The MiniMOB ~ RE-DESIGN STARTED.......... - Page 4

SafeLandings · Mar 10, 2009, 05:57 PM

Mike,
Just add a tail skid!! adding a wheel like the full size pushers will just increase the weight...your observations of the RPG are correct I can make the rear of the boom touch the ground..it now has a tail skid!..please remember the RPG was drawn up in an evening and built in 2 weeks

Im still tweeking it every time it goes out. I do not have the ability to draw and design things on computer like you chaps..Im still 'old school' and prefer a pencil and paper.

Regards Rich

Hephaistos · Mar 11, 2009, 03:51 AM

Hello.......

Rich, I am jealous how fast you are able to design an build a wonderful autogyro like the RPG! I think I have already spend more time with the CAD of the MiniMOB until now than you from the first sketch until the maiden flight with the RPG. The CAD makes a lot of things easier to design, like checking for collisions of the moving parts, but it takes a lot of time to do the programming. I prefer to work with pencil and paper, too, but some things are rather difficult to design on a flat surface.

I dont want to have a fourth wheel instead of the tail skid, which would be some extra-weight of course. I think of two wheels on the tail, fixed left and right to the horizontal stab. And a third, steerable wheel in front, below the battery. That would not be extra weight, instead I save weight because I dont need an axis for the two wheels anymore. But I will make a sreenshot for visualization of what I have in mind.

I am very interested about your opinion to this, because I dont have the practical experience to judge if I will get problems with this idea.

Jochen, I talked with my girl yesterday, its like I estimated, she wants me to stay home on the weekend. But I forget that Sinsheim starts on thursday and I dont go for work this week, so I will go there on friday. Perhaps this would be better, because I expect it to be not as crowded than on the weekend.

Bye
Mike

P.S.: I got my new TX yesterday. I am impressed how easy the programming is, the menues on the display are really good, so most of the things are very intuitive to program. I made some tests with the receiver connected to four older dry-cell-batteries, and with two servos moving at the same time and a little load, I had a "brown-out", a re-boot of the receiver due to too low input-voltage. I could not feel the "brown-out" on the servos, but the status-LED on the receiver indicated it. So the BEC-system for the 2,4 GHz systems needs to be really good, this adds some extra-weight, but this seems to be the price I have to pay for the luxury of not messing round with free frequencies like on 35 MHz.

JochenK · Mar 11, 2009, 04:37 AM

Mike,

I'll also be at Sinsheim on Friday. Sent you a mail.

Jochen

SafeLandings · Mar 11, 2009, 04:41 AM

Mike,
Im sorry I didnt quite uderstand what you were stating, so 2 rear wheels on each side of a lower slung Horizontal stab with a single wheel infront under your battery pack?
The first thing that I would worry about is the strength in which the horizontal stab would have to be to take a landing (well my landing!), plus the strength of the boom..to me it would be very vunerable to unessesary high loads?
The second thing would be surely it would want to ground loop?..with my pusher the rear wheels are just a tad behind the lengthways CG. Because my thrustline is above the CG this keeps the nose wheel firmly on the ground while the blades are spinning up, when they are at full(lifting) RPM the front wheel goes 'light' and starts to lift, I know for sure I can ROG at this stage without any fear of a rollover.
I just cant picture in my head that your idea will work correctly, a drawing to show your sytem would be a good idea?

Regards Rich

Hephaistos · Mar 11, 2009, 05:15 AM

Hello.........

Rich, I think you have the right imagination of what I think. However, piture will follow. Can you please explain the expression "ground loop" ? I never heard this word before and I cannot imagine what it could be.

Do you imagine something like a "stoppie" on a motorcycle? This happens when you brake to much with the front wheel. Then the rear wheel lifts, and if you dont release the front-brake, you are in trouble.

I dont fear stabilty problems for the stab. I think about some GF of 1 mm thickness, cut to shape with some holes to save weight. Because its very near to ground, covering will not be done with monocote. I think about covering with some 0,1 mm thick GF-composite. For having piece of mind with stability, I can make some FEM-analysis to check the stress on the GF for , saying, a two-G impact on one wheel.

