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??? i dont get it...can some one explane it to me?
..if you want to zero the "UP TRIM" on the elevons , you need to get it from "UP THRUST " from your engine .
On your photo you show "DOWN THRUST" and you should require more "up trim " to correct it.
Have you fly with this set up?
Mine does not "pull up" and flies level with UP TRIM when there is no help from the engine thrust ( on landings = airspeed faster that turbine gasses up thrust )
Even if you have correct "UP THRUST" on your engine (your exhaust should look up=the opposite of your photo below) you should dive when you fly idle=no help from engine...
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quote:
ORIGINAL: mauryr
quote:
ORIGINAL: BaldEagel
On the Rookie the instructions say that the elevons have to be 3mm up trim if I remember correctly, never had to trim in upright, just a small amount of down elevator needed in inverted flight.
Mike
My hotspot requires a good 8mm of up trim to hold in level and reducing it would be very welcome. Wouldn't changing the thrust line cause issues with trimming when increasing / reducing power though?
My Rookie has vectored thrust witch I can trim form the rotary knobs on the top of the Tx, but once set up I have not had to touch it, for all intents and purposes it is parallel with the top of the fus at its neutral position, I also have trim on the canards witch I trim for the changing C of G when using up the fuel, I would try a little reflex on the elevons, what does the manual say?
Mike
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On the Rookie the instructions say that the elevons have to be 3mm up trim if I remember correctly, never had to trim in upright, just a small amount of down elevator needed in inverted flight.
Mike
My hotspot requires a good 8mm of up trim to hold in level and reducing it would be very welcome. Wouldn't changing the thrust line cause issues with trimming when increasing / reducing power though?
My Rookie has vectored thrust witch I can trim form the rotary knobs on the top of the Tx, but once set up I have not had to touch it, for all intents and purposes it is parallel with the top of the fus at its neutral position, I also have trim on the canards witch I trim for the changing C of G when using up the fuel, I would try a little reflex on the elevons, what does the manual say?
Mike
Manual says 8mm up trim, and so do all those who own one that I know in person.
It flies neutral at idle and full throttle. It just sucks when inverted (reflex needs to be zeroed out and probably flying reversed needs some reflex as well). Also probably adds some drag. But I do not see changing the incidence of the engine as a solution to this.
Are any of you guys flying one of the "newer" Hotspots? There was a design change in the airfoil, the new wings have some reflex built into them. According to the addendum in the manual you have to build it with the nose on the worktable and have the tail raised by 50mm. The wings should then be positioned 55mm at the leading edge and 60mm at the trailing edge. This should eliminate the need for up-trim. I hope to have mine finished somewhere in january but I am still deciding on a colour scheme, so please keep the pictures coming!
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Score: 100 Joined: 12/13/2011 Last Login: 5/19/2013 From: Holland Patent,
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Hot Spot Drivers, I have the Graupner Hot Spot and it calls for 8-10 mm of uptrim on the elevons. This is due to the non-reflex airfoil on this version. I understand that later versions utilized a true reflex airfoil which is required on tailess delta planform aircraft. A forward canard may eliminate the need for this uptrim. Using engine thrustline changes to compensate may only work at certain airspeeds, typically low speed where the aerodynamic forces are miminal. As the airspeed increases these forces dominate which may help in the overall flying characteristics of the Hot Spot. I don't like the use of elevon uptrim but will live with it on my model. Further discussion on this would be appreciated.
Speaking of Hotspots, mi friend José M. Chuna from Portugal sell his Hotspot building for me ago some years, ready for fly, equiped with Simjet 1700 (8kg), few fligths.
Hot Spot Drivers, I have the Graupner Hot Spot and it calls for 8-10 mm of uptrim on the elevons. This is due to the non-reflex airfoil on this version. I understand that later versions utilized a true reflex airfoil which is required on tailess delta planform aircraft. A forward canard may eliminate the need for this uptrim. Using engine thrustline changes to compensate may only work at certain airspeeds, typically low speed where the aerodynamic forces are miminal. As the airspeed increases these forces dominate which may help in the overall flying characteristics of the Hot Spot. I don't like the use of elevon uptrim but will live with it on my model. Further discussion on this would be appreciated.
