Jamie C

Hi guys,

I have recently bought a new in box BVM Viper kit (not Ultra) which will be built as a DF model with a full house BVM 91/Viojett set up. I have been told/read that the flaperon set up that the Viper incorporated led to a decrease in lateral control effectiveness on landing/slow flight? and to combat this builders were modifying their models to use a standard aileron and flap set up?

I was hoping that some one would be able to give me some idea of the dimensions used for this mod or a rough i guide to work from?

Any help would be appreciated

Thanks in advance

Jamie

mr_matt

My Feedback: (10)

I did not do this on a Viper, I did it on an Ultra but never finished it.

In my experience the Viper flaperons did not generate enough drag, so I added a belly speedbrake, like a bandit had. I cut it into the belly pan and powered it with a micro servo, it worked great.

dbsonic

My Feedback: (3)

The BVM Viper with aileron and flap combo is like a mini-bandit. so it works great. IIRC 60% of span for flaps, 40% ailerons is what you want.

gunradd

My Feedback: (9)

I just cut mine like DBsonic suggested. Still building it so have not flown it yet. But my buddy Sean flew his with this same mod and it worked great.

Jamie C

That's good to hear, thanks for the info guys.

TCHIEF

My Feedback: (15)

i built a viper years ago and built it to specs and it was the worst mistake separate flaps and ailerons would have been the best option

Jamie C

It shows a speed brake in the manual, not sure i will incorporate it though. I will definitely mod flaperons to flaps and ailerons.

mr_matt

My Feedback: (10)

Yep that is what I did, it was fine, I never missed the flaps but that is just me.

Without that speed brake the glide path felt like about 0.1 degrees!

The speed brake also made it easier to bolt the wing on, you would connect the wing servos through the speed brake opening.


this is a very cool project, I am very jealous. Do you have any spare pistons/sleeves?

turnnburn

My Feedback: (49)

First of all why are you building it with a glow engine DF ? I flew my share of Glow DF and primarily with BVM fan and engines so I had the best that money can buy just like you. Lots of tinkering, fiddling, adjusting not to mention the oily mess. One of the happiest days of my modeling life was day I stopped messing with glow DF and went turbine and never looked back. I also have one BVM electric DF unit and it is so much more reliable than glow df. I strongly encourage you to rethink your power choice.

I have a BVM Ultra Viper that I built as glow DF about 18 or 19 years ago and later converted to turbine power. I never did like the flaperons and I eventually cut some small "F-4" like ailerons outside of the flaperons and then used the flaperons as Flaps only. I like this setup much better. I left about 5/16" of fixed wing surface between the aileron and flap. My ailerons are not quite 5" long (span) and have a chord of 3" on the inner edge of aileron and 2 1/2" at the outboard end. I use a super thin aileron wing type servo layed down flat in the wing starting bout one inch in front of the aileron hinge line and extending forward from there about 1 7/8". I cut a channel or grove just wide enough and deep enough to put the aileron servo wire in. It goes from the aileron servo cutout to the landing gear area and from there to the wing center section (root). If you will send me an email I can send you some pictures.

Due to the ailerons being on the small side it takes quite a bit of travel. My hinging allows for 1.5" of travel and if I remeber right I use about 1" to 1.25" up and down on high rate and a little less for low rate (high speed flight).

dbsonic

My Feedback: (3)

I had to face this choice and in my case I went EDF with mine. It never saw a glow engine. One of the reasons was just availability of parts for the 91 and also because I had great success converting an old JHH F86 to EDF where it performed so much better than the original with K&B48. But BVM Viper with a BVM 91 is in a class of its own. It was already optimized as a DF, stays light and gets good flight times that way. As an EDF, well, it goes alright, but its no Electra.

Jamie C

Matt,

Good tip for the speed brake/wing mounting.

With regards to engine parts, i search ebay and keep my eye on the classifieds to see what is about as i know that i will end up getting through a few.

I keep on getting asked, why in the turbine era do you want ICDF ?? my answer is simple, i always wanted a BVM DF model!

I fly a DF at the moment, in the shape of a Jim Fox SAAB Viggen with OS 91/Ramtec combo . . . . . i love it! i also have a partially complete Aggressor II kit waiting to be done, bits missing but not too much of a problem.

Jamie C

I wanted it specifically for ICDF, when the parts i have run out and i cannot get anymore then i will more to the Viofan EVF system. I do love the sound of ICDF so will hopefully keep it going for a long time to come on completion.

The kit was on ebay and situated in Canada, some good friends helped me to get the kit to the UK.

