Piper Flyer Association - Technical Know-how, Serious Fun read more

Q & A: A Patch Repair on a Straight-Tail Lance & the Pros & Cons of the Arrow III OEM Turbocharger

Print
(0 votes)

Q: Hi Steve,

I have a PA-32-300R straight-tail Lance (1976). I just noticed a three-inch by three-inch skin repair on both sides of the trailing edge of the rudder. 

I cannot find a 337 or logbook entry—
it was done before I bought the plane. 

My mechanic advises that this type of repair is taboo on the control surface and the rudder needs to be re-skinned. Is this correct? 

If repairs are okay, where do I confirm and show to my mechanic? Any help is appreciated.


—Pete 


A: Dear Pete,

Damage along the lower trailing edge of Piper PA-28 and PA-32 rudders is a common occurrence, according to Roy S. Williams at Airframe Components, a well-known control surface repair facility in Kendallville, Ind. 

“It’s usually caused by overzealous pilots moving the rudder back and forth during a preflight,” Williams told me. 
The material is only .016 inch thick and 
is easily deformed.

Williams stated that it’s a common misconception that patch repairs are not allowed on moveable control surfaces. This, he said, is a holdover from the Piper PA-24/30/39 Comanche service manuals that had specific statements in the Structures section, including, “…repairs to moveable control surfaces is strictly prohibited. Any repair beyond changing hinges or fasteners will require replacement of the entire component…”.

I was surprised to learn that the 
PA-32 service manual does not specifically prohibit patch repairs on moveable control surfaces. “The Structures section of the PA-32 series service manual only states that ‘…all repairs must be made 
in accordance with AC-43.13…’” 
Williams explained. 

“If your mechanic feels that the repair meets the criteria, he or she would need to create a Form 337 that would describe the repair that has been made. You would also need to perform and document a static balance check of the control surface.

“However, that being said,” Williams continued, “Murphy’s Law would probably go into effect. You would probably be on a cross-country trip when you’re approached by an inspector who believes that patch repairs are prohibited on moveable control surfaces of PA-32 aircraft. 

“You would have to produce the Form 337 that documents the repair and spend time trying to prove that the repair is legal. Worst-case scenario, the airplane would get ‘red-tagged’ and you’d have to come back and retrieve it at a later date with a perfect rudder in hand.

“The effort and expense that you expend repairing or replacing the rudder now might be less than the effort 
and expense required to prove that you have a legal rudder at a later date,” Williams reasoned.

The rudder that is installed on your aircraft is PN 65342-002, said Williams. “This same rudder is used on all straight-tail PA-28 and PA-32 series aircraft from the mid-1970s and following,” he explained. “This rudder is used on current production PA-28 aircraft even today. There should be a plentiful supply of perfect rudders available from various salvage yards.”

You can buy a used serviceable rudder from Dodson, Preferred Airparts and Wentworth Aircraft; all three of these companies are Piper Flyer Association supporters. (PFA can help you find a rudder or any other part; this service is included in your membership benefits. —Ed.)

Or, Williams said, you could also have a new skin installed on your existing rudder structure. “If you choose to re-skin your rudder, be sure to send it to a facility that has proper jigging fixtures to insure that the rudder does not get twisted during the rebuilding process,” he said. All of the skins are still available from Piper.


Happy flying.

 


Q: Hi Steve,

I fly a Turbo Arrow III and have some questions about the turbocharger system. 

In a nutshell, how does the system work? I’ve heard guys at the airport talk about wastegates and other terms, but I’m not getting it. 

Can you provide a turbocharger briefing for the system on my T-Arrow?


—Turbo Ted

 

A: Hi Ted,

Good question. The normally aspirated (non-turbocharged) Arrow III uses a 200 hp four-cylinder, parallel valve Lycoming engine. Your T-Arrow uses a 200 hp Continental TSIO-360F or -FB six-cylinder engine with a fixed wastegate turbocharging system. The turbocharger system, if adjusted correctly, provides sea level power (200 hp) up to 12,000 feet pressure altitude. 

One benefit of turbocharging (and turbo-normalizing) is an increased safety margin when operating in and out of high altitude airports. Another benefit is higher cruise speeds, since 65 or 75 percent power is available up into the mid-teens in altitude where atmospheric drag is lower. 

Finally, cruising at altitudes that are too high for normally aspirated airplanes and too low for turboprops—typically between 10,000 and 17,000 feet—is ideal, since this block of airspace is less populated by other aircraft. This often increases the chances of receiving GPS direct routings. 

The illustration above shows how the system in your Arrow works. The turbine (hot) wheel and the compressor (cold) wheel are mounted on opposite ends of a common shaft through a bearing in the center housing. The bearing is lubricated by pressure oil from the engine. 

Rotational speeds of the wheels are dependent on the pressure and volume of the exhaust gases directed onto the turbine (hot) wheel. The engine exhaust gases are routed either onto the turbine wheel or around the turbine wheel through an adjustable orifice in the bypass tubing. 

This type of system is termed a “fixed” (or “ground-adjustable”) wastegate system. It’s a simple system but since there is no boost control system, the pilot must be very careful when managing the throttle. 

