Take-off performance

Hi,
New here and at the final stages of purchasing my first RV-6A.

I have a question related to take-off performance:
When I test flew the aircraft, and had my buddy do another testflight we both experienced almost the same take-off performance which we both felt was not super impressive.

The RV-6A in question is powered by an O-320, 160 HP and a 70CM6S9-0-77 prop.

On the day of the test flights - We had the following conditions:
2-3 kts headwind.
12 degrees Celcius.
1017 hPA or 30,05 In of Mercury.
Approx Half Fuel.
Two POB of around 170 kg (374 lbs)
Airport is at around 2000 feet MSL, and Pressure altitude was 1888 ft - Density altitude 1958 ft.
Flaps were used ( I guess around 10 degrees).
Take off took 21-23 seconds from wheels stop to lift off on both flights. Rotation was done at 70kts/80 mph.
During the ground roll the engine never exceeded 2200 rpm ?!?!?

To me it seems really slow, and I am wondering if this is right ??

I kind of felt that the owner was overly nursing the Lycoming (my experience tells me that they can take a lot), but should I be worried ?

Any thoughts ?

What was the rate of climb?
What do you mean, 'nursing' the engine? Not full throttle?

BobTurner said:

What was the rate of climb?
What do you mean, 'nursing' the engine? Not full throttle?

Click to expand...

About 34 seconds from lift off to 500 AGL - so close to 900 fpm. Climb speed around 85kts/95mph. He retracted the flaps at around 800 feet AGL.

I looked at his hand, and the plunger is a vernier type, so initially I thought he had two fingers behind the plunger preventing it from going all the way in, but after reviewing my photos I can conclude that during ground roll and until 500 AGL (2500 MSL on the day) he gave it all it could do.

But during airworks he was really scared of exceeding 2200 rpm, however we did some cruise and got around 150 TAS at 3000 feet MSL.

PAN-DENMARK said:

About 34 seconds from lift off to 500 AGL - so close to 900 fpm. Climb speed around 85kts/95mph. He retracted the flaps at around 800 feet AGL.

I looked at his hand, and the plunger is a vernier type, so initially I thought he had two fingers behind the plunger preventing it from going all the way in, but after reviewing my photos I can conclude that during ground roll and until 500 AGL (2500 MSL on the day) he gave it all it could do.

But during airworks he was really scared of exceeding 2200 rpm, however we did some cruise and got around 150 TAS at 3000 feet MSL.

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Interesting technique by the owner...

Having flaps hanging out until 800 AGL is totally unnecessary and will create quite a bit of drag during the climb. Most RVers will use a few degrees of flaps only for short field takeoffs and retract them at very low altitude (100'-150') so the plane will accelerate properly. You will also find the RV-6A climbs very nicely at 115 kts, this allows the engine to wind up and produce more power.

And I can't imagine why he would be afraid of exceeding 2200 rpm, that is about 115 hp......is there something about the plane that concerns him??

"The RV-6A in question is powered by an O-320, 160 HP and a 70CM6S9-0-77 prop."

The prop is 2" under pitched for 160hp..... Should have had a good climb rate. The prop is for a 150hp 6A.... Are you sure it's 160 hp?

I have a 6A O320 and a 79 pitch prop. No flaps on TO. full elevator and let the nose lift asap.... hold just off the ground and let it lift off when it wants to... about 65-70 or so, I don't watch that close. Accelerate to 85mph on the deck and climb out at nothing less than 1200fpm 1/2 fuel and two 180#ers on board. Continue to climb at 120mph and well over 1000fpm.

Holding it on the ground for another 10 mph will eat up the runway.

You do have a concern to question the performance of the plane/pilot.

gasman said:

"The RV-6A in question is powered by an O-320, 160 HP and a 70CM6S9-0-77 prop."

The prop is 2" under pitched for 160hp..... Should have had a good climb rate. The prop is for a 150hp 6A.... Are you sure it's 160 hp?

I have a 6A O320 and a 79 pitch prop. No flaps on TO. full elevator and let the nose lift asap.... hold just off the ground and let it lift off when it wants to... about 65-70 or so, I don't watch that close. Accelerate to 85mph on the deck and climb out at nothing less than 1200fpm 1/2 fuel and two 180#ers on board. Continue to climb at 120mph and well over 1000fpm.

Holding it on the ground for another 10 mph will eat up the runway.

You do have a concern to question the performance of the plane/pilot.

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Yes, I gathered that the prop was not the right size for the 160hp when I looked in all reference tables on Vans Aircraft homepage, but now I am completely sure so thanks for confirming this.

Yes I am sure that it's a 160hp engine or this would be a very good scam I am the victim of.



Do you think this could be a technique problem on the PIC side and not so much an underperforming powertrain ? I have the verified compression # and they are all in the 78/79 range.

There are many possibilities.

First, 2200 RPM isn't ridiculously low RPM on takeoff. There are more than a few fixed pitch RV's which exhibit similar RPM on initial takeoff roll. Generally, RV's have props that are optimized more towards cruise than takeoff, leading to low RPM on the takeoff roll in aircraft with fixed pitch prop's.

