prop-wash questions

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kalabaddon

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Kalabaddon
I am flying a DA-40 for training and when I do my take off roll the prop-wash/torque effect seem almost random. For example during my first solo flights in pattern with next to no winds, on my first takeoff I needed almost no right rudder, however on my next go I needed full right rudder and also had to break steer little and I still was close to needing to abort.

I have also had it where I need a lot of left rudder to keep it straight.

Anyways from flying this plane I have learned to be on the ball during takeoff because of its random reaction.

what I would like to know is what am I missing here? why does it seem so random, what effect or what aspect am I missing?

Thanks
 
Make sure your nose wheel is perfectly straight before you bring in the power. In my twin I also hold the brakes until the engines reach 2000 rpm. That seems to help quite a bit.
 
We used to send new Airmen to base supply all the time to purchase some prop wash.

But then we had many convinced that our dial tone came in drums shipped by rail.
 
LOL flying moose!

Baron, I always crawl a few feet forward to center the nose wheel so I don't think that is it. Any other things I can look for?

I am figuring maybe something to do with that model plane, we have 3 of them and one is a 3 blade the other 2 are 2 blade but they all seem random. Actually to go one further they even fly kinda odd. hard to say, it just seems more difficult then the 172 I started on.
 
Tim, I have sent new Airmen to get exhaust gas samples with a trash bag for f-16's a few times :)
 
It depends on how your pulling up and the speed your climbing out.

The higher your airspeed the less right rudder the plane will require. This happens due to the change in AoA and airflow over the airframe.

If your pulling up too abruptly then the gyroscopical effects of the prop (depends on the weight of the prop too) will counteract the aircraft's left turning tendencies therefore you will not need right rudder.

Try to do a uniform pull up every time and climb out at the same speed, see if that will help.
I flown a DA40 and don't really remember any problems with left turning tendencies.
 
I will have to tell the one the central phone plant people used to pull on the wives of some of our squadron members. Heading out for some errands now maybe afterwhile.

Where were you stationed?
 
kalabaddon said:
LOL flying moose!

Baron, I always crawl a few feet forward to center the nose wheel so I don't think that is it. Any other things I can look for?

I am figuring maybe something to do with that model plane, we have 3 of them and one is a 3 blade the other 2 are 2 blade but they all seem random. Actually to go one further they even fly kinda odd. hard to say, it just seems more difficult then the 172 I started on.
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The number of blades will have an effect.

Yes, the plane is very different from a 172.
 
Also DA40's are more sensitive to crosswinds on the takeoff run due to the castering nosewheel, you might be feeling the effects of random crosswinds vs. P-factor.

The composite props are pretty light, I don't remember ever feeling much in the way of gyroscopic effects.
 
Sac Arrow said:
Also DA40's are more sensitive to crosswinds on the takeoff run due to the castering nosewheel, you might be feeling the effects of random crosswinds vs. P-factor.

The composite props are pretty light, I don't remember ever feeling much in the way of gyroscopic effects.
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Yes, that's a good point regarding the xwind. DA40 will certainly be affected by it on the take off roll. Another reason why that's going to be effective in the 40 is the big V-stabilizer.

Not all 40s have a composite prop, nothing stopping the operator from putting a metal one on.
 
tmyers said:
We used to send new Airmen to base supply all the time to purchase some prop wash.

But then we had many convinced that our dial tone came in drums shipped by rail.
Click to expand...

We have sent new airman over to corrosion to get some id10t.

Worked every time.
 
MachFly said:
Yes, that's a good point regarding the xwind. DA40 will certainly be affected by it on the take off roll. Another reason why that's going to be effective in the 40 is the big V-stabilizer.

Not all 40s have a composite prop, nothing stopping the operator from putting a metal one on.
Click to expand...

Yeah the metal prop models may be a bit different there. Also newer models have a slightly larger rudder. The model I flew seemed a bit lacking in rudder authority.
 
