Fokker DVIII weight & balance

Recently I have done weight and balance on a replica Fokker DVIII.
Because this aeroplane was sold to the next owner without the drawings,
I have no reference for where the center of gravity should be.

The only reference I have are 2 photocopies with the name :
G.H.Ballinger / Bristol / England.

Also I doubt if the position of the landing gear related to the leading edge
is correct.

Can anybody shed some light on this subject ?

Pim Pouw
Earlybirds Foundation
the Netherlands

[baldeagle]

Is that the Fokker D.VIII in Antwerp?

I test flew Brian Coughlin's replica D.VIII (with 160 Gnome rotary engine) and we were worried about how far aft the center of gravity was. If I remember correctly it was at about 39% MAC with pilot and fuel. We found an American report done on a D.VIII at Wright Field in Ohio in the 1920s and the report had weights listed in the level flight attitude for the main wheels and the tail skid. Working these out we got a figure very close to the one we had, so we assumed it would be OK.

The airplane did fly well, but did require a lot of forward stick to maintain level flight. We raised the front of the horizontal stabiliser and raised the trailing edge of the wing, which helped some, but some forward stick was still required in flight. There wasn't much that could be done with adding weight as the nose is so short, and no place to put weight on the rotary engine. The flight characteristics were not dangerous by any means, it was actually a pretty nice flying airplane, but I wouldn't have done a spin in it.

Langdon will probably see this and probably has the Wright Field report.

Say hello to Jaap, I owe him a letter-

Andrew King

Yes indeed it is the Fokker D VIII from Antwerpen , Belgium

But it isn't the one build by Brian Coughlin's. This Fokker replica came from
the Frank Ryders collection. It has an continental 220 radial engine.

This D VIII was involved in a ground loop and hereby the fuselage was
broken ( ofcourse at de cockpit week spot ) and the wing tip damaged.

The original builder must have had an tail heavy airplane because the
battery was moved forward as far as possible. You could see in the way the battery was mounted that this must have been done after the completion of the airplane.

We moved the battery to the back of the seat. Also we put new fabric on the fuselage which I think is lighter then the "original".

Another problem is that this Fokker with an continental is much heavier then an original one.

Greetings, Pim

[baldeagle]

I thought it was the ex-Ryder airplane, Brian's two D.VIIIs are now in California and Florida. I believe the builder of the one you are working on was named Arganbright or something like that. It's now in Belgian colors, correct?
I was using Brian's aircraft as an example, to give you a possible starting point. It's hard to believe that with a 220 Continental on the front that it would be tail heavy. Have you calculated the center of gravity in % of chord?

[gipsymoth236k]

As many already know, Fokker purposely designed his fighters to be slightly tail heavy. This allowed fuel-saving "low cruise power" patrols during that phase of flight. You can see this with in-flight photos of Fokker D.VIIs in formation with their noses sticking slightly up and "down" elevator applied. Of course, during high power settings, more forward stick was necessary to keep the nose level.

The real problem with today's Fokker replicas is that the builders ignore Fokker's original design relative to the tubing WALL thicknesses used. As example, the original Fokker fuselages were made of 1mm (.039") wall thickness, whereas some replicas have been built using larger wall sizes (like 0.049"). More importantly, original Fokker TAIL tubing wall thickness ranged from 1.0mm down to as little as 0.5mm! Often, this too is not being considered in today's replicas, with the results being TAIL HEAVY, OVERWEIGHT, POOR PERFORMANCE replicas. Add to this problem the use of a modern engine that just doesn't have the original's propeller "disk" area of thrust, and the results get dissapointing.

The solution is to do the research and keep things original as designed.

Regards, Gary

The CG on many of the older planes was at the 25% of chord for many airfoils. The Department of commerce (1930's) required aircraft with different requirements to spell them out in the weight and balance sheets. It might be a good place to start. hope this helps...

Dave

[Langdon]

Originally Posted by pim pouw

Recently I have done weight and balance on a replica Fokker DVIII.
Because this aeroplane was sold to the next owner without the drawings,
I have no reference for where the center of gravity should be.

The only reference I have are 2 photocopies with the name :
G.H.Ballinger / Bristol / England.

Also I doubt if the position of the landing gear related to the leading edge
is correct.

Can anybody shed some light on this subject ?

Pim Pouw
Earlybirds Foundation
the Netherlands

Hello Pim,

The original Fokker drawing 93058/1 shows the leading edge to the centre of the undercarriage axle to be 140mm. I have not seen any reliable C of G information, I do have the US Air service wind tunnel test (they made a 1/18 scale model for testing) that Andrew mentions but I do not think it is reliable enough to use as figures, like the distance between the spars, are wrong, also the wing is shown to have more sweep back in its leading edge than sweep forward on its trailing edge, obviously this is incorrect. Having said that the leading edge to axle measurement on their plan works out at 73mm and the C of G is shown to be approximately 440mm behind the axle. They also mention that the most forward position of the centre of pressure is 32.

As far as tail heaviness goes the US Air service flight test report on their two D.VIIIs mentions that it was tail heavy but that the controls were so light that it was not tiresome to fly.

Langdon

[baldeagle]

Langdon,
I thought that the Flight Test Report that we saw showed side view elevations of the full sized aircraft with notations of the weights on the mainwheels and the tail skid in both the three-point attitude and in level flight. Does this sound familiar? My memory may be faulty, I realise now that it's been 12 years. Time flies...

Andrew

[Brad]

One thing to consider is the weight of a modern pilot vs. those 135-140# WWI pilots. Even an average sized pilot today is much larger than that... and folks like me at 100# MORE than the WWI pilots would certainly make it more tail heavy! If I flew an "original" DVIII I'd need to add over 100# to the nose to make it balance the same as it did with the pilots it was designed for.

[Langdon]

Originally Posted by baldeagle

Langdon,
I thought that the Flight Test Report that we saw showed side view elevations of the full sized aircraft with notations of the weights on the mainwheels and the tail skid in both the three-point attitude and in level flight. Does this sound familiar? My memory may be faulty, I realise now that it's been 12 years. Time flies...

Andrew

Andrew,

The one I have (kindly supplied by Roy Houchin) is the wind tunnel test conducted in April 1922 and it is very comprehensive with graphs and simple plans for the aircraft but it was based on findings from a 1/18 scale model, which unfortunately was relatively inaccurate. It doesn't supply the information you mention but possibly - hopefully - it is not the same report, is there any chance in your obtaining a copy of the one you saw?

I will not quote the whole of the document I have as it is quite long but the "results" page starts with an interesting paragraph - remember this is four years after the aircrafts debut which is a long time for the period:-

"The most extrodinary thing about the results is the form of the lift curve, which is quite without precedent. Reaching a maximum at 15° the lift then drops abruptly to a point about 25% below the maximum and starts to rise again, increasing until 42° a second maximum only 10% lower than the first one is attained. The normal force conventionally represented by Z is actually larger at 48° than at any smaller angle. The drag increases rapidly as the angle increases, but the vector point of resultant forces is inclined forward of the normal to the chord at all angles from 37° to 50°."

Towards the end of the document they state:-

"The form of the lift curve suggests some connection between the maintanence of a high lift at large angles and the remarkable maneuverability of the airplane, and suggests that the maneuver of "hanging on the prop" for which the Fokker is noted, may be actual, normal flight at an angle of attack approximating 60°, and not the result of helicopter action primarily."

Andrew please say hello to your parents for me, I had hoped to see them again at the Australian Airshow this year but I understand that the ORA have decided against performing there.

Langdon