201 not meeting performance expectations

[dsking001]

I recently purchased a 1984 Mooney 201.  First off, this is my first Mooney and I can honestly say I think it is an awesome machine.

The aircraft is equipped with a McCauley 3 blade prop and a power flow exhaust.

Here is my problem.  I've performed several TAS checks at varying altitudes.  According to my POH and most everything I've read, I'm getting about 10 kts slower than advertised.  FF and EGT match book numbers.

The "tests" (I am not a test pilot) were performed by: WOT, 2500 RPM (digital and factory tach setting), 50 deg ROP, WX slightly warmer than standard temps. By averaging the GPS ground speed of N, E, S, W, I'm getting around 143 TAS at altitudes from 4000' to 12,000'.

I don't feel as though the aircraft is out of rig, but I've had an A&P look at it.  Gear doors are all closing flush.

If anyone has any thoughts, please let me know.

-Dan

 

[johnggreen]

Dan,

I'm no mechanic, but I've owned a lot of airplanes and had some strange problems including below book speeds.  Check everything I say with somebody with real Mooney knowledge, but here is my two cents.

An airplane is bent in all kinds of directions; especially a prop airplane.  This is done because an airplane is not a glider.  Once you crank that engine there are all kinds of forces that act on it.  The fuselage is not parallel to the wing.  The wing is pitched up slightly in "level" flight to produce lift.  The engine points to the right and usually down to compensate for torque, p-factor and the corkscrew effect of the air coming off the prop, the vertical stabilizer to the left for the same reason.  An airplane is "bent" actually "trimmed" for one phase of flight, cruise.  In climb, descent, slow flight, high speed, etc. you have to make corrections with the controls.  Let's not forget the downforce that must be produced by the horizontial stabilizer by the way.

The point of all this is that very often airplanes are simply not in trim, meaning everything isn't "bent" properly.  In come cases and some airplanes this can be corrected and in some it can't.  Some airplanes come out of the factory more "in trim" than others.  In most cases airplanes like Mooneys are considered within specs if they are plus or minus about 3-5% of book.

Sorry, my wife wants me to take her out to eat, NOW.  I'll finish the post later, but I warn you that the next post will come with the influence of at least one martini.

Later.

[Skywarrior]

Perhaps the 3-bladed prop is stealing a few knots in cruise...

Chuck M.

[takair]

You mentioned WOT, but not the Manifold pressure.  What are you getting for MAP at various altitudes.  Also, are you at gross wt or lighter.  Either way, you are not even getting M20C speeds.  Typical unmodified E models can get 150KTAS at around 2500/24 burning 10 to 11 gph.  I think most J models I see posted here are getting upwards of 160KTAS on average for roughly the same power and fuel. 

Did you mechanic use the Mooney boards to rig.  Did he check flap rigging.  That is a good starting point, in my opinion.  If they are off, you will have extra drag, out of trim aileron and elevator, etc.  It is amazing how much you can get out of proper rigging. 

[KSMooniac]

The 3-blade prop explains at least a few knots of it, but the rest could be due to many factors.  Rigging is always a suspicion, even if it seems to fly hands-off OK.  You could have a lot of "extra" antennae that weren't on the factory planes used to develop the performance numbers.  Your engine and/or cowl could be misaligned due to wear in the cowl or the engine mount donuts, causing some drag at the spinner/cowl interface.  

To properly check the rigging, you need the factory travel boards to measure where everything is.

Other points... 50 ROP is a terrible place to park the mixture but I won't go into detail here as it has been said many, many times on this site and others.  You can also make TAS runs at 360, 120 and 240 degrees and do an RMS average instead of 4 different tracks.  If you didn't wait a few minutes at each heading before taking the speed reading, you could have "left some on the table" since J's are slow to accelerate (and slow to decelerate).

[ToddDPT]

Something just isn't right.  That just is way too slow for our 201s.  I'm definitely interested in knowing what your MAPs are.  We see 158 kts TAS at 11,000/12,000 feet at WOT 2450 RPM.

[Jerry 5TJ]

Does seem a bit slow for a "J" .

