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Old May 11, 2012, 06:15 PM
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Philadelphia, PA
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...finally finished the 52" bird up! Maiden tomorrow - weather and wind permitting...

She's at 38oz with a 2200 3S lipo. Still about 5-6 oz. lighter than the PZ Icon! Another plus is that I have a Monsterpower10 (Power 10 clone) in her - the prop is a T-28 prop (9.5x7.5). The motor is underpropped so it is only pulling 26A and 250W at full throttle. I have well over 1:1 thrust/Weight so I am not worried. It will bw nice to have a bird in the air for more than 5 minutes! Might need a little bit of weight in the nose (with the 2200) - or I have a 2650 lipo that should do the trick.

Let's just hope my CG is on! -- I did not do any glide testing!
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Old May 11, 2012, 06:17 PM
ich bauen groß modell flugzeug
Keenan smith's Avatar
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Joined Dec 2010
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nice SniceA5 ..... Good luck with the maiden
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Old May 12, 2012, 07:53 AM
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The big one looks even SNICER than the 40"! Good luck with the maiden!
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Old May 12, 2012, 08:35 AM
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Very Nice indeed. Most of all, good luck on the maiden, and I'll bet your CG calcs are good to go! I think I saw a micro Mirage 2000 taking shape somewhere too BTW.......

Fred
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Old May 12, 2012, 12:56 PM
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What does the thrust angle test stand help you with? Motor angle? ???
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Old May 12, 2012, 06:11 PM
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Quote:
Originally Posted by Vance1 View Post
What does the thrust angle test stand help you with? Motor angle? ???
Yes - my theory was that if the fuse was supported by a rod on the cg, and throttle was applied -- I could then see how the thrust line was affecting pitch. If the thrust line was correct, the fuse should remain horizontal an not pitch up or down with throttle. This method worked great on the 40in model - no thrust issues at all. However with te 52in, once I got her in the air, it required A LOT of up elevator to keep her level. My motor is now pitched up a considerable amount. We will see if this improves flight tomorrow.

The maiden was ok. Sustained a bit of damage when I tried to take off too early fighting the down pitch. She jumped up into the air, stalled, and cartwheeled. Crushed the side of the nose a bit, cracked the motor cover (all cosmetic damage). Other than that - she is in good shape.

Hopefully things will go a bit better tomorrow. Need to get the pitch issues sorted out so I can really fly her!!!
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Old May 12, 2012, 08:08 PM
Tony Audsley Retired Locksmith
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Australia, WA, Perth
Joined Sep 2011
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Nice looking model mate, sorry to hear abaou the mishap on the maiden, I am sure you will get it sorted

Look forward to seeing it fly when you get chance to do a vodeo

Good luck with the second flight

Lockey
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Old May 13, 2012, 05:07 PM
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Quote:
Originally Posted by SNice View Post
Yes - my theory was that if the fuse was supported by a rod on the cg, and throttle was applied -- I could then see how the thrust line was affecting pitch. If the thrust line was correct, the fuse should remain horizontal an not pitch up or down with throttle. This method worked great on the 40in model - no thrust issues at all. However with te 52in, once I got her in the air, it required A LOT of up elevator to keep her level. My motor is now pitched up a considerable amount. We will see if this improves flight tomorrow.

The maiden was ok. Sustained a bit of damage when I tried to take off too early fighting the down pitch. She jumped up into the air, stalled, and cartwheeled. Crushed the side of the nose a bit, cracked the motor cover (all cosmetic damage). Other than that - she is in good shape.

Hopefully things will go a bit better tomorrow. Need to get the pitch issues sorted out so I can really fly her!!!
You might try using a power system/propeller with higher speed and less thrust so the wings produce more lift to counter the down pitch from the motor thrust.
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Old May 13, 2012, 09:25 PM
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Thanks guys!!!

Quote:
Originally Posted by NuttyPro67 View Post
You might try using a power system/propeller with higher speed and less thrust so the wings produce more lift to counter the down pitch from the motor thrust.
Yes, I think you may be on to something here.... this is what happened today....

So I drastically angled the motor up so that the center of the prop was angled towards the tail. I had mixed feelings about this - I've been researching pod mounts, thrust angles, etc. Just decided to give it a try. It seemed to make a very little difference - I still needed a lot of up elevator for level flight. The prop did not seem as efficient in this configuration and it was making a lot of noise at higher throttle settings.

