I agree on the canard response above. This jet can be set up to fly nice and smooth, or more snappy as you move the CG back. Unless you have the skills to understand the full spectrum of aerodynamic effects from canards (on a jet you didn't design...), I wouldn't recommend changing the model. This design is well proven and flies great as is meant to be built.

I put a nose gear door on my 1st HotSpot (RIP...:() and left the mains open. The kit I got to replace my last one had been started by Al Watson (ex JPO VP) and he molded a set of CF main gear doors to go with the nose. My last nose gear door was driven from a retract servo through a bell crank. It was flawless, and I'll probably duplicate that setup again.

Question, what's the lightest anyone's ever finished a HotSpot with a standard P-120 size engine, with glassed fins and wings?

Kelly

The weather is finally getting better.

http://imagizer.imageshack.us/v2/800x600q90/36/p2oc.jpg

http://imagizer.imageshack.us/v2/800...0/835/ynn9.jpg

Regards, Bart.

Congrats Bart,

She looks fantastic, the SU scheme really suites the Hot Spot! ;)

Regards

John

That has got to be one of the most condescending posts I have read for a long time.

Mike

Dude, relax...

The point I was trying to make is that there's little to gain, and a lot to lose by modifying it. I flew mine for 10 years before is was taken out by an engine failure on climb out, bummer but these things happen... I flew it in a big range of CG's, and was so impressed by the model that I got a replacement kit.

The other part though, 2 good friends tried to retrofit canards onto a very similar model (an old Roo kit) without the resources to do it right, and it flew a grand total of 1 flight i believe... The aerodynamic effects of canards can be very unfortunate if not done right, and the aerodynamic theory is not simple.

Hopefully this post is a little more 'politically correct', and helps to save someone some cash and a little heartache.

Kelly

There's a hot spot at Florida jets for sale for $4k rtf with a low time p80

Don't judge others by your own standards.

Mike

As you said Mike "That has got to be one of the most condescending posts I have read for a long time." That comment itself seems strangely judgmental, with no other purpose that i can see - much less one relating to the purpose of the thread... Just ask yourself which of our prior posts were written to give advice vs. just randomly attacking the character of someone you've never met. (?) I have some background in aerodynamics from years back in university. Not an expert, but I know enough to be concerned if I was asked to modify or test fly a jet for someone without seeing some math behind the change. Not impossible, but it can certainly go wrong. Thus - the reply.

I'm done with this as this has nothing to do with hotspots. To everyone else - sorry the thread got off topic for a few posts.



On a more productive note, Is there a photo / info of the jet for sale at Florida Jets? Every so often I run into others looking for them and its useful info to pass on in the right circumstance. If they are still made and distributed in volume any more, I'm betting they can't be imported at a competitive MSRP into the US / Canada compared to the range of ARF sport jets these days. My replacement kit was a little over $1k US, with robart gear and BVM wheels. It came about 1/4 built, lots to go yet. The previous builder made up a real nice set of gear doors though.

Kelly

Kelly, do you have an idea about increase in speed range when fitting gear doors?

On my last 2 flights with the Hotspot i fitted a GPS sensor, max speed recorded was little over 300km/h. That is with an old Behotec J66 engine wich has about 8-8,5kg of thrust.
I recently bought a Simjet 2300 to replace the Behotec (3kg more thrust) and give it some more topspeed, but maybe i should also start building some geardoors?

Regards, Bart.

Kelly
To supply kits like these which are still available, at an affordable rate would be down to quantity!
Currently this kit will cost you €500 if you pick it up in main land Europe yourself!
The wing has been modified with a reflex to eliminate the visual up trim required for normal flight (level)!


Regards


John

I flown mine with Simjet 2300 and was very fast jet, after take off you can climb to vertical withow problems.
really cool !!!

Really , I guess a guy who has successfully flown one of these for 10 years wit at least 3 different power plants and is an engineer is just trolling. The topic is census on hotspots he is giving his educated opinion on flying one for 10 years, it's know wonder this forum is what it is. Condescending ........... Whatever

Kelly just get ready for spring

Hey Carlos
Are you still going to do the re moulds for the Hot Spot this summer?

