Firewall Forward

I posted this yesterday on Vansairforce.

"I hardly have a problem but am trying to operate with the CHT not more than 400F in the climb. At about about 135/140mph near gross I can make about 1400fpm with everything forward. (160hp O-320 MT 2blade c/s prop, P-mags.) After around 3000' I then have to change something or I break my self imposed 400F CHT limit. I would however like to be able to climb with everything forward to the stratosphere, or at least 10000'.

One solution is to get the speed above 150mph which of course cuts the climb rate. Another is to reduce to around 25 square and keep the same speed. The second is the more effective because I suspect the P-mags retard a little which more than compensates for the reduced fuel flow.

I dont have an oil temp problem. In fact next time the top cowl is off I will reduce the air flow to the oil cooler to get the oil temp up a bit leaving more air for the CHT.


I am wondering if I should cut some of the bottom cowl away. It is clear to me that with the 4-pipe exhaust there is less air outlet area than inlet area. This may well be the real issue but once its cut its gone for ever."

I had a number of interesting replies, though no one was convinced cutting the cowl was the solution, although several agreed the outlet should be larger than the inlet.







My idea is to cut straight across from the left hand pair of pipes until it meets the slightly deeper cut on the RHS.














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The engine is an O-320 from Aerosport Power. Its a Skytec LS starter with dual P-mag ignitions, a two blade MT prop, and an Odyssey battery. Until now every start has been very easy and immediate with no sign of a problem.


To me it looks as though the whole base of the starter is too thick and the little sprocket wheel is positioned too far from the starter ring around the flywheel. An alternative explanation is the starter motor bracket has deformed and it has bent away. I have to say though I can see no sign of deformation.

It is wired as Skytec suggest here. This, plus the dual P-mags, I would have thought would protect it from any kickback problems, though I do not in fact think that was the cause.



All the teeth are on the flywheel, but as you can possibly see in the last two pictures there is some damage to the corners.

It has been hard to get things moving this having happened late on a Friday in the UK. I am trying to be patient and not think too badly with the suppliers involved.



The primary questions that run through my head are:

1) Why did this happen (after just 6 hours - perhaps 20 starts.)?
2) Why will a replacement unit be any better?
3) Will Aerosport Power and Skytec get me back in the air quickly or slowly?

Postscript - 8th July '08
Well Aerosport Power sure came through on this one. On the 7th thy had a Skytec NL model and toothed ring shipped, and as I write I see FedEx have just cleared it through Stansted Airport. Soon be here.

(As always, double click the pictures if you want more detail.)

Heater - I decided a long while ago to take the cabin heat off the oil cooler rather than an exhaust muff. I am in the UK which is a temperate climate, so I do not need Alaskan quantities of heat, to keep warm. (As I write this it is snowing!) Those that do it this way usually report plenty of heat, though there are plenty of folk out there who will argue it is a really bad idea. To me the pluses are a much reduced problem of carbon monoxide, fewer parts/less weight, and those that do it this way report a much nicer, less 'scorched ', quality of air in the cabin. What is the downside? Very little as far as I can see. Worst case I can always buy an exhaust muff and hook it up. I had to make up a shroud to gather the air after it has been through the cooler which exercised my fiberglass skills. It's not pretty but it is reasonable on the inside, where it matters. People will reasonably comment that the efficiency of the cooler will drop dramatically. That is certainly true, but while I don't live in Alaska I don't live in Arizona either. My Supercub with an O-320 and the same cooler struggles to keep warm, and that only travels at 100mph. For break in, I will disconnect the cabin heat system, and seal it up, and remove the collector, since clearly at that stage the engine will be generating more than normal heat. If all else fails I will click the switch which turns on the Mercedes Benz seat heater that I will be sitting on.

Carb Heat - This is now all connected up. Its a tight fit in a -4.

