Keep my 231 or trade up for a Rocket

[231LV]

I know variations of this subject have been done many times on this forum but I'm hoping to get some perspective that I may not have contemplated. I have owned my 231 for ten years...flown it everywhere from the Artic Circle to the Yucatan and absolutely love it in all aspects but one....to get the speeds, I have to fly high which means O2. Those of us who routinely use O2 realize its drawbacks...namely unavailability at many FBO's or difficulty getting full fills.

I am retiring next year and my wife and I plan to do more flightseeing trips around the US and Bahamas...we will still need turbo performance but don't always want to go up high to get the great TAS. I'm looking hard at upgrading to a Rocket. My 231 has a run out engine so if I sell it, I am expecting a low price. The Rocket can go fast down low and burn a lot more gas than my 231 which is no faster than an E model at 10,000 feet and below.

As I watch the price of Avgas climb, I'm wondering whether I should just stick with the 231 and accept the slower speeds down low and deal with the O2 issues when planning for a cross country.

Maybe someone who has switched from a 231 to a Rocket can chime in here with their thoughts....

[chrisk]

I hear you on the O2.  If you have your own hanger, getting your own O2 filling station is around $500 for the initial setup and much more convenient.  It probably pays for it self in 10 fill ups or less.  And no more fretting over:  Should I fill up with half a tank, or will that make it till I get back.  --Just fill it up.  I would think this would take care of most of your O2 issues.

 

As far as trading out for a Rocket.    I hear they are fast, and get to altitude quickly.  But I would think you need to go to O2 levels to really take advantage of that speed.  So, I'm not sure that solves your problem.   Anyway, I'm sticking with my 231, unless a really nice Rocket falls in my lap.

[larryb]

Regarding the O2, I have a few thoughts. I have a portable O2 system and a transfill system in my hanger.

 

First, even with a transfill system you only get full fills when your high pressure transfill tank is full. Second, you are most efficient with your transfill O2 when you start with an empty aircraft tank. That's because you transfer the most O2 from your low pressure tank when your aircraft tank is empty. So you really don't want to fill your half-full aircraft tank just because you can. I learned this one day when I didn't pay attention to starting pressures and actually had O2 flow FROM my aircraft tank INTO the low pressure transfill tank.

 

I solved this problem by buying a couple extra aircraft portable tanks. Now I can always take enough for a trip and be filling near-empty tanks at my hanger.

[Danb]

Chris I'm unfamiliar with what I need and need to do to get a quality transfill system in my hanger, and how do you fill the transfix system etc. Agreed O2 is costly e.g.. I just had mine filled and it cost $75 had no other options. Thanx for the info. in advance

 

Dan

[DonMuncy]

To transfill, you need a relatively large O2 cylinder, but preferably two of them, a pressure gauge, a flexible line to go from the tank to the plane, copper tubing to plumb it together and various fittings. Aerox sells almost everything you need, but some of it you may find cheaper. Your local welding supply will have the fittings to go on the tank, but the fittings to go to the plane inlet are harder to come by.

This presumes you have a built in system on your plane.

First, look around for the cylinder(s) and see if you want to spring for the cost of it (them). The rest is relatively inexpensive.

If you want to continue with the project, call, email, etc. and I will furnish diagrams, more detailed description, etc.

Don 214 207-6744 muncy-d@hotmail.com

[231LV]

Thanks all for the posts...I already use a transfill station in my hangar...the problems I am referring to involve the fills during cross country trips...tough to get an FBO to give me a full refill...they simply don't want to wait while the O2 flows into my tank...many FBO's (especially in more remote locations) don't offer O2 refills. The problems I most often encounter involve departing my home airport with a full tank but half way through the trip, my O2 is depleted and now I am forced to find a fill station who will give me a full fill (very difficult) or stay low and slow all the way home...this is the primary reason that I am contemplating a Rocket...I don't have to have O2 to go fast down low

[jlunseth]

I use the Precise Flight flow valve.  It enables us to dial the flow down from "full blast" to just the flow that is needed.  For about a year I used an oximizer quite a bit until I figured out what flows work.  Precise Flight also has nasal cannulas that supposedly allow using less O2, you could try one of those.  Using the oximizer, we have found that claim to be nothing but propaganda, there is no savings with the "pocket" cannula.  There is, however, a very good saving with a full mask.  I have a miked mask that I use quite alot.  Between the flow valve and the mask, I generally have enough O2 for two people to get wherever I want to go, one way.  A round trip in the Flight Levels is not common, because if I went up there because the wind was good going one direction, it probably is not going to be good going the other direction although it occasionally happens. 

