Piper Seneca in high altitudes?

[BlueLights]

Hi all,

Just a silly little question... Has anyone tried to fly the turbocharged Seneca Seneca II/III/IV/V into FLs? Since their service ceiling is 25000ft.

Just curious how does the aircraft respond at that altitude, and how do those engines respond pass 19000 which I think is the critical altitude if I recall correctly.

Thank you in advance!

[iflyforpie]

Had a conversation with an owner of one.

Even with pressurized mags and an absolutely perfect ignition system, the engines would start misfiring after the plugs were 50 hours old at anything above 20,000 feet. Didn’t matter how they were cleaned or gapped. Only new plugs would solve the problem. He didn’t say whether they were fine wire or massive electrode. His was a Seneca III I believe with TCM TSIO-360s and the Merlin waste gates.

[Big Pistons Forever]

My experience with a straight Seneca 2 with the standard fixed waste gate was that it did not do well in the flight levels. Engines ran hot, and the MP hunted unless the air was perfectly smooth

[BlueLights]

My experience with a straight Seneca 2 with the standard fixed waste gate was that it did not do well in the flight levels. Engines ran hot, and the MP hunted unless the air was perfectly smooth

Thank you both for your answers.

From your experiences, how high realistically would you say is the ceiling for your Seneca II in terms of no engine problems or performance reductions

[lownslow]

This is strictly anecdotal but I had heard funny things can happen early in the descent if you decide to come down at or near redline as many do with airplanes made to routinely fly high and fast. Turns out that while the Seneca doesn’t have a published Mach limit physics dictate it absolutely does have a limit, and comes into play somewhere below the 220(?) Vne on the ASI when you’re up at FL250.

[Big Pistons Forever]

From your experiences, how high realistically would you say is the ceiling for your Seneca II in terms of no engine problems or performance reductions

17,000

[iflyforpie]

This is strictly anecdotal but I had heard funny things can happen early in the descent if you decide to come down at or near redline as many do with airplanes made to routinely fly high and fast. Turns out that while the Seneca doesn’t have a published Mach limit physics dictate it absolutely does have a limit, and comes into play somewhere below the 220(?) Vne on the ASI when you’re up at FL250.

A Seneca at 220 indicated at 250? I’d love to see to see the dive you would need to do to would produce that.

By the time you’re there, you’ll probably be out of the flightlevels and redline nowhere near a critical Mach. I think it would have to be a really really cold day for it to happen.

[lownslow]

By the time you’re there, you’ll probably be out of the flightlevels and redline nowhere near a critical Mach. I think it would have to be a really really cold day for it to happen.

Could be but my point remains that there’s a secret, un-published limitation waiting for you out there. I’m sure someone somewhere would want to see redline speed bad enough to try.

[iflyforpie]

By the time you’re there, you’ll probably be out of the flightlevels and redline nowhere near a critical Mach. I think it would have to be a really really cold day for it to happen.

Could be but my point remains that there’s a secret, un-published limitation waiting for you out there. I’m sure someone somewhere would want to see redline speed bad enough to try.

I’m curious as to what actually is the limitation? Turboprops it seems have limits between 0.50 and 0.60 Mach—far below any airframe critical Mach number I’d think.

I thought it would be the propellers which makes sense because the tips have the fastest linear speed of any aircraft part. Also the larger and faster a propeller is, the slower it is made to turn—probably to keep it below Mcrit as you go at 300+ knots in the 20s. Planes like the Q have swept tips likely to increase the Mcrit of the blades even further.

But what are the actually consequences of a prop going supersonic other than noise and loss of thrust? Maybe destructive vibration if done cumulatively, or is it near instantaneous like control flutter? But a Cessna 185 breaks the sound barrier with the prop while still on the water so it couldn’t be that bad.

Maybe it’s a liability thing? We’re only testing the plane to this Mach and won’t take any responsibility if you fly it faster. WWII prop planes went a lot faster in a dive and it was Mach Tuck and elevator ineffectiveness that got them not props.

[Cessna 180]

The RV-10 is known to have mach issues, especially with bigger engines, at high altitudes. It wouldn't surprise me if it could happen to other piston aircraft, which generally don't fly that fast.

[ChiefTraining]

The II and III are a good aeroplane, but I wouldn't suggest the Flight Levels by any stretch. I flew the II and the III about 15 years ago all around North America on pipeline contracts. They do not like above 14-15,000 at all, I think I put in about 2600 hours on them

[Justjohn]

By the time you’re there, you’ll probably be out of the flightlevels and redline nowhere near a critical Mach. I think it would have to be a really really cold day for it to happen.

Could be but my point remains that there’s a secret, un-published limitation waiting for you out there. I’m sure someone somewhere would want to see redline speed bad enough to try.

I’m curious as to what actually is the limitation? Turboprops it seems have limits between 0.50 and 0.60 Mach—far below any airframe critical Mach number I’d think.

I thought it would be the propellers which makes sense because the tips have the fastest linear speed of any aircraft part. Also the larger and faster a propeller is, the slower it is made to turn—probably to keep it below Mcrit as you go at 300+ knots in the 20s. Planes like the Q have swept tips likely to increase the Mcrit of the blades even further.

But what are the actually consequences of a prop going supersonic other than noise and loss of thrust? Maybe destructive vibration if done cumulatively, or is it near instantaneous like control flutter? But a Cessna 185 breaks the sound barrier with the prop while still on the water so it couldn’t be that bad.

Maybe it’s a liability thing? We’re only testing the plane to this Mach and won’t take any responsibility if you fly it faster. WWII prop planes went a lot faster in a dive and it was Mach Tuck and elevator ineffectiveness that got them not props.

On various Beech products it was the airflow over the top of the wing separating at high speed and causing damage to the hinged bits on the trailing edge.

[Big Pistons Forever]

Of all the things to worry about flying a Seneca in the flight levels exceedence of some urban myth Mach limit is IMO about at the bottom. It was certified to Max altitude of 25,000 and a VNE of 195 IAS. VNE is 90 % of Vd, so the chance you could get into compressibility issues is effectively zero.

The reason that the Seneca was turbo charged was so that it could maintain adequate performance on one engine at altitude, not to routinely fly in the flight levels. It does OK in the teens but really is not happy in the flight levels. There is only so much you can do with 200 hp a side

With respect to the high speed break ups of Van’s aircraft, I believe every single event was traced to control surface flutter caused by inadequately balanced controls or insufficient control cable tensions or both, not Mach issues

If you want fly in the flight levels get a turbo 310

[Roar]

If you want fly in the flight levels get a turbo 310

I agree with you that a turbo 310 is better in the flight levels than a Seneca, it’s still a place they are not happy to be. I used to fly a T310R doing photo survey up to FL 260 And up there the old 310 flew like you were trying to balance on the tip of a needle. It wallowed around and required large control inputs to hold the survey line to within specified tolerance. Although very slowly step climbing it up to FL260 was challenging enough the bigger issue was getting it down without shock cooling the engines. I couldn’t pull power off or the CHT’s would plummet and I couldn’t push the nose over or I’d blast through VNE so it required just tickling some power off and ever so slowly descending at around 100ft/min to start. I can remember being over the front range west of Calgary and it taking the best part of an hour to get on the ground.

[Big Pistons Forever]

My experience with the T310R was not the same. The airplane in my experience handled normally in the lower flight levels with 210 to 230 the sweet spot although I was just cruising straight and level going from A to B not trying to do aerial work. You are right thought initial descent has to be planned well in advance