The only problem I can imagine that it would difficult to make a "tail-low" landing. Due to my non-existing practical expirience, I cannot judge this at all.

Bye
Mike

SafeLandings · Mar 11, 2009, 08:03 AM

Mike,

We have the same problem with Autogyros and generally they roll over onto their left hand side due to the rotors not being at full RPM. This is the hardest thing to overcome with ROG Autogyros and it is what most people 'blame' for a badly designed gyro. Tail draggers are renowned for this and take a little more skill and practice to get it right, however tricycle UC gyros seem to be almost fool proof...Jochen advised me on this one and he is 100% correct.
The way you are suggesting to do your UC would create a long triangle (looking from above)...correct me if Im wrong but to me the best UC is a wider/shorter triangle. This will give you the resistance needed to stop that premature 'roll over'

..the trick is to position it in the correct place.

Through my limited experience most of the damage on my gyros is caused in the ROG phase..if you can get your UC design correct you are on to a winner with your design.
In second place for 'causes of accidents' is the dreaded orientation problem but brightly coloured surfaces can aid this ( just like Peters minimum)

Hope this helps

Regards Rich

PeterO_UK · Mar 11, 2009, 08:37 AM

Quote:

Originally Posted by SafeLandings

Mike,
'Ground Lopp' is a term used for fixed wing so I guess its the wrong term to use. Its when the model is on its take off run and it noses up prematurely and rolls over, basically because the wing has not got enough airflow over it to achieve full lift.

In full size flying a "ground loop" describes the situation when a tail dragger performs a 360 degree turn due to the pilot not countering the propwash induced yaw as the power increases.

Quote:

We have the same problem with Autogyros and generally they roll over onto their left hand side due to the rotors not being at full RPM. This the hardest thing to overcome with ROG Autogyros and it is what most people 'blame' for a badly designed gyro. Tail draggers are renowned for this and take a little more skill and practice to get it right, however tricycle UC gyros seem to be almost fool proof...Jochen advised me on this one and he is 100% correct.

I would say that comparing my Minimum (tricycle) and Rotorshape (tail dragger), the Minimum is more prone to this problem, but it might be more to do with other factors such as the large difference in size, rotor speed (Minimum spins slower), weight, .....

Quote:

The way you are suggesting to do your UC would create a long triangle (looking from above)...correct me if Im wrong but to me the best UC is a wider/shorter triangle. This will give you the resistance needed to stop that premature 'roll over'

My No 2 Rotorshape has wider u/c which helps with stopping rollover on takeoff and landing.

Quote:

Through my limited experience most of the damage on my gyros is caused in the ROG phase..if you can get your UC design correct you are on to a winner with your design.

I agree

Quote:

In second place for 'causes of accidents' is the dreaded orientation problem but brightly coloured surfaces can aid this ( just like Peters minimum)
Hope this helps
Regards Rich

PeterO_UK

mnowell129 · Mar 11, 2009, 09:03 AM

Quote:

Originally Posted by PeterO_UK

In full size flying a "ground loop" describes the situation when a tail dragger performs a 360 degree turn due to the pilot not countering the propwash induced yaw as the power increases.

This is technically correct, but not quite complete.
A taildragger is directionally unstable on the ground as the wheels are ahead of the CG. When yawed the wheels try to go backward as the CG tries to go forward. This increases the yaw moment to the point of no return, i.e. there is not enough steering force from the rudder or tail wheel to stop the yaw and the aircraft makes a circle. The problem can be especially acute when the tailwheel is off the ground but there isn't enough airspeed to have good rudder authority. So the ground loop occurs when the pilot fails to stop and correct any yaw while rolling, not just propwash. A crosswind, sticky wheel, bump, under inflated tire, misaligned wheel can all be yaw sources that will develop into a ground loop. A nose gear aircraft is directionally stable on the ground because the main wheels are behind the CG so the yaw force from the main wheels tends to straighten the aircraft out, not increase the yaw.

