av8tor1977

My Feedback: (6)

Here's the source of that original post:

http://www.rcuniverse.com/forum/m_26...tm.htm#2622138

AV8TOR

ALW Phantom

My Feedback: (2)

Captin, that usually works but for some reason the charts not the article is fuzzy, to fuzzy for me to print it. Thanks for the other tip though !!!!!

AV8TOR, do you know what post the charts came from ?

Thanks to all for everything ..... wow that would be my award speech .....

JCaste

Still I couldn't fire the engine, I had work to do. [:'(] I guess the third try is the succesful one!
I have everything ready (I even bought a cheap spring dynamometer to get some thrust figures) except for the degree wheel (for some reason the full circle ones are hard to find), so knowing the timing will have to wait. I would say it's stock, but after the many mistakes I've made I will shut up.

Again, I have several random questions. First one, the fuel inlet is, according to the "manual", the brass tube with elbow shape in the first pic. The second pic show another tube (next to the WT513 i.d.) which, again according to the "manual", must be tapped. Is this right?
EDITED: The ratchets are a way to fix the throttle and not allow it to go down from a certain position with the starter closed. If the throttle is moved to the full wide position, the device is disabled.




The project where I would like to use the engine (pusher autogiro) would need 2 tanks, to keep the weight and CG low, something I'm unfamiliar with. I planned to use a small tank next to the engine and a big one about 40-50cm away from it (where the seat goes). I did some searches but I didn't find any real useful info, how do I make the setup for that? Do I need a pump or a pressure point drilled in the engine?

And the last one (for now ), is about gear reduction. Most gyros need thrust, a LOT of it, so they have geared engines swinging big props. Also, the big prop not only gives excellent thrust, but also acceleration. So I'm quite confused about the factors that make you think whether you need a gearbox or not.
Theorically, my craft should weight around 6kg, giving me a power-to weight ratio of around 1:1. It's recomended to have at least 0.5:1, so it seems I have power to spare (considering the rotor size, and thus drag, is the optimal for the engine size). Following my chain of thoughts, I assume (probably wrong) the engine has a quite flat power delivery curve, so thrust and acceleration is "available" throughout the entire throttle range, not just the few hundred rpm, so no gearbox is not needed here. Of course, the fun thing is touching the throttle and see the craft rocket straight ahead, or have it descend slowly, hit the throttle and see it disappear again (although top spedd is relatively low). It's of no good to see it change it's attitude slowly and lazy with the engine making a lot of noise and smoke, or have to fly fast and at full throttle.
So I would really thank some help or tips with that. I'd prefer to not use anything, but I'm very unsure if it would be worth (or even worse, necessary) or not.
Autogiros typically are quite small, with rotors no bigger in diameter than 1.1m, and no gearbox (at least for the glow powered). In the oposite side, the biggest RC gyro I've seen (~47kg), has a 4.7m rotor (pretty high disk loading!!) and a DA-150 geared 1:2 swinging a 40:26 prop. Mine, with a planned rotor size of 2.2m and 6kg, is in no man's land, so I have no references.
Please excuse me for the the long chat and questions, I'm very motivated about the project, I think it's something different, with lots of challenges (the first one being able to design an aluminium craft of that size and weight RTF!), and I'd like to make it a reality sometime in a not too far future. [&:]

See you guys!

JCaste

It seems I still can't get some numbers. [:@]
Those last weekends I've been trying to get the engine running, without success.


A half meter blade spinning fast is something to take seriously, so I decided to make a simple but proper mount for the engine.

It has a 24oz tank, the primer that came with the engine (btw, very handy!), fuel filter (just before the carb intake), a primitive throttle control and an ignition switch for added safety.
The throttle linkage required a small mod; the carb throttle arm has wide holes, but it's almost over the manifold, so there is very little space to use any commercial link I could find. In the end, I decided to make a simple mod to a regular 2mm quicklink that seems to be very effective. I turned a small piece of brass on the lathe, made a hole throught it and and put it on the quicklink to widen its diameter. Then I applied some pressure with a bench vise and the soft brass got the right diameter and fixed to the quicklink.