 

The one thing about the 231 that beats all the other higher HP turbos, is the fuel economy.  I get 12.5 - 13, it just depends on the power setting, and a comfortable 4:30 with plenty of reserve.  Hard to beat that with fuel prices continuing up.

[bonal]

You High flyers are a different breed of cat! RESPECT.

[chrisk]

Chris I'm unfamiliar with what I need and need to do to get a quality transfill system in my hanger, and how do you fill the transfix system etc. Agreed O2 is costly e.g.. I just had mine filled and it cost $75 had no other options. Thanx for the info. in advance

 

Dan

 

 

I got the FBO-1 from Aviation Oxygen, with some credit for only getting the scott connector.    http://www.aviationoxygen.com/aerox-aviation-oxygen/oxygen-refill-station-equipment.html.    I lease two 330 cf welder tanks from the local shop for $6.00 per month / tank.   A fill of the 330 cf is around $15 for welding oxygen, or $30 for aviation oxygen.  Given my consumption rate, I sprung for the aviation oxygen, which is the same thing, but tested for moisture and hydrocarbons (where the welders o2 is not tested.) --Oh, the tanks are very heavy.  About 150 lbs each, so you will want a cart.  -$40 at harbor freight.

[aviatoreb]

I use the Precise Flight flow valve.  It enables us to dial the flow down from "full blast" to just the flow that is needed.  For about a year I used an oximizer quite a bit until I figured out what flows work.  Precise Flight also has nasal cannulas that supposedly allow using less O2, you could try one of those.  Using the oximizer, we have found that claim to be nothing but propaganda, there is no savings with the "pocket" cannula.  There is, however, a very good saving with a full mask.  I have a miked mask that I use quite alot.  Between the flow valve and the mask, I generally have enough O2 for two people to get wherever I want to go, one way.  A round trip in the Flight Levels is not common, because if I went up there because the wind was good going one direction, it probably is not going to be good going the other direction although it occasionally happens. 

 

The one thing about the 231 that beats all the other higher HP turbos, is the fuel economy.  I get 12.5 - 13, it just depends on the power setting, and a comfortable 4:30 with plenty of reserve.  Hard to beat that with fuel prices continuing up.

 

I use the O2D2 - love it - really saves on the O2.

 

12.5-13 but what speed do you get with that at what altitude?  The rocket can be flown slower to behave close to like the original 231 airframe it is built from with a slight penalty of larger cylinders.  I was flying 13.2gph at just over 180TAS the other day on the way home from Michigan as an experiment just to see what I could do to extend range.  Or you can pour 20-22gph on the fire and really go faster.  And it is indeed fast even at no O2 altitudes.

[231LV]

I should also say that I fly my 231 LOP....I can get 175 KTAS at 17k on 10 gph...at 10,000 ft, I'm no better than 145 KTAS on the same power set up and I currently use masks above 10,000 ft  to keep O2 sat levels in the 90's...we are moving to Sedona, AZ next year which is at 4500 ft and routinely fly to friends located at 7000ft so we need a turbo...I'm curious what kind of sub-10,000 ft speeds the Rocket turns in running LOP?

[larryb]

If you like the plane you have now, I would solve the O2 problem. You haven't said if the system is portable or built-in. If built-in, can you get a bigger tank? If portable, just carry more tanks. Or carry a couple portable tanks to supplement your built-in system. Or improve the delivery system by using an Mountain High O2D2 instead of the mask. Masks are not efficient at delivering the O2 so if you stay below 18K I would not use the mask. Any of these options will cost much less than changing aircraft.

 

You expressed concern over fuel cost in the OP. To go fast at low altitude is going to take a lot more fuel than you are using now. Is it worth it? Only you can answer that question.

 

Now, if there is more to the question than simply frustration at finding O2 far from home...

