Sagitta 600 tow hook

[rduder]

Guys,
Another Sagitta related question:
The plans for my Sagitta 600 show the towhook 3/4 inch BEHIND the CG.
As far as I can remember, all of my other planes show the tow hook slightly forward of the CG.
Question: Is the Sagitta 600 plan correct ? Is it optimal ?

[Fred_L]

Not sure about the plans or what they say. I have a 2m Sagitta with an E205 airfoil. The CG is at 38% of chord, which I think is the consensus for where to have it, and the tow hook is forward of this location by a little bit - around 10mm or so.

The plane flys well and launches as hard as you would be prepared to launch a built up wing.
F

[rduder]

Thanks,
I have the CG @ 38% also, and it flies well at the slope. I have been hesitant to put the towhook at the location that is shown on the plans. It seems that it would be very prone to pop-off the tow line with the tow hook behind the CG.
I will be guessing, but I think I'll center the tow-hook along a line through the CL that is 15 degrees forward of the CG.

[Esprit2]

The plans for my Sagitta 600 show the towhook 3/4 inch BEHIND the CG. As far as I can remember, all of my other planes show the tow hook slightly forward of the CG. Question: Is the Sagitta 600 plan correct ? Is it optimal ?

Despite being a big fan of Airtronics kits, I've never liked how they handled the CG and tow hook locations on the plans and instructions. Considering that a lot of their kits were aimed at beginners, they could have been more forth coming about the proper CG/ tow hook relationship.

As a generalization, the tow hook should be a little forward of the CG. For most woodies of the period, a location down and forward about 15 degrees from the CG would be a good starting point. However, Airtronics didn't talk about that relationship in the instructions.

What they did do was to usually either show the CG as a range (two hash marks, or a fat, block arrow), or an arrow pointed to the forward limit as a suggested starting point. Then the plans show the tow hook location where they liked it, without any mention of how it should relate to the actual CG location used. There's a disconnect between the two. And unfortunately, many flyers were beginners while the Airtronics guys were experienced fliers, had the model all trimmed out with a more aft CG, and moved the tow hook back accordingly.

The problem is that if the modeler used a forward CG location for a tame first flight combined with an aft tow hook location indicated on the plan, it created a stall-stall-happy combination on launch. I've seen a number of brand new Aquila Grande's snap stall into the ground right out of the flyer's hand. Crunch. "But I set it up just like the plans". Yup, that's the problem.

Having said all that general stuff about Airtronics plans and instructions, the Sagitta does like a more aggressive tow hook location than most of Airtronic's earlier woodies.

The Sagitta plans use a fat, block arrow to indicate the CG. It's max width reflects the recommended CG RANGE. The arrow's point is at mid-range. The tow hook location shown is only appropriate for a CG located at the aft edge of the arrow's width. If you place the CG anywhere other than that, move the tow hook a similar amount in the same direction in order to keep the relationship safe.

If you start with a more benign forward CG than 38%, then you will probably migrate back to 38% pretty quickly as you trim out the plane... moving the tow hook as you go.

A tow hook location 15 degrees down and forward from the CG would be a tame starting point for the first flight; but it would be pretty milquetoast for the Sagitta. If you start there, then you'll probably quickly move the tow hook back to something more directly below the CG as you trim out the plane. However, if you do start with a forward CG, then do not start with the aft tow hook location shown on the plans.

If you're an experienced pilot and not using an adjustable tow hook, then balance the Sagitta at 38% of the chord and put the tow hook right below the balance point. That should be pretty close; but if your only other plane was an Oly II, you shouldn't go there in one step.

Good luck,
Tim

[aeajr]

The Sagitta 600 kit parts that I still have on the shelf has an adjustable tow hook. Is it possible your planes are showing the mount points for an adjustable tow hook rail?

[rduder]

Contrary to the blueprints included in the kit, I balanced the CG @ 38% per Larry Jolly, & centered the tow hook under F4. This is working out very well. The plane has made the transition from slope toy to winch toy with nice stable launches and good control response on tow.

Check-Out the covering job....
http://www.bayrc.com/boards/viewtopic.php?p=30681&highlight=#30681

RD

[dion9146]

I wish I would have had this internet advice 20 years ago.

After spending a lot of my hard-earned college money on a Sagitta 600 kit, putting lots of care into the build and covering of the straight winged aileron version, and finally setting the tow hook location to the plan specs, she popped off a hi-start on its first real launch. It performed a perfect '10' cartwheel and snapped the tail. It never flew again, and I've wanted another Sagitta ever since. :rolleyes:

Dion

[s2000]

Keep in mind that back in the day, a lot of us were using a captured towhook, this was about the time zoom launching caught on, we would pull hard at the top and just release the towhook for a zoom. (and would you believe I saved those releasable towhooks!, they are still in my parts bin, thought they might come in handy someday for something.) I might have to post a picture of one.