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Feb 24, 2006, 02:25 PM
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sparks's Avatar
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Discussion

Super 80 airliner.. again


Well, It's almost done now. I'm on hold for the motors. I think they are stuck in customs.
The plans are 99% done.
I need a few flights to get the stab angle noted on the plans and the CG right on the money, so nothing is quite ready to release now.
As of this date there has been around 40 flights made on the prototype/sister ship.
I ran this thread about two years ago with the prototype to promote the book Building With Foam.
Well I'm back with a slightly heaver better looking model.

Let me get the search words out of the way:
Airliner, MD-80 , American Airlines , foam construction , prop jet ,
Did I miss any?

Wing span 7 foot, Length 6 foot.
weight 5 lb. (covered with Nelson film)
6.25 lb. (glassed) + the plastic windows, landing lights, cockpit detail.

This is the model (glassed) I'm turning in as a construction article for Flying Models Magazine.
I'll let you know when the plans and plastic are available.

Right now there is a guy waiting on the plans that has offered to cut foam as kits.
I'm sure he will make a post when he is ready.
Better jump on it when he does, It's a lot of work to get it right.

The lighter model first flew with 10 NMH cells in her belly.
Given the wing flex that was seen in the turns I quickly went to lipos, 4 ea. 1500 mah kokem's
This brought the flying weight to 4.5 pounds. When those went south on me I started using a single TANIC 3200 MAH lipo pack, weight , around. 4 pounds.
Any wind over 10 mph made it very hard to look scale in the air.
It's like flying a balloon with wings
Mega 16/15/5's and 7x5 props will get her in the air in about 15 feet off of the grass, 10 off of pavement. These are very impressive motors. At full power she will climb at about a 35 degree angle.

That was then.

Now , given the weight savings I found with the Tanic packs I went with .5 oz. glass cloth. It cost me a pound in weight but I have a much tougher model. My wedding band don't leave dents in the skin when I handle the model, but more importantly the wings are much stronger.
I'm a little concerned that the wing flexing in the turns with the prototype gave it stability.
We will soon see. It's all up to the post office and the weather now.
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Feb 24, 2006, 09:42 PM
Registered User

Sparky's MD-80


Here is another shot I took of Sparky's MD-80 taken at the BEST fly-in last October.
Feb 25, 2006, 09:49 AM
Registered User
wow sparky, i saw this when i was out on a trip yesterday and wanted to re read it when i got back to deerfield, its a lot to digest for us simple builders...

its so realistic and extremely impressive..you guys sure have something here..just plane beautiful man!


WOW
T
Feb 25, 2006, 11:47 AM
Turrets Syndrome?
Bomberguy's Avatar
Beautiful job Keith, wonderful detail in that tail close-up
Mar 15, 2006, 12:16 AM
Registered User
D. Strode's Avatar
Hows the progress going?
Mar 15, 2006, 02:08 AM
Account closed
Quote:
Originally Posted by sparks
Any wind over 10 mph made it very hard to look scale in the air. It's like flying a balloon with wings Mega 16/15/5's and 7x5 props will get her in the air in about 15 feet off of the grass, 10 off of pavement. These are very impressive motors. At full power she will climb at about a 35 degree angle.
I realize that you have a twin Brushless motor arrangement and I am assuming from your first post that you have 2S Li-POLY for each motor? Correct?

If so, then, I wonder why don't you consider the APC "Sport" 7 X 7 propellers as this will improve your top air speed and make this balloon effect disappear. This is a Pusher Jet but, nevertheless, it is still a very scale and detailed model after a commerical Jetliner so, why the low 5-Pitch propeller?

Of course, if you are happy and content with your setup...great but, a higher pitch propeller provides advantages such that your motor will spin less RPMs using the higher pitch propeller to obtain a certain speed that your present setup does with a higher throttle setting while using the 5-pitch. Meaning you can throttle back and your model will fly faster at a lower throttle setting.

I have posted the quick and dirty P-Calc estimator for both your present setup and the suggested 7 X 7 propeller combo.

The 7 X 7 increases the Static Thrust, Watts but, most importantly the Top Air Speed for better than 14 MPH at the sacrifice of a little efficiency and AMP draw.
Last edited by guapoman2000; Mar 15, 2006 at 02:18 AM.
Mar 15, 2006, 03:18 PM
RC 4 Life
sparks's Avatar
Thread OP

Props


Thanks for the tip.
Actually I was just bragging about the weight of the model. ( flies like a balloon")
On a dead wind day I can milk the airspeed for a scale looking approach.

The three cell pack and motor's run very cool with the prop I'm using now. and I'm enjoying the rapid acceleration the props give me now.
If the model gets in trouble or I need better wind penetration I just go full power and get out of town.

I'll look into a more aggressive prop if the heavier model looks like she could use a little more.

Strode. . . the spring weather is killing me, It's tough to arrange a crew for the magazine shots and get mother nature in line too.
Not to worry, all the ducks will line up soon. The models are loaded and the packs are topped off.
it shouldn't be long now.
Mar 15, 2006, 08:56 PM
Registered User
Wonderful work sparks! It's beautiful!!!
Mar 15, 2006, 10:03 PM
Zoom, zoom...
Trikster's Avatar
Is this a DF or pusher? I don't see any props in the pictures, but you reference a prop in an earlier post...
Mar 15, 2006, 10:08 PM
swede
denial15's Avatar
here you go
Mar 15, 2006, 10:16 PM
Zoom, zoom...
Trikster's Avatar
Heh, they blend in very well. Is a DF in the future? I know the props are a bit more efficient in this application, but a fan would be super.
Mar 17, 2006, 10:06 AM
RC 4 Life
sparks's Avatar
Thread OP
DF, Well, Sort of.. . .
I've tried Ducted fan models.
Lots of fun if you want to go fast.
But If you want a slower flying model DF is a waste of power.
They are hungry for power and airflow. . . .

Now If I take the same model like this MD-80 , change up the tail a little, stretch the landing gear and move the motors I could do a 757.
Hay Guapoman, what size three blade prop could a Mega 16/15/5 turn on three cells?
I could do a ducted prop 757
Apr 17, 2006, 07:48 PM
RC 4 Life
sparks's Avatar
Thread OP
The test flight went better than I expected. Turns out that the heavier glassed model flies better.
Less wing flex. better wind penetration; and since it's a painted surface it looks better in the air.
Apr 17, 2006, 08:01 PM
Registered User
pda4you's Avatar
Yep it sure did do better.....

Here is a video - poor quality as it was shot with my digital camera, but you get the idea. This plane is difficult to distinguish from it's full scale counterpart when flying!

Simply amazing Keith!

Check it out:

http://media.putfile.com/Keith-Spark...mike-llewellyn

Mike


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