On a taildragger you toe the wheels in so that when slightly yawed the wheel that is yawing backwards straightens out and it's drag goes down, thus lessening the amount of increasing yaw moment by that wheel. The wheel that is yawing forward scrubs more, creates more drag and tries to create a restoring yaw moment. Thus if you keep the yaw below the toe in angle the aircraft becomes more directionally stable. However if you let the yaw get very far past the toe angle .....

SafeLandings · Mar 11, 2009, 09:12 AM

Well they you go..I was totally wrong with what I thought..sorry for the confusion and all these years my inturpretaion of a ground loop was completely wrong!!..LOL..I guess its a tip stall.

Regards Rich

Hephaistos · Mar 11, 2009, 09:13 AM

Hello Rich........

Now I know what a "ground loop" is. I know it from the flight-simulator. When the TX is trimmed correctly, no problem with this, but I have to crash several times until I have the TX trimmed to match with the simulation. I had to re-trim the cheap chinese RC everytime I connected it, I hope this will be better with the new TX.

Your explanitions are very important to improve my design, so I have to say that I am happy that you write some posts to this thread!

If I have understood your last post cerrectly, you are stating that the big problem is the ROG-roll-over, and the tail-diggers are famous for having this problem.

During ROG, the lift increases and the front wheel gets unloaded. If we have the gyro balanced, all the weight that is left now is on the two side wheels. A little more lift and the tail touches the ground. The weight is now on the tail and on the left-sided wheel, the right sided wheel gets more and more unloaded. If things go wrong, we roll over to the left about a line from the tail to the left-side wheel. In this particular situation, the lever arm from this line to the CofG will be shortened in comparision to the situation when the gyro was balanced, When the lecer arm was from the CofG to the left wheel. This effect makes the "tail-diggers" problematic to ROG. Just as the tail touches the ground, the stability is going away.

If the two side-wheels are on the tail, this thing cannot happen anymore. The front-wheel lifts off, and the lever-arm for making a roll-over stays the half of the distance between the two wheels until you take off. If the wheels on the tail have the same distance in between than some wheels below the CofG, we will lose some stability in the situation when the gyro is balanced, but we increase the stability from the point where the tail would touch the ground on the gyro with the undercarriage below the CofG.

Bye
Mike

PeterO_UK · Mar 11, 2009, 09:15 AM

Quote:

Originally Posted by mnowell129

This is technically correct, ....

"You are technically correct. The best kind of correct." A quote from Bureaucrat 1.0 in the Futurama episode "How Hermes Requisitioned His Groove Back"
http://www.geocities.com/zoidberg_fa...isitioned.html

PeterO_UK

PeterO_UK · Mar 11, 2009, 09:22 AM

Mike,

You need build a proven autogyro design and start flying it, then a lot of this stuff will become much clearer to you

I think you are suffering from a problem I often suffer from.... Over Analysis

PeterO

Hephaistos · Mar 11, 2009, 09:22 AM

Hello Peter........

Reading your post, I got almost convinced that "tail-digging" is the biggest problem during ROG. Making a larger UC in the middle is working the same way than moving the UC backwards.

When designing a UC on the back, its only recommended not to make it to small, so the stability is not decreased until the front-wheel is lifting off. This could be problematic perhaps, but I will have a close look to this.

Bye
Mike

Hephaistos · Mar 11, 2009, 09:35 AM

Hello..........

Having the right grade of analysis is also my big problem, too. I prefer to have the problems a little over-analyzed than not caring about them.
But I own the title of a "Großkreuzritter der Bundesbedenkenträgerschaft". Don´t ask this expression for an online dictionary. Its like: "if books about how to make over-analysis and worries about things nobody cares would bestsellers, he would be a rich man".

