Gwfm d vii

[Von Writter]

Originally Posted by Maxim08

A bit of a breather in the hangar today involving general tidying up etc.
A few things accomplished. Rino and the paint team have sprayed epoxy primer on all of the control surfaces.
Created two small jigs for fabricating some pieces and, we weighed the fuselage!

Jeff, take note. Completed fuse with tailwheel spring but no seat or stick, 138 lbs. with your scale. I can't locate my McCook reports so I do not know how this compares. The French report used by the 1918 Flight article included the Damiler/Mercedes engine in it's fuselage weighing so doesn't help much.

An interesting and undocumented feature came up when we trial fitted a crankcase to the engine bearers. Our D VII has the engine shifted approximately 7 inches forward of where it should be. The cowling frames are lengthened as well. It has been flying in this configuration since 1977. Frankly, never having seen it in close proximity to a 'real' D VII, no one ever noticed. Not even on the set of 'The Aviator' where a couple of other D VIIs were sitting beside it.

The pilot reports indicate that this aircraft flys in a tail down attitude. Mind you, reports from the era indicate the same attitude in cruise. The question is really for other builders of Ranger powered D VIIs. Should the engine be shifted forwards?

Interested in any comments (Jeff!!)

Regards,
John

Speaking of this engine position, do you (or anyone else) know the CG location of the Mercedes engine? i.e. X number of inches from the prop hub... Builder needs to know.

[Maxim08]

Gary,
You are correct. It should be all 0.039" material and, ideally 1025 steel.
When first built in the mid 1970's, the team used 0.049" 4130. Our repairs matched this material.
A quick guesstimate suggests that the fusealage should be about 25% heavier than an original.
A local aeronautical engineer recommended 0.035" 4130 as a substitute for Fokker's 1mm mild steel.
Regards,
John

[gipsymoth236k]

Hello John,

Thanks for your answers to my questions! As always, I really appreciate your fine help with my Fokker research. Here are a couple of what I hope will be taken as constructive comments regarding this and other reproduction Fokker aircraft:

FUSELAGE COMMENTS: Yes, I thought this repro D.VII's airframe may have been constructed of the heavier 0.049" (= 1.26mm, or 26% heavier than original) wall thickness. I too would think that 0.035" (= 0.9mm is OK vs. the original 1.0mm) wall thickness would be most suitable and much lighter than the heavier 0.049" wall, even in 1025 mild steel.

TAIL COMMENTS: I've also noticed that in-fight photos of this repro D.VII show that the elevator must be constantly held in the 'down' position (forward stick) much more so than we see in the original wartime in-flight D.VII photos. We know that slight tail-heaviness was intentionally designed into the Fokker fighters for low cruise power, fuel savings patrols, which also resulted in a far less fatiguing 'neutral' control stick position input for the pilot. But this repro appears to have TOO much down elevator, or tail-heaviness designed into it. This is why the repro's lighter Ranger engine (vs the original heavier Mercedes or BMW) was positioned several inches forward from the original design - to help balance against this repro's airframe tail-heaviness. To add to this, I suspect this repro's tail tubing may ALSO be constructed of heavier wall thickness than originally designed for by Fokker. In the original D.VII design, all tail tubing wall thickness was of 0.5mm (0.020") except for the rudder and elevator spars, which were both of 1.0mm (0.039") wall thickness. If this repro's tail tubing was made of all 0.035" or even worse, 0.049", it could weigh as much as TWICE the original's weight! All this added weight my be a throwing unnecessary over-engineering at the expense of aircraft performance suffering for it.

Anyway, I for one dearly love to see these machines get into the air, especially Fokker reproductions, so I really look forward to seeing your repro D.VII get back where it belongs!

BTW, all these design details are featured in the newly updated REPLICRAFT Fokker D.VII Plan Set of masterpiece drawings located here:

About Replicraft

Regards,
Gary Sewall
garysewal@aol.com

[Jeff Brooks]

Gary, I too went through this wall thickness issue with my plane.
Using an excel spreadsheet, I put the weights per foot (as advertized in the aircraft spruce catalog), converted feet to mm, then added the lengths of ALL the tail feather parts. By playing with the varing wall sizes, and tube diameters, I was able to get the horizontal stab & elevator to weigh exactly what they should weigh in accordance with the weights on the mccook report. without distorting the measurements of the outside structure.

