Safety
 

I agree entirely with what David is talking about, we all invest a lot of time and money in the branch of the hobby we have all been waiting for for five decades, we should not allow one neglegent action or occurance to spoil our enjoyment. I also feel it's about time other countries follow the US examlpe and require pilots to have a turbine waiver! In the UK for example it is possible for a complete novice to obtain an almost ready built model fit a 27lbs thrust engine and go and fly!!!very worrying. If the hobby as a whole is not prepared to safeguard it's own interests someone is likely to spoil it for us

BRG Mick

Hotspot Structural Failure
 

yes, and always wear a helmet :(

mec

Unfortunally!!!
 

I also agree with David but......unfortunately the $$$$ is usually the deciding factor in many of these cases.

Remember the days of the Byron F-16 and the rudder flutter problems? Byron (the company ) denied there was a problem right up until they put out a fix for it.

In contrast, when BVM encountered rudder flutter problems in their earlier F-86 model...addendum's were immediately applied and info sent to all kit owners. Different policies for different folks appears to be the norm in this hobby of ours.

Personally, I am also building a HotSpot, w/o doors, and I am going to take heed to the warnings. The wheel wells will be sealed....why take any chances ??

Rod

Hotspot Structural Failure
 

I just flew my first HS but only AFTER fixing the same problem area of this post. The plane is a brand new one and it was clear to me upon inspection that this area had major delamination. I reglued this area and I then pinned it with self tapping screws. I do hope that this will fix the problem. I love the way it looks and flys so far.

If this delamination is shipping or design produced, The manufacturer will be able to fix it for no cost, just a simple mfg change. A " NOTE " in the manual would also be a wise business move.

Who ever said that this is not a problem or that SOME people have no knowledge of this hobby is respectfully in error and should play a proactive role being a dealerr of such product. I think we said enough about this and now it is time for the factory to ignore it or to carry out corrective actions.

Hotspot Structural Failure
 

David Gladwin,

I agree whole heartedly with your comments, I have recently been in contact with Winnie Olgart the editor of Jet Power magazine who recently published a review of a kangaroo2 kit and was pretty scathing about various aspects of its quality,accuracy and structural integrity. At the time he was advised not to be so critical but he felt the buying public had a right to know what they were getting for their £500 or so, The result was that Fiber Classics have carried out modifications to the Kits which will be available soon, Its called feed back and all credit to those concerned.I know there are those who do not like it but unless we use medias like this to inform each other if there are short comings with products etc we may regret it at a later stage.
yours
Brad.

Hotspot Structural Failure
 

When I built my second Kangaroo I had the exact problems as the review article stated. This is the second magazine that I susbsribe to that calls it the way it is. If the manufacturer made changes based on the feedback so much better. I cancelled my subscription to the other three so called honest review magazines. Good work. Now please have the German adds translated into English and I will be really happy. (at least for the next 1/2 hour)
:D

Hotspot Structural Failure
 

Thanks for the support guys. I can assure you all that I only want EVERYONE to enjoy and benefit from this hobby and that includes manufacturers, distributors and their customers but we have got to do it with the discipline and profesionalism I haver experienced in full career of flying real jets of many types and sizes. These models are very high performance machines and like it or not we all live in a very litigious world and a serious accident could finish it for all of us. I Its time the Hotspot delaminatiion problem, a defined possible cause of structural failure as there have been too many reports to dissmiss, was fixed once and for all. If Graupner think the cost of a fix is too high, I can promise them its a drop in the ocean compared with the probable cost involved following a serious accident, now that the problem is known.

I rest my case.

On the subject of honest reviews when you read my reviews in RCJI you read what I found ! Its got me more than a little hassle and unpleasantness from some quarters but as I pay for what I review I absolutely believe that an honest and fair assesment is in the interest of both consumer and manufacturer. Having said that , I generally only review the good stuff, i. e that which I am prepared to pay good money for !
BRG,
David Gladwin

Hotspot Structural Failure
 

Any chance you would like to elaborate on the "exact problems"?

