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PatriciaJB
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Posted: Sat Dec 8th, 2007 03:32 pm |
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Here's a photo of Pete Valentine's double flapper # 3 and a pdf giving details in chronological order. He sent me a terrific video of it taxi-ing, taking off and then flying.
More details from Pete to come... will also try to post part of the video.
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PatriciaJB
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Posted: Sat Dec 8th, 2007 03:36 pm |
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| Details of Double Flapper Experiments - Pete Valentine Attachment: DoubleFlapper.pdf (Downloaded 429 times)
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PatriciaJB
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Posted: Wed Jul 9th, 2008 05:42 pm |
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Here's an update from Pete:
Hello and hoping you are having a great summer!
I thought I would send a progress report:
The attached photos show how I rebuilt flapper No. 4 to have tricycle
gear with steering (call it 4A now).
No. 4 was heavier than I liked and would have repeated the
characteristics of No. 3 if I had installed a steering tail wheel.
I've taxied 4A a little and flown a couple short hops.
The tri-gear set-up is less stable than the tail-dragger set-up: A
slight tailwind can tip the flapper forward and to one side, and if wind
gets under the elevator, I've had it blow all the way over onto it's
back.
Down elevator has to be applied while taxiing to put enough weight on
the front wheel to give it traction for steering.
Up elevator easily rotates the flapper and it takes off with a much
shorter roll than the tail-dragger type.
I think this is a lot due to the greater angle of attack possible when
rocked back on the rear wheels.
The tail-dragger has only so much angle of attack on the ground and
therefore has to get to greater speed to lift itself off. The tail wheel
can't be made shorter without the rear wing tips hitting the ground so
the only fix would be to make the tail dragger main gear even taller.
With the phase angle at about 125 degrees, rear wings leading, it looks
more 'alternating' than the 90 degree phase. Maybe more 'floaty' but
less speed. Need to get video of some long flights to make comparisons.
Meanwhile I am building a No. 5 flapper with a shorter tail, smaller
wheels and the battery located lower and farther back. I plan to make
the phase angle about 110 degrees and with the three flappers, try to
see what difference the phase makes and to decide if it would be worth
it to make it variable while flying.
Best Wishes,
Pete
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Flapangle
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Posted: Wed Jul 9th, 2008 08:45 pm |
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Hi Pete,
Good work!
Hope you show a video soon.
George
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PatriciaJB
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Posted: Sat Aug 9th, 2008 03:57 am |
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Here's another update from Pete and an updated spreadsheet.
----------------------------------------------
Some progress to report!
My camera person became available along with some nice morning weather.
On Saturday we videoed #4 perform an 8 minute flight with short ROG take-off (10-15 ft or less) followed by steep climb to altitude,
I did two loop-the-loops and some glides and I think a glide to landing. The motor was hot after that flight. Then a ~four minute flight.
Unfortunately, the Canon mini disc from the video camera wont play on my DVD player or PC. Only in the camera so far so at least we got the video in some format.
On Sunday we went back to my camera (Sony mini DV). I did a big and a small loop-the-loop. Then some glides and a glide to landing. The second ( 4 min) flight I tried to do touch-and-gos but the direction I chose involved getting a very steep descent over the school. At the end I was trying to glide steeply downwards and turn and it just rolled 180 degrees and went vertical onto the roof of the school. The balsa and plywood nose was shattered but I cant find any other damage so it is repairable!
Some conclusions: I can see the difference in the 125 deg. phase vs. the 90 deg. phase as far as 'more alternating' 'less together' but the performance is very similar.
I guess I prefer the 125 deg. phase because it allows glides to landing whereas with the 90 deg. phase, the power-off wing angle was higher and so the rate of descent looked like it could cause damage.
Some things that complicate the phase comparison: #4 weighs 15.1 oz vs. 14.3 for #3. So #4 works harder and also has more drag with that third wheel than #3.
It still has a great steep climb capability, maybe is a little slower in horizontal flight.
The tricycle gear allows great short take-offs, a big improvement over #3 that had to build speed before it could lift off.
The down side of tricycle gear is that it has to be tall for wing clearance and ends up adding weight. Also it makes good taxing and landings harder due to the possibility of tipping over to one side or the other.
The second time I rebuilt #5 with trike gear and a built up elevator twice the size of the Cybird tail it weighed over 16 oz.
I read on the web where someone had compiled ratios and areas of good flying RC models and had said that the hor. stab. and elevator should be 20% of the main wing area. I checked, and sure enough the Cybird elevator is right at 20%. But now with double wings, I only have 10%. Maybe I need more!?
Because I want the weight at around 13-15 oz, I started building a new #5 as a tail dragger again but with a difference. I had decided it needs more wing incidence on the ground to allow short take offs, but the landing gear will get heavier and tippier if I make it longer. I realized I can tilt the axis of both wing hinges back so that now the hinges (and balls for the trail edge), while still lined up, form about a five degree angle with the fuselage. So while the wings for #3 had about a 10 degree angle with the ground when taxiing, now it will be around 15 degrees. What I have built so far looks good.
I'll send photos and video as it becomes available.
Do you know anyone else building electric RC 13-15 oz flappers with wheels and aircraft-like (and beyond perhaps) performance?
Best Wishes,
Pete
Attachment: PVDoubleFlapperxls.zip (Downloaded 185 times)
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PatriciaJB
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Posted: Fri Sep 12th, 2008 05:12 pm |
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Here's an another update from Pete:
----------------------------------------------------------
Patricia-
Here are a couple photos of new double flapper #5 which is almost ready
for 1st flights.
My hope here was to combine the lower weight and easy taxiing of #3 (my
first wheeled, steerable flapper and a taildragger) with the quick
take-off of #4 (which can lift off as soon as it rocks back on it's
tricycle gear).
As seen in the photos, I've raised the front wing hinge and lowered the
rear wing hinge (while keeping everything in a line) to give more lift
when it's on it's wheels and hopefully a short take off run.
I have a DVD of some flights of #4 and #3 that I will put in the mail
today. With these you can compare the 125 degree, rear wing lead phase
angle of #4 with the 90 degree lead angle of #3.
One trade-off with the phase angle is that the closer it gets to 180
degrees, the closer the wings get to being flat when they cross (which
gives a better glide). On the other hand, the closer to 180, the less
dihedral, and therefore the less chance the wings will stop with both
sets at the same angle. For example, with 90 degrees, the wings snap up
to maybe 30 degrees above horizontal when the power is cut and the rate
of descent is high. With 125 degrees, the wings stop closer to 20
degrees above horizontal and the glide is more suitable for nice dead
stick landings. However with 125 degrees, I've seen the wings stop in an
'x-wing' configuration: there seems to be not enough force on the wings
at low speed to move the gears until both wingtips are at their highest
point.
Gotta go.
Best Wishes,
Pete
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