Flight Analysis

The AFS3400 is very useful for analysing flight data. During a flight it records around 50 parameters every 5 seconds. I have written a macro that takes this information into Excel and charts it. It then performs some additional features. I want to know in particular where my -4 operates most efficiently in the cruise at a reasonable speed. The grey line at the top of the graph (You will have to double click it to get a large enough display I think) shows where the miles per litre is exceeding 6 and the aircraft is not changing height. This has lead me to cruise, at least at 3000' at 22.5" and 2050rpm. I can lean out to 22lph or a little less and still make good progress. I found these charts useful also for adjusting the baffeling to even out the CHT. Its a carburated engine so only so much can be achieved!

The first 100 days. Part II

In Part I, I covered my reactions to flying the –4. Here I thought I would summarise my thoughts about the results of the decisions I made along the way, and the problems I ran into during the first 25 hours of flight test.

Many of the decisions related to weight. I have covered my thoughts and the result elsewhere in the blog, so I wont repeat that here. Needless to say, keep it light. Whatever it is, if you think long enough, you probably don’t really need it. Without it you will be lighter, have more money in your pocket and what you dont have can't go wrong.

The first issue I had was with the 4-pipe exhaust from Larry Vetterman. Pipe #1 just touched the sump. Larry first suggested I bend it, but as soon as that was not going well he said “…best I make you a new pipe.” It was here in the UK in no time. Great customer care! The 4-pipe is undoubtedly slightly noisier, but friends say not a problem. They also comment it has a very distinctive and pleasant tone.

Oil Pressure. I am delighted with my engine from Aerosport Power, and I cant imagine better service, but it did come with the oil pressure set too high. I had to reduce the pressure by about 10 psi, which was about 3 turns of the adjuster, to get it to stay inside the upper limit (90psi). The problem isn’t so much adjusting it though, as deciding if the problem is the pressure, or the gauge. In the end I managed to borrow a test gauge, plumbed it in, and it confirmed my ACS 3400 was right on the money. It was disconcerting on a new aeroplane though, until I got is sorted.

Oil temperature. The oil runs cool. I am not sure I have yet seen more than 179F. I have blocked off much of the entry to the 3” SCAT that takes air to the cooler. This appears to have improved things slightly but I need to do some more flying before I am sure.

I decided to take the exit air from the cooler into the cabin for cabin heat. This is working quite well, though its still only autumn in the UK.

With an electric heating pad in the seat, I think this will be quite adequate. It might yet cause me to put a variable restrictor on the air to the cooler.

Oil Leak. I had a significant leak on the cooler, for no other reason than I had failed to tighten the fitting adequately.. It did not show up after the first brief ground run, but it sure did after I landed from the very first flight. I probably only lost a quarter of a pint of oil if that, but a little goes a long way!

For the first flight I had a very heavy left wing, but a temporary trim tab on the rudder reduced this considerably. I was left with a slightly heavy left wing so I put a small coffee stirring stick on the underside of the right aileron.

This has balanced things up for now.

Sometime I will squeeze the RH aileron which will get rid of it due to the ‘Kutta Condition’. If you want to understand why that works there is an adequate explanation here.

VANS 'heavy wing' article which is worth reading if you have the problem is here.

Rubber Wing Root fairing. It was slightly disconcerting when these came loose in flight. A dab of RTV appears to now be holding them securely to the metal fairing.

I found the AoA in the AFS3400 hard to set. Just me I think, being ham fisted. In the end Rob Hickman gave me the file of settings for his –4, and that has worked well for me ever since.

A small leak in the static side of the ASI had a remarkably large impact on the indicated speed. It was quite frustrating to track down, but I got there in the end. Since the leak was to cabin pressure I was surprised by just how much this must differ from the ambient pressure. Even now, the system over reads slightly, but I put this down to the less than satisfactory rivet heads that VANS use.

