Short Field Take-Offs

[Adam H]

Being spoiled by my home-airport being an airport with a couple thousand foot runway, I’ve never spent much time practicing short field take-offs. Well, a friend of mine is thinking about putting in a grass strip at his home in the country and we’ve gotten down to the nitty-gritty stage where we need to figure out how long of a runway we need and whether or not this project doable. We’ve got 450 feet to work with, grass.
I took 4 measured short-field take-offs yesterday and averaged about 300’. That was off pavement, so my first question is how will that translate to grass? I don’t think it will make that big of a difference, but I’d like some feedback from some guys who do short field take offs from both hard surface and grass.

My second question is about my technique. I don’t have a rotor-tach so I can’t give hard numbers, but I can tell you what I’m doing. My machine is a stripped down Gyrobee with a 503DC and a Wunderlich prerotator and 23’ Dragonwings. I’m holding down my scrub brake and prerotating up to about 3500 engine rpm at which point the blades are singing along pretty good. I’m keeping full back stick and it only takes a few feet for my front wheel to come off the ground. Here’s the part where I have a question; if I keep full back stick and full power, the blades start to shake so then I flatten out the disk for a second or two, ease up on the throttle, pick up a bit more groundspeed and pump the stick back again, still the blades shake so I flatten out again, by the third try, the blades feel good and I take off.

I’m wondering if this is a normal short field take off procedure or if I’m doing something wrong?

[StanFoster]

Adam- In my opinion, there isnt much runway left for errors made in taking off. A good pre-rotator of course is a must. You need a go-no go point...and then enough time to stop after that point if you abort. I know most of the time it will work, but sometimes it wont.


Stan

[Chuck Roberg]

First off people need to know the Dragon Wings are new on Adams gyro. He had a set of Bensen blades before.

Sounds like your trying to use the DW's the same way as your old Bensen blades. The DW's are a lot more sensitive at lower RRPM's to too much air being forced thru them. The Bensen blades are a lot more forgiving in that respect.

Seems like your right on the edge of rotor flap. It can easily progress into rotor flap if you continue what your doing. Try coming in with throttle more slowly. Your trying to force too much air thru the blades before they are up to speed.

What happened to the bicycle rotor tach you used to have. I think it's time for a new bike tach so you can see what's happening and at what speed. Do this before you end up needing a new set of blades.

A grass runway can add 15% or more, depending on the grass length, to your take off roll.

[Alan_Cheatham]

My suggestion is go down to WalMart and purchase a $10 Schwinn digital bike speedometer and install it as a rotor tach, then get some real world numbers as to what your prerotator is doing as it's capabilities is going to greatly determine your short field performance.

.

[Adam H]

I'm already working on getting a new bike speedo/tach hooked up. Thanks for the feedback!

[Resasi]

I’m keeping full back stick and it only takes a few feet for my front wheel to come off the ground. Here’s the part where I have a question; if I keep full back stick and full power, the blades start to shake so then I flatten out the disk for a second or two, ease up on the throttle, pick up a bit more groundspeed and pump the stick back again, still the blades shake so I flatten out again, by the third try, the blades feel good and I take off.

Adam re your question, doesn't sound wrong, perhaps not as efficient as it might be and just a matter of a little more practice. Once your nose-wheel lifts you might perhaps ease the stick forward rather than continuing to hold full back stick. The idea being to allow the blades to accelerate efficiently, and not allow too much air up through the disc for the speed of the blades. The shaking you may be feeling might just be the onset of blade sail/flap indicating that you allowed a little too much airflow too quickly.

Both your actions correct when the 'shake' happens. Decreasing the disc angle and reducing power to cut down on the forward acceleration.

Consider controlling the lift-off of the nose-wheel until you are wheel balancing, and not rocked all the way back by gently easing that full back pressure you had, and, before you have given it full power. Then keep easing the power steadily in, and with a combination of feeling your way with smooth gentle forward and back stick and a smooth steady increase in power, feeding the airflow in to your rotor disc allowing it to accelerate a little more steadily than perhaps is the case now.

