PA30 Twin Comm, Aztec or Seneca I?
 

I know twins have been covered before....but, out of those three which is the best for the MEP and which is the superior plane (in terms of performance, load carrying etc)?

(The prices are all about the same).

For up to four seat touring, the Twin Comm wins hands down.

Aztec is also really only a four seater but has a problem in that if a particular engine fails you have lost not just the engine but also other systems.

The Senneca 1 is also just a 4 person aircraft but with 6 seats so great if you have lots of children but also has the aileron - rudder link that reduces the crosswind limit to 12 knots.

As a twin with up to 9 hours endurance the twin comm is an ideal aircraft.

The tip tanks alone can get you to Alderney from the London area with IFR reserves.

Regards,

DFC

The Twin Commanche is faster. The Aztec is roomier. The Seneca is a little closer to modern and like the Aztec, has very mild flying characteristics. Of the three, the least relatively underpowered is the Commanche, but it will also bite you if you get it in the wrong place.

All three are typical underpowered light twins. You gain an advantage in speed and rate of climb over a single such as a Cessna 206 or 207, but at the sacrifice of safety in the event of an engine failure; both are going down, one just does it faster than the other (while facing directional control issues). Properly flown, any of them can be comfortable airplanes.

We had a twin commanche at an ag operation where I flew years ago. I never liked it. The Apache and Aztecs were great airplanes, but slow. Nice headroom, if that's important to you. The commanche was more like flying a mooney; small inside, and had a similiar ride. I flew Senecas for a time off rough fields and to some remote locations in the mountains. I mostly flew the Seneca II and III, which are turbocharged and do much better at altitude. As a light twin, the II's and III's were some of the few that could maintain 8,000 on one engine with a full load.

Bear in mind when shopping for a twin that it's not a slight increase from single engine ownership. The retractable gear, second engine, and increasd maintenance, added insurance, larger tie-down or hangar space, and so on is more like a three fold increase in costs, vs. a two fold increase. Older twins can be had for a good price, but at a price. Have a very thorough inspection done. I've seen a lot of singles that run thousands of dollars at the first annual inspection, due to the things which need to be repaired. I've seen twins run considerably more.

Fly them all and see what you think; get the pilot handbooks and run the performance numbers for the different scenarios in which you envision using the airplane, and see what adds up. Remember that each of those airplanes were originally type certificated under regulations not requiring actual performance numbers (much of the data is interpolated, and is ideal for a new airplane with a new engine and new propeller, flown by a factory pilot under specific conditions)...and none of them were required to maintain altitude on one engine with any significant load.

Good luck.

DFC, SNS3Guppy, many thanks for your thoughts.

I don't like the sound of that, good crosswind is quite important.

Much as I liked our Aztec a point to keep in mind is that it has an AUW of 2359kg. Anything over two metric tonnes incurs higher charges and these can mount up on a busy aircraft.

Some Seneca's are downrated to 1995kg which makes them more appealing.

Are we talking about the PA23 with the 540 engines and six seats?

Yeah, as oppposed to the older Apache.

I'm not sure about the other two, but I'd steer clear of the Seneca I. The Seneca II is a different animal though.

While I would generally agree with your sentiments DFC (and I wouldn't swap our Twin Com for anything else), most Twin Coms with reasonable kit are not capable of carrying 4 normal adults on a typical tour. With 4 adults plus light baggage and a dinghy, you're down to about 3 hours to dry tanks. Factoring in IFR reserves and the odd alternate that's 45 mins away, that doesn't give much flexibility.

If you're regularly flying 4-up, go for something with a higher load capability.

I know close to nothing about twins (though amazingly I did land one today, mind you that one did have both engines running) but the above can make a vast difference to operating costs if one is to use it for serious European touring.

I would recommend looking up the IFR route charges. About £200 on a decent leg across Europe. That is going to be about half the cost of the avgas!

Somebody thinking they are going to fly a de-iced plane (SE or ME) under "official VFR" (i.e. in IMC if necessary) in N European weather, is in for a suprise. A decent operating ceiling is a must, i.e. FL160+, for airways flight.

