CEF speed contest Design Discussions

Hea Rusty , I have been experimenting with cutting my own engine mounts from some pressure treated black walnut with my table saw and noticed I can cut some really thin stuff . will need a little sanding of coarse . the width is 1 1/4 " if you would like ill cut you some strips and mail them to you no cost . PM me if u are interested with the thickness and address . And I ll see what I can do also have mahogany and I think cherry  and oak maybe ? would have to dig for it   I went to the trouble and forgot       there that's better   

JPvelo wrote:

Cribbs74 wrote:137mph, I can do that lying down.   

Cut that speed in half and you'll be in our ballpark.

Jim

That 137 mph time was for 1/2A class. It was the 1/2A "profile/proto" class 108 mph time in division 6 that I was referring to... which is an entry level speed class. The average between the divisions for the profile class was approx. 97 mph. Like Jim says; we'll probably be averaging 65 to 75 mph with our models.

2-3 layers of carbon veil would be about the same thickness.

Phil

roddie wrote:You know me Rusty... I have suggestions for everything...   You could use that sheet.. (if it's the lightweight contest grade you're looking for) by edge-gluing it back together along the break, with thin CA on a sheet of wax paper.. on a flat surface (holding the pcs. firmly together for 10-15 seconds) Then cut the pc.(s) to the length you need and thumb-tack x2 pcs. of .031 music-wire on either side of the sheet.. and block-sand (with the grain) down to the music-wire, and you'll have 1/32" thick stock. It will sand easily.. so use a fine grit paper. If you can find a nice lightweight pc. of 1/16" sheet.. you could do the same, with a little less sanding. I didn't know that balsa came in 1/32" thick sheet. That's thin!

I was half zeed last night when I read this and didn't fully register what you were saying. That's a great Idea. I'm on it.

Getback, thanks, but I think I'm on track now, thanks to Roddie. Appreciate the offer though. Next time I scratch build, like the plane for my TT15 engine, I will definitely consider getting you to cut me some beams. Thanks.

pkrankow wrote:2-3 layers of carbon veil would be about the same thickness.

Phil

That's something I've never worked with but probably should learn about. Thanks Phil

Rusty

RknRusty wrote: The submission needs to come with a note saying which 10 laps are timed.
Rusty

I will make a sample video closer to "go time" that shows what a official flight will look like. This will include a signal from the pilot on when to start timing. I was thinking of posting the video the last day of March so we are all doing official flights over the same 18 day span.

Jim

pkrankow wrote:Go low tech, get some surveyor's tape and run it out to the pilot's circle in front of the camera.  If there is a "tie" I don't know how to break and have this stay a "fun" level contest.

Phil

Low tech is how we will do it. I am in the process of finding outside judges to time flights and then I will average times. Ideally there will be three judges with the two closest times bring averaged  and the third being thrown out. In the event of a tie all three times will be averaged. I think that is the best way to keep it simple and fair.

Jim

I ran my engine today.. and had some problems... fuel draw/flow mostly. The little uni-flow hard-tank I built, does not flow... and I don't know why. There aren't any blockages and it's tight as a drum. I'm going to make a fridge-magnet out of it.  

Were you trying to run it with both vents capped like that?

Jim

JPvelo wrote:Were you trying to run it with both vents capped like that?

Jim

No Jim. The top vent only should be capped. The upper/front is the uni-flow vent. The top is to fill, then cap. It's like there's a vacuum in the tank for some reason. I had issues filling it as well. I failed to flow-test it before trying to run it. I did "leak-test" it after I soldered it.. and it's tight as a drum.

When "full".. nothing flows out with all the tubes open. The engine only ran with the fuel that was in the feed-line.. and then bubbles would appear in the feed line. I messed something up.

It wasn't a good afternoon... my tach wouldn't give me a reading.. which didn't really matter, because my engine runs were all less than 20 seconds. "Screaming"... but less than 20 seconds.   

RknRusty wrote:

roddie wrote:You know me Rusty... I have suggestions for everything...   You could use that sheet.. (if it's the lightweight contest grade you're looking for) by edge-gluing it back together along the break, with thin CA on a sheet of wax paper.. on a flat surface (holding the pcs. firmly together for 10-15 seconds) Then cut the pc.(s) to the length you need and thumb-tack x2 pcs. of .031 music-wire on either side of the sheet.. and block-sand (with the grain) down to the music-wire, and you'll have 1/32" thick stock. It will sand easily.. so use a fine grit paper. If you can find a nice lightweight pc. of 1/16" sheet.. you could do the same, with a little less sanding. I didn't know that balsa came in 1/32" thick sheet. That's thin!

I was half zeed last night when I read this and didn't fully register what you were saying. That's a great Idea. I'm on it.

Getback, thanks, but I think I'm on track now, thanks to Roddie. Appreciate the offer though. Next time I scratch build, like the plane for my TT15 engine, I will definitely consider getting you to cut me some beams. Thanks.

pkrankow wrote:2-3 layers of carbon veil would be about the same thickness.

Phil

That's something I've never worked with but probably should learn about. Thanks Phil

Rusty

anytime Rusty   

Got my bladder tank bits from Texas Timers today, if anyone in the U.K. listening, they come highly recomended. Anyway, ran my engine on my newly built bladder. Can I just say I'm converted. I ran it a couple times, on a 5x3 then changed to my newly aquired 4.75x4. Wow, I can honestly say I've never heard an 0.49 scream like that. Can't wait to run it on some 30% nitro, once I've ran it in some more on 25%. Tell me guys, how many revs should I be getting on 25% nitro.
As the time to fly my Bugatti gets nearer, I'm now worrying that I have no rudder/engine offset. Will that be ok?