Larry

[cujet]

I should also say that I fly my 231 LOP....I can get 175 KTAS at 17k on 10 gph...at 10,000 ft, I'm no better than 145 KTAS on the same power set up and I currently use masks above 10,000 ft  to keep O2 sat levels in the 90's...we are moving to Sedona, AZ next year which is at 4500 ft and routinely fly to friends located at 7000ft so we need a turbo...I'm curious what kind of sub-10,000 ft speeds the Rocket turns in running LOP?

 

Sounds like you are unwilling to use the power you have to achieve good speeds at modest altitudes. I'd guess that a 252 will achieve close to the book value 171 Kts true at 10,000, at 78% power. An upgrade to 252 engine and a willingness to burn more fuel may be in order. 

 

http://mooneyspace.com/files/download/16-mooney-model-altitude-vs-speed/

[cliffy]

So when you retire-What's your hurry???? :-) :-)

Slow down and smell the roses! Enjoy the trips while you can.

My wife and I decided to do just that and stayed with our C model!

[231LV]

Sounds like you are unwilling to use the power you have to achieve good speeds at modest altitudes. I'd guess that a 252 will achieve close to the book value 171 Kts true at 10,000, at 78% power. An upgrade to 252 engine and a willingness to burn more fuel may be in order. 

 

http://mooneyspace.com/files/download/16-mooney-model-altitude-vs-speed/

not if it means burning up my engine ......wish I could get an upgraded 252 engine....the only engine I can get is the TSIO360-LB...the 252 runs an -MB...not authorized for the 231

[cujet]

not if it means burning up my engine ......wish I could get an upgraded 252 engine....the only engine I can get is the TSIO360-LB...the 252 runs an -MB...not authorized for the 231

 

It's as you say. From the TCDS: 

NOTE 17: A TSI0-360-GB series engine may be replaced with a TSI0-360-LB engine by complying with Mooney Aircraft

Corporation Service Bulletin No. M20-228.

 

What I have been led to believe is that an LB with the magic wastegate and intercooler performs much like the MB. 

 

Does this help any? : NOTE 21: M20K S/N’s 25-1000 thru 25-1230 and 25-2000 thru 25-2012 may be retrofitted to TSIO-360-SB2 engine and gross weight increase to 3130 Lbs. when complied with M20K Gross Weight Increase Retrofit Instructions.

 

http://www.67m20e.com/Mooney%20TCDS%202A3%20Rev%2052%20dtd%209DEC10.pdf

[231LV]

Yes, I should have noted that my plane does not fall into the serial blocs...once upon a time I actually did the cost analysis of getting my plane up to the equivalent of a 252...a 262 which was obtainable at a price of $55k. It was cheaper to sell my 231 and buy the 252....my current 231 does have an inter cooler but the old, fixed waste gate and I am still running the original -GB engine which is why I always run it LOP...the GB was a hot running engine....but back to my original question and I thank all the input...it has been invaluable.....sometimes one must go with "the gut"......I'm in no hurry to replace my plane and watching fuel prices climb, I'm still quite happy to be getting 175 KTAS on about 10 gph albeit at 17k ft on O2 so I will sit awhile and watch....and fly east high with O2 in the tank and west low when depleted and be grateful to be in such an enviable position of choosing between two great planes!

[David Mazer]

In FL, I typically see 185-190 kts TAS with 18 gph and 155 kts with ~14+ gph around 7-8,000 in my Rocket.  Not really E speeds but certainly higher fuel burns.

[Z W]

You should be able to beat 145 KTAS at 10,000 feet by using a higher power setting.  My 262 will do 165 KTAS on 11.5 GPH there, which is my standard headwind altitude.

 

I know you have a different engine and you have to make your temps work, but I think you can beat 145, especially if you are willing to run a higher MP and ROP.  If you go far enough ROP, you should not have temp issues.  You'll be wasting some gas, but way less than you would be wasting in a Rocket at those altitudes, comparatively speaking.  If you're worried about fuel burn difference in your 231, you've answered you own question about the Rocket.  I would bet if you can get 160 KTAS at 10,000 ft, you won't be dreaming of going 170 or 180 in a Rocket burning 5 more GPH.

 

I would love a Rocket and if I were shopping again one would be on the top of my list.  But they are less efficient than a 231/252/262, no question.

