vicman

My Feedback: (10)

You should know better than to use cheap ***** servos for the elevator on a speed ship by now. You got lucky.

combatpigg

My Feedback: (3)

Vic....weren't you the guy who swore up and down that these servos are the Cat's Pajamas...?

I told my wife as we left the field today my favorite old saying......."The most expensive way to do this hobby is to try to do it cheaply".
I set the servo up with tons of mechanical advantage. Full sweep of the servo arm = 1/8" of travel at the flap. In this case I guess vibration killed an electrical connection inside the servo.
The servo was mounted with rubber pads, too.

phatboy

I am learning so much from you and AW! I appreciate you guys taking the time to answer my questions, and post builds.

combatpigg

My Feedback: (3)

phatboy, I'm so glad to have you as an eager modeler at this forum to help enjoy these little planes.
Hopefully you already have a solid background as a model plane pilot before taking on a fast model like the GLH.
Setting the model up properly, checking it for straightness, [no wing warps or twists] and paying attention to details like control surface deflections and balance points will increase your chances for success and will make flying the model so much easier.

As you can see, there are many ways to fail and relatively few paths to follow to success.

vicman

My Feedback: (10)

"Cat's Pajamas"??? Uh, yeah...that was me, sure

I like the plane though.

combatpigg

My Feedback: (3)

I replaced the bad servo with a HS-65 and all is well.
I'm still running the $8 servo for ailerons.
The plane needed just a touch of nose weight, so I made an exhaust "stub" that extends the exhaust out flush with the cowl. If anything it was good "training" to make a small part like that on my drill press.
The plane handles really well now and it's pretty amazing how well it holds a knife edge in level flight. Kind of eerie to do that close to the ground without having a working rudder.
Today's flights were with a 6x4. The engine turns it 22,800 and would need to turn it 25,000 in the air just to do 94 mph. Today's speed recordings were all wind assisted, a couple of them hit 130 mph.
The final flight the prop was slipping on the drive hub....those 1/2A sized APC props aren't wide enough at the hub to engage the knurling on the hub. I hope a bit of knurling on the prop nut helps.

phatboy

I like the exhaust extension you made. You have a pm about the ASP. Im definitly going to learn alot from you I can see.

airraptor

My Feedback: (66)

Good job CP.

I have been using the epoxy/filler method on torque rods since around 1980 or so. I learned this from my dad. Way back and even now the pre made torque rods will have slop in them. Using the epoxy you can get rid of most of the slop.

here is what I do.

Take music wire of enough torsional strength. I then cuck it up in a drill and run 320-400 grit paper over it with some 3n1 oil. this will polish it super smooth.
then make your bends how you need them. On some planes with this ailerons or elevons i will grind a taper on both sides of the wire that goes into the control surface. Like a wedge.
I will then make a hardwood jig where the ailerons go to keep the wire perfectly centered where it exits the balsa in the wing and points out to go in to the surface. If there is space also add a jig block in the hole in the center of the wing to keep the wire centered also dont worry if it gets glued in. I forgot to add once the wire is bent you need to make sure the wire in between the bends is perfectly straight. the straighter it is the better it will be slop free.

mix up your epoxy ( i like 30 min )and filler ( i use colloidal silica ) link below. Make sure you use a fresh batch of epoxy.

http://www.westsystem.com/ss/406-colloidal-silica

use what ever lube you like as long as it will stay on the wire. usally thicker the better.
I will then put the epoxy down in the groove and push the wire down in the groove onto the jigs. Do not wipe the excess smooth or anything. Do not even touch the wire at all as any little movement can wipe the oil off. let set up over night. before you move the wire the next day check the epoxy to make sure it has hardened. when you know its hardened rotate the wire and sand off the excess.

i have also done some models where i use the epoxy as a bearing only near the ends of the torque rod to save some weight. on these 1/2-3/4 in length is plenty.

Larry Driskill

Pigg, I have had that problem with the fiberglass/carbon fiber 1/2A props and helped it by punching out a sandpaper disk from good cloth backed paper and gluing it to the prop.

combatpigg

My Feedback: (3)

Airraptor, the music wire is a good idea to help avoid flutter.
What diameter do you use for 1/2A to .15 sized planes..?
How do you handle the end of the torque rod that attaches to the servo linkage..?

Larry D.......thanks, I remember now you talking about the sand paper trick some time ago.

Today is pretty miserable with wet snow and wind. I did some work on the Enya .11 with my little rotary file / die grinder tool.

Stock timing of the intake shaft closed at 50 degrees ATDC. I moved that back to 60 degrees
I opened the shaft to about .280" [9/32"] with a tungsten carbide drill and lots of oil and patience.
The drill would still get very hot and seize in the crankshaft bore, so I chickened out and finished up with a carbide rotary file freehand.
I notched the counterweight deeper than the shallow scoop that Enya takes.
The bypass ports were opened up...the openings at the bottom of the liner were raised and the piston skirt was notched to match the big notches in the bottom of the liner.
This is done with the hope that when the piston is on it's way down there will be a less obstructed path for the fuel mixture to travel up the boost ports into the combustion chamber.
Opening up the crankshaft and delaying the closing of the intake window hopefully allows more air / fuel to enter.
The stock exhaust duration is 155 degrees and I left that alone.
Everything needs to work together as a unit, but 155 degrees seems to "ring a bell" as a good number for a high rpm / low prop load combo [and no tuned pipe].
These mods didn't make any difference with the 6x4 prop. It runs at 22,800 on 12% nitro.
The biggest difference was changing to the 5x5 prop.
These mods made a full 1000 rpm+ improvement to 25,600 on the same fuel.
I found that the stock head shim works best. I tried running tighter clearance and blew lots of plugs, but didn't see better speed. The clearance [piston to head] is set at .017" now

airraptor

My Feedback: (66)

