29 Mar 2024, 03:47 [ UTC - 5; DST ]
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Post subject: Re: MU2 Pre-buy speed 36 ktas below book Posted: 03 Jan 2022, 14:26 |
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Joined: 04/20/15 Posts: 556 Post Likes: +311 Location: KFAT
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Our flies to book spec, and that's with mismatched engines and one with 5000 hours on it. I'm flying the Crossno, Tarver, Zastrow MU2F model with -1s. Attachment: IMG_7153.jpeg It bounced around 265-270 knots. 54 gph. That's at 25,000', 8300 lbs, 35 psi, 2h45m fuel, ISA+15, EGT temps set on the "weaker" engine to max cruise at 100% RPM and matched fuel flow on the other engine. Here's the closest corresponding chart at slightly heavier weight but slightly cooler temps.. Calls for 35 psi torque, 52.7 gph, and 265 knots at 25,000. Attachment: Screen Shot 2022-01-03 at 10.05.26 AM.png Not sure if I missed it, but did engine parameters look the same between both engines, or did one indicate notably different? Pretty sure you would have caught onto that. Yaw or lots of trim to fly straight would be needed with a weak engine on one side, so I'm suspecting it's pitot static, both engines cooked (borescope it), or small chance you have something big time hanging in the wind.
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Post subject: Re: MU2 Pre-buy speed 36 ktas below book Posted: 04 Jan 2022, 01:27 |
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Joined: 08/03/10 Posts: 1562 Post Likes: +1781 Company: D&M Leasing Houston Location: Katy, TX (KTME)
Aircraft: CitationV/C180
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Username Protected wrote: Our flies to book spec, and that's with mismatched engines and one with 5000 hours on it. I'm flying the Crossno, Tarver, Zastrow MU2F model with -1s. Attachment: IMG_7153.jpeg It bounced around 265-270 knots. 54 gph. That's at 25,000', 8300 lbs, 35 psi, 2h45m fuel, ISA+15, EGT temps set on the "weaker" engine to max cruise at 100% RPM and matched fuel flow on the other engine. Here's the closest corresponding chart at slightly heavier weight but slightly cooler temps.. Calls for 35 psi torque, 52.7 gph, and 265 knots at 25,000. Attachment: Screen Shot 2022-01-03 at 10.05.26 AM.png Not sure if I missed it, but did engine parameters look the same between both engines, or did one indicate notably different? Pretty sure you would have caught onto that. Yaw or lots of trim to fly straight would be needed with a weak engine on one side, so I'm suspecting it's pitot static, both engines cooked (borescope it), or small chance you have something big time hanging in the wind. Remarkable airplane. I do wish I could have just kept it. What an amazing alternate that would be for shorter trips.
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Post subject: Re: MU2 Pre-buy speed 36 ktas below book Posted: 07 Jan 2022, 01:17 |
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Joined: 10/09/21 Posts: 14 Post Likes: +1
Aircraft: Lancair Legacy
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OK I promised to tell the rest of the story, here it is. It's N3GT, ser 277, owned by Mike Laver at Air1st. He called me today and said that he spent at least 10 hours thinking about my info, which took him by surprise; he'd never really compared to flight manual data before. He got back from vacation this week, gassed up the airplane and took it to 25,000 feet and got about 250 knots. Thinking back to his extensive experience in ordinary K models, he thinks this is pretty much how they fly, with some caveats: They do better at 96% rpm than 100% (he said better speed AND economy); they speed up as they lighten, and with more ram air coming in, the turbine cools down and you can add more fuel. So you can get 275kt at some altitude, but it'll be up around 80gph. I've seen and heard enough on this thread (THANKS for all your comments and data!) to understand that there's variation in performance, and some airplanes fly on book or at least much closer than N3GT currently does. As to WHY... something of a mystery. Mike did not identify any airframe problems (neither did I, with a very careful inspection) and didn't volunteer to borescope the engines. I don't think there's anything wrong with the airframe but I did notice a 3.5 deg pitch attitude on the Garmin ADI at my data point. Neema's shows 0 deg, Steve Bankston's 1 deg. But, just to complicate the question: N3GT's gyro ADI shows 0 deg. Argh. So I think the drag is coming from high angle