[greatwarpilot]

Jeff,

Do you have the McCook reports readily accessible? I'm quite curious to hear how the GWFM Fuselage weight John quotes in the above post, compares with the original weight of a fuse.

Gary - John will undoubtedly correct me if I'm wrong on this, but I'm under the impression that the tail feathers of the GWFM D.VII are also made of .049" tube.

Sincerely,

[sheppo]

I had similar experiences with the Dva. The modern tubes from Aircraft Spruce worked out just a tad over double the weight due to wall thickness and the diameters supplyable. Im going with metric seamless mild tube ex Europe. I have to fudge on a couple of tubes but certainly its going to be much closer to the original. With a (most likely) lighter Auto conversion engine up front this is a critical issue for me.

Im obviously deleting the ammo from the Ammo cans to reduce all up weight and most likely slinging a weight battery (or 3 ) up front to keep the C of G and all up weight as close as possible to where it should be.

Chris

[gipsymoth236k]

Originally Posted by greatwarpilot

Gary - John will undoubtedly correct me if I'm wrong on this, but I'm under the impression that the tail feathers of the GWFM D.VII are also made of .049" tube.

Sincerely,

Well if it is indeed of 0.049" - OUCH! Can you say "TAIL HEAVY!"

Here is a YouYube video of two Fokker D.VII reproductions flying that clearly show this tail-heaviness (down elevator) issue. Especially watch for the GWFM red and blue D.VII's scenes, then carefully watch for the down elevator action in the footage. You will see that these D.VII repros indeed fly very tail heavy!

YouTube - Fokker DVII

YouTube - Fokker DVII

Fokker Builders - all this may be good to keep in mind! The correct and original type of metric dimension tubing is indeed available, but you may have to pay more for it! I think it's worth it!

Regards,
Gary Sewall
garysewal@aol.com

[Maxim08]

Gary,
All valid comments and part of our internal discussions. Thank you.

The tail feathers are overweight by 15 pounds.
The tailwheel and spring is about 3.5 pounds heavier than a skid but a necessary 'evil' re hard runways.
The ailerons are each 3 pounds heavy.
The wing is 20 pounds on the high side.
When I find my McCook reports I will let you know how the fuselage compares but I personally believe that your calcs are about right.

If building accuracy was the only consideration for this aircraft we would probably start from square one and use metric tubing, buy Achim's streamline etc. but this isn't my aircraft, it belongs to the museum.
When I took the lead on this project I had to balance my desire for authenticity with other perspectives within the GWFM. The pilots generally just want something to fly, many of the non-flying members want the aircraft completed as quickly as possible, another group wants to build and exacting reproduction and the board wants to ensure that we can continue to fund our other ongoing projects.
The compromise that I put to the board of directors was to rebuild the aircraft to conform to the original Rousseau drawings from 1965 and as defined in the CofA from 1977.
This mandate allows our team to undue many of the 'improvements' engineered in the past and finsh with an aeroplane that will have some improvement in flying characteristics (a little lighter and 0 timed engine), be visually closer to what we now take as an accurate look, be u/s for as short a time as possible and provide a better piloting experience. All this within the thin budget that the museum can provide.
There is a proposal to rebuild the tail surfaces in the future as part of an upgrade program which would certainly improve matters but must be put aside for now.

Don't forget, warts and all, this aircraft has one of the longest continuous histories of airshow work for a WW1 reproduction. Every year from 1978 until August 2007 flying in Canada and NE United States.

Like Jeff, I am incorporating many of the weight saving techniques and more authentic design concepts with my own aircaft.

I am glad that you are following our efforts.

Regards,
John

[Der Grüne Flieger]

John,

As I look at the video, I would say that the other DVII looked to be more tail heavy than the GWFM a/c. Could have been the camera angles, but some of the shots made it look to be really bad. Do you know the a/c, could you comment on it?

P

[greatwarpilot]

Der Grüne Flieger,

Are you asking about the non-GWFM D.VII in the video clip? It appears to be the ORA, Mercedes-powered D.VII replica.

Cheers,