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Mar 06, 2016, 04:55 AM
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DustBen's Avatar
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Fokker D VIII


I am beginning to put together the materials and components to build an 80" (min) Fokker D VIII.

Balsa USA has one available at about the size I have in mind but I've read mixed things about the design; in particular, way too much wing incidence.
If this has been revised in the kit, please tell me.

But, I'm also considering other designs. I can scratch build from plans and enjoy it. If people can recommend a design (with plans available) for a valid D-VIII, I'd love to hear the ideas.
But, I'll be less likely to use a design less than 54" or so I can enlarge drawings to suit the scale I prefer.

I'm figuring the design will need about 100 watts per pound and also imagine an 82" design to come in around 12-14 lbs. So, it'll be around 1300 watts at take-off... fairly easy to do.

I won't do a build log on it. Other than the gear and cabane struts, the model is relatively simplistic. I'm thinking of using 2, 4000 mAh, 4 cells in series. The Lipos will probably mount behind or straddle to the motor. The short nose configuration might be the biggest challenge of all.

So, let's hear the design recommendations. What D VIII's out there really fly well?
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Mar 06, 2016, 09:37 AM
Sleepy Hollow, IL
http://texasrcplanes.com/fodvrcai82on.html

DustBen,

Look into the D-VIII from Texas RC Planes. They have it in 82" and 110" sizes. There may be some threads on the plane for information.
Mar 07, 2016, 07:39 AM
Registered User
WooHoo at 100 watts a pound it will fly like a rocket. for scale like flight 50 or
60 watts will be about right. see Keith Shaw's comment s on scale like flight.
cheers hugh
Mar 07, 2016, 03:03 PM
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Doug Bartley's Avatar
I would have to ask why you would choose an 8S system on a 13 lb +- plane when 6S is perfectly capable of delivering 1300-1500 watts easily with 8 minute scale flights on a single 6s/5000 mah battery. Just curious Doug B
Mar 08, 2016, 02:09 AM
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DustBen's Avatar
Quote:
Originally Posted by Doug Bartley
I would have to ask why you would choose an 8S system on a 13 lb +- plane when 6S is perfectly capable of delivering 1300-1500 watts easily with 8 minute scale flights on a single 6s/5000 mah battery. Just curious Doug B
Simple enough... I think.
I have the batteries already.

The other I have are 5000 mAh, 5 cells (rather large packs).
Below that, I have 2200's... both 3 and 4 cells.

I could double up the pair of 2200's, but not have much duration.

The power array is secondary to the flight characteristics of an existing design.
There's not many variants of a D-VIII around so I want to know about known, successful kits/plans.
Mar 10, 2016, 08:49 AM
So I'M meant to be in control?
Colonel Blink's Avatar
I'm no überexpert but I think this '100W/lb' is outdated now. It came from the days of brushed motors which ran at far lower efficiencies than todays brushless outrunners - I think in the order of 60% as opposed to 80-90%. As the watts we measure is 'input power', a modern motor turns more of that input into propshaft power. Hence although the (not easily measured) output power requirement hasn't changed, the (measurable) input power requirement has reduced significantly.

As Oneson1 says, at 100W input it would very likely want to tear the wings off at high speed (which with the DVIII's reputation, may be a little too much realism for anyone) - I'd agree that it would fly easily @60W/lb - or 70W/lb max if you want plenty in reserve.
Mar 11, 2016, 06:11 PM
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DustBen's Avatar
Quote:
Originally Posted by Colonel Blink
I'm no überexpert but I think this '100W/lb' is outdated now. It came from the days of brushed motors which ran at far lower efficiencies than todays brushless outrunners - I think in the order of 60% as opposed to 80-90%. As the watts we measure is 'input power', a modern motor turns more of that input into propshaft power. Hence although the (not easily measured) output power requirement hasn't changed, the (measurable) input power requirement has reduced significantly.

As Oneson1 says, at 100W input it would very likely want to tear the wings off at high speed (which with the DVIII's reputation, may be a little too much realism for anyone) - I'd agree that it would fly easily @60W/lb - or 70W/lb max if you want plenty in reserve.
What I want in reserve is the weight. The mass on the extremely short nose.
I can always prop the plane down to whatever the airframe needs to fly competently.

It's what I did on my 1/4 scale Corben Baby Ace. The first flights were done with 1800 watts available. I later propped it down to about 1000 watts, and that's still plenty!
------------

But, the power is the easy part of the project. I'm still looking for a known good flying model design.
I don't want a hangar queen that is no fun to fly.
Mar 12, 2016, 07:05 PM
Ron
Ron
Registered User
The balsa USA model flies quite well. On mine I made adjustable rear struts for changing the wing incidence just in case...turns out it wasn't needed....when I discovered that all I needed to do was be fussy adjusting the C of G...once that was set, it flew well...that was 8 years ago, and it's still going.
Mar 13, 2016, 12:27 AM
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DustBen's Avatar
Quote:
Originally Posted by Ron
The balsa USA model flies quite well. On mine I made adjustable rear struts for changing the wing incidence just in case...turns out it wasn't needed....when I discovered that all I needed to do was be fussy adjusting the C of G...once that was set, it flew well...that was 8 years ago, and it's still going.
Ok... this is what I wanted to hear. Thanks.


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