flyinkiwi
25th Sep 2019, 00:17
Mods: I thought about necroing a 2 year old thread for relevancy but ultimately I chose not to for courtesy's sake. Feel free to merge if you wish.
I had the opportunity to be checked out in a Tielert converted 172R in the weekend. A brief background about me, I am a PPL(A) with a tick under 300 hours whose been flying (very) casually for the last 15 years. The vast majority of my hours are in 172s, and in particular the R series which made this flight odd in several ways.
The first was that hopping into the cockpit there was an instant sense of familiarity, yet here are a few new switches and some familiar controls are not present. There is no ignition switch for the magnetos, no mixture control, the push pull throttle has been replaced by a throttle quadrant with a single lever in it (I didn't particularly care for the placement, too low in my opinion). There is a block of switches for the FADEC controls as well as the usual ones. The walkaround was pretty much the same as an avgas 172, except the relocation of one fuel drain and the oil filler hatch. The second peculiarity is that there is this pervading smell of Jet-A everywhere, even inside of the cockpit.
Startup checklist was a bit more involved, you need to prime the fuel system which takes a couple of steps, if you're running the aircraft on diesel you need to let the fuel warm up, as we were running Jet-A it wasn't a problem. Once that is done, just press and hold the start switch until the engine reaches 25%. Then you have a 2 minute wait to let the engine and lubrication systems come up to operating temperatures and pressures, a good time to grab the ATIS and talk to the tower. The single lever operation is a double edged sword. On one hand, you only have one lever to get what you want so there's less to worry about, but on the other the loss of fine control means you need to be quite a distance ahead of the aircraft mentally. More on that later.
Taxi over to the runup area, then runup is just a matter of ensuring both independent FADECs are operating properly, then press and hold the runup switch and the FADEC runs up the engine and exercises the propeller for you.
Line up, get clearance for takeoff, then advance the throttle to full power. At first you get a lot of noise and not much else. The engine only produces a maximum of 155hp and tends to perform like it has a lot less, despite having a more efficient constant speed propeller. Our day was way in excess of ISA, being 1037 hPa and 6 degrees C, and the aircraft was only getting around 650fpm in the climb from an airfield elevation of 180' AMSL.
Once you're in the cruise is where you start to see why diesel is becoming useful in the ever increasing costs of aviation. At 65% power the fuel burn was 5.4 US Gal/hour (thats ~20L/hour) @103 knots IAS. Reduce it to 55% power and you get 4.2 US Gal/hour (~15L/hour) @90 knots IAS. With full tanks the endurance is in excess of 9 hours, way more than my bladder can handle.
Maneuvering was more or less the same as an avgas 172 with one big exception. Weight. The weight of the Tielert diesel and propeller system takes an additional 200kg bite out of the useful load, meaning that weight and balance, and C of G calculations are absolutely vital. With half fuel and just me and an instructor onboard we had to place an 11kg weight in the rear baggage compartment to bring us back within the loading limit as we had exceeded the forward of C of G limit. When you perform a stall you feel the aircraft wanting to drop it's nose well before you reach the actual stall. Wing drop is not as severe and you follow the usual recovery, although thrust production does lag behind throttle position significantly.
We flew a couple of circuits and I always felt as though I was having to feed it a lot of power to ensure I had good response. It felt like I was always behind the power curve, the fact was that the aircraft's setup means that you cannot get thrust immediately when you demand it. Imagine you are in an automatic car cruising on the highway - you want to overtake so you mash the pedal to the floor. The gearbox notes your throttle position change and prepares to change down a gear, then it realizes you want a lot more power so it has to consider which gear it should go to before changing down. That delay is exactly like flying this aircraft. Small throttle changes give you next to no response from the aircraft. The same is also true for deceleration. When you close the throttle the FADEC decreases the propeller AoA so you get reduced aerodynamic braking and the aircraft just flies on. I've not flown turbine aircraft but I can imagine this behaviour would be somewhat similar.
After landing, the shutdown checklist includes a 2 minute wait for the turbo to spool down before you flick a single switch and the engine clunks to an abrupt halt. Not a switch you want to hit accidentally in the air.
