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Old 16th Dec 2007, 12:31   #1 (permalink)
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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).
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Old 16th Dec 2007, 12:53   #2 (permalink)
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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
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Old 16th Dec 2007, 14:05   #3 (permalink)

 
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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.
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Old 16th Dec 2007, 14:29   #4 (permalink)
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DFC, SNS3Guppy, many thanks for your thoughts.

Quote:
but also has the aileron - rudder link that reduces the crosswind limit to 12 knots.
I don't like the sound of that, good crosswind is quite important.
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Old 16th Dec 2007, 15:16   #5 (permalink)
 
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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.
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Old 16th Dec 2007, 15:34   #6 (permalink)
 
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Are we talking about the PA23 with the 540 engines and six seats?
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Old 16th Dec 2007, 16:01   #7 (permalink)
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Quote:
Are we talking about the PA23 with the 540 engines and six seats?
Yeah, as oppposed to the older Apache.
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Old 16th Dec 2007, 16:31   #8 (permalink)

 
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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.
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Old 16th Dec 2007, 16:44   #9 (permalink)
 
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Quote:
For up to four seat touring, the Twin Comm wins hands down.
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.
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Old 16th Dec 2007, 18:03   #10 (permalink)
 
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Quote:
Some Seneca's are downrated to 1995kg which makes them more appealing
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.
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Old 16th Dec 2007, 18:57   #11 (permalink)
 
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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.
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Old 16th Dec 2007, 19:15   #12 (permalink)
 
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Quote:
The Twin Com would be my favourite if it is the PA39 rather than the PA30 - the latter has a vicious stall.
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.
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Old 16th Dec 2007, 20:29   #13 (permalink)
 
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Quote:
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
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:


The link is here:

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

My vote goes to the Aztec.....
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Old 16th Dec 2007, 21:03   #14 (permalink)
 
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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.
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Old 16th Dec 2007, 21:09   #15 (permalink)
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Quote:
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.
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.
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Old 16th Dec 2007, 21:17   #16 (permalink)
 
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Quote:
Our 1966 Aztec C had a usefull load of almost 2200lbs with a max T/O weight of 5200lbs.
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.
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Old 16th Dec 2007, 21:23   #17 (permalink)
 
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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
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Old 16th Dec 2007, 21:29   #18 (permalink)
 
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Quote:
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
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!
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Old 16th Dec 2007, 21:35   #19 (permalink)
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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.

-----------

Quote:
I don't call that a 4 person airplane by a lot shot, that's 6 plus luggage plus full fuel.
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
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Old 16th Dec 2007, 21:40   #20 (permalink)
 
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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!
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