Regards

John

Yep, completely agree John, The supply and demand curve kinda falls apart for getting them over here. Demand wise, it just doesn't make sense. My friends over here think I'm crazy to build another vs get a flash or something more modern. :p That's probably why someone like Dreamworks doesn't import in volume, too much risk... Without that - the landed cost of shipping in low volume across the Atlantic is going to put it out of a competitive price range. If I ever happen to be in the area on a business trip, I'd be hard pressed not to bring a new kit back with me though!



Some time ago in this thread, I asked for photos of the newer kits to compare before and after. A few photos were posted of the fuselage insides and it looked like an identical layup process to ~10 years ago, a very good sign. Does anyone have a photo or info on how much reflex is applied to the new wings? I have 2 unbuilt sets of the older style, so I'm not in the market for the - just curious.

Kelly

My Hotspot is a new kit, i'll take some pictures of the wing root tomorrow!

Regards, Bart.

Bart (awesome avatar by the way, that image my desktop background! :) )

I had an eagle tree system in mine, and recorded a whole bunch of flight data with different turbines and so on. The fastest ground speed I was able to record with GPS was 249mph (400 kmh), which was verified with similar air speed info. That was on a PST 1300R. I switched it out for a JetCAT P-120SX. Never got around to pulling the data out of the Eagle Tree before my crash, and the Eagle tree didn't survive, so its hard to say what it would have been capable of. The 120SX was an awesome combo for that jet, ridiculous vertical performance, and busting through 200 mph in a level pass was very easy...

Since we're talking speed, I need to add a safety note 1st for anyone else reading this... One of the main failure modes on the Hotspot is fin flutter at higher speeds. Been there - and luckily I got the jet down in 1 piece! Fin flutter is avoidable if the builder pays close attention to fin stiffness, using a good quality thin servo+arm, making the rudder chord only as long as it 'needs' to be, and adequate clamping to the fuselage. My 1st fin set had Volz wing Maxx servos with the default arm (as they were the only ones that fit). At around ~230 mph according to the eagle tree, right out of a power dive, It looks as if one servo arm failed - started to flutter - then the vibrations caused the other to go immediately after. The sound was unbelievable... Anyway, I retired those fins and built up a new set with much smaller rudders (in chord and length) and noticed not adverse problems in cross wind yaw control. The new set had a pair of JR DS 378's and heavy duty JRM arms, a big upgrade over the Volz.

According to the MATH, we're dealing with a natural frequency problem. Nat freq = (k/m)^(1/2) where k is stiffness and m is the sprung mass, assuming no damping in the system. Fin flutter is more of a rotational oscillation about the fuse contact point, so the k equates to the stiffness of the fiberglass layers + clamping to fuse, and the M is the spring mass of the system about the center of rotation. Without doing a PHD on it, what this means is overdo the fiberglass (as stiffness rises way faster than mass) and keep the servo mounted as low in the fin as possible (to reduce spring mass radius and maintain the skin strength as it becomes smaller higher up.) The net effect is increasing the theoretical speed limit to higher than the model can easily reach. My build had a layer of 2oz cloth on each side of the fin, plus another layer of 3/4oz cloth rotated by 45 deg to make the skin uniformly strong with good surface. I bolted the fins to the fuse with 3 x #8 countersunk screws each side, then sandwiched the fins to the fuse with the wing's 2x bolts each side. The only stiffer fin set I've seen on a HotSpot were permanently bonded on. In terms of the aerodynamics of the rudder, it makes sense to start from the bottom, and stop well before the tip. Leaving a solid fin at the tip reduces the chances of a fluttering rudder at the extreme radius, and the solid trailing edge should work to stabilize the flow.

This plane can bite if the pilot is pushing the limits. The other end of the scale, a local pilot here had a hotspot with a P-80 in it, and couldn't get past 1/2 throttle due to a fin stiffness issue... He had the default setup from the instructions, and only iron-on film for covering.



On the gear doors, I'm not sure what to expect for decreased drag, but I'm going to run both a JR telemetry system and an eagle tree unit for the 1st few flights to find out. I was planning to fly with and without doors on, limit the thrust to a moderate level, and compare the airspeed curves. I'll post that when I have something concrete, but it'll be a while...

An important note though; the other major failure mode is known to be the rear underside of the fuselage peeling off the jet in flight, separating right behind the gear openings. In my mind, that's the biggest benefit of gear doors, preventing that leading edge of the skin from grabbing the air. Its not necessarily the speed - as there is certainly enough already! :) With or without gear doors, make sure to build up the adhesive layer that bonds the skin immediately after the gear openings.

