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DaJet EDF Stagger wing jet

Old 02-09-2009, 06:00 AM
  #1  
larryross
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Default DaJet EDF Stagger wing jet

Myself and two other builders built one of these beta models for the designer. The plans were easy to cut and fit together. After finishing and test flying (trying to fly) none of the three would fly. I was the only one that installed landing gear the others hand launched theirs. I am posting the plans and pics of my build and the plane as it is now.

I am looking for some good ideas on the possible problem and maybe some good model builders to build one and see if they can make one fly. I guess this could be considered a challange.

I'm sure there are better builders out that understand what they are doing that can make an airborne DaJet.
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Old 02-09-2009, 06:08 AM
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Here are the latest plans... I think I have all the updates added.
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Old 02-09-2009, 06:26 AM
  #3  
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More build pictures. Come on all you master model builders let's make this thing fly.
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Old 02-09-2009, 07:48 AM
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Larry3215
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Hi Larry,

I sure like the looks of the thing!

Any video of the failed flights? Can you describe whats happening thats not working?

Do they dive into the ground or pitch up uncontrolably or?

Do the other have the same controll set up you do?

Where does yours balance at the moment?
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Old 02-09-2009, 03:16 PM
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Originally Posted by Larry3215 View Post
Hi Larry,

I sure like the looks of the thing!

Any video of the failed flights? Can you describe whats happening thats not working?

Do they dive into the ground or pitch up uncontrolably or?

Do the other have the same controll set up you do?

Where does yours balance at the moment?
There are no videos of the failed flights. I didn't get a video and as far as I know the others didn't either.

My flight went like this... there was a 2 to 3 mph breeze with occasional gust to 5 to 8 mph. The first trip down the runway (we have a hard surface runway) the plane went tearing down the runway and went off the end. We moved the battery back as far as we could (about 2 inches) and tried the second time. The second was very similar except the test pilot was half way expecting it to not get airborne and didn't go off the runway. He made the statement that he didn't understand why it didn't get air born. The third trip down the runway a the plane caught a good gust of wind and went vertical for about 30 feet then came straight down on it's nose. There was very little damage a little dent in the foam nose and the front LG was bent back a small amount ( think he must have gotten the nose up a little jist before impact), but the pilot didn't think any further flights would yield anything. I got several suggestions from other people and shifted the main LG forward about 1.5 inches and lowered it some and added the control surfaces to the forward wing. I haven't gotten anyone to fly it since the mods were made.

The current CG with the battery in the forward most location was about 1 inch behind the rear most mark you made on the pic you posted. The other guys stated that the planes would just came down. It was my understanding that they were saying there wasn't any or very little lift. I could find and post some of the quotes from the other builders if you think it would help.

Until I put the control surfaces on the forward wing, they did have the same set up except they made their pushers with the motors mounted on the back.
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Old 02-10-2009, 01:19 AM
  #6  
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That sudden going to vertical followed by a nose down is a perfect description of what happens when the main gear are set too far behind the balance point.

Having the mains set too far back puts more weight on the nose wheel. That in turn means the elevators need to generate more down force to rotate the plane - lift that heavy nose - for take off. The amount of down force an elevator generates is directly related to the air speed.

So the model now has so be going waaaaaay too fast before the nose will lift. Generally the pilot will have pulled full UP trying to get the nose to lift. However, the plane is now already going well above flying speed so as soon as the nose starts to lift it goes to vertical before the pilot can react.

The result is stall and crash.

The mains need to be set just behind the balance point. If you move the balance point you need to move the mains.

The alternate is to set the mains shorter so the plane has a positive angle of attack at all times. It will then just take off as soon as it gets to flying speed. The down side to that is that is tends to cause bouncing or PIO on landing if you touch down even a tad above stall speed.

Best bet by far is to keep the mains near the balance point.

As far as the desired cg - I would pretend the plane has a single large wing. Forget that its a bipe completly. Project the outline of the "single wing" onto the plan and calculate for a 25% CG and call it good. I guarantee it will fly at that point well enough to get it airborn

If your gear legs are say 4" longincluding the wheels, set them about 1" to no more than 1.25" behind the CG point. Less is better here. The plane may well sit on its tail when the battery is not installed but put up with that for easier/better controlled takeoffs and landings.

The plane should still have maybe 1 to 2 degrees of positive angle of attack. No more than that. I prefer zero.

If you had very large elevator surfaces and long moment arms or if they were directly in the prop wash things would be different.

