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DA-85 Question

Old 03-17-2009, 09:16 AM
  #1  
mcmcintyre
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Default DA-85 Question

Hello All,
I maidened my new AW 85CC YAK-54 equipped with a DA-85 yesterday. The airplane flew outstanding right from the start with no trim required to get it flying straight and level. The DA-85 ran very strong with no hesitation on acceleration. When I would put positive G on the airplane (pulling into a loop) the engine would sputter and sound like it might die. As soon as I would relax the G the engine would come back strong. In a negative G push, the engine wasn't effected in any way. Inverted flight and vertical uplines were not a probleml. A long downline at idle didn't cause any problems either. I am at a loss about where I should start looking to fix the problem. Any ideas will be greatly appreciated.
Mike
Old 03-17-2009, 09:49 AM
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altavillan
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Default RE: DA-85 Question

It's gravity affecting the metering side of the carb. I've cured the one engine I have with similar problems by putting an external pulse line to the carbs fuel pump diaphram. The nipple should be centered over the diaphram for the most consistant pumping force. perhaps the stronger pumping fills the diaphram/metering side of the carb fuller with fuel, so the jets get a more consistant amount of fuel to draw from. Anyway it worked for me.
Old 03-17-2009, 11:33 PM
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mcmcintyre
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Default RE: DA-85 Question

Altavillan,
Thanks for responding. Can you describe what an "External Pulse Line" is. I am not familiar with the term. I am definately a newbie to gassers. Any information you can provide will be greatly appreciated.

Mike
Old 03-18-2009, 10:21 PM
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DANIBOY
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Default RE: DA-85 Question


ORIGINAL: mcmcintyre

Altavillan,
Thanks for responding. Can you describe what an "External Pulse Line" is. I am not familiar with the term. I am definately a newbie to gassers. Any information you can provide will be greatly appreciated.

Mike
+1 ... I would also like to see an example if possible.

Thanks
Old 03-18-2009, 10:51 PM
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RTK
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Default RE: DA-85 Question

You could also try increasing the pop off pressure,
Old 03-18-2009, 10:58 PM
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altavillan
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Default RE: DA-85 Question

http://www.bmeengine.com/engines.htm
Picture of the sport 50 shows an external pulse line to the pump. Walbro carbs have a thickened area in the pump cover to drill and tap for an external pulse line. You can remove the carb and it's pump cover to see where to place a nipple centered over the pump diaphram. Typicaly the pulse line runs through the carb base and gasket as well as through the carb. That makes for a long path for the pulse to run to opperate the pump. The external line makes for a clearer path. Looking at the BME engines I see they all have external pulse lines now.
Old 03-20-2009, 09:50 AM
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mcmcintyre
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Default RE: DA-85 Question

OK, now I understand what you were talking about, thanks. FWIW, I called DA and they suggested that it sounded like the engine was being affected by turbulent airflow over the carb causing the mixture to become too rich on high G pullups. I decided to use the tach and readjust the mixture as my first step and if that didn't work, I would start covering some of the openings in the motor box to try and change the airflow. What I found when I tached the engine was that it was set too rich. I was able to lean the engine a full half turn on the high speed screw. I flew the plane and the problem is gone and the extra 400 or so RPM doesn't hurt a bit. Thanks for the help, I will put the pulse line information in my bag of tricks for the future.

Mike
Old 03-20-2009, 07:19 PM
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wind junkie
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Default RE: DA-85 Question

A few of us talked with "DA" Dave at the WRAM show about this phenomenon, and he immediately asked us, "Are you flying Yaks?"

We said, yes, all three of us have TOC Yak 54's. We don't have any special baffling, but now I think it makes sense that when we do inverted vs upright "pushes" this changes the airflow within the cowl and I believe it does effect the diaphram. On one of the planes, the DA 85 will stall every time when doing an inverted elevator (yikes [sm=eek.gif] )

Dave said people have cured this with the external pressure line like you guys are saying here. Another fix is running the line to the infamous "balsa box" inside the fuselage (away from the cowl and its speed /attitude related air pressure changes).

