K4: Inverted Flight Mechanic

I thought I read some where here that the K4 cannot fly inverted for more than 10 seconds as the engine would cut out.

My question is: Is that true, because I was under the impression late model 109's used direct fuel injection systems which was designed to allow later model 109's to fly inverted.

Note: This feature was available on 109G models.

If that is true, why is this not modeled on the K4?

Or is it modeled?

The problem is not the carburetor (or fuel injection for that matter). If it was, the engine would cut out much more quickly. Instead the problem is with the fuel feed from the tank, if you fly inverted for too long, the feed lines aren't submerged in fuel and the lines will run dry. The amount they hold will give you some leeway, but you can't simply fly inverted for prolonged times.

Even if the fuel system could theoretically handle this, you'd still be faced with the problem that your oil pump would run dry after a short time, which would cause a drop in oil pressure, wreaking havoc on the engine.

Indeed. That applies to most of the planes - old, modern, civilian, military, piston, jets, whatever. With the exception of some outrageous aerobatic machines, their fuel and oil systems are generally not designed for prolonged inverted/neg G operations. 10 seconds is a pretty good result!

Indeed. That applies to most of the planes - old, modern, civilian, military, piston, jets, whatever. With the exception of some outrageous aerobatic machines, their fuel and oil systems are generally not designed for prolonged inverted/neg G operations. 10 seconds is a pretty good result!

According to some sources, that was the purpose of fuel injection systems.

Fuel injection systems were forced in nature.

Which means there was a pump of sorts.

The fuel lines may not have been submerged, but the fuel in the lines would have been forced through via fuel pump.

I don't really understand why the lines would run dry?

This also allowed 109's to perform negative G maneuvers without killing it's engine like early model spitfires which used float carbs. The issue of spitfire stalls in negative G maneuvers, and/or inverted flight wasn't fixed until the Spitfire Mk. VC which encompassed the redesigned carb known as "Miss Shillings Oriface." It wasn't until that time that spitfires could perform negative G maneuvers.

Even the ME-109E's could perform negative G's and inverted flight which was a real tactic used by them against spitfires knowing the spitfire engine couldn't perform negative G maneuvers.

Miss Shillings orifice, yes.

The difference is in a (conventionally) carburetted engine, you'd lose power immediately, not after 10 seconds. That is a big deal.

The fuel lines are at the bottom of the tanks, when you fly inverted, the fuel goes to the top of the tank and the lines start to suck air. Power stays on as long as fuel remains in the lines, but once that is depleted, the engine is going to cut out.

Miss Shillings orifice, yes.

 

The difference is in a (conventionally) carburetted engine, you'd lose power immediately, not after 10 seconds. That is a big deal.

 

The fuel lines are at the bottom of the tanks, when you fly inverted, the fuel goes to the top of the tank and the lines start to suck air.

To my understanding; The pump only has to be submerged, rather the lines were submerged or not doesn't matter regardless of inverted flight or not.

Would that be what you mean, the fact the pump no longer becomes submerged when inverted?

If that is true, then would it not be logical to assume with a full fuel tank the 109K4 could in fact fly inverted indefinitely, until lower fuel loads?

Would that be what you mean, the fact the pump no longer becomes submerged when inverted?

Exactly.

Exactly.

Do you have a technical schematic of the fuel system, and tank, which includes placement of the fuel pump system specifically?

Or do you know of a source I can read about it?

I don't, but pretty much all airplanes behave the same in this regard, because prolonged unloaded or neg g flight is not really something that pilots like to do anyway.

I don't, but pretty much all airplanes behave the same in this regard, because prolonged unloaded or neg g flight is not really something that pilots like to do anyway.

Found it

#7 is the fuel pump.

Makes sense now.

I'm surprised after some 100 years of aviation, they haven't redesigned fuel systems to account for this?

:x

I'm surprised after some 100 years of aviation, they haven't redesigned fuel systems to account for this?

Why add complexity for a state that the pilot is almost less able to endure than the airplane?

I'm surprised after some 100 years of aviation, they haven't redesigned fuel systems to account for this?

I think some aircraft have taken it into account, can't remember which but I seem to remember reading some of the modern fighters (F22/Eurofighter/F-35 era) have an extra pump at the top of the tank for fuel delivery during intense maneuvers.

Still doesn't solve the oil and also coolant problem which is a much bigger problem in piston engines.

Still doesn't solve the oil and also coolant problem which is a much bigger problem in piston engines.

It's still a very real problem with turbine engines.

Why add complexity for a state that the pilot is almost less able to endure than the airplane?

All the time as a kid you've never hung upside down on a jungle gym?

I've never passed out because of it, and I've sat there for 10 minutes as a kid.

People also said the avg human being can't withstand 9+ G's of force too. Yet, trained military pilots can withstand 8-8.5G's in excess of times of 30seconds before having to let off. And, there is documented proof that the human body can withstand upwards of 40-50G's, before experiencing major injury.

Why make it more complex?

Simple, rolling inverted to check below the plane for any targets at lower altitudes? Targets that you may not be able to see if they are directly below you?

10 seconds should be sufficient of course in the case of a K4.

I was just saying it was odd that I didn't suspect any design changes even now almost 100 years after maned flight began.

Honestly, the only reason I made the thread was because I was concerned about stalling the K4 when flying inverted, because in some cases pulling a steep high yo-yo against a P51 in a bank turn sometimes can leave you almost inverted. So I've had to consciously make an effort to continue the maneuver keeping a positive G force hoping the fuel in the tank would stay where it needs to be so I wouldn't stall out.

That is a false assumption to make.

It's not an assumption.

And, there is documented proof that the human body can withstand upwards of 40-50G's, before experiencing major injury.

