---------------------------------------------------------- KIS-List Digest Archive --- Total Messages Posted Thu 04/07/11: 8 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 06:34 AM - Re: Re: Landing the KIS TR-1 (Mark Kettering) 2. 07:19 AM - Re: Landing the KIS TR-1 (BlueSkyFlier) 3. 07:53 AM - Re: Re: Landing the KIS TR-1 (F. Tim Yoder) 4. 03:12 PM - Re: Re: Landing the KIS TR-1 (Mark Kettering) 5. 05:03 PM - Re: Landing the KIS TR-1 (BlueSkyFlier) 6. 06:15 PM - Re: Landing the KIS TR-1 (BlueSkyFlier) 7. 08:39 PM - Landing the KIS TR-1 (Graham Brighton) 8. 09:25 PM - Re: Re: Landing the KIS TR-1 (Scott Stearns) ________________________________ Message 1 _____________________________________ Time: 06:34:03 AM PST US From: Mark Kettering Subject: Re: KIS-List: Re: Landing the KIS TR-1 I am a very big fan of Stinton's book "The Design of the Aeroplane". Lots of useful information. It does have a fair number of empirical equations but he tends to use them with care, a grain of salt and with data. This is the first book I look at when I have questions. Julian Bone did some great work on the airflow at the wing root of the KIS. I agree that a much larger radius fairing will reduce drag, reduce turbulence, reduce the adverse pressure gradient especially at high AOA and help delay wing root stall. Yes, delaying stall will decrease minimum flying speed and that is good. But wing root stall (or for that matter any wing stall) will drop the nose! Nothing to do with turbulent airflow over the tail. Airfoils work great in turbulent air. In fact they tend to work better in some ways with a higher maximum Cl. There is of course wing down wash over the tail and this will be reduced when the wing stalls and this will reduce tail down force. But this is a lower order effect then the moment due to the reduced wing lift due to wing stall and more aft stick can make up for this, not that you would want to if the wing is in stall. Was Julian Bone's aircraft conventional gear? What problem did he really solve? I know he decreased the minimum airspeed and this is good. He maybe reduced minimum airspeed such that now the tail can not generate the needed down force (at some forward CG locations) to make the AOA such that the wing will stall. This may be good and was done with some aircraft in the past like the AirCoupe. But maybe now the wings tips will stall first and this is bad. Mark -----Original Message----- From: Larry David Sent: Apr 7, 2011 12:59 AM Subject: Re: KIS-List: Re: Landing the KIS TR-1 Several years ago, Julian Bone did a rather complete study of the airflow effect of the KIS wing fairing. It appears from a book by Stinton, page171, that if the wing fairing needs about an 8 inch radius instead of the ~3 in radius it has. With the ~8 inch radius, the airflow over the tail will not be turbulent and the nose will not drop unexpectedly. Julian modified his plane accordingly and it solved the problem. I found the Stinton book very interesting. (I think the title was "The design of an Airplane." I loaned my copy to another builder so have to trust my memory on the title so I may not be right.). Hope this sheds some more light on the issue. Larry On 4/6/2011 4:48 PM, BlueSkyFlier wrote: Hi Graham, Unfortunately it is never just one thing. Far too much going on at the same time to be that simple :o) The wing effects, flaps effects and changed airflow on the tail section all play their part. The upwash effects on tail plane could vary dramatically with speed, flap setting, angle of attack, and height above ground. Most people (myself included) were told in training that ground effect always increase lift. As the references illustrate that statement should be qualified with the provision that the angle of attack needs to be small enough. With low wing aircraft in particular, the proximity of the trailing edge of the flaps to the ground can work in one's favour if the lift coefficient is small enough, but could just as well have exactly the opposite effect if one is not careful with angle of attack. The bottom line is that unless these adverse factors are avoided, any or all of them can contribute to the craft and/or nose gear coming down faster than one would want or expect. Each pilot will naturally develop their own way of dealing with these effects, but understanding of the various parameters at play can only be beneficial. Regards, Alfred -------- _________________________________________ Read this topic online here: http://forums.matronics.com/viewtopic.php?p=336321#336321 ________________________________ Message 2 _____________________________________ Time: 07:19:19 