I have flown all types mentioned. The Seneca I does not have good single engine climb performance. The Aztec is a big bus with 50s style technology but lots of people like the roominess in them. The Twin Com would be my favourite if it is the PA39 rather than the PA30 - the latter has a vicious stall.
But if you had a choice, then the Seneca 3 has far better performance and my current favourite twin is the BE76 Duchess - a very good training and touring aircraft with 25 knot crosswind capability.

Nah, it's a kitten, particularly with vortex generators fitted. Does the PA39 have airframe difference that affect the stall? I thought it was just contra-rotating props.

Our 1966 Aztec C had a usefull load of almost 2200lbs with a max T/O weight of 5200lbs.
I don't call that a 4 person airplane by a lot shot, that's 6 plus luggage plus full fuel.

Aztec slower then a Twin Comanche? I flight planned ours at 160 kts TAS and that was at 21" MP and 2300 RPM.

Aztec's are available in many different flavors, we had dual vacuum pumps but the hydraulic pump ( flaps & gear) was on the left engine.
There is an STC for dual pumps.

Here's a nice one:
http://www.aso.com/aircraft/92749/ext-2.jpg

The link is here:

http://www.aso.com/i.aso3/aircraft_v...xxxregionid=-1

My vote goes to the Aztec.....:ok:

I'd see the trade-offs amongst the 3 as

Aztec - very cheap to buy with great payload and short-field performance and good speed and range. Oddly dated-looking (IMHO), single-door overwing cabin access not nice for pax, >2t and more expensive to run than the lighter twins.

Comanche - a very efficient design which has the low cost to run of the sub 2t twins but the speed of the larger ones.

Seneca 1 - I admit I have 500hrs in these and I like them more than the other normally aspirated twins (Duchess, Seminole, Cougar). I don't know why they get such a bad rap on forums. They are more modern looking, the cabin is big and wide (much more comfortable than the Beech twins) and the aft door and seats are very nice for pax. They cost approx. Comanche/Duchess money to run (under 2 tons, 200hp a side).

The demostrated crosswind of 13kts is a non-issue (and not a legal limit in any way). I found them no harder to land safely in 25kt xwinds than other aircraft.

The Seneca 1 single engine performance is no worse than other normally aspirated twins - ie. adequate once a safe height and speed are reached after take-off from the great majority of airports you'll depart from, and adequate for cruise over most terrain. Even over the alps, the drift down performance will give you a lot of options to land safely. The non-turbo IO360s are pretty bullet proof, and will cruise nicely at 6000', 18 US gals/hr total, 65% power, ~155KTAS.

The Seneca 1 was the best selling light twin in its day (ok, 1972-74) for a reason. It does nothing brilliantly (except perhaps the cabin space, about as nice as it gets below the "cabin class" piston aircraft like the Navajo/340/Duke) but it does a lot of things ok.

It really depends on your mission. High utility IFR - the Aztec. Fast economical touring - the Comanche. A fairly economical twin with a big cabin - the Seneca 1.

421C exactly what effect does having the rudder/aileron interlink have?

I've never flown a plane with one...but I'd have thought that a crosswind technique like crabbing in and then transitioning to wing low over the threshold (which is what I do) is difficult because of the need to cross the controls over.

I agree.

I asked the question because some of the answers did resemble those from someone who had actually flown a later generation Aztec.

Personally, I think the Aztec is the best of this bunch. Bullet proof in most respects, copes very well with weather and huge carrying capability with very good single engine performace.

Just watch the door opening mechanism!

If you have the money, buy a tatty one and have it refurbished, new panel, zero timed engines and you will have more than enough change left over from the cost of a new twin to pay for the fuel.

Contacttower,
I am embarrassed to say I don't really know what effect it has, except to say not much.