That depends very heavily on the force application axis and the time subjected to such acceleration.

I've never passed out because of it, and I've sat there for 10 minutes or more as a kid.

That's just 1g. The pathology sets on way quicker in negative gs than it does for positive.

You do neg gs and you seriously tamper with your positive g endurance. That aside, anything more than 1g is immensely uncomfortable. Pilots don't like negative gs.

Why make it more complex?

How would you accomplish it without adding complexity to the fuel system?

It's not an assumption.

 

 

 

That's just 1g. The pathology sets on way quicker in negative gs than it does for positive.

 

You do neg gs and you seriously tamper with your positive g endurance. That aside, anything more than 1g is immensely uncomfortable. Pilots don't like negative gs.

 

 

 

How would you accomplish it without adding complexity to the fuel system?

Parallel fuel systems electronically controlled via a vertical gyroscopic switch.

Like I said have you never hung upside down as a kid before?

I know what effects are attributed by negative G's, I'm just wondering how is it excessive enough to be a problem?

The avg pilot can withstand up to -4.5G's.

Flying inverted doesn't increase negative G forces unless you deliberately do so right?

Like a negative G push-over?

Edit, I highlighted more than what was necessary in that picture too. The vertical gyroscopic switch would work cohesively in determining rather or not a plane was inverted, as such it would switch off the primary pump, and turn on the secondary pump. When the plane rolls back correctly; The secondary pump is turned off and the primary pump is turned on.

Obviously it's not as simple as I make it sound, but the idea is simple; The trick being to eliminate air pockets in the line.

Still working on that one!

:D

Edit, I highlighted more than what was necessary in that picture too. The vertical gyroscopic switch would work cohesively in determining rather or not a plane was inverted, as such it would switch off the primary pump, and turn on the secondary pump. When the plane rolls back correctly; The secondary pump is turned off and the primary pump is turned on.

Well i mean adding a second pump and an accelerometer to the system (you'd also need directional control valves) is a lot of additional complexity, that means more weight, increased probability of a mechanical or electrical malfunction, all that for a state of flight that is actively avoided. It may make sense for an aerobatic plane, but in no way does it make sense for a combat, GA or commercial aircraft.

I know what effects are attributed by negative G's, I'm just wondering how is it excessive enough to be a problem?

Like i said, pulling more than 1 neg g and you can kiss your positive g tolerance for that flight good bye. How is that not a problem? :)

Why risk that when it's perfectly possible to avoid it without compromising capability?

Well i mean adding a second pump and an accelerometer to the system is a lot of additional complexity, that means more weight, increased probability of a mechanical or electrical malfunction, all that for a state of flight that is actively avoided. It may make sense for an aerobatic plane, but in no way does it make sense for a combat, GA or commercial aircraft.

 

 

 

Like i said, pulling more than 1 neg g and you can kiss your positive g tolerance for that flight good bye. How is that not a problem? :)

 

Why risk that when it's perfectly possible to avoid it without compromising capability?

Tell that to Spitfire pilots!

:joystick:

You say it was actively avoided, that simply is not true.

German pilots were taught to use negative G maneuvers in WW2. Especially against early model spitfires.

And what exactly does an aerobatic plane do that differs from a military combat plane?

Aside from perform better that is... :P

And that excess weight you are talking about might be less than a few kg's at most.

It's not going to break the flight profile any if that's what your concern is.

And that excess weight you are talking about might be less than a few kg's at most.

 

It's not going to break the flight profile any if that's what your concern is.

Not sure about that. There's still the issue of complexity. Added complexity at practically no gain, something no sane engineer will go for.

I mean, if the capability to fly inverted for more than 10 seconds was so important for flying doctrine, don't you think somebody would have thought of building it into their airplanes to get an edge?

Tell that to Spitfire pilots!

We are just going in circles here.

There's a difference between unloading your plane because your opponent will instantly lose engine power if he attempts to do the same or flying inverted for prolonged periods of time. If you can't appreciate that difference, i guess there's no point for me in discussing this with you. ;)

I just design a system with an auxiliary tank and a counterweight controlling a valve and damper. Also a valve in the cockpit so the pilot can overriding change.

When flying the aircraft upside down, the counterweight attached to a lever is moved by gravity and changes the fuel passage to the line of the auxiliary reservoir. This deposit is a few liters and is designed to feed fuel to inverted. The damper is to be no quick move the counterweight to any movement of G instant negative, but only when flying inverted more than 4 or 5 seconds. We can also add an electric pump to create pressure in the auxiliary line. This pump can be linked with a switch on the counterweight to only be activated when put the plane inverted. The override valve in the cockpit as a backup is for something that the pilot can change at will.

I do not know if this system will work well because I just design in my head, but it's pretty simple. Also you can add a fuel suction at the top of the main tank to simplify even more. This aspiration is in a Y junction with the main aspiration and counterweight manage change.

It was nice to think about this and it took me five minutes to think it up.

Maybe it's because they do not have any meaning or practical utility such thing in the planes of WW2?

Besides, why talk about this if the 109 or any other plane had such a system nor the need for it. And keep in mind that not only fuel only thing that limits the flight time invested in an engine. Also this cooling and especially the oil lubrication system.

LOVE Miss Schilling's Orafice....it gets around

The bottom line is, in usual combat scenarios, since the dawn of air war till modern times, pilots only need negative G capability for short moments - pushing over for the attack run, rolling over for target spotting - a couple of seconds max. Real life aside, Page.Down, how many times in Your sim-flying career did You really need 10+ sec. inverted during Your offline/online engagements?

Direct injection, "orifices" and/or additional compartments inside the tanks were good enough for the job, no practical need for adding more complexity.