Weighing Options

[ghancock]

So you guys have probably wrecked my life plans by planting the turbine seed in my head.  I've been running numbers and have a few questions.

1) Looking at Adams plane as a possible stepping platform I started looking at the differences between it and my plane.  But the numbers don't make much sense.  ie: My plane is supposed to cruise at 210kts at 15k and the 680V is supposed to cruise at 217 at 16k.  The first question would be why don't they give you this number at the same altitude and my response might be that they picked the point where the engines perform at their best.  Looking at other models they used still different altitudes to backup my theory but is it correct?

2) The next obvious issue is that my plane DOES NOT cruise at 210kts at 15k.  I've had her up to 14k and it was around 190kts but I've never gotten much better than that at any altitude so far.  Also, I know the higher I go the less the engine performs.  So while you're fuel burn may get better, I don't think you gain speed just because you go higher.   So the truth is I've never seen any book value that could be reasonably met.  They are all higher than what you actually get.  Having said that, the 680V shows 217kts at 16k, so I'd expect it to be slower as well.  Adams plane has upgraded engines but not sure if that makes it faster or not so that is the next question.

3) TBO's.  I am now aware of the fact that only Twin Commander used the IGSO 540 engines.  This makes them necessarily harder to deal with as time goes on.  I've heard prices of 60k to rebuild one and they have 1200 TBO's.  Factor in the extra cylinders needing to be replaced and I'm figuring 75K for TBO replacement costs.  The engines on the 680V have 5400 hour TBO's and 4 hot section inspections which I have no idea of that cost, but it almost looks like it would be cheaper to operate Adams plane even with the more expensive engines.  Can anyone offer an estimated cost for hot sections and TBO replacements?

4) My airplane out performs Adams on Landing and Takeoff numbers in the book.  ie: I takeoff in 1700 ft and land in 1800ft where Adam takes off in 2260 and 2300 respectfully.  But does his upgraded engines do anything to these numbers?

I was surprised to learn that the Cessna 421's have a 6psi system in them compared to the 3.2 and 4.2psi systems of mine and Adams.  It makes me want to look at a 421 but then I wouldn't be able to deal with the rougher shorter strips.  However, its specs suggest equivalent numbers to the 680V on take off and landing so other than landing gear issues, it should perform as well as the Commander off grass strips.

My estimates for the Hot sections seems to be between 30-60k with a 250k overhaul at 5000 hours.  Is that reasonable?

My main issue that has me even thinking about this is that I have burnt up another hydraulic pump for no apparent reason and had no way to detect it until it was too late.  The pump isn't readily available and I'm currently trying to figure out how to keep my bird flying.  Keeping in mind that it will still fly even without the pump, I just won't have pressurization (which I don't currently have anyway).  So this is not an issue of being able to fly but more an issue of keeping the plane at 100%.

I either need to start a manufacturing facility and start making my own stuff or find a source for an alternative way to keep things going.  Not sure if a 680V is going to be any better in this area or not.  I still love my plane and I know if I give up on her she's probably done.  So not really wanting to do that.  But I have been down now for 4 months and having to cancel trips and schedule on airlines and need to make something happen soon.

Thanks for opinions,

Glenn

[Steve binnette]

Glen

You are asking the right questions.  I think I can help a little.  As you might know the earlier garretts operate like normally aspirated piston engines.

They are rated at say 575shp for the 680, and begin to lose HP with altitude right after TO.  That's where upgrading the engine helps it then becomes a derated engine and can hold the 575shp to a higher altitude before it temps out.  A lot of this has to do with airflow Through the engines.

The -5 engines they do better and can hold their power to a high altitude.

This loss of HP with altitude contributes to the lack of speed as you get higher.  There is a crossover point where climbing won't help.  Piston ngines that are turbo charged or super charge can hold their power to higher altitudes than the early TPs can.  Early on the Commanders and 421 out performed the TPs.  As the TP engines Improved the piston engine development was reaching its peak of development.

As metallurgy improved and new designs to keep the temps down became available the temperatures could be increased.  Then TP start producing more power than the airframes could handle.  So they were derated.  My -10 can produce 1000hp but are derated to 733hp.  Essentially they become like a turbo charged piston.  Meaning they can carry the rated power 733hp in my case to around 13,000ft.

This difference Between early TP engines and the later models means TO performance and cruise performance is impacted by altitude, much more than the later derated engines.

I can not speak to the 680 speeds but at the same weight and HP as your plane the speeds would  naturally be the same.  What altitude do you run out of throttle at cruise? 

You have the hot sections and overhaul cost right, at least for the -10 engines.  I have heard the -5 can be a little more

I owned a 1975 421B and like it. The pressurization is the same as the 690A&B 5.2 psi.  The straight 690 and earlier models had the 4.2.

