DENNY wrote:A Cessna 170 that can slow down to 40 mph and maintain altitude is going to be nose high!!! Even a super cub at 40 mph is nose high I don't care what the CG is

Trying to get this straight.

A more forward CG position requires more downward force at the elevator.
This means more elevator up deflection and consequently higher AoA of the wing (more nose up), which generates more lift to compensate for the downward force, and more drag, ie reduced speed.

Moving the CG backwards reduces this force and thus also lowers the AoA.

On a plane with a trim tab (like a C170) rather than a stabilizer trim a far forward CG also limits elevator deflection by the yoke as some of it is already used to trim.
One would have to have a really extreme case of forward CG (well outside certified limits, or perhaps caused by a less than perfectly rigged airplane, in angle of incidence of wing and/or horizontal tail) to run out of elevator deflection and having to increase airspeed to keep the tail down and the plane in level flight.

Consequently, a CG in the center allows for more elevator deflection and yields less control forces around the elevator’s centered position, which might qualify as “nicer to fly”.
A gain in performance at low speeds would be too small to be noticeable, I think.
It’s a somewhat different story at high speeds where the up-elevator necessary with forward CG causes increased trim drag.

In high performance gliders the drag penalty of a forward CG at typical cruise speeds (around 100 kts) is several percent, too much to be neglected by serious racers.
We typically put the CG at about 25-30% forward of the rearmost position.

To effectively accomplish this in a racing sailplane throughout it's performance envelop, with or without water ballast loaded there is a permanently installed aft water tank that can be dumped when the weight no longer required.

Bigrenna wrote:I ….
That said, If one has to permanently mount 17 lbs aft of the tail cone in a 182, or mount a 25 pound battery 3 feet further aft in a place where it never was designed to be, suggests something is SERIOUSLY wrong with how the aircraft was modified/set up.

….

Not at all, at least for working type planes

Take my skywagon for example, she was built to work be it with a dead moose in the back, a hopper of AG juice, pax, etc

Now you get someone like me (or many here) who mostly just have one or two up front and some basic camping crap in the back, you’re going to lean towards a forward CG

Take this for example, a brand new PC12, no odd mods or anything

Put a normal sized man and woman up front, full fuel, and you’re a hair from busting the forward CG



And if you happen to be into chunky girls, we’ll you ain’t legally going to fly with full tanks, unless you load the back up with some people, or toss a couple dirt bikes in.

It's not the need more the how, velcro & tie wraps doesn't get a nod from me.

I understand why the CG effects the downforce required on the tail but that amount of force/added drag (20 lbs) is not going to cause a significant AOA change at slow speed. Take a video of a low 40mph pass in both configurations and see just how much difference in AOA you have. I suspect it will not be noticeable. People tend to change body position as they pull back on the yoke this will give you a different site perspective pin your shoulder blades to the back of the seat and see if you really notice a big AOA change. Moving the CG makes it much easier for a hands off trimmed approach I do a similar technique with both my cub and Cessna 180 but I can move the stabilizer with trim that is a huge advantage. I can dial in whatever pressure I need before I even start to use the elevator. Finding the right CG for a hands off trimmed approach is a good thing to investigate for any plane. So the general concept is excellent but for most empty aircraft it will not greatly effect stall speed or AOA It just takes some workload off the pilot because the attitude/airspeed is basically hands off on approach, that is the important part of the technique, letting the plane do the work!! Planes usually have the most problems when the pilots are molesting the controls.

Another point is your training was done in a decent configuration. Now add that and power changes you will find a lot of variables to deal with when it comes to evaluating the effects.
DENNY

NineThreeKilo wrote: Not at all, at least for working type planes

Im not sure what “working type planes” has anything to do with it…

The math is the math… if a plane is weighed, CG is calculated, and you find you need to move 25 + # of lead battery from the firewall 3’ past the extended baggage. Something is wrong with how it was set up or choices that were made.

But what do I know… I guess it’s one way to do it.

Bigrenna wrote:

NineThreeKilo wrote: Not at all, at least for working type planes

Im not sure what “working type planes” has anything to do with it…

The math is the math… if a plane is weighed, CG is calculated, and you find you need to move 25 + # of lead battery from the firewall 3’ past the extended baggage. Something is wrong with how it was set up or choices that were made.

