Supercub Thrust Line
- Thread starter skukum12
- Start date
AkPA/18
MEMBER
Big Lake Ak
Bob
If you look at my replies I have not called you any names--said you were lousy pilot or any of that. My contention frankly is that your data is meaningless due to multiple factors. When I posted your data I thought I was posting something that clearly showed that the TL does not enhance TO on 88RF. After reading your data---I can't clearly see that. You say your data clearly shows takeoff roll differences. I can't see anything clear in your data.
A: I assume you were testing for TO performance. Does this mean the shortest TO roll?
B: Why the lack of performance TO's IFyou were testing for shortest TO roll?
C: Do you feel that testing in winds 10kts gusting 20kts are valid conditions for testing?
No name calling here---just looking for some real simple answers to the above simple questions.
Mark
If you look at my replies I have not called you any names--said you were lousy pilot or any of that. My contention frankly is that your data is meaningless due to multiple factors. When I posted your data I thought I was posting something that clearly showed that the TL does not enhance TO on 88RF. After reading your data---I can't clearly see that. You say your data clearly shows takeoff roll differences. I can't see anything clear in your data.
A: I assume you were testing for TO performance. Does this mean the shortest TO roll?
B: Why the lack of performance TO's IFyou were testing for shortest TO roll?
C: Do you feel that testing in winds 10kts gusting 20kts are valid conditions for testing?
No name calling here---just looking for some real simple answers to the above simple questions.
Mark
AkPA/18
MEMBER
Big Lake Ak
Bob
Here is a look at some of your data.
No repeatability----what was the purpose of the Tail high no flap TO? What was the purpose of the carb heat on TO? What was the purpose of 3 point full flap at lift off TO. You used NONE of these takeoffs during your thrustline tests. How can you possibly consider that data valid?
You also show that full flaps hurt your TO run by 30 ft over no flaps and two notches were better than no flaps by 50 ft. Next round of testing show flaps make no difference at all----see below.
Further data shows that 2 notches of flaps was 10 ft worse than no flaps but a full 120better than the next no flap TO. See below
No repeatability---no consistency. How can this be valid data.
Your most consistent results occurred for whatever reason after you tested the TL modified aircraft. Although there were only three TO's with flaps---including a previously untried TO technique---Tail high flaps 2----These flap TO's all produced better results than your no flap TO's. See below
In my opinion this is not data that is meaningful and this is not a well designed test. It shows clearly in the results that are all over the place.
SamSam---I want to apologize to you if I offended you earlier by using your post from the J3-cub forum. It was not my intent to offend----I just wanted to let the readers know that there was at least one reader that was considering Bob's data as "hard and verifiable data". I don't feel it is either.
Mark
Here is a look at some of your data.
No repeatability----what was the purpose of the Tail high no flap TO? What was the purpose of the carb heat on TO? What was the purpose of 3 point full flap at lift off TO. You used NONE of these takeoffs during your thrustline tests. How can you possibly consider that data valid?
You also show that full flaps hurt your TO run by 30 ft over no flaps and two notches were better than no flaps by 50 ft. Next round of testing show flaps make no difference at all----see below.
Further data shows that 2 notches of flaps was 10 ft worse than no flaps but a full 120better than the next no flap TO. See below
No repeatability---no consistency. How can this be valid data.
Your most consistent results occurred for whatever reason after you tested the TL modified aircraft. Although there were only three TO's with flaps---including a previously untried TO technique---Tail high flaps 2----These flap TO's all produced better results than your no flap TO's. See below
In my opinion this is not data that is meaningful and this is not a well designed test. It shows clearly in the results that are all over the place.
SamSam---I want to apologize to you if I offended you earlier by using your post from the J3-cub forum. It was not my intent to offend----I just wanted to let the readers know that there was at least one reader that was considering Bob's data as "hard and verifiable data". I don't feel it is either.
Mark
T.J.
Registered User
Alaska
The Devil made me do it!
Bob:
I just read your recent post. I've got a couple more questions and a couple comments.
First, you said, "...afraid to post anything negative here." You were of course just joshing us, weren't you? If not, Your wrong buddy. I'm a grouchy old fart. You ever see an old dog with a sore butt? Grouchy ain't he? That's me. I don't have a sore butt, I had my roids fixed a few years ago. I was born grouchy and never got over it. I did however, find a good therapy school in San Francisco who is willing to help me get over my problems.
If anyone post BS on here, I'm one of the first ones to call foul, and post "negative" about it.
Now we get to the nice part. This is an honest question.
You said...."For takeoff, the thrust in a Supercub was already pulling up about four to six degrees and we simply increase that to eight to ten. That reduced the thrust in the direction the aircraft is going".
Could you splain to me how the thrust on takeoff is 4-6 degrees up? Perhaps in a 3 point take off? What's the takeoff angle of the fuselage with the tailwheel on the ground? What's the height of the gear? What size tires?
How would that reduce the thrust in the direction the aircraft is going? Its going up. isn't it?
Old guys in Alaska have been adding washers between the lower engine mount/firewall for years. Wonder why? If it didn't work, they wouldn't do it.
Trying to not be an old Grouch, just trying to learn from the older guys here.
Pretty hard to argue with success.