If you are operating at sea level the -5 airplanes offer a lot of value.

[ghancock]

Well the book says the 680V has a top ceiling of 25k where mine is 28.5k.  I run out of throttle to feed in around 12-13k and am around 40" at that point.  After that it just drops off with altitude.

Thanks for the explanation as that helps a lot.

Glenn

[Ted Striker]

2) The next obvious issue is that my plane DOES NOT cruise at 210kts at 15k. 

Disregarding all the obvious stuff about a brand new plane, perfectly rigged... The book values probably have the mixture set for best power or something close (power curve is very flat ROP) and not LOP. Not suggesting you should run them at best power, just another consideration.

[Adam Frisch]

Glenn,

1. The 680V/681 with -1's is a 245-255kts plane up high. Mine did 235kts back from Napa before Xmas, but then I was running out of travel on the power lever at 17000ft already, so top fuel needs adjusting. It should never hit the stops, just temp out up high. Something for Morris to adjust when I get her back. When that's done, I'm very confident she'll do at least 245kts, prob 250kts. On cold days, my friend Stan Perkins's 681 with the -1's does 255kts.

3. Only 2 hot sections, Glenn. 1800hr interval. Expect to pay about $40-60K. On the 5000hr engines, it's only one HS. Add gearbox inspections to this, which I think is every 2500hrs and costs about $12K.

4. Yours probably off a little quicker than mine. I've not flown enough to be able to do full power takeoffs from standstill, but she gets off pretty quick. They really move when you power them up. Before you know it you're at rotation speed. I have no problem whatsoever going into Corona here in Los Angels, which is 3200ft, and that's as a total newbie. I'm off the runway 2/3's down. Mind you, the 690's and Jetprops probably have similar performance, if not better. The bigger wing and the more hp seems to compensate for the higher gross very well. I've flown in Steve's 980 many times and that sucker is off in no time. We embarrassed a brand new TBM930 on one of the flights - despite taking off after, we out climbed it by almost 2000ft/min and beat it to altitude by minutes.

The older turbines will probably eventually run into parts problems. I have not experienced it yet, except for engine mounts. Lorde makes them, but you have to order a minimum run for about $20K or something silly, so we just turned the ones we had around and they should be good for another 1000hrs.

Let's talk later down the road, and see if you're still interested. Or if I'm interested in selling even! Spent so much on her now and she's getting good with new interior and panel, so would be a shame to sell her.

[JimC]

All 421s have a 5.0 PSI pressurization system.

The A and B models are not magic on grass, but it will outperform your 680 in cruise on (slightly) less fuel. They're maintenance intensive and expensive ($5K starter adapters, $25K windshield), but at least the engines are well supported. They'll do 210kts at FL200 and higher - and yes, they do go faster as you get higher. I believe they can make full power at FL200, but the air's so thin you won't get good cooling.

[Steve binnette]

If you are serious about a 421 do not even consider the A model or the early Bs.  I would go with the 690 and I loved my 421.  The 690 just a bunch more plane.

Jim is correct the pressurization is 5.0/5.2 on the 421 and the 690 is 5.2/5.4.

The plexi glass windshields are much cheaper.  My 421 had plexiglass.  The 25k for a 421 glass windshield is cheap compared to the commander glass windshield at 55k.

The cabin on the 421 is fantastic.  I only got about 200ktsout of it burning 40gph. I usually operated the 421 between 16k to 21k and never had any cooling problems even all the way up to 25k.  Getting the injectors and fuel flow set right is critical.

Make the jump to turbine and I think you will ask yourself why you did not do it sooner.

[ghancock]

My worry at the moment is I still count beans.  When I get so many beans that I can't count them any longer then I'm certain I'll be in a Turbine :-)

Glenn

[ghancock]

Just trying to learn the ropes here and have a few questions.

When a turbine such as this is listed as 700 so OH, does that mean I've still got 4800 hours left on them?  and about 1100 before a hot section?

https://www.controller.com/listings/aircraft/for-sale/17771985/1976-commander-690a


What kind of expenses would I be getting into in something like this?
https://www.controller.com/listings/aircraft/for-sale/1422745/1976-commander-690a

How often do you have to do hot sections?

Is it correct to say this airplane has just over 1000 hours left on the engines and the next expensive thing to do is going to be to replace the engines?  This would likely have me flying it for 2 years before I have to spend $500,000?
https://www.controller.com/listings/aircraft/for-sale/17876961/1975-commander-690a

This last plane is interesting to me and I know it is cheap because of the engines.  In 2 years though I am pretty certain I will be able to afford the new engines as business is going crazy.

