DLE 85 Carb Extra Inlet
10-19-2017, 10:44 PM
#1
Thread Starter
DLE 85 Carb Extra Inlet
First let me apologize if this is in the wrong forum, it seemed the most suitable from my search. Looking at many of my friends' large scale craft engines, I've seen this before, and now for the first time I have a larger DLE engine, and I see the same thing on my carb. There is the fuel inlet, and then there's another one that looks like it goes into the diaphragm. I've always wondered what this was, but no one canever give me a str8 answer. I've heard that it's a way to prime without using the choke, but this makes no sense for obvious reasons. I've also heard that it's a pressure tap for the diaphragm, and you can run a piece of tubing or some kind of ram to it to compensate for pressure differential not allowing the diapragm to work correctly. This makes more sense to me, but I'd rather know what this is exactly. I've looked in the manual, and the manual says nothing about this extra inlet.
Anyone know what this thing is?
Thanks!
Anyone know what this thing is?
Thanks!
10-20-2017, 10:13 PM
#3
Thread Starter
Thanx! Annoying how they don't even mention it in the manual. Looks like the fuel inlet, but why would you put line on it? Maybe an auxiliary pump or something?
10-21-2017, 08:55 AM
#4
My Feedback: (19)
In some / many cases, changing pressure inside a cowl caused by different airplane airspeeds and attitudes can affect the carb regulator. Increased cowl pressure can cause the engine to go rich and likewise, reduced pressure can cause the mixture to go lean. Both conditions are unwelcome in flight. By putting a line on that fitting and routing it to a location in the airframe where the pressures are more steady, the engine run becomes more consistent. This area can vary from simply running a line back in the fuselage to a quiet area to connecting a line to a more exotic static air vent. Another common method is connecting the line to a balsa box or pill bottle that has a single pin hole for a vent. Some 3W engines run the line to an area near the choke plate.
Part of the problem is created by poor cooling airflow through the cowl. If the flow is restricted, cowl pressure can build up and this is the most common cause for the above mentioned problem. Sometimes the problem only shows up in certain knife edge, inverted or downline maneuvers. Cure the cooling airflow problem and the cowl pressure problem may just go away. But in many cases the engine will continue to run poorly at different attitudes and airspeeds and the vent solution is necessary.
Part of the problem is created by poor cooling airflow through the cowl. If the flow is restricted, cowl pressure can build up and this is the most common cause for the above mentioned problem. Sometimes the problem only shows up in certain knife edge, inverted or downline maneuvers. Cure the cooling airflow problem and the cowl pressure problem may just go away. But in many cases the engine will continue to run poorly at different attitudes and airspeeds and the vent solution is necessary.
10-21-2017, 04:50 PM
#5
Good answer Truckracer. I saw the post this morning, but was in a rush to leave to go to the Tucson Expo Gun Show. Tomorrow, I'm off to see the final rounds of the Tucson Aerobatic Shootout. Cool! If you go to www.tucsonaerobaticshootout.com, they have videos posted.
The remote vent line spoken of isn't always needed. However, I just always add it as a matter of course on all my builds. Many, (most actually), engines/carbs don't have that fitting provided, and in those cases I solder a fitting in to run a remote static pressure line. It is nice that DA provides one.
AV8TOR
The remote vent line spoken of isn't always needed. However, I just always add it as a matter of course on all my builds. Many, (most actually), engines/carbs don't have that fitting provided, and in those cases I solder a fitting in to run a remote static pressure line. It is nice that DA provides one.
AV8TOR
10-22-2017, 07:46 PM
#7
Thread Starter
Really informative and helpful, thanks! That makes sense, wonder why they connect the line to the reed valve block on the smaller engines, but leave it open on the bigger ones. Maybe smaller engines more susceptible to pressure variances?
10-22-2017, 07:59 PM
#8
My Feedback: (19)
I've never seen a line connected to a reed block unless it was used as a pulse line to provide the necessary pressure pulses that run the pump in the carb. Sometimes the pulse passage is internal between the reed block / carb and sometimes it is an external line.
I have never seen where small engines are more susceptible to pressure changes than larger ones. They all fly in the same air and the diaphragms are the same size for many of the engines we run. Larger engines and many twins use different (larger) carbs but they pretty much exhibit the same traits as the smaller ones.
I have never seen where small engines are more susceptible to pressure changes than larger ones. They all fly in the same air and the diaphragms are the same size for many of the engines we run. Larger engines and many twins use different (larger) carbs but they pretty much exhibit the same traits as the smaller ones.
10-24-2017, 04:35 PM
#9
I've never seen a line connected to a reed block unless it was used as a pulse line to provide the necessary pressure pulses that run the pump in the carb. Sometimes the pulse passage is internal between the reed block / carb and sometimes it is an external line.
I have never seen where small engines are more susceptible to pressure changes than larger ones. They all fly in the same air and the diaphragms are the same size for many of the engines we run. Larger engines and many twins use different (larger) carbs but they pretty much exhibit the same traits as the smaller ones.
I have never seen where small engines are more susceptible to pressure changes than larger ones. They all fly in the same air and the diaphragms are the same size for many of the engines we run. Larger engines and many twins use different (larger) carbs but they pretty much exhibit the same traits as the smaller ones.
Yep, agreed on all. I was just at the DA booth at the Tucson Aerobatic Shootout. I bought one of their nice red anodized aluminum regulator covers for my DA-100. It doesn't have the fitting for a static pressure line. Instead, it has four very tiny holes in opposite sides of the cover. This would help the situation sometimes encountered where ram air smacks right into the cover on some installs, but would not help if the problem were overall ram air pressure build up in the cowl. As mentioned though, overall ram air pressure build up in the cowl means a person needs to re-evaluate their cooling setup.
Anyway, I scored at the Shootout. The Unlimited Freestyle contestant Suzuki Yuhei crashed, and after removing the engine and radio gear, the team all signed the plane and gave it to me! I was thinking just some cool "Man Cave" art and souvenirs, but when I got it home I laid it all out, and it is rebuildable! So I'm going to rebuild it, and of course preserve all the autographs. Then later on, the team from Mexico had a crash, and they gave me two perfectly good, (also autographed), wings. Neat!!
DA had some exceptionally nice looking engines there...
AV8TOR
Last edited by av8tor1977; 10-24-2017 at 04:52 PM.
10-25-2017, 01:43 AM
#11
Thread Starter
I've never seen a line connected to a reed block unless it was used as a pulse line to provide the necessary pressure pulses that run the pump in the carb. Sometimes the pulse passage is internal between the reed block / carb and sometimes it is an external line.
I have never seen where small engines are more susceptible to pressure changes than larger ones. They all fly in the same air and the diaphragms are the same size for many of the engines we run. Larger engines and many twins use different (larger) carbs but they pretty much exhibit the same traits as the smaller ones.
I have never seen where small engines are more susceptible to pressure changes than larger ones. They all fly in the same air and the diaphragms are the same size for many of the engines we run. Larger engines and many twins use different (larger) carbs but they pretty much exhibit the same traits as the smaller ones.
10-25-2017, 06:29 AM
#12
My Feedback: (19)
Yup, DLE 55, DA 50 and many other engines use external pulse lines to the pump. In this case, the line connects to a fitting on the pump cover rather than the regulator cover.
By the way, the line can connect to a tap most anyplace on the engine crankcase depending on the engine design.
By the way, the line can connect to a tap most anyplace on the engine crankcase depending on the engine design.
Last edited by Truckracer; 10-25-2017 at 06:41 AM.