The last point I see that Im concerned about is the controll surfaces on the forward/top wing. They sit almost exactly on the point Im guessing should be your CG. They are very close to it for sure.

The problem is that, for them to function as elevators or canards, they need to be as far from the CG as possible. All they will do where they are is create drag if you try to use them for pitch control. I would disable them or fix them in place for now.

I can see them helping increase the roll rate if they were used as ailerons only but I dont know if you need a super fast roll rate at this stage of the testing

In the pic below the black lines represent a crude "super wing" to calculte the CG from. Use the length from the rear of the big wing to the nose of the top wing as the cord distance and use the span of the rear wing as the span of the super wing and calculate the cg from there.

Id bet that will be close enough for starters.
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Old 02-10-2009, 01:22 AM
  #7  
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By the way, the general rule of thumb for main gear placement is that they need to set back roughly 25% to 30% of the height of the gear leg and wheel.

That equates to an angle of between 15 degrees and 20 degrees.

So a 5" tall gear/wheel set would be set 1.25" back to 1.5"
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Old 02-10-2009, 01:27 AM
  #8  
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Originally Posted by Larry3215 View Post
By the way, the general rule of thumb for main gear placement is that they need to set back roughly 25% to 30% of the height of the gear leg and wheel.

That equates to an angle of between 15 degrees and 20 degrees.

So a 5" tall gear/wheel set would be set 1.25" back to 1.5"
I should also point out that not that many planes Ive seen in the last several years actually follow that rule. That forces them to be well above stall speed to take off.

If you follow the rule, the plane will rotate very easily as it approches take off speed. If you set the gear at the minimum distance back, it will rotate before flying speed and you can do real jet like take off where the nose gear lifts first and then the plane takes off.

It looks much better that way

If your not used to it your pilot may try to yank the plane off too soon.

Dont do that
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Old 02-10-2009, 06:27 AM
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Originally Posted by Larry3215 View Post
That sudden going to vertical followed by a nose down is a perfect description of what happens when the main gear are set too far behind the balance point.
&np;
Having the mains set too far back puts more weight on the nose wheel. That in turn means the elevators need to generate more down force to rotate the plane - lift that heavy nose - for take off. The amount of down force an elevator generates is directly related to the air speed.
&np;
So the model now has so be going waaaaaay too fast before the nose will lift. Generally the pilot will have pulled full UP trying to get the nose to lift. However, the plane is now already going well above flying speed so as soon as the nose starts to lift it goes to vertical before the pilot can react.
&np;
The result is stall and crash.
&np;
The mains need to be set just behind the balance point. If you move the balance point you need to move the mains.
&np;
The alternate is to set the mains shorter so the plane has a positive angle of attack at all times. It will then just take off as soon as it gets to flying speed. The down side to that is that is tends to cause bouncing or PIO on landing if you touch down even a tad above stall speed.
&np;
Best bet by far is to keep the mains near the balance point.
&np;
As far as the desired cg - I would pretend the plane has a single large wing. Forget that its a bipe completly. Project the outline of the "single wing" onto the plan and calculate for a 25% CG and call it good. I guarantee it will fly at that point well enough to get it airborn
&np;
If your gear legs are say 4" longincluding the wheels, set them about 1" to no more than 1.25" behind the CG point. Less is better here. The plane may well sit on its tail when the battery is not installed but put up with that for easier/better controlled takeoffs and landings.
&np;
The plane should still have maybe 1 to 2 degrees of positive angle of attack. No more than that. I prefer zero.
&np;
If you had very large elevator surfaces and long moment arms or if they were directly in the prop wash things would be different.
&np;
The last point I see that Im concerned about is the controll surfaces on the forward/top wing. They sit almost exactly on the point Im guessing should be your CG. They are very close to it for sure.
&np;
The problem is that, for them to function as elevators or canards, they need to be as far from the CG as possible. All they will do where they are is create drag if you try to use them for pitch control. I would disable them or fix them in place for now.
&np;
I can see them helping increase the roll rate if they were used as ailerons only but I dont know if you need a super fast roll rate at this stage of the testing
&np;
In the pic below the black lines represent a crude "super wing" to calculte the CG from. Use the length from the rear of the big wing to the nose of the top wing as the cord distance and use the span of the rear wing as the span of the super wing and calculate the cg from there.
&np;
Id bet that will be close enough for starters.
&np;

Thanks Larry
A lot of the issues you have described have been addressed, but not tested yet.

