ser00

Hi everybody,

I have an Ultrasport 60 kit on the building table and I was wondering if I really need the 2.12° of dihedral in the wing. I fly an Ultrasport 1000 pretty well. I was told that for a pattern plane, you can built a straight wing and it will fly better overall. I really do not need the little bit of correction that the dihedral provides. Any comments on this? Any suggests as to how the plane will fly without dihedral?

Thanks,

Happy Flying!

Ser00

w8ye

My Feedback: (16)

With the wing on the center line IMHO you don't need the dihedral.

With the wing mounted below the C/L as in this case, the small amount of dihedral is needed to balance flight characteristics right side up and upside down

With the wing above the C/L anhedral would be justified

RCKen

My Feedback: (9)

Ser,
This isn't a discussion for the Beginner's forum. I'm moving this thread to the Kit Building Forum.

Ken

XTOL

Is Great Planes adding dihedral to their version? Because the RCM plans
and the original construction article call for no dihedral other than what
is supplied by the wing taper.

I built mine flat. You can lay a straightedge across the top of the wing.
Flies terrific.

Mike Hammer

ser00

Hi everybody,

Thanks Ken for moving this thread to kit building. Hi Xtol, I have seen your US 60 and that is the reason why I wanted one also. I have an Ultrasport 1000 that I fly but it rather large and a slight pain to haul to the field. I think that a US 60 will do just nicely. Great Planes have a dihedral gauge in the kit to set the dihedral on the wing. I built a wing jig (just like Great Planes wing jig) to allow me to quickly build the wing. When I slid the ribs on it, it looked like the top and bottom of the wing tapered the same amount to the tip. If I was going to build the wing from scratch, I would have done as you did, build the top of the wing flat and the dihedral is introduced on the bottom of the wing due to the ribs getting smaller. This is how the Kaos wing is built if I am not mistaken. On the Ultrasport 1000 (also Great Planes), the wing is built with dihedral in it and the wing tapers on the top and bottom equally. I would like to build the wing without dihedral added into it, but that might require me to not use the wing jig that I built to build the wing. Any suggestions Xtol or anybody else for that matter? Minnflyer?
Happy flying!

MinnFlyer

My Feedback: (4)

If the top of the wing is flat, there is still a little dihedral since it is a tapered wing

ser00

Hi Minnflyer,

First, let me tell you that I have enjoyed reading your builds on the Ultrasport 60 and Ultrasport "Lite", as well as Xtol. I only hope that my plane comes out as good as both of yours. I do agree that tapered wing built flat on top of the wing will naturally introduce dihedral into the wing. I much rather build the wing upside down to ensure a flat topped wing than try to cut and add dihedral in it (which is easy to do, I just want a straight wing on top). Do you Minnflyer and Xtol suggest that I build the top of the wing flat? Actually, I have two kits of the US 60 so I could do it both ways. Any suggestions or advice would be greatly appreciated.

Happy flying!

XTOL

Im not sure it would really make that much difference. Im sure there
are plenty of the GP US60s flying out there built according to the supplied
directions. And I would be willing to bet they fly just fine.

All I can tell you is how I built mine. I built it flat as it was intended to
be by the designer. And it flies terrific.

Just build it. Worry less...build more...

Mike Hammer

ser00

Hi Xtol,

I completely agree. Build more and worry less. I will start with the fuselage first. I am still waiting for my retracts (Robarts 608HD) to come in before I build the wing. I will keep everybody posted how the build goes.

Happy flying!

TFF

Too little dihedral can cause problems; it can cause a "down elevator" effect when rudder is used and with some fuse. designs can cause a rudder reversal when the rudder moves one way but the plane reacts the other. I had a Kaos that did these things and I think the Contender does these things too. I had found some old mag articles how to "fix" these problems, but the real recommended method was saw the wing in half and reposition. This was for trimming a pattern plane to fly perfect before computer radios. I experimented with wing tips like the article discussed and it helped but never was as nice as the next one built with more dihedral. I would build it like the plans unless you know there is a problem.

tmproff

My Feedback: (5)

I just finished my Ultrasport 60 and I put in the dihedral as instructed. In my opinion, I think it actually adds to the looks of an already great looking plane. This plane does not feel like a trainer at all and has plenty of control. I think it would be a good idea to follow the instructions!

XTOL

Well since the Ultra Sport does NOT suffer from any of these problems
its a moot point.

Mike Hammer

CrateCruncher

My Feedback: (1)

I like the look of the top wing surface flat myself and it is easier to build straight doing it upside down in one piece. Either way it'll fly extremely well.

While I'm talking to US60 builders, can somebody give me a dimension from "front firewall surface" to "rudder hinge line"? The Kaos 60 is 44.5" and the US 60 looks shorter to me. THX.

XTOL

And that is exactly why the original poster asked his question.
Because the original designer and the original plans from RCM
build a flat wing and the GP kit plans build in a slight amount
of dihedral. Both ways are right.

