Twin Otter flight model

[Bart Mitchell 0]

You might remember that I floew TwinOtters in a former carreer, but I never done all those cool things other pilots seemed to do with it all the time. But now I am old and tired and happy with piloting all the aircrafts I flew in FSX. And I finally got the time and lack of passengers screaming to try it out.

Not easy but after I made her a bit tail heavy it was possible.

Always wanted to do this... We done it a bit on some fields in valleys, but never this extreme. Apart from the fact I would expect a bit more drag from the props it all felt right as I expected it to be. I also tried the single engine options, they never worked very well for me in FS, it always seemed the half the engine power was not enough. But in the Twin Otter I got very close to what the book states, perhaps even a bit more. Having done one landing on a single engine (fuel leak) it's something I feel is lacking in many simulated aircraft.

All in all, still having buckets of fun. Ordered a throtle console at you guys today just for this aircraft.

Bart

[Aerosoft Team [Inactive Account] 51558]

While you are looking at the single engine performance, could you clear up a long standing mystery for me? Why is the performance on one engine not half that of single engine operation (even when take into account you never run at max thrust when you got both engines running?).

I can understand top speed is not double, the faster you go the more power you need, but climb performance for example, I don't understand why it is something like 1750 fpm with twin engines and 500 fpm on a single engine.

[pbearsailor 9]

It has to do with certification requirements and some thinking about thrust and excess thrust, Mathijs.

The rules under which many of these airplanes were certificated only require a small single engine climb rate at 5000 feet, many only little more than 100 fpm on one engine at that altitude.

When you lose one engine, you lose roughly 80% of your performance on most of these planes. That is because by far the majority of your available power is used to maintain straight and level flight. That power that is in excess of what is needed for S&L is what gives you your climb rate. When the Twin Otter loses one, it has lost a huge chunk of it's excess power and therefore doesn't climb well.

A Learjet, on the other hand, has considerable excess power which gives it a fantastic climb rate on two, and still leaves it with a good climb rate on one.

Another consideration is single engine rate of climb per mile, which is like the angle the plane can maintain in it's flight path over the ground as it climbs. Here, the slow speed of the Otter is an assist as you've still got a reasonable climb per mile, whereas something like a Cessna 310 or Baron is using a single engine best rate of climb speed considerably higher and therefore needing much more distance to get to a safer alititude.

cheers,

steve

[Ken Stallings 1]

Steve is right. You lose about 80% of total two engine thrust when you shut down one engine. Primarily this is because to counter the asymetric yaw you have to fly the aircraft in a way that causes excessive drag.

The drag is what robs you of the thrust. So it's really not that you are losing thrust. The engine still produces what it is supposed to. It is that when you factor in the additional parasitic and induced drag caused by countering the asymetrical yaw, you effectively lose 80% of your thrust.

Ken

[Nick - Seria17hri11er 0]

Very good explanations fellers.

[Ken Stallings 1]

And just to clarify, it is 80% of the combined two engine thrust that you lose. So if each engine produces 300hp for a combined 600hp. If you lose the critical engine (the one that forces the engine with the greater degree of asymetrical yaw to do the remaining work) then you are down to around 120hp.

This is why it is so critical to perform the required EP steps to split the ball and bank about 5 degrees toward the good engine. This control response creates the least overall drag.

It is also why it is vital to feather that prop immediately because a windmilling prop causes significant additional parasitic drag. Likewise for a sngle engine go-around (the most demanding maneuver) you must retract the gear and retract the flaps from the full down setting that is designed to create drag for final approach.

One of the reasons why bizjets tend to do better is not only due to the wonderful thrust each turbojet produces, but also because since they don't require prop clearance room, the engines are mounted very tightly against the fuselage in most cases. Therefore, there is vastly less asymetic thrust created when one engine is lost.

In fact, the situation is so dramatically different that the FAA chose to create a sub-category of multi-engine pilot certification -- a centerline thrust restriction. This is why unless they obtained additional FAA or Air Force training, fighter pilots out of the Air Force, Navy and Marine Corps normally cannot legally operate a Beech Baron. The fighter and trainer jets the military uses are nearly all centerline thrust aircraft.

