The International Cessna 170 Association

Hmmmn. Interesting concepts, John.
Would that mean that while reducing power and speed "over the fence" that the fuel might flow forward within the tanks and have a more forward CG?

gahorn wrote:Hmmmn. Interesting concepts, John.
Would that mean that while reducing power and speed "over the fence" that the fuel might flow forward within the tanks and have a more forward CG?

I don't know. I can't say I've ever noticed any effect of fuel moving in the tanks, actually. Are there baffles inside that would slow it down?

John

Yes. At least on the A/B fuel tanks, there's a lateral baffle just aft of the filler neck. My ham-handed landings can't tell the difference if there's any fuel movement. And I'll bet Bruce can't either, since his hands are all numb from vibration.

I like jrenwicks theory that with a light fuel load most of the fuel sits in the back of the tank during a 3 point landing. That would explain things.

buzzlatka wrote:I like jrenwicks theory that with a light fuel load most of the fuel sits in the back of the tank during a 3 point landing. That would explain things.

Why would that be the case, since the airplane is decelerating? Do you suddenly feel yourself being pressed into the back of your seat?

My opinion is:

There should not be any acceleration if you are flying a stabilized approach (which George says we should all be doing). The nose will already be down at normal approach speed with flaps extended, the fuel will already be toward the front of the tank and not moving around.

The only way to get the nose up on approach is if you are very slow and carrying a bunch of power dragging it in on the edge of stall, in which case the approach will again be close to stabilized and the fuel will not be moving.

Of course, gusty winds and cross-wind corrections will involve changes in attitude so who knows what is happening with the fuel during those conditions. The fuel will most likely be sloshing around quite a bit.

I can honestly say I have never noticed fuel movement in any airplane I have ever flown.

I've only flown one aircraft where I could feel the movement of the fuel and that was an AS-350 Astar Helicopter. Picture the white plastic fuel cells popular on weed wackers today. Now picture the exact same cell made of plastic with no baffles with a 143 gallon capacity. Almost any time you came to a quick stop and hover the helicopter would swing back and forth as the fuel sloshed. It was also present in flight but not so pronounced.

I understand that some of the big transports carry fuel in the horizontal stabilizer. I'll bet that a balky transfer pump would drum up some anxiety.

I think some of the large Boeings (747-400) have horizontal stabilizer tanks where they x/fr fuel in flight to move the CG aft (within limits). This reduces angle of attack in long range cruise (less aerodynamic download on tail) and increases range. There is no doubt a x/fr pump test so you won't get your fuel stuck where you can't get at it.

voorheesh wrote:I think some of the large Boeings (747-400) have horizontal stabilizer tanks where they x/fr fuel in flight to move the CG aft (within limits). This reduces angle of attack in long range cruise (less aerodynamic download on tail) and increases range. There is no doubt a x/fr pump test so you won't get your fuel stuck where you can't get at it.

I would also guess that there is more than one pump that will do the job.

Miles

To add to the "tail trim" issue - in my 170, with a "heavy aft" condition ( caused by low quantity in the fuel tanks ? ) a "wheel" landing took a little more forward elevator pressure to keep it up on the mains.

Another scenario - -When I was carrying parachute jumpers, the "intentionally" light fuel load, no back seat and no right side door opened up another totally different can of worms. I had to make sure my jumpers seated themselves for best weight distribution, but after 5 jumpers had exited the cabin I was real quick on the trim wheel ! Also, the first (and only !) time I made a wheel landing in that configuration, I realized it wouldn't be too hard to put the thing up on it's nose.

gahorn wrote:Guess why our 170's have to be in the Utility category before spinning them? It's because the CG must be kept forward of 40.3 (170) and 40.6 (A/B models). This is to avoid a rearward CG from turning that thing into a falling leaf (flat spin) that cannot be recovered.

A little deviation from the thread but some real good words on stall/spin environment.

http://www.bruceair.com/stall-spin/stalls.htm

GAR

Tell me it ain't so ..........6 people in a 170............that's got to be like, "How many people can we get in the phone booth

W.

blueldr wrote:I understand that some of the big transports carry fuel in the horizontal stabilizer. I'll bet that a balky transfer pump would drum up some anxiety.

The A-300 horizontal tail will hold 10,900 lbs. of fuel. If both of the pumps were to fail the tank will gravity feed at around 240 ppm. (Normal transfer rate with both pumps operating is 265 ppm.) The trim tank is supposed to increase effiency by 1%. The company doesn't take this 1% savings into account when flight planning. Within the last year they have been trying to save fuel everywhere they can so they have encouraged us to not take extra fuel "for mom and the kids". It's nice knowing that there is a little cushion built in. On a flight last week from Newark to Oakland the total fuel load was 92,000 lbs. So 920 lbs. is good for a couple of extra minutes. It almost covered the extra fuel we burned waiting in the Conga line at Newark for 21 minutes.

Hi all,

Installition difficulties. We have purchased Selkirk's extended baggage kit for our 170B. It is certified for 50 #.

Our problem is with the installation of the floor and we are discussing that with Selkirk as I post this. When the front lip is correctly positioned, and the aft end of the floor is lowered into position, the edges bind / grind on the rivet heads and the floor cannot be lowered to contact the aft bulkhead for attachment. It is either 3/4" too wide or 3/4" too short. The kit p/n is 61-100 and the floor p/n says 61-02. L: 32 1/4 (lip to top of forward radius) W: (front) 30" W: (aft top outside of tabs) 25 5/8". Due to the strengthening lips on the edges we don't want to cut the aft sides (at this point!)

Has anyone else had this happen? We are thinking it might be the wrong floor panel, even though the number is correct. The a/c has not had any damage / repairs anywhere in the aft fuselage area.

Thoughts?

Each one I have installed has fit exactly as you discribe. I doubt my method to make it fit is Selkirk approved but I sanded a little on the outside corners where they are hitting the rivits, this allowed it to sit down in the bulkhead a little better. Then I used large area washers as spacers between the bulkhead and the ears on the baggage floor. The rear fasteners for the floor go through the washers to hold them in place. You will find that you will also have to trim quite a bit off of the rear baggage wall they give you in order to make it fit as well. Good luck.
Shawn