But what do I know… I guess it’s one way to do it.

If has lots to do with it

If the plane was intended to be carrying a load in its stations aft of the pilot, they will design the plane as such

Same reason the PC12 goes out of CG with full fuel and 2 180 pounders up front, for its mission that wasn’t a expected payload


Now if we are talking a C150, C170, J3, C172 or the like you probably won’t run into this issue as often

You are somewhat correct, buying a 185 or PC12 for just flying you and your girl around up front, probably not the most practical choice and not what the plane was envisioned for when it was on the drawing board

NineThreeKilo wrote:Now if we are talking a…C170…

We ARE talking a out a C170… Thats what this thread was about. PC12 is just noise.

Bigrenna wrote:

NineThreeKilo wrote:Now if we are talking a…C170…

We ARE talking a out a C170… Thats what this thread was about. PC12 is just noise.

The topic was about CG in general

Your comment about having to move a battery was not explicitly mentioned that it was just about the few people with 170s

But I will agree a 170 or 172 or many trainers, you shouldn’t be super far forward with just you, or you and your instructor up front

NineThreeKilo wrote:

Bigrenna wrote:

NineThreeKilo wrote:Now if we are talking a…C170…

We ARE talking a out a C170… Thats what this thread was about. PC12 is just noise.

The topic was about CG in general

Your comment about having to move a battery was not explicitly mentioned that it was just about the few people with 170s

But I will agree a 170 or 172 or many trainers, you shouldn’t be super far forward with just you, or you and your instructor up front

Maybe for you… me and and my instructor put 540# in the front seats, we were always super far forward cg.

DENNY wrote:Planes usually have the most problems when the pilots are molesting the controls.

This is probably the smartest thing said in this thread.

NineThreeKilo wrote:
buying a 185 or PC12 for just flying you and your girl around up front, probably not the most practical choice and not what the plane was envisioned for when it was on the drawing board

This is also also painfully accurate. I've said for years that the 180 and 185 are EGO driven airplanes. The vast majority of them are purchased by guys who will never load them up like old Mr. Wallace envisioned. Oh well, freedom is a scary thing.

Sorry but i respectfully disagree on the ego part. Or I’m just triggered by it. haha. I’m not working mine commercially hauling moose out of the backcountry but i can’t imagine any other plane meeting my mission. If I put myself, 120 lb girlfriend, big dog, bags/ sporting equipment, full fuel, I’m at 3200 lbs, more than even the modified higher gross 180s can legally hold. I’ve constantly read that a 185 is overkill, but I just don’t think so. At altitude and those weights, it doesn’t perform well. People will probably say 550 and Wing X are REALLY overkill, but they will definitely be on my bird as soon as money permits.

I guess youre generalizing but my mission isn’t all that different than most people.

ington6 wrote:Sorry but i respectfully disagree on the ego part. Or I’m just triggered by it. haha. I’m not working mine commercially hauling moose out of the backcountry but i can’t imagine any other plane meeting my mission. If I put myself, 120 lb girlfriend, big dog, bags/ sporting equipment, full fuel, I’m at 3200 lbs, more than even the modified higher gross 180s can legally hold. I’ve constantly read that a 185 is overkill, but I just don’t think so. At altitude and those weights, it doesn’t perform well. People will probably say 550 and Wing X are REALLY overkill, but they will definitely be on my bird as soon as money permits.

I guess youre generalizing but my mission isn’t all that different than most people.

That was a shot across my bow too lol

For me I’m normally around 3,100 TOW

Me, girlfriend, some stuff, and 50g or less of fuel

Perk for me is it’s a amphib that will block 120kts, good stable IMC plane with a A/P and a comfy interior

Being able to land on land or water, day night IFR VFR really makes a perfect plane for me

But yeah it’s overkill, probably could do much of the same slower with less capable instruments with a PA18 or bush caddy

For what I paid for the plane compared to what she’s worth now, it proved to be a pretty good choice

Ego driven. Love it ! I call it "Skywagon Envy" and Sigmund Freud would have written about it had a Skywagon been invented at that time.