Before mounting everything, I took apart the intake assembly. I didn't had my caliper at hand to check for sure, but a rough measurement showed the plastic was in fact smaller in diameter that the carb, so I'll have to enlarge it. At least, it looks like there's plenty of material around the pulse hole! I wasn't sure how to mount it again, but it seems there was only one posible position (the pressure marks on the gaskets helped with that, too).


So once built the mount and after checking that everything fitted where it was suposed to, I attached the fuel line to the 90º tube near the needles - following the "manual" that came with the engine. It's quite a thin tube, so I had to use fuel clips to prevent it from slipping out. I tapped the other tube as told, too.


I proceeded to bolt the muffler, but first I grinded one or two cm from the pipe that were in excess (the exhaust hole also required some grinding). I put some thread locker, but I'll use high temp silicone later on to make sure it stays there and doesn't leak.


Now everything was ready. I filled the tank with fresh 95 octane, lead free gas with about 2.75% (in volume) of oil. I screwed the prop so that compression wouldn't bother me when hand-starting it. Primed the engine, turned the prop several times with the starter closed, throttle about midrange, and switched on the ignition. Deep breath. Another one. With a wood stick, I make the engine turn. And nothing happens. Absolutely nothing. Another deep breath. I try again, but the room still remains silent. I switch off the ignition, I do a general check, but everything seems in its place. So, what is wrong here?
Two weekends later I still don't know, no matter how stupid that looks. I think to myself, "it can either be a problem of no spark or wrong air/fuel mix". I unscrew the plug and make it touch the engine body to check that my coil sparks, and here comes the first surprise. No sparks at all. The original plug is internally broken! Lucky me, I had a chainsaw plug around (it was bigger, but with the same thread) and I could see that the coil worked, in fact. Didn't look like a very powerful spark, but at least there was some activity, so I screwed the new plug.

Now came the "air/fuel mix" part. I reset the needles to the recommended settings ( 1-1.12 turns each, but later I experimented with more), even tried switching the tubes, and in the moments of maximum desperation I put a couple drops of fuel directly inside the engine to make sure it wasn't the carb. I tried to start it again, but nothing worked. After too much priming, some fuel came out of the carb; in such cases I opened wide the throttle and stop the fuel supply, and flipped the prop again several times. Nothing but a tired arm, no matter what I did.
In the best cases, the engine started running for a second or so in the oposite direction, making the prop hub come lose to half its thread.
So I just dont know what can I do now. I think I've tried all combinations of throttle/starter/needle positions, without luck. I don't know what could I've doing wrong, either, so I'll listen to any advice to "reset" the engine and tune it. I read gas engines were easy to tune compared to glow, but for me it's being just the oposite way. I believe a starter would help, but from what I've read those engines should be easy to hand-start.
Still, I'll try again this weekend.
Regards!

captinjohn

Lots of good data for the new guys in this thread. So I thought I would bring it back for the latest round of new questions ...already set...go!!!! Capt,n

buck1856

My Feedback: (49)

I have a stock 30cc homy in my sons 1/4 scale BALSA USA DVIII.it weighs 14-1/4 lbs.it has a wingspan of 84 inches.i had a MAS 18x6 black plastic classic prop on it.i dont remember the rpms but it flys it around at half throttle after takeoff.i have a zinger pro 18x6 on it now but havent had the chance for me or my son to fly it and my tach is acting up so no rpms either.I just finished a small gyro-plane,the whistler so i think the stock 30cc with an 18x6 or 18x8 would fly a large gyro with ease.how big of rotor span are you talking about and what is final weight and disk loading.i am planning to build a bigger one with a 24cc or 25cc engine.a lot lighter than the homys.

JCaste

Capt,n, I hope this is at least as useful for others as it's been to me!