Here are some stock M20C numbers using your same method -- average of N S E W GPS speeds.  You should beat these by a good handfull of knots in your "J"

 

Stock M20C Airspeed Measuements
2000'   2400 RPM 22" MP 7C      12/12/2008
	W	S	N	E
	113	131	115	137
	115	133	116	139
	115	134	119	140
	116	136	118	139
	116	132	119	141
						Average all Quadrants
	115.0	133.2	117.4	139.2		126.2	Knots
4000'   2400 RPM 23" MP 9C      1/8/2009
	W	S	N	E
	131	164	143	109
	132	165	139	116
	131	167	140	110
	133	166	141	116
		165	138	113
				116		Average all Quadrants
	131.8	165.4	140.2	113.3		137.7	Knots
6500'   2400 RP M 23.3"  MP   11C      1/9/2009
	W	S	N	E
	144	161	126	145
	144	159	124	144
	144	160	124	144
	144	160	124	145
						Average all Quadrants
	144.0	160.0	124.5	144.5		143.3	Knots
3000'   2380 RP M 22"  MP   10C      2/27/2009
	125	210	300	30
	122	129	134	124
	122	129	134	124
	121	131	134	126
	122	132	135	127
	123	131		126
						Average all Quadrants
	121.8	130.4	134.3	125.4		128.0	Knots
5500'   2400 RP M 24"  MP   -1C  30.16"       3/5/2009
	240	150	60	330
	146	150	146	132
	147	150	141	132
	148	150	141	130
	148	150	140	130
			140	130
						Average all Quadrants
	147.3	150.0	141.6	130.8		142.4	Knots
6500'   2475 RP M 23"  MP  12C        6/20/2009
	W	S	N	E
	127	140	155	154
	125	138	154	151
	128	138	155	152
	130	140	156	150
						Average all Quadrants
	127.5	139.0	155.0	151.8		143.3	Knots
4500'   2500 RP M 25"  MP  16C       10/2/2009
	W	S	N	E
	136	161	157	132
	135	161	155	134
	135	163	155	133
	136	163	155	134
						Average all Quadrants
	135.5	162.0	155.5	133.3		146.6	Knots
4500'   2500 RP M 25"  MP  12C       12/24/2009
	W	S	N	E
	141	163	146	124
	144	163	146	124
	144	165	145	126
						Average all Quadrants
	143.0	163.7	145.7	124.7		144.3	Knots

 

[johnggreen]

I'm back plus one martini.

I've never owned a J model, but I understand that most J's true around 160-165 so you are definitely outside the parameters of normal.  Assuming that you do not have an airplane that is terribly out of rig, here is a list of things to consider and with your slow cruise speeds it is probably a combination of several.

1.  Prop.  Have a shop check to see if there are any deficiencies you might have missed with the naked eye.  Including rpm.

2.  Flap droop.  Are your flaps coming all the way up when retracted.

3.  Aileron droop.  Happens more than you would think.  Ailerons are simply not properly adjusted and are slightly down and acting like flaps.

4.  Elevators out of rig, one up, one down, don't know if this is possible in a Mooney or not, just an idea.

5.  Dirty wing.  From anything.  Caulk, paint, dirt, oil, this laminar flow wing is extremely sensitive to dirt. 

6.  Dirty belly.  If I don't keep the oil cleaned off the belly of my Bravo I can see a noticeable difference in speeds.

7.  Bent wing skins.  May have one or more on bottom that you never noticed.

8.  Damage.  Check to see if your airplane ever received any strutural damage (not all of that gets logged).  You may have something that was bent and never logged.

9.  Engine mounts.  Simply, is your engine pointing the correct way.  Notice the post on the drooping engine in another thread.  A very common problem.

I'm sure I left some things out.  You need to get the counsel of some really qualified people.  Your speeds would indicaate a rather significant problem.

If you can get a hold of Coy Jacobs with Mooney Mart, he really does know a lot about Mooneys and how to get speed out of them.  He cut his teeth modifying the older models for best performance.  Maybe I can email him and get him to reply to your post.  Then again, maybe not.  Nice guy, just always pre-occupied it seems.