Overall, the changes were not all that difficult to cope with even for a rank amateur like me. Speeds, attitudes, general handling are more or less the same as what I am used to, you just need to appreciate the changes in thrust production and be ready for it.
I had the opportunity to be checked out in a Tielert converted 172R in the weekend. A brief background about me, I am a PPL(A) with a tick under 300 hours whose been flying (very) casually for the last 15 years. The vast majority of my hours are in 172s, and in particular the R series which made this flight odd in several ways.
The first was that hopping into the cockpit there was an instant sense of familiarity, yet here are a few new switches and some familiar controls are not present. There is no ignition switch for the magnetos, no mixture control, the push pull throttle has been replaced by a throttle quadrant with a single lever in it (I didn't particularly care for the placement, too low in my opinion). There is a block of switches for the FADEC controls as well as the usual ones. The walkaround was pretty much the same as an avgas 172, except the relocation of one fuel drain and the oil filler hatch. The second peculiarity is that there is this pervading smell of Jet-A everywhere, even inside of the cockpit.
Startup checklist was a bit more involved, you need to prime the fuel system which takes a couple of steps, if you're running the aircraft on diesel you need to let the fuel warm up, as we were running Jet-A it wasn't a problem. Once that is done, just press and hold the start switch until the engine reaches 25%. Then you have a 2 minute wait to let the engine and lubrication systems come up to operating temperatures and pressures, a good time to grab the ATIS and talk to the tower. The single lever operation is a double edged sword. On one hand, you only have one lever to get what you want so there's less to worry about, but on the other the loss of fine control means you need to be quite a distance ahead of the aircraft mentally. More on that later.
Taxi over to the runup area, then runup is just a matter of ensuring both independent FADECs are operating properly, then press and hold the runup switch and the FADEC runs up the engine and exercises the propeller for you.
Line up, get clearance for takeoff, then advance the throttle to full power. At first you get a lot of noise and not much else. The engine only produces a maximum of 155hp and tends to perform like it has a lot less, despite having a more efficient constant speed propeller. Our day was way in excess of ISA, being 1037 hPa and 6 degrees C, and the aircraft was only getting around 650fpm in the climb from an airfield elevation of 180' AMSL.
Once you're in the cruise is where you start to see why diesel is becoming useful in the ever increasing costs of aviation. At 65% power the fuel burn was 5.4 US Gal/hour (thats ~20L/hour) @103 knots IAS. Reduce it to 55% power and you get 4.2 US Gal/hour (~15L/hour) @90 knots IAS. With full tanks the endurance is in excess of 9 hours, way more than my bladder can handle.
Maneuvering was more or less the same as an avgas 172 with one big exception. Weight. The weight of the Tielert diesel and propeller system takes an additional 200kg bite out of the useful load, meaning that weight and balance, and C of G calculations are absolutely vital. With half fuel and just me and an instructor onboard we had to place an 11kg weight in the rear baggage compartment to bring us back within the loading limit as we had exceeded the forward of C of G limit. When you perform a stall you feel the aircraft wanting to drop it's nose well before you reach the actual stall. Wing drop is not as severe and you follow the usual recovery, although thrust production does lag behind throttle position significantly.
We flew a couple of circuits and I always felt as though I was having to feed it a lot of power to ensure I had good response. It felt like I was always behind the power curve, the fact was that the aircraft's setup means that you cannot get thrust immediately when you demand it. Imagine you are in an automatic car cruising on the highway - you want to overtake so you mash the pedal to the floor. The gearbox notes your throttle position change and prepares to change down a gear, then it realizes you want a lot more power so it has to consider which gear it should go to before changing down. That delay is exactly like flying this aircraft. Small throttle changes give you next to no response from the aircraft. The same is also true for deceleration. When you close the throttle the FADEC decreases the propeller AoA so you get reduced aerodynamic braking and the aircraft just flies on. I've not flown turbine aircraft but I can imagine this behaviour would be somewhat similar.
After landing, the shutdown checklist includes a 2 minute wait for the turbo to spool down before you flick a single switch and the engine clunks to an abrupt halt. Not a switch you want to hit accidentally in the air.
Overall, the changes were not all that difficult to cope with even for a rank amateur like me. Speeds, attitudes, general handling are more or less the same as what I am used to, you just need to appreciate the changes in thrust production and be ready for it.