Art ARRO
Hey Art,
If I can offer some advise, the jet may look a bit unconventional with the offset elevons, but it works very well and does not seem to change vs. airspeed. Don't over think the aircraft. Many of them are still flying after this many years due to the robustness of the design. After your 1st flight, any concerns about the reflex will be a distant memory. If you fly it hard and fast, concentrate on the stiffness of the fin mounts to avoid flutter, regularly check the bonding quality in the aft underside skin, and use extra hinges. I flew mine at the rear end of the CG range in the Wilcox instructions for every flight.
Mine lasted for 10 years + 1 week, but it went down last September in a flame out just after lift-off, not much I could do to save it unfortunately. Bummer, but I'm hoping to get another. My last one has a PST-1300R on it, and it was clocked at 249mph via eagle tree (in Canada.....). I swapped that out for a P-120SX, and it was noticeably more powerful. I never tested the top end on the 120SX, but 249 in the older PST was plenty fast already and the 120SX would break 200 very easily. With ~3.25L on board, the 120SX will also make it go vertical forever immediately after lift-off.
Here's a couple video links from before the 'expiry date' was reached... (Vid 1, Vid 2)
Kelly
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quote:
ORIGINAL: taildragger21
Thanks! AMT mercury 180.. It was sent off 1 hour ago and services also boosted to 20lbs thrust
You will love the AT-180. They are very reliable. BUT... be careful with it turned up. They get hot. That engine was originally designed to run at 140K RPM's, and 15Lbs thrust. Basically... just don't hold it open for long.
My 180 is also mod'ed and running at 152K RPM's. (it's on my Falcon) Have you ever run an AMT air start?
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quote:
ORIGINAL: Dr Honda
quote:
ORIGINAL: taildragger21
Thanks! AMT mercury 180.. It was sent off 1 hour ago and services also boosted to 20lbs thrust
You will love the AT-180. They are very reliable. BUT... be careful with it turned up. They get hot. That engine was originally designed to run at 140K RPM's, and 15Lbs thrust. Basically... just don't hold it open for long.
thanks for the info... i have had a waiver for 4 years but is my first turbine. mostly into giant scale aerobatics. hoever i have some good help wih amt users from nashville.
My 180 is also mod'ed and running at 152K RPM's. (it's on my Falcon) Have you ever run an AMT air start?
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Hi Kelly, Thanks for the advice and I'll follow it for my Hot Spot. The videos were great and inspirational. I did note the demise in the latest Contrails-in the body bag, such a loss. Mine is powered by an old RAM 750, pumped up to a + by Carlos so it should be midway between your PST and JC. I've incorporated most of Wilcox's mods paying special attention to the fin reinforcement and included wheel wells to prevent the lower skin from detaching itself from air pressure. Best wishes for the holidays and New Year-Resolution # 1= no more jet losses!
Some of the stories is about problems with inverted flying. In the past I had a Kangaroo and a Rookie I without canards. (I will not mention my bad landings with the Roo) There was no problem flying inverted with both of them. Now I am building my HS and I read all these scary stories. I thought the HS was bulletproof??
I have heard from Danish rc pilots the manual CG 135 mm is okay. Shall the 135 mm be with neutral plane or shall the nose go down when you check it?
Maybe we all should write in this thread what cg we fly with.. Please write your cg point in this thread
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Score: 100 Joined: 4/4/2005 Last Login: 5/20/2013 From: Latrobe,
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quote:
ORIGINAL: taildragger21
thanks for the info... i have had a waiver for 4 years but is my first turbine. mostly into giant scale aerobatics. hoever i have some good help wih amt users from nashville.
I'm thinking about putting my 180 on my HotSpot... or finding another used one. Originally... I was going to put my Jet Central Falcon on it... but I'm going to use it elsewhere.
Here's a short vid I made on how to manual start the old AMT's.
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Tony Owner of A&L Motorsports (formerly ARO Products) Manufacture of custom alloy parts.