 

I find my O2 tank lasts a pretty long time.  I always get headwinds, so I'm usually at 10,000 ft doing 165 knots and not on O2...

[231LV]

Excellent points....thank you. You are right...stepping it up to run deeply ROP will get me faster at a bit more fuel and something I may have to consider for the lower levels. The fuel burn differential between a Rocket and the 231/252/262 is substantial...with avgas at about $6 now...that fuel burn translates into poverty pretty quickly...my 115 cu ft tank is good for about 4 hours with my wife and I at 17k.

[KSMooniac]

If you really don't want to use O2 regularly, why not consider an Ovation or Missile?  You'll get speeds in the 175-180 knot range <10k' easily for ~13-14 GPH, and have enough power to get up into the O2 levels when needed, although not as easily as a Rocket.  The higher compression IO-550 will give much better fuel efficiency than the TSIO-520 in the Rocket.  

[cujet]

I'd like to understand why your engine won't tolerate it's rated cruise power at 10K. Is that simply the nature of the 231, even with intercooler? Certainly, the 252 had some cooling upgrades, and throttle body/tuned intake/intercooler "fixes". However, you have the intercooler and could upgrade the wastegate.  From what I understand, the upgraded engine helps with temp issues too due to the larger throttle body. 

 

Or is it that you are cautious and don't want to risk higher temps on your current "old" engine? 

 

I'm looking into upgrading to a 231 and would like to know exactly what I am getting into. 

 

Thanks

[231LV]

I'd like to understand why your engine won't tolerate it's rated cruise power at 10K. Is that simply the nature of the 231, even with intercooler? Certainly, the 252 had some cooling upgrades, and throttle body/tuned intake/intercooler "fixes". However, you have the intercooler and could upgrade the wastegate.  From what I understand, the upgraded engine helps with temp issues too due to the larger throttle body. 

 

Or is it that you are cautious and don't want to risk higher temps on your current "old" engine? 

 

I'm looking into upgrading to a 231 and would like to know exactly what I am getting into. 

 

Thanks

Tolerating rated cruise power at 10,000 ft is no problem. My engine can easily run higher power settings at higher temps which leads to shortened longevity. I choose to run LOP and I see cooler temps across the board on less fuel and slightly less speed. All in all a good thing.The limit I have to deal with is TIT of 1650....typically I can't get much over 65% power running LOP without exceeding this temp. The newer -LB engine will alleviate the cooling issues with a larger throttle-body and a more efficient exhaust design. The 231 is a wonderful plane and highly efficient and I would never discourage anyone from taking a hard look at one if it fits your mission. I was looking at a way to fly lower without O2 and get better speeds.....one suggestion is to run deep ROP which I will try. The enemy of all our engines...especially turbos is heat and I try to do all I can to reduce it.

[manoflamancha]

Rockets are awesome in spite of the high fuel burn rate! I saw 200kts at 5500' with close to 2000 FPM climb out now I was at a sea level airport so might vary at a place like Sedona.

[jlunseth]

I'd like to understand why your engine won't tolerate it's rated cruise power at 10K. Is that simply the nature of the 231, even with intercooler? Certainly, the 252 had some cooling upgrades, and throttle body/tuned intake/intercooler "fixes". However, you have the intercooler and could upgrade the wastegate.  From what I understand, the upgraded engine helps with temp issues too due to the larger throttle body. 

 

Or is it that you are cautious and don't want to risk higher temps on your current "old" engine? 

 

I'm looking into upgrading to a 231 and would like to know exactly what I am getting into. 

 

Thanks

I can't speak to the GB because I don't have one, but the LB runs at rated cruise just fine at any altitude so long as you have the wastegate and intercooler.  You will have Compressor Discharge Temp issues above and altitude of around 18-20k if you do not have the intercooler.  The engine has a CDT limit of 280 to protect the engine from detonation, but the CDT becomes irelevant with the intercooler in place.  Other than that, there are no temp problems.  I believe you would see temp problems in the GB above 17-18k because as noted, it is a hot running engine, and the thinner air is not conducive to cooling.

 

Overall the 231 is a great airplane.  Very fuel efficient compared to the later model turbos.