turnnburn

My Feedback: (49)

I have a new in the box never been started Graupner kit for sale. I don't see myself buidling it so its up for sale. Make me an offer@ [email protected]. Pictures available upon request.

cmjets

Shipping to Spain ?

cmjets

Hey !!!!!

Hotspot lovers !!!!

News ????

Kelly W

My Feedback: (2)

Hey a question for you Hotspot guys. I crashed mine a few years ago from a really poorly timed engine failure. Still hurts, but I manager to pick up another kit!

All i have for power this time is a P180RX, which will be heavily de-tuned of coarse... When rolling back the max RPM, the fuel consumption typically suffers due to the lower pressure ratio in the engine. My 1st Hotspot had the ~2.5L main tank, with a pair of dubro 18 oz tanks in series on each side of it. (that made for ~3.5L) The pump was drawing from a UAT, then a DuBro, then the other DuBro, then the big tank in the middle. the big tank drained 1st.
It worked well, and kept from ballooning the big tank too much. I'm wondering though, what is the most fuel capacity that any of you have been able to cram into this jet?
Thx,
Kelly

DelGatoGrande

My Feedback: (23)

mine Dreamworks Model Products LLC

turnnburn

My Feedback: (49)

You seem to be suggesting that by running the engine at lower RPM the fuel consumption will go UP ? This is simply not true. If that was true the engine would burn the most fuel at idle and the least at full throttle. The specific fuel consumption for the power produced is probably less efficient and goes down but not the actual fuel consumption for a given period of time.

I have a Jet Tech kevlar tank in my Hotspot. 105 ounces made specifically for the Hot Spot $ 145.00. I know its enough capacity for a reasonable flight time, and would be even with a RXI 180, especially since you are going to turn the thrust down to that of a 140 or 120 or 100 .

Google search Jet Tech Fuel Tanks.

Kelly W

My Feedback: (2)

I was talking about 'thrust specific fuel consumption' That's what the GTBA used to rate efficiency in turbines back in the home built days. I think the units of measurement were [(oz / min) / unit of force generated]. You'll find the curve is largely parabolic, meaning the engine is most efficient at or very near full throttle. Fuel efficiency is largely a function of the engine's pressure ratio, and the pressure ratio is highest at full power. It also means the thrust specific fuel efficiency drops off quickly if you're not at full throttle. This is the biggest downside of getting a huge turbine, and detaining it for a smaller jet, in addition to possibly more residual thrust. Running a P180 at 30 lb will probably force you to land sooner than a P120 at 30lb and the same fuel capacity.

I know about the jet tech. I have a few of them in other jets, good quality products... I was looking to see what configurations of tanks might have been tried, and what max fuel capacity might have been achieved. I might do the jet tech (3.1L), but I'd like to get 3.5L or better total.
Thx,
Kelly

mr_matt

My Feedback: (10)

Kelly with respect (and I don't doubt your math) in my experience the SFC difference is not appreciable. I have a P-180RX in a Bobcat and with the speed limited to 200 mph with a JetCat integrated speed sensor, I get plenty of flight time. From the telemetry the turbine is hardly ever at full power, and never more than 6-8 seconds at a stretch so it is lightly loaded and appears to be reliable.

and it has a shocking amount of push for low speed vertical maneuvers. I would not limit the thrust but limit the speed.

I will say however the higher residual thrust is a very real problem. And of course dialing down the thrust does nothing for this so make sure you have very effective speed brake (including the push rod geometry) and I might recommend canting the rudders as well. I have not tried this on a hotspot but it is very effective on a stingray and even the bobcat.

Kelly W

My Feedback: (2)

Matt, that's exactly the motivation I needed to hear! I have no data what so ever on the 120SX I had vs the 180RX I have now, but I'm a huge fan of the vertical takeoff. The 120SX had enough push to sustain straight up with full fuel, right from liftoff. I can't wait to see the next on 'accelerate' up... I need to get myself a speed sensor!

I ran 4 different engines on that hotspot in the 10 years I flew it. One was horrendous on fuel, so it got me a bit gun shy on flight time. The same engine also had a high residual, making the landings very tricky. The 120SX was pretty good, my favorite of the 4 engines by a long shot. If I were doing it again, I'd do a 140.

