Rough Field Take Off

[Runtoeat]

I have recently been working with a rough field take off technique which my friend wanted to try out. Conventional rough field takeoff uses 15 flaps and requires one to hold the stick back and allow the aircraft to use high angle of attack (low tail) to gain enough lift to "pop" off the ground. The nose is dropped to gain enough airspeed to start a normal climb out. This method can allow the tail to contact a bumpy terrain and also takes some distance to get off the ground. Our idea is to lift off from a rough grass field in a minimum distance and at a level attitude. In order to do this, we are using full flaps (35 for CTLS and 40 for CTSW) and holding the stick back on initial roll. As the plane begins to lift off, which occurs at around 35kts, one relaxes the stick back pressure to just keep the front wheel off the ground. In another few kts, as soon as the main gear starts to skip off the turf, back pressure is relaxed and when the mains are off the turf, one needs to immediately put significant forward pressure on the stick to hold the plane within a couple feet of the ground and allow it to build airspeed. Once the airspeed gets to 50 to 55 kts, flaps are reduced one notch and the stick is adjusted for 60 kt speed. Once at 60 kt, another notch of flaps is taken away and the climb out is done at 15 flaps and 60kts. During the initial take off stage, the aircraft has high drag and an engine problem would result in a very quick loss of altitude so by being close to the ground, one should be able to land if required. But the trade off for having max flaps is that the aircraft develops lift and reduces harsh input on the gear almost immediately after initial roll and then lifts off the runway at a very short distance and at a level attitude. The feeling is almost like being on an elevator. The CT just rises off the runway all the while at a level attitude. With a little bit of head wind, the vertical lift effect is pretty amazing.

[CT4ME]

'would love to see this on video... would be really neat with wingcam showing gear, and one showing backwards

tim

[josjonkers]

I wouldn't do it like that. I go +15 and get the nose off and accelerate and then pull it it ground effect and let it accelerate further. Seems pretty risky with >15 degrees flaps.

[Jim]

I'm not sure what the risk would be. I've done several go-arounds with the flaps at 40. The plane shoots up like a helicopter.

[Runtoeat]

Josjonkers, my friend started thinking about this full flap method after departing a rough field that also had undulating terrain. We called these undulations "woop-dee-doos" in my dirt bike days. In this instance, the take off was done with the standard 15 flaps and nose was held off with high angle of attack to get airborne at low air speed with intent to drop the nose immediately once off the runway to build speed to 60 kts. What occured though was a tail strike caused by launching off of a woop-dee that was spaced close to the next woop-dee. The CT was launched without enough airspeed to remain aloft and came back to the ground "tail low". (This was not a friendly field!) With this high flap method, the aircraft is in a horizontal attitude and has much more lift early in the take off which helps to prevent ground impacts such as this. As Jim points out, this take off method is not much different than a full flap aborted landing and go-'round". Most of us have probably done a full flap aborted landing with "go-'round" and know that the first time this is attempted, the vertical rise off the runway is impressive and the need for rapid forward pressure on the stick to keep the nose low is probably not anticipated! Once one knows what's coming and realizes there is the immediate need to manage pitch attitude, it becomes easy to input proper pressure on the stick. I would like to hear if others have tried this method and get some feed back on this.

[Roger Lee]

I have done it at 30 flaps. It wasn't an issue. I would advise some not to go to the lower flap setting like 15 until you have sufficient altitude and speed above the runway. If you we're still very close to the runway you could experience a little sink and actually touch the runway again.

[Runtoeat]

Roger, your concern about sink after raising flaps is well founded. Knowing that going to 30 from 40 after lift off will result in some sink allows me to prevent most of the sink by being ready to increase stick back pressure while I'm moving the flap switch. Same seems to happen when going from 30 to 15. It must be said that I have been doing the 40 flap take offs in low wind conditions and cold temps which means I have no cross winds and have optimum engine performance. I must restate: This method may be beneficial to get one's aircraft light on it's feet and off rough ground, in a level attitude, in a minimum distance but may not be best for short field take off with obsticales to overcome. In the later case or if length of runway is unknown, the 15 degree flap departure at Vx speed is the tried and true method to use.

[FlyingMonkey]

Roger, your concern about sink after raising flaps is well founded. Knowing that going to 30 from 40 after lift off will result in some sink allows me to prevent most of the sink by being ready to increase stick back pressure while I'm moving the flap switch. Same seems to happen when going from 30 to 15.

 

Hmm...you are at low-ish speed, reducing lift (raising flaps), and increasing angle of attack all at the same time. Could be a recipe for departure stall, use caution and make sure you have sufficient airspeed. This seems like it has to be a by the numbers procedure, little room for error. Nothing wrong with that, you just have to really pay attention to what's happening and keep your eyes glued to that ASI.