Dave said instead of a box, a flexible vessel like a small sealed fuel tank also is an option. He offered to send us a diaphram cover with a nipple pre-installed like comes with the DA 100 (same carb) to replace the ones we have if we'd like to install our own external pressure feed lines. It's a simple matter to remove the cover and silver solder a tube over the small hole for "do it yourselfers".

It seems to be dependent on flying styles and airframe. The Yak 54 has such a gaping opening in the cowl it really seems to grab the air and as we've seen it does seem susceptible to the direction the plane presents itself to the relative wind.

Dave also said sometimes installing a baffle will fix it. There are 3 of us in our club flying the DA 85 on our yaks, and we'll be investigating this as the weather improves. We may just end up with different 3 solutions.
Old 03-23-2009, 08:45 AM
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mcmcintyre
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Default RE: DA-85 Question

Wind Junkie,
Please keep us posted as you guys check this out. I flew on Saturday and had the problem come up again on my last flight. I will be checking the mixture again and will probably call DA to ask about the addition of a pressure line. How would the small fuel tank help the problem?
Old 03-23-2009, 09:29 AM
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Cyberwolf
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Default RE: DA-85 Question

This is what I did to my DL-50 in my Yak I soldered the original hole shut then redrilled a new hole in the center and tapped it 6-32 then used a standard nipple I picked up at the LHS. I then ran the line inside the fuse and made a loop then put the end inside of a pill bottle. The opening in the lid of the bottle is not tight on the tygon as you can see, that way no vacuum can be formed. You can also use a piece of brass tube and solder than on also then drill a hole in the plate. Just make sure there is nothing on the inside that will hit the diaphram.
I hope this helps .
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Old 03-23-2009, 09:39 AM
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Cyberwolf
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Default RE: DA-85 Question

RTK just wondering why you said to increase the pop off pressure, i'm no expert at these model engines but everything I have read says to decrease the pressure to about 13-15lbs. Am I missing something here?
Old 03-23-2009, 03:26 PM
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RTK
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Default RE: DA-85 Question

If the pop off pressure is really low, it "might" be possible, in certain high G maneuvers un-seat the metering needle. This is only a theory that I have not established yet.
You are correct, most engines like a range similar too what you have stated.

A few years ago I started playing with a balsa box because I was having pressurization problems on a particular air frame. The box worked out well. In experimenting, I did find that you NEVER want to leave the line trailing under your plane. It only took two dead sticks shortly after take off for me to figure that one out
Old 03-23-2009, 04:53 PM
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Eagleburger
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Default RE: DA-85 Question

Yaks, suhkois etc need to be baffled. Yet to see one where the engine performance and even flight performance that didnt improve with a baffle.
Old 03-23-2009, 08:38 PM
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Cyberwolf
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Default RE: DA-85 Question

Thanks RTK for the explaination I thought I had missed something new somewhere.
That popoff pressure was about the next thing I thought about doing to my engine, but I have not seen anyone really complain about that with the DL-50, Just the DA's, so for now I think I will just fly it and see what it does . You know? if its not broke don't fix it sort of deal.
BTW I enjoyed your video of the Yak .

mcmcintyre
Theres 3 ideas you might try to solve your troubles. Baffles,Pop off spring and the hose on the plate . I hope one of them solves your problems.
Old 06-30-2009, 09:15 PM
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wind junkie
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Default RE: DA-85 Question

Update on this : Last weekend I flew with a "balsa box" and it seemed to make no difference at all. Pics show the backplate I ordered from DA which has the nipple and the box.

I put a coat of dope on the box and now I think maybe that was a mistake (it should breathe "slowly" to allow changes in weather and heat so as to not form pressure I think). I went to about 800 feet high, rolled inverted, dropped to idle and held full down elevator for about 8 seconds. Then I gunned it and it abruptly quit.

