Losing lots of airspeed at high alt w/out engine power

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P*Funk
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Losing lots of airspeed at high alt w/out engine power

Post by P*Funk »

I noticed this flying last night after a long hiatus from the Connie. At 22000 at cruise power set according to the manual, 2160RPM 120 BMEP, and for about 2.5-3 hours it was fine, trucking along slowly gaining IAS as fuel burned off. I think I topped out at 181KIAS. Then I encountered some rough air for the last 30 minutes of the cruise and my airspeed bled off steadily to the point that I needed to start trimming nose up then had to start pitching up strongly with the auto pilot. I checked over and over the engines and no loss in power was seen, always the same RPM and BMEP, I checked against icing conditions as its winder and I'm flying over the North Central US but the FE was regularly managing the carb air whenever I had icing danger. All engine indications were in the green. By the time I started my descent I couldn't maintain 140KIAS. I'd lost about 40+ knots in 30 minutes.

Is it merely that the turbulent air was so strong it knocked that much speed off?

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ratty
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Re: Losing lots of airspeed at high alt w/out engine power

Post by ratty »

Airframe icing.
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Alan_A
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Re: Losing lots of airspeed at high alt w/out engine power

Post by Alan_A »

Or pitot icing.

Did your ground speed deteriorate, or only your indicated airspeed?

If it was only indicated airspeed - was your pitot heat on?
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Re: Losing lots of airspeed at high alt w/out engine power

Post by P*Funk »

Ground speed did decrease as well. My pitot heat was on and I know it was since it froze over early in the flight from forgetting to set it! It wasn't a failure of instruments to report because the flying characteristics of the aircraft changed going from level flight with pitch autopilot at -3 to ending up at around +9 or 10 plus several clicks of nose up trim. Ground speed went down in proportion to the loss of indicated airspeed. I had to continually add positive pitch and the natural result was a loss of airspeed yet I can't account for why. There was no present warnings in any of the overlay panels that spoke of icing issues in the engines, and the engineer was observed to use carb heat where necessary. All engine gauges indicated identical behavior to before the speed loss with identical torque and Manifold Pressure with no observed loss in any power or temps over or under norms.

The only variables I can observe was a turn passing a VOR from near right into the head wind to a 40 degree angle off it and coinciding with that was an increase to moderate to strong turbulence that didn't let up for the remainder of the cruise and the ensuing loss of speed progressively over the course of 15 to 20 minutes. Could this have been as someone above says airframe icing creating drag? Could it simply have been I was flying in rough weather that was severely harming my aircraft's ability to fly and I should have dropped my altitude to compensate?

alan CXA651
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Re: Losing lots of airspeed at high alt w/out engine power

Post by alan CXA651 »

Hi.
If speed decreases pitching up would increase the speed drop off and make the situation worse , and you could endup stalling , did you have real weather injected while flyinng or a set weather theme , if real weather from asn or as16 , did you try tuning to 122.05 for enroute weather , also did you use shift+z to check wind speed and heading , in stronge headwinds , your grd speed would decrease , to overcome this , then either increase engine speed or climb / decend to better more favourable winds .
regards alan. 8)
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P*Funk
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Re: Losing lots of airspeed at high alt w/out engine power

Post by P*Funk »

Obviously pitching up when the aircraft wants to sink will cost you airspeed if you don't increase power, but the question is why did it do so so strongly? I had about a 75 knot wind approximately 40 degrees off my track that previously I was flying directly into. The issue isn't a loss of ground speed, its the loss of airspeed. It became impossible to maintain 22000 feet with the cruise power setting in the manual without losing more than 40 knots of airspeed. I'm curious why the change was so radical. To lose 40 knots IAS was surprising to me. It was a real weather injection but the weather was itself consistent throughout the whole flight, a strong headwind with its direction never varying by more than 20 degrees or its strength by 10 knots.

If it was icing then there was no indication. If it was turbulence then I guess that explains it but I never imagined it would be that severe an effect.

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CAPFlyer
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Re: Losing lots of airspeed at high alt w/out engine power

Post by CAPFlyer »

First, I would have tried to cycle the airframe and prop icing even if there was no indication just to make sure you didn't have a short accumulation.

Second, I would double check all of your axis assignments to make sure you don't have something accidentally assigned to the spoiler axis.

Third, make sure you didn't accidentally open the cowl flaps. While the FE usually takes care of it, if one extended, then that's a possible reason.

Finally, check all of your engine readings. Make sure you don't have a power loss somewhere. It should show itself with a significant increase in the throttle position of one engine over the others, but at times you can still have a power loss that doesn't show immediately through the throttle, but does show with a loss of oil or fuel pressure.
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Re: Losing lots of airspeed at high alt w/out engine power

Post by AviationAtWar »

P*Funk wrote: the FE was regularly managing the carb air whenever I had icing danger.
Off on a bit of a tangent:

Are you actually seeing him move the carb heat levers? This was being discussed last winter but I don't think there was ever a resolution. I sometimes hear him change between sheltered and ram air but in ~70 hours of flight time the only time the FE has moved the carb air levers was when icing on the ground. The ice always eventually clears so I have to wonder if the heat is actually being applied but the lever movement isn't being animated.