Hi Kelly, Thanks for the advice and I'll follow it for my Hot Spot. The videos were great and inspirational. I did note the demise in the latest Contrails-in the body bag, such a loss. Mine is powered by an old RAM 750, pumped up to a + by Carlos so it should be midway between your PST and JC. I've incorporated most of Wilcox's mods paying special attention to the fin reinforcement and included wheel wells to prevent the lower skin from detaching itself from air pressure. Best wishes for the holidays and New Year-Resolution # 1= no more jet losses!
Art ARRO
Hey Art, The pressure will still build in the back, even with sealed wheel wells, its a common fluid dynamics principle according to the Bernoulli equation. Where the wheel wells will help is with regards to stabilizing the leading edge of the rear skin, if the pressure starts to push it out - the wind can't grab it, tearing it and the rest of the skin off! If I get another though, I'd do the same as you or add gear doors to cover it up entirely. On mine, I sanded the structural former and skin immediately after the gear opening, and laid in a good thick Hysol fillet, nothing more.
A few other thoughts, for anyone out there still lucky enough to have a kit to build; On the fins, I had 2 sets. I made the rudders rather large on the 1st set and almost lost the jet due to flutter about 3.5 years ago now. I had Volz Wing Maxx servos in it, and the plastic servo arm split and stripped on one, followed by flutter, followed by the other stripping and fluttering as well due to the vibrations of the 1st (or at least that's what i figure happened.) I just happened to buy an extra set of untouched fins and wings on RCU 6 weeks prior! I retired the old fins immediately, and built a new set with smaller rudders, maybe 1.25" chord, and 2/3rds length from the bottom up to the tip. The rigid trailing edge in the tip area will help to stabilize the flow, and it allows an integrated servo to be mounted a bit lower (less pendulum mass, and stiffer skin). The smaller rudders were still responsive enough for cross wind. The servo I used in the 2nd set was the JR 398HV, and I wouldn't hesitate to use it again. I don't know of a better servo choice for the HotSpot fins. The heavy duty plastic JR servo horns are a perfect match for this setup.
My elevon servos were Hitec 5945MG's with the stock aluminum arm, and the speed brake was a 645MG - no need for a digital on the speed brake...
Construction wise, I used 7 Robart large hinge points per elevon, and 5 per rudder. When I cut out the hinge line, I cut back 5/8" and capped the section with hard balsa. Prior to bonding the cap strip on, I also mapped out each hinge location and sunk a hard balsa block behind the strip on both sides of the hinge; lots of meat for the hinge to grab with Hysol. On all surfaces, I oriented the servo linkage about 1/4" offset from a hinge, just to support the torque better, and I used 4-40 threaded rods with DuBro Kwik links everywhere.
Once built up, I glassed the wings and fins. The wings had 2oz cloth with the strands 45 degrees to the leading edge. That allowed a thicker glass to go seamless around the LE and cover the entire top and bottom easily with 1 sheet. A few cycles of sanding and skim coats of finishing resin gave a smooth and very robust wing surface but it took a while. This was good for 9.5 G's according to the eagle tree.
The fins were a different story. It's known that fin flutter is a failure mode on this jet, so stiffness and mounting technique are critical if you want to push the speed envelope. I've even seen it on a Hotspot with a P-80 at less than full power. I coated each side of the fins with the same 2oz cloth as the wing, sanded, then coated each side again with 3/4oz cloth rotated 45 degrees from the 1st. The fins will turn our brutally stiff, and the 3/4oz cloth is easy to finish up for primer. Mounting the fins - I went overboard there too. I bonded a thick plywood doubler on the inside of the wing root wall inside the fuselage, ahead and behind the internal formers, allowing for hard points. I had 3 countersunk screws per fin going into brass inserts in the fuse, 2 in the rear and 1 in the front. Then, I had 2 allen head cap screws inserted from the underside of the fuselage, through the already mounted fin, and into the wing, effectively sandwiching the fin onto the fuse with 5 screws per side. (see images below). Every time I met another Hotpot pilot, I checked his fins to compare stiffness. The only stiffer set I came across was permanently bonded to the fuse! Take it or leave it, but this system worked pretty good and I'd probably do it again the exact same way.
