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Skymaster Hawk 100 1/3.75 Flaps!!

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Skymaster Hawk 100 1/3.75 Flaps!!

Old 03-03-2019, 06:58 PM
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Jetfan20
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Default Skymaster Hawk 100 1/3.75 Flaps!!

Hi All,

I have the large SM Hawk 100. SM recommends to not use the full flap setting on high speed as it will blank out the elevator. I attempted full flap on my slow final approach and it still blanked out the elevator and I almost lost the jet. Quick flip to no flaps and everything went ok.

Anyone happen to have a clue why this is happening on the SM large Hawk? There are other hawks in the 1/3.75 range and I'm not sure if other hawks are experiencing similar issues.

Have any other SM large Hawk owners come up with some good safe settings to handle the flap issue?

Any and all information is greatly appreciated.

Thanks in Advance!!!
Old 03-03-2019, 07:06 PM
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BlueBus320
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Following. Do you have the early version kit, or the latest smaller flaps? If you have an early kit, did you do the recommended flap modification?
Jay
Old 03-03-2019, 07:15 PM
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Jetfan20
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Originally Posted by BlueBus320 View Post
Following. Do you have the early version kit, or the latest smaller flaps? If you have an early kit, did you do the recommended flap modification?
Jay
I bought it in 2016, so I'm guessing it's the earlier version. The only flap mod that I've done was trim the flap slats as recommended.
Old 03-04-2019, 04:31 AM
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basimpsn
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"SM recommends to not use the full flap setting on high speed "
I'm confuse? why would anyone uses full flaps for high speed? maybe it's the low speed full flaps combination they're talking about. I would uses takeoff flaps for landing to be safe.

My opinion

Last edited by basimpsn; 03-04-2019 at 04:33 AM.
Old 03-04-2019, 04:36 AM
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Jetfan20
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Yes that was their recommendation, don’t use on speeds above 95mph. It totally blanked the elevator. I will go with take off setting for landing and that’s it. I have read that SM made some modifications on the newer production Hawks. The surfaces have been cut down about an inch.
Old 03-04-2019, 04:56 AM
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sysiek
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I have seen 3 of them crashed because of the flaps blind the elevators and a lot more good landings with no flaps at all I will go no flaps and actually one of my friends used the flapalieronce mode so just the ailerons go about 15 degrees down but he is trying the spoilers mode it’s working and no flaps in use maybe just like 3-5 degrees.
Old 03-04-2019, 08:30 AM
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basimpsn
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I was going to buying a SM Hawk...then I saw this video. I switch to the Mb 339 instead lol.

Old 03-04-2019, 04:46 PM
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I Have a skygate hawk that was already built and the first thing I did was put a servo amp meter on the radio to measure the amp pull.

Yeap, 1.5 amps ... took the elevator servos off and the amps went down to .5 amps, the rod holding up the elevator was causing the digital servos to adjust too much at different points causing too much whine at resting too.

On another model something similar happen to a digital steering servo except it wasn't whining loud at all it was just adjusting so much at radio center that it was pulling a lot of amps from the BEC.

The steering pin would stick around the center point steering causing the constant adjustment but wouldn't happened every time also the servo was hot .. greased up the steering pin and that fixed the issue

Bottom line; get a servo amp meter and make sure none of the servos are over-amping ... ESPECIALLY ... if the servos are digital.

my 2c

Last edited by erh7771; 03-04-2019 at 04:49 PM.
Old 03-04-2019, 06:10 PM
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Jetfan20
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Originally Posted by basimpsn View Post
I was going to buying a SM Hawk...then I saw this video. I switch to the Mb 339 instead lol.

https://www.youtube.com/watch?v=Z-mO1b_SUfI
The jet flies nice. This flap issue on the earlier models is the only issue I've seen.

The video doesn't tell me a whole lot. That could have been some sort of component failure. It appears that the pilot lost control.
Old 03-04-2019, 08:31 PM
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Hi

this is the problem with the hawks. I built a Carf Skygate hawk. I asked around and unfortunately was told to "dial in all you can" so I put 89mm on the flap and lost the hawk at the end of Maiden flight as the flap blanked the elevator and I had no time to recover. After that, I found the instruction from Skygate (not Carf) and that indicated a total of about 38mm for landing flap. So from what I learned, the amount of flap needed is minimal.

Behzad
Old 03-05-2019, 02:18 AM
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David Gladwin
 
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Default Hawk Flaps

OK, some real world experience based on :
My original Skymaster Hawk.
My current two Airworld Hawks, over 200 flights.
My current Skygate Hawk, thiroughly demoed for its CAA certification.

