rrragmanliam

My Feedback: (1)

For some reason I cannot get this TD to run with the nose of the plane pointing straight up. At all needle settings it will run for about 5-10 seconds then quit. As soon as the nose starts to rotate up it starts to lean out and quit. Richening the needle doesnt help. I've gone through the fuel system, no leaks, clean, clunk works, tank holds pressure. I'm using new fuel 30% nitro, 23% castor. Theres not an excessivly long line run to the engine. Tank centerline is even with the venturi. Tank pressureization is via prop blast into a tube. Is there better pressurisation to be had by utilising the drillout nipple on the carb casing or via backplate/crancase pressure? I realy could use some help. Thanks in advance.

Darren

PS. running a 5x3 prop and the engine absolutly screams in all other attitudes.

flyinrog

My Feedback: (1)

Hairline crack in the plastic housing? that happens fairly often....Rog

combatpigg

My Feedback: (3)

DARREN, assuming that the engine is in good shape, I would put on a pressure tap backplate and a check valve in the pressure line to pump up the tank a little. If the engine is getting worn out, it wont pull fuel up hill as good , but will rev OK level..

DICKEYBIRD

Can't tell for sure from the pic but it looks like the venturi screen is missing? Try another venturi if you can....sounds like it might have been bored out for pressure usage in a past life. IMO, the stock venturi is pretty big for good fuel draw unpressurized. Aren't you up pretty high, altitude-wise as well?

combatpigg

My Feedback: (3)

One other thing the picture reveals is that the engine is mounted a little bit too high relative to the tank position, but your problem with the engines' inability to draw fuel up hill is more extreme than just fine positioning of the tank. If you prime the engine, bring the piston up slowly to TDC, look in through the exhaust ports and see if there are alot of air bubbles. The cylinder should stay pumped up for at least 4 or 5 seconds. The other sources of crank case pressure leaks can all be checked via the "dunk test".

rrragmanliam

My Feedback: (1)

DB, actualy the engine in the pick isn't the one thats in the plane. I just used that pic to show the pressure line. The plane is currently sporting a .049 DBTD with the venturi necked down, non SPI cylinder.

CP I'm thinking the engine is in good shape, I reset the con/rod when I put it together. Holds compression. The plastic ventuti body isn't cracked. Crank to case fit is still good. Everything is snuged up and not leaking. It has a new glow plug (low compression four fins). I tried runnig a throttled engine once with a one way valve and it overpressurised the tank to the piont that the engine wouldn't run, but that was with muffler pressure. Also CP when the engine dies the fuel line is still full right up to the venturi.

Man this is bugging me. I guess I could try screwing around with the shims. I'm currently running 3. If that doesn't work I have a couple of the 6 buck sure start engines. I'm thinking of trying one of those piston/cylinder assemblys on the engine. I guess if that does't work the engines comming off the plane and going on a test stand with a different tank assembly. Mabee it is the tank. Frankly I don't know!

Thanks for the input.

Darren

combatpigg

My Feedback: (3)

Darren, to be honest, I'm amazed by you guys who can get good performance from the TDs on pure suction, I never could and gave up trying long ago. If I run a TD anymore, it is on bladder or at least with backplate pressure. Have you had success in the past with a similar setup?

gcb

Darren,
I'd check the tank again for a small leak on the pickup tube near where it goes external. It will hold pressure because the leak is still inside the tank. When you raise the nose up, it sucks air.

George

DICKEYBIRD

The ones I run set up that way do lean out a little when the plane is held vertical, but not much. The reduced dia. venturi should have really solve typical Tee Dee fuel draw woes on suction. Mine normally run perfect in the air....vertical pulls as far as you can see with no problems. When the tank gets low on fuel, it leans out a little but still runs OK.

Just to be sure, it is at full throttle when you hold it vertical? It won't keep running at idle with the nose straight up. About 45 deg. up it will but not 90 deg. George probably has the answer....why not stick another tank on just to be sure? If that's not it, it may be a tired cyl./piston like C/P said. After all, they are just little pumps and if tired, they don't wanna pump very far.[]

ps: Last minute thought....did you shape the venturi so there's a smooth radius from the opening all the way down to a point just above the fuel entry holes? If not, it won't "suck" too well.

rrragmanliam

My Feedback: (1)

Well you guys have givin me plenty of hope. This is my project for the day( between laundry, my daughters soccer game and shopping for my mom's B-day). I have actualy had the exact problem with the tank george is talking about happen to me before. I thought I checked closely when I had the tank apart for the second time but I'll check again. I'm giong to remove the engine and run it on my fancy 2x4 test stand to see if I can duplicate the problem, That should at least answer the fuel tank question.

