Beaver

[skipperdude]

Marin, Am I to understand you own a DeHavaland Beaver?

I have a short tale to relate on my experience with a 1947 vintage Beaver.

I was on a moose hunt up in the Brooks range. We flew out of Bettles Alaska to the south fork of the Malmute river to a small lake. Landed with no problems. after a 4 day unsucessful hunt the Beaver came back to pick us up. The lake was quite small and sort of kidney shaped. in order to have enough room to take off the pilot backed all the way into the back corner of the lake and as we were gaining speed to lift off he had to sort of roll the Beaver up on one pontoon as we rounded the corner of the lake.
She popped right off the water and we were on our way. Man was I impressed.

As a side note I did find a winter drop of antlers on the side of the lake.
While driving back from Fairbanks I found a place on the side of the road where a hunter had left a moose hide. I tossed it into my truck. I wound up having it tanned into garment leather. I cut it up and my wife sewed it together to make a moose hide coat . We entered it into the Alaska State fare and won a blue ribbon Best of show for the coat.

So my beaver tale wound up with a hollow moose. I got everything but the meat.

One impressive piece of equipment That Beaver, It being older than me.

SD

 

[Marin]

No, I don't own a Beaver at this point. We have a long-time relationship with the family that owns Kenmore Air (Harbor) and we can use one of their Beavers when they don't need it. If you think boats are expensive toys, try an airplane. My wife has had two of them and I'm not sure I'd want to endure the "I told you so's" if we got a Beaver today. Our boat's ownership costs are non-existent compared to something like a Beaver's. A Beaver is a very expensive plane to own, particularly on floats. They burn 23-25 gallons of fuel an hour and they have a never-ending string of ADs that have to be dealt with on a continuing basis. So I'm very happy to use Kenmore's planes especially at the cost we are given.

I've been flying the Beaver since 1980 or thereabouts and have a few thousand hours in them now. The floatplane instructional book I wrote back in 1985 and that went through three editions features a Beaver in most of the illustrations. And my currently published book about Kenmore Air of course has a lot to do with Beavers in the second half of the book.

The technique for rolling the plane up onto one float during a takeoff run after the plane is on the step is somewhat controversial. A lot of pilots, including me, do it as we feel there is at least a degree of benefit from it.

In theory what you're doing is cutting the hydrodynamic drag of the floats in half. Since drag is what's opposing your acceleration to rotation speed, reducing it lets you achieve that speed sooner.

That's the theory. What the opposition says is that the plane weighs the same whether it's on one float or two. So if you roll the plane up onto one float, that one float still has to support the same weight. So it's forced deeper into the water which increases the hydrodynamic drag so you're back where you started in term of total drag resisting your acceleration.

I and a lot of pilots don't deny the theory but do deny the doubling of the hydrodynamic drag when you're up on one float. Particularly on a big, powerful plane like the Beaver. So we use the technique when faced with the need to get off the water as quickly as possible.

The other method which I use in a Cessna 180 which has manual flaps is to "pop" the plane off the water by yanking on full flap for an instant after the plane is on the step. This literally pops the plane out of the water. At that point it becomes a fine-line situation. You have to immediately reduce the flaps or their massive aerodynamic drag will put you right back on the water. So you feather the flaps back at the same time you play the yoke (elevator) to keep from stalling since you are actually airborne before the plane is ready to fly.

The only reason it IS flying is that you are in ground effect, which reduces the induced drag (the drag created by the act of generating lift) so the wing will support the plane at a slightly slower airspeed than it would require to support the plane out of ground effect.

(Counter to what your intuition might tell you, the yoke (elevator) controls speed and the throttle (power) controls climb and descent. So I'm using the yoke to maintain enough speed to keep the wing staggering along.)

But since the floats are now out of the water completely you will accelerate very quickly and so within seconds you are out of that "too slow" mode and have accelerated to a speed where the wing is happy.

This technique works great and I have used it many times in a 180 on short lakes or in rough water when you want to get the plane off that surface asap. (No shock absorbers on a float plane--- rough water can pound it to pieces in short order.)

The pop-it-off-with-flaps technique doesn't work so well in a Beaver because even though the flaps are manual, they are hydraulically operated. You pump them down and up with a big lever on the floor next to the left seat. So they move relatively slowly--- you can't get that "pop" that you can by pulling up fast on the simple mechanical flap system in the Cessna.

Way more than you wanted to know but there it is.

The photo below was the cover of the magazine that ran the very first article I ever had published back in 1984, the launch of my writing career so to speak. The photo was taken by my wife who was standing on a big log raft tied up next to the old Port Gamble lumber mill on Hood Canal. I am doing the one-float takeoff maneuver.

