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HelicopterTurbine Helicopters › Has Anyone on the Turbine Heli Side Tried This
12-03-2005 12:15 PM  12 years agoPost 1
wolfdad

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Southern Maryland

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Quite honestly, while building the BK-117 (StatMedEvac 10), I have avoided the subject of heat build-up and potential resultant damage from the exhaust heat in the rear cabin. Now, the time is drawing closer to start and test fly the beast. Now, the heat build-up and insulation has become a priority one situation and I am still not sure what the answers are going to look like. However, I ran across something on Bob Violett's web site the other day that the fixed wing crowd is using and, evidently very successfully. Bob markets the stuff as "Heat Shield," and it is a paint with ceramic material blended in (NASA helped develope this) and, supposedly does an excellent job of insulating anything it is applied to.

After doing a considerable amount of further research on the product, it is marketed under a number of different brand names such as Super Therm, Thermoplas, et al. If the claims they make about this stuff are anywhere near the truth, this should work like a champ, however like so many other things, the real world is different. I would sincerely appreciate knowing if anyone else has tried this with a turbine heli, how it worked, what brand you used, product cost and any tips or advice you might have for application and use. Super Therm claims a R-19 insulation value with two coats of their product....I have a hard time believing that.

wolfdad sends....

"There are those who have...and, those who will" IRCHA #2117, AMA #70068, Turbine Waiver #105

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12-03-2005 01:01 PM  12 years agoPost 2
Gary Travis

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Utah

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Awhile back I used the Supertherm in a fixed wing application that I had some heat problems with, It worked much better than I had expected. Although I have not tried it in a helicopter, the heat situation in the fixed wing was terrible til I used it and never had a problem after that. I had two coats. Based on how it worked in the fixed wing I would think you would get the same results in the helicopter.
Gary

Bergen R/C Helicopters Duralite Batteries DJI Innovations Magnum Fuels Wren Turbinesl

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12-03-2005 02:59 PM  12 years agoPost 3
wolfdad

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Southern Maryland

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Gary,
Many thanks for the information!! I can always count on you to come through on these odd-ball items. I didn't want to deal with the heat issues so I procrastinated on resolving the problem until about a week ago when Jack Martin and I started throwing it back and forth. Now, probably less than a week from the first test flight, I am still looking for an answer. After seeing the Heat Shield on Bob's site, then doing the research, I thought this might be the answer....combined with some thermal blanketing.

Again thanks..

wolfdad sends....

"There are those who have...and, those who will" IRCHA #2117, AMA #70068, Turbine Waiver #105

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12-03-2005 04:23 PM  12 years agoPost 4
PETER ROB

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Devon UK

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thermal paints

Doc Len Mount has been using this heat resistant paint for a couple of years, he swears by it maybe a call to him will get you facts and figures on the application in the real world,

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12-03-2005 04:55 PM  12 years agoPost 5
WIRLYBIRD

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CAPE TOWN / SOUTH AFRICA.

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Heat Shield

Hi Doc,
I see you are as ever busy as a bee, I've used the heat shield paint from BVM , and can put my head on a block, if applied correctly, as in my NH90, with the huge bifercated exhaust.It used to turn the red paint brown from the heat, after two coats of the heat shield, the paint remains red, I had to apply this to large sections of the body.You can go ahead and use this product with confidence.
Best regards,
Dave.

WHAT GOES UP MUST SURELY COME DOWN.

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12-03-2005 06:59 PM  12 years agoPost 6
wolfdad

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Southern Maryland

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Peter Rob, Jack, Dave and Gary,
Thanks a million for your inputs....very much appreciated. Peter Rob, if Len Mount is using it, it has to be good, however, on Monday morning, you can bet I will either be on the phone with Len or later in the day with Al Wirt, Len's US representative. I sneaked over to Sandy's site and apparently he used the paint both on his BK (same fuselage as mine) and his NH-90. I think I am definitely getting a positive drift in the reaction and information.

