Weight, Balance, and IAS?

N170GA · Post by **N170GA** » Wed Nov 19, 2003 4:33 am

This is a question for anyone who has a thought on the subject.

George, I'd really like to hear your thoughts on this.

My question is this...How much is your IAS affected by the location of the CG during flight?

The reason for the question is this...I have the O-360 conversion w C/S prop so my Empty CG is pretty far forward. 1350# @ 37.1 . I know I can trim the aircraft up to fly straight and level, but does a forward CG result in more drag due to more trim used?

It seems to me that if your trim is pushing the tail down with a great force just to keep the nose up, it has to create tremendous drag.

Throw in the AWB2500 skis and I have to carry lots of baggage/weight in the back just to get the CG within forward limits. Add a passenger and it gets very difficult to get the CG back (unless they sit in the back seat).

With these questions in mind...Is it better to carry 120# of extra weight in the aft baggage compartment to reduce the trim requirements, or fly with lots of trim in a lighter airplane?

My experience with boats and floats tells me there must be a "sweet spot", but how in the world does one find out where it is?

I'm so confused!

Bruce...this is all your fault! I was flying along just (fat dumb and..) happy as you please until you sent me that damn Excel W&B spreadsheet. When I added those skis to the calculation it scared the crap out of me. That was a real eye opener.

I'm almost afraid to ask my next question. If my engine quits...am I going to plummet to earth like a yard dart...OR WHAT?

Help!

Neil

N1478D · Post by **N1478D** » Wed Nov 19, 2003 5:33 am

For the 1 1/2 cents that it's worth:

For speed, and efficiency, always carry baggage as far aft as possible so the tail has less work to do.

Off the subject somewhat but very interesting - two mechanics took a plane up that they had just done maintenance on and while in cruise flight a prop blade left the aircraft. The resulting out of balance vibration tore the engine away from the mounts and it left the aircraft too. The very quick thinking mechanic/pilot had both of them kick the windshield out and then convinced the passenger to climb out and replace the weight of the engine with his body. They landed and lived because of that quick thinking.

zero.one.victor · Post by **zero.one.victor** » Wed Nov 19, 2003 5:43 am

N1478D wrote:

Off the subject somewhat but very interesting - two mechanics took a plane up that they had just done maintenance on and while in cruise flight a prop blade left the aircraft. The resulting out of balance vibration tore the engine away from the mounts and it left the aircraft too. The very quick thinking mechanic/pilot had both of them kick the windshield out and then convinced the passenger to climb out and replace the weight of the engine with his body. They landed and lived because of that quick thinking.

No offense,Joe,but I have to say I have serious doubts about this one! Seems like when the engine departed the airplane,the nose-up attitude would happen so quick that any remedial action would have to happen after the airplane was in tailslide mode. It'd be pretty hard to climb UP onto the nose area of the airplane,especially while ****ing your pants from fright!

Eric

N170GA · Post by **N170GA** » Wed Nov 19, 2003 5:49 am

Joe,

I've heard that old addage before. If it's true, then it's not good that I'm "working my tail off" to stay level. I should load up the aft cargo and have the passengers sit in the back!

I have four cast iron counterweights for the garden tractor that weigh 20 KG (44lbs.) each. I was thinking of using them because they are small, heavy, and I can use them in increments as needed. I was thinking of ways to secure them in the aft baggage compartment. I'll have to work on that!

Thanks!

Neil
51' C170A

Post by **GAHorn** » Wed Nov 19, 2003 6:12 am

The few knots you might gain would not likely be worth the exposure to danger you'd face should those heavy weights shift or get thrown around in turbulence.
An aft CG theoretically improves cruising speed and lowers stall speed, but it also degrades from longitudinal stability and can make it impossible to recover from and inadvertent stall/spin.
I'd recommend against carrying dead weight (ballast) in this airplane because it adversely affects the aircraft in other weighs.

(sorry for the pun)

N170GA · Post by **N170GA** » Wed Nov 19, 2003 2:01 pm

Thanks George,

The guy I bought the airplane from carried a 5 Gal. water jug around in the aft cargo area "to make it fly better". The only problem was that it took up half of my cargo space.
I have a couple of gear boxes with stuff I need in them, but they don't weigh that much. In winter, I carry a tent, sleeping bags, coveralls, etc, but they are relatively light.
With the wheel skis (108lbs@14.5") the CG is way forward. Carry a passenger, and its "out of bounds" unless you have lots of stuff in the back. I would just like to get the CG into the middle of the envelope somewhere for safety and efficiency. The question of airspeed was just an afterthought I had about flying at the leading edges of the envelope all the time. I did notice that if the passenger sits in the back seat with the right (front) seat empty, it helps alot.
The spreadsheet I got from Bruce is a "doozie"!:D You just punch in the weights, and watch the CG move to the new position. It's very visual (I always liked books with lots of pictures), and after mussing around with it a while, you get a very good feel for the effect of weight & location changes. I would highly recommend it for anyone who has "Excel".

I did have a concern about the weight moving around, or shifting on impact (heaven forbid). John Deere was nice enough to design them with an enclosed handle for carrying, and like a flat plate (8" x8" x2 1/2"). I thought I could use the rear seat support bar that bolts into the floor (presumably through this handle) as an attachment point.
Thanks for the input everyone.