Cheers Mike,      Bladder Tanks Rule.

ebeneezer wrote:Got my bladder tank bits from Texas Timers today, if anyone in the U.K. listening, they come highly recomended. Anyway, ran my engine on my newly built bladder. Can I just say I'm converted. I ran it a couple times, on a 5x3 then changed to my newly aquired 4.75x4. Wow, I can honestly say I've never heard an 0.49 scream like that. Can't wait to run it on some 30% nitro, once I've ran it in some more on 25%. Tell me guys, how many revs should I be getting on 25% nitro.
As the time to fly my Bugatti gets nearer, I'm now worrying that I have no rudder/engine offset. Will that be ok?

Cheers Mike,      Bladder Tanks Rule.

Mike,
Glad you like the bladders, I can't imagine going back to a hard tank setup myself. My fast motors will turn about 21500 with the APC 4.75x4. My planes for the contest have zero rudder and zero engine offset. It's a little tricky at launch when the plane wants to tourqe roll in at you. Be ready to back up and aggressively "whip" the model to keep the lines tight until gets up to speed and centrifugal force kicks in. With 1/2 elevators and close line spacing at the handle once my planes get going they are incredibly easy to fly.

Jim

roddie wrote:It wasn't a good afternoon... my tach wouldn't give me a reading.. which didn't really matter, because my engine runs were all less than 20 seconds. "Screaming"... but less than 20 seconds.   

 Roddie ; hows the tank coming get her straighten out? I have my second coat of dope on now wow wow  outside!    

Mike,

Lot of variables going on there. My suggestion would be to tach it with 25% and then again at 30%

No real way of knowing from one engine to the next.

Ron

getback wrote:

roddie wrote:It wasn't a good afternoon... my tach wouldn't give me a reading.. which didn't really matter, because my engine runs were all less than 20 seconds. "Screaming"... but less than 20 seconds.   

 Roddie ; hows the tank coming get her straighten out? I have my second coat of dope on now wow wow  outside!    

My tank? Oh.. you mean the "fridge magnet".. because that's what it is now. It's holding up the $700.00+ fuel-oil bill.   

roddie wrote:I ran my engine today.. and had some problems... fuel draw/flow mostly. The little uni-flow hard-tank I built, does not flow... and I don't know why. There aren't any blockages and it's tight as a drum. I'm going to make a fridge-magnet out of it.  

I would guess that you are not getting enough pressure for the uni-flow tank - the vent seems to be too far from the engine. (My interpretation of the photo but I could be wrong)

I found this as an example for CL set up.



The uni-flow pipe has been extended inboard to improve the flow.

I'm actually having trouble getting the tank to "fill" (fuel squirts out the vent almost immediately.. whether I fuel through the top fill tube or the uniflow tube) and once there "is" fuel in the tank, it doesn't flow out.. even when all tubes are open and the tank is sitting level. I have to pressurize it to empty it... which shouldn't be. There are no clogged tubes.. I can blow through all 3.. and the shank-end of a drill bit; to fit the tubes' i.d., passes through.. all the way to the tank walls (I measured) It's like a "vapor-lock" or vacuum is taking place... and I have to wonder if it's the uni-flows' orientation to the pick-up, that could be causing that kind of condition?  

I can't say I wasn't warned about the problems associated with getting tanks to work right.  

Here's a photo of the uni-flow and pick-up orientation.

Roddie,
Tip it up on its tail end and fill through the uniflow while you pinch off the feed line. Lose that coupling and run the biggest line you can straight to the engine, and move it right next to the engine like Ian said. That's my two cents worth anyway.

Jim

Looks like it should draw to me. There's nothing wrong with that arrangement. I agree with Jim, ditch the filter and filter when you draw the fuel out of the bottle if you want to. Run it with the vent capped and the uni open. I'm sure you know that.
Rusty

The pickup and the vent are too close together. It will never feed clean. Tiny tanks do not benefit from uni-flow, sorry.

Phil

pkrankow wrote:The pickup and the vent are too close together.  It will never feed clean.  Tiny tanks do not benefit from uni-flow, sorry.

Phil

I am suspect of that position of the uni-flow to the pick-up.. and pick-up to the rear cap distance. They are almost equidistant from each other. This could and probably "is" as you say; sucking air down the uni-flow and introducing bubbles into the pick-up.

I think that the uni-flow "principal" still applies; regardless of the size of the tank. Tank volume theoretically should not matter. I'm making some mods to this tank tomorrow, and soldering up a 2nd tank with a further-forward uni-flow position as well.

Paul G. noticed that my vertical fill-tube runs to the tank floor. This explains the trouble with filling. The "air" in the tank has to go somewhere when the "fuel" goes in. As soon as the fuel-level reached the uni-flow.. there was nowhere for the "air" to go.. so fuel spurts out through the uni-flow. If alternately I filled through the uni-flow.. fuel would squirt out the fill-tube in the same way. I was only getting fuel into the bottom of the tank. So simple that I feel very stupid.

We'll get this resolved... and I appreciate everyone's suggestions. I'll let you know how my mods work out.

Thanks everyone!

Sucking the floor can be solved by angling the end of the tube with a file or sandpaper, or just cutting deliberately crooked. You still need a clearance space but the angled end makes it set up a clearance space.

Fluids have surface tension, which will regulate the smallest free-forming air bubble. Draw forms a current which can capture the smallest free-forming air bubble. There is a theoretical minimum separation based on these values. For larger engines it seems an inch (25mm) of separation is desired.

Phil