Jack, as always, you are right on the money and your comments regarding "enough" air were interesting. You actually wind up fighting two heat enemies....one, the turbine operating temp and two, the temp or overtemp brought on by the combustion process. And, each one has its own distinctive causal factors. I can truely say one thing for sure, the futher you go, the more interesting scale gets.

wolfdad sends....

"There are those who have...and, those who will" IRCHA #2117, AMA #70068, Turbine Waiver #105

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12-03-2005 08:50 PM  12 years agoPost 7
PETER ROB

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Devon UK

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heat insulation

Doc as the topic has moved on to insulation
I have tried wrapping the exhaust easy on the Cobra I tried to contain the heat,
Twin wall on the Hughes 500 straight out the back again easy as it is a straight pipe this dropped the temp by 100 degrees,
The EC 135 I lined the fuselage this saved the paintwork but heated everything inside,
On the 1/4 scale Jet Ranger I have only draped a heat blanket over the exhaust where it is within the mechanics and left the split Part uncovered with no insulation to the body only to the side of the fuel tanks closest to the fuel tanks, I tried without this and started to melt the tanks. my conclusion is from all the installations I have tried twin wall is certainly the winner I will add some photos to my gallery on this subject
I would also like to add, the more air you can get moving through the fuselage the cooler it becomes to this end I try to open up any grill that it is possible to, on the Cobra even to cut out the area on the belly between the skids edged with a stiffner and fit wire mesh this painted was not visible when flying and not noticible when static

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12-03-2005 09:33 PM  12 years agoPost 8
wolfdad

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Southern Maryland

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Peter Rob,
Again, thanks for the advice and recommendations. Funny thing....just this morning I was perusing the Vario web site here and found several ventilation grates and plan on ordering them within the next day or so. I also noted that on Sandy's BK, he arbitrarily put a large vent in the roof between the two upward stacks. This, I am still debating, because I will pay a penalty in static points since that vent is not there on the real aircraft, however this all may be about compromising and getting air flow to, through and around the turbine.

Anyway, I appreciate all the advice, information and recommendations. My number one turbine confidant cast her vote for the paint as well and, I ALWAYS listen to Sara.

wolfdad sends....

"There are those who have...and, those who will" IRCHA #2117, AMA #70068, Turbine Waiver #105

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12-03-2005 09:44 PM  12 years agoPost 9
Sara

rrApprentice

Yorkshire, England

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Heat Shield Paint

Doc, I only said that I've heard good reports of the BVM paint from some of the jet guys .... I don't have personal experience!

Sara

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12-05-2005 01:41 AM  12 years agoPost 10
Dr.Tim

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Mojave Desert

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I have used the BVM paint ..... Don't like it! It helps but that is all!! My LM Cobra would get soft in the upper deck area so I glued in some heat sheald fabric for mufflers ...... Yep that stuff from Kragen Autoparts ... It's silver in color and has a peel and stick back. Worked PERFECT!! and CHEAP!! I think it was like $15 ....

Dr.Tim

From Simple minds come simple ideas! Approach Engineering

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12-05-2005 02:24 AM  12 years agoPost 11
wolfdad

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Southern Maryland

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Dr. Tim,
Thanks a million! I've got some of the muffler/header shielding you are referring to. Was the upper deck the only problem area? Did you wrap your exhaust? The only thing I am positive about is I am going to wrap the outside of the flex-drive. It goes right between the two stacks going up. Got plenty of clearance, but still the heat right there, just from radiation is going to cook that teflon, I am afraid.

Thanks for the word on the BVM paint. I wanted to hear honest opinions and thanks to all of you, that's exactly what I got.

BTW, my first multi-blade head set-up is complete and with the Helitronix mixer, it was a piece of cake. Once again, I tried to make it harder than it has to be, however by following Joel's instructions to the letter, it went "as advertised." Also, just finished learning the 14MZ to the ECU on the PJW. Also, a piece of cake, however in a couple of spots, the 14MZ has proven it is definitely smarter than I am...and thank God for the servo monitor function!!!!

wolfdad sends....