Thanks for all the input I'll keep ya posted.

Darren

rrragmanliam

My Feedback: (1)

Here's an update, I disassembled the tank and everything was perfect. There were no leaks internaly or externaly. I diched the piston/cylinder and installed a new one off of one of my $6.00 engines. Per DB post I fine tuned the venturi radius by hand with an exacto knife. I have a couple of new KK NVA's so I put one of those on as DB told me it wouldn't hurt. And finally I had a backplate with a pressure nipple on it so I installed that and ditched the propwash tube.

I took the plane out back and ran it. My origional problem is gone as the engine will now run all day with the nose straight up. However (and there's always a however) now the engine wont run with the plane inverted. It starts to sputter, spit fuel out the venturi and stall. I thought the tank might be overpressurised but if so why would it run fine when upright??????? I'm thinking it may be a problem with the tank level relative to the venturi, but I really don't know, The engine has a very respectable idle but the transition to WOT isn't smooth at all.


Darren

combatpigg

My Feedback: (3)

You need a check valve in the pressure line, DARREN. It is flooding the crankcase VIA the backplate on the negative pulse. Why don't you try to run it with just a vented tank now that you have changed P/L?

rrragmanliam

My Feedback: (1)

CP, Thanks for the heads up on the negative stroke issue. I never knew that. This is the first TD I've run with back plate pressure so I'm a bit naieve . I noticed that there were alternating pressure and vacum pulses at the line but really didn't think through the consiquences. I do have a small one way valve I can install in the line. Your right CP, first I'll just try a regular vented set up and see if the P/L resolved the origional issue.


Darren

rrragmanliam

My Feedback: (1)

Well I think I'm going to give up on the throttle issue. The engine runs great with backplate pressure and the check valve but at the expence of all throttle ability. Even with the new P/L I cannot get the thing to run more than several seconds with the nose up without pressurising the tank. I'll try two more things.

1. Reinstall the propwash pressure system and try that.

2. Decrease the oraface size at the backplate and see if I can reduce the pressure to the tank.

If neither of these alterations work this plane will be converted to 2 channel WOT operation. I'll be sticking with Norvel in the future for my throttled aplications. I have a .010 stick I'm building with a throttle sleeve and I am hoping I don't have the same problems.


Bummed Out Rrragman

combatpigg

My Feedback: (3)

I didn't realize you were trying to get it to idle too! I'm just happy if I can get them to run! I guess you could play with back plate pressure tap. Ideally you could introduce a "leak" into the pressure line via a barrel valve everytime you go lower than 1/2 throttle. It might look like RUBE GOLDBERG had his hands in it, but that would alleviate the over rich condition at idle. They sure do run strong during extreme maneuvers with a pressure system.

DICKEYBIRD

I'm sorry you're having so much trouble Darren....danged if I know why![sm=confused.gif] What's the altitude where you are? If you're way up Rocky Mountain high, I'm thinking the setup I use down here at 375 ft. ASL won't work as well.

The reduced venturi, SureStart piston/cyl and lowered compression (4-5 shims with SureStart glow head and 25% nitro) works every time for me (and others) on throttle sleeve equipped Tee Dees. Crankcase pressure won't work on a throttled engine without some fancy stuff like C/P describes or like the YS engines have....way too much hassle!

Have you successfully run Norvel's under the same conditions?

Good luck and don't give up.

rrragmanliam

My Feedback: (1)

Hey guy's, DB ASL where I fly is basicly 5280ft in essentialy the Ol' Mile high City. Your right CP some type of pressure bleed on the tank from about 1/1 - 1/2 throttle would make the configuration I have set up now work. But as DB eluded to that would be"way too much hassle". DB FYI the Norvels throttle and run great up here. My .061 and .074 engines have nice low idles, great transition and will idle with the nose straight up (makes for nice tail slides and such). I'm going to dink with the back plate oraface and try the propwash pressure again. We'll see what happens. If I can't get'er to run I'll just convert it back to a big ventiri, free porting, pressurised screamer and let her rip!


Darren