Original Posted By: "William Wynne"
Food for thought:What is meant by nose heavy? That a plane with no in-flight adjustable elevatortrim requires aft stick in cruise flight? If this is the case, and the planeis between 15-20", the correction is the angle of incidence on the stabilizer.Because of the seating configuration of the Piet, where the PIC is much furtheraft of the wing than common tandem seated planes like a J-3, a Piet will be muchmore sensitive to variance in PIC weight. Even with a wing shifted back, aPiet pilot's CG is more than 20" further aft than a J-3. If we are speaking ofa 675 lb empty weight Piet and a 775 EW cub, the difference is going to be evenmore exaggerated because the PIC is a higher % of the gross.Ask anyone with a J-3 if the plane will fly hands off with a 50 pound PIC weightchange without re trimming, and I am all piper pilots will say that it wouldneed a trim change. The same weight change in a Piet will have an even strongereffect. It is not reasonable to expect a Piet to fly hands off with no trimchange with two PIC's with a 50 lb weight differenceCompare the trim system on a side by side classic (T-craft, 120, etc) to that ofa tandem piper. The SBS planes use a trim tab on the elevator, but the pipersuse a much more powerful system of altering the incidence of the stabilizer.I am not suggesting that anyone redesign the Piet, I am just pointing out thetypes of systems professional designers used in certain configurations, and therelative power of altering the incidence of the stabilizer. The Piet is anextreme example of tandem CG shift, and it is an easier path to a good flyingplane if the rigging is seen with than in mind.I didn't see it mentioned, but speed is a factor on trimming planes and a guy wholike to cruise at 68mph will have a different story than one who flies at 82mph,even in identical planes. Airfoils with strong pitching moments have strongpitch changes with speed changes. There are also other configuration considerations; a builder with 1929 gear goingfrom 60 to 75mph is going to have a different condition than a guy with 6x6'sdoing the same speed change. There are other factors like the down thrust angleon the mount etc that effect pitch changes with power. Many things to consider,but one must start with the fundamentals of wing incidence, CG, and stabilizerincidence. From there, gather first hand data from a plane with a verysimilar configuration.I understand that the paragraphs above constitutes "ruining a simple plane withnumbers talk" to some Piet fans. Last year a Brodhead a guy told me that I myCG work had ruined a good thing, "A simple club of good old boys who liked flyingaround low and slow and not thinking too much." I politely asked him ifhe understood that his ideal condition fulfilled two and a half of three pointson the saying "Don't run out of altitude, airspeed and ideas all at the sametime." If anything I say is offensive, I am easily ignored and deleted. Justpretend I don't exist. Reading a single word of my input is not a requirementfor building a Piet, I offer it for people who find it useful assistance in gettingthe plane they personally want. Perhaps the most productive thing to do is collect some examples. It would be quick work at Brodhead to measure wing and stabilizer incidence on a number of planes, put this in with CG information and some pilot notes on their experience trimming. With 2 or 3 people we could get this data from 10 planes in 2 hours. We could then stick the data here, or in the newsletter, or with Doc's CG notes, or on my Piet page:
http://flycorvair.net/2013/11/28/corvai ... ence-page/ If builders like the idea, good otherwise I am just as happy sitting around eatingbrats and catching up with friends.Thank you.William WynneRead this topic online here:
http://forums.matronics.com/viewtopic.p ... ___Subject: Pietenpol-List: Re: ###4th FLIGHT###