Hi guys,

I'm a student trying to design a bush aircraft for 5-6 passengers. I was just wondering whether I should have single or twin engines?
What are the advantages and disadvantages of these two configuarations? WHat would you guys suggest?

A single would be much cheaper to operate. IO-520s and IO-540s are common in the bush.

Whatever you do with the door, don't copy the door design of the 207. It's hard to get your feet out when the front seats are forward. A better design would allow the pilot to open his door and exit without first sliding his seat back.

First, definitions of a bush plane vary greatly. Some define the bush as an improved grass airstrip while others are carving out a place to land out in unimproved real estate. Define your mission and then begin addressing all the compromises involved.

For true bush operations, a single engine is more efficient. A twin would be heavier and require more fuel capacity. If you consider it from a maintenance standpoint, there's only one engine/prop to fix. You will potentially also need a good deal of propeller to ground clearance for takeoff and landing, again depending on your mission.

5-6 passengers will have considerable luggage to deal with, so consider that in your design, too.

There's lots of folks here with tons of experience so keep asking questions. Let us know how your project turns out!

b26 wrote:Hi guys,

I'm a student trying to design a bush aircraft for 5-6 passengers. I was just wondering whether I should have single or twin engines?
What are the advantages and disadvantages of these two configuarations? WHat would you guys suggest?

I would go with a single engine turbine. It's hard to beat the power to weight ratio of a Pratt and Whitney PT6, as well as the reliability of the engine itself and the ease of operation across a wide temperature range. For 5-6 passengers, it becomes harder to justify twin engines, and the structure of the airplane is necessarily larger to support the extra engine.

If you look at the airplanes that have been most successful in the bush, you're going to see that they generally share certain characteristics. The Piper Super Cub, Cessna 180 and 185, DeHavilland Beaver, turbine Beaver and Turbine Otter are all legendary bush planes - all "taildraggers", high-wing, and with single, tractor-mounted engines (engine mounted in front, rather than rear-mounted pusher).

People have designed many novel aircraft in pursuit of a better bush plane, but there are good reasons that the successful designs keep coming back to this basic configuration.

The high wing allows for better visibility looking down, which is important for careful surveys of potential off-airport landing sites and for spotting game when hunting. It also keeps the wing out of most of the brush and weeds when on the ground and during very low altitude maneuvering on takeoff and landing. If the airplane ends up on floats, a high wing is a must for ease of docking and allowing you to move around the dock without the airplane's wing in the way. Large, straight wings with lots of camber provide plenty of lift for low-speed maneuvering and slow takeoff and landing speeds. Slow speed maneuvering equates to a safer airplane in confined areas with lots of obstacles and also tremendously reduces the forces the human body has to absorb in the event of a crash or upset.

The front-mounted engine keeps the propeller well ahead of any large rocks and debris that might be thrown up by the wheels during takeoff and landing on rough surfaces, as opposed to throwing that debris into the propellor disk on a rear-mounted pusher. Most airplanes will survive a large rock hitting the horizontal stabilizer, but not that same rock hitting the prop.

The taildragger (conventional landing gear) helps keep the prop elevated and away from debris, helping to protect it, and generally puts the aircraft in the takeoff and landing attitude while it is sitting on the ground. When combined with over-sized, low-pressure tires, this also allows for longer propellers (which gives you better takeoff and initial climb performance. The low pressure tires also will roll over startlingly large objects with much less effect on ground handling characteristics.

The kit plane industry offers a pretty good peek into the newest and some of the most capable designs out there, with airplanes like the Just Aircraft SuperSTOL, the Rans S-series, Bearhawks and others. They pretty much all follow the same basic design of the previously-mentioned airplanes.

For the 5-6 passenger range, with their gear, it would be hard to beat a turbine Beaver clone.

B-26:

Sounds like you should look closely at the Sherpa which now has a turbine option as well as the gas engine.

Bush plane implies to me that it has a hardy cargo capacity. That along with 5 or 6 passengers spells a very big engine and significant load hauling capabilities. The Sherpa has done a great job of developing the capacity to haul a lot of people and cargo while still being able to get in and get out quickly (you just have to be able to afford it). Sounds like your project would benefit from reviewing specs, design, etc.

http://www.sherpaaircraft.com

I can put you in touch with the aero engineer who designed it if you are interested. PM me and give me your email address and I will pass it along to him.