of attack, which is either from being heavier than I calculated (which was 9000 lb), or being slow, or being too high. It's a vicious circle, but I think it starts with crummy engine performance. The props are 100hr since overhaul, the engines are supposedly 275hr since HSI. The airplane was flown by the Air Force as a target, along with several other K models that Mike has back in his hangars now that the Air Force contract has concluded. The props are from one airplane, the engines from another. So -- airframe good, props good, the gear and flaps were retracted. Airspeed indicators matched and confirmed the TAS calculation; also, Mike got the same TAS and I think he checked it with a two-direction run. I have to think engines. I enclose the two pics I took, the Foreflight profile of the flight, and the flight manual page. Sorry I didn't find a smoking gun; still curious. Sorry the pics are crummy; it was a very UNplanned data point. You can barely see the 253 ktas reading on the left side of the Garmin if you magnify it. Fuel flow was 65 gph; and the flight manual says 289 ktas at 64 gph. So we had the fuel flow right for max cruise. Attachment: 211212a G600 display.JPG Attachment: 211212b Engine instruments.JPG Attachment: Flight Profile.png Attachment: 211212e Performance Markup.JPG
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Post subject: Re: MU2 Pre-buy speed 36 ktas below book Posted: 07 Jan 2022, 08:38 |
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Joined: 06/18/15 Posts: 529 Post Likes: +182 Location: Idaho
Aircraft: Helio Courier, MU2
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I’ve had three MU2s. They make book speed unless there is a problem and they certainly don’t go faster @96% rpm
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Post subject: Re: MU2 Pre-buy speed 36 ktas below book Posted: 07 Jan 2022, 08:55 |
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Joined: 08/13/20 Posts: 194 Post Likes: +111 Location: KLOU/KJVY
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I agree with mike here. Pulling the props back to 96% is for economy and lower noise, it definitely decreases speed though. Sorry you couldn’t find the smoking gun. I’m guessing you passed on the purchase?
_________________ -MU-2 -C501
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Post subject: Re: MU2 Pre-buy speed 36 ktas below book Posted: 07 Jan 2022, 09:09 |
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Joined: 06/18/15 Posts: 529 Post Likes: +182 Location: Idaho
Aircraft: Helio Courier, MU2
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Are my eyes deceiving me or are you way below the ITT limit?
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Post subject: Re: MU2 Pre-buy speed 36 ktas below book Posted: 07 Jan 2022, 09:13 |
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Joined: 08/13/20 Posts: 194 Post Likes: +111 Location: KLOU/KJVY
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Looks like he’s at 875, which is around what most folks limit to. I was taught 900 and use that for my personal max.
_________________ -MU-2 -C501
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Post subject: Re: MU2 Pre-buy speed 36 ktas below book Posted: 07 Jan 2022, 09:29 |
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Joined: 08/10/12 Posts: 311 Post Likes: +209 Location: KTKV KBKV
Aircraft: B100
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Username Protected wrote: Our flies to book spec, and that's with mismatched engines and one with 5000 hours on it. I'm flying the Crossno, Tarver, Zastrow MU2F model with -1s. Attachment: IMG_7153.jpeg It bounced around 265-270 knots. 54 gph. That's at 25,000', 8300 lbs, 35 psi, 2h45m fuel, ISA+15, EGT temps set on the "weaker" engine to max cruise at 100% RPM and matched fuel flow on the other engine. Here's the closest corresponding chart at slightly heavier weight but slightly cooler temps.. Calls for 35 psi torque, 52.7 gph, and 265 knots at 25,000. Attachment: Screen Shot 2022-01-03 at 10.05.26 AM.png Not sure if I missed it, but did engine parameters look the same between both engines, or did one indicate notably different? Pretty sure you would have caught onto that. Yaw or lots of trim to fly straight would be needed with a weak engine on one side, so I'm suspecting it's pitot static, both engines cooked (borescope it), or small chance you have something big time hanging in the wind. Yep! NO other airplane will do what an F model will do. It’s truly amazing. Glad you’re enjoying her Neema.