This isn't just bravado; and I'm not claiming a demonstrated x-wind limit should be lightly ignored. It's just that I started cautiously when I transitioned to the Seneca 1 (my first twin type) and it was never a problem to land in strong crosswinds, not even close to a problem. Being safe in a light twin demands all sorts of things (eg. recurrent training in single engine drills) and the x-wind thing just wasn't on that list of demanding things.

rgds
421C

The problem with this approach is that when you come to sell it, it will be worth......not much more than a tatty one. The market in old twins is brutal in this way. You have to be sure you will amortise the money over a long ownership period.

The best aircraft to buy is a twin where the previous owner has done what Fuji suggests!

Bookworm,

I did say "up to". However, in such an aircraft 3 hours is not bad when you take in bladder endurance.

However, 3 hours flying is 21 gallons per side i.e. 42 USG total. Can be 18 a side if I am careful or even less with a tailwind.

You must have some heavy friends.

-----------

Have you had to sit (as an adult) in the back row for any length of time?

I am not big but it is far from comfortable.

However, 2 Adults and 4 Children works a treat.

Regards,

DFC

I have flown all three and I do like the Aztruck a lot. But like 421 I have several hundred hours in the Seneca range with majority in the One and it is a good work horse.

The interlink on the controls just means you have to be a bit more adaptive in strong winds but has never been a problem.

They are cheap in twin terms to operate and reliable. The one I fly is deiced and IFR equipped, being my winter mount when it gets a bit icy for the Cessna!

Now that is very true.

Also single engine climb is pretty good - definitely not in the marginal category.

Light friends, heavy aeroplane. ;) With 4 x 180 lb people and 70 lb baggage (excluding the emergency equipment) I get 38 USG in. My rule of thumb is 14 USG/hr (which includes a contingency) + 4 USG excess for t/o and climb. So that's 1.75 hours to destination and alternate + 0.75 hr FRF.

The interlink on the controls means that when you apply left rudder, the control column rotates left and thus applies left down aileron.

This means that when you are landing in a right crosswind, when you kick it straight with the left rudder you will get left roll caused by the yaw and increased by the input of interlinked aileron.

It is not something that you can be adaptive about and the later models with this removed have higher crosswind limits.

---------

Bookworm,

I would not describe 3 13 stone friends as being "light".

Surprised that your limited by so much.

Thus you must spend a lot of time with the aux and tip tanks empty. Does this cause a problem with the bladder in the aux tanks drying out?

I can't believe that you can only carry round about 1/3 of the aircraft fuel capacity when going flying. I have not had such a problem. OK, not full tanks and full seats but I am sure we could carry more fuel than that.

Have you had your aircraft weighed recently?

Regards,

DFC

If I were in the market for a light twin personally, I'd be shopping for either a Cessna 310 or a Beech Travel Air. Both can still be had for good prices and have much better performance in my opinion. I wouldn't consider either of them a six place airplane, of course...but then one of the only light twins I'd put six people in would be a Twin Commander.

Think about your mission. Sometimes people start looking for an airplane based on the largest amount of people they might carry, when 90% of their missions will be solo. If that's the case, you're better buying something suited to the majority of your flying, and rent or otherwise improvise when the occasional need comes up to do more.

There is another twin, so far not given a thought here. Generally cheeper to buy than the others, even when fully equipped with de-icing equipment. Good short field performance, good range, six persons (just) four with baggage, easy passenger access (with the exception of the very rear seats), reliable and just as cheep to maintain as the Seneca and certainly cheeper than an old Aztec. Intrested? Not everyones cup of tea mind you, but if its twin engine safety and reliability you want above anything else then take a look at the good old Cessna 337 Skymaster. The Twin boom Push-me Pull-you.

The skymaster is okay when both engines are running. It's not when one isn't. It also puts you in a position between two weights with fuel all around, and hot exhuast at each end, a considerable amount of noise, and one way out if the cabin's bent.

Dunno about that mate, it may be a difficult concept for you but I have managed for well over 500hrs to put it down in some howling winds. I guess it's what you get used to.

On the contrary, I very rarely put 4 people in the aeroplane.