The most frustrating thing of all was the intercom. Having indicated my interest in mono, with stereo would be “nice to have”, I got no suggestion from PS Engineering that I needed to allow for this in the wiring. I would strongly recommend people to go to Flightcom, since their documentation and understanding is far superior. They even supply the little switches and labels you need. The story is in fact much longer, uglier and expensive than that. Never an apology from PS for all the grief and expense they caused me, though I am pleased to see they have updated their FAQ to reflect the issue.

The Skytec LS starter bent its bracket after just a few hours of use. Aerosport Power had a new starter shipped to me in no time, and chose to replace the LS with the NL model at no extra cost. This is a much more serious looking piece of equipment. The LS normally has a problem when the engine kicks back, but since the P-mags retard when starting, Skytec guarantee the LS unit against this. My own view is the bracket is just too weak for a new engine with good compression, and a fully charged battery with a low resistance starter circuit. Who knows?

The dual P-mags have run faultlessly to date. I have little paper tell tales, that change colour if they overheat. Overheating has been a problem on some installations. They are still white. In the interest of simplicity I decided not to install a fuel primer, and rely on the carburettor pump to prime the engine. 3 strokes of the throttle, both P-mags on, and she starts really easily. Lets see what happens come the winter.

My oversize tyres work well. Near my hanger I have some gravel which I have to pull the aeroplane over. The –9a with the standard tyres I had, used to sink in and get stuck. With these, its not a problem. Despite their size they fit well inside the wheel pants, and to date they are not getting clogged with either the output from these sheep, who mow the runway, or mud.

The 2-blade MT prop is a delight. Really smooth in operation. The governor had to be very slightly adjusted slightly initially to stop it over speeding. Now it maxis out just below 2690. My only reservation is that it would be easy to scratch target="_blank"in the hangar. I am quite clear a 3-blade would have been a big mistake for the reasons I gave before.

The current outstanding issues are:

1. I would like to get a little more cooling on #3 and a little less on # target="_blank", so I am playing with a baffle to push more air over the top of #1.
2. #2 CHT can run a little hot, and the EGT cooler than the others, so I am wondering if I have a tiny induction leak, or if this is the variability of a carburetted system. Next time the lower cowl is off I will have a good look around at #2 induction.
3. Taxiing I have a very slight rattle in the gear. My thought was that it must be the gear leg fairing moving wrt the wheel pant, but a friend has suggested possibly the brake callipers can rattle. I will try taxiing with the brakes gently on.

Finally, I would just like to say what excellent and warm service I have had from Aerosport Power, E-mag, Robbins Wings, Larry Vetterman, AFS, Becki Orndorf who made the seats, and John Stahr, who painted it.

The first 100 days! - Part I

The first 100 days with an RV4! What a blast its been. This is the second VANS aircraft I have built. Last time I was disappointed, I built one of the designs for geriatrics, this time I am ecstatic. I thought it might be useful to other -4 builders, to gather my impressions and experiences while its still all new and fresh in my mind.

As I was building, I had to make many decisions that would have a bearing on its future utility, and as I moved towards the first flight I had many queries as to how she would handle.

Details of my -4 are covered in much more detail elsewhere on my blog, but G-IKON is powered by an Aerosport Power O-320 160 hp engine, driving a two blade MT c/s prop. She is the first aircraft in the UK approved to run on twin P-mags.

I’ll start with the flying, because that is what this is really all about, but then cover my experiences with some other items in Part II. Before I start I should say I have over 400 hours on Supercubs, and more on other taildraggers, so tail draggers are not strange to me.

To date I have about 29 hrs on G-IKON so am far from experienced. I have just finished a much longer than normal flight test because of the P-mags. Because of the flight test I have only once flown 2 up. I have only flown on/off grass so far, so all-in-all, plenty yet to learn.


Takeoff. I have a flap position indicator on the wing. Early takeoffs I set this to around 10 degrees, though I now set around 15, and find this may be marginally better. This gets me off the ground in about 300’ which is VANS number. I had seen tail dragger RV pilots have quite a bit of a problem with torque steer as they initially put the power in, but I have not experienced this at all. I do find a distant tree or cloud to focus on, so perhaps this is the reason. I am not aware of putting any rudder in, but some say I must.

