Diesel 172 - review from a PPL
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Diesel 172 - review from a PPL
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 There is no ignition switch for the magnetos, no mixture control, the push pull throttle has been replaced by a throttle quadrant with a single lever in it (I didn't particularly care for the placement, too low in my opinion).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.
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I flew a diesel Warrior some years ago. All i can say is that it seemed like a cruiser aircraft, smoother and slightly faster in the cruise but needed lots of anticipation on approach if you wanted power. Also i think it was only about 145 as opposed to 160 hp. Having to pay the VAT on fuel for private use negates any real savings.
Also the early reliability issue, if they had gone straight to the private owners they would have gained more ground, due to less hours to failures. As it was the clubs thrashed them and the faults appeared quickly.
Also the early reliability issue, if they had gone straight to the private owners they would have gained more ground, due to less hours to failures. As it was the clubs thrashed them and the faults appeared quickly.
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.
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.
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.
To top that all off, it's a bloody expensive conversion. I struggle to see how such a conversion would make economic sense to most owners.
You have to be doing a huge swag of hours to make any worthwhile savings. Even then I understand the engine operating costs eat up a lot of the savings. The fuel might be cheap but the engines aren't cheap to maintain/overhaul.
Additionally, go tech at any GA airport and you won't have to wander far for an engineer who can work on a Lycoming and access a spare parts inventory. The same is definitely not true of Thielert/Centurion diesels.
Diesels work for commercial schools where the VAT and economies of scale on flying hours come into consideration, not for private owneers.
Diesels work for commercial schools where the VAT and economies of scale on flying hours come into consideration, not for private owneers.
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Total Agreement - doesn't work for private owners
The numbers quoted confirm that for a private owner, there is no worthwhile saving. I looked at all this when changing engines and just the cost of installation was unrecoverable for a regular private user, despite fuel saving. Diesel was in vogue at time I needed to re-engine, but now I've seen the limitations too, I'm so glad I went 0-360 and improved weight, payload, speed......
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As for me, I don't think I will fly it, the rate they charged me is the same as an avgas plane so there's no point, but that was the general idea in that they don't want the weekend warriors flying them. Fine by me.
Dry leasing is a smart move, provided there isn't an onerous minimum monthly hours requirement. I doubt most schools in New Zealand would turn over near enough hours to justify converting these aircraft in comparison to sticking with the Avgas models.
A very fair appraisal that matches my experiences with Diesel engined 172s. Two things I would like to add:
- When using them as trainers, the PFL exercise can be a bit tricky in that the engine will continue to produce a bit of thrust with the power lever closed. If you decelerate a bit more, to just below Vglide, you can tell that the prop slows down and the glide performance is much more realistic. If you don't address this, the student will get the impression that you can pick a field miles away and still reach it.
- Climb performance is not all that good on high fields/hot days but thanks to the turbocharger, the engine will continue to provide this climb performance and you can easily reach 10,000 feet or higher if you'd want to. I think they would be well suited as an IR training aircraft or for someone who would use it to travel longer distances regularly.
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May be the Delta Hawk 180hp turbo super charged direct drive inverted V4 two stroke diesel with no electronics will be a better choice as close to the same weight as Lycoming 360. Should be certified this year perhaps. Being flown in an SR20.
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Some things don't add up for me, but I may be too suspicious.
- First, it is Thielert and not Tielert.
- Second, there never was a 155HP Thielert conversion until they went bankrupt.
- Third, the CD155 from Continental Diesel is based on a similar engine block, but very far from the one Thielert (ab)used.
- Forth, I am missing the topic of far exceeding install price and a comment on the TBR instead of TBO issue.
- Fifth, I am missing the topic of the quite bad restart capability of a Diesel engine at altitude.
- Sixth, I am missing the issue of dependency on power - the electrickety dies, the engine stopps (yes, I know they put backup batteries in, but the principal issue remains).
- Seventh, as far as I am aware the use of Diesel fuel instead of Jet-A1 is not certified for Continental CD155 conversions, but I may be wrong.
- Eighth, all conversion I know restrict the amount of max. fuel carried to the same max. weight as the Avgas version, so you cannot use full tanks - too heavy for W&B, too forward W&B sounds like this may have been ignored?
- Ninth, for good C172 climb performance CG is well known to be better more backwards - about 15kg in the baggage compartment is usually thought to be about right, cannot image what should be there for a similar AOA to compensate for the heavy engine block in front
