Wheel landing

A nice description of a wheel landing:

  • With the main landing gear touching on the runway,
  • push the stick forward to pin the main landing gear on the runway.
  • Stay in that level attitude until you can’t hold the tail up any longer.
  • Then and only then let the tail fall and
  • pin the tail with pitch up elevator (stick back).

How much compression

Just starting to think about what’s needed to get the compression ratio up, towards what I saw with the Verner radial engines.

In a piston engine, it is the ratio between the volume of the cylinder and combustion chamber when the piston is at the BDC of its stroke, and the volume of the combustion chamber when the piston is at the TDC of its stroke. The compression ratio for the Velie is 1 : 5.4

Now below I am going to calculate how much smaller the combustion chamber needs to get, by razing the piston head, to get a 1 : 7 compression ratio.

Cylinder bore = 4 1/8 ”
Piston stroke = 3 3/4 ”

Displacement of one piston = Pi * (2 1/16)**2 * (3 3/4) = 50.115 “cube

compression ratio = (piston displacement + combustion chamber) / combustion chamber
compression ratio = (piston displacement / combustion chamber) + 1

compression ratio – 1 = piston displacement / combustion chamber

combustion chamber = piston displacement / (compression ratio – 1)

So for the 1 : 5.4 ratio, the combustion chamber is 50.115 / 4.4 = 11.39 “cube
And for the 1 : 7 ratio, the combustion chamber is 50.115 / 6 = 8.35 “cube

So yes as expected, the combustion chamber needs to be reduced in size. About 3.04 “cube smaller.

If I was just going to extend the top of the piston, that would be equivalent to:
piston head = 3.04 / (Pi * (2 1/16)**2) = 0.227” = 5.7mm

So that’s not to bad really. Just need to make sure the new piston head is not touching the spark plugs, and I don’t think the valves are going to be in the way, as they will be almost closed when the piston is at TDC.

Looking promising 🙂

Power output possibilities

Possibilities, of power output with higher compression ratio:

Was just looking at the website of the “Verner Motor”. They have three radial engines; 3, 5 and 7 cylinder. An interesting thing is that the 5 and 7 cylinder engines run at similar rpm and have a similar engine volume as my Velie:

Scarlett 5SI: 3615 cc, 78 BHP (57 kW) @ 1900 RPM

Scarlett 7Hi: 4466 cc, 97 BHP (71 kW) @ 2000 RPM

The average of these two, looking at he displacement is about 4000 cc (my Velie) with the same rpm as my Velie, would give about 87 HP. All of this with a compression ratio of 1 : 7.3

Oh and these engines run on 95 octane fuel !

So all I am saying is if we can increase my compression ratio from currently 1 : 5.4 to somewhere higher then 1 : 7 , we should get quite a bit more power !!!  🙂

So yes Wayne, believing more and more in what you have been telling me 👍👍👍

1/2 Vernier

Forget what I said about the vernier running at 1/6 of the crank shaft. It’s the CAM drum that’s running at 1/6 of the crank shaft.

The vernier for adjusting the CAM timing is running at 1/2 of the crank shaft!

This means that when the 4 bolts are out and moving the prop one revolution as I described here, is not changing anything, as the number of holes in the vernier is a multiple of 2. So every vernier step of 4.5 deg is all you get, no steps in between by turning the prop one revolution.

Now this makes sense, as I have just adjusted the timing, by about 4 degrees, so that’s good.

Valve fully open timing
MixtureExhaust
Timing as of last successful flight122 deg ATDC119 deg BTDC
New timing118 deg ATDC122 deg BTDC

 

Next time when I am back I will start assembling the back of the engine again, and see what difference it had made.

Plus will try different fuels as well. Now running 100 octane, but I will try and see what happens with 95 and 91 octane.

Lesson 23; more solo

Another beautiful winters morning, have my lesson booked for 9:30, so I arrived at 9 and did all the checks on the plane, refueled it, topped up the engine oil and checked the plane log book.

When Dave came, I talked about radio calls, the ones you make when coming back into the circuit, so I can write them down.

The plan for today is more circuits and more “landings“, and I assume more solo. And yes at some stage Dave mentioned he was going to sit in the plane for one circuit, but he ended up sitting with me for 3, when he said (after we landed and I was about to apply full power again) : “I will have the controls”.

So he turned of the runway, got out and said, just go and fly circuits !  🙂

I looked at my watch, it was 10:45.

So I crossed the runway, to get to the taxi way and taxied back to the beginning of RW25. Checked for traffic, went across again!!!! and did my final traffic check, my “lining up” radio call, went on the runway, and my “rolling” radio call. Here I go !!!   🙂

In the end I flew solo for more then 45 minutes, around and around. Most of my landings were pretty good, but the last one went a bit wrong:

I suddenly remembered from last week that during the last landing we flew a bit further before landing so you don’t have to taxi that far back to the hangar. So I thought while I was landing, sort of at the later stage of the landing: Oh yes get a bit more power and fly a bit further. Then after 10 seconds or so I put the engine to idle again to land, when I had a quick glance at my air speed. That was VERY low. To low really. I should be falling out of the sky at that speed, so I started pulling the stick.