All fly beautiully in all configurations, with NO handling problems

In addition, I had the opportunity to explore the handling, except spinning, ( as a former jet QFI myself) , of the real Hawk as a guest of 4 FTS at Valley and the late Duncan Simpson, Hawk test pilot, helped me with techical data on, and handling of, the Hawk. On the first Hawk test flight it pitched down severely on flap extension.

This was cured by removing the outboard 15 inches of the flap vane.
Later Hawks have the vane slot restored BUT have SMURF s added at the stab. LE.

My models have the vane slot and proper placing of the vane.

The real Hawk has 25 degrees of flap for T/o and 50 for land. Only minor up trrim is required with landing flap on all models.
I suggest ignoring those who say dial in all you can get !
On my models I use a more conservative 15 and 35.

My stab, travel is much as SG Recommends which is rather more than the real Hawk. ( 15 degs up and 5 down)

It may be that if models have too much up stab. travel, coupled with downwash from the flaps, it may be possible to stall the stab.

The real Hawk has multiple vortex generators and these are correctly set, 15 degrees toe in, on my models,

Finally, the SG Hawk has a brass tube bearing for the stab. Shaft, which COULD seize if heat dries out the lube. On my SG Hawk I can, and do before each flying session, lubricate this bearing tube with access through the GTS exhaust hole.

A further point. On my Airworld Hawks, the dual stab. Servos are EXACTLY matched throughout their travel, using dual ammeters, current drain is minimised.

Using my Weatronic radio I have measured currents in flight, and even on my SG. Hawk on which I have changed the stab pivot point to the scale location it is quite reasonable. The flap extension, during travel, draws the largest current.

I know the Reynolds numbes of these models is different to the real jet, BUT the result if all this is that I have three Hawks all flying beautifully , and vice free, totally benign, although I have not tried spinning, but stall tests suggest any tendency to spin will be minimal, a spiral being more likely.

Last edited by David Gladwin; 03-05-2019 at 02:29 AM.
Old 03-05-2019, 07:47 PM
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David Gladwin, could you please show us some picture of the vortex generators ? How do you measured 15 degrees toe in ?

thanks in advance
Old 03-06-2019, 03:21 AM
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David Gladwin
 
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Default Hawk

After my post yesterday I requested some info on PPrune on just how tge flap vane cutaway works.

I was referred to the following paper:
www.aerosociety.com/media/48...hawk-story.pdf

p 28 to 30 are particularly relevant.

It is a long document, 120 pages, but covers all the aerodynamic quirks of the original Hawk and how they were fixed.

Of particular interest were the stalling characteristics and the phantom dive (which seems to have claimed several models ) and how they were cured on the original Hawk and later versions such as the Hawk 100 and the T45.

My earlier recommendations were sound, particularly limiting flap angle, and have produced a most docile model.

If you want BAe drawings of the Hawk wing buy “Red Arrows “ ISBN 1-85443-217-6.

A copy was sent to me some years ago by Duncan Simpson as he recommended the drawings, the original being no longer available.

Set up your Skygate/carf/Airworld Hawks as I have suggested based on professional recommendations and you will have a delightful handling , safe and docile model Hawk.
Old 03-06-2019, 03:25 AM
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David Gladwin
 
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Default Hawk

sorry, one click too many.

Last edited by David Gladwin; 03-06-2019 at 03:27 AM.
Old 03-06-2019, 04:52 PM
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ravill
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This is a well known phenomenon of the Hawk.

I wonder how many real pilots had to die to learning all this info....
Old 03-07-2019, 12:54 AM
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David Gladwin
 
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Default Hawk flaps.

None did. It was discovered and rectified at a very early stage of flight test. It was released for service as a trainer, no handling problems, but the fix, the slat cutaway and reducing flap angle did slightly increase stalling speed, but still acceptable for RAF trainer service.

You may be confusing this with the “ Phantom dive” of the Meteor T7 which DID kill a number of pilots.

This was caused by slowing with the airbrakes out, selecting flap, and extending the gear which lowered asymmetrically, causing blanking of the tailplane.

Going back to the Hawk, the “ Phantom dive” phenomenon, its discovery during test flying of the prototypes and its complete cure is described in considerable detail in pages 68 to 74 of the paper I mentioned.

Sadly, Duncan Simpson died last year ( as did the other main Hawk, and Harrier, test pilot, John Farley, ) or I could have got even more detail from them.

