HK Specter 1800 - Page 5 - RC Groups
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Aug 14, 2012, 01:45 PM
JimNM's Avatar
The tails are stripped of covering at the contact points then epoxied jtogether. Once set, sand the saddle and epoxy tail to fuse.

The wing bolts have pre drilled holes that are covered by monocoat. Locate and punch through.

The wing pins I skipped...might have to re look at that. But the wings once epoxied, are pretty solid.
Last edited by JimNM; Aug 14, 2012 at 02:26 PM.
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Aug 14, 2012, 02:19 PM
Registered User
For the tail I did as Jim did. I just taped some plastic wrap to the tail mount and used it as a gauge and it came out at 117 degrees. Since V-tails seem to be anywhere from 100-120 I figured that's good enough. I did poke some shallow holes in the butt joints to provide a physical bond and then i sanded the fiberglass and made some dimples, like a golf ball, to grab the epoxy when I mounted the tail feathers.

For my pins I began by sticking some music wire in the holes thinking I would just use them to position the wing and found that I could grind a slot and just use the wire. I did, however, screw it up a bit so I had to do it over again and used some chunks of hardwood in the wing saddle. If I were doing it again I would get the bolt holes right and then use the holes in the wing saddle to position dowel pegs. Because I screwed it up the first time I ended up cracking the wing sheeting and now I've glassed the center section. I'll get some pictures up ASAP.

The pins wouldn't be needed if you join the wings but i don't quite trust tape. But? You don't need much strength because the leading edge fits into the fiberglass fairing pretty tight.
Last edited by peterlngh; Aug 14, 2012 at 02:32 PM.
Aug 14, 2012, 02:51 PM
Registered User
Oh yeah. The bolt holes aren't drilled out on the Specter. I had an extra nylon bolt that I just ground to a point and screwed it into the blind nuts to mark the holes. After I realigned my wing I then drilled them a little oversized, 3/16", and used washers which I tacked on with some CA to get the right alignment. Then I just sanded down a couple pieces of dowel, greased them with Vaseline, and filled the voids with epoxy. Now they are perfectly aligned.
Aug 14, 2012, 03:23 PM
Registered User

Wing mounting.

Here are a couple pics. I left the pointy bolt sticking out. For locating the holes one will want it screwed in until just the point is protruding then one just presses on the wing to form a dimple. The pictures of the fairing aren't too good because i filled all the gaps with gorilla glue. Then, once I had the holes in the right place, I hardened it up with CA.
Aug 15, 2012, 01:39 AM
Registered User
peterlngh- I just finished my specter build, and appreciate you taking the time to explain your build, it really helped. 2 questions...1- what is your "normal" cog set at, and where are you measuring it from? 2- were about in Minnesota are you? I am just north of the cities and it shure would be nice to have someone look over my settings/throws so I dont lawn dart this on its maiden.
Aug 15, 2012, 11:26 AM
Registered User
Hi, Montecarslow. I'm in West Saint Paul. I use a CG, measured from the leading edge of the wing, of 68-72mm depending on wind. Frankly, it's not terribly sensitive to the CG and it could be flown with it anywhere around 70mm but I tend to let it balloon when I turn back into a wind with the aft CG. I think it has more to do with my style than the plane.

I would be happy to look things over but I wouldn't worry too much. It flies quite well and it would need some serious and obvious screw ups to turn into a lawn dart. If you have a very small hill (10 feet or so) and/or someone to toss it for the first hand launch I wouldn't worry. This bird likes to fly.
Aug 15, 2012, 03:50 PM
Registered User

Final evolution?

The paint job after glassing the center section is now dry. The wings fit a bit on the tight side but it will loosen up when I wear some of the paint off.
Aug 16, 2012, 02:40 AM
Registered User
I finally got my watt meter up and running. The KD A22-20l pulls 250watts and 21.4A with the 9.5X8 prop. I figure that's just about optimum for the motor. I'll post RPM and estimated thrust tomorrow.
Aug 16, 2012, 03:03 PM
Registered User
Here's the rest of the motor data.

I get 9000 RPM at 11.6 volts for a calculated thrust of 850grams. I'm not thrilled by the thrust calculator since one must guess at the efficiency of a given prop but it will still provide a reference. Still, it's fairly close since my 780gram plane obviously has a better than 1/1 thrust ratio. I'll have to compare the 9.5X8" prop to the 10X6" in the air to decide if it's actually useful data.