As NuttyPro67 suggested above, at higher speeds, the model required less elevator, as well as when the flaps were down. After the first flight, I came in and decided to change the wing's angle of inicdence. I rolled up two dollars - one on each side, and wedged them between the fuse and the wing. It definitely made a big difference...until I losst control of her --- not sure exactly what happened -- she was at the far end of the field - she was going away from me so perhaps i slowed her down too much. I was in a steep bank, and then she violently rolled the opposite way. The ailerons seemed to become ineffective. I should have used rudder, but I kept trying to bank her. The prop sounded like it was just beating the air (is it possible to stall a prop?) I never regained control and she flipped over in a nose dive and went straight in to the ground.... It looks much worse than it was -- already got her back together and ready to go for tomorrow. All she needed was some glue and a new gear in one of the flap servos. I've taken the upthrust out of the motor and now have foam "plates" to change the incidence of the wing. The nose is pretty well smashed up but I will patch it up after I get the wing incidence sorted out. Luckily, no damage to the tail or bottom of the model (those coffee filters sure made her strong).... hopefully tomorrow I will have a better report!
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Old May 13, 2012, 10:46 PM
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Glad my suggestion helped.

It sounds like your plane tip stalled. Seems like a U-2 Spy plane like problem. They had a flight "coffin" when they were flying over a country, the plane had a top speed of 700 mph but stalled out at 690 mph, so you had to stay within that 10mph window or bad things happened.

The wing incidence just acts like flaps, it produces more lift as your speed increases. Looking at your pictures I suspected that the wing on the 52" model is too small to fly the model well. If increasing the incidence of the wing makes the plane flyable then this is for sure the problem.

The motor angle takes the edge off the pitch down effect, but it doesn't get rid of it if your wings aren't producing enough lift.

I think the added drag of the larger fuselage is preventing the motor from pushing the plane to a speed necessary for the wings to produce enough lift to counter the nose down effect. You can solve this a few ways without setting up a wing incidence of 20 degrees.

A - Larger wingspan/thicker wing for more lift
B - Smaller, less draggy fuselage
C - a more powerful motor with a higher top end speed so the added drag isn't an issue. You may be able to just get a smaller prop with a higher pitch.

By the way the higher wing incidence raises your stall speed drastically since it's increasing the wing's angle of attack. If you keep the incidence I would install some leading edge extensions on the edges of the wings to bring your stall speed back down.
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Old May 13, 2012, 11:37 PM
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Philadelphia, PA
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Yes, It definitely felt like a tip stall.

I think the motor I have in her is more than powerful enough -- it is a 1050KV monsterpower 10. I originally had it in a super- modified PZ p-51 gunfighter (flaps, retracts, rudder) - the plane was a pig at over 40oz, but that motor could still take her vertical with an 11x7 prop. The 52" bird is essentially the same size as the PZ Icon A5. Mine is a bit lighter with a more powerful motor. The prop is a bit small for the motor (9.5x7.5) but it still produces more than enough thrust to overcome sliding friction to get off the ground/water with power to spare. She is also much faster than I thought she would be. I could probable safely fit a 10" prop but I do not have any on hand. Perhaps I need to switch to a 3-blade prop - but I do not know how they compare to 2-blade props performance wise. Perhaps a stronger APC prop is the answer - the PZ T-28 prop has thick paddles and feels a bit "soft".

Once she is in the air, and the elevator is trimmed out, she handles fine -- fast and slow ..with flaps down - super slow. She is definitely not a floater - glides but looses altitude pretty quickly.

The issues I am experiencing are mostly in the takeoff phase. I have raised the leading edge of the wing by 6mm. I hope this will be enough. It is almost as if the wing is pointed down with respect to the ground, so the model wants to "stick" to the ground. The propwash over the elevator still allows the plane to rotate and then she shoots up into the air. I think the 6mm will allow enough air under the wing for a smooth takeoff. Takeoffs with flaps were not a problem.

The fuse is draggy but I feel like the large, wide surface area acts like another flying surface (thoughts?). When you get close to the ground with this model, she just floats along in ground effect.

I think my stall troubles were also complicated by my control surface throws. Right now, all of the throws are at full with lots of expo. I generally do this with new models to get the feel of where I want the limits. My aileron throws are waaaay too much - so that probably did me in too. What i will do is point both ailerons up a bit in hopes of warding off another tip stall!

Thanks for the suggestions... we will find out more tomorrow! Hopefully i will get some video worth sharing!!!
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Old May 15, 2012, 01:17 PM
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Omaha Nebraska
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Can't resist...... Those full scale warbirds make you look short! Hahahaha.... and WOW. How cool is that. Hope the boys had as much fun as Dad, BTW. My Dad used to fly P-51's, but that Jug is just awsome and HUGE!

Sorry about the issues dialing everything in. Your photo of up thrust looks like twice what you need???? I usually use the proverbial 3 degrees on everything to start. I know you will get it, but hope it is sooner than later.... Good luck and she is a beauty!

Now where did that micro Mirage go to?

Fred
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Old May 15, 2012, 01:57 PM
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Attica, MI
Joined Dec 2006
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Snice,
Sounds more like a center of drag vs. center of thrust issue. It may sound counterintuitive, but trying some upthrust may help. Pitching moment is caused primarily by center of thrust being offset from the center of drag. Use upthrust, much as we use downthrust for a low mounted motor on a high wing.