Jamie C

To own and fly a BVM DF model is something i have wanted since i first saw one in 1991, it was a Viper flown by Steve Elias in the Top gun UK speed competition . . . . fastest model i had ever seen at the time! i do fly turbine models as well but i have always been keen on ICDF, BVM especially! i love the tinkering/fine tuning, smell of glow fuel and the sound of a screaming DF. When the engine supply drys up, i will go for the Viofan.

I have an Agg II waiting to be finished and in time i am hoping that an Agg III, UV and Mav pro kits will come my way. The gloss red UV with the winglets pictured at recent events is absolutely stunning!

PM sent

Jamie C

Last year Ron Sweeney very kindly gave me his DF video collection which spans from the early days of DF to the turbine era. On a few of these videos were the Top gun UK events including the 1991 event, which included footage of the Viper i was watching at the same event. I extracted the clip and here it is, it is only the first 55 seconds the rest of the video is at a different event at RAF Debden.

https://www.youtube.com/watch?v=iEG7jn5J34A

The the second video is of a Viper being flown in New Zealand, not bad for an old model !

https://www.youtube.com/watch?v=5YSlq3RYXJY

dbsonic

My Feedback: (3)

Quite a performer. Jamie, one note although you may already plan to do this, but be sure to bottom hinge the flaps. That's the best and cleanest way to do it to maintain a clean wing with flaps up.

roger.alli

I understand exactly Jamie.. The sound of a Viper/0.91R coming down hill, wide open, is music to my ears.. I have always loved high performance 2 strokes, and these BVM engines were the top of the tree.

Getting one of these engines operating requires some skill and experience, and is very rewarding in itself. Yes, EDFs are more powerful, cleaner and just modern, but they don’t offer the same “challenge” as a piston at 28k rpm.. Turbines are plug N play these days, and EDS are comparatively easy.

I have a Mavrick/KBV 82 under the bench, waiting for me to resurrect it. Plus I have a NIB 91R with Viofan, as a spare (not for sale).. I would really like an Aggressor III one day.. I know they are out there.

I guess there might be a new sub group forming, Vintage Jets!!

Jamie C

If there is enough room i was planning to have the flaps actuated the same way as the Bandit, bottom hinged as you say with the same style of hinges but with the rod/horn connection coming from a servo recessed in the wing. Will take a more detailed look and see what room i have to play with, if not then the servo rod will have to exit from the bottom of the wing.

Jamie C

I am lucky in that i fly with a friend who ran a lot of KBV's and Nelson's back in the day, so will be relying heavily on his knowledge. My biggest problem with getting hold of these models is that all of them so far are the other side of the pond! I have a couple of spare used BVM 91's and a KBV 82 which i am stripping and cleaning, but i also have some unused motors which have not even been mounted in a fan unit, such beautiful motors that they will remain unused.

Always checking out ebay for parts/models. Have a few small packages heading my way across the Atlantic.

f16man

Also the Rossi 81s have huge transfer ports for their day and could spin up real well, We ran a lot of os77s with a needle bearing on the crank pin, I machined the rods out of titainium, a little port work and 10%nitro with some castor, they were not power houses on take off but once unloaded, we got some good speed out of them........

Art ARRO

My Feedback: (5)

Jamie and All,
Note that the stock flaperon configuration works just fine on the BVM Viper and Ultra Viper as proven by numerous examples. However, your MUST ensure that the flaperons exhibit some upward deflection once they are deployed as flaps. This can be done mechanically by linkage geometry, radio programming or both. You will/may not have sufficient lateral control if a flaperon is not deflected upwards. My former jet partner had a Viper and we almost lost it before rigging the flaperon in this manner. Mixing some rudder movement with the flaperons deployed also helps steer the Viper during landing.
A long time glow (ICDF) pilot flew a Viper at our Highland Jets event this past weekend. He showed the turbine guys a thing or two about speed. This pilot intends to start a club of ICDF or glow DF jets and is calling it "Nostalgia Jets" , very much in line with your "Vintage Jets" concept. I personally flew a glow DF earlier this month powered by a Fan Jett 50 in a Turbax fan unit. Long live glow DF with noise and slime.
Rgds,
Art ARRO

gunradd

My Feedback: (9)

Few pics of my viper I'm building for my son.

gunradd

My Feedback: (9)

It was in very bad shape when I got it. Just got done making new formers for it.

dbsonic

My Feedback: (3)

What are you guys planning for retracts/struts?

gunradd

My Feedback: (9)

I have some springair retracts and tamjets struts. I had them on my other BVM viper and they worked great. This one will get a K60 for power.

dbsonic

My Feedback: (3)

Nice!