AM PST US Subject: KIS-List: Re: Landing the KIS TR-1 From: "BlueSkyFlier" Chuckle ... don't worry guys. Long toes are not my strong suit :o) This is developing into exactly the kind of conversation I was hoping for. Fully agreed with Mark that, if the resultant vertical momentum is too high at touchdown, the weight of the engine will take the upper hand in forcing the nose down. I was merely looking for potential causal factors of such undesirable end result which could catch one unawares even when apparently doing nothing overtly wrong. In that sense the equation did point out that - as rear end of flaps get closer to the ground - flow velocity becomes restricted and probability of flow reversal increases; all of which reduces lift of the inner wing area. Empirical or not, it seems to make intuitive sense and I shall at least keep that effect in mind when I have full flaps deployed in approach. Also good to hear from Mark that TR-1 will not easily get into the CL > 2 region. Unfavorable air flow on the tail section is probably also strongly influenced by angle of attack. Julian had a tail dragger and was therefore more likely to end up with the tail lower than we would normally do. Must admit that I have not personally experienced nose dropping - perhaps because I don't hold off, but instead fly the gear into touch with conservative angle of attack as I was instructed to do at hot and high fields. I seems to work everywhere else too. Happy landings :o) -------- _________________________________________ Read this topic online here: http://forums.matronics.com/viewtopic.php?p=336351#336351 ________________________________ Message 3 _____________________________________ Time: 07:53:20 AM PST US From: "F. Tim Yoder" Subject: Re: KIS-List: Re: Landing the KIS TR-1 Julian's was a tail dragger. ----- Original Message ----- From: "Mark Kettering" Sent: Thursday, April 07, 2011 6:29 AM Subject: Re: KIS-List: Re: Landing the KIS TR-1 > > I am a very big fan of Stinton's book "The Design of the Aeroplane". Lots > of useful information. It does have a fair number of empirical equations > but he tends to use them with care, a grain of salt and with data. This > is the first book I look at when I have questions. > > Julian Bone did some great work on the airflow at the wing root of the > KIS. I agree that a much larger radius fairing will reduce drag, reduce > turbulence, reduce the adverse pressure gradient especially at high AOA > and help delay wing root stall. Yes, delaying stall will decrease minimum > flying speed and that is good. But wing root stall (or for that matter > any wing stall) will drop the nose! Nothing to do with turbulent airflow > over the tail. Airfoils work great in turbulent air. In fact they tend > to work better in some ways with a higher maximum Cl. There is of course > wing down wash over the tail and this will be reduced when the wing stalls > and this will reduce tail down force. But this is a lower order effect > then the moment due to the reduced wing lift due to wing stall and more > aft stick can make up for this, not that you would want to if the wing is > in stall. > > Was Julian Bone's aircraft conventional gear? What problem did he really > solve? I know he decreased the minimum airspeed and this is good. He > maybe reduced minimum airspeed such that now the tail can not generate the > needed down force (at some forward CG locations) to make the AOA such that > the wing will stall. This may be good and was done with some aircraft in > the past like the AirCoupe. But maybe now the wings tips will stall first > and this is bad. > > Mark > > -----Original Message----- > > From: Larry David > > Sent: Apr 7, 2011 12:59 AM > > To: kis-list@matronics.com > > Subject: Re: KIS-List: Re: Landing the KIS TR-1 > > > Several years ago, Julian Bone did a rather complete study of the > airflow effect of the KIS wing fairing. It appears from a book by > Stinton, page171, that if the wing fairing needs > about an 8 inch radius instead of the ~3 in radius it has. With > the ~8 inch radius, the airflow over the tail will not be > turbulent and the nose will not drop unexpectedly. Julian > modified his plane accordingly and it solved the problem. I > found the Stinton book very interesting. (I think the title was > "The design of an Airplane." I loaned my copy to another > builder so have to trust my memory on the title so I may not be > right.). Hope this sheds some more light on the > issue. Larry > > > On 4/6/2011 4:48 PM, BlueSkyFlier wrote: > > > > Hi Graham, > > Unfortunately it is never just one thing. Far too much going on at the > same time to