Bye
Mike

P.S.: Currently I am over-analyzing the thrust line and the design of the motor-mount. Next Screenshots are on their way.

mnowell129 · Mar 11, 2009, 11:04 AM

Mike,
A problem with design in the absence of practical experience is that every detail is equally important and it takes forever to apply the analysis to every detail. Many details on an aircraft only have to be correct to 1 significant digit, not 3 or 4. As example the roll and pitch settings need to be about 20 degrees. No amount of analysis will tell you if it needs to be 18 or 21 except flight test, so spending more than a minute or two on roll/pitch angles is non-productive. You just need something around 20, not something around 10 or something around 30. You are apparently a very bright person, but you are spending a lot of your considerable ability on details that can't be predicted that accurately.
I'm with Peter, build one of the designs that exist. Learn to fly it. Determine from practical experience what needs 3 significant digits and what doesn't. Then you can zip through the design spending effort where it's needed. This is the value of practical experience, you don't spend time over analyzing something that doesn't deserve it. It's a sure bet that even Boeing and Airbus make changes to the aircraft after a real pilot flies a real airplane, even with the money they spend on design and simulation.
My definition of engineering is "technical development in an economically constrained environment". Thus you spend resources on the areas that need it, not uniformly everywhere in the development.

Mar 11, 2009, 03:51 AM	#47
Hephaistos Tannenzäpfle-Terminator Join Date: Dec 2008 Location: Baden-Baden, Germany Posts: 397	Hello....... Rich, I am jealous how fast you are able to design an build a wonderful autogyro like the RPG! I think I have already spend more time with the CAD of the MiniMOB until now than you from the first sketch until the maiden flight with the RPG. The CAD makes a lot of things easier to design, like checking for collisions of the moving parts, but it takes a lot of time to do the programming. I prefer to work with pencil and paper, too, but some things are rather difficult to design on a flat surface. I dont want to have a fourth wheel instead of the tail skid, which would be some extra-weight of course. I think of two wheels on the tail, fixed left and right to the horizontal stab. And a third, steerable wheel in front, below the battery. That would not be extra weight, instead I save weight because I dont need an axis for the two wheels anymore. But I will make a sreenshot for visualization of what I have in mind. I am very interested about your opinion to this, because I dont have the practical experience to judge if I will get problems with this idea. Jochen, I talked with my girl yesterday, its like I estimated, she wants me to stay home on the weekend. But I forget that Sinsheim starts on thursday and I dont go for work this week, so I will go there on friday. Perhaps this would be better, because I expect it to be not as crowded than on the weekend. Bye Mike P.S.: I got my new TX yesterday. I am impressed how easy the programming is, the menues on the display are really good, so most of the things are very intuitive to program. I made some tests with the receiver connected to four older dry-cell-batteries, and with two servos moving at the same time and a little load, I had a "brown-out", a re-boot of the receiver due to too low input-voltage. I could not feel the "brown-out" on the servos, but the status-LED on the receiver indicated it. So the BEC-system for the 2,4 GHz systems needs to be really good, this adds some extra-weight, but this seems to be the price I have to pay for the luxury of not messing round with free frequencies like on 35 MHz. Last edited by Hephaistos; Mar 11, 2009 at 04:05 AM. Reason: P.S. added

Mar 11, 2009, 08:03 AM	#51
SafeLandings Registered User Join Date: Dec 2007 Location: Stourport on Severn ,Worcestershire, United Kingdom Posts: 2,142	Mike, We have the same problem with Autogyros and generally they roll over onto their left hand side due to the rotors not being at full RPM. This is the hardest thing to overcome with ROG Autogyros and it is what most people 'blame' for a badly designed gyro. Tail draggers are renowned for this and take a little more skill and practice to get it right, however tricycle UC gyros seem to be almost fool proof...Jochen advised me on this one and he is 100% correct. The way you are suggesting to do your UC would create a long triangle (looking from above)...correct me if Im wrong but to me the best UC is a wider/shorter triangle. This will give you the resistance needed to stop that premature 'roll over' ..the trick is to position it in the correct place. Through my limited experience most of the damage on my gyros is caused in the ROG phase..if you can get your UC design correct you are on to a winner with your design. In second place for 'causes of accidents' is the dreaded orientation problem but brightly coloured surfaces can aid this ( just like Peters minimum) Hope this helps Regards Rich Last edited by SafeLandings; Mar 11, 2009 at 09:12 AM.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Build Log 70g/2.5oz. dc head pusher - the Nanomum	JochenK	Auto Gyros	134	Oct 23, 2009 09:18 AM
Build Log 500 g/17.5 oz. dc head pusher - the Minimum	JochenK	Auto Gyros	214	Jul 29, 2009 11:11 PM
Build Log 200g/7oz. dc head pusher - the Micromum	JochenK	Auto Gyros	216	Mar 16, 2009 01:19 PM
12 volt DC power supply	reallynewflyer	Power Systems	15	Jun 11, 2008 10:25 AM
What Voltage and Amperage does a 12 Volt DC charger need?	Jamie-	Power Systems	3	Aug 08, 2001 01:02 AM