Sac Arrow said:
Also DA40's are more sensitive to crosswinds on the takeoff run due to the castering nosewheel, you might be feeling the effects of random crosswinds vs. P-factor.
Click to expand...
...and in a stiff crosswind, the weather-vaning effect can overcome the torque/p-factor/spiraling slipstream effects. This is true of all the castering nosewheel planes including the Diamonds, Cirrui, and Grummans.
 
Other than being sure the tires are all correctly inflated, the brakes aren't dragging and the mechanic set the caster friction right there isn't much to be done other than just do what it takes to keep the nose pointed down the runway.
 
Used to send apprentice machinists to the tool crib for a bolt stretcher. They would usually come back and tell me I didn't specify the thread and the tool crib guy needed to know. This could go on for several trips. When that got old, we would send them to the power plant for a bucket of steam so we could steam clean the machine tools.

Cheers
 
OP, maybe you're shoving the throttle in on some take offs, and easing it in on others.

That may account for some squirreliness. :dunno:
 
Tarheelpilot said:
it could be the fact that you are flying a diamond aircraft. Never liked them myself. especially the ones with the 912 engines.
Click to expand...

I really like the DA-40. It's got more speed than every other IO-360 aircraft I've flown. The fact that it has tubes for control linkages vice pulleys and cables to the ailerons makes it feel much tighter in roll. It's got some quirks: the long wings make it not a pleasant ride in thermals and the nose gear is weak. Overall, it's a nice change of pace from Pipers and Cessnas
 
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Machfly, this is all withen the first 1/2 of takeoff before wheels off the ground.

Tim, Misawa 13th, and Shaw 79th

Action, the day I talked about there was no crosswind, wind sock was not even wavering

Off Field, I may have done that, will have to watch how I handle the throttle on takeoff next few time to see if i vary it.

Tarheelpilot, its a 360, same as the 172 i started in, but got to say the diamond seems to perform much better with it!

Hook Dupin, I remember a nasty day where I would hit a updraft and cut throttle 100% and nose down and still be gaining alt and then the next moment I would 100% throttle and raise nose and loose alt. as a new pilot that was really disconcerting to me!!!


here are some take off and landings that day.

Takeoff
Landing
 
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yes it is a personal problem. I just don't like the airplane. As wonderful as I am even I don't think I know whats best for everyone else. ;) I do not think my personal preference has any bearing on facts of the aircraft performance or wether or not anyone else should agree with me. Didn't intend the initial post to imply that.

The whole temperature limitation on the airframe gave me the creeps too. I'm just old fashioned i guess. Actually I'm not a fan of any of the new composite airframes.

To address the op's actual question....

I have instructed in the da series aircraft a little. ~300 hours in the type. I never experienced what you are talking about in calm winds. When it was windy there were times when it behaved similar to what you are describing. Thats my best guess.

Good luck
 
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kalabaddon said:
here are some take off and landings that day.

Takeoff
Landing
Click to expand...

One instructor's thoughts...

The landing looked very "flat" to me.

Conditions permitting, I'd rather see the mains touch first (they did), but with the nose up a lot more - and then held off the runway a lot longer. In many small GA Aircraft maybe 3 or 4 seconds or even longer, coming down only after it can't be held off any more with the stick. I only have a smidgen of time in DA20's and DA40's, but I don't recall anything in particular odd about their takeoff or landing characteristics.

Anyway, to help visualize, fast forward to about 3:45 in the video below to see what I think your goal should be.

http://youtu.be/dhauE4oUeE0
 
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Winds will have more effect during the rolling portion of a takeoff than the theoretical effects of P factors, slipstream, etc. And, the wind effects can change as you trundle down the runway - I have seen the wind blowing in opposite directions at points a couple hundred feet apart (most common on light wind days with thermal activity). Just do what you need to do to keep it straight.
 
The crosswind component is probably the only thing that varies from takeoff to takeoff, so it's likely to be that. I finished my PPL in the DA-40 after starting in the DA-20.