Flying, I've witnessed the deep stall issue but never had it happen myself. If the CG is rearward, keep the speed reasonable and it won't be a problem from what I could tell. The instance I witnessed was when my flying buddy was trying to do a slow rolling circle... I can agree that the solution to the 'chicken flop' is NOT to power your way out - it will not happen. Pull off the power, let the nose drop, and fly it out if you still have altitude. The erratic flight path in deep stall may be a result of gyroscopic effect of the engine, which gets worse with more RPM as you try to power out of it!
Speed wise, I'm really curious to see what sort of hardware was used to measure the speeds claimed earlier in this thread. I had to push mine really hard to hit 249mph, and did not use a 'stock' 1300R to get there. (I use to be a service rep, mine was cranked up to 127k, stock is 120k...). I found that atmosphere conditions actually did very little with respect to top speed, possibly since the air density that effects the engine performance also effects the drag, and drag is a squared function vs velocity... You will probably notice better verticals near sea level though! The 120SX was stock, and essentially new. I'd love to see what a 140 or 180RX would do. I don't know of many other turbines that would work well if you want to overpower it, since anything over 1.2lb of residual thrust will make a power on landing much more difficult IMO. When the PST 1300R was 1st introduced it had an idle speed of 40k, on a 66mm exhaust turbine platform that equated to around ~2lb +/- of idle thrust and it was a bi&#$% to get down without a 'roo hop'. I lowered the idle to 34/35k and it became much more reasonable. The 180RX appears to have a really good residual spec according to the last RCJI I just read, so that would make a seriously exciting model, but holy cow would you ever need to practice good energy management with the left stick. (imagine accelerating up at what would be normal gravity acceleration down, ~2:1 thrust to weight! )
Below is a series of photos showing how I mounted the fins and wings. It was a lot of work, but it was wickedly strong. Hope this info helps someone out there if they need a hand.
Kelly
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Kelly Williams, MAAC Jet Committee Chairman, JPO Member
I have one too. Kelly test flew mine in September and I have put one more flight on it since. Can't wait for winter to be over so that I can fly it again. Doing some structural fix-ups and finishing the repaint over the winter break but will have it flying again soon.
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Kelly and All, Thanks for the Hot Spot building tips and photos. On mine, I incorporated wheel wells to seal off the fuselage interior from any air pressure build up. I also added trailing edge stock (parallel to the struts), fore and aft, to help divert the airflow over this area. For the fin mods, I embedded a JR hi-torque MG servo in the middle of the fin with HD linkage to the narrowed rudders (as req'd for AMA rules). CF strips were added spanwise to the fins followed by 1.4 oz F.G. cloth in a diagonal orientation, 3/4 oz. cloth was added on top of this. My fins are secured to the fuselage by 10-32 flat head bolts thru hardwood dowels fore and aft. The wings and fins are retained by the plywood tab as per Wilcox's directions. The obechi skinned wings are glassed with 3/4 oz. cloth with overlap at the leading edges. I used JR 8411 servos, one per panel, with the servo and HD linkage perpendicular to the hinge line instead of at an angle as shown in the Graupner instructions. The linkage is on top of the wings to prevent any gear stripping from a wheels-up landings. HD Klett hinges were sunk into 1/8" basswood on the hingeline and pinned for retention. The model is provisioned for smoke with a 16 oz ventral tank off my DL Cyclone and I have a BVM F-16 centerline tank with an internal Dubro 24 oz tank also. I don't intend to fly my HS like a speed demon and I'm pretty much a mild flier anyway- especially at my age. I've discussed these mods with John W. from Model Aviation Products and he approves of them also. Hope these mods meet your approval also and I look forward to flying mine during the next season.
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quote:
ORIGINAL: BaldEagel
The Rookie does not suffer from this, Possibly this is down to the canards coupled to the elevator, it may be possible to retro fit them onto the hotspot.
Mike
Mike. I know you been flying your Rookie for a time now and was just wondering. What do you set your canard deflection up to in relation to the elev. deflection? also. Do you program to have your pitch vectoring to cut off at a high throttle setting? Thanks and happy holidays to ya.
Roy.
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RE: Census of Hotspots !!! - 
