Slooooooow 170b

[ArcticCowboy]

Good morning everyone, I’m new to the the forum so bear with me.

I recently bought a ‘53 170b with Sportsman Stol kit, 180 legs, 31”AKBW, and an 80/42 mcCulley prop. I have two friends with identically set up 170’s. I’ve noticed when we fly, I am running 2550 RPM to keep up with them running 2200-2300. At 2550rpm I’m cruising about 95mph, while they can cruise about 105-110. I’ve verified the rpm gauge is reading correct, and when we fly wing to wing with same ground speed, they are running a significantly lower rpm setting. We all weigh about the same and carry the same gear. One of them actually has a 80/40 prop, so theoretically I should be faster all else considered. For the life of me I can’t figure out why I’d run almost 15% slower.

[GAHorn]

Surfaces condition and rigging can be issues. Antennas, brake-lines, prop condition, engine condition …. would add/subtract minor differences as well.

[ArcticCowboy]

Surfaces condition and rigging can be issues. Antennas, brake-lines, prop condition, engine condition …. would add/subtract minor differences as well.

Wing rigging was my initial thought, but I can’t find anything in the logs showing it was changed. The other two planes I fly with are painted, and I’m a stripped aluminum, and I knew the little stuff could make small changes. I was just shocked to see almost a 15 mph difference. I was concerned there’s something mechanically wrong that I’m just missing. It just came out of annual in November, and my mechanic said everything was tiptop shape.

[c170b53]

Welcome to the forum, somehow I think your engine may not be producing as much power as your flight mates but as George mentioned it could be a sum of issues. I know when I first had my plane with a high time continental, it ran smooth. When I went to overhaul it I found a cam lobe pretty much worn down to nothing. So it obviously was not making rated power but as the plane was new to me I was happily unaware. Let us know what you find.

[Bruce Fenstermacher]

I have observed that there are 170s that are fast with no effort, some are faster because of effort, and some are slow no matter what. And there are a lot of average examples as well. I've owned two slow 170s. I could cruise around at 105 or 110 but all the others where doing 115-120. I studied both of the airframes I had, even went through the trouble to rig the wings equally and with the least incedence. Never got either to go faster.

I've also found there are no two props the same. Oh they can be marked the same length and pitch but they don't perform the same. I owned a clipped wing Cub for 20 years. There was something special about the McCauley prop I had. Despite buying the same model, length and pitch a few others couldn't duplicate the performance I got out of it. It fit the performance of the engine and airframe well.

And of course no two engines are exactly the same either.

[ArcticCowboy]

Welcome to the forum, somehow I think your engine may not be producing as much power as your flight mates but as George mentioned it could be a sum of issues. I know when I first had my plane with a high time continental, it ran smooth. When I went to overhaul it I found a cam lobe pretty much worn down to nothing. So it obviously was not making rated power but as the plane was new to me I was happily unaware. Let us know what you find.

I had considered that, but wouldn’t the prop and rpm dictate a speed? X RPM with Y Prop = speed - drag

My takeoff roll is excellent, at least as good as my friends with identical setups. I am a fairly new pilot and brand new to the 170’s (I owned a pa12 setup for bush flying before this).

[ArcticCowboy]

I have observed that there are 170s that are fast with no effort, some are faster because of effort, and some are slow no matter what. And there are a lot of average examples as well. I've owned two slow 170s. I could cruise around at 105 or 110 but all the others where doing 115-120. I studied both of the airframes I had, even went through the trouble to rig the wings equally and with the least incedence. Never got either to go faster.

I've also found there are no two props the same. Oh they can be marked the same length and pitch but they don't perform the same. I owned a clipped wing Cub for 20 years. There was something special about the McCauley prop I had. Despite buying the same model, length and pitch a few others couldn't duplicate the performance I got out of it. It fit the performance of the engine and airframe well.

And of course no two engines are exactly the same either.

I’ve kinda come to the realization I may never know. I think my next step is to swap props with a friend for a quick trial. Engine will get either a top end or full rebuild soon so maybe that’ll change it.

[GAHorn]

Wing rigging was my initial thought, but I can’t find anything in the logs showing it was changed. …

I’m fairly certain there are Many who can confirm that a Lack of any Record in the “logs”….. does not equate to a “Lack of Alteration or mechanical work performed”. This can be obvious when an STC is found to be installed in airplanes….which do not have the required paperwork to support that Major Repair or Alteration.

…OR… it can be work performed which is not in-accordance with acceptable standards and practices…OR work perhaps accomplished by persons unqualified or not certificated to do that work… even work which is well-performed may be undocumented. Soooo….

I have been informed by FAA personnel that work performed which is un-recorded…. is regarded by the “authorities” as more onerous than work performed by uncertificated persons. (if you work on an airplane…. RECORD IT… even if you are not properly documented to perform that work. When the next Inspector sees that entry….he/she will be able to inspect the result and find it “airworthy” or Not.)

