KR> Horizontal stabilizer incidence
It's the latter, Although it would be nice not to need any trim, what i do not want is to need massive amounts of trim to hold the nose up (or down). My current aircraft had a nose-down tendency and no amount of trim would alleviate the pitch down when pulling off the power. I eventually found out that the fix was a CG issue. Since the baggage was empty, I was usually toward the front of the CG range, but with weight back there, the plane was a whole different animal at the aft CG limit. Other owners noticed the same. Faster cruise, no lawn-dart tendencies or stick forces needed to hold the nose up. So I called the designer himself, and he informed me that this was no surprise, the aft limit was quite conservative, so flying at the aft limit was a good way to get a balanced situation. I could load the baggage compartment and adjust power any amount and still be able to keep it level hands-off the stick. This KR conversation concerned me because of the stabilizer incidence issue. I do not want to build in a pitch tendency and then have to fight it with trim, or worse, have full trim and still have stick forces at various power levels. I'm hoping to choose an incidence that is balanced and, along with a good CG, will allow me to reduce power on approach without having to crank in tons of trim and still have to hold the stick back. Because of all the fiberglass etc, this is one area I need to get right during the build, if possible > > I want neutral trim at all speeds from 60mph to 200 (if my build > > is non-LSA spec) > >+ > > If you are saying you want to build a KR that requires no movable > pitch trim tab, you've got a tough hill to climb. Every airplane is > full of compromises, what works at one speed is wrong for other > speeds. No airplane I've ever seen or flown requires neutral trim at > all speeds. Some aircraft have such a small speed envelope that when > set up correctly they really don't require pitch trim tabs. Variable > pitch propellers are another example of where you need to change > characteristics of components depending on speed. Then there are > flaps, lead edge slats, etc. > > If you are saying you want zero control forces at any speed, then > it's just a matter of sizing the tabs and building in the necessary > range of movement. > > Larry Flesner > >
KR> Horizontal stabilizer incidence angle and pitch trim
I hope more folks chime in on this. I wills ave this topic aside for when I make my build. So far, it looks like horizaontal stabilizer incidence angle, and size of tail are to be considered. I want neutral trim at all speeds from 60mph to 200 (if my build is non-LSA spec) > Yep. As built, mine pitched down rather badly. I had wedges bonded to the > bottom of the elevator to fix the trim for several years until I finally cut > the horizontal stab and elevator off to build a much larger tail to address > the pitch instability that was also designed into the plane. I adjusted the > incidence by 1? when I built the new tail. The trim is now flush with the > elevator at normal cruise speeds. > > My wing is also set up with 3 1/2? incidence and 3? washout, although with a > bit longer wing than Larry's. > > -Jeff Scott > Los Alamos, NM
KR> Horizontal stabilizer incidence
> I want neutral trim at all speeds from 60mph to 200 (if my build > is non-LSA spec) >+ If you are saying you want to build a KR that requires no movable pitch trim tab, you've got a tough hill to climb. Every airplane is full of compromises, what works at one speed is wrong for other speeds. No airplane I've ever seen or flown requires neutral trim at all speeds. Some aircraft have such a small speed envelope that when set up correctly they really don't require pitch trim tabs. Variable pitch propellers are another example of where you need to change characteristics of components depending on speed. Then there are flaps, lead edge slats, etc. If you are saying you want zero control forces at any speed, then it's just a matter of sizing the tabs and building in the necessary range of movement. Larry Flesner
KR> horizontal stab