Mike Hammer

XTOL

Looks like you are correct. On my RCM plans it measures 43 13/16".
Thats from the front surface of the firewall to the rudder hinge line.

Mike Hammer

tmproff

My Feedback: (5)

I just went out and measured mine and it's right at 44 inches.

foodstick

I know some people add a tiny bit of dihedral to a flat wing because sometimes a dead flat wing will actually LOOK like it is bent downward, like anhedral.. I suppose that it sounds silly, and its only an optical illusion..but I have known people that dislike that look.

foodstick

SORRY, double post.

ser00

Hi everybody,

Again, thanks for all the replies. As I said, I have an GP Ultrasport 1000 built according to GP instructions and it flies great. I guess the best way to really answer this question is for Xtol (who built his wing with a flat top) to measure the height of his wing tip from the table surface. I ask this because if the top of the wing is built flat, you will automatically have dihedral because the wing ribs get smaller as you go from root to tip. It looks to me that if you build the wing on the wing jig or as per GP instructions, you have equal dihedral and anhedral which cancels itself out. The wing tips are to be blocked up 1 1/8 inches and the halves glued together to put in the correct dihedral per GP instructions. I am here at work but the more that I think about it, there might be about an inch difference in height between the root rib and tip rib. If that is the case, my question about dihedral is moot because the dihedral will be built in by building a flat topped wing and not having to add it by building using GP instructions. Also, if this is the case, wouldn't it be easier for GP to tell people to just build the wing upside to get the correct amount of dihedral? Maybe they are trying to get people to buy their wing jig. That is okay, i built my own jig. As always, thanks for the replies and suggestions. Please keep them coming.

Happy flying!

XTOL

I think you have hit upon it. It nows makes a bit more sense. What GP
has done with their kit is NOT add dihedral but actually a bit of anhedral.
They have canceled out the built in dihedral of the of the double tapered
wing. This...if my understanding is correct...results in equal amounts of
taper both on the top and bottom of the wing. Unless I am completely
misunderstanding what you are saying. I dont have a copy of the GP
plans to compare.

Before I couldnt understand why they would add dihedral to a wing that
will spend a great deal of time inverted. (at least mine does). But by
introducing a slight anhedral the wing would be the same inverted as
it is upright. I can see some justification for that.

I dont have my wing handy to measure but it does have significant
taper only on the bottom.

As far as the GP wing jig goes in years past a lot of the GP/Tower
kits had holes precut in the wing ribs to use that wing jig.

I still dont think it would make a great deal of difference but adding
the anhedral would result in slightly better inverted characteristics.
If I was building another one I would still do it flat. I have a number
of planes with double tapered wings and I built them all flat. Its one
way to insure a straight wing. (If your building surface is flat...)

Mike Hammer

CrateCruncher

My Feedback: (1)

Good eye Serr00! I just looked at my GP Kaos 60 plan (same wing) and there is a front view of the wing showing the top surface flat and EXACTLY 1" distance underneath each wingtip measured at the tip rib. I calculated +1.17 deg per panel or +2.34 deg total.
The calc is: Degrees = TAN(-1) Rise/Run

FWIW, it's important to measure the rise at the chordlines of the root and tip rib, if you use the bottom surface angle the dihedral comes out too large. (Yep, I did it that way the first time and got 2.07 per panel! Wrong....)

I got the flat upside down idea from a Rainedave thread. He squares up all the ribs perpendicular to the board and it works great. (XTOL, how did you do yours?) I've since used the idea in a twin I'm designing. I use a 1/4 stick at an angle to the panel to keep the chordlines parallel with the build surface. It's easy to build, looks great and flies even better.

XTOL

Build wing upside down. Pin the top spar down and install the ribs
making sure they are square with the building board.

Install trailing edge...
Kaos plans show jig blocks to use to prop up the trailing edge
to account for the taper. Ultra Sport uses a tapered length of
wood for the same purpose.

Once the jig blocks or tapered stick is in place and pinned down
add leading edge and bottom spar using weight to keep everything
down flat against the building surface.

There are some pictures of this on my Ultra Sport 60 page:

http://tesla-2.dyndns.org/~mhammer/us60/

Mike Hammer

foodstick

It may or may not interest you, but one of the reasons the world war 1 airplane the fokker D7 was such a good plane was that the wings are dead flat across the top, thick in the center section then tapering down to thin tips, it builds alot of dihedral and washout in the wing, but its all in the bottom surface... very similar evidently to this planes performance wing...

ser00

Hi everybody,

Excellant comments all around. I feel alot better about building the wing my way and not GP's way. Xtol, you did understand me correctly in my description of the dihedral / anhedral of the wing. Hopefully my retracts come in Thursday. One more thing Xtol, I really liked the photo of the US 60 in your gallery that has an air intake underneath the propellar. I might do mine like that. I wish everybody many happy flights and great landings!