Feb 28, 2008, 09:39 AM
Red Merle ALES VII SJ
Discussion

# Tinamou

Hello,

History:
The view of a swept flying wing is just beautiful. I saw an article from RCSD http://www.rcsoaringdigest.com/ about a hand launched flying wing by Herk Stokely. http://www.glide.net.au/on-the-wing2/101-Two-HLGs.pdf I've been an internet acquaintance with Herk for many years and thought upsizing this model to 100" would be very interesting. After many emails with Herk and the decision that I'd like to power it with an electric motor we came up with the final design considerations. So I had foam cores cut with 4.5 degrees of twist as per Herk's suggestion. Then life got busy and it ended up in the rafters of the garage. A few months ago I decided to get busy and had to reacquaint myself with the design parameters. As one who needs to know why something is done I got knee deep into Dr. Walter Panknin's design paradym on wing twist for swept flying wings and as such designed a spreadsheet to make the math easier. I call the spreadsheet Flying Wing Calc. http://h1.ripway.com/cloudyifr/files.htm.

Herk had suggested and is correct to reduce the wing twist from 8 degrees he had on his HLG to 4.5 degrees based on my assumption of wanting the model to be electrified. However, as you can see in the next few posts the twist, calculated by Dr. Panknin is a little low for a pure sailplane/glider. This is all based on a desired speed range and Designed Lift Coeffecient. So in order to be able to change the twist to suit and hopefully have a successful flying model the first time out I have cut the elevons into sections so that I may mix additional twist into the outer portion of the wing to obtain a pure sailplane thermalling flying wing.

More......

Curtis
Montana
 Feb 28, 2008, 09:45 AM Red Merle ALES VII SJ Here's my final design. Last edited by Curtis Suter; Feb 28, 2008 at 09:57 AM.
Feb 28, 2008, 09:54 AM
Red Merle ALES VII SJ
Here I'm starting on the spar for the wing joiner. I'll have a one piece center section with plug in tips.

I'm making the model with a center section of about 60" and will have plug in wingtips. So I needed to cut the foam to insert a spar/joiner tubes. What you see here is my hand made foam wire cutter and templates to cut the slots. I pushed four wires down through the top template so that I can align it with the bottom template.

The forward spar joiner is cut and inserted, perfect fit!

Curtis
Montana

### Images

Last edited by Curtis Suter; Feb 28, 2008 at 10:01 AM.
 Feb 28, 2008, 11:03 AM Herk Curtis - It may seem just a bit premature to think about tow-hook location and attachment. Still, the structure needs to be there and in the right place. Since you had once mentioned a fuselage pod under the wing, its depth adds an extra issue for locating the hook. (this is usually more critical on a flying wing than on a more conventional configuration.) As to why it's not premature to consider this question now, is the option of using a bridle tow, with two hooks right on the bottom surface of the wing a bit outboard of the fuselage pod. This option usually works very well and can help avoid the pitch-up-propeller-spin launch disaster that flying wings seem particularly prone to. If you decide to go with that choice, you will need to put the attachment structure into the wing before you skin it.
Feb 28, 2008, 11:17 AM
Red Merle ALES VII SJ
Quote:
 Originally Posted by HerkS Curtis - It may seem just a bit premature to think about tow-hook location and attachment. Still, the structure needs to be there and in the right place. Since you had once mentioned a fuselage pod under the wing, its depth adds an extra issue for locating the hook. (this is usually more critical on a flying wing than on a more conventional configuration.) As to why it's not premature to consider this question now, is the option of using a bridle tow, with two hooks right on the bottom surface of the wing a bit outboard of the fuselage pod. This option usually works very well and can help avoid the pitch-up-propeller-spin launch disaster that flying wings seem particularly prone to. If you decide to go with that choice, you will need to put the attachment structure into the wing before you skin it.
Herk,

I was thinking towhook location last night and this morning so it's funny you mention it. How far out from the center of the wing do you recommend? Also, then how far forward from the balance location. Normally I use about 3/8", but I really don't know where it's going to balance. Would a hard block in between the skins be sufficient?

Not sure I understand the pitch-up-propeller spin.....????

Initially Tinamou will not have a motor but perhaps with a second pod someday. However, I think you're just relating the hi-start launch to a powered launch.

Thanks
Curtis
 Feb 28, 2008, 12:07 PM Herk Pitch-up-propeller-spin -- When the tow hook is too low down or too far back, the towing force causes the plane to pitch up violently into a stall -- followed by a situation where the plane literally goes into a tailspin on the tow-line. It's worse with a hi-start because you can't stop the pull. With a winch you can at least let off the switch and avoid having the model-now-wreckage dragged across the field. Does that sound like personal experience??? More than one!! If you choose bridle tow, you eliminate the depth of fuselage part of the equation. You still need to have the hooks forward of the CG, and even with the hooks on the bottom of the wing, they are still going to be a bit below it. If you figure the CG is on the chordline of the root airfoil, draw an angle from the CG at 30 degrees below the chordline with the vertex at the CG. Draw another angle the same way on this one at 60 degrees below the chordline. If you figure the CG will be above or below the chordline, adjust the vertex up or down accordingly. I like to be able to adjust my towhook in the range between where those two lines intersect the bottom of the wing -- or the bottom of the fuselage -- on any model. Needless to say, with a new plane, I start with the hook at the front of that range. If I put the towhooks in the wing surface, I'd like a riblet, somewhat longer than the range I described above, for them to screw into. It probably doesn't need to be full-depth of the wing, but it wouldn't hurt. Putting them out four or five inches on the wing helps the plane track straight on tow.
 Feb 29, 2008, 11:29 AM Registered User Curtis , I'll be watching your build with interest. I was wondering where the name "Tinamou" comes from.
Feb 29, 2008, 11:43 AM
Red Merle ALES VII SJ
Joel,

Everyone seems to be asking where I got the name from.

Tinamous are strictly neotropical birds -- not found outside the tropics, and nowhere but in the Americas.
Tinamous are large-bodied, almost tailless birds with slender necks and small heads, maybe 30% larger than a bobwhite. They look a bit like emus, but smaller. They fly but prefer to walk or run, and they're secretive.

Hopefully my Tinamou will prefer to fly rather than walk!

Curtis
Montana

### Images

Feb 29, 2008, 04:32 PM
Herk
This is really strange. Curtis is designing a really elegant soaring wing and he names it after what is essentially a flightless land bird that lives in deep tropical rainforests. It's seldom seen and occasionally heard - a reclusive non-soarer.

Gene Dees did almost as bad when he named his 10 foot soarer Icarosaur - an extinct lizard. The lizard at least had rudimentary gliding capability, but --- really -- what's with these guys. Joel at least named his designs after things that really fly.

### Images

 Feb 29, 2008, 11:31 PM Red Merle ALES VII SJ You guys are cracking me up!
 Mar 01, 2008, 08:43 AM Registered User Well, you can probably bet there isn't another wing out there with the same name.
 Mar 03, 2008, 01:40 PM Surf's up!! Great work as usual Curtis. I am subscribing to this thread. Keep the updates coming. Happy Building Chip
Mar 05, 2008, 12:20 AM
Red Merle ALES VII SJ

# Wing Joiners

Well I got one side of the wings joiners completed and glued into the cores. I was so afraid they wouldn't align properly but they came out great.

Here you can see the plywood joiners with the angle cut which will dislpace the loads better than if not cut. They are wrapped with Spyder wire and superglued to make sure they don't come apart and the CF rods installed.

Curtis
Montana