Hi there,

 

After I did learn to fly inverted it comes that this only can be done with Mustang plane, all the rest I tested (Hawaii pack) after i got inverted it lasts for about 10 seconds, then the engine stops.

 

Any idea?

http://www.airspacemag.com/flight-today/Upside-Down.html

The RV does just fine inverted.

 

All the other aircraft may not have fuel systems that can feed fuel to the engine while inverted. You can starve many airplane engines of fuel just by pushing the nose over into negative G's.

Can't remember... does the RV-6 require the boost pump running for fuel flow while inverted?

A cheap way out is to get a flop tube for your gas tank.

hi,

 

Can't remember... does the RV-6 require the boost pump running for fuel flow while inverted?

 

I tried again this morning and yes, it works fine, so i could have been confused, so only RV-6 and Mustang can perform inverted flight in MSF.

 

As per your question, the answer is not, I tested it in both ways, with pump on and off with same results. Boost pump is primarily to prime the engine for cold start.

 

Still surprise me that Stearman can not do it (???)

The Stearman uses an old fashioned carburetor. You turn it upside down in 0 G or negative G territory and and gravity will not be able to pull any fuel through into the needle jet. The only work to fly "inverted" in the Stearman is to do it while pulling positive G's to "create" gravity. The Stearman is probably not approved for certain aerobatic maneuvers as a result of this limit.

 

This fact was used in the training of German pilots early in WWII. Most early allied aircraft were not fuel injected and therefore could not nose over into a dive without cutting out their engine. The German pilots were taught to do just this to gain precious seconds when maneuvering.

 

On aircraft with fuel injection, the carburetor issue is eliminated, but you still have the worry about getting fuel out of the fuel tanks and under positive pressure all the way to the engine while inverted or in other unusual flight attitudes.

 

Lastly, another consideration is structure. Most aircraft can not handle anywhere near as much negative G force as they can positive. In order to maintain level flight you may already be coming very close to some aircraft negative G limits at just -1 G!!! If you try to perform a level turn in a steep bank while inverted you may overstress the airframe. I am sure most fighters and purpose built aerobatic aircraft can handle it, but I have no idea what the Stearman's negative G limits are.

No problem. but yes, the engine will stop on the Cubby and is not easy to restart after being inverted for some time. You might have to dead stick it if you do not get a restart in time. The Cub will roll over easily but remember your control movements will be reversed.

The Stearman can supposedly handle plus 12 and minus 9 G, with its manufacturer figure being 9 positive and 7 negative. This is not surprising, since most biplanes can handle a lot of stress owing to the very strong braced box structure formed by the upper and lower wing, with many flying and landing wires and struts being there to take the loads. The Stearman was after all, designed to be exposed to rough handling, since it was a military ab initio trainer, and when you sit one, it feels like it is built like a tank in comparison to the Tiger Moth.

 

The inherent strength found in the biplane design was in fact one of the reasons why early aviators had a mistrust of monoplanes, particularly under neg G, even when they had a lot of bracing wires in evidence, even more so when stressed skin airframes started showing up. You will still find that many aerobatic performers prefer a biplane, since they are invariably a lot cheaper to construct than aerobatic monoplanes, which usually have a lot of titanium in them to aid in their strength.

 

Most aeroplanes for aerobatics will either have a dedicated header tank for inverted flight, which is on the bottom of the aircraft and thus continues to gravity feed the carb when inverted, and will have either a flop tube, which is a flexible fuel feed pipe in the tank with a brass weight on the end of it, or they will have a pressurised fuel system, or fuel injection, where there is no traditional carburettor. The Stearmans you see going inverted at airshows will almost certainly have one or more of these systems in place.

 

One of the problems you will have with inverted flight in an aeroplane not specifically designed for it, is a more traditional aerofoil, with basically a flat or concave underside and a curved upper surface, which will need a high angle of attack to fly effectively when inverted, to give it some curve on the top in order to provide lift. Aerobatic aircraft typically have an aerofoil which is more or less symmetrical, so it works either way, but then has the disadvantage of needing a higher speed to create lift when at a low angle of attack. Aerobatic aircraft often have a slab sided design too, so that the fuselage will provide some lift when doing knife edge maneuvers. The Pitts Special is a good example of that.

 

Al

The Stearman uses an old fashioned carburetor.

 

Yeah... more specifically, the old float type carb that we had on our cars from the '70s. And on e.g. your John Deere lawn mowers (some anyway).

 

If you take a look at this wiki pic http://en.wikipedia....:Carburetor.svg you will see how turning it upsidedown will choke off fuel flow (the float flops down and the little thingy called "float valve" shuts off the flow) and whatever fuel remaining in the float chamber that can be sucked out is what time you have remaining (seconds) to remain inverted.

 

That said... there are some 450Hp (Pratt R-985) Conversions that have been done for Ag (crop dusting) and Air Show purposes... The Airshow types will have inverted fuel and oil systems installed (as Al described... to still draw fuel / oil while inverted). Not sure but I think they use a Stromberg pressure injection carb.

 

what the Stearman's negative G limits are

 

+6.67 to -2.67 (acrobatic category... from the Type Certificate Data Sheet) so it is a stout bird... and has a reputation far exceeding that... but I would never intentionally go beyond those limits. That's a lot of G to begin with... both positive and negative.

 

Rob

RV-6 worked for the One Hour Inverted Award during the first month of Hawaii. MS may have changed the specs along the way.

 

Ray