Climb speed?

I would be interested to know what speed folk are using to climb. I am finding that once the speed drops below 100mph the cooling drops away quite abruptly.

My theory is that below 100 the nose starts to come up and the pressure increases on the cooling exit due to the increased AoA.

My oil temps sit quite low most of the time, normal flying 155/160F. (Yes, I need to reduce the air flo to the oil cooler.) The only time the oil temp gets near 170/180 is in the circuit when the CHT are dropping right away and the manifold is back at 12/15" but the flaps are out and I am trying to get the speed off.

Is this familiar to other -4 owners?

100 kts.

I haven't noticed any cooling issues when climbing slower though.

Steve Sampson said:

I would be interested to know what speed folk are using to climb. I am finding that once the speed drops below 100mph the cooling drops away quite abruptly.

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My old -3 had bad over-heating problems. For some reason my new -4 is astoundingly cool, even mid-summer 100 degrees. I can climb to 10000 at 85KTS and CHTs don't go over 380 and OT's are under 200. I suspect the -4's cowl is sealed better and I have a larger outlet, that is probably helping a lot.

BTW... I typically cruise-climb at 100kts and it's even cooler.

-Bruce

BruceMe said:

I can climb to 10000 at 85KTS and CHTs don't go over 380 and OT's are under 200. ...

BTW... I typically cruise-climb at 100kts and it's even cooler.

-Bruce

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Thanks for the replies.

Bruce I would be interested to see a picture or your lower cowl air exit if you have one and its not too much trouble. I regularly return to the idea that mine is too small though dont want to cut it unless it really is too small. (VANS say put more hours on the engine.)

The evidence that says I have plenty of airflow is that I have never seen oil temps above about 180F.

In fact I dont have a practical cooling problem but would just like to be able to follow Bruce to 10K!

Deven, I think there is just one dimension that would be of interest. If you could measure from the lower rear edge of the fiberglass cowl to the bend in the firewall, where the stainless folds under the bottom skin it would be of interest. Perhaps if you could measure it on the center line and just beside the gear legs, along the fore aft axis, it would be pretty indicative of the outlet area. The width is controlled by the gear legs so we must all be the same there.

I have a 4 pipe exhaust which further reduces the space the air has to pass through.

It would be great if you can, thanks.

PS Glad you like the paint. I am pretty pleased!

Deven - I cant see a picture or a link on that last posting of yours.
Sorry. Steve.

Deven - perfect thanks! I will compare with mine tomorrow. It certainly looks similar

Deven,

I assume you are using the Vetterman 4 pipe exhaust system as I am. What struck me about your pictures is how long your exhaust extentions are. Are these special order? The ones I got with the exhaust pipes were a lot shorter than yours. When I wacked them off even more so the turn downs would just exit the cowl, the noise level went up significantly in the cockpit.

Jerry Isler
RV4 N455J
156 Hours

Some men are longer than others...

Jerry,

Many of the earlier Vetterman 4-pipe systems had the longer extensions. The newer ones I have seen are shorter. I bought one of Larry's first 4 pipes for my RV4 in 95', it had LONG pipes exactly like Deven's, really sounded great! The new system he made for my Rocket sounds even better!

Smokey
HR2

Steve Sampson said:

My theory is that below 100 the nose starts to come up and the pressure increases on the cooling exit due to the increased AoA.

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Two things:

- Up to about 15? AoA, for all intents and purposes properly designed inlets are not affected as the flow is more or less re-aligned,

- During a steady state climb, therefore high power, the flow is essentially "straightened" parrallel to the propeller axis (aft of it of course !).

As a result of the above, if your powerplant arrangement is known to provide good results on other installations and same a/c, I would look for other culprits such as leaks (indeed, on a "proper" typical certified installation NASA demonstrated leaks in excess of 50%).

Have you departed from existing known powerplant installations that give good results ? If so, what have you changed ?

FG

going down the list

Air in (is the air disrupted and not flowing well - rough area causing disruption of flow)
Leaking air (baffle leak)
Oil not cooling (cooler blocked, air leaking around it, lines to small, etc...)
Air exit (looks like a good sized opening)
Fuel (too lean on a climb)

My vote, pull cowl and look for tell-tell signs dirt signs that air is leaking. Just a guess but is it possible the baffle seal is a bit loose until pressure is high enough to hold in place (ie: higher speed)?

One thing that can be done is to measure the delta static pressure accross the cylinders (that delta Ps is the one that gets the cooling air mass flow across the cylinders, nothing else !); How to do that...here is an easy way:

- take 2 aluminum tubes of 3/16 inch dia by the length of approx 2 cylinders and drill through (2 holes) with a 0.050 in bit at 90? apart (that is 4 holes); Repeat every inch or so longitudinally;

- Longitudinally and at mid cylinder height install one tube on top and one tube on the bottom of one cylinder bank; Attach properly so they will not fly-off in flight; The tube have to be perpendicular to the cooling air flow so as not to get any dynamic pressure component;

- Take a known good sensitive airspeed indicator and connect the previous tubes with it using rubber flex tubes; Attach the upper tube to the Total Pressure port and, the bottom tube to the Static Pressure port of the ASI.

- Perform a flight test and, at about the same altitude record the "Airspeed" from that ASI, OAT and, Pressure Altitude (Set your altimeter to 29.92, BUT WATCH TERRAIN AND COMPLY WITH ANY ATC REQUEST WITH THE PROPER QNH: Best is to use a TEST Altimeter set to 29.92) for various climb speed; This will give you the Delta Static Pressure across the cylinders expressed in Knots (or whatever the ASI you are using is marked with) vs Climb Speed;

- Use the following formula to convert in inches of water (if my memory is good, Lycoming cooling requirements tables are usually expressed in inches of water):

Delata Ps = (KIAS/100)^2 X 6.5078

If in mph, convert to knots using: KIAS [kt] = MIAS [mph] X 1.15078

Use the proper engine manufacturer cooling chart check where your installation is on the chart; That should tell you if everything iaw the book;

From there you could determine how much Delta Static Pressure you need and improve your installation and re-test until things are OK;

Give us some of your numbers; have fun.

FG

One more thing, run the rubber flex tubes inside the cabin by making sure they are not compressed anywhere (pressure has to "flow") and, on external surfaces cover them with aluminum tape.

JetA4GA said:

- Longitudinally and at mid cylinder height install one tube on top and one tube on the bottom of one cylinder bank; Attach properly so they will not fly-off in flight; The tube have to be perpendicular to the cooling air flow so as not to get any dynamic pressure component;

Click to expand...

ERRATA: I meant parrallel