Major engine/prop overspeed event

[Richard L Bentley]

Richard L Bentley

Did you cycle the prop several times to make sure all air was expelled from the lines and prop dome was full of oil ? Sounds like you lost prop control due to air in the system. When oil finally filled the system prop control returned.. CU Dick Bentley

 

[Noah]

Kevin,

First of all, I almost puked when I read your initial post. Like everybody, I'm glad you and your bird are ok and look forward to your report of the engine internals. If you need any parts that you can't get quickly, my A1B6 is completely disassembled and ready to go back together, which won't happen for several months. Let me know if I can help, as I have everything that is required for reassembly on-hand.

My knowledge of engines is pretty basic, so please forgive me if this theory seems overly simplistic. You indicated a couple of times that you had 8.5 quarts in the system - including the governor, prop, lines, and inverted oil system. Clearly these items lower the oil level in the sump, as indicated on the dipstick. In other words, isn't it the LEVEL OF OIL SHOWN ON THE DIPSTICK which is important in ensuring the oil pickup remains flooded? What was the INDICATED oil level on the dipstick? Isn't that the measure which is most important, not how many quarts you had to dump into the engine? Is it possible that you were indicating 5 quarts (or some such low number), which was insufficient to keep the pickup flooded at 20 degree pitch down and a (somewhat significant) deceleration vector due to the windmilling prop?

 

[Kevin Horton]

My knowledge of engines is pretty basic, so please forgive me if this theory seems overly simplistic. You indicated a couple of times that you had 8.5 quarts in the system - including the governor, prop, lines, and inverted oil system. Clearly these items lower the oil level in the sump, as indicated on the dipstick. In other words, isn't it the LEVEL OF OIL SHOWN ON THE DIPSTICK which is important in ensuring the oil pickup remains flooded? What was the INDICATED oil level on the dipstick? Isn't that the measure which is most important, not how many quarts you had to dump into the engine? Is it possible that you were indicating 5 quarts (or some such low number), which was insufficient to keep the pickup flooded at 20 degree pitch down and a (somewhat significant) deceleration vector due to the windmilling prop?

The Lycoming Operators Manual for my engine lists the maximum oil sump capacity as 8 quarts, with the minimum level for safe flight as 2 quarts.

The relationship between height of the oil on the dipstick and actual oil quantity in the sump will depend on the attitude of the engine when the aircraft is on the landing gear. Given that my engine overhaul shop (Aerosport Power) had no way to know what the attitude of my engine would be, they supplied a dip stick with no markings. So, when I got ready to run my engine for the first time, I poured in 8 quarts of oil, did my engine run, then after the engine sat for a while I noted the level of the oil on the dip stick and put a mark there - my reference for 8 quarts system capacity.

I agree that the oil level in the sump is one of the variables at play in my oil pickup issue. Maybe my engine needs to run with more oil than I think if I am going to be subjecting it to such manoeuvres.

 

[airguy]

Before you pull the prop, run the engine and cycle the prop a few times to ensure the dome is full, then shutdown and drain the oil from the engine. The quantity drained will tell you your sump volume (mark the dipstick as well), I'll bet you are down by at least 2 quarts by filling the lines, filter, and prop dome.

 

[cdmiller]

Rpm excursion, my 2 cents. Long

Hi Kevin,

I have read this thread and would like to throw in my 2 cents worth. Like others, who have followed your building progress for years, I am happy that you and your plane came through this episode in one piece. I don?t have an answer as to why your oil pressure dropped during this test, but it is an anomaly with your plane. There are many other RV-8?s similarly configured that do not have this problem. My plane is a case in point. I have an RV-8 with an IO-360 M1 (with forward facing sump off an IO-360 A series Lycoming), a Christen inverted system, and a Whirlwind 200 RV propeller. My oil sump is the same as yours and has the oil screen and extended sump modification from Christen. Bart at AeroSport Power assembled my engine.

I was initially concerned that the propeller might run away during transitions from positive to negative G?s and back, due to temporarily low oil pressure as the ball-valve in the inverted system switched. I have observed this phenomenon regularly in my Jungmann with a Lycoming and Christen system; the oil pressure drops temporarily from 70 to 40 psi and then pops back to 70, when doing G transitions. This causes no problems with a fixed-pitch prop.

Like Danny King, I installed an oil accumulator in my RV-8 to maintain oil pressure during G transitions. The combination of Christen system and accumulator worked well during both positive and negative G aerobatics with no propeller excursions. After a couple of hundred hours, I decided that the RV-8 is not well suited to negative G maneuvers and sustained inverted flight, and I removed the accumulator, which had a persistent oil seep that I couldn?t seem to fix.