That said, do you know that the tach was correct? If it was, are the throws on the throttle properly adjusted so the engine actually achieves full power? Did the airplane have a manifold pressure gauge? If so, what were its readings?

As far as the cruise RPM are concerned, it would be interesting to hold the airplane at full throttle and see what RPM and speed the airplane will generate after giving it a couple of minutes to accelerate to top speed.

On a somewhat related question, are all of the fairings (intersection fairings, wheel pants, etc) installed? They will have a significant impact on top speed.

Bottom line, there are more things to verify regarding this airplane...

Take off

Hi

I have a couple of questions to try to answer this.

First you say two passengers 170 kg....... is that 170 kg each passenger or total weight of both passengers?

What does the engine pull static?

What was rate of climb at full throttle?

Are you able to exceed 2700 at full throttle straight and level and RPM in the climb?

Are you getting any brake drag, either through the brakes binding themselves, or because the pilot is applying brakes on the take off roll ( easily done).

Have you done a compression check on the engine.

23 seconds for take off is crazy for an RV usually they are off the ground within 5 seconds.

As that prop appears under pitched I would have expected 2300 perhaps more static which should have got you in the air much earlier.

The first thing to make sure of is the brake drag, if there is none and the pilot has definitely dropped his feet onto the rudder bar so is not applying them in error, the you need to look at what appears to be a lack of power from the engine.

RPM on the roll

Howdy,

Our 6A with O-320 and Sensenich makes somewhere around 2270 to 2300 RPM on the takeoff roll. I hold the nosewheel just off and let it fly when it wants to. I like to see 90 or 100kts on the initial climb and often cruise climb at around 130 or 140kts. It helps with cooling and I still see maybe 700fpm. As someone else said, higher airspeed means higher RPM = more power and better rate of climb.

Ed

When I first started flying my 7 off my grass strip, I would use 15 deg flaps. I remember several times forgetting to retract them and thinking "what in the world is holding me back?" Then I would remember the flaps and retract them and it felt like I had hit the afterburners!

Wow a lot of great information here - thanks guys !!! I will try to answer what I know so far:
During level flight the engine did not seem stretched to relatively quickly reach 148kts TAS at 3000' - that said the owner was flying the aircraft extremely gentle and not pushing it hard. I would not know if we could exceed 2700 rpm's in level flight.

The aircraft is fully stocked with fairings, wheelpants etc. All in all a very clean configuration.

Two PAX - total weight together was approx 170 kg.

I don't know what the engine pull static. It rev'd at 2200 rpms before we started roling. ther is no Manifold pressure instrument.

I don't know if the brakes are dragging - or even if the owner was riding the brakes. It's almost impossible to noticed when you are not at the controls and it's the first time in an aircraft. I could suspect that the throttle cable is not adjusted 100% and maybe the engine just can't give 100%.

Compression test was done a little over a year ago: 78-79 all of them.

I have told the owner it's a do-over and that I want to see another takeoff - no flaps and to the firewall with the plunger. He is a bit upset, but will do it for me. He also told me that he likes to keep the aircraft slightly longer on the RWY and build some speed before rotation - I don't know why.

I really appreciate all your advice - keep'em coming - It's certainly going to be included in my second test of the aircraft - and this time I will be at the controls.

Just a thought..... Check and see if the motor has ECI cylinders. If so, make sure they are up to date. ECI had a problem with the heads blowing off the cylinders. There may be a reason he wants to keep the RPM down, to reduce the stress on defective ECI cyl's.

I sure hope I am wrong about this.

PAN-DENMARK said:

I have told the owner it's a do-over and that I want to see another takeoff - no flaps and to the firewall with the plunger. He is a bit upset, but will do it for me. He also told me that he likes to keep the aircraft slightly longer on the RWY and build some speed before rotation - I don't know why.

I really appreciate all your advice - keep'em coming - It's certainly going to be included in my second test of the aircraft - and this time I will be at the controls.

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My advice is to find another RV. This owner is either grossly uninformed about how to fly his RV (or really scared of it) or he is hiding something. There is no reason for him to get upset about demonstrating his aircraft to its expected potential unless there is something he doesn't want you to know. This prospective sale has already gone sour.

Move on, leave this RV to somebody else. Best wishes in your search for your ideal RV!

I agree. There's something wrong here. If the seller of anything has become impatient (angry) with you, it's definitely time to move along.

If you are new to RV's, start hanging around airports with a few regular RV fliers. You'll learn a lot about what is normal, and make some new friends at the same time.

Consider some dual training with one of the transition trainers to learn how to properly fly these aircraft.

Bevan

I agree with Sam. Something doesn?t sound right. Follow your gut feeling, it usually is right on. Larry

Thanks Guys.

Here back home, I have been hanging around the airfield close to the homebuilders community and have also been flying in another 6A - which performed like a rocket - granted it's a 180 hp but still with Fixed Pitch.

I took a look at my video from the flights and cruise seems ok. I saw the following:
3000' MSL: 140 KTS IAS / 2230 RPM's. 150 KTS IAS/2420 RPM. That seems about right to me on a 160 hp engine.