[Runtoeat]

Andy, thank you for your comments. I appreciate the thoughts since I am open to any pros or cons regarding this. You are correct in that this is being done "by the numbers" but it is also being done in order to reduce the angle of attack during take-off compared to using 15 flaps. Using 40 flaps allows one to take off with less angle of attack and to keep the aircraft in a level attitude. It allows one to lighten the aircraft almost immediately off of it's gear after initial roll is started. As the aircraft lifts off the ground, it is in a nose level attitude but is also rising at a rapid vertical rate. As for "using the numbers", liftoff occurs around 35 kts. Once airborn and when above Vs0 of 39 kts, the flaps are raised from 40 degrees to 30. Note the speed is above the Vs0 stall speed of 39kts. Actually, I'm running about 42 to 45 kts at this time. What adds a good margin for safety is that the aircraft is under full throttle and the weight is ALWAYS below max. gross. Stall speeds of Vs0 (with flaps) and Vs1 (no flaps) are certified at the condition of max gross and at idle engine speed. As you point out, this exercise could end poorly if the engine should quit when the aircraft is at low speed and high drag and this thought is not taken lightly. I consider my work with this excercise is being done responsibly and not recklessly and offer this as a thought starter to perhaps be an alternative method one might want to pursue to lessen the harsh inputs to one's aircraft due to rocky, rough, undulating runways or even poorly maintained grass runways.

[FlyingMonkey]

Andy, thank you for your comments. I appreciate the thoughts since I am open to any pros or cons regarding this. You are correct in that this is being done "by the numbers" but it is also being done in order to reduce the angle of attack during take-off compared to using 15 flaps. Using 40 flaps allows one to take off with less angle of attack and to keep the aircraft in a level attitude. It allows one to lighten the aircraft almost immediately off of it's gear after initial roll is started. As the aircraft lifts off the ground, it is in a nose level attitude but is also rising at a rapid vertical rate. As for "using the numbers", liftoff occurs around 35 kts. Once airborn and when above Vs0 of 39 kts, the flaps are raised from 40 degrees to 30. Note the speed is above the Vs0 stall speed of 39kts. Actually, I'm running about 42 to 45 kts at this time. What adds a good margin for safety is that the aircraft is under full throttle and the weight is ALWAYS below max. gross. Stall speeds of Vs0 (with flaps) and Vs1 (no flaps) are certified at the condition of max gross and at idle engine speed. As you point out, this exercise could end poorly if the engine should quit when the aircraft is at low speed and high drag and this thought is not taken lightly. I consider my work with this excercise is being done responsibly and not recklessly and offer this as a thought starter to perhaps be an alternative method one might want to pursue to lessen the harsh inputs to one's aircraft due to rocky, rough, undulating runways or even poorly maintained grass runways.

 

So you are raising the AOA, but you are already pretty flat compared to the normal technique, so not a problem as long as you watch the speeds. Coolio!

[Runtoeat]

FWIW, After thinking about bush pilot videos I've seen where they're competing for shortest take-off, I figured I'd look at a few videos of them doing this. It soon became apparent that any bush pilot who happened to read my post on using flaps at take-off is probably laughing out loud about my approach to all of this.

 

This video shows a typical bush pilot short field take-off. Note the initial roll at no flaps and then just after staring the roll, the flaps come in and after lift off, the flaps go back to zero. My big experiment is nothing new for these guys. They take off like this all of the time.

 

What most of the videos I watched appear to show is a start at zero flaps to get a drag free start, then the pilots put in flaps. These guys are using a lot of angle of attack because they must typically clear obsticales. My method differes in that I keep the CT level and try to get the airplane light and off the ground in a minimum amount of distance but not worry about clearing obsticals. The other point to be made is that the CT has sufficient power to keep it flying at a high drag (full flap) condition.

[ozairangel]

Try full rpm , zero flaps, and dial in 30degrees at 40kts. up up and away

[johngpilot]

I flew a 185 in Alaska.

 

If that engine quits and you are at high gross weights the ensuing "landing" breaks things. You are relying heavily on the performance of the engine. As long as things work - they work well with these sorts of demonstrations however it is when things go wrong that you better have your logbook endorsements in order for the ensuing FAA "discussion".

[Runtoeat]

Johng, you are a voice of experience and I shall heed your warning. It is understood when the fan stops, gravity takes over. Emulating the bush pilots by gaining altitude quickly is not what I am trying to do, just seeing if it is possible to get light and break free of the ground until speeds warrant normal climb out.