Neil

JDH · Post by **JDH** » Wed Nov 19, 2003 2:14 pm

How about moving the battery behind the cargo area. There must be previous field approvals out there that move the battery back behind the blanket?? JD

N170GA · Post by **N170GA** » Wed Nov 19, 2003 2:56 pm

Good thought JD, but I don't think the CG would move much because the battery and box doesn't weigh enough to make a big difference.

In fact, I just plugged it into the W&B spreadsheet and the CG moved to the rear 2 tenths of one inch!

Neil

N1478D · Post by **N1478D** » Wed Nov 19, 2003 5:10 pm

zero.one.victor wrote:
N1478D wrote:

Off the subject somewhat but very interesting - two mechanics took a plane up that they had just done maintenance on and while in cruise flight a prop blade left the aircraft. The resulting out of balance vibration tore the engine away from the mounts and it left the aircraft too. The very quick thinking mechanic/pilot had both of them kick the windshield out and then convinced the passenger to climb out and replace the weight of the engine with his body. They landed and lived because of that quick thinking.
No offense,Joe,but I have to say I have serious doubts about this one! Seems like when the engine departed the airplane,the nose-up attitude would happen so quick that any remedial action would have to happen after the airplane was in tailslide mode. It'd be pretty hard to climb UP onto the nose area of the airplane,especially while ****ing your pants from fright!

Eric

Hi Eric,

Think about it! If the guy is FAST talking enough to convince someone to climb thru a broken windshield of a plane about to crash, and hang on where an engine use to be, he's probably fast enough!

Can't remember if I read the story, or if it was told to me, but it was suppose to be a real event. But I never bet on my memory, but it has helped ease the pain of going deaf - couldn't remember it, even if I could have heard it type thing!

JJH55 · Post by **JJH55** » Wed Nov 19, 2003 7:05 pm

The very quick thinking mechanic/pilot had both of them kick the windshield out and then convinced the passenger to climb out and replace the weight of the engine with his body.

Joe,
I heard that story too.

Just prior to the prop/engine departing their company, I understand the pilot leaned over and asked the mechanic if he heard a â€œrattleâ€ somewhere.

Iâ€™m trying to gain a mental picture of those two fellers trying to â€œkickâ€ out the windshield after the engine departed the aircraft. Yea, right! Unless of course these two mechanics were members of the Cirque du Soliel flying team. I certainly canâ€™t imagine the contortions one would have to get in to to kick anything much less the windshield. Heck, its hard enough to maneuver ones self around from the front seats to smack the kids!
JJH55

N1478D · Post by **N1478D** » Wed Nov 19, 2003 7:29 pm

That's really funny Jim!

Like George often says, don't take me literally. Maybe they pushed the windshield out.

Hey, remember that thing that Saturday you said you really wanted one really bad. Well, I did find an extra one, lucky you. But, I was laughing so hard at your response to my story, I must have dropped it, and now I can't find it.

JJH55 · Post by **JJH55** » Wed Nov 19, 2003 8:52 pm

Oh yea, pushed it out, thats better.

I guess I'll have to start being nicer to you!
JJH55

N1478D · Post by **N1478D** » Wed Nov 19, 2003 8:57 pm

Hey, what do you know, looks like I found that thing. I'll be at the hangar this evening if you want to come by and pick it up. Don't make a special trip, it will be there whenever we happen to be out there at the same time.

Maybe we could go to your hangar and start banging some parts together so you can start recognizing sounds.

Something in the glovebox . . ., yeah, right!

zero.one.victor · Post by **zero.one.victor** » Thu Nov 20, 2003 12:58 am

JDH wrote:How about moving the battery behind the cargo area. There must be previous field approvals out there that move the battery back behind the blanket?? JD

Several years ago,a friend of mine home-built a set of amphib floats for his home-built airplane,a Fisher Super Koala (52 thundering horsepower!). They came out great,and worked great,except that they moved the CG too far forward. He ended up mounted a small lead weight on the tailspring,in place of the (removed) tailwheel. I don't know how much it weighed,but being so far aft,a little weight went a LONG ways toward correcting his CG problem.
I seem to recall back on the yahoo 170 site that someone who had done either a 220 Franklin or 210 Continental conversion on their 170 mentioned that they added some lead ballast way back there.
Battery relocation further aft than previously mentioned might be a possibility--like a couple bulkheads farther back.

Eric

Post by **GAHorn** » Thu Nov 20, 2003 1:55 am

I can't imagine what kind of airplane would 1) allow it's WS to be "kicked" out, or 2) would still fly after the windshield had been removed. The major issue with converiting many airplanes (including 170's) to single piece WS's is the possibility that the WS might depart the aircraft. (The additional upper retaining fasteners are specifically for the purpose of preventing the WS from popping out in flight. It might also be of interest to know that pressurized airplanes primary concern with cracked WS's in flight is the prevention of the WS from blowing out of place. That's the major reason a reduction of cabin pressure is called for in such events. Think about it: 8 p.s.i. of cabin pressure against 575 sq. inches (4 sq. ft.) of WS equals over 4600 pounds of pressure attempting to expel the WS.)
Aeronca's suffer from an AD that specifically addresses this issue and directs the owner to assure the WS will remain in place. Not many airplanes of this category will continue to fly (other than straight down!) without their WS's.
Hey, Joe! Isn't this story perhaps along the same lines as your stories about your 170A speeds?