Bob:
I just read your recent post. I've got a couple more questions and a couple comments.
First, you said, "...afraid to post anything negative here." You were of course just joshing us, weren't you? If not, Your wrong buddy. I'm a grouchy old fart. You ever see an old dog with a sore butt? Grouchy ain't he? That's me. I don't have a sore butt, I had my roids fixed a few years ago. I was born grouchy and never got over it. I did however, find a good therapy school in San Francisco who is willing to help me get over my problems.
If anyone post BS on here, I'm one of the first ones to call foul, and post "negative" about it.
Now we get to the nice part. This is an honest question.
You said...."For takeoff, the thrust in a Supercub was already pulling up about four to six degrees and we simply increase that to eight to ten. That reduced the thrust in the direction the aircraft is going".
Could you splain to me how the thrust on takeoff is 4-6 degrees up? Perhaps in a 3 point take off? What's the takeoff angle of the fuselage with the tailwheel on the ground? What's the height of the gear? What size tires?
How would that reduce the thrust in the direction the aircraft is going? Its going up. isn't it?
Old guys in Alaska have been adding washers between the lower engine mount/firewall for years. Wonder why? If it didn't work, they wouldn't do it.
Trying to not be an old Grouch, just trying to learn from the older guys here.
Pretty hard to argue with success.
S2D
MEMBER
Montana
bob turner said:
First Bob, I went back thru my posts and I can't find where I called you any name. if I did and missed it, I apologize.
Second you keep saying that Mark Drath posted the only valid data. If you go a few posts before him, I posted Data that was almost identical to his.
S2D said:
18% is a hell of a lot better than the 6.7% the HP increase should gain you
third you accept the premise that the borer prop and 10 hp increase will get you off faster without any data to back it up, just because your slide rule says it should, but you call Marks thrustline Mod a POS because your slide rule doesn't calculate and justify this with data that a first grader would recoginze as crap
The big problem Bob is we don't have the luxury of keeping our airplane light. We can start out with a light aircraft, but by the time we load it with fuel, people, necessary gear etc we are heavy. and we need mods that will increase our performance over the whole range including over gross at times. the thrustline mod is one that increases performance without increasing the EW of the aircraft, and does it quite well for those that not only have a need, but know how to use it.
bob turner
Registered User
S2D - that was a reasoned reply. Let me see your actual numbers - trials, weights, techniques, weather, and then we can compare.
Mark - I gathered that information just so folks could go through it as you did, and draw conclusions. You will note of course that you cannot do that with any other data so far posted.
I did get the feeling that I was being beat up on, but as far as I can tell you have been a gentleman about this stuff. From everything I have read here, as soon as you get someone to do before and after tests in zero wind with titrated fuel loads, you will have data that is better than mine. My data is better than no data, and just drawing conclusions without stating the parameters is no data.
I think that flaps shorten takeoff rolls - I think my data proves that. I think if you want to advocate a particular technique for shortest take off rolls, you need to get some data - not only on your favored technique, but on all others. That's why I started my data thread. I have numbers - I would love to see some other numbers.
Mark - I gathered that information just so folks could go through it as you did, and draw conclusions. You will note of course that you cannot do that with any other data so far posted.
I did get the feeling that I was being beat up on, but as far as I can tell you have been a gentleman about this stuff. From everything I have read here, as soon as you get someone to do before and after tests in zero wind with titrated fuel loads, you will have data that is better than mine. My data is better than no data, and just drawing conclusions without stating the parameters is no data.
I think that flaps shorten takeoff rolls - I think my data proves that. I think if you want to advocate a particular technique for shortest take off rolls, you need to get some data - not only on your favored technique, but on all others. That's why I started my data thread. I have numbers - I would love to see some other numbers.
bob turner
Registered User
And a question for TJ - what is the optimum angle of attack for liftoff in the shortest distance? My guess is about 13 degrees, but that is strictly a guess. The direction the aircraft is going is not the same as the angle of attack, by definition.
We have a wing with 2 degrees angle of incidence (1.8 at aircraft c/l). We have wash-in that is supposed to be 2.6 degrees less than that. If the engine is pointed down with respect to the x-axis by four degrees, and if the angle of attack at liftoff is 13 degrees, averaged somewhere in the middle of the wing (I again do not know what that number really is), then the engine is pulling up with respect to the flight path of somewhere near eight degrees. Put thrustline in there and the up-thrust is obviously four degrees more. If up-thrust is better than thrust in the desired direction of motion, why not pitch it up more? (sorry - I am repeating myself - not a good sign for an old guy)
We have a wing with 2 degrees angle of incidence (1.8 at aircraft c/l). We have wash-in that is supposed to be 2.6 degrees less than that. If the engine is pointed down with respect to the x-axis by four degrees, and if the angle of attack at liftoff is 13 degrees, averaged somewhere in the middle of the wing (I again do not know what that number really is), then the engine is pulling up with respect to the flight path of somewhere near eight degrees. Put thrustline in there and the up-thrust is obviously four degrees more. If up-thrust is better than thrust in the desired direction of motion, why not pitch it up more? (sorry - I am repeating myself - not a good sign for an old guy)
http://www.youtube.com/watch?v=bCFc74W9_ek
Here's a video I made last year, I was just getting to use to the thrustline at that point, I can get the plane off with 1/2 fuel anywhere from 75 to 100 feet, good enough for me! Some people like some people don't.I like Mine
Here's a video I made last year, I was just getting to use to the thrustline at that point, I can get the plane off with 1/2 fuel anywhere from 75 to 100 feet, good enough for me! Some people like some people don't.I like Mine
Dave Calkins
Registered User
Anchorage, Alaska
bob turner said:
you mean 'washout'
We knew what you meant.