By the time I am off the ground I start putting the flaps away, and start the transition into the climb as soon as I see 100 mph. Below 100 she is very draggy. This speed comes up about 1000’ after the start of the takeoff roll. My immediate reaction on the first flight was one of a solid predictable and responsive aircraft.

I feel I still do not make quite the clean transition from rolling to flying that I would like. There always appears to be an instant when we don’t quite know which we are trying to do. Perhaps I think I get a message saying its time for flight half a second early. What I have found is that its best to get the tail wheel off the ground ASAP, but then leave the tail low, so once we are flying, during the acceleration I am actually pushing ever so slightly forward as the speed builds, until its time to climb.

Landing. My home runway is short. Fence to fence is 1020’ and it has many other complications. Confidence to return to it, came after 27 landings at a local grass airfield where we got to know each other, after the initial take off from my home strip. I still don’t quite believe it, but a –4 is a remarkably easy plane to land compared with a Supercub, and needs about the same landing distance. I typically use 600 to 700’. At first I struggled a little doing 3 point landings, which didn’t always work so well. The problem was the tail wheel would hit a small bump which would throw it back in the air, sometimes worryingly high. Now I flare until the tail wheel is, at a guess, just 3” off the ground. That so far has produced a winner every time. Not to do quite fully held off landings has been quite hard to learn, but she still lands nice and slow. (I should qualify this. Landing two up is completely different, though I have only done 3; very ragged. I havn't cracked that yet. Its a completely different aeroplane! As the speed bleeds away in the final second, possibly it needs a push on the stick to hold the attitude. Perhaps its just very light. It has caught me out each time somehow.)

I said easier to land than a Supercub. This is true, but I suspect much less forgiving. Partly for that reason I have an AFS AoA installed, and I expect 'Jennifer' to give me a good talking to, if I fly abusively slow. So far she has only done it as the wheels touch. "Angle, angle, push!"

Somewhere in the circuit, with full flap, I trim for, and settle at 60 mph, solo, and let that start to bleed away just before the fence. She is still very ‘solid’ at that speed. I approach on the flat side which requires quite a bit of power, but I find that helpful, since as you start feeling for the ground, as soon as you are confident there are only inches between the wheels and the grass you can shut the throttle and she gently settles with no intention to bounce. I usually lift the tail once the mains are on. I can see better, my strip is narrow, and the rudder is more effective, though I still find myself using differential braking.

I have little cross wind landing experience with G-IKON so far, but the one I had to do went well. I crabbed the approach and converted to wing low quite late. This worked. Once on the ground, rudder, with the tail high, plus differential braking, enabled me to track as I wanted. As the autumn winds set in across my strip I will soon have much more experience. The equinox was 2 hours ago.


Cruise. Not a lot to say here. She is extremely exact to fly which is very pleasing. VANS say I should see 207 mph with 160 hp, and that, if you wait long enough, is exactly what she does. I have been breaking in the engine, so have far too much experience at high power in the local area. (I am limited during flight test to 35Nm from base.) In the last few days I have been hunting for a normal operating regime. Its beginning to look like perhaps 2300rpm and 23.5” which gives me a 180 mph cruise. 2200 rpm at 22.7” which leans out to about 24lph - about 6 little US galls. – and results in 165mph is also a regime I return to. I will be more exact about these numbers once I have been on some trips and have an established regime.


Handling in general. Fantastic, harmonised, delightful. I don’t know what else to say. If you are still banging rivets to build a –4, keep at it. If you are disappointed, there is something wrong with you. If you cant get in a -4, stop going to McDonalds. Do build it light though. (See 9/5/06 and 6/10/08)

I will come back with some more observations in Part II about the technical problems I had to fix, and how some of the systems have worked out, but that’s it for now.

Flight testing - 2

Flight testing continues. I have done about 8 hrs now and am beginning to settle in. The rudder is now trimmed to put the ball in the centre and the ailerons are also now in balance. Its a much more comfortable way to fly.