As to your “slow” airplane: Are your doorseals and fairings properly placed and in good condition? Is your engine cowling and Baffling in accordance with design? (One thing proven to early aviators was the need for and importance of proper engine-cowling and baffling, not only for proper cooling…but also for speed. Air which enters your cowl can add significant “drag” if it is not properly directed and exited.

Anyway, the First thing I’d do is read thru the “Rigging Instructions” (found in the MX Library viewtopic.php?t=8196 ) and compare those notes to the airframe. Drag increases as the SQUARE of Velocity…. and unnecessary drag will hurt top-speed more than low-speed (take-off field length). When investigating your airplane rigging…don’t forget to confirm if your airplane is symmetrical as described in the “rigging instructions.” If an airframe is not symmetical it will suffer from drag.

Engine performance can be generally acceptable if static RPM limits (posted in the Type Certificate Data Sheet) is met, and if the engine/prop meets design. (This is the grey-area that often enters the imagination…but which rarely is the actual cause of low cruise-speed performance. If your airplane meets the published TO Runway length data….and the engine/prop are the correct models and meet the static rpm limits…you can probably disregard engine performance as the issue.)

Also… considering that your airplane is being compared IN FLIGHT and ALONGSIDE similar models…. the actual difference in obtained speed can be believable. What might be UN-believable…. is the accuracy of your friend’s instrumentation. They MAY be seeing 2450 RPM on their tachometers….but MAY ACTUALLY be running somewhat higher RPM….therefore producing more power. (But frankly that is a low probability due to that Drag vs Velocity law…. they’d have to produce Considerably More power to overcome the increase drag…but the “perception” of greater speed can be misleading during formation flights. The average person during a “brisk” walk…only makes about 3 mph. Are your friends airplanes making more speed than your airplane comparable to a “brisk walk”…?? If so…. it means that a 3-1/2 hour flight ..(the practical fuel-flight-time of these airplanes with reserve) …would result in an eleven mile difference in that timeframe. Your “slower” airplane would take only 4 minutes longer over the entire fuel-range of the airplane. How much money do you wish to throw at this..??

FINALLY… if you REALLY want to make a difference…. a RED PAINT JOB will cost you about $10K. Is Four Minutes worth $10K..?

(sorry…couldn’t resist)

[voorheesh]

“I have been informed by FAA personnel that work performed which is un-recorded…. is regarded by the “authorities” as more onerous than work performed by uncertificated persons. (if you work on an airplane…. RECORD IT… even if you are not properly documented to perform that work. When the next Inspector sees that entry….he/she will be able to inspect the result and find it “airworthy” or Not.)”

While there may be exceptions, FAA Inspectors do not inspect general aviation aircraft other than during accident/incident investigations and occasional ramp checks. When nonconformity is discovered, it can result in a “Condition Notice” which gives the owner an opportunity to either justify the condition or correct it prior to further flight. It can also result in an enforcement investigation if it is proved the aircraft was either returned to service improperly or operated in an un airworthy condition. The FAA cannot “ground” an aircraft except in the case of one that is engaged (ready to operate) in air transportation and is found to be in an unsafe condition.

In my experience, the FAA does not make subjective findings such as “more onerous”. Investigations do have sections where an inspectors opinion is expressed and these can include observations of how onerous or unsafe a condition is. However, the FAA is strictly bound by its responsibility to provide a preponderance of evidence if they wish to prove that any condition is contrary to airworthiness standards. It either is or it isn’t. These days, punitive enforcements proceed when there is evidence of bad intent. If a pilot or mechanic demonstrates a cooperative attitude and takes corrective action, the matter is typically settled without penalty.

The FAA relies on A&Ps with IA authorizations to conduct thorough airworthiness inspections on GA aircraft annually. If nonconformity is discovered during an annual, the IA is the person with the ability and authority to identify, verify, and correct it. Except in egregious or “onerous” cases where the condition is so wrong as to be not fixable, most aircraft can be brought into conformity and be made airworthy once again. That is really the bottom line here. Find a responsible and knowledgeable IA and rely on them to keep your aircraft both safe and reliable. You won’t have to be worrying about the FAA.

[GAHorn]

Individual FAA Inspectors are “human”…just like owners, pilots, and workmen. They can make and verbalize personal observations in conversations which may or may not be the “official” viewpoint. “More onerous” was My phrase in boiling-down the bottom line of the conversation. The inspectors comments reflected the seriousness of working on an airplane secretly and without recording the event.

That was what was discussed in my private conversation with an FAA Mx Inspector at the FTW-FSDO…and was my reference in my previous post.

Work performed on aircraft which is unrecorded is a serious violation of FARs…regardless of who performed the activity or the quality of that work.

[darhymes]

Your post brought a smile to my face. I thought my 170 was the slowest around. It gets around 108 mph true…and the plane is even painted RED!

My plan is to check rigging and maybe eventually remove the venturis. I’ve also tried meticulously cleaning and polishing the plane. Didn’t help at all with speed but the plane sure looked good.