The mains issues are pertinent to my plane, but the other two didn't install LG and hand launched theirs. They didn't have lift either and their planes lost altitude till they met the ground.

There were suggestions that my plane didn't have enough thrust. I didn't think that was an issue (I should have had at least 1 to 1 thrust to weight ratio) till I was checking the motor and thrust out one day and noticed that above half throttle the motor would pull down to a certain rpm and hold there no matter if I added throttle. I look down the exhaust tube and about half throttle a piece of the plastic liner in the tube collapsed and blocked about 1/4 of the exhaust tube.

I really think the forward wing is the problem. When you mentioned the fact that the flaps on the froward wing was too close to the CG made me think of a radical idea. What if I wire the forward wing flaps as elevators and have then actuate in reverse if the rear elevators? My thought was in doing that when the real elevators go down to ROG (push the tail down) if I what the forward wing flaps going up an the same time this would tend to lift the front to give lift to the front which should aid in ROG. Also my thought was that the upper wing might be causing a high pressure on top of the lower wing and having the froward wing flaps going up might aid in creating a low pressure on the lower wing giving it lift. I am in no way an aircraft engineer and don't know very much about how one flies, but this just made sense to me. I have learned a lot from building and the help I get from others, but have a long way to go.

The plane might fly with the mods I have made, but I am not confident of it. I do agree that the flaps on the forward wing would be a problem if not operated right. Let me know what you think about the elevator reversal idea.

Oh one more thing... I used glide test to determine CG originally, but didn't really know what I was doing.

Your pesky friend
Larry
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Old 02-10-2009, 07:20 AM
  #10  
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Hi Pesky Friend I was just wondering, if you were to get it to fly, as a delta, with just the rear wing first, then add the second wing, that would tell you that the front wing may very well be the problem, I remember seeing a small wing/Tap on some planes/jets in front of the main wing, on the fuselage, that is suppose to creat some kind of turbulence over the wing, for better lift, but it was a small tap/wing, i will see if i can find it, Darn, I could not find it, i think i saw it in Popular science, I found out that they are called Vortex generators, they even use them on the enging nacelle, these were mounted above the main wing towards the front, on the fuselage

http://images.google.com/imgres?imgu...%3Den%26sa%3DG
&np;

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Old 02-10-2009, 08:02 AM
  #11  
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Did the other guys have working "elevators" or canard surfaces on the top wing?

Where was their CG?

I am quite certain that having elevators/canard controlls on the top wing is a major mistake. It will only cause extra drag with little to no benifit in the pitch direction.

Elevators or canards work by forcing the nose or tail up or down. They work kind of like a teeter totter. The elevator needs to be out at the end of a long arm and the CG is the pivot point. Imagine trying to work a teeter totter if you were sitting in the very center of the thing where it pivots. It wont work very well no matter how hard you push.

The control surfaces need to be as far from the CG as possible. Thats why elevators are always at the extreme rear of a plane and canards are as far forward as they can be and not block the pilots view. There is a very good reason you never see them at or near the CG. It doesnt work

When you have them right at the cg all they do is create drag. They will not cause any significant pitching moment and will not raise or lower the nose of the plane. It wont matter which way they move - all you will get is drag.

You might see some slight benifit if they were slightly drooped as flaps but I suspect any extra lift would be lost in the extra drag because the air would be forced down onto the bottom wing.

I think you're far far far better off leaving then straight untill you get it airborn and work out some of the other bugs.

I really really think you need to leave them alone for now.

Really

You already have a relatively in-efficient aerodynamic situation. What you have is basically a stagger wing bipe. The rule of thumb for a bipe is that the distance between the wings needs to be at least 1 to 1.5 times the cord distance.

You are a lot closer than that. The result is that yes, the air flow coming off the top wing will interfere with the air flow over the bottom wing to some degree.

I dont think thats a major issue though. I have built several other models with two flat lifting surfaces that were way to close together and they flew fine.

Flying cars, Batmobiles, wierd odd ball things. Foamies generally are so lite we can ignor many or the "rules" and they are so over powered they still fly

So what if its not the most efficient lifting plan form. It looks cool and its fun The loss of efficiency wont be enough to keep it from flying. It just wont be a great glider.


