Are Vertical Stabilisers on enclosed gyros large enough

[asra]

Hi guys,whilst i have been around aircraft almost all of my life...i am no expert. I have only flown hang gliders and lots of model aircraft.I have wondered this for a while, and since im going to get back into flying powered stuff i havent decided on paramotoring or building a new gyro...however...i notice in looking at photos online, it seems like almost all of the pod design aircraft have their aerodynamic center of gravity on the fuselage way in front of the centre of rotation. Doesnt this tend to make it difficult to keep enclosed machines flying straight?

[Greg Mitchell]

Hi guys,whilst i have been around aircraft almost all of my life...i am no expert. I have only flown hang gliders and lots of model aircraft.I have wondered this for a while, and since im going to get back into flying powered stuff i havent decided on paramotoring or building a new gyro...however...i notice in looking at photos online, it seems like almost all of the pod design aircraft have their aerodynamic center of gravity on the fuselage way in front of the centre of rotation. Doesnt this tend to make it difficult to keep enclosed machines flying straight?G"Day Adam,I see your question still outstanding.......The answer to your question is YES if the said gyroplane reacts by turning into the prevailing wind. If there is enough plate surface area behind the center of pressure to counter that plate area in front, then the aircraft will weather **** as it should.If there is insufficient or inadequate vertical tail surface, then you will have problems.Even single place gyros with pods up front have been known to "swap ends" due to insufficient vertical tail surface.Most modern day gyroplane designs have adequate vertical and horizontal tail surfaces to effect the correct restoring moments.Perhaps one of the ASRA Technical Officers/Training Officer will comment further.Hope this helps.Cheers,Mitch

[Adrian S]

Adam,The Australian/ASRA design and construction standards mandate flight testing to prove adequate directional stability in all critical phases of flight including engine out autorotations so there should not be any gyro"s registered in OZ that have such a problem. This said as a ASRA TA I have had a number of homebuilts presented to me for inspection that needed modification in this area. Like you I have seen many photos of gyros both homebuilt and "factory" that originate outside of Australia that appear that they may not be able to comply with our stability standards.Please ensure a experienced ASRA Technical Adviser reviews any design or gyro before you commit your hard earned money.Unfortunately a year doesn"t go by where I am asked to inspect/review a gyro that doesn"t comply with one of our standards. These standards are there to save lives and unnecessary injury.Just my 10c worth,Adrian S

[Greg Mitchell]

Adrian said:

[bosca]

Really Greg!!Confidentially has not worried you before??.What has changed??

[Brian]

Hi guys,whilst i have been around aircraft almost all of my life...i am no expert. I have only flown hang gliders and lots of model aircraft.I have wondered this for a while, and since im going to get back into flying powered stuff i havent decided on paramotoring or building a new gyro...however...i notice in looking at photos online, it seems like almost all of the pod design aircraft have their aerodynamic center of gravity on the fuselage way in front of the centre of rotation. Doesnt this tend to make it difficult to keep enclosed machines flying straight?Depends a bit but roughly speaking, pod machines[ 2 place, side by side] usually benefit greatly from having winglets on the stab. Looks better too. Seems having doors off creates less problems than having doors on.TA"s opinions do vary greatly, this should not be the case but it is happening. Steps are in the pipeline to address this very frustrating situation.

[Greg Mitchell]

Depends a bit but roughly speaking, pod machines[ 2 place, side by side] usually benefit greatly from having winglets on the stab. Looks better too. Seems having doors off creates less problems than having doors on.TA"s opinions do vary greatly, this should not be the case but it is happening. Steps are in the pipeline to address this very frustrating situation.Thanks Chopper.I understand there are programs in place to try and standardise TA"s opinions and understanding of gyroplane physics and mechanics, design and construction materials. Simply wanted to give a heads up on gathering that required opinion/s.Cheers,Mitch

[Greg Mitchell]

Really Greg!!Confidentially has not worried you before??.What has changed??

[bosca]

Greg you have absolutely no intelligence.

[Waddles]

Is this sort of thing really necessary here?Waddles.