During the past 300 hours, I have flown hundreds of positive-G maneuvers, including Cuban 8?s, hammerheads, and all kinds of loops and rolls, with the Christen system and my Whirlwind 200 RV non-aerobatic prop. I have never experienced low oil pressure or any rpm excursions during these maneuvers. I normally run my engine with the dipstick showing just under 6 quarts; if I fill it to 8 quarts, it just pukes the first two quarts fairly quickly.

I have no idea why your plane behaved as it did, but I don?t think that you need to buy an aerobatic propeller to fix the problem. There must be some other problem either with the Christen system or with your oil pickup in the sump.

Best of luck finding the problem and getting back into the air. Please keep us posted on what Bart finds during the tear down of your engine.
Best regards,

Dan Miller
RV-8 N3TU 500+ hours

 

[Kevin Horton]

Before you pull the prop, run the engine and cycle the prop a few times to ensure the dome is full, then shutdown and drain the oil from the engine. The quantity drained will tell you your sump volume (mark the dipstick as well)

Excellent suggestion. Thanks.

 

[Kyleag04]

VNE vs. VNO

Kevin,

First of all, thank God you are alright! And thanks for your extensive writeup and thoughts on this subject. You have brought attention to an oil supply issue that is worth keeping in the back of our minds.

However, after reading FAR 23.161(c)(3) that you mentioned as your reasoning for doing this flight test, I see that it specifies the flight be conducted at VNO, not VNE! And VNO is defined in FAR 23.1505(b)(2)(ii) so that it can never be greater than 0.89 VNE! That is a big difference.

I'm not sure what you are using for a VNE, but using round numbers: With a VNE of 200 knots, VNO would then be less than or equal to 178 knots. There would be a great deal less aerodynamic braking at this speed (roughly 20% less).

Regardless, good luck getting back in the air.

 

[cyrilmclavin]

overspeed

Hi Kevin i am glad all is well with you metal can be fixed. While testflying 33nc rv8a i had slight rpm increase always at low power settings in a dive fortunately i stopped them before reaching above redline.I believe the problem lies in oil pressure setting of youe engine @ low power the lack of compression in the cylinders allows the prop to drive the engine so keep some power or raise the min oil pressure range setting so there is more pressure to the prop remember these small light rv's we fly accelerate very quickly and so impose high negative load on the engines very quickly especially at low powes settings.I have a few friends among them is dave windmiller i will discuss this with him and a couple of ia. engineers i know. I will post again when i get some feedback. Another way to get a weird reaction from an engine prop combination (io-360 200hp 776 c/s) is to with full fuel and two aboard an 8a is to accelerate at 20 ft above the runway to 130 mph and pull up agressively and sustain a high g climb you will starve the prop of oil and the prop control will only work again when you level off.

cyril mc lavin

ps to clarify above at high power settings the compression acts as a brake against the negative load on the system imposed by a high speed dive.

 

[Kevin Horton]

Kevin,
However, after reading FAR 23.161(c)(3) that you mentioned as your reasoning for doing this flight test, I see that it specifies the flight be conducted at VNO, not VNE! And VNO is defined in FAR 23.1505(b)(2)(ii) so that it can never be greater than 0.89 VNE! That is a big difference.

Kyle - You are 100% correct. I spend most of my day job working with aircraft that use VMO, and it is easy to miss the difference when you read the requirements too quickly.

I'm not really concerned about the pitch trim aspects. I do however, want an aircraft that will tolerate any throttle position from idle to full power anywhere in the flight envelope. So, I want to get to the bottom of my oil supply issue.

 

[TSwezey]

Kevin,
I am glad you got the plane down safely. I thought I would be the one posting about engine troubles in the air not you! Since mine hasn't flown yet I guess I still have a chance. Your conservative nature has probably saved you and a future passenger from a possible off field landing or worse. Sorry to hear about it and I am sure you will be more than conservative on the repairs!

 

[Bill Wightman]

Kevin - Thanks for your reply. Some day I hope we can clink a couple beers together.

Kevin's airplane was completely in the normal envelope, positive G, not over VNE, no maneuvering, so it is hard for me to say the airplane shouldn't be in that situation. To say we shouldn't go there because we probably never will in the flying we plan is something I disagree with. Lots of unexpected things can happen.

Larry - I didn't say or intend to convey the idea that we should ignore places in the airframe/engine envelope simply because we don't anticipate operating there. Rather, it was to say that using FAR23 as a guideline for testing our RV's isn't really appropriate. This FAR is for testing aircraft for certification. The RV8 is in my view now a well proven design (but wouldn't pass FAR23 in all areas anyway). Kevin's want to know he can operate his engine at any point in the envelope is something any pilot desires.