Think of it as two throttles. The actual throttle controlling the engine and the forward thrust, and the stick as the rotor throttle and governing the amount of air you are allowing into and through your rotor disc by the disc angle of attack

Not as easy as it sounds but might stop you having to cut back from full power and push the stick forward, then start the process over again. After a bit of practice producing a possibly more efficient short take off.

I was made to sit stationary in a strongish wind and play the disc and get the feel of what it took to accelerate it up smoothly without going into blade flap/sail. Different types of blades of course behave differently and the DW's are a little more touchy at the lower RRPM's

In my experience grass definitely does make a difference. It's length, and the surface beneath, hard dry or soft damp can produce very variable TO distances on the same strip.

Is there a prevailing wind? How heavy are you? What elevation? What temps? If there was normally a good steady prevailing wind right down a firm smooth cut grass runway around sea level and you were around 180lbs, 450' could be plenty. In other circumstances could be too short

I am sure others more experienced will add to or correct this but hope it helps.

[ckurz7000]

Adam, I believe you are wasting some runway by going back and forth with the stick until "the blades feel right". Here is my short field take-off technique:

(1) Prerotate to as high as it will go. This is about 240 rrpm on my Calidus.

(2) With the stick full aft, apply full throttle.

(3) As the nose wheel starts to get light, I push the stick forward decisively to flatten out the rotor disc.

WARNING!!! Keep a good eye on the rotor tach and watch for the rrpm not to fall below 200 rrpm !!! Because with the disc flat, the rotor will not continue to accelerate but lose rrpm gradually.

When the disc is flat, the gyro will surge forward and accelerate to Vx (90 km/h) in a matter of a few seconds. In my Calidus the rotor will, at this point, still be spinning with slightly above 200 rrpm.

(4) When the ASI shows Vx (and the rotor is spinning with at least 200 rrpm) pull back on the stick and fly the gyro off the ground.

(5) Start your climb but make sure your ASI never falls below Vx. If necessary you'll have to stay in ground effect a bit to accelerate.

The tricky part is to keep the gyro going straight on the ground while bumping along at 90 km/h. The Calidus has nose wheel steering and requires sensitive toes on the peddals. It's easier on asphalt, where the take off roll is smooth.

If the grass runway is particularly rough, I may not accelerate all the way to Vx but rather only to about 70 km/h. At that speed, the gyro will lift off alright but you need to accelerate in ground effect before climbing away.

-- Chris.

[GrantR]

Adam,

How wide will the runway be? If it is wide enough to amke a turn with the baldes spinning up you could always back taxi and get the blades up to speed and turn into the wind and be off in no time.

It does sound like you are about to flap the blades. On my gyro When the blades pull the nose up, I can hold full back and hold it on the tail when easing into more throttle to get the blades over 200 RRpm rather quickly. The ground roll is very slow as the rotor drag is high. Once over 200 I ease forward and balance and add power to takeoff.

IMHO 450 feet is too short for a runway any number of factors could cause you to need more space.

[Passin' Thru]

First off people need to know the Dragon Wings are new on Adams gyro. He had a set of Bensen blades before.

Sounds like your trying to use the DW's the same way as your old Bensen blades. The DW's are a lot more sensitive at lower RRPM's to too much air being forced thru them. The Bensen blades are a lot more forgiving in that respect.

Seems like your right on the edge of rotor flap. It can easily progress into rotor flap if you continue what your doing. Try coming in with throttle more slowly. Your trying to force too much air thru the blades before they are up to speed.

What happened to the bicycle rotor tach you used to have. I think it's time for a new bike tach so you can see what's happening and at what speed. Do this before you end up needing a new set of blades.

A grass runway can add 15% or more, depending on the grass length, to your take off roll.

