CARF Skygate Hawk in the house !
08-23-2015, 11:38 PM
#1101
Gents, not that its possibly relevant but the full size Hawk I understand did have issues with flaps blanking the elevator, the fix I understand was to add the inboard flap airfoil blade which allowed air to pass through the flap closer to the wing TE. Again not completely sure but this blade was later shortened to increase the airflow further too.
Models don't often mimick the FS in aerodynamic terms but those more in the know might see a correlation.
Those who do know the FS might be able to be more accurate in the flap design.....
marcs
Models don't often mimick the FS in aerodynamic terms but those more in the know might see a correlation.
Those who do know the FS might be able to be more accurate in the flap design.....
marcs
So the 'blanking' design problem was fixed? - Anyone?
Bob
08-24-2015, 07:03 AM
#1103
Yes, it's true, especially for the early Hawk variants.
As presented by the Hawk Chief Designer.
The larger and closer to true scale we get, the closer we replicate all the aerodynamic characteristics of the full-size.
http://aerosociety.com/Assets/Docs/P...r-Mitchell.pdf
Quote;
(b) Howling and the Phantom Dive.
During one of the early stalling flights, before the flap vane had been cut back, two curious phenomena had been noticed. The first of these was a report from the pilot that when the flap was travelling from ‘up’ to ‘mid’ there was an intermittent ‘howl’. Now the flap vanes were fabricated from glass-reinforced plastic, and it quickly became clear that at an intermediate position the local internal airflow was causing them to vibrate. This was easily cured by putting in more stiffeners between the vane and the flap.
The second of these was more serious and demanded immediate attention. It was first discovered when recovering from a stall with full flap and undercarriage up. It was found that at forward centre of gravity in that configuration, rapid fore-and-aft movement of the control column could induce an uncontrollable nose down pitch, with the nose down attitude and speed increasing quite rapidly. Recovery was straightforward, either by retracting the flap a few degrees, or by extending the undercarriage, but this was not acceptable as an operation, even though the configuration was unlikely to be used normally. It was dubbed the “Phantom Dive”.
This term had been coined after an initially unexplainable series of fatal approach accidents on the Gloster Meteor, because in those events there was a sudden loss of control under conditions which were normal and correct for final approach (“It came like a phantom, from nowhere”), and the aircraft dived into the ground from low altitude. After investigation it was found that on the Meteor, selection of airbrakes when the flaps and wheels were down, a seemingly logical operation, gave rise to an interference which caused the tail unit to become ineffective. It is believed that a tailplane stall had also been experienced on the F-4 “Phantom” but the expression did not derive from that.
It was shown with the half model of the Hawk at Hatfield that high local downwash at the tail, coupled with the very large nose down pitching moment induced by the flap, was causing the tailplane to stall on its lower surface, so that it could no longer provide adequate balancing power. It needed more lift, extended to higher angles of attack.
In the case of the F-4K Phantom aircraft this was achieved by installing a fixed leading edge slot to the tailplane, harking back to demonstrations of such devices by Handley Page on wings in the early Twenties! A fixed slot with its associated drag was not an option on the Hawk although a cambered tailplane was tried on the model with some success. Removal of the outboard vane of the flap reduced the flap pitching moment to such a value that the standard tailplane could cope, so this was the quick solution for the RAF. However, for the US Navy VTX project, (and for later combat versions of the Hawk) the maximum possible lift was required, so that at least the outer flap vane had to be replaced. The dive phenomenon had to be fixed.
An example of the cross-fertilization of knowledge due to the matrix working of the design department now occurred. Barry Pegram, then Section leader of the Fluid Dynamics section of the Aerodynamics Department, had been working on the adoption of leading edge root extensions (LERX) for the “Harrier” wing, and this work had shown that these devices extended the lift of the wing to higher angles of attack by virtue of the non-linear lift developed by the vortex flow they created. He proposed that these should be added to the tailplane of the Hawk model, but this would have had a serious effect on the tailplane hinge moments. The author, who was working with Barry in the V/STOL tunnel at Hatfield, suggested that the ‘tailplane canard vane’ (TCV), as it was called, could be fixed to the fuselage at such a position that it was lined up with the flow at normal conditions, but with its trailing edge adjacent to, with a small clearance, the leading edge of the tailplane at its maximum nose down position.
Experimenting showed that these vanes could be made quite small and they gave a complete cure to the problem in the wind tunnel, with very little drag in the normal flight regime. To prove the concept in flight, some temporary vanes were manufactured which could rapidly be fitted to one of the test aircraft which had flaps with the full vane. First, the aircraft was flown without the TCV to establish the conditions under which the ‘Phantom Dive’ occurred on that particular aircraft. On a later flight, the TCVs were fitted and the aircraft flown again to the identical conditions as before. Despite every attempt by the pilot to instigate the phenomenon, it did not occur – the vanes were a complete success, even though they looked inconspicuously small for such a large effect.
