Keep those first flights short

Well, today didn't turn out as I had hoped.

I went to the hangar mid-day, to pull the cowlings and do a good inspection ahead of the firewall before going flying to do some more engine break-in. But, I discovered two significant issues that needed dealing with ASAP, and another issue that will need correcting eventually.

1. The alternator pulley had been touching the lower cowling, and put a pretty good gouge into it.

2. The throttle cable showed signs of heat stress where it passed close to the exhaust system. I had thought that there was enough clearance, but obviously not. The damage doesn't look too bad after 20 minutes of running. I think the cable would have been trashed with an hour of high power running time.

3. There were signs of a bit of rubbing on the upper cowl from part of the oil cooler mount. Also, four of the screw heads that hold the plenum chamber cover on showed signs of rubbing on the cowling - three of these were very minor rubs, but one was more significant.

Tomorrow, I'll pull the prop and change the alternator belt for a shorter one. I'll put a piece of tape over the gouge in the cowl to act as a witness for future clearance issues. If I still have a clearance problem with the 7355 belt, I'll have to fabricate some sort of pad on an arm to prevent the lower cowl from being pushed closer to the engine by the ram air pressure. Once I am sure the clearance problem is resolved, I'll fill in the gouge.

I'll put a heat shield on the exhaust where the throttle cable passes by. That'll be a quick, easy fix.

As for the oil cooler mount, today I removed a bit of metal from the mount in the affected area. I'll put a piece of UHMW tape on the cowling, and see how it does. I can remove more metal if needed. As for the screws that touched, eventually I'll replace those four with flush head screws. For now, I'll remove those screws, as there should be enough other ones to hold the cover in place. I'll put some UHMW tape on the cowling to act as a rub guard. In the end, it may be necessary to rework the contours of the plenum chamber cover to move the outer edges closer to the engine. This would be a big job, so I am hoping to avoid it, if possible.

I'll do another 20 minute flight to see how things are doing. Maybe late tomorrow, or maybe some other day if the work takes too long.

Originally, I had planned to fly for an hour on the first flight, in order to minimize the low power running time. But, Ron MacEwen, the local Aircraft Maintenance Engineer and EAA Flight Advisor suggested that it would be better to only fly for 20 minutes or so, and then do a big firewall forward inspection before flying again. I am very glad I took his advice - I believe that the alternator pulley would have completely worn through the lower cowling if I had flown for an hour, which would have necessitated a lot of fibreglas work to fix. As it is, I only need to mix some resin and fibre to fill the gouge - that'll be a quick fix, and it can wait for a few flights.

Moral of the story - keep those first flights short, to minimize the risk of undetected small problems quickly becoming big problems. A lot can happen in the course of an hour.

Yup

Just ask Howard Hughes about that one..

Frank

I Certainly Agree

My first flight was once around the pattern then it was inspected for problems and failures. It took a good part of the 25 hour test flight period to get all of the bugs out.

I don't think the pulley problem is operational time driven but instead it is operational/flight cycle driven. That is a common problem with RVs. Mine included. Mine never cut through but it would have with enough flights. Some people put larger pulleys on the alternator to reduce the RPM and the resulting cut cowl is predictable. I have the small pulley on my 60 amp alternator but I still saw the contact marks. Under static conditions there is significant gap but even with the small pulleythere is incidental contact in some operating mode (landing, starting, shut down? who knows?). I fixed the problem several hundred hours ago by cutting a blade off of one of my wife's stainless steel butter knifes and bonding it to the inside of the cowl with structural adhesive as a strike plate. The pulley still marks it but there is no damage.

Do you know what the EGT is on the pipe that caused heat damage to your cable? Early in my flight testing the timing of my LASAR system from the Lycoming factory was approximately 65 degrees ahead of the specified 25 deg. BTDC of the compression stroke of cylinder #1 (approximately 90 degrees BTDC in other words). The engine would run but the EGT was very high and I had to throttle back to get the EGT needle off of the peg. I flew it to the test area but flight was not comfortable. I call Van's and I was told that Lycoming runs all of the new engines in a test cell (I had the test cell data sheet) and it should run properly right out of the box. I worked with Unison the west coast tech rep for Lycoming and Pecision Airmotive via telephone for some time before I ordered a LASAR timing box through Van's and fixed the problem.