Much more often and recently than most aircraft, I think. 2610 lb. I obviously can't speak for the aircraft you fly/flew, but I get the impression that a lot of owners/operators do a lot to avoid having their aircraft reweighed for fear of bad news.

Luving it.

:ok: :D

:confused:

What are you going on about?

I thought with 500 hours on type is was a sound comment.

In which case I humbly apologise. Perhaps I still have a raw nerve or two.

No problem, and no need.

I appreciate you dont agree with my approach, but hopefully it is not something we ever need to really fall out over.

:)

Bookworm wrote:
...most Twin Coms with reasonable kit are not capable of carrying 4 normal adults on a typical tour. With 4 adults plus light baggage and a dinghy, you're down to about 3 hours to dry tanks.

I have a problem with your numbers.
If you have tip tanks you can carry 90gl but your W&B shows only the 60gl in your main tanks (keep your AUX empty), the tip's fuel is FREE weight, that is 180lbs that you can forget about. 90gl @14gl/h should give you 6.5h to empty tanks or 1040nm. As far as I can recall your aircraft has tips or am i wrong?

ACDC

Haven't got the spreadsheet in front of me but from memory...

I'm assuming the tips are carrying at least 125 lb of the fuel, hence the MTWA is 3725 lb. With the tips empty, I'm down to 3600 lb MTWA

2610 lb aircraft
720 lb people
70 lb baggage
20 lb anti-ice
75 lb emergency equipment (mostly the 4 man dinghy), tools, cover etc.
230 lb fuel = 38 USG (of which at least 21 USG must be in the tips)

Total 3725 lb.

2610 has to be a turbo Twin Comanche. A non-turbo would be more like 2450 to 2500. Gross with tips is 3725 IF you have at least 125 pounds fuel in the tips. Otherwise gross is 3600. There are some Robertsons with gross of 3800.

A Twin Comanche is a great airplane IF you don't get into icing. With only 160hp per side, it isn't going to handle ice very well. It will do 165k easily on 16 US gallons/hour, and 155k on 14.5, and that is total, both engines.

A non-Trubo, 5:15 total fuel at 16gph.

And no, it doesn't cost twice as much as a single to run, the reason is the systems are so much simpler than most twins.

If you want to carry a big load and deal with some ice, buy an aztec, they may be ugly, and they burn a lot of fuel, but they will fly through a lot of messy weather.

Aztec, but get a good one and look after it. Rock solid in cloud, almost the same payload as a Navajo, built like a tank and handles grass, mud and gravel no problem. lowest fatal accident record of any twin. bit noisy in the cabin - get anr headsets for passengers and yourselves.
Get a good E model, and stay clear of the turbo ones.
500 m wet grass, 6 up into st Mary's scilly isles, Stuttgart/London night IFR 6 up...takes it all in its stride. Bit thirsty. Nip over to alderney with those big fat longrange tanks and fill her up!

Nope, not a turbo, but with de-ice (boots and prop anti-ice).

Bookworm

Your aircraft is an heavy one. You can store 30gl in he tips (180lbs) that can be kept out of your W&B. In any case, flying 4 men is always hard. I did it but had to leave the cover behind, then I was 20lbs below Max.

That may be the case. But the only other person I've known who has bought a Twin Com also got a nasty surprise when he got the real W&B sheet. The message is clear -- weigh before you buy.

That's a strange way of putting it, and numerically incorrect. The installation of tip tanks increases the MTWA from 3600 lb to 3725 lb, with the condition that any weight in excess of 3600 lb is fuel in the tip tanks. So in essence you can have 21 USG (125 lb) in the tip tanks without having any impact on the passenger and baggage load.

Now that is 1.5 hours at normal cruise power settings.

Thus one could use that fuel for a 1 hour diversion at long range cruise and a 45 minute hold at max endurance power all including contingency.

That leaves all the rest of the fuel you carry to get you to destination.

There are very few such aircraft where the limiting factor is not the endurance of your bladder!

Regards,

DFC