Nose heavy problem twin comanche

[ComBE]

Thanks for the comments, let me double check that data I used.

[AlanBreen]

Your empty weight C of G is pretty similar to our PA30B.

Take a look at the spread sheet I have attached it is a copy of what I use for our PA30B. I have modified it using the data you have shown for your aircraft and "americanised' it putting in USG instead of litres.

Only highlighted (outlined) boxes can have data entered. The fuel weight is entered by entering the fuel quantity in USG.

The spreadsheet is locked to stop inadvertant changes to the fixed data.

It can the unlocked by clicking on "Tools" then "Protection" then "Unprotect" to allow changes to empty weight data etc. Be sure to enable the protection after any changes.

Hope this helps.

Alan

[John Moore]

[Jay]

[N8632Y]

Just an observation, no one mentioned the small nose wheel mod?
Granted, location of CG affects Vmc, this and ability to recover from unusual attitudes, stalls, all very important, but secondarily, how it affects landing the twin, which is a common discussion.
On this note, landing only, and a forward CG most people complain of a 3 point landing, or a hard landing, and trouble keeping the nose off.
I have a normal 6 in. nose wheel, in the winter my nosewheel strut was inflated to normal pressure, but now, the air-oil filled strut is looking fully inflated, creating an increase angle of attack, which I believe I am feeling on take off and landing?

Possibly even affecting my CG, moving it slightly posterior.
On takeoff, she wants to fly prior to rotation, the nosewheel gets very light, prior to flying and on landing, once settled on the runway, the nosewheel can easily bounce slightly.

So my point being that the people complaining of landing the comanche, WHAT nosewheel do you have and use that factor in your "ground" CG relation.
I believe the point of the smaller nosewheel was to decrease the angle of attack on takeoff, allowing the twin to stay grounded until reaching Vmc.......

I'm usually airborne but always try to stay in ground effect and ready to chop power until blue line..
steve

[Zach Grant L1011jock]

Steve,
You are right that the aircraft attitude while it sits on the ground affects many things in a Comanche. One thing it does not do is affect CG. CG is constant around the 3 axes, and no pitching, yawing or rolling causes that to change. In fact, as you say, the increased AOA of an over inflated nose strut (or UNDERINFLATED main struts) does cause tha aircraft to fly sooner (only for the same reason a 172 comes off the ground at rediculously slow speeds when the nose is held high on a soft field T/O). Takeoff AOA is/can be managed with slight variences in strut extension. Adding a half inch to the mains, and reducing a half inch on the nose accomplishes about the same thing as the small nose tire!

The small nose wheel reduces the total possible length of the nose strut assembly by 1", not much in the great scheme of things. What everyone forgets is that when the airplane comes into land, ALL of the struts are fully extended, so yes the shorter strut assembly length on the nose may make a small difference initially, but only for a short while. Now we need to think about a few things that affect a landing. When you sit in a big soft sofa, it is hard to get enough leverage to stand up isn't it? The same can be said for landings. You need a good solid fulcrum to be able to rotate around. The only way to hold the nose off is to have something for the tail to have a reactant force with. In the air it is the center of lift, but when on the ground it is the main gear. Now we go back to how most of these planes sit all the time, nose strut extended 2-3", and mains extended maybe 1" (even the book calls for 2.75 inches extension at full static load all the way around, and I like 3.5 on the mains). When you come into land with all of the struts fully extended, and the mains have less resistance than the nose, the fulcrum now becoms the nose as you sink into the struts, and this makes it always seem like the nose is hammering on. How can you hold the nose off if the main struts immediately get 6 inches shorter, and nose was only six inches off the ground in the first place. The nose gear is on the ground, and you haven't changed your pitch. The smoother the initial landing (low sink rate) the more noticable this is because you have no way to hold the nose off, but it seems like it was a good landing, and it was!

Moral of the story is, if you want to have the control to hold the nose off, first, you need enough power in the tail (a function of C/G and airspeed. Too fast you will land nose low, to slow and you will stall, CG needs to be just right so you can find the sweet spot), and you need a good fulcrum to use as the weight comes off the wing and onto the gear. Proper extension is key, and servicing with both fluid and nitrogen should be done, not just the air.

-Zach

[steen]