Glad to hear we have students involved in the aircraft engineering realm!! We need more of you.

Larry

All good responses. I am also thinking something along the lines of the Beaver, Sherpa, or a smaller version of the Quest Kodiak. The SHerpa has been listed on BS for a while and I would think something along its lines would be the least expensive to build and maintain.
A local guy flew one on amphib floats into our fly-in a couple weeks ago. He landed in roughly half the length of the strip which I though was awesome. If I remember correctly the gras strip is 2200' . Getting the Kodiak into roughly 1,000', with it on amphib floats, looked like quite spectacular performance to me for such a large floatplane. I used to fly my Champ on floats out of this seaplane base, a hidden treasure in my neck of the woods. If I ever win the lottery this airplane on amphibs would be at the top of my 'gotta have it toys'.

Rather long video but the Kodiak landing is within the first couple of minutes. The takeoff is at the 25 minute mark and it is equally spectacular. The yellow cones are NOT at any specific distance but you can still get a rough idea of the short takeoff distance.
http://www.youtube.com/watch?v=u0kq-qQX ... e=youtu.be

WWhunter wrote:Rather long video but the Kodiak landing is within the first couple of minutes. The takeoff is at the 25 minute mark and it is equally spectacular. The yellow cones are NOT at any specific distance but you can still get a rough idea of the short takeoff distance.
http://www.youtube.com/watch?v=u0kq-qQX ... e=youtu.be

It's always fun to fly an airplane like this with reverse. Makes short landings pretty impressive, when done right.

MTV

B26, you might want to take a gander at the BCP Knowledge Base for bush aircraft if you're trying to figure out what is already out there.

https://www.backcountrypilot.org/knowledge-base/aircraft

CapnMike wrote:

b26 wrote:Hi guys,

I'm a student trying to design a bush aircraft for 5-6 passengers. I was just wondering whether I should have single or twin engines?
What are the advantages and disadvantages of these two configuarations? WHat would you guys suggest?

I would go with a single engine turbine. It's hard to beat the power to weight ratio of a Pratt and Whitney PT6, as well as the reliability of the engine itself and the ease of operation across a wide temperature range. For 5-6 passengers, it becomes harder to justify twin engines, and the structure of the airplane is necessarily larger to support the extra engine.

If you look at the airplanes that have been most successful in the bush, you're going to see that they generally share certain characteristics. The DeHavilland Beaver, turbine Beaver and Turbine Otter are all legendary bush planes - all "taildraggers", high-wing, and with single, tractor-mounted engines (engine mounted in front, rather than rear-mounted pusher). <various snips>


For the 5-6 passenger range, with their gear, it would be hard to beat a turbine Beaver clone.

This here, in so many words, is exactly what I was going to say. CapnMike is a mind reader. Understand though, that if a Turbine Beaver was a viable new commercial product, dehavilland would be making them. The Pilatus Porter IS in production and for a couple of million bucks you can buy one tomorrow.

Thanks so much guys, all the responses were helpful And really helped us clear some difficulties we are facing at the start of the university project It is great I stumbled upon here as this is really helpful. We are currently thinking of going with single engine, taildragger for 5-6 passengers. Ill update info about the project as we progress futher

Borrow a set of plans for a 185 and you should get an A+ with distinction

mtv wrote:

WWhunter wrote:Rather long video but the Kodiak landing is within the first couple of minutes. The takeoff is at the 25 minute mark and it is equally spectacular. The yellow cones are NOT at any specific distance but you can still get a rough idea of the short takeoff distance.
http://www.youtube.com/watch?v=u0kq-qQX ... e=youtu.be

It's always fun to fly an airplane like this with reverse. Makes short landings pretty impressive, when done right.

MTV

Off topic here but, YES!! Especially a plane on floats, reverse capabilities, is a want to have item. While at Oshkosh this year I looked at an electricly controlled prop (Airmaster?) for the Rotax 912 that had a Beta switch. It sure got the gears turning in my head of the possibilities of this prop if it were mounted on my RANS S-7 whenever I get the floats on. Backing up to a dock....too cool!!!

