Engine restart speed

[abgd]

This video contains analysis of two light aircraft accidents. Somewhat to my surprise there is a reference to an engine restart speed for a 152 and the commentator states that he hopes the pilot is trying to restart the engine.

Is there such a thing as a best speed for restarting an engine? I have read of techniques for restarting hand-propped aircraft in flight, but for anything with a starter motor does it really matter?

Would anybody here have advocated trying to restart the engine at any point for the first accident discussed?

[Pilot DAR]

I find Mr. three stripes to be marginally persuasive at best. The thing she said, which I believed the most was: "I don't know". I'd go with that for a lot of what he said.

There is no published airspeed for an inflight restart of a stopped Cessna engine. It's actually pretty hard to get mechanically sound Cessna 152 engine to stop turning in flight. So, if the engine actually stops completely, I would be suspecting a mechanical failure inside. Sure, at any airspeed you like, try the electric starter, if it's going to run, that's a really good first step. If the starter won't turn it over, I'd be setting up for a forced approach. Though Cessna POH's do specify an airspeed following engine failure, that's for optimum glide, 60 knots is not going to windmill start a stopped Lycoming engine with decent compression. They do say that if the engine has stopped, to use the starter.

Turbine engines are different, and do have start envelopes, which may include a specified airspeed.

[megan]

Restarting a stopped prop in flight was a demonstration item when I started flying in my youth in the DHC-1 which had no starter. The first impression was how hard it was to get the prop to stop, the second was the amount of nose down and speed to get the thing to begin rotating again.

[ShyTorque]

The RAF CFS course taught me that the best way to rotate a stopped engine in flight is to pitch the aircraft hard. It’s to do with the change in the angle of air flow past the blades. Obviously, you need some excess energy in the airframe to do that.

I can recall at least two personal experiences in the Bulldog when the engine stopped during spin training. The prop began rotating again during the recovery (i.e. pitching nose up from the steep descent) once the spin had been stopped. It was by no means uncommon; RAF guidance was to ignore the stopped engine and concentrate on the spin recovery, simply because it might restart itself during the recovery in that way.

[nickp]

Restarting a stopped prop in flight was a demonstration item when I started flying in my youth in the DHC-1 which had no starter. The first impression was how hard it was to get the prop to stop, the second was the amount of nose down and speed to get the thing to begin rotating again.
I remember the same experience of stopping and restarting the prop in the Chipmunk as a cadet at Henlow. I think their Chipmunks were fitted with cartridge starters but I can't remember how you already knew that you had used the last one.

[Fl1ingfrog]

An interesting extract from the Robin 2160 POH:

"In a spin of more than 3 rotations, the engine is likely to stall. This raises no difficulty: the propeller should windmill once airspeed is restored and restart the engine.
(CAUTION: engage engine starter only if propeller stops rotating)"

The Robin 2160 has a fixed pitch propeller and a Lycoming 160 hp engine. The above strongly infers that the propeller will be caused to rotate at very low speeds.

[Aneas]

To restart a hand start prop in flight involves a dive to near Vne and a hard pull to left or right depending on the rotation of the engine. It works, but uses some altitude up!!

[Pilot DAR]

a dive to near Vne and a hard pull

Things which should not be combined while flying an airplane, unless you're referring to a G meter while you're doing it!

[excrab]

It’s a long time since I’ve done it, but used to do demo and practise of restarting in flight without using the electric starter in C152 aerobatic when teaching for the old AOPA aerobatic certificate (in the U.K.). To stop the engine windmilling you had to get the airspeed back almost to the stall, and to get it over compression to start windmilling again needed a dive to about 140 kts, if I remember rightly. Obviously used to do this at about 5000 ft over the airfield, just in case for any reason it wouldn’t restart. Fortunately it always did...

[Duchess_Driver]

As part of the FI course before things got “health and safety conscious” I would get the student to stop the prop “for the experience.” C152 with Lycoming.

To actually get the thing to stop rotating you’d have to slow to about 40kts before it would shudder to a halt. It was a good opportunity to compare the difference in ROD between idle/rotating and stopped. Not much in it.

To get the thing rotating again it would require about 110-115kts - which few students appreciated the pitch angle required to achieve.

We’d have a hard deck of 3,000’ which if we weren’t rotating by then then a quick flick of the starter would usually resolve the issue and we’d always be within gliding distance of an RLG/good sized field for a PFL. Never required that bit though.

In the Duchess the manual stated an air start would require 104 (?) before the blue lever forward but always found about 114 meant the accumulator worked so much better. Air starts without the accumulator were horrible - seemed to vibrate for hours until the blade settled down again.