[Waddles]

Gidday Adam,From your post, you seem to be looking at this issue from a purely theoretical aspect. Whilst it is true that there are "recipes" to address issues such as these in the planning stages, the proof is always in the pudding, as they say. Both Adrian and Brian allude to this fact. Aesthetics and pure looks are not always the best indicator of satisfactory in-flight performance.I"m not really sure what you mean by "centre of rotation", but for this expose, I"ll assume you mean the point about which the gyro yaws, that is the nose moves from side to side. We call this point the centre of mass (CoM) and it is used for many references in the gyro world.To get a theoretical solution to your problem, and very basic idea can be obtained simply by taking a side on photo of the gyro you are interested in. You most likely won"t have the position of the CoM, but it can be estimated. If you hung the gyro from the highest point on the mast and dropped a line vertically down, the CoM will lie somewhere along this line. This procedure is termed a hang test. Now, ASRA recommends that a gyro hang in the range of 9* to 12* nose down. For ease of drawing, let"s assume a hang of 10*. As most gyros are set up such that when in normal cruise the keel is horizontal, if we drew a line at 80* to the horizontal such that the line passes through the highest point of the mast and intersects the plane of the keel forward of the mast at 80*, this is our hang line (theoretical in this case).Next comes the real guessing. You need to estimate the total area of the section of the gyro that lies in front of the hang line. To do this it is easiest to draw a rectangle or square around this area and divide that shape up into smaller squares of known dimension, if possible. Otherwise, just choose a dimension on the photo. As long as you use the same scale for the forward as well as the aft sections, the relativity should be the same. Having done that, estimate where you think the forward centre of pressure will be ( no known tips for this one!). Mark it and measure the distance from this point to the hang line making sure that you measure parallel to the plane of the keel.Now repeat the procedures for the aft section. With these figures to hand, multiply the forward area by the distance between the hang line and the forward centre of pressure and you have a theoretical "fueslage volume". Repeat this for the tail section and you have a "tail volume". If the tail volume is larger than the fueslage volume, theoretically the gyro will by dynamically stable in the yawing plane in normal flight. All well and good in theory, but it is the test flight that is the real proof.Hope this helps.Waddles.

[jumeau]

i have built 4 enclosed pod machines,my way around determining if the tail is sufficient is to hang her up in a tree or whatever with no obstruction to a very stiff breeze and see which way it points, with the pods doors on or off,and curved surfaces of the cabin there is no set calculation will tell you how big that tail has to be ,every machine i have found is different, its just trial and error, i think a lot of pilots have walked away from bad crosswinds because we can land into wind with no roll,burren junction with a winter westerly comes to mind, landing sideways in a strong crosswind is not an option,

[Russell]

Gidday Adam,From your post, you seem to be looking at this issue from a purely theoretical aspect. Whilst it is true that there are "recipes" to address issues such as these in the planning stages, the proof is always in the pudding, as they say. Both Adrian and Brian allude to this fact. Aesthetics and pure looks are not always the best indicator of satisfactory in-flight performance.I"m not really sure what you mean by "centre of rotation", but for this expose, I"ll assume you mean the point about which the gyro yaws, that is the nose moves from side to side. We call this point the centre of mass (CoM) and it is used for many references in the gyro world.To get a theoretical solution to your problem, and very basic idea can be obtained simply by taking a side on photo of the gyro you are interested in. You most likely won"t have the position of the CoM, but it can be estimated. If you hung the gyro from the highest point on the mast and dropped a line vertically down, the CoM will lie somewhere along this line. This procedure is termed a hang test. Now, ASRA recommends that a gyro hang in the range of 9* to 12* nose down. For ease of drawing, let"s assume a hang of 10*. As most gyros are set up such that when in normal cruise the keel is horizontal, if we drew a line at 80* to the horizontal such that the line passes through the highest point of the mast and intersects the plane of the keel forward of the mast at 80*, this is our hang line (theoretical in this case).Next comes the real guessing. You need to estimate the total area of the section of the gyro that lies in front of the hang line. To do this it is easiest to draw a rectangle or square around this area and divide that shape up into smaller squares of known dimension, if possible. Otherwise, just choose a dimension on the photo. As long as you use the same scale for the forward as well as the aft sections, the relativity should be the same. Having done that, estimate where you think the forward centre of pressure will be ( no known tips for this one!). Mark it and measure the distance from this point to the hang line making sure that you measure parallel to the plane of the keel.Now repeat the procedures for the aft section. With these figures to hand, multiply the forward area by the distance between the hang line and the forward centre of pressure and you have a theoretical "fueslage volume". Repeat this for the tail section and you have a "tail volume". If the tail volume is larger than the fueslage volume, theoretically the gyro will by dynamically stable in the yawing plane in normal flight. All well and good in theory, but it is the test flight that is the real proof.Hope this helps.Waddles.GEEEEEEESUS..........ask and you will be told, ( i take it reading in bed at nights improves knowledge )........bloody hell, i sleep ( after obligations ) Al ol son.........you is deadset a well of knowledge................second only to the mistro of "homebrew" liquid amber ;D ;D

[Brian]

GEEEEEEESUS..........ask and you will be told, ( i take it reading in bed at nights improves knowledge )........bloody hell, i sleep ( after obligations ) Al ol son.........you is deadset a well of knowledge................second only to the mistro of "homebrew" liquid amber