As you can see from the attached graph, double click for a larger version, the oil pressure is now under control.

These 6 flights all occurred on the 4th July. I took off, and soon landed back to adjust the aileron trim. I then took off and flew at quite high power for a little over an hour, to work on breaking in the engine, and at the same time flew calibration triangles. The yellow line is calculating VANS approximation for HP. So 45 is 65% power and 48 is 75%. It is multiplied by 10 for clarity. There is a break in the middle while I worked on calibration of the AoA.

At the end you will see after a break, I did 4 circuits to work on landing technique.

There are some interesting points that show up:

1. At about 11:49 there is a tiny leaning of the mixture (magenta). There is a clear, if slight, increase in power (yellow line), and a very significant change in the EGTs. In particular EGT1 (green) goes from second coolest, to hottest.
2. At the same time CHT4 does the same thing.
3. By 12:18, with 75% power set, and fuel flow increased the EGT and CHT relationships have switched around again.
4. CHT1, the green line always sits lower than the others. I wonder if there is a case to reduce the airflow to this cylinder.

At the end of the flight I did 4 circuits in about 16 minutes. It is interesting to see that with the low air speed involved, the oil temperature climbs quite a bit higher than it had previously reached. It ended at 190F, still a well controlled temperature, but worth remembering. The ambient temperature recorded at this point was around 70F.

I am sure I should be observing far more information in this data, than I am. at least I am learning.

My main conclusions are that the CHTs, oil temp and pressure are well under control. I am spending a significant amount of time with the power above 65% which is good for break in.

Test Flying

(Double click the graph for a better view)

Here is some data from my third flight. The good news is the CHT temps are all staying well within bounds below 400F. With less than 2hrs on the engine that pleases me. the OT is not a problem either, in fact it could be a bit warmer ideally, but I understand this is typical for an RV4.

Where I do perhaps have a problem is the OP. That is the red line. I presume the pressure relief valve is opening at 104psi and there it sits. I am a bit concerned about this because on the dyno at Aerosport Power it was recorded as running at 76 then 85 psi with cooler oil and a thicker grade.

The heavy left wing I have reported before was proved to be the need for a rudder tab. At the moment a firm foot on the RH rudder pedal makes the heavy wing problem go away.

I am doing my testing between 2/3000'. Not much is getting done because of English 'summer weather'. Because I am running everywhere at 75/80% power she seems like a one speed ship; 180mph (uncalibrated). Gentle downhill, and VNE becomes a problem. The highest speed I have seen recorded yet is 209. It will be interesting to see what happens at 8000' against VANS' numbers.

She remained a pussycat for the fourth landing. She has a personality change once slowed down to 70mph for approach.

Postscript
I have finally run down why the oil pressure is so high. The explanation is here.

First Flight

G-IKON flew for the first time today under a 4000' cloudbase and with a light and variable wind. I went along for the ride.

Takeoff was reminiscent of a winch launch in a glider. The transition from ticking over at the end of my strip, to climbing at a very high rate, being seriously abrupt. With me and about half tanks, gross was 1260lbs. With 160hp and an MT c/s prop on the front takeoff was not a problem. Prior to take off I had done one short acceleration to ensure that I could cope with the torque steer (my strip is narrow marginally more than the span), and that full power was going to come in smoothly. It was so clear that she was extremely easy to track straight, and that getting off the ground was not going to be a problem, I backtracked and repeated the process for real.


She was off in about 60 yds. Being unfamiliar with the trim (or anything else) I had a slight fight to keep the nose down and aim for speed for cooling, rather than climb rate. It is a new engine.

I climbed to 4000' overhead, before letting go of RAF Leeming with 10000' of concrete located just 5NM from my own strip, and headed for Bagby, my local airfield. Once in range of there, I slowed down and did a few gentle stalls and a very brief slow flight practice. IKON clearly has a heavy left wing which needs to be sorted, and that limited how slow I wanted to go. Stalls with small amounts of flap gave the impression of being sporty, but at full flap everything appeared very predictable. I made a clear decision to settle on finals at 70mph until the heavy left wing and stalls, have been investigated further.