If you find a sneaky “smoking gun” that has caused the inexplicable slowness, I’m curious to know what it is.

[cessnut]

"The FAA relies on A&Ps with IA authorizations to conduct thorough airworthiness inspections on GA aircraft annually. If nonconformity is discovered during an annual, the IA is the person with the ability and authority to identify, verify, and correct it."
This is the problem with general aviation. IAs are expected to find every non-conformity during an annual inspection and have to live in fear of lawsuit and revocation if they miss something. This is George's point. Undocumented maintenance is more heinous than illegal maintenance that is recorded, because it can be almost impossible to detect during the scope of an App. D inspection. How do you know that someone didn't slip high compression pistons in the engine? Did somebody stop drill a crack in an area you can't see?etc...How many IAs check wing twist to see if undocumented repairs were made? Granted, the more experience you have with a certain type of aircraft the easier it is to identify discrepancies, but without a record of maintenance you are at the mercy of whoever was there before you. This is one of the reasons I decline most requests for annuals, and why it's hard to find a really good IA to work with you.

[voorheesh]

I agree that failing to record maintenance is serious, especially for unsuspecting persons who may end up with an improperly modified aircraft and be totally unaware. I also don’t argue with FAA inspectors or other aviation professionals who have opinions and positions based on their years of experience. It is not uncommon to hear words of frustration. I was trying to point out that in the grand scheme of things, opinions and hidden secrets within aging aircraft have minimal impact on how the FAA regulates general aviation. In the case of unrecorded maintenance or alterations, there is very little the FAA can do. Those cases are nearly impossible to prove. At least in determining the who, what, when, where; all of which are necessary for the FAA to take any meaningful response or corrective action. So the concept, at least to me, of “more onerous” is kind of beside the point. That’s all I was saying.

Once again, the responsibilities for inspection and conformity of the GA fleet rest with IA rated technicians. They are where the rubber meets the road. This is how our system is set up. For the most part, it works very well. I wonder if there are any better ideas out there.

IA’s should be thanked every day by any of us who depend on them for the continued airworthiness of our aircraft. If some are reluctant or backing off, that is understandable and hopefully others will step in and keep the system going.

Aviation relies on the integrity of pilots and mechanics. We should all respect and meet those standards as best we can.

[GAHorn]

Your post brought a smile to my face. I thought my 170 was the slowest around. It gets around 108 mph true…and the plane is even painted RED!
…

It’s good that it’s RED!…. I’d hate to think of how slow it might be in Green!

More seriously, one of the things which perturbed me was the amount of water soaked into the carpet of my airplane discovered after a torrent while it was tied down on Dauphin Island. Jamie and I were stopping to visit her cousin on our return from the Wilmington convention and had dodged numerous thunderstorms in the southeastern U.S. that trip. We were happy to find a tie-down on that little island airport. But that night a real frog-strangler developed and when we checked on the plane next morning the carpet was like a sponge.

This prompted me to inspect the windshield-to-wing root fairing seal…. Or better said…. Lack thereof….

Water would enter that wing-root fairing and easily penetrate and follow the front doorpost downward…. funneling the water directly onto the carpet at the pilot’s seats…which in the tie-down position…. then ran aft, soaking the rest of the carpet.

When I got it home I removed all the seats and carpet to dry it out…. then I opened up the wing-root fairing and saw how little “seal” exists in that area.
The solution I chose was to use high-quality duct-tape to seal the windshield-to-wing-root and above the cabin, sealing the gap/area beneath that root-fairing …(leaving the lower wing-surface-to-cabin open.) This has performed as intended, keeping water out of the cabin…. and a side-benefit of reduced drag…. I believe, because the cabin became less noisy and breezy in-flight.

Every little bit helps. Just sayin’…..

[ArcticCowboy]

…

Also… considering that your airplane is being compared IN FLIGHT and ALONGSIDE similar models…. the actual difference in obtained speed can be believable. What might be UN-believable…. is the accuracy of your friend’s instrumentation. They MAY be seeing 2450 RPM on their tachometers….but MAY ACTUALLY be running somewhat higher RPM….therefore producing more power. (But frankly that is a low probability due to that Drag vs Velocity law…. they’d have to produce Considerably More power to overcome the increase drag…but the “perception” of greater speed can be misleading during formation flights. The average person during a “brisk” walk…only makes about 3 mph. Are your friends airplanes making more speed than your airplane comparable to a “brisk walk”…?? If so…. it means that a 3-1/2 hour flight ..(the practical fuel-flight-time of these airplanes with reserve) …would result in an eleven mile difference in that timeframe. Your “slower” airplane would take only 4 minutes longer over the entire fuel-range of the airplane. How much money do you wish to throw at this..??

FINALLY… if you REALLY want to make a difference…. a RED PAINT JOB will cost you about $10K. Is Four Minutes worth $10K..?

(sorry…couldn’t resist)

Since I’m time building it’s definitely not

Lots of variables to consider, but good way to help me learn the system. Thanks for the insight.