World record today.

[Thruster88]

Big problem seems like lack of pressure to push oil from the tank to the oil pump, only about 3.3psi @ 36,000 v 15psi at sea level. I guess this is a problem for all piston engines but more so with the Rotax due to length of delivery hose and the oil cooler.

[facthunter]

EGPT's 1750?   nev

[skippydiesel]

19 hours ago, Thruster88 said:

Big problem seems like lack of pressure to push oil from the tank to the oil pump, only about 3.3psi @ 36,000 v 15psi at sea level. I guess this is a problem for all piston engines but more so with the Rotax due to length of delivery hose and the oil cooler.

Doesn't sound correct;

 

Rotax engines use a pump to take oil from the remote tank, to the engine.

 

Once that oil hits the crankcase, its returned to the remote tank by crankcase pressure ie blow-by from combustion.

 

As long as the engine is rotating crankcase pressure will be created & oil will return to the tank. I assume the high climbing Rotax was still running at the altitude reached.

 

😈

 

 

Edited November 6 by skippydiesel

[Thruster88]

11 minutes ago, skippydiesel said:

Doesn't sound correct;

 

Rotax engines use a pump to take oil from the remote tank, to the engine.

 

Once that oil hits the crankcase, its returned to the remote tank by crankcase pressure ie blow-by from combustion.

 

As long as the engine is rotating crankcase pressure will be created & oil will return to the tank. I assume the high climbing Rotax was still running at the altitude reached.

 

😈

 

 

You need to re read what I wrote. Atmospheric pressure pushes oil FROM the tank to the oil pump. Would the system work with zero pressure in the tank?

[facthunter]

No one concerned about the High Exhaust gas Temps? That's what you get with Turbocharging.  Nev

[skippydiesel]

4 hours ago, Thruster88 said:

You need to re read what I wrote. Atmospheric pressure pushes oil FROM the tank to the oil pump. Would the system work with zero pressure in the tank?

So, your theory is that the pump can not suck (create a vacuum) & then pressurise oil into the galleries, without significant atmospheric pressure, thus being the factor that limited its further climb into the heavens - doesn't sound plausible.

 

Seems to me that in a closed system ie , tank - pump - to crankcase - tank,  the pump will work, as long a it does not loose prime, with or without atmospheric pressure.

 

In a vacuum & zero gravity, the oil may be lost from the open tank - the pump would loose prime. 

 

Further - as long as there is sufficient O2 for combustion to take place, the tank may be subject to a constant pressure from crankcase gas/ blow- by. The degree of pressure would depend on tank venting which , for the purpose of breaking altitude records, could, if needs be,  controlled either by an automatic pressure relief valve or a pilot operated valve. 

 

May be the aircraft reached space ?😈

Edited November 6 by skippydiesel

[Blueadventures]

42 minutes ago, skippydiesel said:

So, your theory is that the pump can not suck (create a vacuum) & then pressurise oil into the galleries, without significant atmospheric pressure, thus being the factor that limited its further climb into the heavens - doesn't sound plausible.

 

Seems to me that in a closed system ie , tank - pump - to crankcase - tank,  the pump will work, as long a it does not loose prime, with or without atmospheric pressure.

 

In a vacuum & zero gravity, the oil may be lost from the open tank - the pump would loose prime. 

 

Further - as long as there is sufficient O2 for combustion to take place, the tank may be subject to a constant pressure from crankcase gas/ blow- by. The degree of pressure would depend on tank venting which , for the purpose of breaking altitude records, could, if needs be,  controlled either by an automatic pressure relief valve or a pilot operated valve. 

 

May be the aircraft reached space ?😈

Thrusters on the money, also its not a closed system as such as its vented.

[onetrack]

Quote

So, your theory is that the pump can not suck (create a vacuum) & then pressurise oil into the galleries, without significant atmospheric pressure, thus being the factor that limited its further climb into the heavens - doesn't sound plausible

Sorry, Skippy, but not only is Thrusters "theory" plausible - it's not a "theory", it's basic science. When a centrifugal or gear pump sucks, it creates a low-pressure area at its inlet, and the higher atmospheric pressure on the liquid's surface pushes the liquid into the pump, to try and equalise the pressure each side of the pump.

 

If you've ever tried to get a centrifugal pump to extract water from a well, you would know the maximum depth level you can draw from, is around 8 metres (approx 27 feet for us old timers), and the absolute maximum well depth you can draw from, is 10.336 metres (33 feet), by using a vacuum assist pump primer. This is all due to the fact that MSLP can only lift water to those maximum heights before the water pressure equalises with MSLP.

 

A jet venturi pump can lift water from much deeper levels, but this requires a pressure pipe going down the well to the water level, where a housing that uses a venturi effect, utilises the pressurised water from the surface pump, to provide additional water lift ability.

 

If the surrounding air pressure is zero, a centrifugal or gear pump cannot work, because it needs air pressure to make it work.

A vacuum cannot "suck", it simply relies on external pressure such as air pressure or gravity, to provide that pressure, to move the liquid to the area of vacuum  - i.e., the area of low pressure.