Chuck, This is the most sensible reply so far to the question. :yo::first:

Adam, keep in mind that when the machine rocks back on the tail wheel you have instantly increased the disc AOA by at least 9°. That's good! You're catching more air which will further accelerate your blades, but you must give them time to accelerate. The rate at which they accelerate can vary wth different blades. Next time you're out, try giving a slow 3 count after rock back and before adding more power. Add power smoothly, again a slow 3 count is a good starting point and adjust with experience.

As the machine starts to accelerate, ease the stick foward until the tail wheel is just grazing. You will quickly feel the blades start to "bite" and the drag increase noticably. At that point, give the stick a slight forward nudge and come up balanced on the mains. The machine should then quickly lift off in ground effect. Ease the nose down and maintain about 2 feet while accelerating to best climb angle until clearing any obstacle, then get on with your fun!:D

[scottessex]

I would not feel comfortable with less that 700 ft. 450 leaves no room for error,and every takeoff will be a max effort event. What are the approaches like?
just my $0.02 your mileage may vary.

[oldsparky]

Grant has the answer to your problem, the good thing about private strips is the ability to taxi both ways, so if you are not ready for takeoff simply turn arround and taxi back at suitable speed to maintain or increase rotor speed.

If wind is present your downwind taxi will have to be quite fast to maintain rotor rpm.

most would have been taught short field takeoffs by their instructor, seems you have missed this lesson.

It is important not to place yourself under pressure to force a takeoff, if in doubt go back and start again.
good luck, I'm sure you will master this field.

flying from a private field is good value, but dont annoy the neighbours too mutch.

Cheers Bruce

[Passin' Thru]

I would not feel comfortable with less that 700 ft. 450 leaves no room for error,and every takeoff will be a max effort event. What are the approaches like?
just my $0.02 your mileage may vary.

Good point! On a hot, humid, low-pressure day gravity REALLY sux! :Cry:

[Timchick]

My KB-2 had Dragon Wings and my airfield I was flying from was grass. I tried several different techniques for getting off the ground the quickest. This was my preferred technique. I would prerotate to at least 200 rrpms. I don't know what my engine rpms were to get them up to that. When I released the brakes I would hold full aft cyclic and slowly increase the throttle. My front wheel would come up immediately but I kept the cyclic full back. It didn't take long for the rotors to drag me off the ground but I wasn't at flying speed yet. I eased the cyclic forward to stay in ground effect and if I wasn't at full throttle yet I'd give it full throttle, pick up airspeed and then climb out. I could consistently get off the ground in under 500'. What obstacles do you have past your projected runway? If you have to climb over trees a certain height that will add more to your takeoff technique.

[GyroDoug]

I know... Here I go pluggiing Butterfly Gyros again, but...

If you have a powerful enough pre-rotator (like the Butterfly's Metro Launch System) that will let you pre-spin the rotors to about 325 RRPM, you can routinely take off in about 100 ft. With that kind of performance a field that was 450 ft long would give you enough extra to be a reasonably safe airstrip. But with typical performance and a 300 ft takeoff distance there really isn't much room for error.

Anyone can accomplish the same thing you just need to design a powerful pre-rotator for your machine. (or take the easy way out and just buy a Butterfly :)

[Chuck Roberg]

Here's a Bike spedo that can be used as a rotor tach for $4.

http://www.meritline.com/14-function-bicycle-lcd-odometer-speedometer---p-35788.aspx?source=nl100716&hq_e=el&hq_m=2008276&hq_l=64&hq_v=07159c9c8a

[GYRO J]

YouTube - grass strip (http://www.youtube.com/watch?v=RP7N2xBC99I) 450ft is a bit short depending on what is at both ends

[scandtours]

You need to know/practice " The Performance Take Off "
Much is covered by Chris (ckurz7000, post 7) above, and can be practiced by experienced pilots.
There are several things you must have in mind, and dangers, like flipping the gyro, and much more.