If the throttle is advanced too quickly during takeoff, the manifold pressure will shoot past redline. When the pressure is too high, the overboost safety valve will unseat, thereby opening a hole in compressor discharge tubing to relieve the high pressure and protect the engine. 

The other disadvantage of this type of system is that the wastegate is fixed; the pilot can’t control it to increase the exhaust gas flow to the turbine wheel when air density decreases in the climb. 

Turbocharging (and turbo-normalizing) systems with adjustable wastegates are more efficient at higher altitudes since closing the wastegate is the best way to compensate for the decreased air density at altitude. 

The other drawback to a fixed wastegate system is that the turbocharger is always online and since the system is always bypassing some of the exhaust, the system works harder to maintain the desired manifold pressures. This results in higher compressor discharge temperatures (CDT) and, in turn, higher cylinder head temperatures (CHT). 

There are a couple of modifications that have been developed with the goal of reducing the heat-related stress of the fixed wastegate turbocharging system in your Arrow.

The first is the installation of an intercooler in the air path between the compressor outlet and the engine inlet. An intercooler is an air-to-air radiator. Cool ram air is ducted across the intercooler as the compressor discharge air flows through the cooler. 

According to Turboplus, its $5,500 mod drops CDT by up to 160 degrees. The intercooler mod cools the induction airflow so much that manifold pressures have to be adjusted down from the Piper power charts to compensate for the increased power resulting from the denser inlet air. 

Benefits of installing the Turboplus mod are better fuel economy (lower manifold pressures to get equivalent power), increased detonation margins and lowered risk of heat-related cylinder problems. 

The second mod is the installation of an automatically-controlled moveable wastegate in place of the fixed wastegate. Merlyn Products’ Black Magic was developed 27 years ago and retails today for $3,290. 

The Black Magic system is simple and results in greater turbocharger efficiency since the total compressor output is available to maintain manifold pressures. This results in lower compressor speeds required to maintain desired boost. Lower compressor speeds result in cooler CDT, which in turn result in lower CHT. 

This system is so much more efficient than the original system that the critical altitude is increased from 12,000 feet to 18,000 feet pressure altitude. (Critical altitude is defined as the altitude where the turbocharger system is no longer able to maintain sea level pressure.) 

Black Magic is not a totally automatic system, so the pilot still has to be vigilant when adjusting the throttle to set manifold pressures, but it’s a big improvement over the OEM fixed wastegate system.

Occasionally, a pilot may decide to crank in a “performance increase” by adjusting the wastegate adjustment bolt to increase the critical altitude. This is counterproductive since it ratchets up the CDT throughout the entire operating envelope. 

Two adjustments are required to ensure engine health. The first is adjustment of the altitude compensating fuel pump in accordance with the chart and instructions in the service manual. These adjustments provide the correct fuel flow at high power operations (and thus throughout the engine operating range). 

The other adjustment is at the wastegate. A flight to 12,000 feet pressure altitude is needed to determine if the wastegate is set to provide the recommended critical altitude performance. If your manifold pressure drops off at a lower altitude—or doesn’t begin to drop off at 12,000 feet—the wastegate will need adjustment. 

This adjustment can only be done on the ground. It consists of loosening a lock nut and turning a large bolt either counterclockwise or clockwise; then tightening the locknut. The adjustment will then need to be checked by a test flight. 

Both the Turboplus and Black Magic mods address the main shortcoming of the fixed wastegate system and are well worth looking into. Suzanne Evans, owner of Merlyn Products, suggests that the Black Magic system should be installed first since it improves engine performance at all altitudes, but went on to say that the Turboplus intercooler works very well in combination with the Black Magic system, especially for pilots that consistently fly at higher altitudes. 

Remember that in a fixed wastegate turbocharging system the throttle is the direct controller of manifold pressure boost, especially at lower altitudes. Pilots that are experienced with this type of system never firewall the throttle on takeoff; instead they slowly advance the throttle to obtain approximately 30 inches manifold absolute pressure (MAP), then wait a few seconds for the turbocharger to get up to speed before gradually advancing the throttle to takeoff power redline. 


Happy flying.

 

Know your FAR/AIM and check with your mechanic before starting any work.

Steve Ells has been an A&P/IA for 44 years and is a commercial pilot with instrument and multi-engine ratings. Ells also loves utility and bush-style airplanes and operations. He’s a former tech rep and editor for Cessna Pilots Association and served as associate editor for AOPA Pilot until 2008. Ells is the owner of Ells Aviation (EllsAviation.com) and the proud owner of a 1960 Piper Comanche. He lives in Templeton, Calif. with his wife Audrey. Send questions and comments to 

 

RESOURCES >>>>>

Used rudders – PFAsupporters

Dodson International Parts, Inc.

dodson.com

 

Preferred Airparts, LLC

preferredairparts.com

 

Wentworth Aircraft, Inc.

wentworthaircraft.com

 

Control surface repair

Airframe Components by Williams, Inc.

airframecomponents.com

 

Fixed wastegate turbocharging system mods

Merlyn Products, Inc.

merlynproducts.com

 

Turboplus

turboplus.com


Login to post comments