For the ends of the wire i just use brass tubbing soldered on then crimp the end in pliers and drill the hole size you like. I usally use 3/32 for most short ones and then next size up to around 1/8th I am not sure of the exact size since i have a box full of wire lol some of them are missing tags. I use the TLAR techniques lol.

i will have to see what numbers i get on my LA's with that prop. Is that the APC electric 5x5 prop or the graupner?

combatpigg

My Feedback: (3)

It's the APC E prop....very thin, undercambered.

combatpigg

My Feedback: (3)

There was a break in the weather so I tried out the modified engine with 5x5 prop.
The engine ran great, but still burns the plugs pretty often.
The speed recordings were typically 0-1 mph faster than before the engine work...if that much.
This shows that a 4% increase in power isn't even worth 1% increase in speed. If you were racing other planes it would seem like a pretty big deal if your flying skills were able to squeeze the extra speed out flying tight laps.
So, it looks like this project has run it's course. 120 mph is about all I'm able to get.
Flying consecutive 300 foot pylon laps brought the top speed down to 105 mph. This is where the 6x4 prop might do better.
I can easily see how .10 sized racing was popular in some countries / areas. They are cheap, rugged, easy to run engines and 1/2A plane designs work OK with them.

flyingagin

Thanks cp. I always learn something from your build threads.

combatpigg

My Feedback: (3)

You're welcome.
Let's review the lessons....

A $8 servo can be a good way to get introduced to single channel flight.

Running these little engines with undersized props and high revs can keep the folks who work at the glow plug factories busy.
IIRC, Fox Mfg. has had the same lady working on glow plugs for something like 30 years....?

Running belly landed planes and wafer thin props will put you on a first name basis with the folks at APC.

flyingagin

Now that is funny. You got a real good chuckle from me with that one.


I had to edit this post like crazy. When I pasted the " " I also pasted my last post that I made in my build thread. Not real sure exactly how that happened, but it's fixed now.

forsakenrider

what was the wing area finally? I looked but never found it.

combatpigg

My Feedback: (3)

30 inch span, 7 inch root chord and 5 inch tip chord [1 inch sweep].....so 180 sq inches. It works pretty well at almost 21 ozs and with only a 5 inch prop for launches. The 6 inch prop makes the launches much more solid, but if you know which direction the wind is the 5 inch prop will get the plane flying with just a little struggle.
The stab has 11 inch span, 5 inch root chord and 3 inch tips [2 inch sweep].
The L.E. of the wing is 2 inches from the firewall.
The L.E. of the wing is 16.5 inches from the L.E. of the stab.

So anybody could take these basic dimensions as a rough layout and build a similar plane for a .10 sized engine without muffler. The added weight of the muffler would make such a small plane less feasable to fly well and would negate the object of building a small speedster.

lfinney

My Feedback: (44)

cp

your cx11 uses 155 degree exhaust timing, the F1 K&B and 7.5 cc engines used a base of 168 degrees so maybe that cx11 could use more duration FWIW

combatpigg

My Feedback: (3)

Thanks for that info LF. I thought about raising the exhaust timing as well as opening up the combustion chamber slightly.
I'll sneak up on exhaust timing carefully [since you twisted my arm]. I don't want to ruin the engine's ability to swing a 6x4, so that will be the target load to work with.
Another detail would be to polish the pitting off the top of the piston.
Right now I'm getting ready to order some short glow plugs and wonder which type would give me the best value..? I had been using McDonnel plugs but blowing them to smithereens after the faster passes.
I'm also suspicious about the fuel system's ability to ramp up with demand. Running through a TD .049 NVA using Sullivan small fuel tubing might be too restrictive past a certain rpm.
If you try to launch extra rich to compensate, that is too much of a crap shoot.
I'm tempted to rule that theory out by trying a latex bladder for a few runs. If the problem goes away from using the higher pressure...then running a bladder would be a neccesary evil.

Lifer

My Feedback: (1)

CP,

I am using crankcase pressure on a K&B 3.5 on an old Combat 20. Sullivan fuel tank. No splits, no leaks after 5 years. Very good engine runs.

combatpigg

My Feedback: (3)

Lifer, the thing is that you aren't using the same components [NVA, fuel line, engine, load, etc.] so individual results may vary.
I had a similar problem with a piped Webra .50 that would "out run" the fuel delivery system on the plane.
Switching from medium to large fuel line cured that problem but that isn't an easy option with this .10 sized plane and the TD .049 NVA. The existing plumbing job is compact enough already with the small fuel line.
I'll bet a bladder cures it, but it's a messy option for sure.

Your Combat 20 sounds like a pretty fun plane..!

Lifer

My Feedback: (1)

It's one wild ride! The 3.5 turns an 8x4 at slightly more than 20k. I am using a ST needle valve assembly the passes thru the conter of the spigot thru the grub screw holes. Standard neoprene tubing. Going to give it to my friend in Texas this Summer. Once they pass 10 years of age, I give them away to friends.

lfinney

My Feedback: (44)

the piston pitting is bad, it allows oxidized aluminum to break away and coat the glowplug element which causes failure.. you deck height is of .017 isnt too tight
the raising of exhaust timing reduces compression which will help with plugs. the head may need more volume, is the right direction to go. most pylon engines run .010-012 deck height. got any cold plugs? that may help or try a run with two glowplug washers, if it stops the plug failure then you know you need less compression. FWIW

combatpigg

My Feedback: (3)

Hopefully you're right and raising the liner kills 2 birds with 1 stone.
Liner shims are a pain to make [for me]. I know a guy who can whip them out with cuticle scissors using .004 brass sheet. Someday I should learn how to make custom die punches.