As each additional system is installed, despite my utmost efforts to think ahead and plan what else has to be added, the systems maximise their efforts to claim the same space. A good example was the screw on the heat box in the picture above. Its nut was claiming the same space as the tail of the bolt on the gear leg. If I had known this when I was putting the gear leg on I could have packed the head out with two more washers. I contemplated pulling it out in situ, but ended up by filing some of the tail off. To bolt the heat valve on, 8 #6 nuts and bolts still took 4 hours!




Pressure Sensors - FP, OP, MP have all found a home in front of the battery on top of the step. They are accessible if they ever need replacement and the hose runs are quite reasonable. I took advice from VANS as to which hoses to buy for a -4 and they certainly mostly erred on the long side. Better than short I guess.

There has been a little discussion about the oil tube/ dipstick for -4 on Vansairforce recently. Many people end up with one that is too long. Aerosport Power knew of the issue. This is what they supplied to me. If you cross their palm with silver I am sure they will sell you one.



Postscript - 30/7/08 - Carb Heat

It turns out that the carb heat muff works well as you can see from the graph below.

After an initial 2000'climb from 300'ASL, the engine settles down at about 23 square, and the engine leaned. The OAT is around 58F, and the carb temperature due to the venturi and vapourisation of the fuel, running at about 51F. On pulling full carb heat the temperature rises to around 63F. It looks as though if I had left it on a little longer, I would have had a slightly higher gain since the gradient of the curve is not yet flat. I do this 3 times. At around 13:05, I reduce power and again pull the carb heat. This results in a much larger gain, which is in fact when you really want it. This time with the engine developing little power for the descent, it goes more than 15F above the ambient temperature.

Finally the oil cooler has come to rest.

From above it looks like this.

With the c/s unit for the prop it is becoming very crowded back here.

The oil lines to the cooler are not yet finalised but will almost certainly end up like this. It looks like I will need a new 90 degree fitting to get the oil from the engine to the cooler safely on its way. I have seen other folk cut into the prop governor bracket, but this does not make sense to me when it could come straight up.

You can see the control cable runs. The prop cable does a 270 degree turn. This was not to use up length but to ensure the tightness of the turn did not appear excessive.

So far I have managed to preserve some space around the oil filter. I just about know where everything goes and this will remain with room to access it when it needs replacing.

I have had some difficulty setting up the throttle, because everything need to be adjusted exactly, in order to achieve the full travel of the carburetor lever. Ideally the middle hole in the lever arm here would be 1/16th further up, or VANS quadrant would give you a tiny bit more range. I have an idea to fix it so you can be sure the carb is controlling the range, not the quadrant, but for that you have to go to the other end of the cable. http://gikonfuse.blogspot.com/2008/02/throttle-cable.html#links

The mixture was much simpler in that it requires only about 95% of the quadrant travel to give full range here.

I am a bit concerned about the tightness of the bend in the mixture cable, though it runs quite freely.

The baffles are all cut to shape and the rubbers installed on the rear baffles. The rear baffles are primed, but I do not intend to paint them.

The front baffles wont go on until I have painted them to match the front exterior of the cowl, since they are quite visible from the front.
The exhaust stays turned out to be easy to make and adjust for length. At the moment they only have one large washer at each end, but when I have more large washers I will run another bolt through before priming them.
Here is a picture of the stay on the LHS.
In this picture you can see where the fuel exits the fuselage. From here it goes directly to the mechanical pump. The rest of the fuel system is inside the fuselage and you can see it here.

With so little of the fuel system forward of the firewall I am hoping that there is no tendancy for vaporisation in hot weather. I think I am thinking about the day when I can find no 100LL to get home.

I had some difficulty deciding how to mount the duct that brings carb heat down from the exhaust. In the end I have mounted it slightly high. The intent is that there will be some flow through the system when the flap is closed. When the engine is sucking heated air I think plenty will flow through the duct though there will be some leakage at the bottom.