Landing, the thing we probably all worry about the most on first flight, was a complete non event. Considerably better than most landings in my Supercub, and I have done over 1100 of those.

So with perhaps 20 minutes in the air, it was time to take a look and see if all was as it should be. It then became clear that the oil had decided to try to migrate to the bottom of the fuse'. It turned out after a lot of swearing, and at one stage believing the cooler was ruptured, that it was all emanating from the cooler/hose junction. It was a bit less than tight! In all perhaps half a pint of oil had leaked, but it makes a great mess!

With full tanks and a little more confidence back in the air for the short flight, 30 minutes including an extra circuit and slow flight, to Fishburn, my other local airfield where she is to remain until I have learned to land short, and can return to my own strip. Time was pressing for my ground crew, who had promised to drive me home, so only two landings before she was pushed into the hangar until tomorrow, when I will take the cowl off and have another good look around. Possibly a very little more oil had leaked, but my guess is that is just some of the mess from before, finding its way out.

A 70mph approache to be safe, faster than I expect to use in the future, resulted in very short easy landing each time. As I said before, quite as easy as my Supercub. Extraordinary!

Looking at the data coming off the AFS one cylinder went briefly to about 410F, the rest of the time they sat at about 360 at the back and 325 at the front. This is probably reasonable, since the lowest power I used was about 25 square. The EGT were giving temp warnings, but in retrospect I think the warnings are probably set lower than they should be. The highest they got to, with the whole flight at full rich, was 1500F at the back. Possibly the sensors are sitting just a little close to the engine end of the pipe.

I need to review the data again, but I don't think the oil got above 170F though that was right at the end of the flight, so perhaps with a longer run it might get to the magic 190.

G-IKON is the first Lycoming style engine in the UK (in this case an O-320 from Superior) with dual P-mag electronic ignition from E-mag. Getting approval for this from the LAA has been quite an interesting journey, though I have now arrived. I will have a longer test period than normal as a result, in terms of hours, chained to the two airfields mentioned above.

And now for the thank yous. First of all to my wife for being so supportive with coffee tea and cake, though I can honestly say the entire plane was built without her ever touching a rivet gun, bucking bar, screw driver or wrench. (She has just pointed out that she did make two aileron pushrod cuffs to keep the draft out! Oops!!) To Andy Ratcliffe and Fred Parker for supporting me throughout the build whenever I needed > 2 hands, and today, departing from my strip. To Mark Golding who has signed his name about 60 times to my work, for the LAA. To Andy again, and Peter Pengilly, who supported me in making a case to the LAA for electronic ignition, and finally to Francis Donaldson at the LAA who at all times took a jaundiced view of the idea, which only serves to look after my safety. It appears to be working well, but of course it is early days. US experience is well reported. I will report mine in due course.










There is a short clip of the first lift off here.



And just to remember where in time this occurred two political quotes which cheered the UK in the summer of 2008.

"The one good thing about global warming is that as the waters rise, Hazel Blears will drown first."

That thought just makes me want to burn more fuel and speed the process!

"Our Leader [Gordon Brown] is utterly useless. If you asked him which of the two doors from this room he was going to exit from he would be incapable of choosing. And if someone else chose the door for him he wouldn't be able to make his way there. "

Both are attributed not to the opposition party, but to their colleagues. It is reassuring to see that the true awfulness of our government is understood by Labour party membership.

Time to go flying!

....well not quite though I am nearly there.

It needs to be weighed and the upper gear fairings installed.

We did a snagging list the other day and it was trivial except for one item. I may yet have to take the engine out to change the fitting where the oil pressure comes out of the engine. It appears it was damaged and does not make a good seal.

Hopefully, it will be weighed by this time tomorrow.


It was scary specifying the colour scheme though I am extremely pleased the way it has worked out. It certainly gathers and shows dust though.

John Stahr did the painting and had massive input into the design detail. He is Oregon based and I highly recommend his work.

(Double click the pictures if you want to see detail.)