My Fokker DVII Project

Von Writter · 26 October 2009, 08:27 PM

Quote:

Originally Posted by jumpinjan

The loads are on the bolts and the holes, not on top of the spars

Thanks Jan, I was going to point that out but you beat me to it.

franzkait · 26 October 2009, 08:48 PM

about metal fittings and wood . You mount the fitting to the spar with no play at all . 2 weeks later you can turn this fitting easy with your fingers and shake it a little . Again some time and the fitting is like solid and you can not move it . Same with the wires in the wing , after you gave the turnbuckles some tension , a little bit later the wires are lose and you can move them up and down . Some weeks later this wires have so much tension that you get scared something will break .So the hard wood spacer is necessary .

The fitting and bracket are 2 separate parts . If you pull the fitting up the bolts take all the load , but if you pull this fitting down , the top of the spar takes the load .

John McKenzie · 27 October 2009, 04:18 AM

A Question for the Engineers ....!
Jumpinjan ..The loads are NOT just on the bolts ...These will look after tension loads pulling the fitting up away from the spar, ( In case of lower wing ) ..The COMPRESSION load from the " N " strut is taken , Thru' the flanged socket , directly TO the SPAR face ....Thus the need to consider the compressive strength of the spar wood accross the grain , and then wether or not there is a need for " Hard facing " of the spar .
The D VII wings , ( Although the spars have adequate strength individually )are not deseigned to be completely " Tortionaly" independant .Due to C.P movement under varying flight conditions , there exists the tendancy to twist accordingly....(This in the EV/DVIII being resisted by the ply stressed skin ).
In the DVII , the deseigner has elected not to use this method ,..Neither has he made the individual spars so strong ( And therefore Heavy )as to be able to resist this twisting on their own .
Rather , he has , in order to better save on weight , but still retain the reqd. strength ,..." Invented " the " N " Strut , which through its rigidly tying of the upper & lower spars together , prevents any twisting of Either upper or Lower wing .
In performing the above resistance to the tendancy of both wings to twisting under ALL varying conditions occuring ,. the loads imposed through the " N " strut at the socket ends , at the 4 joints to the spar , can therefor be either tensile OR compressive ( normal to the spar face )...depending on the conditions .
I hope that this explanation , along with Udo's post clarifies the loading situation at these fittings .
Best regards John

jumpinjan · 27 October 2009, 05:20 PM

Quote:

Originally Posted by franzkait

The fitting and bracket are 2 separate parts . If you pull the fitting up the bolts take all the load , but if you pull this fitting down , the top of the spar takes the load .

OK, I understand, I didn't know they were two pieces. I suppose the socket needs to rotate to align to the pin holes in the ball end of the strut for assembly.
Jan

Maxim08 · 27 October 2009, 06:09 PM

Jan,
The socket is one piece and the strap/bracket another. The socket has a flanged base that is retained by the strap/bracket. Many drawings show this base to have two flats milled on the sides of the socket which would prevent rotation.
My previous post pointed out no evidence of an additional piece on top of the spar and under the 'N' strut socket so, my question is, how would this harder wood be intorduced to the beam of the spar? Inlet into the top and flush? While we are discussing harder woods, it is not uncommon to insert hardwood plugs into softwood spars where bolts will be located. Is there evidence of this on Fokker swallowtail blocking or does the ply web on the spar perform this function?
BTW, the GWFM wings with 900+ hours of use have neither hardwood inserts or anything under the sockets with no sign of damage to the top of the spars.
Regards,
John

Maxim08 · 27 October 2009, 06:19 PM

Jan et al,

I very poor image, but the best that I have. This was taken about 10 years ago while there was still access in Ottawa to bits left over from the D VII restoration performed in the 1970s.

The socket on the right is the style commonly shown in 'new' drawings. The other appeared just as old but there was no documentation to indicate where these came from. The interior of both sockets is the same radius and depth. The left hand style is what the GWFM has used successfully on their reproduction.

Regards,
John

franzkait · 27 October 2009, 08:25 PM

There is an old and a new one

?I do not know what kind of drawings you guys use

. A D7 has both , the round one and the one with the flat sides .

John McKenzie · 28 October 2009, 03:32 AM

Hi John (Maxim ).Jeff and Udo .
Looking at the photo ( post 1676 ) of " Fokker " built wing , which was " Re-built " in the 70's by Joe DeFiore etc. There are a couple of points that I'd like to point out , that might make the establishment of this particular area around this fitting ,as perhaps a little suspect as due to the rebuild of course , the " Chain of evidence " has been broken .
1) Looking at the visable front face of the spar,- This has , during the restoration , been..a) Either packed out with a veneer , or b) Re-faced with a veneer ,... it having been tacked on ,or doweled on at 4 ( visable ) points .Thus it is impossible , even if the bracket were removed , to establish IF the holes below this re-facing are in the original position .
2) The bracket , whose job it is , to hold the flanged fitting down tight against the spar face ,(Or spacer ,if this is the case ) is " Notisably tilted " over to the right .....This would Not have been built like this originaly as it does not fullfill the aforementioned objective .
3)This indicates that " at least" one of the " Bolt holes " are NOT NOW in their original positions .
4) For a variety of reasons ,( which can only be conjectural now ),The original holes may have at least been " Plugged ", and redrilled inaccurately . It is also possible that considerable other New work was undertaken in this area ...We'd have to see documentation of the area , " Pre- Restoration " by JD.
5)..THEREFORE , If the fitting is not proved to be in the original position , then all derived conclusions from it Re ." Hard wood spacer - or not " will be invalid .....In respect to THIS PARTICULAR fitting .
*HOWEVER ,*
6) Should most of the other (3) places , where the N strut fittings attach be " Un restored ", then these will prove wether there " Were" , or "Were-Not" , spacers fitted to these particular wings,..And this then should be taken as the provenance .
Regards John M

Addition to point No2....The top face of the bracket also looks Twisted and the gap under it (supposedly 2mm ) does not look at all right , especially visable on the far RH top side . In fact , it doesn't even look like the bkt fits or alleigns to the spar top bevel ( +2mm ) at all.

Jeff Brooks · 28 October 2009, 05:12 PM

Hi all,
Today, I got in the mail the hand pump Pavel made for my plane.
She looks awsome.
I attached it to the frame temporarily. I still have to paint it and make a few modifications to the forward clamp.

zffltd · 28 October 2009, 05:17 PM

Quote:

Originally Posted by Jeff Brooks

Hi all,
Today, I got in the mail the hand pump Pavel made for my plane.
She looks awsome.
I attached it to the frame temporarily. I still have to paint it and make a few modifications to the forward clamp.

Jeff
I made the clamps for frame of set so the clamp holding pump do not need a spacer's. Turn them around and use shorter bolt's. Use a AN24 bolts sloted head. I sent you cople emails how to conect pump. The way whic you mount a pump will be very looseto long bolts.

Pavel