Good call on the speed brake options. With the inward leaning fins it might make sense to deflect the rudders inwards to counteract a nose up moment. Won't know till I try it...
Thx,
Kelly W

Air Works

Hi,

I have a two servo per wing setup. Can you tell me

Movement up
Movement down
Are movements same per wing i.e. outboard and inboard surfaces move by same amount
Any reflex
Any braking i.e. CROW and if so movements

Thanks
Paul

mauryr

My experience with underrating turbines is very different, but it might be also due to the engines used.
I have a velox XL, which has been flying for a few years with a k180 detuned to about 12~13 kg of thrust. This year I took it out to put it into a bigger plane and replaced it with a k120 and the fuel consumption went down VERY noticeably, while the power of the airplane is very comparable (the 180 had a much better low rpm push and spools faster, but that's about it). I suppose the k120 is an overall more efficient engine than the k180, but anyways, this is what I experienced
I went as far as removing one of the 3 tanks and only filling up the second tank up to half this season.

mr_matt

My Feedback: (10)

Yes it whould be worth experimenting, I had inward canting on the stingray and outward on the Bobcat.

On one bobcat I had, I carefully set up the rudders with big servos and a lot of throw. When I threw them out it was like slamming the brakes in a car, far too effective!

I think you will be pleasantly suprised. The canting rudders, good speed brake, wheel brakes you can preset on landing and keep that P-180 at full tilt, should be fun

dave.windymiller

Having previously got my hotspot down to 7kg dry (to be able to fly at my local field), i discovered that even with a VT80, it could fly indefinately on idle power. Landing it became a problem as it was too slippy and the runway was too short. After a few mishaps with fast landings i decided to abandon the 7kg limit of our local site and fly elsewhere. This meant i could now add an airbrake, wheelbrakes and add redundancy in the power supply and beef up the turbine battery.

Having painted the fus, burying the airbrake outine cast into the surface, i was pleasd to find i could see the shape using a bright led torch from the inside. My brake uses a servo that latches by virtue of an inline linkage. I have also added a pair of magnets to grip the airbrake when fully shut (magnets close but not touching) to stop the digital servo "singing".

skunkwurk

My Feedback: (18)

Hi Carlos,

Sorry to change the subject, but that is a nice F-18 in the background. Who makes that one and what scale is it?

sc

cmjets

Ha,ha,ja, yes, you changed !!!
it's a F-18 1/8 of Jet Legend modificated to Two seats version, I sold it the last year.

Regards from Spain
Carlos

skunkwurk

My Feedback: (18)

Very nice... Thanks.

sc

cmjets

Come back to Hotspot, I'm installing Electron Retracts, the best landing gears in the market. In sort photos !!!
i'm anxious for see the result !!!! and fly it, of course.

i will make a new tank too, my Hot has the nose heavy because it's painted, I think this is reason, and not has logical install a tank that is all in front CG, and of course, will be available in CMJETS Website.

and ...... the next month at last, the new Hotspot fuselage ready for molds !!!!!!

Regard from Spain
Carlos
www.cmjets.com

smoknrv4

My Feedback: (11)

Carlos how’s the Hot Spot kits coming along?

cmjets

Hello, the new Hotspot project go slow that I want, I have too much job with my tanks and I not begin the molds yet.
in short, I hope, I will have it. As soon I have it, I will show it here, sure.

i have my actually Hot with Electron and go superb,
I will try upload pictures.

Thanks for contact.
Carlos

www.cmjets.con

turnnburn

My Feedback: (49)

Ok Hotspot experts I need some balance help. I need to know the correct procedure and range for Center of Gravity. I presume it is done with gear down and fuel tank empty ? 7 to 7.5 inches outside of the vertical fins. Is any one flying with CG less than 7 inches or greater than 7.5 inches outside of the verticals. I am having some troubles getting my cg that far aft even with batteries all the way aft.

Randy M.

My Feedback: (38)

Going by memory, it's been awhile, measure down the leading edge about 6inches from the root. Should end up about 1.5 to 2in. In front of main landing gear. Not super critical with the hot spot. If you need more tail weight, move the engine back a little.

turnnburn

My Feedback: (49)

The hotspot instructions call for 7 to 7.5 inches. They do not say if that is with empty fuel tank (which is the norm) and with gear up or down. I imagine it is with gear down and no fuel.

Randy M.

My Feedback: (38)

I'd go with that. I always cg in landing configuration

cmjets

cmjets