I'd vote for weather vaning.
 
cool, Coma, how much different was the flight handling of the DA-20 vs 40? My school is getting some 20's in and I thought I might start using those if they fly similar to the 40.
 
I failed my checkride yesterday because I could not control the nose of the DA40 :-(
Every takeoff or landing is different (over 200 so far), I am almost always drifting to the left side no matter how much is the crosswind or how hard I press the right rudder whether it is takeoff or landing. Any ideas?

Guess what, I was fearing gusty crosswinds, it so happens that the day of the checkride there was barely 4~5 kts of winds but than these "thermals" started in our area. I flew just a day before and handle almost 13 knts of xwnd component and feeling good but these thermals threw me off, already nervous with DPE, than somebody cut me off in the pattern, botched my landings because I was bounced around, in other words everything that could go wrong had gone wrong for me but he failed me because I drifted to the left during takeoff and landings. Which means I have work on my rudder control. During takeoff and landings I feel like a fish with my rear wagging left and right. Any ideas from more experienced pilots please who are familiar with DA40-XLS? Thanks
 
Sohail said:
I failed my checkride yesterday because I could not control the nose of the DA40 :-(
Every takeoff or landing is different (over 200 so far), I am almost always drifting to the left side no matter how much is the crosswind or how hard I press the right rudder whether it is takeoff or landing. Any ideas?
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I would guess that your sight picture is off - you are trying to keep the center of the cowl pointed at the end of the runway which makes you drift left.
 
Sohail said:
I failed my checkride yesterday because I could not control the nose of the DA40 :-(
Every takeoff or landing is different (over 200 so far), I am almost always drifting to the left side no matter how much is the crosswind or how hard I press the right rudder whether it is takeoff or landing. Any ideas?
Click to expand...
Get some training with an instructor with a lot more experience in castering nosewheel planes like the Diamond, Grumman, and Cirrus. Work on proper control positioning prior to and after touchdown for landings, and continuing to fly the plane with all available controls after touchdown all the way until you stop.

For takeoffs, work on runway alignment before brake release and control positioning and brake use after brake release. Two tips that will help a lot on takeoff are:

  1. Lining up on centerline but pointed about five degrees to the right before applying throttle, and
  2. Stopping on the runway, holding the brakes, and advancing to 1800 RPM before releasing the brakes.
I've found both of these to be very effective in aircraft like these for keeping the plane close to centerline on takeoff until the rudder becomes effective.
 
Thank you Capt Geoff and Ron. A dumb question.. so I am at the numbers in DA40 on the left seat looking down the runway centerline, should I push the right rudder all the way before pushing the throttle or only push the rudder in reaction to turning left. About the sight picture, I understand what you said is to start my roll a bit towards right, but what about the rudder? Leave it neutral or keep it pushed to the right? If my understanding is correct, rudder will not be effective at least until I reach 10~15 knots, so should I be using right brake instead?

I will try #2 in my next flight to see if that works. Its like a short-field takeoff.

Thanks
 
Sohail said:
so I am at the numbers in DA40 on the left seat looking down the runway centerline, should I push the right rudder all the way before pushing the throttle or only push the rudder in reaction to turning left.
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If you are doing a standing start, and wait for the nose to yaw left before pushing the right rudder, you will be halfway to the runway edge before the rudder becomes effective. This is a point any instructor with experience in castering nosewheel planes would have taught from your first flight in the Diamond, and would not have allowed you to go to the practical test until you were controlling the aircraft properly.

About the sight picture, I understand what you said is to start my roll a bit towards right, but what about the rudder? Leave it neutral or keep it pushed to the right? If my understanding is correct, rudder will not be effective at least until I reach 10~15 knots, so should I be using right brake instead?
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If you run the engine up to 1800 before releasing brakes, the propwash over the tail will make the rudder effective almost immediately, but if not, then yes, you are going to need a tap on the right brake to keep the nose from swinging too far left. Again, something you should have been taught from the git-go in a castering nosewheel plane.

