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Old 02-18-2011, 05:59 AM   #1
sgillmore
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Default Balsa USA 1/4-Scale Fokker D-VIII Conversion

Hi everyone. I have a 1/4-Scale Balsa USA Fokker D-VIII that has about 10-15 flights powered by a Kalt KG-22 (22cc) gas engine. I recently accquired the plane from a friend and I'm planning to convert it to electric. For those not familiar with the plane, here are the advertised specs:

Wingspan: 82"
Wing Area: 1100 sq/in
Air Foil: Flat-Bottom
Length: 59.5"
Weight: 12-14 lbs
Rec Engine: G-23 Gas or .90-1.20 4-Stroke

Now...a little reality. The finished airframe with servos, reciever and a separate RX pack weighs in at 10.5 lbs. The overall weight of the previous gas setup was about 16 lbs. The Kalt KG-22 weighed about 4 lbs , add-in 8 oz for fuel system and another 1 lbs of ballast was required at the firewall to acheive proper balance. So I'm looking for an electric system in the neighborhood of 5 lbs for motor, esc and batteries. It will be very easy to mount everything (including the batteries) under the cowl.

I'm really hoping to use a system that I already purchased for another project:

E-flite Power-160
Castle Creations Phoenix-85HV
12S2P 2300mAh A123
Xoar PJWWI (Lance) 18x10
(I'd like to get 8-10 min of scale flying)

I've been experimenting with MotoCalc and one thing that's confusing to me...when I use the wizzard, MC shoots back an error basically saying that all the combinations it tried are too heavy. It instructs me to try a different performance level or shorter flying time. Even if I choose "Sedate" and "4 min" I get the same answer. However, when I plug the data into MC manually it looks fine. Am I just reading the reports wrong? This is my first time using MC. I've attached 2 printouts...one at 70% throttle and the other at 100% throttle.

I would really appreciate some advice before I get too deep into the project.


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Old 02-18-2011, 08:06 PM   #2
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Hmmm... how does this plane fly if the weight is 254 oz and the "lift" is less than 200 oz?
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Old 02-20-2011, 12:37 AM   #3
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The plane is too heavy to fly "sedately". If I enter the specs into the MotoWizard, and select "Sport" and for performance, MotoCalc finds hundreds of suggestions. Note that currently, the MotoWizard won't try anything beyond 8S LiPo cells, or 24 NiMH cells, so it isn't going to find the power system you're planning to use.

If you already have a power system in mind, you should be using the MotoCalc Workbench, not the MotoWizard. The MotoWizard is intended to give you a place to start if you have no idea what sort of power system would be suitable.

Looking at the output you posted, the plane should fly quite well with the power system you've selected. The static pitch speed is in the right range (2.5 to 3 times the stall speed as a rule of thumb), and the plane can fly with neutral elevator at 70% throttle. Pretty amazing (an un-scale-like) rate of climb too!

I'm not sure where gyrocptr is seeing the 200 oz. of lift.

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Old 02-20-2011, 03:11 AM   #4
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Originally Posted by stefanv View Post
The plane is too heavy to fly "sedately". If I enter the specs into the MotoWizard, and select "Sport" and for performance, MotoCalc finds hundreds of suggestions. Note that currently, the MotoWizard won't try anything beyond 8S LiPo cells, or 24 NiMH cells, so it isn't going to find the power system you're planning to use.

If you already have a power system in mind, you should be using the MotoCalc Workbench, not the MotoWizard. The MotoWizard is intended to give you a place to start if you have no idea what sort of power system would be suitable.

Looking at the output you posted, the plane should fly quite well with the power system you've selected. The static pitch speed is in the right range (2.5 to 3 times the stall speed as a rule of thumb), and the plane can fly with neutral elevator at 70% throttle. Pretty amazing (an un-scale-like) rate of climb too!

I'm not sure where gyrocptr is seeing the 200 oz. of lift.
Thank you for your input. It's my fist time using MotoCalc and I'm still trying to figure it out. I wasn't aware of the 8S limit on the wizard, but that explains it. I thought it looked OK on the workbench.