be that simple :o) > > The wing effects, flaps effects and changed airflow on the tail section > all play their part. The upwash effects on tail plane could vary > dramatically with speed, flap setting, angle of attack, and height above > ground. > > Most people (myself included) were told in training that ground effect > always increase lift. As the references illustrate that statement should > be qualified with the provision that the angle of attack needs to be small > enough. > > With low wing aircraft in particular, the proximity of the trailing edge > of the flaps to the ground can work in one's favour if the lift > coefficient is small enough, but could just as well have exactly the > opposite effect if one is not careful with angle of attack. > > The bottom line is that unless these adverse factors are avoided, any or > all of them can contribute to the craft and/or nose gear coming down > faster than one would want or expect. Each pilot will naturally develop > their own way of dealing with these effects, but understanding of the > various parameters at play can only be beneficial. > > Regards, > Alfred > > -------- > _________________________________________ > > > Read this topic online here: > > http://forums.matronics.com/viewtopic.php?p=336321#336321 > > > ________________________________ Message 4 _____________________________________ Time: 03:12:07 PM PST US From: Mark Kettering Subject: Re: KIS-List: Re: Landing the KIS TR-1 >Fully agreed with Mark that, if the resultant vertical momentum is too high at touchdown, the weight of the engine will take the upper hand in forcing the nose down. Actually even if there is no (or almost no) vertical momentum on touchdown the nose can still slam down due to the upward force that was being generated by the wing now being generated by the main gear farther aft. > >I was merely looking for potential causal factors of such undesirable end result which could catch one unawares even when apparently doing nothing overtly wrong. In that sense the equation did point out that - as rear end of flaps get closer to the ground - flow velocity becomes restricted and probability of flow reversal increases; all of which reduces lift of the inner wing area. Empirical or not, it seems to make intuitive sense and I shall at least keep that effect in mind when I have full flaps deployed in approach. Also good to hear from Mark that TR-1 will not easily get into the CL > 2 region. I agree with looking for any potential causal factors. I also agree that with big flaps near the ground there could be flow restriction and maybe reversal. But I am not so sure this will produce less lift. Not that I am at all a fan of wings in ground effect craft but they do work and tend to have very low aspect ratios and very low trailing edge ground clearance. Most do not have flaps but have lots of camber. >Must admit that I have not personally experienced nose dropping - perhaps because I don't hold off, but instead fly the gear into touch with conservative angle of attack as I was instructed to do at hot and high fields. I seems to work everywhere else too. > Do you know if your main gear are at the stock location or at some other location? Mark ________________________________ Message 5 _____________________________________ Time: 05:03:12 PM PST US Subject: KIS-List: Re: Landing the KIS TR-1 From: "BlueSkyFlier" Mark, I'm not sure what the actual height of CoG is for the TR-1, but I know that my wheels are located about 10 inches behind the nominal location of my CoG. Attached herewith a table in which I explore the aircraft angle (away from horizontal) required at touchdown in order to bring the wheels underneath the centre of gravity. Assuming that CoG is about 36 inches above and 10 inches behind the wheels, it seems that one would need to have the aircraft at a 15.5 degree angle to get the wheels underneath the CoG. Does anyone have nominal figures for height of CoG and/or aircraft angle at landing? -------- _________________________________________ Read this topic online here: http://forums.matronics.com/viewtopic.php?p=336372#336372 Attachments: http://forums.matronics.com//files/aircraft_angle_at_touchdown_167.jpg ________________________________ Message 6 _____________________________________ Time: 06:15:30 PM PST US Subject: KIS-List: Re: Landing the KIS TR-1 From: "BlueSkyFlier" Earlier in this thread I referred to the tendency of NACA 6-digit wing profiles to prefer operation within their laminar flow design ranges. The KIS TR-1 uses a modified 6-digit profile which can be described as 63(2)A-215. The 6-series was derived using an