lml@lancaironline.net Mailing List Archive

Bob,

Thank you very much for the excellent, thorough and detailed explanation. You covered everything!

My IV is an earlier model, #84, and has the original two piece main gear doors--with the smaller outer doors instead of the wing root extensions. That certainly changes the geometry and wind loads. I can only guess at how much. They work well and have had no issues. The later one-piece doors certainly look sleeker, but I suspect the loads are higher on the larger area and the single piano hinge instead of two hinges.

The smaller outer doors stay open, held by springs, when the gear is extended, unlike the large doors which close. So, when the gear is retracting, only the large doors need to open to allow the gear to retract into the fuselage. This design has much less door area at the aft end of the door (covering the wheels) and thus, I think, less likely to block the wheels from entering the fuselage. Your description indicates that excessive wind load causes the aft end of the doors to twist closed, while the forward end is being pushed open by the gear legs. Did I get that right? So, the wheels could be on the outside of the wider aft end of the doors, while the legs are mostly inside the fuselage, partially covered by the forward part of the now twisted doors, The doors would then fully open upon gear extension, resulting in no more than some possible scratches and cracking in the doors.

I've not been able to find any changes/differences in the max gear up speeds between the two designs. It seems that the two piece design would allow higher retraction speeds.

Do you know why they changed the design to the one piece--other than aesthetics or to simplify the build process?

Thanks again for your help.

Bill

On Thu, Mar 13, 2014 at 6:53 PM, Robert R Pastusek <rpastusek@htii.com> wrote:

Bill wote:

What happens when the L IV gear is retracted at a speed exceeding the 120 kts maximum?

Bill, the most common occurrence is that the main gear doors flex closed at the back due to air loads, and “trap” one or both mains, preventing them from fully retracting. Note that the retraction speed is lower than the extension speed--I suspect to compensate for the very strong prop blast under the airplane during takeoff? If the gear doesn’t retract because of this problem, reduce the power, slow down, extend the gear and try it again. If you suspect other gear problems, I’d put the gear down and if it extends normally, land and check it out. There are some malfunctions that can keep the gear from extending. This is not good…but having them hang up on retraction should be a minor issue; at most some chipped paint.

The gear actually tends to hang on the bolts holding the axle to the gear leg, or part of the brake assembly. You can usually tell after landing by the chipped paint on the inside of the gear door(s). In any case, the stiffness of the gear doors will have a lot of influence on whether the main(s) get hung up or not. Lancair modified their gear door build plans in about 2002 to significantly stiffen them. I incorporated this change and have had no trouble at all with mine. I tested retraction to 130 KIAS during my Phase I, but am probably lifting the gear more quickly than I should during normal operation, so I don’t think I get to 120 before the gear is secure during normal ops. By the way, I have only one (2 specified) springs on the back of each main gear door to close it.

You didn’t ask, but if you fail to re-connect the nose gear door operating linkage (after replacing the lower cowl?), the nose gear doors will swing shut a bit under air loads and trap the nose gear in a partially-retracted position (this one I know from personal experience!) It should extend normally by pushing the doors out of the way in the process. The only fix for this problem is to land and re-attach the linkage. I have not tried, but would bet money you’ll not get the nose gear past the doors, and even if you did, you’d have the doors flapping in the breeze.

By the way, I’m talking about mild exceedence of the published limits above. If you’re talking extending/retracting above 150 KIAS, then I’d think you could expect damage/loss of the gear doors, and possibly to other aircraft damage.

Bob Pastusek