Gordon Misch
MEMBER
Toledo, Wa (KTDO)
Ok, here I go again - I never can seem to resist getting into these technical discussions!
First, re the data - sure, there is some posted, but it's incomplete and lacks adequate controls, so it's far from conclusive. I think everybody agrees with that.
Bob, re the up and down angles of the thrust line affecting thrust in the direction of flight: Keep in mind that the component of thrust in the direction of travel varies as the cosine of the angle measured between thrust and direction of travel. Let's play with a variation of 4 degrees. The cosine of 4 degrees is .998. That means the forward component of thrust is greater than .998 times the total thrust for any angle between -4 and +4 degrees. If total thrust is 500 lb, that is a maximum variation of 1 lb.
On the other hand, the component of thrust perpendicular to the direction of travel, call it the vertical direction, varies as the sine of the same angle. The sine of 4 degrees is .070. That means varying the thrust angle between -4 and +4 degrees varies the vertical component of thrust from -.07 to +.07 times the total thrust. For 500 lb of total thrust, that is a variation in the vertical component of plus or minus 35 lb.
So the vertical component of thrust is very sensitive (approximately linear) to thrust angle, while the horizontal (flight path) component is essentially unaffected by the small angles we're dealing with.
So what is the plane's reaction to changes in vertical thrust component? The vertical component is being applied to the airframe at the propeller, some distance ahead of the center of lift on the wing. If the thrust is pointed down, that will tend to pitch the airframe down. To keep the airplane at the desired pitch angle, the tail will have to also push down to balance the downward thrust of the prop - to balance the moment. So there is a down force from thrust, and a down force from the tail. To maintain a flight path, the wing must create more lift, equal to the two down forces. The increased tail and wing angles of attack make more drag. Also if the wing is near its max angle of attack, it doesn't have anything left for more lift, so maximum available lift is reduced by the downward forces at prop and tail.
Now point the thrust angle up a little, and the opposite effect is realized. Less down thrust, which means less down tail force, which means less angle of attack required for level flight, which means reduced drag, and more angle of attack available for climb.
So - there's a simplified analysis that I'm sure is correct, but I'm equally sure it's incomplete. Bob, I'm interpreting what you wrote as expecting that the forward thrust would be adversely affected by engine angle. Assuming the relatively small angles we're dealing with here, that is incorrect, as shown by the above analysis of summing static pitching moments. If I misinterpreted what you wrote, I apologize.
The insensitivity of forward thrust to engine angle is why Piper could tilt the engine down 4 deg (is that the correct number??) without SERIOUSLY degrading the plane's performance. I'm guessing that the downward angle was a comfort / ease of control compromise for the target market. I'm thinking the downward engine angle probably reduces the change in pitching moment as power is varied, by directing the thrust line closer to the center of drag (ease of control). That's just a guess. And of course there's the visibility factor (comfort).
Somebody MUST have done some controlled testing of this mod (Mark?), but maybe that data is proprietary?
[/i]
First, re the data - sure, there is some posted, but it's incomplete and lacks adequate controls, so it's far from conclusive. I think everybody agrees with that.
Bob, re the up and down angles of the thrust line affecting thrust in the direction of flight: Keep in mind that the component of thrust in the direction of travel varies as the cosine of the angle measured between thrust and direction of travel. Let's play with a variation of 4 degrees. The cosine of 4 degrees is .998. That means the forward component of thrust is greater than .998 times the total thrust for any angle between -4 and +4 degrees. If total thrust is 500 lb, that is a maximum variation of 1 lb.
On the other hand, the component of thrust perpendicular to the direction of travel, call it the vertical direction, varies as the sine of the same angle. The sine of 4 degrees is .070. That means varying the thrust angle between -4 and +4 degrees varies the vertical component of thrust from -.07 to +.07 times the total thrust. For 500 lb of total thrust, that is a variation in the vertical component of plus or minus 35 lb.
So the vertical component of thrust is very sensitive (approximately linear) to thrust angle, while the horizontal (flight path) component is essentially unaffected by the small angles we're dealing with.
So what is the plane's reaction to changes in vertical thrust component? The vertical component is being applied to the airframe at the propeller, some distance ahead of the center of lift on the wing. If the thrust is pointed down, that will tend to pitch the airframe down. To keep the airplane at the desired pitch angle, the tail will have to also push down to balance the downward thrust of the prop - to balance the moment. So there is a down force from thrust, and a down force from the tail. To maintain a flight path, the wing must create more lift, equal to the two down forces. The increased tail and wing angles of attack make more drag. Also if the wing is near its max angle of attack, it doesn't have anything left for more lift, so maximum available lift is reduced by the downward forces at prop and tail.