Ken

[Nick - Seria17hri11er 0]

One of the reasons why bizjets tend to do better is not only due to the wonderful thrust each turbojet produces, but also because since they don't require prop clearance room, the engines are mounted very tightly against the fuselage in most cases. Therefore, there is vastly less asymetic thrust created when one engine is lost.

In fact, the situation is so dramatically different that the FAA chose to create a sub-category of multi-engine pilot certification -- a centerline thrust restriction. This is why unless they obtained additional FAA or Air Force training, fighter pilots out of the Air Force, Navy and Marine Corps normally cannot legally operate a Beech Baron. The fighter and trainer jets the military uses are nearly all centerline thrust aircraft.

Ken

Did not know that. Quite interesting Ken!

[Aerosoft Team [Inactive Account] 51558]

Thanks Steve, Ken... Now you explained a bit it all makes sense.

I got some new documents about single engine operation and I simulated a engine failure after V1, climbed to circuit altitude and cruised along a bit. Certainly learned that turns into the dead engine are easier and that you need to make sure you line up correctly. The moment you need to correct (=add drag in some way) you soon run out of horses. Never realized that crosswind becomes such an issue on single engined operation.

You all heard about that B52 and F16 squadron who were both on approach? After the tower told everybody that the B52 had an engine out and because of that had priority, a unidentified F16 pilot was heard muttering: "Oh boy now he has only 7 engines left, hope he makes it...."

[Nick - Seria17hri11er 0]

You all heard about that B52 and F16 squadron who were both on approach? After the tower told everybody that the B52 had an engine out and because of that had priority, a unidentified F16 pilot was heard muttering: "Oh boy now he has only 7 engines left, hope he makes it...."

roflmfao. I have not heard that one, but that is great. Priceless.

[Ken Stallings 1]

True story, oft told ...

An F-4 unit is crossing the ocean for a training exercise in Europe. They have a KC-135 tanker to drag them across the pond. One of the pilots of the F-4 is a hot dog who is drilling the tanker pilot about all the things his airplane can do that the KC-135 cannot do.

Finally, the tanker pilot comes on the radio and says, "All right hot shot, watch and see what I can do that you cannot."

Several uneventful moments go by with the tanker doing absolutely nothing it wasn't doing before and no words from the tanker pilot.

Finally, the tanker pilot comes back on the radio and says, "How'd you like that, Hoss?"

The F-4 pilot replies, "You did nothing!"

The tanker pilot replies, "Sure I did! I got out of my seat, stretched my legs, went to the ######er and took a leak and got a cup of coffee and sat back down. Now enjoy the remainder of your five hour flight, Hoss!"

The F-4 pilot said not another word!

Ken

[Nick - Seria17hri11er 0]

True story, oft told ...

An F-4 unit is crossing the ocean for a training exercise in Europe. They have a KC-135 tanker to drag them across the pond. One of the pilots of the F-4 is a hot dog who is drilling the tanker pilot about all the things his airplane can do that the KC-135 cannot do.

Finally, the tanker pilot comes on the radio and says, "All right hot shot, watch and see what I can do that you cannot."

Several uneventful moments go by with the tanker doing absolutely nothing it wasn't doing before and no words from the tanker pilot.

Finally, the tanker pilot comes back on the radio and says, "How'd you like that, Hoss?"

The F-4 pilot replies, "You did nothing!"

The tanker pilot replies, "Sure I did! I got out of my seat, stretched my legs, went to the ######er and took a leak and got a cup of coffee and sat back down. Now enjoy the remainder of your five hour flight, Hoss!"

The F-4 pilot said not another word!

Ken

Hahaha, thats great. Fighter jocks ###### me off. All high and mighty on there horse.

[ross1562 0]

The tanker pilot should have just not given him any fuel!! That would have stumped him! :wink: :wink: