DR-1 (Sands): Builders Group

[vongrube]

Thanks a bunch!
Would sure love to have a copy of that issue!!!

[Fokker210]

Worked a little this afternoon on building a test spar bracket - just to get a feel for it.


One question ?? What is the most accurate way to drill the mounting holes ? I constructed a drilling fixture just as outlined in the plans but just have the top and bottom plates...the plans call for plates on the sides as well to locate the brackets for drilling but I am just not seeing how this would line the brackets up correctly. What am I missing here ??

Could anyone post a pic of their fixture or at least shed some light on what I am missing out on ?? I'm sure this is something terribly simple and I'm just suffering from a little brain fade but any help would be appreciated.

[Fokker210]

As far as the spar nutplates go....the plans call for a piece of aluminum backing .030 thick and specifies that this plate be countersunk on the reverse for the rivets. How exactly does one countersink such thin material...or would it be better to just use a thicker piece of aluminum here...???
Once again, many thanks !

[joepilot]

The current EAA article on the flight characteristics of the Dr.1 was very good and probably gives us all a first hand description that few of us have. The comment he made about the F-16 and the computer flying the jet was right on target. For those who do not know, the modern jet fighters have varying degrees of Computer Augmented Systems (CAS), where the computer actually moves the flight controls minutely throughout the flight. Imagine "stirring" the stick and that is what the computer does only much smaller. The F-15 had a mid-air and tore off the entire right wing. The computer stab system augmented the loss of the wing and it flew home successfully. These fighters are likened to sitting on top of a pin, and so too, the Dr. 1 sits on a pin and we the pilot must fly this inherently unstable aircraft. Fokker built it this way as that is the success formula for combat. When someone shows up at your 6 o'clock and starts throwing lead your way, the only survival tactic is to do what we in the business called, "The Funky Chicken". There is a good book on the Tripe called "Three Wings for the Red Baron" by Leon Bennett. In Chapter 11 titled "Maneuverability and the Triplane" he writes,

"Whatever their views on aerobatics, all fighter pilots agree that two maneuvers were critical; fast evasive turns and tight pursuit circles. In these crucial areas performance determined life or death." pg. 149 [This is still true today, now technology gives you speed also. The old fighter pilot saying of "God will let you turn or go fast but not both" no longer applies.]

"The Fokker Triplane, given the smallest span of any production West Front fighter (23.6 ft), was capable of an extremely quick reversal." pg. 156

The significantly unstable Triplane gave the fighter pilot the ability to get out of harms way. The crate skids, slides, pitches, etc. like a true fighter. Stability = Being Killed that is what bombers do. Having done the Funky Chicken and having seen it done in my gunsite, I can attest for instability. Those who do not have any tail dragger time get some before you take this crate up. Those who do not have aerobatic time, specifically in unusual attitudes & upset recoveries, get some. If you are unfamiliar with what I am talking about email me and I can give you some of these flying critical maneuvers to practice. I use to have a 2-ride safety school in a Decathlon. The Pitts is too fast, you won't be at those speeds or "feel" in a Tripe. Get some Decathlon time in unusual attitudes. Remember Rudder is the primary flight control - think in terms of Top & Bottom Rudder.

A level low altitude turn can kill if you aren't speed aware. The author spoke of not being able to look inside at his instruments, especially his airspeed. Speed is Life and there are techniques you can do to prepare you for flying without reference to an airspeed indicator. This talent is critical for dogfighting and to flying in general.

My 2 cents worth

Joepilot
check 6
joepilot@integrity.com

[baldeagle]

There was some discussion of flying a Triplane on page 58 of this thread. My 2 cents from about 70 hours in them is to get comfortable in the front seat of a Stearman with a good instructor in the back, and in the Fokker make wheel landings (into the wind) at first, and most competent tailwheel pilots shouldn't have any problem with a Triplane. I recently bought a Pitts, and not much about flying it translates to a Triplane, although there's no doubt that a Pitts makes you a better pilot in general, and more prepared for any other type. Maybe the Triplane prepared me well for flying the Pitts....

I haven't read the Sport Aviation article yet.

[Dogtail2]

Originally Posted by Fokker210

Worked a little this afternoon on building a test spar bracket - just to get a feel for it.

One question ?? What is the most accurate way to drill the mounting holes ? I constructed a drilling fixture just as outlined in the plans but just have the top and bottom plates...the plans call for plates on the sides as well to locate the brackets for drilling but I am just not seeing how this would line the brackets up correctly. What am I missing here ??

Fokker210,

Nice looking bracket.
I have not made a drilling fixture or started any brackets yet, but took a look at the drawings and am also slightly baffled.
The side plates (for sideways location) would need a lot of packing, as each set of holes is 1" from the sides of the fixture. If the brackets are located by placing the 'hook' of the bracket over the top of the fixture(for up/down location) with top and bottom plates removed, then some provision would have to be made for the radius on the inside of the 'hook'.
Is any of this making sense?

Also I note from the drawing that only flat template dimensions are given for the brackets, with 'bend lines' shown. What exactly is meant by 'bend line'?
Everything Ive read on metal bending refers to 'set back' lines and bend allowance, and usually finished item dimensions rather than (or as well as) flat template dimensions are given. I have a problem with the term 'bend line' and lack of dimensions of item after bending.

Maybe worldcrusier or vongrube can shed some light?

Also, Fokker210,

have you trimmed the 1/8" off each side of your webbed spar ladders yet and what method did you use. Dont fancy my table saw with those long lengths

[vongrube]

"Maybe the Triplane prepared me well for flying the Pitts...."

Oh!..I love that comment!!! Probably true..probably true!
I love the idea of another challenge. The last two times I was REALLY challenged in an aircraft were when I was flying aerobatic competition and flying helicopters.
Helicopters.....now THERE is a "beast" for ya!!
And probably closer to the instability of the triplane than anything else is?
Opinions anyone?

[van der Laan]

Dogtail2


You have hit the nail on the head with Sands plans, he tried to give us a bit of ‘knowhow’ concerning how to build it as well at the plans them self, but as we all have discovered Sands was a bit weak on the engineering side of things. His was a practical plan. Personally, I use his dimensions as absolute and his building technique (e.g. his jigs and methods descriptions) as mere suggestions. Some of them don't make much sense given the number of times I’m going to do certain things. Unfortunately the plans are a little cartoonish in this respect. I’m not drilling anything out until I’ve placed everything in the spars, it’s a bit more custom than, I’d planned but I’m not redoing any of this when I find out Sands was wrong.

anyway my 2 cents

[Fokker210]

Dogtail2, van der Laan, et al.....
What follows is a quick and dirty explanation ( if you can call it that ) of my bracket construction method. Experienced metal fabricators might want to stop reading now or run the risk of uncrontrollable laughter.....

This first photo shows my spar drilling fixture - made using a CNC mill so the hole measurements are as accurate as I can feasably get them....



The next photo shows a fixture I made, again on the CNC mill, for fabricating the interplane strut brackets. Kudos to fellow forumite Worldcruiser for sharing this information and allowing me to benefit from his knowledge ! You can also see a stack of plates covered in layout fluid which have been scribed as per the dimensions by Mr. Sands, and a test piece.....



When this form was milled, I only had the machine drill the two tip holes and one of the middle holes. I added the final hole using the spar drilling jig to insure that the holes were exactly the same distance apart. I know I could have done this all at once but since the fixture and jig were two separate items, I just wanted to be sure that the two sets of holes mated before I started punching holes in my spars. I feel that these are as close as I can get them so I am confident in my ability to make good interplane brackets.

I start by taking one of the marked plates and lining it up with the top of the fixture. When it is aligned, I carefully and securely clamp the plate to the top and proceed to drill drill one hole. This hole then has a bolt placed through the plate and the fixture and it is secured. This is repeated until the entire plate is secured to the top of the fixture ( 3 or 4 bolts depending on the bracket you are making ). The best thing about this fixture is that it can be used to make any of the interplane brackets. Thanks again, Worldcruiser !

After securing the plate, I begin to hand form the flanges over the sides. The fixture is exactly 1" wide so I know my inside width of the bracket will be correct. Once that is completed, I remove the plate from the fixture and place it in my brake to try and attain that nice 90 deg. bend. Then back to the fixture, rebolted and the tapered end pieces are formed around the ends and it is welded up.

The next photo shows a set of spar mounting brackets that were also CNC machined. If you look closely at the photo ( sorry its so bad ) you can see where I had the mill create tiny lines, just a scratch but enough to see. I use these lines to guide me in making that bend on either side....



Now I use the interplane strut fixture pictured above and position the mounting bracket across the top. The inside width of the spar bracket is 1" which is the precise width of the fixture. The piece is clamped down and the sides are hand formed over. These methods have worked out well for me so far.

As I stated in my earlier post, my problem concerns the backing piece for the mounting brackets, the piece that actually gets the mounting holes. Mr. Sands calls out very specific dimensions for the placement of the mounting holes and it seems that these can be thrown off pretty easily unless you are really, really good with your bending brake....especially when making two bends in opposite directions.

I know the plans call for using the spar drilling fixture for accurate hole placement but I can't see how it is supposed to work out. Again, I think I am missing something here.....

Anyway, I am confident that when it comes time to actually start drilling on the spars for the bolt bearers, they will be as close to right as I can get them. I also feel good about the interplane strut brackets. Just these pesky backing plates for the mounting brackets.

As for my above listed methods, if anyone has a simpler, more accurate or just downright better method please let me know...it would definitely make my life easier !

Hope this wasn't too much nonsense !!

[Jeff Brooks]

Obviously you own your own CNC machine. I am having trouble finding someone to machine the landing gear attaching points. (the little socket and sturrup looking thing that you weld into the streamline tubing.) what does it normally cost to make these kind of parts? If I can find someone local to do the work, I am worried that i might be gouged!
Jeff