[scifi]

I used to have an old Petter Stationary engine, with a BTH Impulse Magneto which was timed for a spark at tdc. It would start from zero speed, just pull the flywheel slowly over compression, and 'Bump' the thing would start.
Most Magneto GA aircraft retard the Impulse ignition below slow idle speed to tdc. So as long as the engine doesn't leak it's compression, it might just start if the prop is pulled slowly over tdc compression.
.

[Aneas]

Things which should not be combined while flying an airplane, unless you're referring to a G meter while you're doing it!
You are right, I was looking at a G meter in a Stampe.

[Forfoxake]

To restart a hand start prop in flight involves a dive to near Vne and a hard pull to left or right depending on the rotation of the engine. It works, but uses some altitude up!!

Do not recall the hard pull to left or right bit, but remember reading that restarting a (hand-start) VW engine in flight lost so much height (with no guarantee of success) that it was usually much better to use the height to plan and execute a good forced landing without power. I suppose exceptions would be over water out of gliding range of land, over really hostile terrain or with LOTS of height, However, generally, this sounds like good advice to me.

[TheOddOne]

As part of the FI course before things got “health and safety conscious” I would get the student to stop the prop “for the experience.” C152 with Lycoming.

DD,
At the same place I did my course, I suspect. It took all of the space from 6,000' to 3,000' to get the stopped prop over the compression, even then at almost VNE and rocking back and forth to get just the right AoA. Demo'd by the FIC instructor, not practiced by the student (me). One of the stand-outs (amongst many) from the course. The actual advice was 'if the prop has stopped and the electric start won't work, secure the engine (mixture ICO and mags off) and carry out a forced landing without power, forget about trying to restart using airflow'. The demo was all about how hard it is to restart, not how to do it.

TOO

[India Four Two]

I used to do type-conversions for glider pilots in a Motorfalke motor glider. It had a very reliable VW-conversion, with electric start, that worked first time, every time, provided you remembered to pull the choke out, if the engine was cold.

However, as part of the conversion process, we were required to do dive starts, in case the starter had failed. To start the engine required a very alarming nose-down attitude and a speed of 70-80 kts before the prop would turn over. I vaguely recollect that the height loss was more than 1000'. Vne was 100 kts.

[Aneas]

I also seem to recall that metal bladed engines were harder to air start than wooden bladed ones.
Cannot remember why - metal heavier?

[sycamore]

If you wish to restart a `stopped` prop in flight,by diving,is it better to open the throttle fully,or keep it closed...?

[Jim59]

Engine Start Procedure:

1. Ensure mirror pointing to correct place to see propeller.

2. Crack open nose air vent – otherwise nose pitot gives excessive position error; it’s in the vent air intake.

3. Operate pneumatic switch to change from fin mounted Pitot to nose Pitot.

4. Operate pneumatic switch to increase variometer damping.

5. Lower undercarriage in case engine fails to start.

6. Ensure fuel cock is on.

7. Turn on ignition.

8. Fly at between 49 and 65 kts.

9. Move engine switch to up position to raise engine.

10. Wait for green LED to indicate engine in raised position. It should be visible in the mirror.

11. Press and hold down electric fuel pump button. Simultaneously pull decompression handle – this should result in propeller hub rotation and any of the five blades still folded unfolding. If any blades still folded waggle rudder to help unfold them.

12. Increase speed to about 65 to 70 kts. Release decompression handle. Monitor via mirror.

13. If engine starts release fuel pump button when rpm stable.

14. If rotation stops back to 11 and try again – with higher airspeed up to 76 kts permitted.

15. If started climb away at 49 to 54 kts (blue line at 51 kts) and raise undercarriage – otherwise land if below your safety height.
Clearly this is a glider procedure doing an air start without an electric starter. Expected height loss around 200' I test the motor for about 10 seconds at the start of every cross country flight once airborne. I won't bore you with the shutdown procedure.
Before beginning the 'starting the motor' procedure one should have found a suitable landing place, and be positioning to land whilst starting the engine - in case it fails. Workload is moderately high.

Flight Manual says,"Below 300 m (984') AGL, starting attempts are to be avoided so as to have a safe height for plannig the approach pattern should the engine fail to run."

[Pilot DAR]

1. Ensure mirror pointing to correct place to see propeller.

Happily, I can see my prop by just looking up high over my shoulder, :), perhaps Jim59 would tell us which airplane these interesting instructions apply to!

metal bladed engines were harder to air start than wooden bladed ones.

For my experience, it's actually the other way around, metal props have more helpful inertia once you get them turning at all.

If you wish to restart a `stopped` prop in flight,by diving,is it better to open the throttle fully,or keep it closed...

In the absence of a flight manual procedure, I would choose an idle throttle setting, particularly if it's a constant speed prop. You would not like to induce an overspeed when it begins to run, particularly if you're already diving!

[oggers]

to get it over compression to start windmilling again needed a dive to about 140 kts,

Yes I have air started a 152 and remember being surprised at how far into the yellow arc I had to go to get the prop turning.