Another thing to consider is where your "bush" flying is, and the terrain under you, and the distance to the next town. Two engines gives you two chances to get home in the event of engine problems, of course at the cost of the extra engine, structure, etc. as mentioned.

If I was looking down at the Amazon jungle, or hungry cannibal natives in PNG, I'd sure like to have that extra ace in the hole.

Availability of fuel and type of fuel might also be a major issue. If you can only get roadside pump automotive fuel, then the high compression big 300-350 HP Continental and Lycoming engines may not be able to run well, or make their rated power. All that famous FAA certified reliability and trustworthiness could go right out the window running on car gas, or it might sit parked instead of flying while waiting for airplane fuel to arrive.

In this case, a 400 HP aluminum V8 based engine, de-rated to 300 HP, might be the best choice in that specific environment. An Australian glider club put one of these engines on a Pawnee towplane in daily hard service for several years and saw very good results, cost reductions, reliability in service, etc.

I'm not saying that the V8 is a no-brainer drop-in replacement for any O-520. It's not. It's a significant-brainer option, that may be advantageous where the situation favors it because of fuel, or cost.

The Sherpa layout, essentially a double sized Super Cub, would be appropriate if you need to get your 6 people into a 400 foot clearing on a mountainside. But you suffer aerodynamic efficiency and cruise speed and range. The Gippsland / Mahindra Airvan (perhaps with a tailwheel) would be a good starting point for operations where you need a little more speed and have a little more space to land in.

One of the biggest issues you're facing with the load you've targeted (5-6 pax plus baggage, of course) is that there are simply no current production gasoline burning aircraft engines that could reliably carry that kind of load. Note that all the gas powered airplanes that have that load capability (the Beaver comes to mind) use ancient radial engines that haven't been in production for 60 plus years.

This limits your possibilities to turbine or diesel engines. Both are very expensive (PT-6 Pratt and Whitney engines are well north of $300 K US I believe. I don't know of any diesels in the power range you'd need for that size airplane either, so you're pretty much limited to turbines.

Which may be a good thing anyway. While avgas (or gas for that matter) is readily available in the US and Canada, it's really scarce in most of the rest of the world. Jet fuel, on the other hand is widely available, world wide. This was one of the driving factors in the design of the Kodiak airplane, which was purpose designed as a bush airplane to serve the missionary community throughout the world. Take a look at that airplane, which has some very practical design features (Tri gear is preferable to tailwheel in this case, I'd say) and some innovative features (like two batteries to ensure good solid starts in remote sites.

I've flown the Airvan, and I loved it, but it isn't of the size you're talking.

MTV

Understand though, that if a Turbine Beaver was a viable new commercial product, dehavilland would be making them. The Pilatus Porter IS in production and for a couple of million bucks you can buy one tomorrow.[/quote]

Ummm, deHavilland cannot put the turbine Beaver back in production.....they no longer own the Type Certificate, Viking Air, Ltd in Victoria, BC owns the DHC-2, DHC-3, and DHC-6 Type Certificates now. And they are building new DHC-6 airplanes-Twin Otters.

You're right, though, there's no market for Turbo Beavers, though I'll bet Viking is looking closely at all the Single Otters that are being converted to turbine power.

And, while Pilatus will build you a Turbine Porter, you have to special order it...they don't build them in normal production.

MTV

EZFlap wrote:Another thing to consider is where your "bush" flying is, and the terrain under you, and the distance to the next town. Two engines gives you two chances to get home in the event of engine problems, of course at the cost of the extra engine, structure, etc. as mentioned.

Worth remembering two engines also gives you twice as many chances to have an engine failure; generalising.

mtv wrote:
And, while Pilatus will build you a Turbine Porter, you have to special order it...they don't build them in normal production.

Actually I was speaking to their regional sales rep in the weekend, I think they are making something like 6 per year? But I was drinking at the time... and were mostly talking about the PC12.

I think Cirrus run that model, where they don't produce "shelf stock", and only build to customer requirements with a 3 month lead time.