HK Specter 1800 - Page 4 - RC Groups
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Aug 04, 2012, 12:15 AM
Trex 700, Gaui X5, 450DFC
SoarWest's Avatar
Did any of you consider wing bolts on the front of the wing, or are the pins pre-aligned and provided as the install method? I hadn't seen pins used like this before.
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Aug 04, 2012, 01:32 AM
JimNM's Avatar
On the passer x, there is a 45 degree bevel on each wing leading edge that fits the bulkhead on the fuse. Dunno about the spectre...
Aug 04, 2012, 02:22 AM
Registered User
Hi, guys. I've been dodging thunder storms here on the frozen tundra and forgot to log out. Minnesota was hit by a huge line of T-storms that looked a lot scarier on radar than any events I saw. But there was a pretty decent light show. All that lift I was in today had to go somewhere!

I decided to play around with some high speed stuff today so I didn't set any duration records but I sure had fun. There were lots of small but violent thermals that, judging by the varying vectors, were rotating almost enough to become dust devils. After my little disorientation episode yesterday I decided to bail out of boomers early. I know how fast I can dive without folding the wings and it's fast enough to sing if not howl. I'm not sure if my cooling scoops added to the noise but it was a great sound!

To the best of my knowledge the music wire wing pins were my idea. The so-called instructions didn't say what to use but they showed something sticking out of the wing and I didn't find anything in the box that looked the part. Plus there are two holes provided in the thick fiberglass at the front of the wing fairing and the leading edge. They're right at the apex of the 45 degree bevel Jim mentioned (I'll shoot some pics tomorrow.) which places the leading edge in a solid fiberglass pocket. The holes in the wing are about 1/16" into what seems to be solid wood- the ones in the fairing are around 3mm(?)- so I stuck a couple pieces of music wire in them to see how the holes lined up. I was thinking I would just get the wing bolted down and drill 3/16" holes from the nose and use dowels.

Well? They wouldn't quite line up without a little bending but I realized that I could work a tiny notch into the fiberglass to capture the pins so I could bend them for fine adjustment while locating the holes for the wing bolts. I would have just drilled a slightly bigger hole and the notch would be gone.

Long story short: I discovered that the wire provided as sure a fit as any dowel I've used so I enlarged the notches, glued the wires into the leading edge, and made slightly deeper notches at the top of the female holes where any possible crack would move towards the thickest part of the fairing. The wire provides a little bit of give, allows fine adjustment, and securely holds the wings together. There's been no sign of stress cracks and I've been flying the poor Specter pretty darned fast. I wouldn't hit full elevator when it's loud enough to hear but it rolls real nice.

NOTE: Just this evening I started thinking that I should put some heat shrink tubing on the locating wires to add a little more cushion. But it's past my bed time.
Aug 05, 2012, 09:58 PM
Registered User
No flying this weekend but I discovered the first damage to the Specter. A short crack in the leading edge sheeting at the root. My guess is that the air loads, especially during my harrowing bailout from a thermal, combined with an imperfect fit at the fairing created enough stress to split it. It's easily fixed with a little thin CA but I'm going to have to rework the fairing a bit.

Most importantly, I'm going to "glass" the center section with Sky-Loft, which is a nylon silkspan-like covering. It's lighter than the lightest glass cloth and surprisingly tough with good flexibility and surface hardness. This is by no means a necessary mod and I wouldn't bother if I hadn't missed the poor fit after my wing pins were in. (BTW. The pins didn't fail in any way and I took them out by heating the music wire with a torch and I'll replace them after I get my fairing reworked.) Now that I found the problem it will just take a few minutes with the Dremel to get rid of a couple protrusions. Then I'll have to do some putty work.

I'll decide on what I use after I get done grinding. If I get the profile right for the glassed wing root I may not need any filler or be able to just dress it up cosmetically with a little Gorilla Glue.

This is not the fault of the kit. I misaligned the wing pins and holes and didn't realize it because the fit was nearly right. I wouldn't have noticed it if I hadn't mounted the wings separately and realized there was a gap. The only reason that I'm "glassing" the center section is the split sheeting. Secondarily its so I can take advantage of the slightly bigger profile to reduce grinding.
Aug 05, 2012, 11:45 PM
Trex 700, Gaui X5, 450DFC
SoarWest's Avatar
Thanks for sharing, it sounds like a picture or two to help understand this would be very helpful ;-)
Aug 06, 2012, 01:54 PM
Registered User

I ran out of hands.

I wasn't really able to get a decent picture of the wing when it didn't fit but here's a shot of the wing saddle/fairing. A small drop of epoxy resulted in the wing being about 1/32" away from the leading edge and that allowed the wing to move under stress. The crack in the sheeting was right at the end of the fairing and ran about 1 1/2" in from the root rib. Now that I have the offending epoxy out of the way I don't think I'll need to bother glassing it. I'm still working on exactly what I'm going to do to make the pins self-aligning so I'll post another pic when I get it figured out.