Before I take things further with the baffles I want to be sure I know where the oil cooler is to be located. If you are building a -4 you know space is very tight. I roughed out some brackets to enable me to hang it, as you see, on the outside of the engine mount. This will work, and allow me to use this otherwise dead space and allow access to the oil filter.

The baffles progress.

The part for the rear wall on the LHS of the aircraft reflects the cowl shape of the RV4, but the RHS part has way too much material. I wonder if VANS shipped me the wrong part or if they always do this.

Routing the oil line over the top of the engine appears to be a vast improvement to going underneath. The path is probably slightly shorter, and it is not competing with the electrics for space along the top of the sump. If you do decide to do it this way you will need a 45 degree fitting on the front of the engine.

One issue I am pondering is how to stop the oil line from chafing where it passes through the rear baffle wall. There is no plastic bushing in the VANS catalogue that is big enough.

One of the desiccation plugs started to turn a little pink. I think it must be on the cylinder with the open valve. I took all the plugs out of the engine and regenerated the crystals. They are all a nice shade of mauve once again.

I am starting to work on the baffles and the front of the engine. It raises a couple of questions:

1) Why is the 'normal' route for the c/s oil line from the fitting just to the right of the two clecos, underneath the engine? It would be much simpler to use a 45 degree fitting and go over the top of the push rod tubes, and then through the rear baffle wall. I doubt it is any longer. Is this ever done? I can find no pictures of it done that way.

2) The baffle floor on #1 will slope down at nearly 45 degrees. I can see nothing unusual about my installation. Are all the -4 like this? Is it because of the c/s prop? I don't think I cut off much of the cowl at the back.

Postscript - 11th December
1) Aerosport Power, the supplier of the engine, say there is absolutely no reason not to go over the top.
2) D-EXTL, a very well built German RV4 has a very similar steep slope to the baffle in front of #1. So onwards, and one day upwards.

In order to provide a better run for the hose bringing fuel to the fuel pump, and to make room for the control cables and exhaust hangers, I would like to replace the 90 degree fitting (center of picture) on the input side of a the fuel pump with a 45.

Rotation of the fitting is blocked by the constant speed oil pressure unit. This leaves me in something of a quandary as to which unit is easier to remove in order to replace the fitting.

If I take the fuel pump off by undoing the two Allen Key studs, will the unit in fact be removable? Remember on a -4 there is almost no room between the fuel overflow takeoff on the back of the pump and the firewall, as you can see in the picture. With the studs removed does it slide off backwards or could it rotate downwards?

The alternative is to remove the entire constant speed unit. Yes, only 4 nuts, but some are very hard to get to, at least with my fat spanners and the poor access behind the engine.

Postscript 1/12/07 - Today I took the constant speed unit off having been advised the fuel pump was not going to be easy. To get the c/s unit off I had to take both mags off. It was clearly the right way to do the job, I had the 90 degree fitting exchanged for a 45, and everything was back together in 80 minutes.

A very supportive phone call and email from Larry Vetterman.

"I have never seen the pipes this close to the tunnel. You can adjust the pipes however. They are new and very flexible. Take hold of the #1 and pull it towards the center. Give it a good push. No you cannot break it with just your amount of force applied. Then re align the #3 to it. Yes you can trim the extensions. We leave them long on purpose as some builder prefer them that way. My preference is to trim about 1.5 inches off the end. "

I spent a few minutes on it today and believe this will work. (Larry has other plans if not.) I will have some time tomorrow and when it is sorted will post some more pictures. It is great to have a supplier who is committed to having a happy customer. Larry clearly is.

Postscript 8th Dec - I wrestled with the pipes for a long morning and made a considerable improvement. Took some photographs and sent to Larry. His immediate response was that he would make me a new pipe for #1. How is that for good service. It was here in the UK 10 days later and fits a dream.

I seem to have a problem with the exhaust. I am wondering if it is just my set up, or if they are all like this.