Now point the thrust angle up a little, and the opposite effect is realized. Less down thrust, which means less down tail force, which means less angle of attack required for level flight, which means reduced drag, and more angle of attack available for climb.
So - there's a simplified analysis that I'm sure is correct, but I'm equally sure it's incomplete. Bob, I'm interpreting what you wrote as expecting that the forward thrust would be adversely affected by engine angle. Assuming the relatively small angles we're dealing with here, that is incorrect, as shown by the above analysis of summing static pitching moments. If I misinterpreted what you wrote, I apologize.
The insensitivity of forward thrust to engine angle is why Piper could tilt the engine down 4 deg (is that the correct number??) without SERIOUSLY degrading the plane's performance. I'm guessing that the downward angle was a comfort / ease of control compromise for the target market. I'm thinking the downward engine angle probably reduces the change in pitching moment as power is varied, by directing the thrust line closer to the center of drag (ease of control). That's just a guess. And of course there's the visibility factor (comfort).
Somebody MUST have done some controlled testing of this mod (Mark?), but maybe that data is proprietary?
[/i]
sj
Staff member
Northwest Arkansas
Hooooollllly CATS! I have been so fat dumb and happy with my Thrustline mod that I have not bothered to even read the Thrustline thread of late.
Golly have I been missing out! I don't have a television anymore and this thread provides hours of entertainment, it's part documentary, part humor, part intrigue, part self-help, some mystery, and certainly part sitcom. Will the forces of evil win? Will Lassie be able to save Timmy? Can Flipper wriggle out of the old fishing net? There is even a culinary angle with the $100 burgers. Emeril would be proud!
I do want to thank all of you for conducting yourselves in a mostly civilized manner
. There are a few unnecessary peanut gallery potshots, but everyone does seem to be working toward understanding, which I like to see.
If I could wish for one thing as a result of this thread, is that other manufacturers could see the value of openly supporting and debating their products in this fashion. I feel like Mark has really conducted himself in a manner attempting to educate and understand in this thread, I would like to see other manufacturers do the same - because I believe we all benefit.
Now let me correct a couple data points. There are not 10,000 different computers a month reading this site, there are over 20,000 bot-free unique visitors. It peaks out in the winter months at over 30,000 per month.
Finally, some of the greatest pilots, and smartest minds of the cub world have weighed in on this thread. It is a sincere privilege for me to be in some way associated with you all, and to read your commentaries
thanks everybody, and thank you Mark Englerth for setting an example for others.
sj
Golly have I been missing out! I don't have a television anymore and this thread provides hours of entertainment, it's part documentary, part humor, part intrigue, part self-help, some mystery, and certainly part sitcom. Will the forces of evil win? Will Lassie be able to save Timmy? Can Flipper wriggle out of the old fishing net? There is even a culinary angle with the $100 burgers. Emeril would be proud!
I do want to thank all of you for conducting yourselves in a mostly civilized manner
. There are a few unnecessary peanut gallery potshots, but everyone does seem to be working toward understanding, which I like to see. If I could wish for one thing as a result of this thread, is that other manufacturers could see the value of openly supporting and debating their products in this fashion. I feel like Mark has really conducted himself in a manner attempting to educate and understand in this thread, I would like to see other manufacturers do the same - because I believe we all benefit.
Now let me correct a couple data points. There are not 10,000 different computers a month reading this site, there are over 20,000 bot-free unique visitors. It peaks out in the winter months at over 30,000 per month.
Finally, some of the greatest pilots, and smartest minds of the cub world have weighed in on this thread. It is a sincere privilege for me to be in some way associated with you all, and to read your commentaries
thanks everybody, and thank you Mark Englerth for setting an example for others.
sj
aktango58
FRIEND
18AA
hhhmmmmmmmmm,
Steve, does that mean that we can get a better hot dog rating for less $ if all them 30,000 send you a buck?
Test Data:
science, (If I am remembering from my lectures years ago) is the ability to concistently repeat a test with the same results, (allowing for some variables).
for thrust line, it would mean to show some change in performance by doing the same manuver multiple times, showing the same results, with and without the mod.
Most planes will fly different from each other. Are there any two that do fly exactly the same? (anyone of you guys with two cubs want to help here?)
So to do this test for accurate results one would have to demonstrate a particular manuver multiple times with and without; or a series of manuvers with and without the TL. It will be most accurate if you keep your fuel, load, wind, density etc. the same for tests with and without.
So Bob, testing in gusty winds is a waste of time, because your data will not allow for the consistency needed for accurate tests; yet what ever configuration/tecnique you choose is ok, as long as you use it for both with and without. Also, using different planes/pilots will also nullify the test because each have their different abilities so will skew the results.
You can not compare a takeoff in 10 kts of wind with one in calm winds, nor can you compare a zero flap takeoff with a 20 degree flap takeoff.
Bob brings up a good point, does the TL mod work in all of these other takeoff configurations?
How does this mod work heavy compared to light?
I posted over a year ago when I put the mod on. no, sorry, I did not get hard data; I could not get anyone to stay out on the water long enough to measure multiple takeoffs on floats.
So I must return to my "religious" fervor, "arm waving" and other such actions to talk about the mod. I did not get much wheel time on this cub before the TL either, and I don't have the $ to take it off for more testing.