Anyway, I need to try the baffle idea next. This box was easier for the time being as I needed to do maintenance on the muffler and smoke system anyway.

BTW, a friend with the same problem tried using a small 2 oz header tank with the same sort of arrangement and he said his motor wouldn't run with the line connected. I think maybe he did have a pressure build up but I can't prove it other than his ran "normally" when he disconnected the line. With the line on the header tank to the diaphram nipple, his engine sounded rich to him.
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Old 07-07-2009, 09:21 AM
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Cyberwolf
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Default RE: DA-85 Question

Nice set up but one thing I see that I don't think is going to work.

Is the tube hole in your box needs to be larger to allow it to get air in it. also where you doped the box that will stop any filtered air from getting in , Myself I don't think even a undoped box would allow enough air to get in with the tube as tight as it appears in the pic. A person dosen't want a tight fit on the tube, I use a pill bottle with the cap drilled for the tube to fit with slop and tie off the tube so it can't come out. All this is doing is moving the hole in the plate away from any high or low pressures the cowl or wind might make on it, in other word its a shelter from the pressures or wind.
I have seen several that just went to the inside of the fuse and ran fine, No box or bottle, However I like the pill bottle myself. I have heard of some going as far as the use of a condom in a bottle to get a air tight seal that allows only the air within itself to operate the diaphram I think thats going a little bit to far.
Old 07-07-2009, 11:15 PM
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Default RE: DA-85 Question

Cyberwolf, so let me get this right you're saying that the box needs to "breathe"? Well, I definitely did not allow for that as I sealed the tube to hole in the box with Goop, and doped everything.

I honestly don't notice any difference in this setup vs the stock hole in the backplate. I've flown it 2 weekends now. I would have expected some tuning diffs, but it seems to run fine except for the inverted stoppage at idle of course.

What if I got rid of the goop on the tube, and then poked some pinholes into the box? I thought the point of having the wooden box in the first place was to give a reservior which was immune to (abrupt) pressure changes inside the fuselage? I chose balsa because I thought it was important for it to VERY SLOWLY acclimate to pressure changes caused by weather and temperature differences (ie, from the basement to a hot car to outside air for example) a balsa box would allow that due to its porosity while a sealed bottle would not. I'm thinking poking holes would defeat the purpose of the box in the first place. Maybe only 1 small pinhole would do it?

One should keep in mind that in my plane (TOC Yak 33%) the pressure seen in the cowl is probably very close to the pressure in the entire fuselage as the firewall and engine box bottom have been cut to clear the carb and other installation features. The carb really isn't IN THE COWL as it sits so far to the rear and is exposed to the same air as my box. The cowl just serves to scoop all the air and at one point I convinced myself it ws causing a problem when inverted due to a wierd turbulence situation due to the angle of the incoming air and the orientation of the motor/carb etc.

When you installed your bottle as you say, did you definitely experince the inverted idle stoppage and see it cured by your installation?
Old 07-08-2009, 06:38 AM
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Default RE: DA-85 Question

My set up didn't change the tune at all but allowed the engine to run in any direction W/O any issues. The Yak cowl & Suk cowls are the worst for air currants from what I have read, But my extra sure needed one, ran fat as all get out in a K/E one way only and sometimes in midrange depending on what I was doing The bottle stopped all that nonsense.
From what I have read and experenced myself, the bottle with a slighty larger hole for the tygon tube has worked well for me. The diaphram does need a certain amout of air pressure to operate, all your doing with the box or bottle is limiting the drastic change from low to high to obtain a even pressure for a level constant flow of fuel.