To summarise, jf you have a SkyGate, Carf or Airworld Hawk:

Limit max flap angle to no more than 30- 35 degrees.

Do not use excessive stab. travel.

If flap vanes are fitted do not omit the cutout.

Fit the Fences parallel to the cl.

Install the vortex generators set at 15 degrees toe in to Cl.

Install the breaker strips.

Seal the stab. pivot cutouts with bacon slicers.

In other words, make it scale, it works !

Do not extend flaps at high speed !

HSA used models, inc 1/3 scale for aerodynamic evaluation and produced a very fine flying machine with no vices as befits a trainer, which I found to be a delight to fly, although some QFIs feel it is too easy to fly , being just mid way between a JP5 and the more complex and higher performance Gnat, a real hotrod.

Its all in that paper, including a very nice description of Hawk handling by my former colleague ( and leader of the Red Arrows) Brian Hoskins who converted the Reds to the Hawk in 1979.


Last edited by David Gladwin; 03-07-2019 at 05:49 AM.
Old 03-07-2019, 10:24 AM
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Hi David,

you mentioned SMURF’s in your post, I have no idea what your referring to (I assume not the blue cartoon characters), can you educate me please?

Smokey
Old 03-07-2019, 02:49 PM
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Hello Smokey,

The "SMURF" on the later model BAE Hawks stand for ;
Side Mounted Unit Root Fin
And there you have it.
Franko
Old 03-07-2019, 03:27 PM
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Smokey,

Sorry, the ole sausage fingers clicked send before I was thru....
The “SMURF” on the later Hawk version improved the relative slip stream at high angles of attack during menouvering.
They provide a significant amount of laminar flow over the Stabilizers “root area”, and thus would mitigate airflow separation on the stab preventing
the pitch down results.

Franko
Old 03-07-2019, 05:37 PM
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Thanks Frank, even with your sausage fingers your response made sense to my meat head.

I was kind of worried that a SMURF may have been some poor LAC who was given the old “hold onto this flap while we just practice taking off” kind of thing
Old 03-07-2019, 10:20 PM
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Dave Wilshere
 
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FYI the video is nothing to do with flaps, the elevator linkage failed and the very expert pilot put the flaps down to slow the airframe as much as possible before impact.
Old 03-08-2019, 02:20 AM
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David Gladwin
 
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Originally Posted by Frank Alvarez View Post
Smokey,

Sorry, the ole sausage fingers clicked send before I was thru....
The “SMURF” on the later Hawk version improved the relative slip stream at high angles of attack during menouvering.
They provide a significant amount of laminar flow over the Stabilizers “root area”, and thus would mitigate airflow separation on the stab preventing
the pitch down results.

Franko
Actually the SMURFs, TCVs ( Tail Canard Vanes) in HSA parlance, was all about LOW speed handling with flaps out.

The vane cutaway cost about 5 knots on stalling speed.

On the later Hawks and the T45 the vane was full length to increase Cl to reduce stalling speed to the original value.

To counter the pitchdown caused by the full flap vane, the SMURFs were found to be the answer giving a considerable benefit for such a small addition.

Its all described in great detail in the paper I mentioned and since Duncan Simpson, the lead Hawk test pilot, was involved in its preparation I have no doubts about its accuracy.

Last edited by David Gladwin; 03-08-2019 at 03:39 AM.
Old 03-08-2019, 06:58 PM
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Can you post a photo of the mods you are talking about. Very interesting.
Thanks
Gary
Old 03-09-2019, 03:51 AM
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David Gladwin
 
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All three of my Hawks are of the T1 version without SMURFs but have the vane cutaway etc. as mentioned.

I enclose two photos of the T45, actually Paul Dunkley's superb model which clearly show these fins.

You will have to research the dimensions yourself, but the essential aspect is that at full nose down stab travel (ac nose up) the fins are exactly in line with the stab LE.

I had a note from John Farley a few years ago, sums it up most succinctly:

more flap vane, more lift, more downwash, higher induced A of A over the stab., more back stick = tailplane stall !

Apparently , on one early Hawk test flight, this nose down pitch took the Hawk past the vertical, recovered after flap retraction. Jim Hawkins was the driver, sadly killed some years later in Hawk 100 G- loc case.

Last edited by David Gladwin; 03-09-2019 at 04:48 AM.
Old 03-09-2019, 05:17 AM
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Thanks. What are the flap vanes, cutouts, and breaker strips? Any photos?
Gary

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