So here is some info:
First, if you do not fly the plane by feel, you won't know the difference in the TL, or VG's for that matter. Most of the gains in these have to do with how the plane feels in the edge, (square corner area???)
YOU may not notice a difference, but I do, and it is not just hocus pocus belief, it is rock clearing, willow jumping, not stalling on the edge fact.
The one area where a novice can see the difference on the TL is cruise speed. I picked up about 6 miles per hour. Lots for a float cub. Wheels I saw about the same percent increase. (this one is a matter of math, check before and after speeds, devide, ola )
Now for my cigar smoking, ( I don't smoke), beer drinking, (only a little), arm waving, (lots) pontification of an uneducated, two left footed, club handed hack that makes his living running machinery in tight spaces and flying a HEAVILY loaded cub at low levels counting fish:
I cut about three seconds off of the time getting to the step with the TL, I dropped a second or two on step, and when I break out of the water I can climb immediatly. (public use aircraft, light cub on EDO's, two 220 lb people with 54 gal. fuel and 20 lbs of gear)
When I am light, I don't really care, a light cub tends to jump out anyway, it is only when I have my hunting partner, his gear, my gear, two deer and a lake too small for water skiing that I ask myself will it?
On wheels, she lifts off, accelerates and climbs in one motion. No more of this hovering forever getting speed to climb.
When I put the mod on I did not tell the passenger, (he had about 175 hours sitting behind me in this plane) and he made a comment about how quickly we departed the harbor the first day with no wind. Yes, the TL was that noticable.
So Bob, I hear you on the engineering, it does not make complete sense. But that becomes part of the beauty of this mod, someone somewhere was smoking somthing good
and says "hey, what if we point the engine thataway??".
Mark may not have come up whith the original, but he put the effort into making it available to all of us (except TJ you lucky guy); and when he talks to us, he admits it is not for every cub.
(if you are still reading this you are a dedicated cub guy!)
Steve, does that mean that we can get a better hot dog rating for less $ if all them 30,000 send you a buck?
Test Data:
science, (If I am remembering from my lectures years ago) is the ability to concistently repeat a test with the same results, (allowing for some variables).
for thrust line, it would mean to show some change in performance by doing the same manuver multiple times, showing the same results, with and without the mod.
Most planes will fly different from each other. Are there any two that do fly exactly the same? (anyone of you guys with two cubs want to help here?)
So to do this test for accurate results one would have to demonstrate a particular manuver multiple times with and without; or a series of manuvers with and without the TL. It will be most accurate if you keep your fuel, load, wind, density etc. the same for tests with and without.
So Bob, testing in gusty winds is a waste of time, because your data will not allow for the consistency needed for accurate tests; yet what ever configuration/tecnique you choose is ok, as long as you use it for both with and without. Also, using different planes/pilots will also nullify the test because each have their different abilities so will skew the results.
You can not compare a takeoff in 10 kts of wind with one in calm winds, nor can you compare a zero flap takeoff with a 20 degree flap takeoff.
Bob brings up a good point, does the TL mod work in all of these other takeoff configurations?
How does this mod work heavy compared to light?
I posted over a year ago when I put the mod on. no, sorry, I did not get hard data; I could not get anyone to stay out on the water long enough to measure multiple takeoffs on floats.
So I must return to my "religious" fervor, "arm waving" and other such actions to talk about the mod. I did not get much wheel time on this cub before the TL either, and I don't have the $ to take it off for more testing.
So here is some info:
First, if you do not fly the plane by feel, you won't know the difference in the TL, or VG's for that matter. Most of the gains in these have to do with how the plane feels in the edge, (square corner area???)
YOU may not notice a difference, but I do, and it is not just hocus pocus belief, it is rock clearing, willow jumping, not stalling on the edge fact.The one area where a novice can see the difference on the TL is cruise speed. I picked up about 6 miles per hour. Lots for a float cub. Wheels I saw about the same percent increase. (this one is a matter of math, check before and after speeds, devide, ola
)Now for my cigar smoking, ( I don't smoke), beer drinking, (only a little), arm waving, (lots) pontification of an uneducated, two left footed, club handed hack that makes his living running machinery in tight spaces and flying a HEAVILY loaded cub at low levels counting fish:
I cut about three seconds off of the time getting to the step with the TL, I dropped a second or two on step, and when I break out of the water I can climb immediatly. (public use aircraft, light cub on EDO's, two 220 lb people with 54 gal. fuel and 20 lbs of gear)
When I am light, I don't really care, a light cub tends to jump out anyway, it is only when I have my hunting partner, his gear, my gear, two deer and a lake too small for water skiing that I ask myself will it?
On wheels, she lifts off, accelerates and climbs in one motion. No more of this hovering forever getting speed to climb.
When I put the mod on I did not tell the passenger, (he had about 175 hours sitting behind me in this plane) and he made a comment about how quickly we departed the harbor the first day with no wind. Yes, the TL was that noticable.
So Bob, I hear you on the engineering, it does not make complete sense. But that becomes part of the beauty of this mod, someone somewhere was smoking somthing good
and says "hey, what if we point the engine thataway??".Mark may not have come up whith the original, but he put the effort into making it available to all of us (except TJ you lucky guy); and when he talks to us, he admits it is not for every cub.
