AX-O's Fastback RV-4

[AltonD]

Axel, make sure the oil cooler inlet line is on the bottom and the outlet is on the top for a vertical mounted oil cooler.

By circumstance I will not discuss, I know my oil temps run substantially hotter when I have 8 quarts on an IO360 (might have been a tad more).

[AX-O]

Wanted to give you guys feedback on Phase I. DanH, I have not mapped the pressures yet. Trying to get her flying and not be completely consumed with temp monitoring.

It has been a slow process. I have been fighting temp problems and trying to find the right prop pitch. The plane currently has about 8 hours on it. There has been a lot of fly, fix, fly going on. And some major mods too.

The plane handles nice although the controls feel a little heavier than my previous airplane. The plane stalls similar to the standard 4 however, it is stalling about 2 kts faster than my previous plane. It could be a difference in IAS caused by errors or the fact that I have been flying without the aft wing root fairings until I get the flaps/ailerons where I want them. It has a lightly heavy left wing.

In a solo configuration, the elevator counter weight is about 3/4 of an inch lower than the horizontal stab. At some point in the future I will take the shim out under the horizontal stab and make another tail fairing (so much work).

Now for some mods:
I have tried 2 different oil coolers. The first one was so subpar that I did not know how hi the oil temps would go (standard vans 7 row). It was place behind #4 at a 30 degree slant.

The second oil cooler did better but temps were still too high. It is a SW 8432R 8 ROW DUAL PASS. It was also installed at a 30 deg slant behind #4. It would hold around 225 deg but not with full power because my engine would reach 2700 rpms way too soon.

Being that I did not have the space for a larger cooler I started looking for different approaches and figuring out how to clean the airflow and make it work more efficiently. The biggest limitation is that I have to place the oil cooler low due to the upper cowling. That causes the oil cooler to get blocked by the Cylinder fins. So I came up with this approach. Maximize the airflow by completely cutting the aft baffle/plenum, raising the plenum by approximately half inch and mounting the cooler at 85 deg slant behind #4.

Picture below show mod:

Figuring out how close the plenum was to the cowl. Clay layed on to of plenum then both cowlings put on the aircraft.



Aft baffle and plenum flange cut.



Inner air dam to ensure air was not being sucked out of the oil cooler as airflow went down the cylinder fins.



Molding the new plenum.

[Mike S]

Ahaaaaaaaa been wondering how things were going.

A thought for you--------in the photos above about cutting the cowl exit------have you thought about putting a hinge on the part you cut out, and making it into a cowl flap that can be opened for climb, closed for cruise???

A quick flight with the aft wing fairings on would let you know if the sluggish handling and heavy wing are due to flying without them...........or is this a part that is not readily removable when installed???

[AX-O]

Cont. Sorry Mike.

After this mod the oils temps went down and I was able to find the top of the temps in cruise (2700 rpm due to prop). CHTs stabilized at 360s and oil temp at 217 deg. Huge improvement.





and completed. I used the plenum to give the structure the strength and stability I took away by cutting the aft flanges. The small indentation on top of the plenum bump also helps with bending.


From the first flight I knew that the exit air was misbehaving (due to oil trails after the flight). The air flow is turbulent and recirculating above the exhaust turndown. The next step will be to make a metal fairing that will extend from the firewall around the bottom landing gear tube to mitigate the almost 90 deg turn the air needs to make to exit the cowl. So I was thinking..... How could I quickly and representatively be able to make a "fairing" without drilling and spending a lot of time. Some type of proof of concept. Then It came to me. Aluminum tape!!!! So in approximately 30 minutes I wrapped aluminum tape from the tube to the bottom of the firewall. I use two layers of tape at 90 deg. I don't have that great of pics. Look in between the exhaust pipes. BTW, oil on the first pic is for airflow visualization after flight.




Results: Although OATs at 8000 DA were 2 deg warmer than previous data collected, the oil temps went from stable at 217deg f to stable at 209 deg f. The crude test worked! OMG, 8 deg cooler (everything else almost constant) just because some tape. I did not even wrap tape from the top of the firewall to the tube. So that will be the next thing I attack. A nice exit fairing. I will also figure out a way to redirect the exit air so it does not exit via the landing gear fairing. I will use left over engine rubber baffles.

[AX-O]

Prop:

I have tried 3 different props. Each one is better than the previous one but we have not found the right one yet. Craig is making another test prop. He is changing to a narrower cord and going with a 70X78. The 340 is making good power. But it is also presenting new issues that I have not experienced with my previous plane. For example, after 2 hrs of flight time I changed the prop for more pitch. Pics below show what I found. The torque must have backed off.



I talked to Craig and he said "she is definitely talking to you. It is not bad but here is how you fix it". He sent Nicole over to grab these cone shaped washers. I forgot the name of them. Put 4 of these back to back on each bolt and also a regular washer. Kind of like take 2 of these and call me in the morning. I had to order longer bolts so I call Saber (as always, extremely great customer support).

I could not find anywhere if it is bolt : 4 cone washers : standard washer or bolt : standard washer : 4 cone washers. I decided to go with bolt : 4 cone washers : standard washer because the standard washers fit the shape of the crush plate hole better. I think that is why I originally lost the torque on the bolt. The standard washers coned and took the shape of the crush plate hole.





Prop progression
1st


2nd


3rd


I got bored

[AX-O]

Originally Posted by Mike S

A thought for you--------in the photos above about cutting the cowl exit------have you thought about putting a hinge on the part you cut out, and making it into a cowl flap that can be opened for climb, closed for cruise???

A quick flight with the aft wing fairings on would let you know if the sluggish handling and heavy wing are due to flying without them...........or is this a part that is not readily removable when installed???

Mike,
Cowl flap will be implemented in the future. I have been researching that in great detail. I don't want one like the one currently being sold for RVs, I want one that the entire surface moves (to include the trailing edge).

The aft wing fairings are not a quick on/off thing. In fact I have not made them yet. I am going to tuff the interface of the wing/fuse and see what is going on back there before a make them. I also have some F1 fairings that I will cut up and play with. Aerodynamically, there is a lot to be gained back there. I never said "sluggish". The plane has heavier control forces when compared to my previous RV. It could be the radius of the trailing edges or it could be the geometry on the controls/bell crank/tubes. The holes are where I drilled them, not where they came from the factory

[DanH]

Originally Posted by AX-O

He sent Nicole over to grab these cone shaped washers. I forgot the name of them. Put 4 of these back to back on each bolt and also a regular washer.

Ax, they're called Belleville washers, and they're installed like this, between a pair of 960 or 970 washers:

Results: Although OATs at 8000 DA were 2 deg warmer than previous data collected, the oil temps went from stable at 217deg f to stable at 209 deg f. The crude test worked! OMG, 8 deg cooler (everything else almost constant) just because some tape. I did not even wrap tape from the top of the firewall to the tube. So that will be the next thing I attack. A nice exit fairing.

So what did the CHT's do?

[AX-O]

Thanks Dan. Will add another washer. Although when i called saber he only added the thickness of one regular washer.

Dang it. Forgot about the CHTs. No change. They remained at the 360s.

[AX-O]

Respectfully requesting no thread drift. Thanks.

[Whitman]

Axel, it would be a shame if this thread went to 38 pages