I use the inside of the upper cowl as the top closure of the plenum so no information there.

Bob Axsom

No need to be up any more than 20 minutes on the first one. You never know what the gremlins can get into. They've been waiting for some time to screw with your new creation.

I can think of two cases where rather large oil leaks developed on first flights and in a couple more minutes, very bad things would have happened. As it was, it took a good hour for these guys to clean the belly and it oozed from all the skin laps for another 6 months afterwards.

I removed the cowlings after every flight for quite some time on mine and checked everything very thoroughly. Of course mine was all non-standard FF.

Pilots doing 90 minute first flights are just asking for it IMO.

Kevin,

Congrats on your first flight.

As for the alternator pulley rubbing on the cowl- I think the shorter belt should do the trick nicely. I had the same trouble until I went to a shorter belt. I don't know why Van's continues to recommend the 7365, it is just too big for most installations, and there is no downside to going a size or two smaller. Fortunately they are commonly available locally.

Here's a little fitting info from PP...

* The supplied 15355 Dayco V Belt will fit the 9 3/4" diameter ring gear support pulley, for applications which have a 7 1/2" diameter ring gear support pulley locally purchase XL7300 Gates V Belt or equivalent.

http://www.plane-power.com/images/Alt 60 Fit w9.75 Pulley.pdf

http://www.plane-power.com/images/Alt 60 Fit w7.5 Pulley.pdf

Throttle Cable

Mayday.... there have been several instances of the throttle cable fusing and "freezing" in the last position. You might consider sheathing the entire cable with heat protective tape or "heat shield" hose. Van' refuses to publicize that this is occuring.... anyone else with such an experience?

Tim Morris
N187TM
Rv-8/ "Betty Jane"

Kevin, congratulations on your first flight! I can see the engineer in you-- all technical reporting and stuff! Tell us how it felt! After almost 11 years of building, I'm sure it brought a smile to your face.

Any pics?

Vern

Toga 1 said:

Mayday.... there have been several instances of the throttle cable fusing and "freezing" in the last position.

Click to expand...

I'm not sure what state the inside of the cable is in now, but the outside sure has a large bubble in the green plastic. It feels normal when I move the throttle, but to be safe I will order a new one, and replace it at a convenient opportunity. Better to do this now, than have it fail when I am on the road some day in the future.

I replaced the alternator belt today with a shorter one, and put a heat shield between the exhaust system and the throttle cable. I did a 25 minute flight, then pulled the cowlings - the alternator pulley no longer touches the cowl, and the throttle cable looked the same as it did before the flight. I think I am now ready to launch into longer engine break-in flights. But, I'll be on the road from Wednesday until October, so testing will take a pause.

Not just 1G

Kevin Horton said:

...I replaced the alternator belt today with a shorter one,...

Click to expand...

I know it is a different airplane, but my RV-6 alternator pulley was fine at one G but when I started pulling 3 to 6 in testing is when my pulley started contacting the cowling. In my case, there was no alternative but to make a bubble in the cowling.

n5lp said:

I know it is a different airplane, but my RV-6 alternator pulley was fine at one G but when I started pulling 3 to 6 in testing is when my pulley started contacting the cowling. In my case, there was no alternative but to make a bubble in the cowling.

Click to expand...

Yeah, I'm very aware that this may be an issue. I'll investigate the effect of g after I finish the engine break-in, and can go up to altitude for the first pulls to 6 g.

Heat Shield

I had the same problem , had some cable juice coming out, made some SS heat shields (use Monel Pop rivets the AL ones get loose)
If you have belt problems you could try shaving down the Alt Pully (worked for me)
Cheers and Congrats
Peter Cavallo RV 6.2

Kevin Horton said:

Well, today didn't turn out as I had hoped.