This all happened, I don’t know, maybe 1 meter above the runway,so no disaster, I landed maybe a bit harder then normal but nothing to be worried about.

BUT what I have learned from this is that this went wrong because I suddenly changed my mind about what I was doing. Especially during landing and when you are not experienced, you DON’t do this. Think of this in advance and prepare !!!!!

And when you see that the airspeed is that low, you don’t pull the stick, BUT apply more power !!!!! That’s probably the biggest lesson for today 🙂

High power F1 engine

While looking at YouTube videos, I found this video. Its about getting more power out of an formula F1 engine. These engines are relatively small, but by using high precision components, in this case cylinders and pistons, they produce a lot more power. Only because of the better fit of the piston, and the use of better piston rings.

Something to think about !!

What I am thinking is, if we try to get more compression using new pistons (with a dome shape head) and modern rings, that might give more power as well just because we will lose less pressure because of the better fit 🙂

Vernier cam timing

OK, so yesterday I tried adjusting the CAM timing.

The thing in the middle is the vernier used for adjusting the CAM timing. Its called “gear timing flange” in the Velie Installation and Maintenance manual. This gear is running at 1/6th of the crank shaft.

By removing the 4 bolts, moving the front disk a bit and screwing the bolts into the next hole, the whole timing is moved by about 10 deg or that’s what I thought.

That was a bit to much, so I thought if I hold the front disk and rotate the prop one hole turn then I might be able to get smaller steps. But it looks like its exactly the same 🙁 or that’s what it looked like.

_1398587297

So how does the CAM vernier work:

The front disk driving the CAM has 16 holes with thread in it. This is 22.5 deg per hole.

The disk behind, is driven by the crank shaft has 20 holes with thread. This is 18 deg per hole.

So by removing the bolts, moving the crank shaft a little, and putting the bolts back in the next lot of 4 holes, the CAM timing is shifted a bit. In fact it’s a step of 4.5 deg (22.5 – 18 deg). This is less then what I had seen yesterday, but oh well….

Another thing that can be done is when the bolts are out, is holding the front disk with the 16 holes, and spin the prop one full revolution. This will move the CAM and the disk with the 20 holes, 60 deg (360 deg / 6) as the CAM moves 6 times slower then the crank shaft. The 60 deg is 3 times a 18 deg step plus 6 deg. In combination with the 4.5 deg from the paragraph above, this gives a 1.5 deg minimal step!!! So in total there are 240 possible positions for the CAM for one complete full 4 cycle of the engine.

So I am thinking that what I have now is maybe 1.5 deg different from before and that’s why I don’t, or hardly see the difference !!!!

Lesson 22

Had a lesson with Doug Anderson, the Chief Flying Instructor of our club 🙂

As he didn’t know my flying experience/skills, we left the circuit and did some turns, left and right… They were going a bit to slow, so he showed me some sharp turns….    Hooohohhhoh is what I felt in my head 🙂 Like you are falling out of the plane, or something.

One of the things important when flying sharp turns, is how the elevator behaves:

Because you are banking quite sharp, pulling the stick (lifting the elevator) results in the turn going even sharper. So if you are doing a left turn with the rudder going left, in a sharp turn, lifting the elevator (pulling the stick) will have a horizontal element in it or call it a vector going left as well. So be careful when making sharp turns when using the elevator, as that will make the turn go even sharper.

Its probably safer to apply more power if you want to raise the nose a bit in stead of pulling the stick. In fact before going into a sharp turn, you apply more power, because the vertical element of lift from the wings drops drastically, resulting in loosing height, so you need more power to compensate.

 

Afterwards we rejoined the circuit again flying at 1500ft AGL over the airstrip, over the end where we will be landing. That is were I make the “overhead” radio call. This is were the descend begins down to 1000 AGL, and a turn going downwind on the non traffic side of the circuit, and another turn, flying over the other end of the runway, the end were we take-off. And finally another turn which gets us in the downwind leg of the circuit. Be really careful here as other traffic will fly here in the circuit. The remainder is like all other circuits.

Oh yes one comment from Doug, about turning into the Base leg, this is the last bit before turning into the Final leg: The stronger the wind, when landing into the wind as you do, the earlier you turn into the Base leg. Makes scene, as you will go slower in that Final leg but still decent with the same rate.

We did half a dozen circuits I think. All my landings were really good 🙂

Below a little video compilation of my lesson.

  • Preparations,
  • Takeoff,
  • Sharp turns, 360 left turn, 360 right turn,
  • Touch and go’s,
  • Full stop.

Went really well !!!  Love it !

Piston movement

Made a graph with the piston movement.

That is sort of interesting and relevant when looking at the valve timing as the piston is not moving up and down in the same way the shaft of the crankshaft moves.

Length of (master) conrod = 197 mm

Crank shaft movement (stroke) = 95 mm

PistonMovement