Mar 10, 2009, 05:57 PM	#46
SafeLandings Registered User Join Date: Dec 2007 Location: Stourport on Severn ,Worcestershire, United Kingdom Posts: 2,142	Mike, Just add a tail skid!! adding a wheel like the full size pushers will just increase the weight...your observations of the RPG are correct I can make the rear of the boom touch the ground..it now has a tail skid!..please remember the RPG was drawn up in an evening and built in 2 weeks Im still tweeking it every time it goes out. I do not have the ability to draw and design things on computer like you chaps..Im still 'old school' and prefer a pencil and paper. Regards Rich

Mar 11, 2009, 04:37 AM	#48
JochenK Registered User Join Date: Jan 2005 Posts: 1,041	Mike, I'll also be at Sinsheim on Friday. Sent you a mail. Jochen

Mar 11, 2009, 04:41 AM	#49
SafeLandings Registered User Join Date: Dec 2007 Location: Stourport on Severn ,Worcestershire, United Kingdom Posts: 2,142	Mike, Im sorry I didnt quite uderstand what you were stating, so 2 rear wheels on each side of a lower slung Horizontal stab with a single wheel infront under your battery pack? The first thing that I would worry about is the strength in which the horizontal stab would have to be to take a landing (well my landing!), plus the strength of the boom..to me it would be very vunerable to unessesary high loads? The second thing would be surely it would want to ground loop?..with my pusher the rear wheels are just a tad behind the lengthways CG. Because my thrustline is above the CG this keeps the nose wheel firmly on the ground while the blades are spinning up, when they are at full(lifting) RPM the front wheel goes 'light' and starts to lift, I know for sure I can ROG at this stage without any fear of a rollover. I just cant picture in my head that your idea will work correctly, a drawing to show your sytem would be a good idea? Regards Rich

Mar 11, 2009, 05:15 AM	#50
Hephaistos Tannenzäpfle-Terminator Join Date: Dec 2008 Location: Baden-Baden, Germany Posts: 397	Hello......... Rich, I think you have the right imagination of what I think. However, piture will follow. Can you please explain the expression "ground loop" ? I never heard this word before and I cannot imagine what it could be. Do you imagine something like a "stoppie" on a motorcycle? This happens when you brake to much with the front wheel. Then the rear wheel lifts, and if you dont release the front-brake, you are in trouble. I dont fear stabilty problems for the stab. I think about some GF of 1 mm thickness, cut to shape with some holes to save weight. Because its very near to ground, covering will not be done with monocote. I think about covering with some 0,1 mm thick GF-composite. For having piece of mind with stability, I can make some FEM-analysis to check the stress on the GF for , saying, a two-G impact on one wheel. The only problem I can imagine that it would difficult to make a "tail-low" landing. Due to my non-existing practical expirience, I cannot judge this at all. Bye Mike

Mar 11, 2009, 09:12 AM	#54
SafeLandings Registered User Join Date: Dec 2007 Location: Stourport on Severn ,Worcestershire, United Kingdom Posts: 2,142	Well they you go..I was totally wrong with what I thought..sorry for the confusion and all these years my inturpretaion of a ground loop was completely wrong!!..LOL..I guess its a tip stall. Regards Rich