"There are those who have...and, those who will" IRCHA #2117, AMA #70068, Turbine Waiver #105

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12-05-2005 03:30 AM  12 years agoPost 12
optikaman

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EnglishTown N.J.

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Doc, here is what I did on my H500 which had a heat problem in the beginning. I applied 4 coats of BVM heat shield and I used a heat blanket from Vario, which was glued to the fuse with high temp silicone.

The heat blanket from vario is a heavy fiberglass cloth with a reflective metal layer on the outside.

My H500 had a 1mm gap between the pipe and the fuse at the exit and after the above changes I could place my hand on the rear of the fuse and feel no heat!

You can also wrap the pipe with the blanket to help keep residual heat in the pipe. This has been tested in Wojtek's old bell 230 with great success.

Alan

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12-07-2005 05:13 AM  12 years agoPost 13
Sandy S.

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FLORIDA USA

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the bvm stuff works ok, but it is not a 100% solution. it is needed though.

on the big turbine BK I built with the HP5/PHT3 it was best to insulate the heli, not the pipe. after using several pipe wraping matierials on the exhaust most of them failed.gluing the right insulation to the glass as alan mentioned works best .

the trick is, as with other models I am desiging and have built is the double wall tips where the inner pipe is inside the outer by at least 10mm or more producing a venturi effect. Of course double wall helps all the way down to the first bend if you can and is pretty easy to accomplish... but my double wall tips proved to be enough on my model. Yes, I had vents on my upper deck but I wanted function and was willing to sacrifice scale in this case. the only true scale exhaust I have seen that is very close on any turbine model is 500,NH-90, and possibly cobra-huey... the rest are pretty tough. the model I have most recently finsished came very close to full scale looks, but in the end we had to have it function correctly, so its about 90% which is good enough. In the end, its still a model that must work and work all the time.
The big BK is cavernous inside and thus has a lot of pipe... this does not help matters. For a 70 mm outlet, both pipes in a bifuricated set up must be at least 40 mm or more to avoid high egt. The extra pipe acts like an oven heater and thus the solutions mentioned above must be used. I was lucky with my model as the balance of solutions worked well... but the latest models, not only from myself are featuring less pipe, simpler designs and better function. The latest pipe for our new model is less than 7 inches long straight back and double walled 3/4 of the way. the pipe tam made for me for my big a-star project runs so cool I can touch it while running..double wall again with venturi effect.
If youre gonna use the bvm paint, use at least three coats and it does help a good deal.avoid directly wraping the pipe with products that are not intended for this and space is your friend here...better to have more gap between the pipes and glass work than not.
and lastly, points are worthless if your model melts... so test, spool down
and check before youre sorry you didnt.

hope that helps a little.

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12-07-2005 09:57 AM  12 years agoPost 14
WIRLYBIRD

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CAPE TOWN / SOUTH AFRICA.

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Cooling

Hi Guys,
As with evrything we do in life , life is full of compromises, and modelling is no different.My NH90 has 9 extra vents, covered with steel mesh, placed to help remove the build up of hot air in the body, like Sandy says what good is a scale model that melts , and ruins the paint.Not to mention the much higher heat range that the turbine will have to contend with, the proof is if I remember correctly my turbine runs 80-100 degrees cooler.the BVM heat shield is only a protective layer to prevent heat discolouring your paint to a point, you must vent the heat out somewhere!!
What's better, a was good looking scale model that's melted, or a beautiful almost scale model that just keeps flying??
Best regards,
Dave.

WHAT GOES UP MUST SURELY COME DOWN.

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12-07-2005 10:29 AM  12 years agoPost 15
wolfdad

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Southern Maryland

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Sandy/Dave,
Thanks a million for both of your inputs and, I think I had arrived at the same conclusion as just about everyone has and that this effort is going to take a combination of resources to solve the problem.