(if you are still reading this you are a dedicated cub guy!)
bob turner
Registered User
I could not agree more with the last several posts. In fact, I have previously agreed with these things. It is indeed the vertical component of thrust that gets big in a hurry, at only a .003 expense of the horizontal thrust.
My point is, and has been, that testing is good. Rigorous testing is better, and no testing is of no use at all. There is no test for "feel". When I bought my Cub, I bought it for "looks", and there is no test for that, either.
My only tests with numbers are for takeoff roll. No wind around here is at 6 AM, and I am never awake enough at that hour. The way I get around such variables is more data. You cannot make one trial before, and one trial after, and get meaningful data. However, you can do a hundred in all kinds of winds and loads, and get fairly precise data.
My original tests were not for Thrustline. They were to determine if raising the tail on takeoff was of any significant benefit. I was also checking to see if delaying flap extension was of significance. My answer to both, to my satisfaction, was no. Your answer is vastly different, but I have seen no evidence of your having tested these things. When I say "you" I do not mean anybody in particular - just my fellow participants. ThrustLine arrived suddenly - had I not done the pre -tests for other reasons, I would have had no data.
Using data from contests is worse than just doing one trial. It is one trial with different aircraft, different pilots, and different wind. Contests are fun, not scientific data-taking. My trials are fun, as well, and not highly scientific. They are only an indication. As far as I can tell, Jim C and I are the only folks hereabouts who are willing to share individual tests with associated parameters. Conclusions mean nothing without preserved original data. You may look at this as opinion, but I submit that it will survive analysis by flight test departments.
My point is, and has been, that testing is good. Rigorous testing is better, and no testing is of no use at all. There is no test for "feel". When I bought my Cub, I bought it for "looks", and there is no test for that, either.
My only tests with numbers are for takeoff roll. No wind around here is at 6 AM, and I am never awake enough at that hour. The way I get around such variables is more data. You cannot make one trial before, and one trial after, and get meaningful data. However, you can do a hundred in all kinds of winds and loads, and get fairly precise data.
My original tests were not for Thrustline. They were to determine if raising the tail on takeoff was of any significant benefit. I was also checking to see if delaying flap extension was of significance. My answer to both, to my satisfaction, was no. Your answer is vastly different, but I have seen no evidence of your having tested these things. When I say "you" I do not mean anybody in particular - just my fellow participants. ThrustLine arrived suddenly - had I not done the pre -tests for other reasons, I would have had no data.
Using data from contests is worse than just doing one trial. It is one trial with different aircraft, different pilots, and different wind. Contests are fun, not scientific data-taking. My trials are fun, as well, and not highly scientific. They are only an indication. As far as I can tell, Jim C and I are the only folks hereabouts who are willing to share individual tests with associated parameters. Conclusions mean nothing without preserved original data. You may look at this as opinion, but I submit that it will survive analysis by flight test departments.
aktango58
FRIEND
18AA
Mark,
Any chance you can send me a set of original engine lugs? Maybe I can get Bob to come up, and I will do some test landings and takeoffs on wheels here, then put the old stuff on and do it again, then put the TL back.
might as well get this discussion over with.
Bob, the seconds I mentioned on floats are data. Think about how far a plane travels at 20, and 40, and how four seconds makes a difference.
"Feel may not be a scientific measurable unit, however, when feel equates to slowing down the approach three miles an hour, and feeling more comfortable in gusty winds, it becomes more important than the hard data you are looking for.
Again, if you are not flying the plane by "feel", you are not getting performance out of the cub. When your landing spot has two plane length to spare, "feel" morphs into shorter landing distance, and better control to achieve higher safety.
Now we should think about one other point, Mark has said it is not a Takeoff mod as much as a control/landing mod. I gained speed which pays for the mod, it is nice to get the benifits of shorter landings, takeoffs and steeper climbs, but is that why I bought it, NO.
Bob, your data would not "survive analysis by flight test departments". In fact, flight tests would not be done in the conditions you described except for handling characteristics which you say can not be measured.
Flight tests would be done at 6:00 with calm winds, so accuracy and consistency would be available, and the safety element of a "test flight" would not be jeprodized by a gust causing a low level out of control mishap.
Any chance you can send me a set of original engine lugs? Maybe I can get Bob to come up, and I will do some test landings and takeoffs on wheels here, then put the old stuff on and do it again, then put the TL back.
might as well get this discussion over with.
Bob, the seconds I mentioned on floats are data. Think about how far a plane travels at 20, and 40, and how four seconds makes a difference.
"Feel may not be a scientific measurable unit, however, when feel equates to slowing down the approach three miles an hour, and feeling more comfortable in gusty winds, it becomes more important than the hard data you are looking for.
Again, if you are not flying the plane by "feel", you are not getting performance out of the cub. When your landing spot has two plane length to spare, "feel" morphs into shorter landing distance, and better control to achieve higher safety.
Now we should think about one other point, Mark has said it is not a Takeoff mod as much as a control/landing mod. I gained speed which pays for the mod, it is nice to get the benifits of shorter landings, takeoffs and steeper climbs, but is that why I bought it, NO.