[lanichol]

Here's a Bike spedo that can be used as a rotor tach for $4.

http://www.meritline.com/14-function-bicycle-lcd-odometer-speedometer---p-35788.aspx?source=nl100716&hq_e=el&hq_m=2008276&hq_l=64&hq_v=07159c9c8a

Anyone have a picture of this tach installed on a gyro. Just curious.

[lanichol]

(2) With the stick full aft, apply full throttle.
..clip
-- Chris.

Chris, I find it interesting that magni & MT03 guys can go full throttle. The magni 16 I rode in the pilot did the same thing. It is not how I was trained with Sportcopter blades.

[Passin' Thru]

Larry, I find several things "interesting". Not the least of which is this; When the disc is flat, the gyro will surge forward and accelerate to Vx (90 km/h) in a matter of a few seconds. In my Calidus the rotor will, at this point, still be spinning with slightly above 200 rrpm.

(4) When the ASI shows Vx (and the rotor is spinning with at least 200 rrpm) pull back on the stick and fly the gyro off the ground.
I must be missing something! :noidea:

[Lee Scatt]

The biggest problem for me getting off a grass strip, was that they are not as smooth and the slightest bouncing would slow the rotor acceleration. I never had a very effective prerotator though.
Without a good stiff headwind, 450 ft is gonna be iffy.

[GYRO J]

Depends on how many rpm your prerotor will spin up the blades

[Riff Raf]

503DC and a Wunderlich prerotator and 23’ Dragonwings. I’m holding down my scrub brake and prerotating up to about 3500 engine rpm at which point the blades are singing along pretty good.

At this point your only at about 130 - 150 rotor RPM, and this all depends on you pre rotor technique.
Get a rotor tach

[PalmPilot]

(Get a rotor tach)... And a Helicopter... :D "just kidding"




Chris, "WOW" and congrats... When did you get a Calidus...
rrpm on my Calidus.
In my Calidus , The Calidus has

Mike

[Vance]

Hello Adam, I am sorry I cannot give you the answer you are looking for.

Some of the advice given here gives me enough trepidation to feel the need to post.

I feel the reason the FAA likes to define the obstruction and most people use 50 feet is because that what is important. In my opinion the point that lift off occurs is much less important than when you can clear whatever there is to clear. In my experience with different takeoff techniques the climb profile changes.

I have not flown a Gyrobee like Adams so I would not offer advice on how to horse it off the ground or the best way to clear an undefined something 450 feet from the beginning.

In my opinion the technique Adam describes invites rotor flap and makes the engine running without interruption very important to a successful aviation experience. Takeoff is a time when the engine is at greater risk of going quiet. I always fly the length of the runway in order to have the most options if the engine decides to act up. I check my altitude and that the temperatures and pressures are in the green every time I reach the half way point of a runway.

In all of the gyroplanes I have flown the feel of the rotor blades and how they are providing lift and drag has more to do with what to do next and how soon to do it then dodging the signs of impending disaster.

I love to measure progress so I love consistency. I feel that the least repeatable part of my flight is the take off.

I have found the wind and the air density can easily make a significant change in the take off performance at the same airstrip.

Santa Maria, KSMX has a 6,000 foot runway. Depending on where I start, the extremely localized conditions can affect my lift off distance by as much as 40%.

Oceano, L52 has some winds that can change my lift off point by as much as 50% and they have a bunch of houses at the end of the 2,325 foot runway. My climb out profile changes radically with technique and conditions.

I feel that Adam makes an excellent case for training with a CFI on a grass strip so the CFI can watch what is actually happening rather than offer advice based on Adam’s incomplete descriptions. I have found that a good CFI can ask questions that will get me to think about things I may have missed and pointed in a better direction.

I am sure I could fly the Predator off of a 450 foot grass strip. I would not because the reduction in options if things don’t go as planned and the increased variables with the condition of the surface would take the joy out of it for me. I won’t fly off of a runway that isn’t at least twice as long as my lift off point.

I hope I have not offended anyone with my strong opinions.