 

If the fluid being pumped is located in a reservoir considerably higher than the pump, then gravity can be used to supply the fluid to the pump inlet. However, for small quantities of fluid, and small diameter supply lines, a lack of weight and the internal restriction in a small diameter supply line, can often mean there's little pressure at the pump inlet, so the pump ends up being starved of adequate fluid to pump.

 

https://www.completepumpsupplies.co.uk/resources/why-cant-water-be-lifted-above-10-metres?srsltid=AfmBOor_On-I8TC5d_1nb21mtLvS2jXI1eu4K8qYddEXsf41KhTw947w

 

 

Edited November 6 by onetrack
addendum...

[skippydiesel]

10 hours ago, Blueadventures said:

Thrusters on the money, also its not a closed system as such as its vented.

True! Except that it is likly that the crankcase gases contribute some pressure and could be controlled, via a relief valve to deliver more.😈

Edited November 6 by skippydiesel

[skippydiesel]

Thank you for the refresher Onetrack. In particular the workings of a centrifugal pump, which I have used throughout my life.

 

You are, of course, correct.

 

I still find difficult to imagine that the Rotax oil reticulation system could be compromised, by lower atmospheric pressure,  to the extent suggested by Thruster88, such that this was the limiting factor in the climb to 36,000' (see my comment to Blueadventures above) 😈

[facthunter]

Why would the Oil even flow at the temperatures there? At similar Temps (at the Poles) oil systems have to be diluted or Heated. Check Oil 'Pour Point'.   SUCKING only lowers pressure differential. In a vacuum it doesn't work at all. Nev

[sfGnome]

Of course, this being a record attempt that was likely to generate vast amounts of positive publicity, it’s possible that the engine was intended to be discarded afterwards. It only had to work once, not forever. 

[facthunter]

It's a STUNT. Proved a bit about the Plane. Turbine engines do it all the time, safely.  Infinitely More reliable than Piston engines. Engines can be turbo charged to reach those altitudes easy enough. The P&W turbo'd 1830s got Liberators to well above 30,000 feet but the Plane limited  operation much above that. Flight at absolute ceiling is touchy. You are right on the stall. Service ceiling is Lower where you reach 500 FPM Positive ROC.   Nev

[skippydiesel]

Back to oil pressure/flow at high altitudes;

 

From Rotax Owners Forum;

 

"The oil tank pressure is relative to the atmospheric pressure.  The incoming pressure that drives the oil from the crankcase, from blow-by gas pushing into the crankcase by normal ring leakage, will always keep the pressure over the oil in the tank just slightly higher than ambient.  There is always some light pressure in the top of the oil tank that requires venting.  

In regards to very high altitude this causes oil pressure drop relative to standard oil pressures you see at or near sea level.  High altitude drones sometimes use a device on the oil vent line to trap some of this venting air to keep oil pressures in a more normal range.  These are switched on (I have not seen an automatic one as yet) starting around 20 to 25k MSL.  This maintains the pressure over the oil in the tank to flow better and you see it in less drop of oil pressure compared to without such a device.  The one i am thinking of maintains about 5 psi in the oil tank over ambient."

 

😈

[Thruster88]

Another issue with high altitude flight is freezing up the inside of the crankcase or crankcase/oil tank breather tube. Water is a by product of combustion, the vapour can freez in the end of the tube as it exits the cowling. Some aircraft have a whistle-stop opening in the tube inside the warm area of the cowl as a failsafe.

[skippydiesel]

Thankfully, none of these issues apply to me. I have no intention of flying much above 10,000ft in my Rotax powered chariot😈

[sfGnome]

Look on the bright side. If your engine quits at 35,000ft, you have plenty of glide time to find a good landing spot…

[facthunter]

 At Minus 56 C you'd not want to Linger Longer. You'd have to watch Flutter.. The air is thin and IAS is well below TAS.. How brittle are some of the Elements of the Structure?  What happens when the coolant freezes. The engine won't be putting out much Heat. Nev

[BrendAn]

35 minutes ago, facthunter said:

 At Minus 56 C you'd not want to Linger Longer. You'd have to watch Flutter.. The air is thin and IAS is well below TAS.. How brittle are some of the Elements of the Structure?  What happens when the coolant freezes. The engine won't be putting out much Heat. Nev

The flight is done and dusted without any problems so no point speculating on what could happen.

I doubt it will be done again any time soon.

[facthunter]

I just mentioned some of the factors about the hostile environment up there that Most passengers in their Pressurised and heated cabin are blissfully unaware of. Nev

[BrendAn]

42 minutes ago, facthunter said:

I just mentioned some of the factors about the hostile environment up there that Most passengers in their Pressurised and heated cabin are blissfully unaware of. Nev

on the video they were concerned about flutter .

 

on an airliner doing 500 knts does the skin heat up from friction even at those temps

[onetrack]

Quote

on an airliner doing 500 knts does the skin heat up from friction even at those temps

Yes, it does by a few degrees, enough to warm the fuel a little, but not enough to damage anything in the airframe.

See "Ram Rise" in the link below. Interestingly, air data computers have to measure the temperature rise, to compute TAS exactly.

Over Mach 1, the temperature increase on an airframe is rapid.

 

https://en.wikipedia.org/wiki/Total_air_temperature

 

[facthunter]

It's much more than a  few degrees. It's around 30C at 480 Knots/ Mach.82. Nev