Thanks

Hot Spot
 

I am in the process of building one as we speak. What should be done to minimize delaminating? Should gear doors be made at this point instead of having simple openings? I am using Robarts gear, will that be a problem since I have had to modify the openings already to accommodate the gear. Any advice would help.
Thanks
Jester

Hotspot Structural Failure
 

my hot spot is now two years old and has approx 100 flights on it. as i mentioned in a previous post, it was the 10th flight, we heared a high frequency whine because of a failure of the bonding joint near the main gear openings.

IMHO we all should do thoroughly preflight checks (as it is a must for all planes) and in case rebond these joint. this would eliminate the initial cause for delaminating the fuse.

we use turbines from 85N to 130N.

this hot spot was one of the first that has been sold (by peter liebetrau). it has gear door for the steering wheel, but no gear doors for the mains.

our second hot spot is 5 months old (maybe the graupner hot spot comes from another source, manufacturer?) with 50 flights on it. it has gear doors for all wheels. no delaminating tendencies occured till now.

mec


btw: two weeks ago i saw the longest (involuntary) hover of a turbine aircraft (our second hot spot). pilot ernst started with a rolling circle, however and unfortunately too slow. in the inverted flight passage the HS suddenly snaped to a hover position. i estimated it was 200/300 meters away, therefore it was difficult to gain controll over the plane again. the HS hovered at full power, 30 meters above ground. it took 10! seconds till the HS slowly turned to an inverted flight position. with full down elevator ernst seemed to gain control over the plane again. but suddenly the HS stood again vertical loosing altitude more and more. this took again 10 seconds. 10 meters above the ground i advised ernst to shut off the engine. in inverted flight position our HS kissed the earth. it is still repairable.
the damage done is a delamination of the rear fuselage. and it showes bonding techniques of not the best quality (however good enough for safe flights if checked from time to time).

Hotspot Structural Failure
 

Gentlemen,

I am currently building my second HS, which I received from Graupner two months ago. While building it, I have found that this airplane has all the formers and landing gear supports beefed up with what seems to be an Aeropoxy of some sort, contrary to my previous one, which I bought two years ago. So, it is my belief that Graupner and their HS kit makers (Peter Liebetrau) have taken care of this problem.

BRG
Chris

Hotspot Structural Failure
 

despite the fact that I I have done thoroughly preflight checks all the time, my HotSpot delaminated during a high speed pass.
I saw pretty huge parts of the fuselage fly away, did everything to slow down imediately, the HotSpot seemed to be under control. I decided to cruise around for some minutes to burn fuel. I saw there was a wooden coloured part hanging approx 30cm below the fuselage in the air. I thought it to be part of one former or retract mount hanging on the airline. surprisingly the gear operated normally and came out. landing was fine, but after some meters the engine quit and the plane was dead, without current.
as I approached the plane, I realized it was the reciever battery pack that was hanging out of the plane. on touch down one wire ruptured.
thats what I call luck!

Hotspot Structural Failure
 

for security reasons I decided to fix this problem by screwing the most critical parts of the fuselage to the formers as can be seen on the picture.
I strongly recommend to use screws additionally to the glue of these joints if you are using an engine with more than 80N thrust.

mec

Hotspot Structural Failure
 

You call it luck. (See item I highlighted in red)

I reserve my comments

Hotspot Structural Failure
 

I may have offended some with my previous posts on this subject. That was not the aim, merely to focus on this issue of HotSpot delaminations and get it fixed before there is a serious accident. Clearly Graupner and their agents are burying their heads in the sand as nothing has been heard from the manufacturer or their agents, regarding a solution to the problem, since this thread was started.

I know what would be done in fullsize aircraft operations if a similar problem were to be discovered: The whole fleet would be grounded until the manuacturer and the regulatory authorities had fully investigated the problem and devised a solution.