As usual, you are doing some beautiful work. Congratulations!

Ken
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Old May 15, 2012, 02:26 PM
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Philadelphia, PA
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Quote:
Originally Posted by Freddie B View Post
Can't resist...... Those full scale warbirds make you look short! Hahahaha.... and WOW. How cool is that. Hope the boys had as much fun as Dad, BTW. My Dad used to fly P-51's, but that Jug is just awsome and HUGE!

Sorry about the issues dialing everything in. Your photo of up thrust looks like twice what you need???? I usually use the proverbial 3 degrees on everything to start. I know you will get it, but hope it is sooner than later.... Good luck and she is a beauty!

Now where did that micro Mirage go to?

Fred
Lol! Yes, they did! When they saw the warbirds, they started running towards them shouting "those are Daddy's Planes!!!" lol. There was a Mustang, a Thunderbolt, and a Warhawk -- I have models of all three! I wanted to run with them, but I had to do the "fatherly" thing and holler "Walk boys, Walk! Slow Down!" lol! So cool seeing the real things. Amazing that your father flew P-51's -- that is my all-time favorite aircraft!!! WOW! My oldest remarked at how small the real aircraft were -- he thought they would be MUCH larger! There was also an L-4 Grasshopper... after thourougly inspecting the plane - my seven year old asked the pilot -- "Where are the servos?" lol! .. We all had a good laugh - then the pilot showed my son how the stick and pilot were the "servos".

Had the 52" Icon out yesterday and got some decent video - will post a little later. Yes, that upthrust was way more than what I needed - infact, it doesn't need upthrust at all -- the problem was the wing incidence. I have since reduced the upthrust to only 1-2 degrees up (might take it out completely). I have raised the leading edge of the wing by 12mm (two thicknesses of foam) - that did the trick. I still need to dial it in and get the right foam thickness - it will be lifting the LE of the wing somewhere in the neighborhood of 8-12mm. But now it rises off the ground nicely with flaps and porpoises a bit without flaps - but I think that can be fixed with elevator trim. Once in the air, it is fine. I need to get the smooth liftoff to ensure safe water takeoffs.

In the air, I have noticed that this model needs rudder input to turn smoothly. It is almost as if a bit of rudder input gives the ailerons a bit of a boost. Without rudder , the tail tends to "slip" towards the ground in a bank. Tip stalling is definitely an issue with this model (not surprised). I have raised both ailerons a bit to ward off a stall, but I definitely think it needs some leading edge extensions as NuttyPro67 suggested above. Interestingly enough, I've been doing additional research on this and look what I found on the actual ICON website. It turns out ICON has made changes to the original design to improve takeoff and spin/stall performance-- FLAPS and LE Extensions!!!... Here's an excerpt :

"The design process began with an all-new cuffed wing, a feature that emerged from the NASA studies and proved successful on the Cirrus and Lancair/Columbia/Cessna aircraft for improving stall and spin characteristics. All told, the wing uses several different proprietary airfoils across its span. These unique airfoils were not suited to the no-flap wing design ICON had previously planned to use on the A5, so ICON engineers chose to reintroduce wing flaps to preserve takeoff performance on the water. The resulting wing provides a stall that is more progressive than that of an aircraft not designed for spin resistance."

Full article Here
http://www.iconaircraft.com/news/beh...e-program.html

Pretty Cool! Sounds exactly like what I have been experiencing !
...So now it's back to the drawing board for a bit to fabricate leading edge "cuffs" similar to what they have done on the Full Size aircraft...

Definitely gonna be on the lookout for that micro mirage!!! the micro EDF's are looking very good to me at the moment!

Thanks again for all the help and suggestions guys!!!
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Old May 15, 2012, 02:38 PM
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Quote:
Originally Posted by dz1sfb View Post
Snice,
Sounds more like a center of drag vs. center of thrust issue. It may sound counterintuitive, but trying some upthrust may help. Pitching moment is caused primarily by center of thrust being offset from the center of drag. Use upthrust, much as we use downthrust for a low mounted motor on a high wing.

As usual, you are doing some beautiful work. Congratulations!

Ken
Thanks for the suggestion, and kind words, Ken! Also, thank you for the material - Model Plane Foam! (www.ModelPlaneFoam.com)

Center of Drag - Didn't think of that one! Yet another directional force to add to the mix ( I am assuming it points rearward - at a height related to the model's surface area distribution). In this model, it would definitely be low and would rotate the model down -- makes sense. It there a way to reduce all of these forces to vectors and resolve them?
We have:
Center of gravity
Center of lift?
Center of Mass?
Center of Drag
Thrust - the acting point of the thrust - can we resolve the entire thrust of the prop to a single point?

Do any of these forces ALWAYS line up with each other or are they all acting at different heights?

Thanks again, guys!
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