Thank you, Vance

[Resasi]

Since your strong opinions are based upon sound judgement and good common sense I doubt that they would offend anyone Vance.

On the contrary an excellent post with sound advice.

[RotorTom]

With a powerful pre-rotator and sound throttle application, I like to treat all take-offs (and landings) as "short fields". If it is NOT a short field I simply fly low level to check power and gauges. If there is an obstacle, I adjust rate-of-climb (or descent).

I do this to keep short field skills sharpened (which can also be used in emergencies).

[ckurz7000]

Larry, I find several things "interesting". Not the least of which is this;
I must be missing something! :noidea:

Can you tell me what is baffling you so that I can elaborate a bit more? I guess it is the point of accelerating while the rotor is free wheeling with a flat disc.

Generally, the point is to get the gyro moving at flying speeds as quickly as possible. This takes a lot longer when the rotor is being used as a drag chute. Therefore, if you have the luxury of a powerful prerotator, you can spin up the rotor to a point high enough so that it won't decay below 200 rrpm while you are accelerating with an essentially flat rotor disc. At the end of this maneuver you find yourself moving with about 80 km/h and a rotor spinning with 200 rrpm. There is nothing unsafe about this, when you then gently pull back on the stick and lift off normally.

The danger comes in when you let the rotor decay below 200 rrpm or the ground is too rough for taxiing with that kind of speed.

!! Mind you, this is not a maneuver I recommend practicing without having a CFI look over your shoulder. However, if performed correctly, it will get you off the ground quickly and safely !!

-- Chris.

[ckurz7000]

(Get a rotor tach)... And a Helicopter... :D "just kidding"




Chris, "WOW" and congrats... When did you get a Calidus...


Mike

Hi Mike, I got the Calidus about 2 months back. It is truly a great machine that hits my sweet spot. So far I have only about 25 hours on it. The longest cross country so far in the Calidus was 500 miles and I enjoyed every minute of it. The rest of the time I spent exploring its envelope and making some measurements. It's been great fun so far.

-- Chris.

[Passin' Thru]

Can you tell me what is baffling you so that I can elaborate a bit more? I guess it is the point of accelerating while the rotor is free wheeling with a flat disc.

Chris, first off, I have no wish to be contentious or argumentive. It’s simply that your description does not fit my experience. I am dismayed that you can accelerate to that velocity on the ground with such relatively low rotor RPM and a flat disc. Are you saying that you can lift off with blade speed that low? Considering the advancing – retreating blade lift differential, the flapping angle must be close to the hitting the stops. Relative wind head-on to the leading edge does nothing for accelerating the rotor rotational speed.

I gain most of my rotor flying speed while rocked back, feeding air into the rotor (make a wing) and then lower the disc a bit for forward acceleration to lift off. I think the drag you refer to is the affect of the rotor developing full autorotation and significant lift. When I feel it really “catch” ( or as Vance says, start to “bite”) that’s the signal the blades are ready to fly. Full power , lower the nose, slip up on the step (sort of like water skiing) and you’re flying under full control while accelerating to Vx or Vy. It accelerates much quicker when those silly wheels clear the ground! And much less wear on the tires!

In the past 38 years and well over two thousand hours I have flown a considerable number of gyros, both mine and others, but I have never flown a “factory built” gyro. These were all experimental homebuilt, generally light weight open frame machines. A number these were Maiden flight of newly completed machines where I helped the owner – builder adjust and trim the new machine for best flying.

I am well aware that all gyros fly a little different, but I have never even approached 80kph (~50mph) with a gyro on the ground. I am off at 25 – 35 mph depending on air density. The majority of my gyro flying has been off cow pastures, goat paths, ect. About the only time I use hard surface is when testing a new machine or major modification.

Talk this over with your instructor and try it, you just might like it!