I went to the hangar mid-day, to pull the cowlings and do a good inspection ahead of the firewall before going flying to do some more engine break-in. But, I discovered two significant issues that needed dealing with ASAP, and another issue that will need correcting eventually.

1. The alternator pulley had been touching the lower cowling, and put a pretty good gouge into it.

2. The throttle cable showed signs of heat stress where it passed close to the exhaust system. I had thought that there was enough clearance, but obviously not. The damage doesn't look too bad after 20 minutes of running. I think the cable would have been trashed with an hour of high power running time.

3. There were signs of a bit of rubbing on the upper cowl from part of the oil cooler mount. Also, four of the screw heads that hold the plenum chamber cover on showed signs of rubbing on the cowling - three of these were very minor rubs, but one was more significant.

Tomorrow, I'll pull the prop and change the alternator belt for a shorter one. I'll put a piece of tape over the gouge in the cowl to act as a witness for future clearance issues. If I still have a clearance problem with the 7355 belt, I'll have to fabricate some sort of pad on an arm to prevent the lower cowl from being pushed closer to the engine by the ram air pressure. Once I am sure the clearance problem is resolved, I'll fill in the gouge.

I'll put a heat shield on the exhaust where the throttle cable passes by. That'll be a quick, easy fix.

As for the oil cooler mount, today I removed a bit of metal from the mount in the affected area. I'll put a piece of UHMW tape on the cowling, and see how it does. I can remove more metal if needed. As for the screws that touched, eventually I'll replace those four with flush head screws. For now, I'll remove those screws, as there should be enough other ones to hold the cover in place. I'll put some UHMW tape on the cowling to act as a rub guard. In the end, it may be necessary to rework the contours of the plenum chamber cover to move the outer edges closer to the engine. This would be a big job, so I am hoping to avoid it, if possible.

I'll do another 20 minute flight to see how things are doing. Maybe late tomorrow, or maybe some other day if the work takes too long.

Originally, I had planned to fly for an hour on the first flight, in order to minimize the low power running time. But, Ron MacEwen, the local Aircraft Maintenance Engineer and EAA Flight Advisor suggested that it would be better to only fly for 20 minutes or so, and then do a big firewall forward inspection before flying again. I am very glad I took his advice - I believe that the alternator pulley would have completely worn through the lower cowling if I had flown for an hour, which would have necessitated a lot of fibreglas work to fix. As it is, I only need to mix some resin and fibre to fill the gouge - that'll be a quick fix, and it can wait for a few flights.

Moral of the story - keep those first flights short, to minimize the risk of undetected small problems quickly becoming big problems. A lot can happen in the course of an hour.

Click to expand...

Pulling G's

Kevin,
First off congratulations on your first flight. I am very much looking forward to reading about your test flight results. Your professional and I'm sure methodical approach to your testing is awaited by all of us. I hope you will share your results with us. On that note I have a couple of questions for you.

1. What is the best way to accomplish "G" testing? Having no formal(or informal for that matter) training in test flying I would like to know the correct procedures. Is finding a way to see 6 "g's" on the meter good enough? Or do the "g's" need to be applied at a range of speeds.

2. On stall speed testing, is the stall speed number the one at the break or is it the number on the Dynon digital airspeed window with the stick held back and the airplane in a stalled attitude in a descent?

3. I would be interested to find out if anyone else has been frustrated trying to do accelerated stalls and finding the numbers are the reverse of what you'd expect. For example: This summer flying 2 nearly identical RV8's I found a clean stalling speed of 56 KIAS. That's 56 knots at the break.
In a 20 to 30 deg. bank it might be 53 or 54 knots. At around 45 to 60 deg.'s of bank I finally see #'s bigger than the clean stall #'s.
These #'s are at about 1500 lbs. gross wt.
These planes are equiped with Dynon D180's, Dynon pitot probes. Safe air static vents(non flush).
Airspeed calibration runs are right on the money(at least at cruise speeds).