It will be a while until I can get this one on the bench, but I'll post some conversion pictures and result once it's done.
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Old 02-20-2011, 03:30 AM   #5
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Originally Posted by gyrocptr View Post
Hmmm... how does this plane fly if the weight is 254 oz and the "lift" is less than 200 oz?
I'm not sure where you're getting the 200oz. If I understand the MC report, the wing should produce over 254 oz of lift at 44 mph and 520 oz of lift at 63 mph.
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Old 02-23-2011, 11:18 PM   #6
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Try a little different approach......mine is 1/4 scale, weighs about 14 pounds, and flies well on 6S 4000 mah lithiums and a 24X12 prop.

Not positive on the RPM per volt rating of the motor, but my 14 pound DR1 flies well on power 160, 24X10 prop and 6 lithium cells ( 4000 mah zippy's)

If you want the RPM/Volt on the D V111 ,motor, I'll check it out for you when I go to collect it from the hobby shop where it's on display.

Was flying electrics waaaay before it was cool
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Old 02-24-2011, 07:19 AM   #7
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Originally Posted by sgillmore View Post
I'm not sure where you're getting the 200oz. If I understand the MC report, the wing should produce over 254 oz of lift at 44 mph and 520 oz of lift at 63 mph.
I think the confusion comes from the lift figures shown in the MC report in the 'lift column' (third column on the report)

What might be confusing is, for example, at the 'optimum' flying speed of 37mph the lift reported in the 'lift column' is 179.7oz. The model weighs 254.4 oz so how can it fly if the lift is less than the weight

The answer of course is lift does not only depend on speed, it also depends on angle of attack and therefore 'Coefficient of Lift' (Cl). The Figures in the 'lift column' are reported for a low angle of attack and a correspondingly low Cl of 0.46 (see 'style key' at bottom).. the Cl at optimum flight is 0.63 and the Cl max (Cl at stall) is 1.11. to find the maximum lift at any airspeed you would have to multiply the figure in the lift column by 1.11/0.46

Steve
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Old 07-20-2011, 11:07 PM   #8
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sgillmore-- Did you ever get this project completed and flying? I just ordered a 1/4 scale Fokker DVIII myself so I'm curious to see how you made out.

Are the photos you posted of your plane? Beautiful looking model.

Mike
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Old 07-20-2011, 11:40 PM   #9
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Originally Posted by CarreraGTSCS View Post
sgillmore-- Did you ever get this project completed and flying? I just ordered a 1/4 scale Fokker DVIII myself so I'm curious to see how you made out.

Are the photos you posted of your plane? Beautiful looking model.

Mike
Unfortunately, I haven't touched it yet. My Summer has been consumed by home improvement projects and I have a couple R/C projects ahead of it in the queue. I really hope to get started on it soon.

Yes, those are pictures of my plane flying with Kalt-22 gas engine. Thanks.
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Old 08-24-2011, 02:43 AM   #10
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I can assure you, the Razor is a wonderful flyer... at least on wet power =)


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Old 08-24-2011, 04:02 AM   #11
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Tommy-- You must be tired of her by now. You should think about selling her to me.

Mike
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Old 08-24-2011, 06:19 AM   #12
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Originally Posted by tommytorino View Post
I can assure you, the Razor is a wonderful flyer... at least on wet power =)
I hope to find out for myself soon. I'll let you know how it performs on "dry" power.
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Old 10-13-2012, 04:00 AM   #13
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I am building the Balsa USA Fokker D V111 in 1/4 scale, I plan on using the E Flite 110 with an 18x6 prop on 8S lipo ,based pon my experience with this motor, it should have enough power for scale flight, the 160 might be a better choice for added Weight up front , might also spin a larger prop for more scale, does anyone have any pics of batterry install from under the front of the fuselage. Cheers.
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Old 01-29-2013, 12:51 PM   #14
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I am planning a electric conversion on this kit anybody with any inputs apprieated

thanks zz
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Old 01-09-2014, 03:03 PM   #15
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Any updates on the DVIII anyone?
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Old 07-31-2014, 12:02 PM   #16
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Hi All,

I hope this does not come across the wrong way; but, I just launched a iPhone app for this exact purpose. Its called rc-wingman propeller found at rc-wingman.com. If you like to check it out and if you have a iphone 5 I would be happy to set you up with a complimentary version, and if you don't have an iphone I would be happy to send you some of the application calculation results for your reference. All I will need is:

1. Total weight of the Aircraft
2. Total wing area
3. Maximum Diameter of Prop that can fit on the model.

The application will figure out and number of combinations with Thrust to Weight rations, Motor Watts, Burst Amps, Lipo sizes etc for a number of flying styles.

Cheers!

Art
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