[twistair]

Here’s the part where I have a question; if I keep full back stick and full power, the blades start to shake

It's hard to guess what may be the reason for them to do so. If rotor has good rpm then full back stick and full throttle load rotor lifting a nose wheel. But there isn't any apparent reason for shaking. Probably if you add full throttle and prerotator is still engaged then this shake is caused by mast vibrating from the prerotator loads.
Anyway adding full throttle right from the start isn't good habit. I use slightly different sequence on gyros with flex shaft pre: after prerotating release brakes and move stick full forward so gyro starts to move with pre still engaged and engine rpm are still same (otherwise you overload flexshaft). After it has some forward speed (5-10 mph) release prerotator and add throttle to see that rotor rpm increase. 200-220 rrpm is enough to add full power but this is for 27-28' DW rotor. Don't know for smaller DWs.
Anyway rotor tach is good thing for gyro and - to me - necessary if you want to train shortest TOs.

[Doug Riley]

I wouldn't fly routinely from a 450-foot strip. I might drop in occasionally to socialize, if (1) it wasn't too hot/humid; (2) the approaches were clear and landable and (3) there was a nice breeze down the runway to provide some insurance.

A gyro takeoff is about building up energy -- mostly rotational energy in the rotor, and secondarily airspeed of the whole craft. The key to max-performance takeoffs is taking full advantage of the prerotator while also continually extracting the maximum usable power from your engine. To do so on grass:

Do your stationary pre-spin into the wind, to as high a throttle setting as your brakes (or calf muscles) can stand. With the prespin engaged hard, this is apt to be 4500-5000 with a Wunderlich and a 503. The blades should be at or near 200 RPM -- they should not be likely to flap. Keep the stick all the way back.

Leave throttle where it is and the prespin engaged, release brakes and start rolling. The prespin will act as a governor on the engine, keeping it from pushing you so fast that you overrun your blades. But do back off if you feel any flap. Keep stick all the way back.

When the nose pops up, put it back down with the stick to a balanced position, allow speed to build (it will, because your drag is now lower). Then release the prespin. The engine will surge from the lightened load (back off throttle a little if this is alarming, but after some practice you can keep the throttle open). You should have flight speed and full throttle, and can lift off.

If you are not used to keeping the prerotator engaged after you start rolling, practice it at lower power and very low ground speeds. The prerotator prouces a fair amount of torque that will yaw you toward the right side of the runway. You need to compensate for it with rudder -- your nosewheel steering will be useless almost the moment you start rolling, because the nose is ready to come up. Make sure that your rudder authority is adeqate to handle this torque effect, on top of the yaw created by the slipstream hitting the tail.

This is an advanced technique. Don't try it unless you have 100 hours or more, or dual training specifically in this technique (some instructors normally use a more gradual takeoff method on training flights). Work up gradually to more aggressive use of prerotator and power; back off power if anything feels as if it's getting away from you.

[greg spicola]

Yep! To what Doug said.:yo:

[RotoPlane]

Some may have had similar instruction as Doug's post #33 many flying hours ago and may fly routinely from a long hard surface. When the time comes that you know you will need to do such a short take-off…it is comforting to know you have this excellent instruction handy for review and it should be in the training section. Hopefully someday this section will have many such clearly written instructions for both special and "mundane" flight activities. I even understood it…….thanks Doug!

[MrGrey]

If anybody has good video of the Time to Climb Contest from Mentone 2009 you could see a textbook short field take-off that I used in team Bisers Dominator. If you can get DW's to 200 RPM I would bet any money you won't flap em w/ a 503. I fly 50-75% of the time now off a grass strip and I know ya personally Adam and your machine.....450ft isn't enough for ya. Your 447 bee w/ DW's took 1200 ft at Bass Lake if you remember flying with me there. If you're gonna practice soft field and test whatcha need, come out to Knox and lets see what she can do. I got 2200' of soft field to play around with.

I had a bee too and the suspension sucks and its hard to tell what your blades are doing when you are getting your ass kicked on a homemade runway. NEED a rotor tach especially when learning. Good Luck and can't wait for Mentone!