This won't make you feel any better, but the difference from one airplane to another is sometimes astonishing.  I flew a new Ovation demo once that couldn't break 175 knots in a dive.  My Bravo on the other hand is 7-8 knots over book at all power settings and all altitudes and does it at gross weight.  Book speed are calculated at "mid-load weights".  To rub salt in the wound, my Bravo does this with TKS.. I had an acquaintance with an Acclaim and there wasn't 5 knots difference in our performance numbers.   Just as a teaser; at 12,000' I true 177 knots pulled back to 13 gph and that is at gross weight.  No, my Bravo is not for sale.

Well, hope this helps give you some ideas and direction.  Now, talk to somebody that knows what he's talking about.

John Green

[johnggreen]

Dan,

One more thought and I'll shut up.  You've gotten some good posts tonight by the way from several guys.

When i said that if your airplane wasn't terribly out of rig, I meant in the way it was built or bent. Sometimes wings, stabilizers, control surfaces are simply not in line when they are put together at the factory.  Then it could have had an incident that bent it though I certainly hope not.  Severe turbulence, hard landing or and accident that was fixed and never reported.  Then there is "rig" of the controls for instance that you can have redone.

For sure, I would want to find out why this J is this slow.  If, heaven forbid, it from a bout with severe turbulence, your cruise speeds may be the least of your worries.  Let's hope not.  Just make sure to find out.

JG

[johnggreen]

Dan,

One more thought and I'll shut up.  You've gotten some good posts tonight by the way from several guys.

When i said that if your airplane wasn't terribly out of rig, I meant in the way it was built or bent. Sometimes wings, stabilizers, control surfaces are simply not in line when they are put together at the factory.  Then it could have had an incident that bent it though I certainly hope not.  Severe turbulence, hard landing or and accident that was fixed and never reported.  Then there is "rig" of the controls for instance that you can have redone.

For sure, I would want to find out why this J is this slow.  If, heaven forbid, it from a bout with severe turbulence, your cruise speeds may be the least of your worries.  Let's hope not.  Just make sure to find out.

JG

[jetdriven]

That 3 blade prop is costing you 5 knots likely right there.   Make sure it is washed and waxed. Rain costs 3 KTAS on a laminar flow Mooney wing and dirt is going to cost you some too. Also, if you have a low cylinder or a bad cam lobe thats the full ten knots.  An innacurate tach where it indicates 2500 RPM but is actually 2400 RPM costs you 3-4 knots. Ours was like that at first. I think most early J's before the nice wingtips and smooth belly are 155 TAS machines and the later models are in the 160 maybe 165 range at optimal altitude.  I would like to see a 165 knot J model. Maybe an MSE. 

[KSMooniac]

There aree variations from plane to plane due to the hand-built nature of our planes.  This can result in some twists in the wing or control surfaces that are very difficult to detect, even with rigging boards and other tools.  Engines are the same way.  It could be any number of issues, some of which are correctable and some of which are not, at least in a way that makes economic sense.  I'm battling a bit of this myself with my J.  You should be able to get in the mid 150's KTAS at 6000-8000 or so in a hi-cruise setting.

One easy thing you might check is speed vs. CG position.  Our planes are faster at aft CG, and your heavy 3-blade prop is doing you no favors in terms of cruise speed loss from the 3rd blade but also from the extra weight on the nose.  You might ballast-up the baggage area and see if you can measure a difference in IAS.  Also try putting your seat all the way back in cruise if your back seat is empty.

[Parker_Woodruff]

-Make sure the rigging was checked with the Mooney travel boards and is to factory spec.

-Make sure your gear is retracting all the way

-Washing a dirty plane is worth a couple knots, seriously.

-Your 3-blade prop is probably hurting you 2-3 knots and also contributing to a farther forward CG with the extra weight.

[jetdriven]

also a leaky cabin door seal or baggage seal is worth a couple knots.  Extra LORAN antenna = 1 knot.