The aerodynamicists had a surprisingly difficult job to ‘sell’ the idea. Before the use of the TCV was sanctioned, tests were demanded with the high speed model at ARA and with the spin models at Lille. They were shown to have negligible effects under all normal conditions. Later, their effectiveness was again demonstrated using the 0.315 scale model of the Hawk in the RAE (Farnborough) 5 metre, high Reynolds number, wind tunnel. They became standard for the T45 aircraft, and for the 100/200 series of the Hawk.
As presented by the Hawk Chief Designer.
The larger and closer to true scale we get, the closer we replicate all the aerodynamic characteristics of the full-size.
http://aerosociety.com/Assets/Docs/P...r-Mitchell.pdf
Quote;
(b) Howling and the Phantom Dive.
During one of the early stalling flights, before the flap vane had been cut back, two curious phenomena had been noticed. The first of these was a report from the pilot that when the flap was travelling from ‘up’ to ‘mid’ there was an intermittent ‘howl’. Now the flap vanes were fabricated from glass-reinforced plastic, and it quickly became clear that at an intermediate position the local internal airflow was causing them to vibrate. This was easily cured by putting in more stiffeners between the vane and the flap.
The second of these was more serious and demanded immediate attention. It was first discovered when recovering from a stall with full flap and undercarriage up. It was found that at forward centre of gravity in that configuration, rapid fore-and-aft movement of the control column could induce an uncontrollable nose down pitch, with the nose down attitude and speed increasing quite rapidly. Recovery was straightforward, either by retracting the flap a few degrees, or by extending the undercarriage, but this was not acceptable as an operation, even though the configuration was unlikely to be used normally. It was dubbed the “Phantom Dive”.
This term had been coined after an initially unexplainable series of fatal approach accidents on the Gloster Meteor, because in those events there was a sudden loss of control under conditions which were normal and correct for final approach (“It came like a phantom, from nowhere”), and the aircraft dived into the ground from low altitude. After investigation it was found that on the Meteor, selection of airbrakes when the flaps and wheels were down, a seemingly logical operation, gave rise to an interference which caused the tail unit to become ineffective. It is believed that a tailplane stall had also been experienced on the F-4 “Phantom” but the expression did not derive from that.
It was shown with the half model of the Hawk at Hatfield that high local downwash at the tail, coupled with the very large nose down pitching moment induced by the flap, was causing the tailplane to stall on its lower surface, so that it could no longer provide adequate balancing power. It needed more lift, extended to higher angles of attack.
In the case of the F-4K Phantom aircraft this was achieved by installing a fixed leading edge slot to the tailplane, harking back to demonstrations of such devices by Handley Page on wings in the early Twenties! A fixed slot with its associated drag was not an option on the Hawk although a cambered tailplane was tried on the model with some success. Removal of the outboard vane of the flap reduced the flap pitching moment to such a value that the standard tailplane could cope, so this was the quick solution for the RAF. However, for the US Navy VTX project, (and for later combat versions of the Hawk) the maximum possible lift was required, so that at least the outer flap vane had to be replaced. The dive phenomenon had to be fixed.
An example of the cross-fertilization of knowledge due to the matrix working of the design department now occurred. Barry Pegram, then Section leader of the Fluid Dynamics section of the Aerodynamics Department, had been working on the adoption of leading edge root extensions (LERX) for the “Harrier” wing, and this work had shown that these devices extended the lift of the wing to higher angles of attack by virtue of the non-linear lift developed by the vortex flow they created. He proposed that these should be added to the tailplane of the Hawk model, but this would have had a serious effect on the tailplane hinge moments. The author, who was working with Barry in the V/STOL tunnel at Hatfield, suggested that the ‘tailplane canard vane’ (TCV), as it was called, could be fixed to the fuselage at such a position that it was lined up with the flow at normal conditions, but with its trailing edge adjacent to, with a small clearance, the leading edge of the tailplane at its maximum nose down position.
Experimenting showed that these vanes could be made quite small and they gave a complete cure to the problem in the wind tunnel, with very little drag in the normal flight regime. To prove the concept in flight, some temporary vanes were manufactured which could rapidly be fitted to one of the test aircraft which had flaps with the full vane. First, the aircraft was flown without the TCV to establish the conditions under which the ‘Phantom Dive’ occurred on that particular aircraft. On a later flight, the TCVs were fitted and the aircraft flown again to the identical conditions as before. Despite every attempt by the pilot to instigate the phenomenon, it did not occur – the vanes were a complete success, even though they looked inconspicuously small for such a large effect.