Clearly this latest incident shows that the problem is serious and continuous and needs to be solved once and for all.

Its time Graupner recalled ALL hotSpots for a detailed airframe examination and if neccessary replaced the models with new kits (or, if at all possible, devised a modification programme for existing airframes ) which have been so modified as to eliminate the possibility of in flight delamination.

Should Graupner fail to take action then there is a further possibility and that is that the AMA in the US and BMFA in the UK and DMFV in Germany should remove insurance cover from these models, effectively grounding them, until the problem is fixed.

High speed gas turbine models some of which are KNOWN to have a serious structural weakness simply cannot be allowed to fly unrestricted, its a form of Russian Roulette the hobby can do without.

And if the manufacturers distributors, agents and owners don't like what I say I think they would find it preferrable to hearing that someone had been killed or injured following an inflight breakup with all the consequences that might bring.


Before Graupner and all HotSpot owners get too upset perhaps they could recall the Comet breakups in the early fifties. The Comet airliner was redesigned and restressed to make it incredibly strong and the basic airframe continues in service almost 50 years later as the Nimrod. A hotSpot fix should be failrly straightforward but urgent action is required.

I have no personal agenda other than to speak out to protect the hobby BEFORE there is a serious accident, which could have been avoided, with all the consequences that could bring to all of us who so enjoy the hobby.

David Gladwin

Hotspot Structural Failure
 

David you are absolutely right.

But there are a few things I have to mention:
My hotspot was one of the first series, bought and flown immediately after the Jet WM in Zeltweg 1999. till now it burned 300 litres of kerosin, surviving three crashes. It’s a pretty old (nevertheless always best maintained plane) jet.
At that time Graupner had nothing to do with selling Jets. In addition to this, in 1999 (first year of Hotspot have been sold) 120N (or even more) turbines had been a dream and no reality at all.
From what I have been told, at the JetRookie Meeting last weekend, held in Karbach, Germany, a Kanguruh, a very fast one, exploded in the air.

Conclusions:
IMHO it is and always will be in our responsibility to do all we can do for safe flying.
Nevertheless ist´s a shame that manufacturers are burying their heads in the sand and do nothing to fix those problems.

mec

Hotspot Structural Failure
 

Could someone please elaborate on where the suspected delamination is occurring.

I'm starting a new Hot Spot and want
to be aware of what to look for....

Thanks
W.G.Hunter

Hotspot Structural Failure
 

Clearly, the bottom line is this :
SOME HotSpots and Kangaroos are absolutely fine, SOME are not, problem is we dont know which ones are which.
We now have a known problem which requires action and it is required NOW, not after an accident.

Would anyone continue to drive a car which was fitted with tyres which were known to explode, I doubt it, so why fly a HotSpot or Kangaroo which may disintegrate in flight at very high speed ?

No doubt there are those who will take umbrage at my comments but I ask them to consider the possible very serious consequences of continued operations.

I am prepared to put my money where my mouth is too. If Graupner and Fiber Classics have kits in Australia or are prepared to send one here I am prepared to look at these structures and give an unbiased and honest view of the structural integrity and construction quality and see if and how things can be improved. With 50 years of modelling experience and extensive experience of building and flying model (and fullsize) jets I MAY be able to help. No charge for my time and the kits will be returned intact and complete but some investigative surgery may be required to examine inaccessible areas.


To date I notice the deafening silence from the models' manufacturers, distributors and dealers, lets hope that will change.