 

[skipperdude]

Excellent.
I was under the impression the he couldn't take off going straight so had to roll on to one float while making a right turn on the lake. To get enough runway so to speak.

Regardless very impressive.

SD

 

[Marin]

Well, that's a legitimate takeoff technique too. I've used it in the Beaver to follow a curving river during a takeoff run. You don't turn a plane with the air rudder, you turn it by banking. (You can fly a plane around all day without using the rudder at all. It won't be particularly comfortable but you can do it.) So once the plane is up on the step you in essence bank it to follow the curve of the river. So the float on the upwing side comes out of the water. So that may very well have been what your pilot was doing.

 

[Peter B]

Marin, great photo that. Hey wouldn't the sheer speed negate that 'doubling of hydrodynamic drag' effect anyway, because the float would be 'on the plane' wouldn't it? To me that would mean the physics of the weight being divided between one or two floats is not applicable, because that implies displacement mode rather than planing mode...? In other words, to me the physics supports there being less drag from one float versus two, as long as you are going fast enough to be planing, and with floats being quite short, at anything even close to take-off speed they would have to be wouldn't they..? Comparable to the way a catamaran goes faster flying one hull. So I suspect your impression it does help is probably right.

 

[Marin]

While the float stil on the water has to support the entire weight of the plane, which is being reduced as the plane accelerates and the wing takes more and more of the load, the question of how much farther into the water the one float is forced remains.

In the displacement mode you are right, the float would have to displace twice the water than if the plane was sitting on both floats. Add the hydrodynamic force acting on the underside of the one float when it's planing and I have no idea how this effects the equation. Which is why I and a lot of other floatplane pilots think that the drag is not doubled when all the weight of the plane is put on the one float in a planing condition. I've never tried a full comparison--- take off "conventionally" with both floats on the water and then repeat the takeoff using the one-float method and see how the rotation points differ.

There will be a wee bit more aerodynamic drag with the one-float method because the ailerons will remain deflected to keep the plane in the "bank." But I very much doubt that bit of extra aerodynamic drag makes any difference even worth noting.

Anyway, I use the technique if conditions warrant it and it's safe to use it as I believe it does shorten the takeoff run by a bit. But almost all of my floatplane flying has been into pretty large bodies of water, salt or fresh, so I have used the technique more to stay in practice than because I've actually needed it.

 

[Baker]

Beavers are EXPENSIVE!!!!!...jus sayin'!!!

 

[Marin]

Yes, 23 gallons per hour in cruise and a string of expensive ADs that have to be complied with on a regular basis that just keep on comin.' But a wonderful plane to fly, particularly in the back country. On our trips north we load it until the rear of the floats are just awash. It's overloaded in this condition and the CG is a wee bit out of the envelope aft (we move it back forward once we get airborne with fuel management) but you'd never know it by the way it performs and flies.

Interestingly the designer of the DHC-2 knew it would be flown in overloaded, aft CG conditions, which is why the horizontal stabilizer is big and is mounted way aft. Even overloaded and out of CG, it and the elevator have the leverage to keep the plane stable.

 

[Larry H]

I have witnessed many Beaver takeoffs and landings in our travels in the PNW. I always watch as there is nothing like it.

Except when the Beaver has a gas turbine engine. Then the pilot just powers up, speeds up and pulls the plane up, popping it off the water, and climbs like crazy. No need for the one float maneuver, horsepower overcomes all.

 

[Marin]

I''ve got some time in a Turbo Beaver. Kenmore's are not stock Turbo Beavers but were re-engined (by Kenmore) with a Pratt & Whitney PT6A-135, the same turbine that is used in the Cessna Caravan. The original PT6A-20 550 shp turbine deHavilland put in the Turbo Beaver is not suited for salt water operations and over time will put out less power than the piston Beaver's engine. The PT6A-135 is rated at 750 shp (Kenmore detuned them to 600 shp in their converted Turbo Beavers) and is optimized for salt water operations so the performance of the engine does not deteriorate over time.

Empty Kenmore's Turbo Beavers don't even get on the step. They come up onto the hump and fly right on out of the water. Loaded, they perform pretty much like the piston Beaver. This is because the Turbo Beaver has a stretched fuselage and another row of seats. So even though the plane has more power it's also carrying more weight if it's fully loaded. So fully loaded on a short lake or in rough water we still use the one-float takeoff in the turbines to get off faster.

Like most turbines, it also has a beta prop, which means you can back up (to a degree) on the water. It also means you can fly a REALLY steep descent because you can put the prop in zero pitch which generates drag and steepens the descent, and I've even used a bit of reverse pitch on short final on occasion to drop the plane onto the water after clearing trees along the shoreline.