As an amatuer builder who strives to build it better than a professional I would like to compile a complete and professional POH for my plane that I could share, and solid numbers is what I'm striving for.

Hopefully you'll share not only your numbers, but your procedures for aquiring them.

Thanks in advance
Jon
RV8 N486JT 1100 lbs. OX-360- A1A 9N , Hartzell 7497, 2 mags. Dynon D180

Cable Binding

I had my mixture cable internally freeze up on me. There are two other instances that I have heard of with the same symptoms. The fix is to slide a long piece of "fireproof" over the cable and secure it.

Works good now.

First, congratulations for a successfull first flight;

For the clearance issue, a rule of tumb we have is 3/8" to 1/2 " between any fixed and moving parts firewall forward; Also, I observed that not only gs will give you rubbing, Vd testing as well.

As for the overheated cable, I would try to put the shield on the cable side if possible rather than the exhaust side to avoid the shield to radiate due to conduction. If you have any concerns about heating some parts due to exhaust proximity, you could probably get some temperature witness stickies from the Flight Test folks in Uplands.

See you next monday at our meeting

Francois

JetA4GA said:

As for the overheated cable, I would try to put the shield on the cable side if possible rather than the exhaust side to avoid the shield to radiate due to conduction. If you have any concerns about heating some parts due to exhaust proximity, you could probably get some temperature witness stickies from the Flight Test folks in Uplands.

See you next monday at our meeting

Click to expand...

Francois - Thanks for the comment on heat shield location - I had been a bit bothered by the fact that the heat shield would heat up, but hadn't jumped to the obvious conclusion to put the shield on the cable. I'll move it.

I won't be at the meeting on Monday - I'll be on the road.

Stall testing

jthocker said:

2. On stall speed testing, is the stall speed number the one at the break or is it the number on the Dynon digital airspeed window with the stick held back and the airplane in a stalled attitude in a descent?

3. I would be interested to find out if anyone else has been frustrated trying to do accelerated stalls and finding the numbers are the reverse of what you'd expect. For example: This summer flying 2 nearly identical RV8's I found a clean stalling speed of 56 KIAS. That's 56 knots at the break.
In a 20 to 30 deg. bank it might be 53 or 54 knots. At around 45 to 60 deg.'s of bank I finally see #'s bigger than the clean stall #'s.
These #'s are at about 1500 lbs. gross wt.

Click to expand...

It sounds like you may be at greater than 1g for the 'clean' stall? The technique for a straight stall is not like your CFI taught you. The aim is to slowly decelerate the airplane until the wing stalls. Start by trimming at 1.3Vs (about 70 kt) in level flight. Now shut the throttle (or set what ever rpm/mp you are testing at) and use the stick to achieve a 1 knot (or mph) per second deceleration rate. With the throttle at idle the airplane will descend. Concentrate on the slow and constant deceleration. When the 'break' occurs or the stick reaches the back stop is usually taken as the 'stall'. Perform several stalls and take the average. Be aware that the descent rate can be quite high, so look outside in between each stall and ensure you have plenty of altitude. A slow deceleration rate is the key to getting an accurate stall speed.

Pete

Pete
Thanks for the reply.
I have always been aware of the 1 knot per second deceleration rate but thought it was difficult to obtain at flight idle and trying to maintain altitude until the stall. Your way seems much easier, that would put my stall speed closer to the numbers I see in the descent in the stalled attitude. 48-49 knots.
Thanks

The internet access at the hotel was down yesterday, hence the delayed reply.

jthocker said:

1. What is the best way to accomplish "G" testing? Having no formal(or informal for that matter) training in test flying I would like to know the correct procedures. Is finding a way to see 6 "g's" on the meter good enough? Or do the "g's" need to be applied at a range of speeds.

Click to expand...