Regards,
David Gladwin

delam
 

i am currently building a hotspot and i will certainly add wheel wells. i feel that when the hotspot and kangaroo were created we were not bolting on so much power. build a 500 hp motor and drive your car at 200 mph with the windows down and see how long the rear window stays in, should the manufacture build the car to stand this stress because you may overpower their product, i am not saying some lamination may be subpar, but all of the pics i have seen of damaged aircraft have no doors or full doors and no wheel well, the air must go somewhere and overtime it will take its toll. just my 2 cents. it is we are pushing the envelope and everything gets more critical. barry

Hotspot Structural Failure
 

Update : I started this thread on behalf of Mr Birkett, the owner of the delaminated Hotspot.
Despite writing to Graupner via registered mail he has still received no response.
I want to make it clear that the aircraft was not overpowered (AMT Mercury) ,it was less than 10 flights old and it was being flown by a trainee under my supervision at mid throttle. This aircraft had nose and main doors.
I think the solution MEC has suggested ie using screws to hold the skin to the mounts and former is probably the best fix so far.
The addition of wheelwell liners is also a good idea, however they are not a fix on their own. The skin bond in the undercarriage area is obviously not strong enough.
I'm not surprised one has disintegrated at high speed, we suffered major damage at low speed.
I mentioned in an earlier post my concern that batteries should not be placed in the area behind the undercarriage mounts, MEC had a lucky escape, make sure batteries are firmly secured elsewhere.
I will update you all if Graupner ever reply to Mr Birketts letter

Thank you

Hotspot Structural Failure
 

Hi,
I had read about the California delamination and tested mine as per the instructions from the author. I noted that the skins did indeed separate with the inner cloth still adhering to the formers and the outer cloth waving in the breeze. I leeched CA into the edges of the skins and drilled 66 holes along and into the formers through the skins. These hole were about 1/4 inch apart across the whole fuselage at the tank former, and also ont the rearward gear formers.
I inserted thin CA and then thick CA and pounded round toothpicks into the holes. Once sanded smooth I again used thin CA on the ends of these "rivets". The skins no longer would separate and the plane has been at 180 ~ 200 mph and still looks fine. I did not use wheel well liners, but that does seem like a good idea to keep the buffeting air out of the tail end of the fuselage.
Len

Hotspot Structural Failure
 

think of the fact that wheel wells will prevent air coming in the fuselage but also will prevent us from doing periodically examination of the suspected bonds.

mec

delam
 

the last 3 posts are excellent suggestions and i will certainly take a close look at my hotspot as i construct it and no matter the reason for the delam graupner should have a dialog with you, it is good customer relations. barry

Hotspot Structural Failure
 

Lets have some constructive thoughts:
What causes the fuselage to delam?

1 too much airspeed by overpowered models
2 previous minor, undiscovered defects after hard landings, belly landings a.s.o.
3 improper glue joints

the thousands of faultless flying HotSpot and Roos prove that the basic construction is able to handle even the 120N and more engines.

The part of the fuselage that came apart during last flight showed some significant distorture on the border near the landing gear cutouts. This border was bent like a vane, directing straight into the airstream. It seems that this was the point where the misery begun. I do not believe that at highspeed there is so much pressure in the fuselage that it tends to explode.

Some points to consider:
Cause of a belly landing my Hotspot suffered from a weakened rear fuse joint. The repairs had been done with CA. But this will be a weak point forever.
As you can see in one of the pics above, I did enlarge the main gear cutouts to fit the new legs. This helped to let more air in the fuselage during flight.
If you use a smokertank, pressurized by the engine pressure, think of the fact, that this will not help the fuselage to stay together when the tank blows up and comes in contact with the upper and lower surface of the fuselage´s body.

What to do?
As mentioned above, I will never fly again my HotSpot without having srewed the suspected parts to the 7x7(?) wood former. In addition to this, with the help of my heatgun, I bent the border near the cutouts to help staying to the glue joints. Airstream will pressure this laminate to the former.
Len´s idea with the toothpicks is also worth a try.

For all new Kits:
It is in the responsibility of the manufacturers to fix this problem.


mec

Hotspot Structural Failure
 

If you look at the shape of the hot spot there is no release out the back of the fuz for the air to release through , so the air builds up inside and then pop,there gose ur fuz ,put some air vents in the back of the fuz to allow air flow through , thats why the ones with doors on tend to blow out