All joking aside. My CG changed to more forward position moving the battery firewall. I have lost a ton of weight over the years and I like the weight savings moving the battery FF. I will get it on scales after it gets painted - shooting for Fall 2024. I have a Hartzell prop that weighs 75 lbs. I load 50 lbs of survival gear in the extended baggage. It can almost fly power off full aft trim in this configuration. I have thought about adding this mod below: It adds about 5 lbs of weight to the horizontal stabilizer and I believe increases the skin thickness by 2 mm.

https://tanalianaviation.com/leading-ed ... fications/


5 lbs of weight at the rearmost station would be probably all I need for it to fly the way Larry describes in his video. It is also STC'd. I could try a 2 blade MT prop but I like the heavy props out front and the truth is that even with a mild forward CG - the airplane lands ridiculously short and unless I start flying in STOL contests - There really is no need. I use 700 feet as personal minimum for a sea level strip with a good approach in either wind direction. This gives me a huge margin for safety.


Josh

Dog is my Copilot wrote:Ego driven. Love it ! I call it "Skywagon Envy" and Sigmund Freud would have written about it had a Skywagon been invented at that time.

All joking aside. My CG changed to more forward position moving the battery firewall. I have lost a ton of weight over the years and I like the weight savings moving the battery FF. I will get it on scales after it gets painted - shooting for Fall 2024. I have a Hartzell prop that weighs 75 lbs. I load 50 lbs of survival gear in the extended baggage. It can almost fly power off full aft trim in this configuration. I have thought about adding this mod below: It adds about 5 lbs of weight to the horizontal stabilizer and I believe increases the skin thickness by 2 mm.

https://tanalianaviation.com/leading-ed ... fications/


5 lbs of weight at the rearmost station would be probably all I need for it to fly the way Larry describes in his video. It is also STC'd. I could try a 2 blade MT prop but I like the heavy props out front and the truth is that even with a mild forward CG - the airplane lands ridiculously short and unless I start flying in STOL contests - There really is no need. I use 700 feet as personal minimum for a sea level strip with a good approach in either wind direction. This gives me a huge margin for safety.


Josh

Is that kit a rubber boot or thicker leading edge metal?

I called the company a few years ago because it interested me. It is a thicker aluminum skin - I believe 6 mm over the standard 4 mm. I have a rubber abrasion boot horizontal stabilizer and would add the same if I do this mod. I was curious what it weighed because of the CG benefit and was told it was 5 lbs heavier than the standard skins. I forgot the cost - I believe 3K when I called a few years ago. I have the tail AD coming up on 2 months. So I have decide soon. Bought the doubler so I won't have to do the tail inspection until 2033.




Josh

Dog is my Copilot wrote:I called the company a few years ago because it interested me. It is a thicker aluminum skin - I believe 6 mm over the standard 4 mm. I have a rubber abrasion boot horizontal stabilizer and would add the same if I do this mod. I was curious what it weighed because of the CG benefit and was told it was 5 lbs heavier than the standard skins. I forgot the cost - I believe 3K when I called a few years ago. I have the tail AD coming up on 2 months. So I have decide soon. Bought the doubler so I won't have to do the tail inspection until 2033.




Josh

Thanks, I like the idea of that

Question, what’s the skin swap have to do with the tail AD? Thought that was just a jackscrew inspection?

The horizontal stabilizer will be coming off for the Tail AD. So just figured it would save some labor cost and be the most convenient time to get it done. Plus I am painting the airplane in about a year. Now after this thread - you got me thinking about it. It would be great to reinforce the horizontal stabilizer and add a little weight at the rearward station.


Josh

Dog is my Copilot wrote:.... I have the tail AD coming up on 2 months. So I have decide soon. Bought the doubler so I won't have to do the tail inspection until 2033.

Josh, unless it's been revised, the AD reinspection is every 500 hours TIS or 5 years, whichever comes first.
I'm pretty sure that no one has gotten an AMOC to that approved, no matter what has been added or replaced.

Eric,

You can buy this doubler kit which gives an STC extending the inspection to 10 years/1500 hours. It costs 3K. The tailcone inspection takes about 20 hours of labor if I remember so almost a wash at 105/hr - my IAs shop rate. In 5 years his shop rate is likely more. Plus down time. I am likely to do it again in 2033.

https://www.mcfarlaneaviation.com/artic ... ackcountry


Josh