In my experience, testing a new sport plane is initially much more a test of the engine rather than the airframe. This has come true once again here with the prop overspeed, unfortunately. On the other hand, these airframes are pretty solid.

Respectfully,

 

[L.Adamson]

In my experience, testing a new sport plane is initially much more a test of the engine rather than the airframe.

I feel the same. I didn't bother with any type of slow speed/ stall test before my first 6A landing; because I've been around RV's for a lot of years, and am very aware of the airspeed ranges that I could expect. My airframe would have to be totally out of the ordinary, to be different. And as it turned out, it was just what I expected.

L.Adamson

 

[Doug]

Kevin,
I am stunned to read this! So glad you are safe.
I can add nothing to the analysis so I will not presume to comment.
Best regards,
Doug Gray

...and I thought my canopy problems were bad ...

 

[penguin]

Oil Port Locations

Kevin,

Really sorry to hear about your mishap. I was wondering about the positions of the oil pick ups and the transition to the inverted oil feed path. I don't know the details of the 4 cylinder angle valve engine, but used to fly an Extra 300 and now have a One Design, as well as the RV-6. The Extra used to lose oil pressure in the vertical (up), but the counterweighted prop meant the rpm reduced momentarily. Looking at the way the sump was plumbed, the erect feed was at the front of the sump and the inverted feed from the vacuum pad. That made sense to us - on down lines the oil runs to the front of the sump and on up lines the oil goes to the back of the engine. We also tipped the 'balls' so that they transitioned to the negative feed at about 70 deg nose up - so that in the true vertical the oil is using the inverted (rear) feed. If your erect feed is toward the back of the sump can you change to the front? Is there a blanked off boss at the front that can be used? I also like Danny's suggestion - I have heard of those accumulator systems being used on rally cars to maintain oil pressure. I believe they only weigh 3 or 4 lbs and can be fitted with a solenoid to trap oil pressure in after engine shut down - then the engine can be "pre-oiled" before start up.

Best of luck with the repairs.

Pete

 

[frankh]

Accumulator

I like my accumulator with the invert system..If I leave the accumulator valved off I see all sorts of oil pressure fluctuations as it transitions form upright to inverted.

With the accumulator on line the oil pressure is constant..That and the seeing th oil pressure up to 25psi before start gives me the warm and fuzzies..

Frank

 

[Wicked Stick]

Frank,

Would you have some pictures of your installation you could share ?
Also, what size/type of accumulator do you have ?

I'd like to install one on mine and the pictures would help a lot.

Thanks,

 

[Kevin Horton]

I heard back from Aerosport Power yesterday - they found no internal damage using NDT and visual inspection. The engine is being reassembled, and should get a run in the test cell tomorrow.

 

[pierre smith]

How 'bout the prop....

....Kevin? Seems that it'd at least need a new hub since it was somewhat overreved

Regards,

 

[Kevin Horton]

....Kevin? Seems that it'd at least need a new hub since it was somewhat overreved

I'm going to scrap the prop. It may end up on a wall somewhere, but it will never fly again. A new counterweighted MT is on order, and should arrive sometime in December.

I've got a lot of travel coming up - on the road for four of the next six weeks, so the plane won't fly again until January, at the earliest.

 

[az_gila]

Quite an impressive...

I heard back from Aerosport Power yesterday - they found no internal damage using NDT and visual inspection. The engine is being reassembled, and should get a run in the test cell tomorrow.

...testimony to the design margins and strength built into our Lycomings!!

Glad to hear you didn't have to buy any expen$ive bits...

 

[garnt.piper]

angle-valve oil pickup

Hi kevin,

Just read your post - ouch. I concur with the loss of oil pressure in nose down decelerating attitudes with the angle-valve style (i.e. 'eared') sump. I have the same sump on my Giles (TMX-390) with inverted oil system. The standard Christen oil pickup at the back of the sump is ~2" long from memory, and does get unported when decelerating nose down, as when you pull the throttle in descent (at the very least it sucks foamed oil). Christen have an alternative pickup that extends ~4" into the centre of the sump pan, similar to where the finger screen housing normally sucks the oil from. I've modded mine by removing the standard aluminium tube from the fitting and epoxying in a longer one.

I had a spare angle-valve sump, and measured water into it, and found that 5 litres filled it completely when in a level attitude - 8.5 quarts on the dipstick should be heaps, but I don't know how much is circulating in the engine when running.

Good luck