Navajo Chieftan Engine

[goingnowherefast]

Mostly a theoretical discussion as I don't have the means or desire for R&D.
What are peoples thoughts on replacing the TIO-540 with a IO-720?
I know you are losing the turbo, but you are gaining 50hp at sea level, still making the original 350hp at 4000' and making MCP at 7000'.

From a mechanical side of things, that turbo is worth $5000, and you are replacing it with 2 more cylinders worth about $2500 each. Reliability will be about the same, but you'll make the engines much less susceptible to abuse and shock cooling. No annoying turbo lag too. Removing the turbo and associated pluming will allow room for the extra cylinders. Installed weight will remain similar once you remove the turbo mount, extra pluming, waste gate, controls, etc.

The biggest downside I see is performance above 7000'. As it's an unpressurized aircraft, for 99% of operations, I see that as trivial. I'd happily give up climb performance at 10000' to gain single engine performance at 2000', especially in a piston twin. (Maybe add rudder boost, or is that dreaming?)

Open for criticism and discussion!

[Glasnost]

While you're looking up component prices look up what two case halves, a crank and a camshaft are worth.

[PilotDAR]

look up what two case halves, a crank and a camshaft are worth.

Or worse, four case halves, two cranks and two camshafts.

And then you have two very expensive, and much less easy to repair engines. If you must modify engine installations, modify toward more common/economical engines.

[Big Pistons Forever]

The TSIO 540 is a pretty good engine. With a modicum of pilot knowledge on how to operate it and an AME that keeps on top of it, this engine will IMO last as long as a IO 720 and is significantly cheaper to buy.

In addition the 720 has a rep for case cracking and cranks getting junked at every overhaul, both due to the fact that it is so long.

[goingnowherefast]

Would the IO-720 have such a bad rep if it were operated in commercial operations in the same regard as the TSO-540 is? The 720 is typically installed in private aircraft. I guess case cracking happens regardless of frequency of operation?

[valleyboy]

If you have the money to look at conversions a diesel is becoming a possible option.

[gwagen]

720 also has a reputation as a gas guzzler and depending on the rated output and application only sustain full power for a brief period. IIRC

Just ask anyone who flew a Comanche 400, they sound fantastic however!

[Glasnost]

Chieftain is a dying breed. Replace the whole airplane with a Caravan.

[Heliian]

Slap some orenda v's on that.

[40echotango]

While we are up to outrageous conversion ideas, why not a V12 Merlin conversion for the chieftain? or TPE331 with AWI?

I like your "dreamer spirit", but why upgrade something that is just waiting to become beer cans? Anything a Ho can do, a King air or Carrotvan can do better! Not cheaper mind ya.

40ET

[co-joe]

Slap some orenda v's on that.

I really think they had something there, but trying to talk people into taking the -28's off their 100 in favour of a liquid cooled V-8 was a losing battle. Who would do that? But now strapping them V-8's on a Ho, or 421 and you'd blow the doors off the book numbers.

[goingnowherefast]

I like your "dreamer spirit", but why upgrade something that is just waiting to become beer cans? Anything a Ho can do, a King air or Carrotvan can do better! Not cheaper mind ya.

I agree with you there, I'd even add the PC-12 to your list. However, the Chieftain is cheap. You can buy one for 1/3 the price, burns less fuel, parts are significantly cheaper when they break. Customers often are not willing to pay turbine prices though. Customer calls a King Air/Caravan operator and gets a $4000 quote. They call the Navajo operator and gets a $2500 quote. Money speaks, and until that price gap is made much smaller, the Navajo isn't going anywhere.


I'm surprised nobody has suggested replacing the TIO-540 with a PT-6 and call it a Cheyenne instead.

[rxl]

T1040

[Saxub]

When maintained well, TIO540's run great.

Chieftain is a dying breed. Replace the whole airplane with a Caravan.

A dying breed? Really? The amount of Navajos flying around in Canada is pretty extensive. They are cheaper to operate, handle ice better, and have decent range and payload. If maintained properly they will continue to run routes all over Canada.

[Glasnost]

I must have missed something.

Did Piper restart production?

Are there a large number being rebuilt and refurbished like Beavers and Otters?

Are the banks reversing their decision to digitize bank data?

Is there now a wide availability of 100LL in the north?


There is a market for it. Not one that is expanding though. Any more it's just an attainable plane for bottom feeders who don't have the cash for something better.

