Real speed numbers of -5 longwings?

[Adam Frisch]

Just wanted to get some real numbers of how fast a -5 840 or 900 model (are there any left with -5's?) goes? I heard the 690A/B's do about 270kts on the same engines, but this longer wing might give better performance up high?

[donv]

270 is higher than I recall going in a 690, but others here will probably tell me otherwise. And I have always run -5s conservatively-- 850 degrees at cruise. Some people run them right up to 885...

I more typically remember 260 or so, maybe a bit less depending on how tired the engines are.

It's been way too long since I've flown an 840 with -5s to give you a good answer, though.

[Adam Frisch]

Thanks Don.

Didn't know it was that low. Means the delta from mine to the 690's is pretty small, then. 245-250kts vs 260kts. Not a huge difference.

[Bruce Byerly]

Corey can verify but last healthy -5 840 I tested was 275 KTAS all day long at 885. Add 20-30 knots for a -10

[donv]

Bruce, have you noticed any issues with hot section interval when running 885 consistently, as opposed to a lower temperature?

In the air ambulance program I used to fly for, we often did hot sections early on the -5s, although a lot of hot and high takeoffs were certainly a contributor to that as well.

[Bruce Byerly]

Bruce, have you noticed any issues with hot section interval when running 885 consistently, as opposed to a lower temperature?

In the air ambulance program I used to fly for, we often did hot sections early on the -5s, although a lot of hot and high takeoffs were certainly a contributor to that as well.

Don,

My take away after looking at a lot of T wheels on the bench is that it has less to do with the temp you run and more to do with how your fuel nozzles flow. If they are plugged, they create more carbon and more erosion. Then there’s the question of whether or not someone has hamfisted a start or twenty, run 100% avgas, flown through ash, started on worn out batteries, done hot sections with a crook, etc.  A -5 plane will have one engine with a $30k hot and the other side will be $130k. Same plane, same pilot, same mx, same hours.  I think all you can control is focusing on best procedures and best MX. Life is short, run it at 885 for 690B and later with the better exhaust and higher temp limit. Go fast. -10’s are generally bulletproof but subject to the same risks.

[schrambow]

Bruce is right, our 840 with -5, i have seen anywhere in the last 5 months between 272 knots through 279 knots.  Now, i was not aware of running at 885c on the ITT in cruise, i have been using exactly 900c in cruise. 
Bruce/Don or anyone else, i know the book calls for 905 as max continuous for cruise, but running it this high will cost me more in the long run than using 885c?
Please let me know your thoughts and your experience with the hots and the overhauls of the numbers you are using and seeing.  Thank you,
corey
 

[donv]

I don't have a -5 AFM handy, but I'm pretty sure 885 is max recommended cruise. I learned 900 for takeoff and 850 for cruise in the -5, but i'm conservative. 900 for cruise sounds too high, unless something has changed-- which is entirely possible.

I always figured there might be instrument error in there, who can read the analog gauge that precisely, etc which is why I liked 850-- if it creeps up a few degrees, no problem.