It depends on the purpose of the test. If you were attempting to demonstrate structural integrity, the load distribution varies with angle of attack. The structural engineers will usually look at two design cases - max g at VNE (low angle of attack) and max g at a speed where the wing stalls at the max allowable g (i.e. Va - high angle of attack). From a loads point of view, forward CG gives the highest loads. But, Van has done a full set of wing static load tests on the ground, so I wouldn't worry about a flight test to demonstrate structural integrity.

From my point of view, the purpose of a max g test is to determine if the aircraft has acceptable stick force per g. The stick forces are lightest at aft CG, so this is the worst case. I'll do a build up by first doing the test at mid CG before moving to the aerobatic aft CG. And of course do lower g tests before higher g tests. I'll do tests near Va, at a mid speed, and near VNE. A secondary test objective is to confirm no alternator pulley to cowl contact, so I'll be pulling the cowling after each flight, increasing the target g by one g per flight. I'll do another test at the full aft CG limit, at the limiting load factor for that CG.

The normal test technique in a professional test environment is called a wind-up turn. It consists of slowly increasing the bank angle and g, while holding a constant airspeed. You need a range of altitudes that has smooth air and little air traffic. You want to be several thousand feet above the ground for safety reasons. Carefully trim the aircraft with wings level at the test airspeed at power for level flight (or even a bit more). Without changing power (power changes will affect the trimmed airspeed), slowly increase the bank angle. As the nose falls, the airspeed will want to increase - you apply aft stick to keep the airspeed at the trimmed airspeed. Slowly increase the bank angle, and g, until you reach the target g. The nose will be lower and lower as the g increases, otherwise the higher drag would cause you to slow down. If the airspeed starts to get away from you, reduce the bank angle without reducing the g - the nose will rise, and the airspeed will decrease. As you increase the g, note how the stick forces change You want a progressive increase in stick force, with no tendency for the stick forces to level off, or decrease.

This test techique takes a lot of practice to master - it is common for new guys to increase the bank too quickly, and then have the nose fall too quickly, and have the airspeed run away. Do the initial practice at a speed well below VNE for safety reasons.

jthocker said:

2. On stall speed testing, is the stall speed number the one at the break or is it the number on the Dynon digital airspeed window with the stick held back and the airplane in a stalled attitude in a descent?

3. I would be interested to find out if anyone else has been frustrated trying to do accelerated stalls and finding the numbers are the reverse of what you'd expect. For example: This summer flying 2 nearly identical RV8's I found a clean stalling speed of 56 KIAS. That's 56 knots at the break.
In a 20 to 30 deg. bank it might be 53 or 54 knots. At around 45 to 60 deg.'s of bank I finally see #'s bigger than the clean stall #'s.
These #'s are at about 1500 lbs. gross wt.
These planes are equiped with Dynon D180's, Dynon pitot probes. Safe air static vents(non flush).
Airspeed calibration runs are right on the money(at least at cruise speeds).

Click to expand...

Pete (Penguin) have a good description of the normal test technique. The stall speed you observe will vary with g, power and deceleration rate. You'll only get consistent results if you have a consistent test technique.

jthocker said:

As an amatuer builder who strives to build it better than a professional I would like to compile a complete and professional POH for my plane that I could share, and solid numbers is what I'm striving for.

Hopefully you'll share not only your numbers, but your procedures for aquiring them.

Click to expand...

I'll try to share techniques, but it can be difficult to communicate some of this stuff via text. For example, when learning the wind-up turn test techique at test pilot school, we probably discussed the test for a couple of hours in a classroom, then another 10 minutes during a preflight brief with an instructor. Then we went flying and he demonstrated how to do the test, then I tried several times while he provided helpful comments. Then I went up with a flight test engineer student in another aircraft to practice. A few lines in an internet forum can't hope to replace all that.

Thanks for the reply Kevin.
After 10 years of building and chronicling you deserve to be able to just kick back and enjoy your new ride. Enjoy the countryside while you break in your engine. No need for an exhaustive report on how you accomplished a test either.
Best regards
Jon