That means it's a dying breed. Like the Cessna 402 that is all but gone.

[valleyboy]

And the 402C was a far better aircraft than a Chieftain - still, both are dangerous and should not even be allowed in a commercial operation hauling passengers. Same goes for single engine turbines on wheels in IMC or at night.

[NotDirty!]

T1040

Beat me to it!

[goingnowherefast]

We can argue all we want about the plane, but in the current regulatory and economic environment, it's not going anywhere for the next 10-20 years. It is only dying in the sense that eventually all the airframes will get worn out, but that's still a long way off.

As for AVGAS availability, if you called up a fuel supplier and asked for 25,000L per month, they'll set up a tank. That's what 3 planes will burn doing 50hrs a month each.

The large Cessna twins died because of the maintenance requirements on the old airframes. In short, they got worn out. I know Cessna changed the maintenance requirements, but it only shows they didn't have faith in the design as it aged.

My main intent in starting this thread is to ask why the TIO-540? Is there a better option in terms of maintenance, economics and safety? The IO-720 seemed like a possible candidate because it eliminates the turbo

[Saxub]

I'm less concerned about the turbo, and more concerned with the poor mag design. Single drive feeding a dual mag unit. No redundancy.

I had an engine failure last year because the bearing holding the driveshaft to the dual mag unit decided to blow itself to infinity. I know I have not nearly as many hours on a Navajo as some, but at nearly 1400 on type I have never had a turbo issue. Stage cooling is annoying but the plane is completely manageable so long as you stay ahead of it and plan. All in all these engines are more than reliable enough to operate 80+ hours a month as long as you stay on top of maintenance.

[Rowdy]

Turbo lag on an aircraft engine? Are you nuts? As a very famous auto industry person once said 'if you've got lag you're driving it wrong.'

I'll keep the stout 540 with a turbo over the bigger beast of a fuel hog any day

But I'm also partial to the 985...

[PilotDAR]

I know Cessna changed the maintenance requirements, but it only shows they didn't have faith in the design as it aged.

I see it differently - Cessna has excellent faith in their design. However, Cessna did not design these aircraft to still be in service 40 hard years later, without some more in depth inspection. Now they are specifying the inspections. I attended a seminar in Wichita many years ago, at which Cessna presented this new maintenance initiative. Their research and program development were very convincing.

Some of the inspections are burdensome, there's no question. But as there was never a life limit on the Cessna airframes as a part of the original type design, now it's catch up. Other airframes are not immune, there's a recent AD on Navajos which is pretty burdensome too!

Engine change approvals are a lot to achieve. There must be a minimum critical mass (number of owner customers), willing to pay, to make it worthwhile. If the change is to an Avgas engine, the market should be southern North America, as the market outside that area is not growing for Avgas (un)availability.

[all_ramped_up]

I think something like the Continental CD-300 might be an interesting STC. Similar HP range, less fuel consumption, no reliance on AVGAS supply...

http://www.flyingmag.com/continental-in ... 2100-hours

Some potential to be had there.

[PilotDAR]

I think something like the Continental CD-300 might be an interesting STC. Similar HP range, less fuel consumption, no reliance on AVGAS supply...

http://www.flyingmag.com/continental-in ... 2100-hours

Some potential to be had there.

Yes, it would. However, be prepared for challenges not common with gasoline engines, like only non metallic propellers and extremely strict maintenance and tolerances on their wear, cold operation limitations, and substantial flight testing and performance analysis to approve in each type.

I think that diesel engines are a good thing for the future for general aviation aircraft which do not justify turbine engine conversion costs. But, after working towards STC approval of an SMA diesel, an with SMA's interest in my client's project, we still could not bring all the elements together for program completion. Instead, a new carburetted Continental 550 engine was used. The overall cost saving over the SMA diesel in my client's modified aircraft, will likely approach the cost to operate the Avgas engine to its TBO.

I believe that it will be the large emerging Chinese GA market, which will spur on GA diesel development. Diesel is a natural fit for China, who has airports, and a thirst for GA, but little if any infrastructure for Avgas.

[anofly]

Did the B Navajo with no turbos run much better or cheaper than the turbo'd models? Were they ever in regular service like the C models? I know(or think?) they only came without turbos on the short fuselage? cheers

[Saxub]

like only non metallic propellers

That right there is the killer. With low hanging props like the PA31, those props would get trashed flying out of gravel runways.