The only reasons a plane would go down and not fly would be

1)not enough power and/or to much drag for the power to over come
2) CG too far forward or
3) this goes with #2 - not enough elevator authority to keep the nose up

If the cg is close and if there is enough power to over come the drag - anything will fly

What is the over all length from the front tip of the top wing to the trailing edge of the rear wing and what is the span of the rear wing?
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Old 02-10-2009, 08:37 AM
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Maybe Im missing something but how big is this thing?
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Old 02-10-2009, 08:38 AM
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So I am just wondering if there is too much of a vortex having the wings so close together,and staggered, Just a thought, Take care, Chellie
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Old 02-10-2009, 08:39 AM
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If there was anyone who knows getting strange ships to fly its larry, dang some crazy flyers there...awesome.
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Old 02-10-2009, 08:42 AM
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Originally Posted by LipoPilot View Post
If there was anyone who knows getting strange ships to fly its larry, dang some crazy flyers there...awesome.
&np;
I will drink to That
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Old 02-10-2009, 06:11 PM
  #16  
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Originally Posted by CHELLIE View Post
So I am just wondering if there is too much of a vortex having the wings so close together,and staggered, Just a thought, Take care, Chellie
Its not that bad really.

In a 'proper' biplane set up where the wings are far enough apart, the plane will fly ilke it has 2 wings and you can count on the total area of both wings together to support the model.

If the wings are too close together, you loose some of the effective area of one of the wings as far as lift is concerned but you still have all the drag from both wings.

So if you have two wings and the total area is say 1000 sq inches, if they are too close together it might fly like it only had a wing area of 800 sq inches - but still have the drag and weight from the 1000 sq inch wing.

It will still fly as long as there is enough thrust/power to over come the total drag and as long as the CG is close enough. It just wont fly quite as well

Thats why I said to pretend its a plane with a single large wing. Thats how its going to fly most likely.
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Old 02-10-2009, 07:27 PM
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Originally Posted by LipoPilot View Post
Maybe Im missing something but how big is this thing?
31" long
28 1/2" main wing
710g AUW

Specs for the motor
EDF Fan Unit 53mm / 5300kv / 680g thrust w/ Motor
Motor Type:
2409H-7T Delta Turn
Outer Dimensions: 62 x 71mm
Shaft: 3.175mm
Weight: 71g
kv: 5300rpm/v
Fan Diameter: 53.5mm
Voltage: 14.8v (4s)
Current: 57A
Thrust: 680g+
Power: 840W
EDF Fan Unit 53mm / 5300kv / 680g thrust w/ Motor
Motor Type:
2409H-7T Delta Turn
Outer Dimensions: 62 x 71mm
Shaft: 3.175mm
Weight: 71g
kv: 5300rpm/v
Fan Diameter: 53.5mm
Voltage: 14.8v (4s)
Current: 57A
Thrust: 680g+
Power: 840W
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Old 02-10-2009, 07:35 PM
  #18  
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"Re: Oh one more thing... I used glide test to determine CG originally, but didn't really know what I was doing."

Presumably trying to glide the actual model?.....................has anyone made a simple flat plate (even scaled down) balsa chuck glider to prove beyond doubt the CG position, etc, etc?

Many builders would consider that is the first stage.
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Old 02-10-2009, 07:36 PM
  #19  
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Thats a nice size little plane. Me I would say more wing area and go with larry on the single wing theory, then add other stuff to see improvements or obstractions. I like the plane I just think I would lesson up on the inturnal duct fan construction and other items to save weight. Im thinking because its ducted fan, light will be the key to good flight., Maybe some lessor weight wheels stuff like that.
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Old 02-10-2009, 07:59 PM
  #20  
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Originally Posted by Larry3215 View Post
Did the other guys have working "elevators" or canard surfaces on the top wing?
NO


Originally Posted by Larry3215 View Post
Where was their CG?
See picture below (17" from nose of plane)

AUW is 710g

As it stands right now with the mains brought forward without battery the nose stands up (Battery weight is 157g). With the battery in the possition in the picture it takes 125g to lift the nose.



Originally Posted by Larry3215 View Post
I think you're far far far better off leaving then straight untill you get it airborn and work out some of the other bugs.

I really really think you need to leave them alone for now.

Really
No problem just unhook the servo leads and make sure the flaps are at 0 angle.

Originally Posted by Larry3215 View Post
You already have a relatively in-efficient aerodynamic situation. What you have is basically a stagger wing bipe. The rule of thumb for a bipe is that the distance between the wings needs to be at least 1 to 1.5 times the cord distance.

You are a lot closer than that. The result is that yes, the air flow coming off the top wing will interfere with the air flow over the bottom wing to some degree.