The aerodynamicists had a surprisingly difficult job to ‘sell’ the idea. Before the use of the TCV was sanctioned, tests were demanded with the high speed model at ARA and with the spin models at Lille. They were shown to have negligible effects under all normal conditions. Later, their effectiveness was again demonstrated using the 0.315 scale model of the Hawk in the RAE (Farnborough) 5 metre, high Reynolds number, wind tunnel. They became standard for the T45 aircraft, and for the 100/200 series of the Hawk.
08-24-2015, 01:02 PM
#1104
I just completed the installation of the flap servos and I notice this time I have a lot more flap travel. I never messured the flap extinsion before but with the most travel I could get they would only deploy to just about completly exposing the small airfoil between the flap and the wing. I had noticed in many a pictures it looked like other hawks simular had a lot more travel. He is a picture of the them deployed for you guys to compare.
On the wings I just finish for my new one the flaps travel much farther. I could increase the travel at least 20% in the radio. I not sure what I did different in installation but I see a big difference.
After reading this new information I plan on using a safe approach to my first couple of flights. I will not deploy no farther that the my first one was. I will test them once I feel comfortable witht he trim and setup.
I really want to use the more travel with hopes of slower flights with increased power compaired to my old one.
On the wings I just finish for my new one the flaps travel much farther. I could increase the travel at least 20% in the radio. I not sure what I did different in installation but I see a big difference.
After reading this new information I plan on using a safe approach to my first couple of flights. I will not deploy no farther that the my first one was. I will test them once I feel comfortable witht he trim and setup.
I really want to use the more travel with hopes of slower flights with increased power compaired to my old one.
Last edited by jws_aces; 08-24-2015 at 01:08 PM.
08-24-2015, 01:14 PM
#1105
Hi Jeff
Yes, I remember posting and asking how much flap everyone is using and your reply was something like "use all you can get". well, my next question should have been how many mm? but, I did use all I could get !
and it was a lot! almost twice as Skygate recommendation. I need to build another one.
Behzad
Yes, I remember posting and asking how much flap everyone is using and your reply was something like "use all you can get". well, my next question should have been how many mm? but, I did use all I could get !
and it was a lot! almost twice as Skygate recommendation. I need to build another one.Behzad
08-24-2015, 01:29 PM
#1106
Yes I was the one that said use all you can get. I guess I didn't have the geometry setup right on the first one. As you can see in the picture that was all I could get. I am using the same servo arms and servos but this time I see a lot more travel.
Dang I am sorry if I misslead you in anyway.
Jeff
Dang I am sorry if I misslead you in anyway.
Jeff
08-24-2015, 01:34 PM
#1107
No worries at all. It was my job to do due diligence. These are built different times with different engines and set-ups. also, Carf instruction indicated more amount of flap. now we know and hopefully future builders learn as well. since all my parts including radio plates, tank, pipe seem to be untouched,my build will be faster if I get another one.
Behzad
Behzad
08-24-2015, 01:38 PM
#1108
From the same document as above;
Quote;
Soon after the condition was first encountered it was recognised that the tailplane was not producing enough downwards force (negative lift) to counter the nose down pitching moment from the large flaps in their fully down (50 deg) position. When the undercarriage was deployed, the main wheel legs spoiled the flow through the flap slots to some extent, and this reduced the flap pitching moment sufficiently for the tailplane to cope. Similarly, reducing the flap angle by a few degrees also reduced the flap pitching moment, but there was a loss of lift and drag, essential for landing.
The solution adopted for the Hawk T.Mk.1 was to remove the outer portion of the flap vane of the double slotted flap, as shown in Figure A3.1. This was a quick and effective solution, but when combined with the use of a fence and ‘breaker strips’ for stall warning, lost about 5 knots of stall speed, though the behaviour was benign.
I don't have the full-size current flap max rigging angle, but with a quoted reduction of a few degrees from 50, I would think that a 40deg max flap deflection would be safe from approaching the Phantom Stall effect.
Paul
Quote;
Soon after the condition was first encountered it was recognised that the tailplane was not producing enough downwards force (negative lift) to counter the nose down pitching moment from the large flaps in their fully down (50 deg) position. When the undercarriage was deployed, the main wheel legs spoiled the flow through the flap slots to some extent, and this reduced the flap pitching moment sufficiently for the tailplane to cope. Similarly, reducing the flap angle by a few degrees also reduced the flap pitching moment, but there was a loss of lift and drag, essential for landing.