[201er]

Did you make sure cowl flaps were closed? Ram air open? Did you check if the MP you were actually getting matched book values? If you didn't open ram air, prehaps a clogged intake filter?

Also I wanted to mention that in my '78 20J I typically get 10ktas less than book values. They seem overly optimistic (brand new, no antennas, no step, etc). For example at 4000ft the POH says 2400RPM 26.2" MP should yield 161ktas. No way! I'd be lucky to get 150ktas in that configuration. But 143ktas sounds really slow and almost 20ktas under book value.

[Bob]

Is your manifold pressure gauge accurate?  It may be reading high so you think you are at full power, but realy are not? My 30 year old gauge is 1.5in off.

[dsking001]

Thanks for all the inputs.  Answer to previous posts: MP are matching book numbers during tests; GWs are mid range with full fuel and me (200 lbs) and 25 lbs of random stuff; flaps are retracting fully.

I think the rigging is going to be my first point of interest.  I'm not familiar with the "factory travel boards", but I’ll ask my A&P.  Next will be the engine mount (droop).

I’ll do a couple more test runs with a little more weight in the AFT.

Thanks for all the help.  Work calls.  TO BE CONTINUED...

[danb35]

To see what the travel boards look like (and rent them, if needed), take a look at http://hangartoolbox.com/Tools/135.aspx.

[John Pleisse]

If you're gonna get into rigging, consult MAPA for a previous article written by Kerie McIntyre on how to rig a Mooney. It is highly simplistic and informative. Have a MSC do it. The know-how, rigging boards and ability to do it in under 2/3 a day is already there without any on the job traing or renting boards.

Also, check your logs and make sure a control surface was never replaced....before you pay to rig it.

[Txbyker]

Daniel,

I have not had the chance to do the N,E,S,W averaging test in my 20J yet.  But I often set the airspeed indicator against outside air temperature and it is pretty consistent.  By any chance did you check you airspeed indicator corrected for temp against your averages?

Also, I see you tag is in Abilene.  Don Maxwell is great at rigging over in Longview.

Russ

[Jeff_S]

I'll add a few thoughts from another direction, after agreeing with much of the above.

I do think the 3-blade prop costs a few knots, because I have one and I know it has made the plane more nose heavy. This means that unless you carry extra weight in the baggage compartment, the horizontal stabilizer is having to do more work in any given configuration and that creates drag. So one thing to do is simple: carry an extra 50 pounds in the back if your load is otherwise light...you will be amazed at the speed effect. (This was covered extensively in a thread about racing your Mooney.)

Also, the premise of the 4 cardinal point GPS ground speed test is somewhat flawed, because it doesn't factor in that when flying at the speeds we fly in a J (or most any of the piston-prop planes except maybe the highest performance ones) you have an effective head wind at least 2/3 of the time. Think about your x-wind correction charts as an example. For a tailwind to really give you a meaningful push, it can be no more than 30° off the tail in either direction. More than 30° off the tail your drift compensations start robbing you of forward speed, so you are losing some of the tailwind effect.

"But wait!" you say; "in the 4 point cardinal test I'm not compensating to stay on a heading, I'm just going with the flow and keeping the nose on the compass point." Yes, but your airplane is still effectively going in a diagonal and not straight along its path of thrust compared to the ground (which is what you're measuring!) so your ground speed is still skewed by this. Factor in that even in a localized setting the winds can change dramatically from point A to point B, and you have no way of knowing for sure how this affects your stats.

So if you factor in these two additional ideas, my conclusion is that your TAS's may not be quite as bad you think they are. Certainly they do seem low, but perhaps not horribly so. Just something to consider...

[74657]

Quote: Jeff_S

I do think the 3-blade prop costs a few knots, because I have one and I know it has made the plane more nose heavy. This means that unless you carry extra weight in the baggage compartment, the horizontal stabilizer is having to do more work in any given configuration and that creates drag. So one thing to do is simple: carry an extra 50 pounds in the back if your load is otherwise light...you will be amazed at the speed effect. (This was covered extensively in a thread about racing your Mooney.) 