But.... it's a gas hog so unless you've got a lot of money to play with or you put the plane to work earning money as Kenmore does, the piston Beaver's the better deal I think.

 

[Larry H]

Got a picture of this Kenmore turbo last summer in Port McNeil.

Marin, Have you flown this one?

 

[Peter B]

Back in the days when I was a kid and we were back on the farm, they used to often use Beavers for top-dressing...that's where I got to love the Beaver. It was the first plastic model plane I ever constructed, and I painted it yellow.
They also used Tiger moths when I was really young. Eventually Fletchers took over from the Beavers, mostly. Might have been cheaper to run, Doubt they could hold more fertiliser...they were an underwing monoplane.

 

[Marin]

Duplicate post.

 

[Marin]

Marin, Have you flown this one?

Yep. Kenmore only has two of them and I've flown them both. 55 Tango was the first one they converted and it was featured in an article I wrote about it for Private Pilot magazine back in March 1989. 44 Tango was the second.

Originally none of Kenmore's Beavers had the third (rear) side window in the passenger cabin. Only the bubble window in the door and the rectangular window behind it that replaced the as-built porthole. (Both the bubble window and the rectangular window are Kenmore-developed mods.) The second rectangular window began making an appearance in the 1990s. Since then all of Kenmore's Beavers, piston and turbine, have been modified with the second rectangular window. There are no seats next to it but it makes the cabin more spacious feeling and puts more light into the baggage area.

I've also flown some of their Vazar Dash-3 Turbine Otters. Totally different plane than the Beaver. VERY heavy on the controls, particularly in banking the plane. The turbine conversion of the single-engine Otter made a very realiable money-maker out of what had been something of an unreliable dog in it's original piston configuration. But I didn't enjoy flying the Otters near as much as I do the Beavers, both piston and turbine.

 

[markpierce]

Plane landings in Alaskan port waters seem to be continuous, or is it just because the visiting cruise-ship passengers are in town. And even obvious to this non-pilot, these aren't Beavers:

 

[markpierce]

Some people are fortunate enough to ask themselves "shall we go flying or boating today?"

 

[Larry H]

Turbine Otter in Ketchikan.

 

[Marin]

Larry--- The following is probably a lot more than you want to know, but since you seem interested in these planes, here's some of the story.......

These photos are of the first certificated turbine Otter conversion. Back in 1990 I was hired to write and photograph a couple of feature articles on this plane which at the time was a "rumor" in the aviation press. I was asked to find out if the rumor was true.

While other attempts had been made to convert a DHC-3 Otter to turbine power, and at least one conversion had made it into the air in Renton, WA, no one had been able to take the idea all the way to certification until Canadian-born Dara Wilder of Bellingham did.

Dara owned a big gold mining equipment manufacturing company and had customers all over the world and he realized that if the Otter could be given more power, and reliable power, it would be much more cost effective to the mines than the big helicopters they were using to transport people and equipment. So he came up with his conversion concept and hired a fellow in California (Floyd Perry) who did turbine conversions of crop dusters and other single and twin-engine planes to build it for him.

The result was the Vazar (the name of Dara's company) Dash-3. Dara had three basic requirements for his conversion. It had to be bolt-on, ready-to-run, it had to require no modifications to the Otter aft of the firewall, and the conversion time had to be no more than three days. He accomplished all three goals.

The certification process took a full year and Dara told me it was far more difficult and frustrating than creating the conversion itself but he persevered.

The second photo shows why all these turbines--- the Turbo Beaver, the Vazar Otter, and other conversions or turbine versions of piston airplanes--- have such long noses. Compared to the radial engine the turbine replaces, the turbine is very small and very light. In the black and white photo, the 750 shp turbine is contained inside that white housing at the very front of the nose. All that space between it and the firewall is empty except for the tubular structure.

Since the goal is not to change the characteristics of the original plane in terms of its center of gravity envelope the only way to retain the piston airplanes CG envelope is to hang that light turbine way out on a long moment arm. Even with the long overhang the Vazar Otter still has to have a container of lead shot mounted in the open space between the turbine and the firewall to retain the CG envelope. (This is not a new idea-- the Boeing 727 has lead bars up front to accomplish the same thing.)

If you were to take the cowling off the Turbo Beaver you would see much the same thing as the Vazar Otter although the turbine in the Beaver is not hung out so far. This is because when deHavilland of Canada designed the Turbo Beaver they not only hung the engine out farther but they lengthened the fuselage. The extra length is in the passenger cabin under the wing, which moves the flight deck forward. So they accomplished maintaining the CG envelope they wanted by changing the design of the fuselage itself. Since Dara's objective with his Otter conversion was to require no modifications to the plane aft of the firewall, he hung the turbine out as far as practical and then added some weight out there, too.