If you wish to restart a `stopped` prop in flight,by diving,is it better to open the throttle fully,or keep it closed...?

That is an interesting question to ponder. After the above mentioned experience it occured to me that opening the throttle would have reduced the speed required to air start the thing - but I remain unsure as to the effect or advisability of such an action. With the engine stopped the MAP and cylinder pressure will be unaffected by the throttle position so I expect you will need the same airspeed to get the thing turning to begin with. As the prop starts to rotate I'm pretty sure the thing will turn over quicker with the throttle open. How much difference this makes I could not say.

[Jim59]

perhaps Jim59 would tell us which airplane these interesting instructions apply to!

Schempp-Hirth Discus-2cT - which is still in production. It has a 2-cylinder 2-stroke Solo 2350 engine with a 5-bladed folding propeller. With a full tank of 13 litres of AVGAS / 2-stroke oil mix it has, in still air, a range of up to 200 nm without reserve.
The same glider is also available with a 'FES' Front - Electric - Sustainer motor. They have become popular because with the electric motor and prop in the nose it is a single lever operation for instant power - the drawback is battery capacity. Experience shows that trying to climb away gives very limited range - but may get you to another thermal - alternatively cruising at low level will get you further - but the range is probably in the order of 40 nm. There have been a few battery fires - with EASA banning there use in some gliders for a while - but I believe that the cause was identified and all restrictions now removed.
A small number of gliders have a gas turbine motor - these jet engines are small and lightweight, erect quickly, and the starting is pretty well full automated. Run on Avtur - but fuel consumption is high so range probable around 100 nm. But they do cruise under power at a good speed! You can hear them coming.

Right now petrol engines have greatest range - but most complex management. Improvements are being made to the petrol engine control systems to automate as much as possible and electric starters are now starting to be offered.

[sycamore]

Since the objective is to get the prop to turn and windmill,it would be prudent to leave the magnetos `off`,to prevent an overspeed if diving,then turn back `on` after recovery. I would have thought that ,with the throttle closed,there would be minimal airflow into the cylinders,but at speed,if the throttle is quickly opened,there maybe sufficient`push` on a piston to turn the engine..`.However,I expect `DAR` may like to subject his 152 to some definitive restart trials...!!
Slight thread drift..I used to teach student t-ps and ftes at a civlian t-p school,at the spinning phase in a CAP-10 ,that we would initially do a couple of spins,in both directions,with the prop stopped.this should demonstrate the true spin characteristics of the aircraft.This was then followed by spins with the engine at idle,where one could see that most prop-engined aircraft have different spin characteristics due to engine power and prop rotation...
Perhaps DAR could try this ,feathering a PT-6 on a `Caravan....?

[Pilot DAR]

Perhaps DAR could try this ,feathering a PT-6 on a `Caravan....?

I've feathered the PT-6 on Caravan, DHC-6, and DC-3T. It works fine, and the engine runs happily at idle while the prop luffs at only a couple of RPM. However, great care is required bringing it out of feather, as it is easy to surge and overspeed. Handled gently, it's fine, but too quick hands will be expensive and damaging. The Caravan glides very much better prop feathered - like a push from behind as it goes in to feather!

[ShyTorque]

Slight thread drift..I used to teach student t-ps and ftes at a civlian t-p school,at the spinning phase in a CAP-10 ,that we would initially do a couple of spins,in both directions,with the prop stopped.this should demonstrate the true spin characteristics of the aircraft.This was then followed by spins with the engine at idle,where one could see that most prop-engined aircraft have different spin characteristics due to engine power and prop rotation...
Perhaps DAR could try this ,feathering a PT-6 on a `Caravan....?

One of my first instructors in a C150 told me to carry out a PFL to the runway, which I did.
On finals he asked me if I was confident of making the runaway. I said I was. He leaned over, turned off the mags, took out the ignition key and put it in the top pocket of his jacket!

[Forfoxake]

One of my first instructors in a C150 told me to carry out a PFL to the runway, which I did.
On finals he asked me if I was confident of making the runaway. I said I was. He leaned over, turned off the mags, took out the ignition key and put it in the top pocket of his jacket!

Used to do much the same at least once with each student when I was instructing in 3 axis microlights. It was probably frowned upon by the BMAA but I felt it was important to show students that the aircraft kept flying even if the engine stopped, particularly in those days when most microlights had two stroke engines which were more likely to stop than typical light aircraft engines at the time.

Indeed the philosophy in microlight training in those days was this is what you do WHEN the engine stops, not IF!

(Maybe it still is.}

[Jan Olieslagers]

(Maybe it still is.}

:) It certainly was for me, even if almost all of my training was behind a 4-stroke 912-er. I still have a deeply embedded habit of ever always looking around for the best field nearby for an emergency landing - if it doesn't help, it never hurts.