 

One thing I noticed on my CC trip last week was that with the plane loaded (full mains, wife @ 110 lbs, 50 lbs in small children, 25 lbs in car seats and 25 lbs of misc. stuff in the back my trim indicator was half way between "takeoff" and full nose down.  You could see the tips of the elevator sticking up higher than the horizontal stabilizer.  This has to be creating a lot of drag.....  You guys see the same situation in your planes?

[jetdriven]

Our 201 elevator is just like that and so is a friend's E with 3 people in it.  I dont know how you could load outside the aft limit unless you had one skinny person in the front and two large people in the back. It has to be worth a couple knots.

Quote: 74657

[jetdriven]

I know its a different plane but a friend of mine had a Cardinal RG with an IO-360-A1B6 and the same McCauley prop as a 201. He went to a 3 blade Hartzell and it for a fact lost 4-5 knots in cruise and climbed better.  A 2 blade is simply more efficient. Now when you get to the 300 HP level, 3 blades are needed to absorb all that horsepower and convert to thrust.  Again, different airplane, FWIW.

Jeff, your comment on the 4 way test got me thinking. I have done the 4 point cardinal heading method and came up with 150 KTAS (that day)  but in a 30 knot winds aloft day it was  averaged at 145 TAS. However, the IAS (corrected for CAS and DA) corresponded with 153 KTAS.  I remember reading about a 3 point test, and in this thrread they talk about it.

http://www.beechtalk.com/forums/viewtopic.php?f=7&t=56902&start=40

Quote: Jeff_S

I'll add a few thoughts from another direction, after agreeing with much of the above.

I do think the 3-blade prop costs a few knots, because I have one and I know it has made the plane more nose heavy. This means that unless you carry extra weight in the baggage compartment, the horizontal stabilizer is having to do more work in any given configuration and that creates drag. So one thing to do is simple: carry an extra 50 pounds in the back if your load is otherwise light...you will be amazed at the speed effect. (This was covered extensively in a thread about racing your Mooney.)

Also, the premise of the 4 cardinal point GPS ground speed test is somewhat flawed, because it doesn't factor in that when flying at the speeds we fly in a J (or most any of the piston-prop planes except maybe the highest performance ones) you have an effective head wind at least 2/3 of the time. Think about your x-wind correction charts as an example. For a tailwind to really give you a meaningful push, it can be no more than 30° off the tail in either direction. More than 30° off the tail your drift compensations start robbing you of forward speed, so you are losing some of the tailwind effect.

"But wait!" you say; "in the 4 point cardinal test I'm not compensating to stay on a heading, I'm just going with the flow and keeping the nose on the compass point." Yes, but your airplane is still effectively going in a diagonal and not straight along its path of thrust compared to the ground (which is what you're measuring!) so your ground speed is still skewed by this. Factor in that even in a localized setting the winds can change dramatically from point A to point B, and you have no way of knowing for sure how this affects your stats.

So if you factor in these two additional ideas, my conclusion is that your TAS's may not be quite as bad you think they are. Certainly they do seem low, but perhaps not horribly so. Just something to consider...

[jetdriven]

how about this:

from here;  http://williams.best.vwh.net/avform.htm#3gs

TAS and windspeed from three (GPS) groundspeeds.

Determine your groundspeed on three headings that differ by 120 degrees (eg 40, 160 and 280 degrees), call these v1, v2 and v3

Let

     vms = (v1^2 + v2^2 + v3^2)/3

     a1= v1^2/vms -1

     a2= v2^2/vms -1

     a3= v3^2/vms -1

     mu= (a1^2 + a2^2 + a3^2)/6

Let bp and bm be the roots of the quadratic b^2 -b + mu =0 ie:

     bp= 1/2 +sqrt(1/4-mu) 

     bm= mu/bp

The TAS and windspeed are then given by sqrt(vms*bp) and sqrt(vms*bm) provided that the TAS exceeds the windspeed. If this is not the case, the roots are exchanged. This is a handy way to check your TAS (and the calibration of your airspeed indicator) using your GPS groundspeed, even though the wind is unknown.