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Re: Losing lots of airspeed at high alt w/out engine power

Post by P*Funk »

AviationAtWar wrote: Are you actually seeing him move the carb heat levers?
Yes actually I very specifically checked to see if he was applying the air when he said he was. I saw the levers move in flight. I in fact saw them staggered with 2 engines on one setting, another on a slightly stronger setting indicating that he was applying them with more than a convincing level of sense. I also observed my FO apply the wing and prop de-ice boots periodically in the flight.
CAPFlyer wrote:First, I would have tried to cycle the airframe and prop icing even if there was no indication just to make sure you didn't have a short accumulation.
I remember trying this but the FO immediately returns them to off when he doesn't seem to consider them a concern, or I suppose maybe its the FE who does that but the switches are on the FO's station.
Second, I would double check all of your axis assignments to make sure you don't have something accidentally assigned to the spoiler axis.
That's an interesting possibility. I didn't think that the Connie had spoilers. A search of the manual shows no mention of them. Checking my throttle the axis I have assigned to spoilers is out of the stowed position but I've never thought to concern myself with that in a flight with the Connie since it doesn't have any.
Third, make sure you didn't accidentally open the cowl flaps. While the FE usually takes care of it, if one extended, then that's a possible reason.
That's another though far less likely possibility. I did during the early cruise use the FE station to carefully set all the engines to a given RPM individually. That said this was early on and after nearly 3 hours of cruising for it to suddenly become an issue when I hadn't touched the FE station in easily more than hour except to adjust throttles and hadn't disengaged the FE control of it in nearly 2-3 seems unlikely as the drag should have made itself apparent almost right away. An invisible not modeled but somehow modeled spoiler seems more possible as the control could have spiked at some point then applied a drag but that still doesn't explain how there are spoilers.
Finally, check all of your engine readings. Make sure you don't have a power loss somewhere. It should show itself with a significant increase in the throttle position of one engine over the others, but at times you can still have a power loss that doesn't show immediately through the throttle, but does show with a loss of oil or fuel pressure.
I definitely checked the indications thoroughly and periodically during the half hour I contended with this issue. The engines were showing nothing abnormal, all indications for power output, RPM, Manifold Pressure, Oil Pressure, Oil Temperature, Cylinder Head Temperature, etc, were nominal and unchanged from before the loss of speed occurred. The very reason I posted this thread was my inability to explain a loss of speed when no loss of power was there.
I'll go experiment with that spoiler and see what happens. Maybe you can explain to me why I may need to be concerned iwth it though given your tester knowledge.

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ratty
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Re: Losing lots of airspeed at high alt w/out engine power

Post by ratty »

Airframe icing.
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Oracle427
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Re: Losing lots of airspeed at high alt w/out engine power

Post by Oracle427 »

The spoiler axis always remains active in FSX even if it isn't a party of the aircraft. This has caused a problem with all the A2A aircraft. In some cases it even caused the aircraft to climb vertically off the ground like a helicopter, but with no control.
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Lewis - A2A
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Re: Losing lots of airspeed at high alt w/out engine power

Post by Lewis - A2A »

Oracle427 wrote:The spoiler axis always remains active in FSX even if it isn't a party of the aircraft. This has caused a problem with all the A2A aircraft. In some cases it even caused the aircraft to climb vertically off the ground like a helicopter, but with no control.
yes yes, it has caused some interesting issues when people have a spoiler mis-mapping on there control layouts
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CAPFlyer
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Re: Losing lots of airspeed at high alt w/out engine power

Post by CAPFlyer »

Your spoiler axis being out of stowed was almost certainly the culprit. You probably bumped it on accident which overrode whatever setting it had. I don't remember if the Connie uses it or not, but it's common to use the spoiler axis on Piston-driven aircraft to allow FSX to simulate the drag of the cowl flaps and even airframe icing (which isn't really a default feature of FSX).

Even if it doesn't, FSX is wierd with that axis and will do strange things when it's triggered on an airplane that doesn't even have the "Spoilers" section of the Flight Dynamics (.cfg & .air) files present. I've had airplanes literally stop mid-air when I accidentally moved my spoiler axis by a fraction of an inch, which is part of why I use FSUIPC and make sure that the spoiler axis is only assigned on airplanes which actually have the need for that axis to be active.
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P*Funk
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Re: Losing lots of airspeed at high alt w/out engine power

Post by P*Funk »

Having gone through another flight carefully ensuring my spoiler axis wasn't disturbed I had nothing resembling this issue. I never encountered it before because I hadn't assigned the axis until recently for a different aircraft. I'll likely rebind it via a different method to ensure this isn't an issue again. Thanks for the help guys.

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