Sandy, I followed the construction of both your BK and the NH-90 very closely. In fact, between some things I read with regard to their construction and coming across the "Heat Shield" product was initially what made me start asking questions about the ceramic insulated paint. Also, it is rather obvious that there is a line between functionality and appearance and the "model melting" advice is understood, accepted and appreciated.

Sandy, from what both you and several others have said, I gather that wrapping the pipes doesn't have a lot of "value added" and that effort expended in insulating the fiberglass, as Alan mentioned, pays a higher dividend. Based on that, is there really any benefit gained by wraping the pipes at all....even with an automotive header blanket-type of product?

wolfdad sends...

"There are those who have...and, those who will" IRCHA #2117, AMA #70068, Turbine Waiver #105

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12-07-2005 12:07 PM  12 years agoPost 16
PETER ROB

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Devon UK

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Doc The only advantage with wraping the pipes is to stop the direct heat that you get in the hot spots at bends and joins, the blanket absorbs the heat and displaces it over a larger area, but does not stop the build up temp inside the fuz, back to air flow through the fuz, Doc will post some photos of sliding windows I am making to allow a lot more air through the fuz and they are to scale, back to the blanket I have been getting good results from some thing called plumbers blanket, normally lt put behind pipes that are being soldered to stop the flame burning the decoration it is possible to lay the blanket on your hand and apply a flame to it without burning your hand, it does get hot after a while though

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12-07-2005 01:04 PM  12 years agoPost 17
wolfdad

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Southern Maryland

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Peter,
Again, many thanks for the recommendations!

Man! For me, this has been an excellent thread! I thought I knew "thermal dynamics" fairly well, however it is again obvious that I still have a LOT to learn.

My BK build, to a large extent was "patterned" after Sandy's work on his big BK.

Two things have really been made clear in my mind....ventilation and insulation.

wolfdad sends...

"There are those who have...and, those who will" IRCHA #2117, AMA #70068, Turbine Waiver #105

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12-07-2005 02:31 PM  12 years agoPost 18
PETER ROB

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Devon UK

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Doc I know this is a scale item but it is what i did to improve ventilation and cooling but still stay scale like,sliding windows and the extra grill as full size behind the landing lights


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12-07-2005 02:56 PM  12 years agoPost 19
wolfdad

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Southern Maryland

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Peter,
That is way cool and a super recommendation. I noted, with interest, as I "cyber-thumbed" my way through the Vario catalog, that they offer sliding windows...don't know if they were functional or decorative only.

My thinking now, after considering all that has been recommended, is to provide a good bit more ventilation (scale if at all possible...otherwise ventilation and I'll take the points hit) and insulation. One question I have based on your previous recommendation is, how much higher does the EGT run with the insulation wrapped around the pipes? Since the exhaust wrapping serves to retain residual heat, does this also affect the operating EGT? I've got to go back and do a search on past threads, because I remember another discussion on this same subject and don't recall where it finally wound up.

Anyway thanks again and I will be posting the "how I did it" and "what happened after I did it" press releases right here.

wolfdad sends...

"There are those who have...and, those who will" IRCHA #2117, AMA #70068, Turbine Waiver #105

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12-07-2005 03:02 PM  12 years agoPost 20
GCguru

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Exit 164, NJ

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Gentlemen,

Although I know very little regarding turbine aircraft I have a bit of experience in the high-temp insulating department. I work in the chemical industry and operate specialized equipment that have heated zones that must maintain >1000c for extended periods of time with <0.1c change in temp at any given time (for experimental purposes).
The material I have used is a 1/8" ceramic fiber blanket. This material contains no asbestos, is very flexible, superb thermal resistance, and has a melt point of 3200F (1760c) , continuous service temp of 2300f-3000f , density of 8lbs/cubic foot. Many auto manufacturers use this material as a wrap on their turbochargers and it is also used as an insulator in kilns and ovens. I purchase the material in 1/8"x24"x25ft rolls.. Let me know if this may work as I could possibly send a sample for one of you to experiment with. -Robert

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HelicopterTurbine Helicopters › Has Anyone on the Turbine Heli Side Tried This
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