But you are right - his annoyance could indicate that he is hiding something - or it's just because I am Nordic and he is Hispanic. there can be a lot of mentality difference between "Up Northern Europe where I come from" and South Europe where the aircraft stands.

I could also share the videos of the flights if anyone is interested to take a look ?

I would love to see the videos of takeoff, climb and cruise. I have a -6, 160hp and a new catto three blade prop that i would love to compare.

Thanks

titanhank said:

I would love to see the videos of takeoff, climb and cruise. I have a -6, 160hp and a new catto three blade prop that i would love to compare.

Thanks

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Here are the first 2 take offs... Keep in mind the aircraft is close to MTOW and also that the density altitude was about 1900'

http://gofile.me/2Tqtu/27InCLbIL

http://gofile.me/2Tqtu/wjtuD00Bt

and then another without me or my friend in the aircraft - on a day where it was loaded to MTOW and density altitude 2800':

http://gofile.me/2Tqtu/udF0Oa9sJ

I would really like to see what you get out of a 3-blade Catto which is my dream for the O320. Can you share more info on this ?

PAN-DENMARK said:

Here are the first 2 take offs... Keep in mind the aircraft is close to MTOW and also that the density altitude was about 1900'

http://gofile.me/2Tqtu/27InCLbIL

http://gofile.me/2Tqtu/wjtuD00Bt

and then another without me or my friend in the aircraft - on a day where it was loaded to MTOW and density altitude 2800':

http://gofile.me/2Tqtu/udF0Oa9sJ

I would really like to see what you get out of a 3-blade Catto which is my dream for the O320. Can you share more info on this ?

Click to expand...

Max performance will come from the 2 blade. Max bling and smoothness come from the 3 blade. I have a 6A with IO-320 (160) and a catto 2 blade. I am a tad under pitched. At 8000', I get 190 @ 2700 RPM and 200 @ 2800. I get around 1400 FPM solo / full fuel at 100 MPH down low.

lr172 said:

I am a tad under pitched. At 8000', I get 190 @ 2700 RPM and 200 @ 2800. I get around 1400 FPM solo / full fuel at 100 MPH down low.

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It looks perfect to me, unless you only fly in the flat lands and never go above 8000'.
Your prop will likely give you 2600-2650 RPM WOT at 10,500-12,500 which is perfect (those of us that live out west where there are real mountains use that altitude range a lot).
Any less pitch and your climb performance would get even worse and it sounds slightly off the mark already.

PAN-DENMARK said:

...

But during airworks he was really scared of exceeding 2200 rpm, however we did some cruise and got around 150 TAS at 3000 feet MSL.

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At cruise, with a FP prop, to get 75% power at 8,000' you need to fly it wide open throttle (full in) and let it spin up to the red-line. However, with that prop, it might have the RPM restriction and he may not want to get close to that.

That can be fixed by putting a Catto on it and selling the metal prop.

The engines are designed to make TBO when flown that way.

With a Constant Speed prop you typically fly it wide open throttle and set the prop for around 2400 RPM.

For some reason i can not download the videos. I did a max weight takeoff with my rv 6 and catto 3 blade prop yesterday. The takeoff weight was 1730 lbs. This was 1064 empty weight, 245lbs pilot, 240lbs pax and 30 gallons of fuel. The density altitude was 1500ft as reported by asos and temp was 31deg C with relative humidity of 85%. We used 1 notch of flaps to approx 300 ft and WOT showed 2200 rpms. This gave us an inital climb rate of 600-700 fpm at 80-90 mph to clear the trees on a 4000 ft concrete runway. After reaching 300 ft at about mid field, flaps were retracted and established a 110mph cruise climb at 2450 rpms with 700-800 fpm climb rate. It flew very much like a cessna 172 departure profile at high weights and temps. This weight and balance solution gave us 8 gallons to burn without the aft cg limit being exceeded. We climbed to 2000ft and did a series of stick pull phugoid manuevers to check the pitch stability. The airplane respond with slow, but positive stability all the way to the aft cg limit. It did become slightly more pitch sensitive, but nothing scarey. I would not exceed the aft cg limit under any circumstances after this test. I used 5 mph higher speeds in the pattern, 95mph downwind and 85mph on final. It three point landed very nicely. The landing weight was 1675lbs with a landing cg of 76.79".

All of these numbers are coming directly from steam gauges with unverified pitot static system condition or calibrations. Checking these systems is the next thing on the list.

PAN-DENMARK said:

Here are the first 2 take offs... Keep in mind the aircraft is close to MTOW and also that the density altitude was about 1900'

http://gofile.me/2Tqtu/27InCLbIL

http://gofile.me/2Tqtu/wjtuD00Bt

and then another without me or my friend in the aircraft - on a day where it was loaded to MTOW and density altitude 2800':

http://gofile.me/2Tqtu/udF0Oa9sJ

I would really like to see what you get out of a 3-blade Catto which is my dream for the O320. Can you share more info on this ?

Click to expand...