improved theoretical method that relied mathematics to derive the geometrical shape required to realise the desired pressure distribution. The goal of this approach was to design airfoils that maximized the region over which the airflow remains laminar. In so doing, the drag over a small range of lift coefficients can be substantially reduced. To illustrate that, herewith attached a diagram in which the characteristic drag "bucket" associated with laminar flow can be seen - in this case for the NACA 64(2)-415 profile. This is from p.238 of Torenbeek's "Synthesis of subsonic aircraft design". As can be seen from the diagram the drag increases rapidly as the lift coefficient moves beyond the optimal range, which helps to slow down rapidly but also results in high sink rate at non-optimal angle of attack. However, these profiles do exhibit docile stall characteristics. A modification of the standard 6-digit series is the A-series in which the curved contours of the trailing edge is replaced with straight contours which run from about 80% of chord backwards - as manifested by flat surfaces on the TR-1 flap and aileron. The TR-1 wing therefore nominally represents a 63(2)A215 profile. Just one more reason to avoid high angles of attack during landing ... -------- _________________________________________ Read this topic online here: http://forums.matronics.com/viewtopic.php?p=336377#336377 Attachments: http://forums.matronics.com//files/lift_and_drag_of_naca_airfoils_780.jpg ________________________________ Message 7 _____________________________________ Time: 08:39:58 PM PST US From: "Graham Brighton" Subject: KIS-List: Landing the KIS TR-1 This is the only close Airfoil diagram i could find ..but its not the TR1 profile is it .. Anybody got the correct one ..? Graham TR1 #80 ________________________________ Message 8 _____________________________________ Time: 09:25:09 PM PST US From: Scott Stearns Subject: Re: KIS-List: Re: Landing the KIS TR-1 I'm pretty sure the pitch down issue on landing is due to the main wheels b eing a bit too far aft and the elevator being a bit too small.- It doesn' t take much of an error in wheel placement to make a big difference in rota tion speed and pitch down after touchdown.- - When I was an engineer working on the proof of concept airplane-for the A dam A500 we ended up with the main-wheels a few inches aft of where-the y should have been (long story, not my fault!).- The airplane hit about 1 00 KIAS before it could be rotated for takeoff and there was no holding the nose off after landing.- Proteus is another good example.- The main wh eels are well aft due to the design and the nose comes crashing down right after touchdown.- - Scott - --- On Thu, 4/7/11, Mark Kettering wrote: From: Mark Kettering Subject: Re: KIS-List: Re: Landing the KIS TR-1 >Fully agreed with Mark that, if the resultant vertical momentum is too hig h at touchdown, the weight of the engine will take the upper hand in forcin g the nose down. Actually even if there is no (or almost no) vertical momentum on touchdown the nose can still slam down due to the upward force that was being generat ed by the wing now being generated by the main gear farther aft. > >I was merely looking for potential causal factors of such undesirable end result which could catch one unawares even when apparently doing nothing ov ertly wrong. In that sense the equation did point out that - as rear end of flaps get closer to the ground - flow velocity becomes restricted and prob ability of flow reversal increases; all of which reduces lift of the inner wing area. Empirical or not, it seems to make intuitive sense and I shall a t least keep that effect in mind when I have full flaps deployed in approac h. Also good to hear from Mark that TR-1 will not easily get into the CL > 2 region. I agree with looking for any potential causal factors.- I also agree that with big flaps near the ground there could be flow restriction and maybe r eversal.- But I am not so sure this will produce less lift.- Not that I am at all a fan of wings in ground effect craft but they do work and tend to have very low aspect ratios and very low trailing edge ground clearance. - Most do not have flaps but have lots of camber. >Must admit that I have not personally experienced nose dropping - perhaps because I don't hold off, but instead fly the gear into touch with conserva tive angle of attack as I was instructed to do at hot and high fields. I se ems to work everywhere else too. > Do you know if your main gear are at the stock location or at some other lo cation? 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