Kelly
(sorry for the long post, never hurts to publish safety info... Hope that isn't take the wrong way by anyone...)

Here's the gear door set on the kit I picked up. The builder molded them from carbon fiber. Can't wait to see what it looks like built up an paint, in the air with a 'clean' underside.

K

Kelly,
Thanks for posting on this HS thread as I am keenly interested in completing mine-just awaiting the shop to warm for final glassing and paint. I took your excellent advice on reinforcing the vertical fins-using 2 layers of 1.4 oz glass applied on the bias. Also fitted JR 368 servos in Graupner servo mounts. The wings will be bolted to the fuse via 1/4 x 20 AL bolts, with the fins in the sandwich. In lieu of gear doors I plan on fitting wheel wells to prevent the buildup of slipstream tearing off the rear fuselage bottom. Nice job on the CF doors by Al W. though. Power will be either an ancient RAM 750 pumped up to a + or a Rabbit.
As an aside on fitting canards, several years ago I spoke with Steve Elias (noted UK jet pilot) and he stated that canards were not worth the effort on a HS. He also warned on fully extending the airbrake on tight turns to final as the turbulence may blank out the fins.
Again, thanks on distributing valuable information on the HS-a classic sport jet.
Rgds,
Art ARRO

Hi John & company:

yes, really I want built the molds this summer, until the date I am working in the fuselage, for to have it ready.
I will tell you news as soon as possible.

Carlos.

Carlos

So sorry that this thread has degenerated into a bean fest for one person to try and demonstrate how cleaver they are.

I thought it was only in the US that they thought there was only one MATHS calculation.

Deleted.

it started at post 254 getting off topic , ,Kelly spend your time getting ready for princeton in the spring your wasting it here

Well i'm not really that worried about the flutter problem on the fins since i don't have rudders. I don't miss them (yet) and at speed i can do a four point roll just fine without any noticable drop. For knife edge and long slow rolls i have other planes.
But it is mainly the lack of rudders that makes me want it to go just a little faster.

Regards, Bart.

Kelly hauled the mail with his and flew it well for 10 yrs. I was present for the rudder flutter and any other pilot would probably have totalled it. I give him the gears all the time on getting it done. But in the end he builds a well thought out airframe that will fly well and last. He knows the hotspot well.

No problem Art, its good to see this site can still work for guys to offer help to each other. Ya, Al W is a good friend, and it took a while to convince him to let me have the jet when I lost mine... It was either this kit from Al, or a used jet with some (fixable) nose damage hanging in a hobby shop near Toronto. I think that one's still there if anyone in the East is on the prowl for a jet, but it has the Euro gear and I think Du-bro wheels... Not traditional hardware.

Hey, on the speed brake... Are you going air or servo operated? If servo, can you post a pic or 2? My speed brake frame survived my crash but isn't worth using in the new fuse. Kinda feel like a scratch build at times, and I could use some inspiration...

Interesting note on the turbulence at high alpha, makes sense. I heard there is a similar theory on F-16, having the nose blank the fin, which is apparently the reason for the relatively large fin + ventral fins. Don't know for sure, just what I was told. On the HS, I only extend the brake full on final but half extension and gear down sure makes it feel mushy... No idea what it would turn like on full brake.



The biggest HotSpot instability issue I've witnessed was from my buddy Jon. He's on to his 2nd hotspot, with a homebuilt UT-160 for power. The jet can get into a Roo-like chicken flop if the airspeed comes down too far, while flying on a rearward CofG. His 1st one crashed twice because of this, both times rebuildable though. At least, if it does crash, it goes in at low speed. Forward CG doesn't seem to have the same problem. If it happens - pilots say the way out is to just cut the throttle and wait for the nose to fall - then fly out if it still has altitude to recover. Jon tried to power our of a spin the 2nd time, and it didn't work out well... I once saw a guy at Superman do this on purpose. He floored it in the spin and the jet went ballistic flopping all over like a bouncy ball. Guessing that is a gyroscopic effect from the turbine. Looked cool, but probably beat the hell out of the bearings!

Man, this thread is making me want to go out into the garage and get on with finishing it. winter - please go away...:(

K