Mar 11, 2009, 09:13 AM	#55
Hephaistos Tannenzäpfle-Terminator Join Date: Dec 2008 Location: Baden-Baden, Germany Posts: 397	Hello Rich........ Now I know what a "ground loop" is. I know it from the flight-simulator. When the TX is trimmed correctly, no problem with this, but I have to crash several times until I have the TX trimmed to match with the simulation. I had to re-trim the cheap chinese RC everytime I connected it, I hope this will be better with the new TX. Your explanitions are very important to improve my design, so I have to say that I am happy that you write some posts to this thread! If I have understood your last post cerrectly, you are stating that the big problem is the ROG-roll-over, and the tail-diggers are famous for having this problem. During ROG, the lift increases and the front wheel gets unloaded. If we have the gyro balanced, all the weight that is left now is on the two side wheels. A little more lift and the tail touches the ground. The weight is now on the tail and on the left-sided wheel, the right sided wheel gets more and more unloaded. If things go wrong, we roll over to the left about a line from the tail to the left-side wheel. In this particular situation, the lever arm from this line to the CofG will be shortened in comparision to the situation when the gyro was balanced, When the lecer arm was from the CofG to the left wheel. This effect makes the "tail-diggers" problematic to ROG. Just as the tail touches the ground, the stability is going away. If the two side-wheels are on the tail, this thing cannot happen anymore. The front-wheel lifts off, and the lever-arm for making a roll-over stays the half of the distance between the two wheels until you take off. If the wheels on the tail have the same distance in between than some wheels below the CofG, we will lose some stability in the situation when the gyro is balanced, but we increase the stability from the point where the tail would touch the ground on the gyro with the undercarriage below the CofG. Bye Mike

Mar 11, 2009, 09:22 AM	#57
PeterO_UK Registered User Join Date: Aug 2006 Posts: 1,375	Mike, You need build a proven autogyro design and start flying it, then a lot of this stuff will become much clearer to you I think you are suffering from a problem I often suffer from.... Over Analysis PeterO

Mar 11, 2009, 09:35 AM	#59
Hephaistos Tannenzäpfle-Terminator Join Date: Dec 2008 Location: Baden-Baden, Germany Posts: 397	Hello.......... Having the right grade of analysis is also my big problem, too. I prefer to have the problems a little over-analyzed than not caring about them. But I own the title of a "Großkreuzritter der Bundesbedenkenträgerschaft". Don´t ask this expression for an online dictionary. Its like: "if books about how to make over-analysis and worries about things nobody cares would bestsellers, he would be a rich man". Bye Mike P.S.: Currently I am over-analyzing the thrust line and the design of the motor-mount. Next Screenshots are on their way.

Mar 11, 2009, 11:04 AM	#60
mnowell129 Registered User Join Date: Nov 2004 Posts: 1,869	Mike, A problem with design in the absence of practical experience is that every detail is equally important and it takes forever to apply the analysis to every detail. Many details on an aircraft only have to be correct to 1 significant digit, not 3 or 4. As example the roll and pitch settings need to be about 20 degrees. No amount of analysis will tell you if it needs to be 18 or 21 except flight test, so spending more than a minute or two on roll/pitch angles is non-productive. You just need something around 20, not something around 10 or something around 30. You are apparently a very bright person, but you are spending a lot of your considerable ability on details that can't be predicted that accurately. I'm with Peter, build one of the designs that exist. Learn to fly it. Determine from practical experience what needs 3 significant digits and what doesn't. Then you can zip through the design spending effort where it's needed. This is the value of practical experience, you don't spend time over analyzing something that doesn't deserve it. It's a sure bet that even Boeing and Airbus make changes to the aircraft after a real pilot flies a real airplane, even with the money they spend on design and simulation. My definition of engineering is "technical development in an economically constrained environment". Thus you spend resources on the areas that need it, not uniformly everywhere in the development.