I will try #2 in my next flight to see if that works. Its like a short-field takeoff.
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A little bit, perhaps, but you're only going to 1800 RPM, not full throttle, and your handling of the pitch control and rotation will be normal, not short-field.

Thanks
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You're welcome. If you live/fly anywhere near Salisbury MD, I'd love the opportunity to do your reexamination training and prep you for the retest. As you may have guessed, I have around 3000 hours in castering nosewheel planes, mostly Grummans, but that includes about 75 hours in DA40's, too, and the characteristics are much the same in this area.

BTW, there are no dumb questions -- only unasked questions and dumb answers.
 
kalabaddon said:
I am flying a DA-40 for training and when I do my take off roll the prop-wash/torque effect seem almost random. For example during my first solo flights in pattern with next to no winds, on my first takeoff I needed almost no right rudder, however on my next go I needed full right rudder and also had to break steer little and I still was close to needing to abort.

I have also had it where I need a lot of left rudder to keep it straight.

Anyways from flying this plane I have learned to be on the ball during takeoff because of its random reaction.

what I would like to know is what am I missing here? why does it seem so random, what effect or what aspect am I missing?

Thanks
Click to expand...

Crosswinds?

The airplane will want to weathervane with crosswinds, especially after you lift the nose.

If it's gusty, you'll need to make a lot of corrections going down the runway.
 
Ron, thank you for your feedback. I trained in Leesburg and Winchester VA. I don't think it's my instructor, its me 'the clumsy guy' who is unable the grasp the fundamentals even though I have done quite a bit of solos and solo xcountry. I have about 75 hours so far and when I am alone I am extremely careful and would go around if I a little bit uncomfortable with my pattern or approach except I drift to middle of the lift half of the runway. May be I am too old to learn flying
 
Sohail said:
May be I am too old to learn flying
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No, you just haven't flown with an instructor who beats you enough when you don't use your right foot hard enough and soon enough. :D

Seriously, try my suggestions and see what happens.
 
Ron, will do and let you know. Thanks again.
 
If you are drifting left on landings, it's not due to how you line up for the takeoff or due to P factor.

How much rudder do you use? Whatever it takes. Depending on wind, it may be a little, it may be a lot. Ron's suggestions will help you get started straight, but I get the impression that you continue to drift left even after the initial roll.

If it's just a takeoff initial roll problem, then lining up and stuff will help. If it's both takeoff and landing, the problem is that you are making the airplane turn left - probably because what you think looks "straight" is actually a bit of a left turn. If you trade seats with the instructor, you will probably drift to the right because you are trying to pull the centerline of the cowl in line with your sight - but you are sitting way over to the left side.
 
Geoff, unfortunately it's both, takeoff and landings that I drift to the left... Scared the hell out of me on at least twice. Beside a heavy right foot, I am still trying to understand what visual clues I could look for while I sitting on the left based on what you said to have a reference on the cowl... What if I align the centerline right underneath my left seat and look out to the far end of the runway?
 
For me at least, it's a mental game. Get the sight picture right and allow no deviations. Use positive and confident control inputs to make the airplane go where you want it to go... Be the pilot, not a passenger, and 'show no weakness'.

Using this mindset and technique, I land on the centerline whether winds are calm or a 20 knot crosswind.
 
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Sohail said:
Geoff, unfortunately it's both, takeoff and landings that I drift to the left... Scared the hell out of me on at least twice. Beside a heavy right foot, I am still trying to understand what visual clues I could look for while I sitting on the left based on what you said to have a reference on the cowl... What if I align the centerline right underneath my left seat and look out to the far end of the runway?
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If you are always going to the left, then you are making it go left.

I've never sat in your airplane so I can't say "line up with the third rivet" or something like that - but obviously, the nose needs to be further right than you think it should - the spinner will look like it is somewhere to the right of the centerline You can put the centerline between your legs - that works for at least some people.
 
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