There is a disadvantage to this long nose when you put the plane on floats. On the piston Beaver and Otter the first thing to arrive at the dock are the bows of the floats. On the turbine versions of the two planes, the first thing to arrive at the dock is the prop. So you have to be very mindful of what's in front of you as you come in.

At the time I did the articles Dara had two Vazar Dash-3s flying in service. One of them was on wheels at a mining operation in central Canada. But the other one was on amphibious floats and was owned by a logging company just up north in Campbell River. So after interviewing Dara in Bellingham my wife and I flew up to Campbell River, interviewed the owner of the logging company (Irvin Olsen) and his chief pilot, flew the plane around and then landed in a bay near April Point where Irvin had a bunch of log rafts moored. My wife and I got out onto the logs and then the company pilot did some landings and takeoffs and water work in front of us for the magazine shots including the cover. The third photo is Irwin (r) and his chief pilot. On amphibs, the Otter is a big plane.

Dara ordered several hundred reprints of the articles and used them in his sales campaigns. All of Kemore's Otters are Vazar Dash-3s. So far as I know, every DHC-3 turbine conversion you see--- in SE Alaska, at Harbor Air out of Vancouver, etc.--- has the Vazar conversion kit on it. I'm not aware of any other certificated turbine conversion of the single engine Otter although there may be by now.

The engine Dara used is the same one Kenmore used in their Turbo Beaver conversions, the Pratt & Whitney (of Canada) PT6A-135. However in the Otter it is not derated and delivers the whole 750 shp. This compared to troublesome 600 hp geared radial the plane was originally equipped with.

 

[Larry H]

Marin,

Thanks for the report. I did not know that the nose was mostly empty space. I took the pictures I posted in Ketchikan from our slip at Bar Harbor North in 2011.

 

[Marin]

Marin,

Thanks for the report. I did not know that the nose was mostly empty space.

Yes. Some models of the Cessna Caravan have a weight-limited luggage compartment up there.

 

[Larry H]

How does the turbine engine compare to the piston engine as to fuel economy and maintenance expense?

 

[Marin]

How does the turbine engine compare to the piston engine as to fuel economy and maintenance expense?

The turbine burns a fair amount more fuel although the cost of Jet-A is--- or used to be--- considerably less than the cost of avgas. The piston Beaver burns about 23 gph. If memory serves the turbine Beaver burns 40-something gph. But if flies faster and carries more.

Another difference is that it's not really worth hauling a piston Beaver up very high unless you have to clear mountains. All a long climb does is add to the overall trip time, burn lots of fuel, and potentially overheat the engine. My wife and I never take the plane above about 1,000 feet when flying the Inside Passage. We have flown for several hours at a stretch at 50-100 feet under a solid overcast but we never go above a thousand unless we're going back into the mountains.

A turboprop, however, gets more efficient with altitude up to a point. So the turbine Beavers and Otters are typically flown at significantly higher altitudes on their routes than the piston planes.

The real benefit of the turbines is tremendous reliability, reduced maintenance--- not many moving parts--- and greatly extended time-between-overhauls (TBO). Where the radial on the Beaver has a TBO of between 1200 and 1800 hours the TBO of the P&W PT6A-135 can be up around 8,000 hours. And there are monitoring programs operators can use to significantly extend the TBO of both piston and turbines engines.

But there's no free lunch. The cost of overhauling the radial is relatively low. The cost of overhauling a turbine can run well into the hundreds of thousands of dollars.

But the main benefits of the Turbo Beaver and the Vazar Dash-3 Otter is more power and greatly increased reliability. Which translates into lower maintenance and operating costs, too.

 

[Larry H]

That 8,000 hour TBO turbine is almost as good as a 10,000 hour TBO Lehman!! LOL

How does the 23 gph and 40gph numbers translate to Miles per Gallon? I was told by a piston Beaver pilot that his plane got about 6MPG usually loaded with loggers and their gear.

If the P&W turbine costs several $100K to overhaul, what is the initial cost of the powerplant?

 

[Marin]

That 8,000 hour TBO turbine is almost as good as a 10,000 hour TBO Lehman!! LOL

How does the 23 gph and 40gph numbers translate to Miles per Gallon? I was told by a piston Beaver pilot that his plane got about 6MPG usually loaded with loggers and their gear.

If the P&W turbine costs several $100K to overhaul, what is the initial cost of the powerplant?

A piston Beaver on floats cruises at 110 mph and burns about 23 gph.. Kenmore's turbine Beavers cruise at 140 mph and burn 41 gph.

IIRC when Kenmore did their Turbo Beaver conversions a new P&W PT6A-135 cost half a million dollars. I suspect they are considerably more today.