Thanks,

Glenn

[ghancock]

And one more thing.  I fly into a lot of small airports and some controlled.  How often do you get hit with extra landing fees and stuff due to either flying a Turbine aircraft or because of weight?

Thanks,

Glenn

[Steve binnette]

I would not worry about extra fees at little airports it's the bigger ones that seem to get you.

The first two are from hill Aero that's up in dons neck of the woods.

The first one looks like a good deal just because of the engine times.  The way I read it there is 4300 hrs left.  That's on a 5000hr too and a 2500 hr his sechedule.  When you overhaul your engine you have the choice of 5400hr tbo and 2 HSI at 1800hrs or the 5000hr tbo with one HSI at 2500hrs.

The last one has the 10s but is close to overhaul and you will be upside down when you overhaul the engines.  That's is not a bad thing it is easy to do, but I would say the first one is the best value if it truly has newly overhauled engines.

None of these have had the spar replaced which adds value.  Look for ones on the 36 month inspections, if it's a shorter inspection time it means they might have found something.

[ghancock]

What about this one?  https://www.controller.com/listings/aircraft/for-sale/1425661/1972-commander-690a

They want $295,000 for it due to the engines being almost out but they have enough time to get me a year to year and a half out.  I don't know if they are dash 5 or 10's though.  Not sure of the cost difference between the 2 engines and the radio stack needs a bit more work.  I'd be able to update things as I go and could be saving up for the engines in another year or so.

I don't look at engine replacements as putting me anywhere since they all need it at some point but maybe I'm thinking wrong.  I'm really wanting my next purchase to be my last purchase though as I'd like to do more flying than working on the airplane.

I'm still a little concerned about that big ass airplane taking off and landing from this 2900' strip but everyone seems to think it will be fine.  Obviously I won't be flying out of here fully loaded (ever) so probably concerned about nothing.

I've just about talked myself into a turbine though. :-)

It is crazy running the numbers but it will take 4 engine replacements on my current plane to equal one replacement on the turbine which actually will end up costing more on the current plane.  I have to add in hot sections and other required stuff which will make the turbine more expensive in the long run, but my time and ability to just go will far outweigh that difference.

Like how I'm talking myself into spending a million bucks?  :-)

Glenn

[donv]

I have a bunch of time in the Aero Air airplanes. They have, I think, some flexibility to mix and match engines and airframes to get you something which would fit your needs.

The engine math is this:

Dash 5: TBO is 5400 hours, with a hot section every 1800 hours. So, new engine: fly 1800 hours, hot section. Another 1800 hours, hot section. Another 1800 hours, overhaul. Start over.

Dash 10: Can be the same as the Dash 5, or you can have a 5000 hour TBO with a 2500 hour hot section. So, new engine: fly 2500 hours, hot section. Fly 2500 more hours, overhaul. I believe the choice has to be made at overhaul.

There aren't any "top overhauls" or cylinders to replace or anything like that. Dash 5s can end up needing a hot section early because they won't make power over time, but that almost never happens on a Dash 10.

So, the Eagle Creek airplane (N3869F) appears to have 4900 hours since new (probably never been overhauled), and 800 hours since hot section. If I'm reading that correctly, then it would have about 500 hours to go until overhaul. The hot sections were probably done early at some point, due to what I mentioned above.

It is a bit more complex than that, because some components in the engine have cycle limits. So, depending on how many cycles the engines have will impact how expensive the overhaul or hot section is.

[donv]

The nice thing about the Aero Air airplanes is that they have pretty decent avionics already, have been flying regularly, and have been well maintained for a long time. And, Norm is a great guy.

[ghancock]

I'm starting to think I should just stay where i am for now. :-) . Here is the latest:

N95LF has -5 engines and only 700 hours on them.  (First link from above).  They want $500,000 for it which looks pretty good.  However, after speaking with them it needs a landing gear inspection every 5 years that costs a cool $15-20,000.  It has a 150hr inspection due that he said runs around 7-10k .  Also I'm being told the wing spar inspection is due next year and it runs around 15k.  Assuming I fly like I have been and honestly the need is increasing not decreasing, then I'd be putting between 400-600 hours a year on the plane.  This means that every 3 months I'd be spending another 7-10k depending on needs plus the annual and other things that will need to be done.

So while the initial investment is huge compared to my bird now, the ongoing is also not something to laugh about.  So at the moment I'm thinking about just sticking to my bird and getting her going 100%.  It will help me to sell it later and hopefully find a good home and it gives me at least another year to become so rich I don't care about 50k a year just to keep the maintenance done on the plane :-) . I'm just not at that point yet.

Please point out errors in my judgement.

Glenn