back in its place. A frequent visitor walked in, looked around and said "I can tell you're making progress. The pile of parts on the floor is getting smaller."

The transmission was set in a cleaned compartment and all mechanical and hydraulic systems were reconnected.

Then the engines were reinstalled. Everything is cleaner and shiner now than when we started, making it easier to work on and ensure that everything is in ship-shape condition.



Completing the process was an actual engine run and spin up of the unit. The original video shows a smoothly spinning rotor. Because of variations in download speed and machine speeds, videos can appear jerky when replayed on a computer. If the rotor hub appears stationary or "jerky" on your computer, it is an artifact of the computer replay.

All pumped up

After we received the replacement pump, Jon installed it and placed an order for massive quantities of hydraulic fluid so we could proceed with ground checks for the various aircraft in waiting.

This pump has two impeller sections and each section is connected to a separate filter and pressure control. This gives the mule two separate systems that can be simultaneously connected to an aircraft. Our larger aircraft (MiG-21, MiG-23 and Mi-24s) typically have two isolated hydraulic systems, primary and secondary.

In its first two days of operation, the mule was used for tests on the Mi-24s, Bord 118 and Bord 120.

The mule is shown here outside the maintenance hanger where it was just connected to Bord 120 to test hydraulic integrity after the transmission was re-installed. The service loop for the mule reaches all of the service bays inside the 14,000+ ft² hanger as well as the adjacent taxiway.

Bord 120 Transmission Top off

After the transmission was rebuilt, it had to be reinstalled.

With an assembly weight in excess of 1000 kilos (more than 2200 pounds) and an installed mast height of more than 4 meters (about fourteen feet), it promised to be a demanding exercise for our crew. After lunch, the volunteers and associates not directly involved gathered to watch. Despite Phil's yawn (we had all come in early), there were some tense moments.

The first step was rigging the assembly for the lift operation.

Not shown here was the substantial "discussion" that took place before everyone involved was satisfied that we would safely achieve our goal.

Thanks to that substantial preparation, the operation went smoothly once it was started.


When the unit was first lifted, everything was checked. Then the operation continued with the unit being raised and moved into place over the top of the helicopter.

A side panel has been removed to provide easier access to the top compartment, even so, the forklift had to be carefully operated within inches of the side of the fuselage. The driver and the crew on top of the helicopter had to shout to be heard over the noise of the forklift engine. The coordination worked well. While we had been prepared for several placement attempts, we were successful on the first try.

The transmission attaches to four mounting points on top of the fuselage. Panels surrounding the transmission and engine compartments provide substantial access for maintenance and repair.

The transmission and rotor components are said to be designed to withstand the impact of .50 cal projectiles.

Brad smiles as he surveys the installation.

Bord 120 - Off to the Races

When work first began on the transmission in Bord 120 the roller bearings in the planetary gearbox were frozen in their raceways.

After chemically cleaning and lubricating the bearings, they were gently tapped until they came free.

The gears were then rotated with a mechanical aid until all the bearing and raceway surfaces were treated. Once the assembly was freed, treatment and cleaning continued until the gears could be rotated smoothly.

Here the entire upper section is receiving a bath. A pump circulates fluid through the unit to thoroughly flush the assembly.

Bord 120 Transmission RTS

After their bath, the transmission assemblies went through several
more stages of cleanup, checkout and lubrication before they were ready to Return To Service (RTS). The planetary gears in the upper section connect the inner hub gear and outer ring gear in this lower section.


Nearing the final step, the assemblies were test fitted and spun by hand to feel for any remaining tightness or binding.

To successfully mate the halves, a template was made to preset the planetary gears so they would drop down between the lower gear head and ring gear when mated.

After the insides were cleaned and ready to go, the exterior was thoroughly cleaned and repainted.

Then the rotor head, which was also cleaned and serviced was reattached.

The entire assembly will be lifted back to the top of the helicopter and installed in a cleaned compartment.

Mi-24 Bord 120, Gearing Up

When the gear box on Bord 120 was opened up, we found plenty of cleanup work to be done.

The smaller(!) parts were removed and cleaned and lubricated by hand to restore free and smooth operation.

While the larger parts were first cleaned and treated in place.

After cleanup and lubrication, all of the assemblies were visually inspected and checked for free and smooth operation before reassembly.

Bill and Brad are looking at the operation of the planetary gearbox in the upper transmission section.

Mi-24 Transmission Shop

The first step in rebuilding the older transmission was taking everything apart.

A lot of people are good at taking things apart. Fortunately we have some people that are pretty good at putting things back together as well. Here the upper section is suspended while the planetary gears are being chemically washed and cleaned. Suspending the section allowed gunk and grit to be washed out of the bearing races instead of being driven further into the races.



The lower section has been cleaned and all gearing now rotates smoothly.

Each piece of the housing is cleaned and gears and bearings are cleaned and lubricated to restore smooth operation.

And individual parts are laid out so they can be cleaned and checked.

Mi-24 Transmission Transition

In January, we reported that we had removed the transmission from Mi-24 Bord 120 in anticipation of receiving a replacement transmission.

Well, the replacement transmission arrived, but when we set about installing it, we found that even though it had the same part number, there were some differences.

The guys evaluated moving the "front end" from the old transmission to the new, making a hybrid of sorts, but then decided to see if they could restore the old unit to working order.


One of the good things about working with this equipment is, "there is no miniaturization involved". When we opened this baby up, we didn't have to worry about a bunch of little parts falling out. This is real "manly" stuff. Of course it must be strong to act as a transfer case for more than 4,000 horsepower. This picture shows the upper section being lifted from the lower section. At the front of the lower section is where the drive shafts from the two 2,250 horsepower turbo-shaft engines connect.

Unfortunately, when we got inside, we pretty much found what we had expected. Either the transmission was not properly conserved, or the conservation had failed and water had gotten in. In following posts we will detail the cleanup process.

Mi-24 #2 repairs underway

Repairs have begun on the second CWAM Mi-24. Because of the volume of projects in January, this work has started in Hanger One where the aircraft is normally on display. In order to remove the transmission, the rotor blades, rotor hub and both engines were first removed. The transmission is shown after removal. More than one person has remarked on its resemblance to a "Lunar Lander".