Bob, your data would not "survive analysis by flight test departments". In fact, flight tests would not be done in the conditions you described except for handling characteristics which you say can not be measured.
Flight tests would be done at 6:00 with calm winds, so accuracy and consistency would be available, and the safety element of a "test flight" would not be jeprodized by a gust causing a low level out of control mishap.
AkPA/18
MEMBER
Big Lake Ak
Bob
(I hope some of you actually take the time to read below---but won't blame you if you don't)
I happen to read SC.org often and I had to sit through a month of you talking about Thrustline testing before and after. I have this data---12 data points--baseline data--my testing emphatically shows---opinion backed with numbers etc....etc... I asked three different people if they thought you were sounding like a pretty good tester. Unanimously they agreed you were sounding like you really had some good test data. So I had to watch all this damage to our product take place when you emphatically showed the TL did not help TO performance with your DATA. That is when I started posting because I know after all this time that you are flat out wrong. Then without getting any direct answers to my pointed simple questions---I have to read this today:
Below are highlights of what I had to sit and watch for a month before this definitive DATA was posted. Chronological order.
(I hope some of you actually take the time to read below---but won't blame you if you don't)
I happen to read SC.org often and I had to sit through a month of you talking about Thrustline testing before and after. I have this data---12 data points--baseline data--my testing emphatically shows---opinion backed with numbers etc....etc... I asked three different people if they thought you were sounding like a pretty good tester. Unanimously they agreed you were sounding like you really had some good test data. So I had to watch all this damage to our product take place when you emphatically showed the TL did not help TO performance with your DATA. That is when I started posting because I know after all this time that you are flat out wrong. Then without getting any direct answers to my pointed simple questions---I have to read this today:
Absolutely UNBELIEVABLE!. YOU WERE NOT EVEN TESTING FOR THRUSTLINE DATA????????? But yet you write that " Alas. my data seems to indicate a decrease in takeoff performance"
Below are highlights of what I had to sit and watch for a month before this definitive DATA was posted. Chronological order.
Takes time.
Steve Pierce
BENEFACTOR
Graham, TX
Mark, How many people have taken the Thrustline Mod off?
I don't have cub in this fight.
I will however thank Mark for being the most courteous at last years Alaska Trade Show. Mark kindly offered "THE" expecting mother I was traveling with a spot to rest/relax. Not wise, but generous 8).
That alone was the single best sales pitch ever.
Thanks,
Mike
I will however thank Mark for being the most courteous at last years Alaska Trade Show. Mark kindly offered "THE" expecting mother I was traveling with a spot to rest/relax. Not wise, but generous 8).
That alone was the single best sales pitch ever.
Thanks,
Mike
Gordon Misch
MEMBER
Toledo, Wa (KTDO)
No, you cannot. You would only get 100 anecdotes.
Well, "precise", sure - but accurate and meaningful, no way. My 9th grade science students know the difference between 'accurate' and 'precise', and they know that 'precise' can be highly misleading. Furthermore, to pass the Washington Assessment of Student Learning, 10th graders must be able to design investigations that properly control for variables not being explicitly tested, and to provide for measures that ensure experimental validity.
I am dismayed when I read assertions that a unorganized and uncontrolled assortment of measurements constitutes 'data', especially when written using a smattering of engineering jargon which tends to lend an aura of authenticity and veracity - deserved or not. Such assertions make me doubly glad that the Washington Legislature expects ALL of its young citizens to acquire and demonstrate a practical understanding of the elements of meaningful inquiry and investigation. I'm confident that my 14 year old students could produce correct critiques that would debunk purported meaningful interpretation of the 'data' offered above. Wind, air density, a/c weight, a/c balance, and flight profile are not controlled or accounted for. And I haven't even tried to think of all the variables that should be controlled, so there's gotta be more.
I recently read an editorial in Scientific American that criticized someone's work as being so scientifically improper, so bad, that "it isn't even wrong" - the implication being that it was simply meaningless.
S2D
MEMBER
Montana
bob turner said:
Bob
go back and look at my post. It gives my load configuration, temp, wind, type runway surface, technique, etc. .
aktango58 said:
I think that is the best assessment yet of why you not only can't do an accurate test, you can't tell the difference in performance.
I officially give up. There is an old saying that you can't argue with a fence post. I just hope I wasn't the one that turned to wood.
Thrustline
Here's one that didn't work and came off.
After giving Mark the measurements and describing the engine prop combination he said it probably will not work. But I went ahead anyway and sure enough Mark was right, I couldn't detect any improvement.
For the before and after tests I couldn't reliably duplicate takeoff performance so opted for climb vs speed, IAS vs power setting (3 power settings) and slowest possible touchdown speed. Same pilot, same fuel load, temps and wind very close, almost calm.
With repeated before and after tests the results were very consistent, virtually no change. Reluctantly I took the kit off, repeated the tests and got the same results.
So the bottom line for me is this: If Mark was confident that it wouldn't work, and it didn't, then I'd have to believe it would work if he says it will.
And for customer service, now that's another Gold Medal Performance.
Now here's a shameless plug, if you want a helluva engine with the same kind of service give Bart LaLonde a call.
Brian T
Here's one that didn't work and came off.