I think I posted some numbers, but I have a bad memory so I'll post them again.
The project is a pusher-type gyro, with a rotor diameter of about 2.1m, and a disk loading around 5oz/ft^2. The problem with that is that it gives a max weight of around 5kg, a number which will be difficult to respect when your frame is all metal and steel screws. The two main wheels already weight about 0.5kg!
A slightly bigger rotor and/or heavier disk loading will be almost vital to allow a higher max weight, taking into account that a larger rotor also brings, amongst other things, more drag to overcome, and a higher disk loading a degraded performance.
As I see it now, the Homelite would be a good choice for a Cierva-style autogiro. Those can be made pretty light, and had a big rotary engine, so the Homelite will do very well (if I get to start it, that is). [:@]But for a bensen design.... I guess I could buy one of those new chinese engines (DL-50, Gfi-45, etc.) which seem to be very light and powerful. I don't know much about them, but I've seen some threads here so I'd only have to search and read.

As for the Homie, I put a BM6F plug on it but still does nothing. I'm sure there must be a problem with the carb, since the plug sparks. []
I can only think of two possible mistakes:
- Air leaks in the tube conections, that would defeat the pumping action of the carb, not allowing it to suck fuel. This mostly refers to the fuel inlet:

I'll try to find a fuel nipple or machine that fits over the tube inlet, so it makes an airtight fitting.
- Obstructed pulse hole. I made sure when mounting the carb assy that gaskets where the right way, but still the gaskets have some play ad the pulse hole could be partially closed.
I hope the problem is somewhere here, because I just don't know where else to look.[:@]

Have fun!

av8tor1977

My Feedback: (6)

Any tiny air leak in the fuel system will cause the pump not to function. Connections that started out tight might loosen after the tubing is exposed to gasoline. I use a small diamter wire twisted around all my fuel connections to avoid this problem.

Sometimes a newly assembled engine needs to be physically primed with fuel and/or spun over for a while with a starter to fire up.

Good luck,
AV8TOR

JCaste

Yes, the oily fuel mix really makes the tygon tube "slippery". I did realize when I put an inch or so of brass tube inside it; it would take a lot of force to remove, but once I ran the mix throught them, it was very easy to separate them. Now I only have fuel clips on the intake, but still is a very lose conection and plenty of air can get throught there.
I'm going to machine a brass inlet, epoxy it over the fuel inlet and use fuel clips in each conection; that should seal the fuel circuit. [>:]

I tried that too. [] I've had glow engines for some years, so I have at least the most basic experience with engines. I know sometimes it just takes a "starter spin" to make the fuel "wet" the guts of the engine and make it fire for the first time, and then you can use the stick method and it fires each time.
What bothers me is that even when pouring a couple of drops inside the engine (to know if the carb was or not doing its job) and using the starter (I had to use a common drill with a starter cup), it would not even pop once. Also, you could prime it till it spit the fuel out; no way. All of this, while playing with needle, choke and throttle settings. So if it still doesn't work after I make everything airtight, I won't know what to look for.
The fuel is fresh, the plug sparks, so I either spin the engine too slow (so the spark is too weak or inexistant, but so far that doesn't seem to happen) or there is a problem between the carb and fuel tank.

Thanks again!

av8tor1977

My Feedback: (6)

It is either too lean. (not enough fuel)

Or too rich. (flooded)

Or there is a problem with the spark.

If you have primed it, and if it has fuel to the carb, and you have spark, then the most likely cause is that it's flooded. It can take a good long spin of the starter with the throttle wide open and the ignition on to clear a flood. Check to see if the spark plug is wet. If it's not, prime it some more. If it is, suspect a flooded engine.

AV8TOR

buck1856

My Feedback: (49)

i must have been typing my response when you typed yours so i missed the numbers until now.anyway,i plan on using foam to build mine looking similier to the one used in the movie The Road Warrior with mel gibson.my motor weighs 3lbs ready to fly(24cc) with evrything on it(including ignition).the foam would be skinned with balsa for strength.ill make my rotors out of balsa with the leading edge being hard balsa or pine and a strip of carbon fiber on the bottom.really cant help much more,just put the 30cc numbers i have for reference to let ya know what prop it will swing..this is my first gyro(whistler).I have the plans for the DC-Gyro.