If you look at the top picture you will see that the pipes are offset to the left (RHS of aircraft). This may well be because they do not allow for the fact that the engine is offset. The problem that arises is #3 is very close to the F-451 fairing. Perhaps 5/16". The #1 pipe, the inner one is about 1/16" from the sump if that.

As you can see pipes #2 and #4 do not have this problem.



Nothing to complain about here.

















But this seems really tight.











I wonder if I need the tails as long. If I took about 1.5" off the pipe, so the bent tail moved forward, the problem would reduce.
Hopefully other builders have been here, otherwise I will have to track down Vetterman.
I must say I would prefer more symetry,
but more importantly I am concerned they could hit the fuse when the engine stops/starts etc.

My P-mags arrived fresh from Texas. I had ordered an E-mag and a P-mag, but since there were no E-mags on the shelf they upgraded my order to P-mags, at no extra cost. That's what I call customer care!

I have found it hard to find picture of e/p-mags bolted to engines, so I thought I would put a couple here. If you don't know what they are, go to this link. http://emagair.com/Index.htm

This picture shows the right p-mag. The first thing to understand is that unlike a conventional mag.., you can bolt it on rotated into any position you choose. The electronics takes care of the alignment.


In this second picture, you can see the green connector block, the manifold pressure sensor, currently covered by a shiny black cap, and just to the right of it, a LED, which is used in setup. (If it is hard to see double click the pictures, you will get a better view.)







In the third picture below, you can see the left hand p-mag. It is rotated nearly 180 degrees. I would like it further around, but the casing of the mag., interferes with one of the oil paths to the cooler. The slight disadvantage of it in this position, is the LED is somewhat hidden underneath, but no big problem.





In the fourth picture, below, you are looking down from above. As well as the major performance advantages of P-mags., and the weight saving, you can see that in the constrained area in front of the firewall of an RV4, there is a significant space saving.

(In case it confuses anyone, the control cable and hose across the bottom of the picture are just parked there while I work on the plane. This is NOT a final location.)

We hung the engine today. It is a constant speed O-320 from Aerosport Power. It took two of us about 2 hours in total. It would have been less, but I messed up with the order of the washers so we had to back up at one stage.

Aerosport were kind enough to install a special fuel pump overflow fitting. Without it you might well have contact between the fitting and where the firewall sticks out. You might want to remember this when you order an engine if you are building a -4.

There is also an oil pressure takeoff point that needs to be installed before you you start, near the bottom right corner of the engine mount. Aerosport Power had taken care of that though.

The engine as it came from Aerosport looks superb, though of course it will be a while before I know how it is in action.

One thing that is worth mentioning. I have the VS, HS and rudder plus tail wheel on the back end. It is now very light and can easily be lifted in one hand. When I next remove say the rudder I will have to be very careful it does not tip forward.

My O-320-D1A arrived today from Aerosport Power in Kamloops, Canada.

I thought a couple of pictures might be useful if you have never bought an engine before, and wondered how it is shipped.

It will be quite a while before it is started, but I have to say it is beautifully presented, as you can (just about) see from the attached pictures. It is inhibited so I wont open the bag for now.

It has arrived with a good set of records from its test run, and docs for the ancillaries that are included.

Right now it comprises:

• Superior Cylinders


• Sky-Tec Light Weight Starter


• Carburetor


• Fuel Pump


• Primer System


• RV4 Fuel pump and dipstick mod.


• Denso 40 Amp Internally Regulated Alternator

I will probably go with the e-mag / p-mag ignition, but thought I would leave it for now, in case there are more minor mods to their system, or software updates, by the time I need them.

I wasn't planning to put a primer on it, just use the throttle pump, but now it is here I might just get seduced into installing it. What I have against it is the weight thing.

.


[Note added 7 Jan '07. Aerosport Power advised me "The plastic wrap should be removed as condensation can accumulate under the plastic."

I therefore have the chance to take a few more pictures which at least I will find useful since I keep forgetting what goes where on the back of the engine, when I think about the firewall.]

Labels: engine