After giving Mark the measurements and describing the engine prop combination he said it probably will not work. But I went ahead anyway and sure enough Mark was right, I couldn't detect any improvement.
For the before and after tests I couldn't reliably duplicate takeoff performance so opted for climb vs speed, IAS vs power setting (3 power settings) and slowest possible touchdown speed. Same pilot, same fuel load, temps and wind very close, almost calm.
With repeated before and after tests the results were very consistent, virtually no change. Reluctantly I took the kit off, repeated the tests and got the same results.
So the bottom line for me is this: If Mark was confident that it wouldn't work, and it didn't, then I'd have to believe it would work if he says it will.
And for customer service, now that's another Gold Medal Performance.
Now here's a shameless plug, if you want a helluva engine with the same kind of service give Bart LaLonde a call.
Brian T
bob turner
Registered User
You guys make me feel like I should be defending myself. Remember, I said I cannot feel anything in an airplane - I was indeed an airline driver who didn't know anything except the book speeds. I did say it will be a cold day in hell when I land on one of those short rock-filled sandbars. And I gave you all the parameters of my tests, so you could see exactly what I did. I made no claim of using ninth grade science project accuracies; indeed I stated that I had no confidence in less than +/- ten feet.
I am not sure why it is necessary to beat me up. All the things you are beating me up about I have admitted beforehand. The right way to beat me up is by presenting data that refutes mine. Just stating that you are always airborne in less than a hundred feet is not particularly convincing - and telling me that detailed data is posted elsewhere is not helpful unless you tell me where. I went through this thread, and so far I haven't seen any specific trials posted, except for the ones I posted.
Sure, my data is suspect. I expected a couple percent improvement - I too thought that pointing the thrust up slightly ought to yield a slight improvement in takeoff roll. I have drawn only one conclusion from all of this - that is, if somebody says something you do not like, hold him or her in some gentle form of contempt. No real point in countering with any factual data.
You may find my skills as a Cub pilot not up to your standards - you are all welcome to come down here and fly with me in my aircraft. That way you can determiine my skill level by my flying, as opposed to my sub-ninth grade grasp of engineering terms. And as a bonus, I get to see you fly. Maybe I can learn how to consistently cut my takeoff rolls in half, just by changing my technique!
I am not sure why it is necessary to beat me up. All the things you are beating me up about I have admitted beforehand. The right way to beat me up is by presenting data that refutes mine. Just stating that you are always airborne in less than a hundred feet is not particularly convincing - and telling me that detailed data is posted elsewhere is not helpful unless you tell me where. I went through this thread, and so far I haven't seen any specific trials posted, except for the ones I posted.
Sure, my data is suspect. I expected a couple percent improvement - I too thought that pointing the thrust up slightly ought to yield a slight improvement in takeoff roll. I have drawn only one conclusion from all of this - that is, if somebody says something you do not like, hold him or her in some gentle form of contempt. No real point in countering with any factual data.
You may find my skills as a Cub pilot not up to your standards - you are all welcome to come down here and fly with me in my aircraft. That way you can determiine my skill level by my flying, as opposed to my sub-ninth grade grasp of engineering terms. And as a bonus, I get to see you fly. Maybe I can learn how to consistently cut my takeoff rolls in half, just by changing my technique!
behindpropellers
Registered User
NE Ohio
bob turner said:
Bob-
Don't you have a J-3 and a decathalon? Why would the thrustline even matter to you?
S2D
MEMBER
Montana
bob turner said:
dang Bob guess you read my snipe before I thought better and changed it.
We are beating you up because you admit you can't feel anything, don't know how to make High Perf takeoffs etc etc and then bash the thrustline mod.
If I ever get down in that area I'll look you up and we can compare takeoff techniques.
Lance
Registered User
Gonzales, Louisiana
I have no desire to get in a bashing contest, but I have to agree with S2D. There is no need to claim someones product does not work on a public forum unless you are absolutely positive that your testing procedure clearly shows it to be the case. From were I sit it seems to me that your data shows to many variables to give an irrefutable result.
So, I can understand Mark being upset because of some people that may never give his product a chance because of this. You (people) can't go wrong with Mark's offer on the Thrustline, so you owe it to yourself to at least talk with him if you are considering it.
Yes, I do have the Thrusline on my plane and no I do not have any before/after data. The mod was added to the plane during rebuild and it flies so nice I have no intention of changing it whether it works or not.
Lance
So, I can understand Mark being upset because of some people that may never give his product a chance because of this. You (people) can't go wrong with Mark's offer on the Thrustline, so you owe it to yourself to at least talk with him if you are considering it.
Yes, I do have the Thrusline on my plane and no I do not have any before/after data. The mod was added to the plane during rebuild and it flies so nice I have no intention of changing it whether it works or not.
Lance
Gordon Misch
MEMBER
Toledo, Wa (KTDO)
Hey Bob, I apologize for writing in a way that could sound like bashing you. That wasn't my intent, though I did intend to bash the notion that the data you shared (limited, as you said) in any way demonstrated a causative relationship between TL and takeoff performance. I have relatives in San Diego, and I'll look forward to looking you up and sharing a chuckle over how technical discussions can get so dang heated. :-?