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Post subject: Re: MU2 Pre-buy speed 36 ktas below book Posted: 07 Jan 2022, 10:32 |
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Joined: 06/18/15 Posts: 529 Post Likes: +182 Location: Idaho
Aircraft: Helio Courier, MU2
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Username Protected wrote: Looks like he’s at 875, which is around what most folks limit to. I was taught 900 and use that for my personal max. Not sure who is teaching that. That leaves a huge amount of performance on the table
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Post subject: Re: MU2 Pre-buy speed 36 ktas below book Posted: 07 Jan 2022, 10:49 |
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Joined: 06/09/09 Posts: 4573 Post Likes: +3298
Aircraft: C182P, Merlin IIIC
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96% is a slower turning engine therefore ingesting less air therefor you will reduce fuelflow to maintain the same temp and will be going slower.
Last edited on 07 Jan 2022, 11:39, edited 1 time in total.
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Post subject: Re: MU2 Pre-buy speed 36 ktas below book Posted: 07 Jan 2022, 11:34 |
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Joined: 10/09/21 Posts: 14 Post Likes: +1
Aircraft: Lancair Legacy
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Yes I did pass for now. I'm impressed with the airframe and props, but unsure of the engines. More story: I did homework last night (enclosed), sent it to Mike L this morning, and finally had a lengthy conversation with him this morning which I wish we could have had a month ago. He said: -- It's basically speed vs fuel flow, and the dash no. of the engine doesn't really alter that. -- His own airplane, N50ET, is an outlier because it has a pressurization system that doesn't use bleed air, and ... it's just a faster airframe for unknown reasons. -- N3GT will go faster but will take more fuel flow to do it. My data point had room for more speed, because we weren't right up against ITT limits, but would have used more fuel. -- He acknowledged Steve Bankston's data point and noted that Steve had everything set pretty much right. Said N3GT would probably get close to 280 kt if we had gone down to 15000 feet and maxed it out. -- He didn't address N18BF and I didn't press it. -- He reiterated that N3GT is typical for a K model, and that if he spotted the 253 KTAS and 65gph fuel flow on his flight planning tool it would go 1150nm (no wind) with IFR reserves. Attachment: TAS vs FF.png I'm sure there's a bias in my data also. Shall we collectively admit that we really don't take pictures of our poorer data points... ? But several of you have checked and found airplanes that do perform right on book. I think I'm done for now. For the record, I'm in the market for a short-body MU-2, any variant that's basically sound and fairly priced. Doesn't have to be pretty, doesn't have to be low time. Should perform close to book. Hey Kirk, N18BF is one great airplane for sure, but I'm rapidly learning there's a lot of variation among airframes so be careful what you claim for all F models. I don't know why there'd be a systemic performance difference between F and K? K's are nominally 130 lb heavier, that's not much. (... said the 2-hour MU-2 pilot. )
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Post subject: Re: MU2 Pre-buy speed 36 ktas below book Posted: 07 Jan 2022, 11:42 |
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Joined: 10/09/21 Posts: 14 Post Likes: +1
Aircraft: Lancair Legacy
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PS -- Some of you may know N3GT as "Don Taylor's airplane". Incidentally, he had it painted in 2004 and changed the N number at the same time, and I think it's no coincidence that his wife's name is Gail Taylor. Kinda neat...
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Post subject: Re: MU2 Pre-buy speed 36 ktas below book Posted: 07 Jan 2022, 11:51 |
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Joined: 11/22/08 Posts: 2914 Post Likes: +922 Company: USAF Propulsion Laboratory Location: Dayton, OH
Aircraft: PA24, AEST 680, 421
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We looked at N3GT a few years ago. I thought it was a pretty decent airplane at a pretty decent price.
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