The solution adopted for the Hawk T.Mk.1 was to remove the outer portion of the flap vane of the double slotted flap, as shown in Figure A3.1. This was a quick and effective solution, but when combined with the use of a fence and ‘breaker strips’ for stall warning, lost about 5 knots of stall speed, though the behaviour was benign.
I don't have the full-size current flap max rigging angle, but with a quoted reduction of a few degrees from 50, I would think that a 40deg max flap deflection would be safe from approaching the Phantom Stall effect.
Paul
Last edited by JSF-TC; 08-24-2015 at 01:41 PM.
08-24-2015, 01:54 PM
#1109
Paul that is great info.
You know at KY jets I have a friend who purchase an older kit and repainted it there. It flew very well. When we compaired the 2 jets we noticed that his inner flap was like your diagram. Mine ran pretty much the whole lenght of the flap. His didn't not. I can remember which end was shorter on his. It could have been like the fix on the real one.
You know at KY jets I have a friend who purchase an older kit and repainted it there. It flew very well. When we compaired the 2 jets we noticed that his inner flap was like your diagram. Mine ran pretty much the whole lenght of the flap. His didn't not. I can remember which end was shorter on his. It could have been like the fix on the real one.
08-25-2015, 06:19 AM
#1111
Hi Marc, thank you. Comparing to these pictures, I had the same amount of flaps maybe even a little less. Did this plane fly well and did it survive many flights? Now I am puzzled again.
Thanks again.
Behzad
Thanks again.
Behzad
08-25-2015, 07:15 AM
#1112
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I only have these shots from a folder of Hawk pictures I was given by a friend who was building an SG Hawk a few years back, I suspect the flap 'issue' may only be one piece of the jigsaw but I guess dialing back the flaps and testing at high altitude for nose down pitch without elevator authority would be a process worth checking.
Remember these shots are all static without power (I suspect) so the droop sydrome is likely to be in play here.
Here is one of Ali's on finals ...
marcs
Remember these shots are all static without power (I suspect) so the droop sydrome is likely to be in play here.
Here is one of Ali's on finals ...
marcs
08-25-2015, 12:15 PM
#1114
I've just come back from the JWM, there are a lot of SG Hawks flying in the competition, I watched five or six yesterday alone. Built stock its a "bag of air" so hardly any flap is actually required.
Maybe in the various videos posted you can get an idea.
Dave
Maybe in the various videos posted you can get an idea.
Dave
09-03-2015, 03:00 PM
#1115
Hi, HAve about 30 flights on my SG HAwk now and I'm definetly in love with it is an awesome bird... the only thing I don't like at all are the brackes, they just wont do the job, they slow it down but not strong enoght specialy if you are at short field.. I cleaned the grease hopping to get more friction but I didn't, what else have you donne to get a better bracking???
09-03-2015, 03:19 PM
#1116
I wish I could say "I have break problem!".
, Joking aside, mine worked well in stock form. The new one is ordered and soon I will start the build again. Hopefully this time goes a lot faster with better result.
Behzad
, Joking aside, mine worked well in stock form. The new one is ordered and soon I will start the build again. Hopefully this time goes a lot faster with better result. Behzad
09-03-2015, 04:51 PM
#1117
I used the BVM smooth stop on mine and did really well. I have a Up3 I am going to use this time because I have it and really want to see how it does. The volume of air is the key. Yes mine took a bit to get better. The first few flights I had a time stopping also.
09-06-2015, 03:19 PM
#1119
his is a video to see the movement and settings on my new Skygate Hawk. I have a ton more travel on this compared to the first I had that I lost at KY jets. The first amount of flap is what I had in full down position.
I measured about 46 degrees using a Hanger 9 angle meter.
As you can see I can get a lot more on this one. Right 65 degrees of down. I am only going to fly it using the 46 degrees
hope this helps.
https://www.youtube.com/watch?v=a_QU5f7nl6k
I measured about 46 degrees using a Hanger 9 angle meter.
As you can see I can get a lot more on this one. Right 65 degrees of down. I am only going to fly it using the 46 degrees
hope this helps.
https://www.youtube.com/watch?v=a_QU5f7nl6k
09-06-2015, 04:51 PM
#1121
One more question. Do you guys paint the inside. I spent hours brush painting all the wood formers inside the first one but then realized that none of them could be seen after equipment is installed.
Behzad
Behzad
09-06-2015, 05:30 PM
#1124
Thank you guys, this time I will have to do only one leg cover as one came out of the crash perfect. I also have the gear doors. I am. Thinking that it might be more time efficient if I paint the doors that I have than building new ones. We will see how it goes. At this point, there was some cinfusion at Carf side with my order so I am not sure what is going to happen.
Behzad
Behzad
09-22-2015, 09:53 PM
#1125
Behzad