BTW. I'm using the Turnigy 7 in 1 Mega meter. The battery checker, watt meter, and tachometer are all I would expect but the thrust calc is questionable and the internal resistance function seems useless and others have found that it's inaccurate. Still, it's a lot of meter for the money and I'll give it a solid "B" so far.
Aug 16, 2012, 03:47 PM
Registered User
More number with a fresh battery hot off the charger.

9.5X8" gives 9,540 RPM and 950grams of thrust
10X6" gives 9,900 RPM and 1280 grams thrust while drawing 218 watts at 19.16 amps.

I definitely need to try the 10X6" in the air!
Aug 17, 2012, 01:30 AM
Trex 700, Gaui X5, 450DFC
SoarWest's Avatar
I ordered 1 each of the 9.5x8, the 10x8 and the 10x6 and figured I would give each a shot and see how things go. I have a few motors that should also fit in well. I haven't been able to start the build yet but perhaps Sunday evening.
Thanks for sharing the info, it'll be really interesting to compare.
Aug 17, 2012, 12:45 PM
Earthbound Skyhound
StarHopper44's Avatar
Hi Peter;
Your praise has purt' much sold me on a Specter. (Sure wish they'd spelled it the proper 'Spectre'....the used one's for some unknown reason seems uncomfortably close to 'sphincter' for me) *LOL*
(Waiting for the inevitable pun!)

A bit of advice, if you will please? The HK spec'd spinner says 30mm; your suggested one shows D33xH30.5
First, I usually prefer 'Turbo' style spinners when I'm upgrading - as usually the motor can use all the cooling it can get. But your KD A 22-20L is showing outstanding coolness in running, so would you feel a Turbo would offer any advantage in that application? (Besides, the equivalent non-turbo I'd use is a buck cheaper -- unusual but true in this case!)

And more the case for my query, my choice (the BB Aluminum) only comes in 3mm shaft sizes of the spec'd 30mm, & next graduation is 34mm. Which one in your considered opinion would be the better size for the *ahem* Spectre?
And thanx for your counsel!

If any other owner or knowledgable person would like to chime in, I'm all ears!
Clear Skies!
Aug 17, 2012, 01:16 PM
Registered User
Hi, SH.

Just to throw a wrench in the works; I noticed that R2 has the "real" Passer-x on sale for $84.00. It actually might end up cheaper even with shipping from Hong Kong but I haven't crunched the numbers. I'm even considering getting one to see if the airframe is a little lighter and setting it up with a lighter electronics package.

I don't think the Turbo spinner would help much because there really isn't much room to cut cooling holes in the motor mount. The existing cooling holes in the fuse are far enough forward that one gets air blowing over the back half of the motor. Now I kinda wish that I had tried it with just the bigger exit hole before I added my scoops because they do get the paint knocked off by the prop. It's something you have to get real close to notice but I hate getting nicks in my paint jobs even if I can fix it with a Q-tip.

The 33mm spinner is about 1mm bigger than the front of the fuse but you have to get within about a meter to see it. I did mount up the 28mm spinner and with it one would have to get about 2-3meters away. I think that anything from 30-34mm would look fine.
Aug 17, 2012, 04:29 PM
Registered User
I tried out the 10X6 prop. There isn't a great deal of difference except low speed vertical is better than the 9.5X8. Since the 10X6 uses a little less power I think I'll stick with it since I flew 20 minutes with 8 climbs and the battery was only down to 11.8 volts. I also tried a 9X5 I had lying around too and it has a noticeable drop in performance but it's still more than adequate. So?

I would guess that any motor of around 1,000kv that will spin a 9 inch or bigger prop on 3 cells will be a good match.
Aug 17, 2012, 04:36 PM
JimNM's Avatar
+1 to Peter's summation. For those that may not know, the first number is the diameter, the second is the pitch. Diameter value governs the thrust produced and the pitch governs the speed produced. Diameter increases load on the motor by the 4th power, pitch increases by linear. A jump from a 9" to a 12" diameter is a huge increase, but 6 to 8 pitch in crease is not so much.

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