Just to reiterate: This was my screw up
Aug 06, 2012, 07:23 PM
Registered User
Just an update.

I think I've got everything fixed but my camera batteries died and I'm waiting for some glue to set so I'll post pictures tomorrow. I bored out the bolt holes and filled the gaps with epoxy and talcum and added hardwood pieces for the wing pins. My biggest setback was when my 30 year old Dremel crapped out.

I decided to save $20.00 and try a Menard's brand rotary tool. It's a little bulky but seems like a decent tool. I'll probably post a mini-review after I've had a chance to play with it more.
Aug 07, 2012, 12:21 AM
Registered User

cool plane if you have room to land it

I had a heavy passer x that was fantastic for the price. In a straight line its glide ratio was amazing. Ended up losing it in the lee side of a 1000 ft ridge but had a lot of fun with before that. You can shove a carbon tube through the balsa ribs all the way up to the servos as a super stiff wing joiner.
I found those ailerons too little to be effective as spoilerons, and the thing was a real challenge to land in a tight spot, requiring hard 360s at 5-10 feet. If I ever got another (and I may) I'd rig either flaps or spoilers into the wing.
Aug 07, 2012, 01:13 AM
Registered User
Well, Adriel_, is it possible that the Specter has bigger ailerons? I have found the
"spoilerons" to be quite effective.
Aug 07, 2012, 01:30 AM
JimNM's Avatar
I get lots of throw... 40 degrees at least. Like throwing an anchor.
Aug 07, 2012, 08:00 PM
Registered User
Still no pics but I've got my wing mount all fixed up. I just glued a couple pieces of hardwood inside the fuse and filled the gaps with Gorilla Glue; mostly just to provide a channel, hardened with a little CA, to steer the pins to their holes. It's funny how sometimes one fails to recognize a weak point until it's fixed. I feel much more confident about going fast enough for the Specter to sing.

Jim, I get a little over 50 degrees of spoiler and I agree. It's like an anchor. With any headwind at all I can let it mush for a nearly vertical approach. It did take a bit of trial and error to mix in down elevator with spoilers but now it's very easy to fly on approach.
Aug 09, 2012, 03:36 PM
Registered User
I've been paying with my new batteries. I picked up 2 Zippy Flightmax 1600mah 3 cells from HK. Big surprise? They are actually a bit lighter than advertized and only 4 grams heavier than the Sky-Lipo 1300s I've been using. I figure I can climb 6-8 times and have a total flight time of over an hour but I doubt I'll ever manage that even if the lift cooperates because my neck and eyes start barking at me before that long of a flight.

I also finally got around to checking my cg and throws now that I have everything trimmed out.

CG is at 72mm from the leading edge for very light wind and I move it forward to about 68mm for more breeze. That's about 25mm forward with the new batteries.

Ailerons have 11mm up and 8mm down. I actually use negative expo of 20% to keep them really sensitive around center.

Spoilerons go up 23mm and I have 1-2mm down elevator mixed in.

Elevators are 8mm up and down with 30% expo and they move about 9mm for rudder which has no expo at all.
Aug 09, 2012, 06:30 PM
Trex 700, Gaui X5, 450DFC
SoarWest's Avatar
Really useful information! This is wonderful to have and when I setup mine will use this as a starting point before the first flight. This along with the engine, ESC, Prop info you've shared really make these threads wonderful. The kinds of info you only normally get through pain, trial and error! Thanks.

A couple of questions, when you say "that's about 25mm forward with the new batteries" can you clarify the meaning there?

Negative expo might be normal depending on what radio you are using, which is this? An Aurora isn't it?
Aug 09, 2012, 07:34 PM
Registered User
You're welcome.

I move the battery forward about an inch when it's fairly windy and that moves the CG forward about 4mm. That much movement of the CG does little but improve penetration. My personal preference is to keep any glider trimmed so that it approaches it's maximum lift to drag when it's hands off. I just hold a little back stick when I want to slow down in lift.

I'm using Turnigy 9x radio. Positive expo makes it less sensitive around center and negative expo makes it more sensitive around center. I like the ailerons to respond to the lightest touch of the stick. I would recommend going with perhaps 1-2mm less throw on everything and no expo until you start feeling it out. I had the elevator a bit too sensitive for my maiden and it was a bit twitchy.
Aug 14, 2012, 01:35 PM
Trex 700, Gaui X5, 450DFC
SoarWest's Avatar
I received my Specter today. I hope to start building it next week.

In looking over the package I have a few questions. Concerning the tail feathers, how did you go about attaching those? Second is the wing mounting. I'm not sure how to line up the wing with the pre-installed holes in the fuse to drill the wings and assure I get things centered properly. That and installing the wing pins seem to be a tricky part of the build.

I'll review the thread, look for pictures and make a start at this.

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