I put my bottle in the fuse with the opening facing the rear of the plane, so it will block any wind coming in from forward movment and it must stop any turbulances also both the planes I have done this to runs super in any position.
A few guys are cutting the springs also to help pressure issues and adding velocity stacks for less puddleing. So far I have not needed either of those mods.
Good luck
Old 07-13-2009, 06:29 PM
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Default RE: DA-85 Question

I hope someone can HELP. On my DA 85 from the very first start up, the mid range has a detonation popping sound
with a small amount of surging rpm's in the mid range more so. The idle seems good, the high end is ok at 6500rpm's. The engine
was returned to DA where they did the upgrade, but did not address the mid range problem. I have tried leaning out the low end a
little but has not helped. I have about 20 flights on it and it's not getting any better. I have this engine in a Aeroworks Yak 75
Any suggestions you guys have would be greatly appreciated.
Old 07-15-2009, 01:48 PM
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Default RE: DA-85 Question

What you describing is a compression issue and to my knowledge that should not be a issue. Does the engine smoke when its doing this ?and burble? also have you done the diaphram mods yet ,if not that is where I would start. Theres other things you can try but I would do the tube and pill bottle first.
Good luck let us know how it works out.
Old 07-15-2009, 11:31 PM
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Default RE: DA-85 Question

What are you guys running cannisters using for the stuff that looks like fuel tubing to help secure the cannister within the brackets?
Looks like glow fuel tubing. I decided my old H-9 Sukhoi needed to get quiet. I put the DA85 on it with a pitts muff. Every time I fly everyone says it's too loud. I just say "what?" But I am trying to do my part and preserve the peace. That and get better sound scores.
I have an MTW cannister but did not get all the mounting stuff.

Murray, I hope you get yours sorted out. I know that burble is aggrivating. Mine does it too. If you have the engine tuned correctly at both ends and it's not over heating, has good spool up from idle and doesn't quit on you, then I'd say just try and live with it for now. 20 flights is a good start, but probably not even close to getting it truly broken in.

Greg
Old 07-16-2009, 09:11 AM
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yarom
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Default RE: DA-85 Question


It's actually silicon tubing. You can find that in various places.

I've also seen people using the black tubing that is normally used for smoke.

Be aware that the canister sends the vibrations into the fuselage. You will also need to put a piece of silicon exactly where the can passes under the gear. If they touch, it could create interferences and mess up with your radio. We lost three of these at my club...
Old 07-16-2009, 10:38 PM
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Default RE: DA-85 Question

Thanks yarom, I'll check for some tubing at NAPA, they have everything. Appreciate the heads up on interference issues about the contact between the gear and the cannister. Mine may only have 1/4 inch clearance. I'll glue a formed block of wood there and make it another point to keep the cannister even more solid.
Thanks.
Old 07-17-2009, 11:37 AM
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Default RE: DA-85 Question


You need to be careful there - on one hand, you want to isolate the canister from the gear - a piece of teflon should do that. On the other hand, you need to give the canister some room to vibrate, as this engine moves a lot.

If the canister is fixed too tight (as in two formers), my experience shows the stress point will move to the header area and it might develop a crack fairly soon, especially on flex headers.
Old 07-17-2009, 02:28 PM
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Default RE: DA-85 Question

Yarom thanks again,
That is good information. I do have a flex header wrapped with teflon. I am striving to bolt everything in place with a little stress to that flexable section as possible. I have rebuilt my engine box due to pilot error and couple weeks ago. I will now bolt the DA85 directly to the firewall instead of a bunch of stacked light plywood cut outs. Not that the previous engine mount was bad, but I would rather have a very solid mount and then be able to actually see and reach the carb instead of it being stuck inside a tunnel of sorts.

Yes, I can see that the cannister will need to stay free to move a little within its mount (I was going to use two mounts on the cannister, now just the one) due to the flex of the header joint and vibration of the engine running through differnt RPM ranges, heat, expansion, etc. That makes total sense. I've seen that some installations also have a stopping bracket of sorts at the rear of the cannister to keep it from blowing away. That seems like a good idea given the teflon tube and light weight hose clamps holding it to the header.

I appreciate the insight. Now if I can just break away a little early this afternoon and get back in the shop. May get to fly it this weekend.
Have a good 1

Greg

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