I dont think thats a major issue though. I have built several other models with two flat lifting surfaces that were way to close together and they flew fine.

Flying cars, Batmobiles, wierd odd ball things. Foamies generally are so lite we can ignor many or the "rules" and they are so over powered they still fly

So what if its not the most efficient lifting plan form. It looks cool and its fun The loss of efficiency wont be enough to keep it from flying. It just wont be a great glider.
That's why I have stayed with this while the others have dropped it and moved on.

Originally Posted by Larry3215 View Post
The only reasons a plane would go down and not fly would be

1)not enough power and/or to much drag for the power to over come
2) CG too far forward or
3) this goes with #2 - not enough elevator authority to keep the nose up

If the cg is close and if there is enough power to over come the drag - anything will fly

What is the over all length from the front tip of the top wing to the trailing edge of the rear wing and what is the span of the rear wing?
Tip of top wing to TE of lower wing is 24"
width of lower wing is 28 1/2"

I think I have answered all the questions. If I haven't please bring my attention to the question.

Thanks
Larry
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Old 02-10-2009, 08:12 PM
  #21  
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Originally Posted by bravedan View Post
"Re: Oh one more thing... I used glide test to determine CG originally, but didn't really know what I was doing."

Presumably trying to glide the actual model?.....................has anyone made a simple flat plate (even scaled down) balsa chuck glider to prove beyond doubt the CG position, etc, etc?

Many builders would consider that is the first stage.
Yes it was the actual model before anything was installed or even complete (completely bare airframe) and it glided extremely well IMHO.

Probably many builders would... please consider I am a wannabe builder. I have made and will make many mistakes on the learning road. I should have never tried to build this as it wasn't a tried model, but when the glide test went so well I didn't think there would be ANY problem. Well... so much for thinking. :o

Thanks for your comments
Larry

Last edited by larryross; 02-10-2009 at 08:34 PM.
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Old 02-10-2009, 08:33 PM
  #22  
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From all the comments I have gotten, this thing may very well fly now with the mods I did.

1) Found fixed a restriction in the exhaust tube.

2) Set the mains forward 1 1/2".

3) Lowered the mains 1/4".

4) Added throw to the elevons.

I will disconnect the servos for the top wing.

As a last resort I will cut off the top wing and try it or just give up.... WHAT DID I SAY GIVE UP... NEVER !!!!!!

There is one thing I think needs to be done and that's verify the CG. With the wing measurements you asked for Larry were you thinking about locating the CG?

It is very unhandy not being able to do your own test flights and not knowing someone that is readily available.

I'll just keep plunking away

Thanks
Larry
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Old 02-10-2009, 08:50 PM
  #23  
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Originally Posted by LipoPilot View Post
Thats a nice size little plane. Me I would say more wing area and go with larry on the single wing theory, then add other stuff to see improvements or obstractions. I like the plane I just think I would lesson up on the inturnal duct fan construction and other items to save weight. Im thinking because its ducted fan, light will be the key to good flight., Maybe some lessor weight wheels stuff like that.
A few things I might reiterate here...

1) All planes were build with the same templates (except the DF construction).

2) The other builders did not use LG.

3) The other builders used pusher prop setups.

4) Since they didn't use the DF they didn't have the internal ducted fan construction. My DF construction was designed to make the fan removable for replacement.

I was really hoping someone would through one of these together and come up with a flyer.
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Old 02-10-2009, 09:24 PM
  #24  
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Originally Posted by larryross View Post
&np;

My thought was in doing that when the real elevators go down to ROG (push the tail down) if I what the forward wing flaps going up an the same time this would tend to lift the front to give lift to the front which should aid in ROG. Larry
Hi Larry
I have enjoyed this string, and I really like your airplane and the way you built it. I noticed something in your quote above. When you have a control surface aft of the CG, for elevator control, when you add back stick or up elevator, the trailing edge of the surface needs to move up, I assume that is what you meant by this quote, but I had to make sure. I have been hesitant to comment, because you have been getting good input from a lot of people who know more about this than I do. I hope this helps.
Mike
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Old 02-10-2009, 10:40 PM
  #25  
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Larry - I would start with the CG set 12" back from the tip of the top wing.

Anywhere from 11.5" to 13.5" should work but Id start at 12 and see how it handles. That should be nice and stable as thats the 25% mean cord point. It should be just a tad nose heavy if anything.

Other than that, sounds to me like your ready to fly it again
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