Low RPM on takeoff

[sichars1968]

Hi Goran

I'm having a bit of a strange situation suddenly in the Duchess in that when I advance the throttle to maximum on takeoff the prop RPM only reaches 2250 with MP of 27. This is making it very difficult to get airborne but when I do the RPM rises gradually to 2700 as should be, can you shed some light on this?

This is in XP10 and I know you are planning to do an update for the Duchess for the new platform as you told me in answer to my previous post, I was just wondering if there is anything you can suggest in the meantime?

Many thanks

Simon

[Goran_M]

Unfortunately, there is absolutely nothing I can do atm to make it work properly.

I have been working on what can be worked on. Rest assured, it'll be ready soon after 10 is considered stable.

[sichars1968]

Thanks for the reply Goran.

Okay that is no problem at all, I just thought it strange that it works okay in XP10 then all of a sudden doesn't. I look forward to the update to the Duchess to make it compatible with XP10.

In the meantime I am looking forward to the DC-3, it looks absolutely marvellous.

Cheers

Simon

[Muskoka]

Me too Goran, was going to send you a message and ask about it until I saw this post. Was having a nice flight this morning and was climbing through 6,000ft, then all of a sudden very little power from the engines. I actually had to land in a field, and then I sat there for at least 5 minutes trying to figure out if I had done something wrong. I was looking all over. Made for an interesting situation, was kinda fun, but had me scratching my head.

Glen

[Goran_M]

Me too Goran, was going to send you a message and ask about it until I saw this post. Was having a nice flight this morning and was climbing through 6,000ft, then all of a sudden very little power from the engines. I actually had to land in a field, and then I sat there for at least 5 minutes trying to figure out if I had done something wrong. I was looking all over. Made for an interesting situation, was kinda fun, but had me scratching my head.

Glen

Could you give me the flying conditions you were in. As much detail as possible. There are a couple of gauge issues that I have actually fixed a couple of weeks ago, but there are still 2 or 3 other issues that are being a bit stubborn.

Also, just a shot in the dark, but was your mixture set correctly? If you're at a reasonably high altitude, and air pressure is lower than normal, having a Full Rich mixture setting will drop the engines power. In some cases, it will also stall the engines.

Edited March 1, 2012 by Goran_M

[Muskoka]

That's why I was scratching my head, she was climbing out fine, then it was as if I pulled the throttles back. I was able to land, and then sat on the ground for at least five minutes thinking maybe the carbs had froze, or something had iced up. After the five minutes everything still looked ok, temps were fine, it was idling fine, but had no rpm if I pushed the throttles, so I quit the flight.

Can't give too much info on conditions, didn't record anything, just going from memory. Flying in Canada this time of the year it's cold, I think the temp was just below 0 Celsius. There was snow in the area and I had gone through some, but it was only for maybe 15 seconds at a time, it wasn't constant. The pressure was low, 29.60's I think. I'm thinking she may have just got heavy with ice maybe, she didn't drop like a rock, but definitely didn't have enough power to sustain flight.

I did have one flight this afternoon, and the snow closed in, and then I was in trouble, she went down pretty quick. Again, didn't crash, but it was noticeably different from the flight before. I'll pay more attention to the conditions and see if I can find anything repeatable. She's still nice to fly, looks great, and is easy on the frame rates.

Glen

[Goran_M]

You MIGHT have warnings turned off. Turn them back on under "operations and warnings" and see if you get a carb ice warning. I'm only guessing but you may have Carb icing. The Carb heat levers are on the center column under the throttle console. I have just taken it for a small test flight to try and duplicate what is happening but I got no engine problems. Granted, I was over Hawaii, that's why I think it was carb icing.

Edited March 1, 2012 by Goran_M

[Muskoka]

Well, just tried a few more flights and seem to have found something in common. The aircraft will not climb through clouds, it seems fine until you get into the "total white out cloud conditions" that we see in XPX. If you can still see the ground, even though your in the clouds it seems fine, but as soon as you go into the soup, the rpm's start to drop. I have warnings turned on, didn't get any warning in three separate flights, and every time the rpm's started to drop I tried various positions with the carb heat levers, made no difference. Conditions were cold, below freezing, overcast conditions, pressure was 29.80's.

The last time I had her trimmed out nice, everything looked good temperature wise, was in and out of clouds, 3,500ft, then all of a sudden, total white out cloud, no precipitation, and the rpm's started to drop, no warnings on the screen, dropped down out of the soup, made no difference, rpm's never came back, down to the ground we went. I'm going to try another flight right now in another aircraft I have (similar size and makeup) and see if the results are the same. I want to see if it climbs through the clouds, and if I get any warnings.

Glen

edit: Goran, I don't think it's a problem with your aircraft, I think it's a XPX issue. The other aircraft "Bonanza" exhibited the same behavior. Everything was fine until I got into the soup, total white out, and then the rpm's start to drop to a unrecoverable situation. There are no warnings on screen, nothing. Some weather related effect in the program appears to be over done, like the turbulence. Within less than a minute, you go from normal flight, to these "ridiculous" white out conditions, and the aircraft starts to fail with absolutely no warnings. If it's a icing issue, you should get a warning. All the flights I tested were with real weather.

Edited March 3, 2012 by Muskoka

[Goran_M]

Thanks for that, Glen!

I just filed a bug report.

Should get fixed soon.

[Goran_M]

Glen

I ran a few tests after getting a reply from Austin and I would like to know if you had roughly the same settings.

This was tested with the default King Air to eliminate whether or not it's an add on issue or an x plane issue.

From what I can see, flying through clouds at a low enough temperature, will cause a lot of ice build up and the engines will lose power.

Took this screenshot a few seconds before my engines died. Full power and flying almost straight and level. Note the ice output in the top left of the screen.

Edit: Further correspondence is happening on this issue. I'll post an update on this as soon as I have it.

Edited March 4, 2012 by Goran_M

[Goran_M]

Got a final response from Austin.

He confirmed it is definitely ice.

My suggestion, stay away from clouds in temperatures that promote ice build up. Keeping in mind, Icing can happen in above 0°C temperatures...if there is enough humidity while flying through cloud.

[Muskoka]

Hi Goran, did a test flight this morning, temperature was -18 Celsius, little cloud, more like ice crystals from the cold. Flew the Duchess, and turned on all the ice data outputs, as well as carburetor heat. The flight was great, and yes, if I got near cloud the ice started to build up. In that case I would turn to avoid anything looking like cloud and the readings would start to drop, very cool. This must be the issue, really need to avoid those clouds in freezing weather.

Glen

[Goran_M]

I had a bit of a "wow" moment myself when I was going through these tests for the exact reasons you describe.

Happy it's been cleared up.