> >Yep. As built, mine pitched down rather >badly. I had wedges bonded to the bottom of the >elevator to fix the trim for several years until >I finally cut the horizontal stab and elevator >off to build a much larger tail to address the >pitch instability that was also designed into >the plane. I adjusted the incidence by 1?? when >I built the new tail. The trim is now flush >with the elevator at normal cruise speeds. >My wing is also set up with 3 1/2?? incidence >and 3?? washout, although with a bit longer wing than Larry's. >-Jeff Scott + Jeff and I both have the RAF48 airfoil on a longer than plans fuselage. I'm assuming Jeff set his HS lead edge to one degree negative when he enlarged his tail assembly. Larry Flesner
KR> LOAD TESTING spar / horizontal stab
At 12:51 PM 2/24/2015, you wrote: >If wing spars or whatever are being load tested, rather than make sandbags >one could go to the garden centre or agriculture supply and borrow bags of >chemical fertilizer. >Bill Weir ++ No intent to stifle discussion on the spars but it seems that thousands of hours of flight on KR's in the 1100+ pound range, with spars built to plans, has shown they are quit adequate, IMHO. I know Marty Roberts tested his 760 pound empty KR to 6 G's on his G meter. The forces were great enough to cause his baggage compartment to tear loose and limit the travel of the elevator cables. It came very close to being fatal. After landing he called it a day and requested a "root beer". Another subject that has seldom been discussed, except when Mark Langford built his KR to do testing in that area, is the incidence of the horizontal stabilizer. I bring this up for those still building to consider when setting the AOA of the horizontal stabilizer. The plans, on page 57, call for the incidence to be set at zero degrees. That is where mine is set. My KR is a 24" stretch but I don't think that is a variable to consider here as zero is zero but mine is on a longer arm and may amplify a problem. My KR, with me and fuel on board, has the CG dead center of the 8" range. If I take off with pitch trim tab set to zero, when I reach cruise , 150 mph, and let go of the stick, I get a near violent nose down pitch, enough to toss things up off the seat. My wing is set at 3 1/2 degrees AOA with a 3 degree washout. That might very well be a variable to consider. When accelerating to cruise I get increasing forward pressure on the stick. I normally adjust the pressure off with pitch trim while accelerating so it's not a problem but I think it could be rigged to be a little more aerodynamic and eliminating a bit of drag. Could my wing AOA at 3 1/2 degrees be generating too much lift and causing a nose down force, or is a slight nose down attitude causing the airstream to apply a slight down force on the elevator, or would a slight negative AOA on the horizontal eliminate or add to the problem. Inquiring minds want to know. I hope this doesn't keep anyone up nights trying to solve the puzzle. Have any other flyers noticed the same thing or is it just my KR? I normally leave my pitch trim set as it was for landing so the problem is minimal on takeoff and cruise. Larry Flesner
KR> LOAD TESTING
If wing spars or whatever are being load tested, rather than make sandbags one could go to the garden centre or agriculture supply and borrow bags of chemical fertilizer. They will already have their weight printed on them and so on. Bill Weir
KR> Spar and WAF stress analysis
the conclusion of the German Test of the Kr Spar and WAF's calculated by Otto Bartsch is: Any reliable built Kr with a MTOW of 1050 pounds is a 4,2 G's plane with a 1,45 safety factor,or a 3,8 G 's x 1,6 plane! Otto Bartsch assured me,that the calculation was carried out somewhat conservative ! Herbert F?rle German Kr Von meinem iPad gesendet
KR> Spar and WAF stress analysis
That's nice to know... Thanks! On Feb 24, 2015 12:39 PM, "Herbert F?rle" wrote: > > the conclusion of the German Test of the Kr Spar and WAF's calculated by Otto Bartsch is: Any reliable built Kr with a MTOW of 1050 pounds is a 4,2 G's plane with a 1,45 safety factor,or a 3,8 G 's x 1,6 plane! > Otto Bartsch assured me,that the calculation was carried out somewhat conservative ! > Herbert F?rle > German Kr > Von meinem iPad gesendet > ___ > Search the KRnet Archives at http://tugantek.com/archmailv2-kr/search. > To UNsubscribe from KRnet, send a message to KRnet-leave at list.krnet.org > please see other KRnet info at http://www.krnet.org/info.html > see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change options
