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For your consideration,
I have had the privilege of meeting and getting to know Martin Hollman. For those that may not know him and his role in the development of the IV, an excerpt from his webpage gives a general description of his involvement in the design, stress and flutter analysis of the Lancair-IV.
"In 1988, Lance contacted Martin to help design a four place aircraft around a Continental TSIO-550A engine which had 350 hp at 2,700 rpm. From the outset the aircraft was designed to be pressurized and fly at 24,000 ft. I called my good friend and aerodynamicist, Rick McWilliams to design the wing and I designed the structure and stressed everything. The Lancair IV was built in 1.5 years and introduced at Oshkosh in 1990. The first prototype and kits were not pressurized. On a Friday in July, 1990, Lance and Dave Morss took off for Oshkosh, flying at 19,000 feet and using oxygen, the cruise speed was 300 kts. About 25 Lancair IVs were sold that year at Oshkosh. The Lancair IV was fast and Dave Morss went on to set many records with it such as flying from Los Angeles, CA to Florida in 6 hours and 2 minutes at 24,000 ft. averaging 385 mph. Below, left Don Goetz is clowning around during
the lead shot load test of the LIV wing test. Lance with his back to the picture is not amused. "
In my meetings with Martin we discussed several issues that have come up over the years in the building and flying of the Lancair-IV.
The one issue that we're dealing with in this thread is the cutting of holes in the aft fuselage.
He thought it was inadvisable due to harmonics and flutter. No testing, computer or otherwise have been completed that would give you assurance that you can handle turbulence-- to whatever degree-- that you encounter. I suggested that if we were to reinforce skin around the hole-- would we be able to regain the strength??-- his answer was no.
Airframe breakup analysis of the IV's that have encountered thunderstorms has been unavailable.
We could debate forever the forces of thunderstorms and the inability of our aircraft to sustain such loads, but I do remember that post-World War II testing put fighter aircraft into thunderstorms and nearly all were able to fly out. Our cap strip method, carbon fiber materials, hardware backup for critical bonds, overdesigned bid schedules (Martin said that all schedules were to designed strength plus 30%!!). I have flown the Mountain West in my IV many times. And I am very grateful for these margins of safety.
It would be an extremely interesting study to determine how many aircraft that have had in-flight structural failures correlated to their fuselage modifications. Sad to say, but if you have a failure in this area, there will not be many pieces left. Just another insurance claim.
Point of interest--- where do you think the "weak link" is in the Lancair IV??
What would you inspect after a hard landing or severe turbulence encounter?
Write me off line and I'll give you the answers.
Charlie K.
--- On Mon, 1/26/09, Robert Pastusek <rpastusek@htii.com> wrote:
From: Robert Pastusek <rpastusek@htii.com>
Subject: [LML] Re: air intake
To: lml@lancaironline.net
Date: Monday, January 26, 2009, 7:42 AM
I assume that the air intake in the tail is originally designed to be used for the ac unit and that the previous owner cut a hole in the bottom of the fuselage to force more air through the heat exchanger of ac unit. I want to close the hole in my tail now since I am not using this air intake.
Would you recommend my plan or does the air intake in the tail serve another purpose?
Ralf,
The “original” Lancair IV did not have air conditioning, and was not pressurized. The air intake in the tail was used to collect high pressure air in this area and duct it forward for cabin ventilation/cooling. It worked extremely well. When later models of the IV were pressurized, a flapper valve was added where this ventilation air passed into the cockpit at the rear pressure bulkhead so ventilation air could move forward into the cockpit, but cockpit pressurization air could not “leak” backward through the ventilation ducting. This system also works well, but you can either have a “ventilated” or a pressurized cockpit; but not both at the same time. As a result, some builders, especially those who installed air conditioners, just eliminated the cockpit ventilation feature completely and used the A/C for cooling. From your description,
that’s the configuration you have…the air intake in the tail has not been connected to the cockpit through ducting—typically along the fuselage top.
Before closing off the tail inlet, I’d check carefully on the air flow through the A/C heat exchanger. It’s possible the heat exchanger uses air from both sources, although either should be adequate in most conditions. You didn’t say where the air exited the fuselage after it passed across the heat exchanger…this is a consideration as well, as the total A/C effectiveness/efficiency depends on the condenser working properly. If you’re satisfied with the outflow, I’d suggest plugging the tail opening with Styrofoam to test the effect, and if the A/C and aircraft ventilation systems still work to your satisfaction, glass over the plug and paint…
Hope this helps; glad to exchange information with you off-line if desired.
Bob Pastusek |