 

Oz, looks like you've done some high flaps take-offs. The CT is probably like an elevator going up when flaps are brought in at 40kts. Do you think there may be an advantage going with flaps from the start to get it light on the gear compared to rolling until reaching 40kts? The CT has enough power to get itself moving and lifting with full flaps compared to most aircraft. My attempt is to use this capability to lighten up impacts with rough terrain from the very start of the take-off.

[ozairangel]

Dick ,I guess it depends on whether the issue one is trying to beat is woop de doos or just short field

[ozairangel]

Have just noticed that I have "0 warning points" listed under my name. what is that all about?? Am I going to get into trouble soon?

[Ed Cesnalis]

Zero is good, if you want to get into trouble you will need some points.

[johngpilot]

A full flap take off in a CTsw or CTLS is an elevator ride for sure.

[Anticept]

I got linked to this thread from here: http://ctflier.com/i..._120#entry26074

 

I have used the 0 to 35 technique once as a test. My concern with my CT is getting the nose gear off the ground as soon as possible, the main gear can take the terrain. In soft and rough terrain training that i was given, the nose/tail gear is what dictates the procedure. 0 to 35 mid roll out gives you a slightly shorter roll out and gets off the ground sooner, but the nosegear stays on the ground longer with greater pressure, which is the real concern. CTs have very delicate nose gear, something at must get off the ground, and stay off the ground, as much as possible. When I start with flaps at 35, I can immediately notice how much pressure is taken off the nose wheel with full back stick vs no flaps, and the rollout only needs to barely be started and you can get it off the ground. Also, when you land, you can raise the flaps before the nose touches down, and it will give you an extra second or two to keep the nose off the ground.

 

Remember that STOL competitions use aircraft with extremely strong structure in the landing gear, and are very often taildraggers that can lift the tail while in full power with brakes applied.

 

There is a mod for the nose gear in the LOA section of this forum that is probably worth considering if you do a lot of rough terrain ops.

 

EDIT: I just noticed that it was approved in July, 2007. I do not know if CTLS come with this mod included.

[Tip]

How do I get to the LOA section of this forum?

[Roger Lee]

Okay Tip, you're starting to scare me. You have 2700+ post. Shame on you not knowing where this was.

 

Look down the first section under the post on the left side and open the one that says Flight Design Letter's of Approval.

 

http://ctflier.com/i...rs-of-approval/

[Tip]

Thanks Roger and CT. I have never been able to find this. Only been around since 2007 though.

[Anticept]

It's located here: http://ctflier.com/index.php?/forum/58-flight-design-letters-of-approval/

 

Here's the nose strut: http://ctflier.com/index.php?app=core&module=attach&section=attach&attach_id=113 . I just noticed that it was approved in July, 2007. I do not know if CTLS come with this mod included.

[sandpiper]

I have never thought of the nose gear damper modification as doing much to strengthen the nose gear and prevent damage on rough terrain. if your landing surface is rough, the nose gear needs to be off the ground soonest. I have found that flaps 15 works fine. You won't hit the tail if you are paying attention and have practiced. As for popping the flaps to 30 or 40 as you abruptly rotate, that works best with manual flaps. And, where are you going to have your CT where the advantage this might, or might not, give you is needed?

[Runtoeat]

Anticept, here's my concept of what's happening when I use full flaps on takeoff. I'm not pulling back on the stick to get high angle of attack to "pop" the plane off the ground. Instead, I am just letting the plane fly when it's ready - about 40 kts. Keeping the plane level with some forward stick, my initial roll develops into a level liftoff in a very short distance and this occurs much more rapidly at 40 flaps than at 15. I actually must hold greater forward pressure on the stick as the plane lifts off to force the nose to stay level and to keep the plane a few feet off the runway as speed builds to my target 50kts. Here, I raise flaps to 15 and climb out at 60 kts. This rapid liftoff with full flaps at a level attitude takes much load off of both my nose and main gear. I am not trying pull the plane off the ground with back pressure on the stick. This would load the main gear as you point out. There is much less pounding from rough and uneven terrain because the plane gets light very quickly and is up off the runway in a very short time. On your CTLS with composite main gear, rough terrain isn't as bothersome as it is on the CTSW with aluminum main struts.

 

FWIW, the link you've posted refers to the urethane "pucks" to replace the strut spring. The retrofit kit can be obtained from FD for installation on all older CT's to replace the spring. This was done on my 2006 CTSW. There is also two different front struts for the older CT's. There is the standard strut and there is also a reinforced front strut/engine mount that was installed when one ordered the Tundra option. My 2006 CTSW, since it has Tundra option, received the reinforced front strut/engine mount.