Why not take off with flap?

[Adam Frisch]

On the 680V you take off with 1/3 flap, or about 10 degrees. But on the 690/Jetprop models, that seems not to be the case. Why not?

[donv]

That's a good question. Swede used to do what he called a "fishing takeoff" which involved doing a static runup, releasing the brakes, push the flap lever down, pull back on the yoke, gear up, flaps up. I don't think the flaps ever got much beyond 1/3 during this...

My guess is that it simply wasn't necessary, and the gains involved were so little that it wasn't worth the effort to certify it that way. Flaps on a Turbo Commander really don't do a whole lot other than add drag.

[Dhavillandpilot]

When I did an initial 500 endorsement I did the usual short field take off with flaps.

When I bought the 685 I found the Flight Manual didn't have any flap settings for short field. As the 685 is basically a 690 with Pistons I guess the earlier post answers why.

However whilst doing an endorsement on one touch and go the checking pilot forgot to retract the flaps. The aircraft went up like an Otis elevator.

Can anyone enlighten me???

[Steve binnette]

You are trading take off distance for single engine performance.

Maybe Commander wanted  better OEI numbers and revised the manual?

[donv]

The performance on any 690 or subsequent Turbo Commander is so strong, one or two engine, that I think they just felt it wasn't necessary. And it would add complexity-- one of the joys of flying a Turbo Commander is that it's so darned simple, and requires a minimum of switch flipping and fiddling...

You are trading take off distance for single engine performance.

Maybe Commander wanted  better OEI numbers and revised the manual?

[Ted Striker]

Lurker here 

Looking at the CAR 3 (origin of FAR 23) that the aircraft was certified under I would speculate that a take off with flaps would result in the best numbers. i.e Shortest distance over the 50ft screen, no need to account for the acceleration segment, OEI can just magically use zero flaps etc.

I am guessing the manufacturer (or maybe the lawyers...) decided it was more practical (given the gaps in certification requirements versus the real world) to provide data just for zero flaps.

Other aircraft that spring to mind are the bonzana and baron, where the take-off charts with flap disappeared...

[Steve binnette]

Hi Ted, welcome!

I agree with you it was not a regulatory change but an internal Commander change.

You guess on why is agood one.  It would be interesting to know for sure what caused the change?

[Ted Striker]

Thanks,

Quite, enjoy reading the posts on here, Adam's how to (re)build a plane thread etc. Been twenty years or more since I sat in a commander, (only a few hours mind and very inexperienced too).

Also I guess they were competing with other FAR 25 aircraft in terms of safety, and the no flap setting, with subsequent longer book distances would give results closer to balanced field lengths.

If the aircraft was certified today with a brand new type certificate, I wonder what the handbook would contain.

[Bruce Byerly]

I think you guys have it right.  You're moving numbers around but adding drag and reducing overall climb performance whether on two or one engine.  Flaps might get it off the ground quicker on a short/soft field but overall that wing doesn't seem to need them especially with turbine power pushing air over it.  I played around with the book 1/4 flaps/no flaps settings years ago in the 500S and concluded (right or wrong I don't know for sure) that flaps didn't make sense for me in that plane either if I want the best single engine performance. And it was hard to notice if it shortened the ground roll on pavement at all.  Plus it's one less thing to forget to do if the plane is already clean.  Of course I wasn't doing the Swede dirt strip stuff either.  Where's the "bow down" smiley?  

Not to totally derail the conversation into technique, but for me in the piston anyway, once it's willing to fly off the ground, it's gear up asap, accelerate until close to blue line then hold that speed for the initial climb. If one quits before blue line, abort. I even knock the cowl flaps down to about 2/3 open to save some drag. As far as I can tell it's the same in jets for max performance - the 400' business before raising flaps is really an artificial rule to help keep the cockpit monkey motion orderly. For max performance, as soon as the plane is off the ground it's gear and flaps up for max climb performance ... assuming you still have both donkeys pulling ...   so why have the flaps out at all in a Commander unless you need to shorten the ground roll? 

[Adam Frisch]

I do pretty much the same as you, although I do delay flaps. But gear comes up as soon as possible. I often get criticized for that, but to me that makes sense in a twin, or any aircraft. Flaps seem to come up a little later, when I feel the "flap up sink" is safe to execute, but normally around 200-300ft.

[ghancock]

I'm with you Adam, The second the grass stops touching they are on the way up.  I figure if I have to ditch at that point even on pavement it will be a belly landing and I'll be happy as shit that I didn't do it on my back :-) . As for flaps I wait until I'm 1-200 feet up but now going to have to test to see how many less feet I get off with or without them. :-)


Glenn

[MikeDelta]

We operate a 690 and 2 680FL's (though not for much longer) from 1000m. Technically not even enough.

We always use 1/4 flap to get her up. After that clean ASAP. We can ditch the flaps quite fast as the terrain is flat.

What some pilots say is that taking pressure off the nose wheel (not lifting it) really helps with acceleration. I have a hard time noticing it personally but then again, the 690 doesn't need that anyway. She just goes 

[Steve binnette]

Mike
What are you going to do with the 680s.  Sounds like you might park them?

You operate from 1000m of grass?  Is it a nicely cared for strip or a bit rough?

I have yet to take my Commander off road, still too worried about paint and props.