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Old Sep 15, 2012, 06:12 AM
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United Kingdom, England, North York
Joined Nov 2004
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Test run engines in plane

I took the plane up to the field one afternoon just to test run and set up the engines in the plane and check out the TwinSync settings as this was not used on the test stand. The engines are giving a good idle at around 1800rpm, I could go lower but want to get confidence first. They are peaking at 5,000rpm on one engine and 5,400rpm on the other as they still need to loosen up a bit. They are both giving very good throttle response with no sign of oiling up and dying at low rpm the TwinSync comes with onboard glows which really help to keep the RCVs firing at tick over. Just after finishing the one video the tank ran dry on one engine and gave the TwinSync a test although I had not planned it, the TwinSync took the running engine to idle as per expectation, so I know the system works.

Also shown here after some requests are photos of the cooling baffle with the engine installed to give an idea of how well fitting the air scoop is, taking the air from the front inlet and up over the fins and then down the back and out over the exhaust.

A video walk around with the engines running can be found at
Movie 015 walkaround.wmv (0 min 32 sec)


A video showing the engine throttle response with the TwinSync working can be found at
Movie 014 checking engine running and set up.wmv (1 min 40 sec)
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Old Sep 15, 2012, 06:15 AM
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United Kingdom, England, North York
Joined Nov 2004
332 Posts
Final assembly before maiden

Work continues on all of those final jobs once you know the airframe is complete and the engines are running OK. Loading up all the RC gear has taken a little while given all the stuff, especially the TwinSync which bristles with cables. I have made a bracket for the air fill valve for the retracts but the switches are still loose at this time awaiting determination of the battery location and the C of G check (more later).

I have finally fitted the cowls now that the engines are running well having to cut a small number of holes for fuelling valve, starter wand, low running jet and the main needle valve. I have then moved on to the spinners something I have been leaving to last as I have never cut spinners before. After some searching various forums I followed some advice and used the tungsten carbide cutter in my Dremel with machine oil to stop the aluminium frog clogging the teeth on the tool. This worked a treat leaving a pile of aluminium filings on my workbench, albeit damp with oil. The spinners still need balancing and painting. I had left this to last because I kept wondering about using 3 blade props but have decided against this, although the engine could turn them, the rpm would be down and I think I will need all the grunt they can deliver.

Next came the stage I have been concerned about for some time, checking the C of G. I know the RCV engines are heavier than conventional engines and was worried that I would be front heavy. I was waiting to see where the Rx / servo battery needed to go to achieve the C of G, perhaps needing a rearward position to counterbalance the engines. Anyway, the battery needed to go where it normally goes, in the front of the cockpit section to give a spot on balance. It can be seen here taped on to the bottom of the cockpit as a trial. Interestingly, although the RCV engines are heavier they have a lot of their weight at the rear of the engine and they are longer than normal engines, which have more of their mass further forwards. SO perhaps the heavier weight is not so much of an issue.

I decided to weight the plane to see where this came out, with an answer of 17 lbs 12 oz / 8.05 kg so somewhat heavier than the target weight from the plan (13 lb 10 oz / 6.18 kg). However, the plan states that the original engines were OS 40s and these were replaced with Laser 70s, which would have added by my reckoning around 1 lb / 0.45 kg or so. I will have to see how it behaves and keep the speed up on turns and especially landing. I am not too concerned about the engines, there are many people who have run 9lb planes on a single RCV60SP or a 40lb 4 engine on 4 of them.
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Old Sep 15, 2012, 06:18 AM
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United Kingdom, England, North York
Joined Nov 2004
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Maiden flight

The final bits and pieces involved installation of the batteries in the nose cone. As I had left all the nose formers in place I had to cut a series of rectangles and install a box. Then came installing the switches for the batteries and painting the spinners red. When all was completed there were no excuses left. It is ready for flight, some 4 years after buying the kit and 3 1/2 years after starting the build.

The weather forecast was for a gentle 10mph wind straight down our runway. Once ready both engines were running well from 2,000rpm to 5,300rpm.

Then it was time for some trial runs down the field to see what the ground handling was like. It has a tendency to swing left but nothing that could not be controlled by starting the run with some right rudder and then the gyro held it and the manual input could be eased off. The thrust these RCV engines can put out is phenomenal, there was no shortage of acceleration and I knew it would take off OK. Back to the pits to refuel and take stock, then out to the strip again.

Right rudder, hold the elevator up to keep the tail down, start push the throttles forward to just over half, planes rolling, release the elevator to allow the plane to come onto its main wheels and loose the offset thrust (P factor) turning it to the left, ease off on the right rudder and tracking as straight as a die, push the throttles full forward, wait for the extra burst of acceleration to reach full speed, bleed in a bit of up elevator and she’s up, gently climbing away, engines on song, raise the gear and the speed builds up some more, few clicks of aileron trim, ooops it is quite sensitive, more sensitive than I expected given the throws are not huge, gentle inputs only. Landing was without flaps and a bit fast and bouncy but no issues really.

First flight was just to get the measure of the plane, right and left circuits and figure eights only. There is no problem with the weight it flies magnificently. The RCV60SP engines are good but the flight is between half and full throttle and I have the engine curves set so this truly means between 50% rpm range (3,500rpm) to max (5,300rpm). Flaps and wheels do not seem to affect the flight trim much, I have a little flap to elevator trim set.

On the next flight I started experimenting a little more with the flight envelope – large wingovers look truly impressive, fast low passes, twin engines in sync – brilliant. The landing caught me a bit off guard though and I was too slow and it dropped the last 2ft, split the undercarriage mounts from the ribs and punched it up through the sheeting. Damn, I knew before I started these flights that I would have to keep the speed up, not too bad to fix and one day I will learn to keep the speed up with this type of model.

Now I have flown it some more I can say that it is a very easy plane to fly once it is in the air, the controls are well balanced, the plane tracks very smoothly and consistently, a real pleasure to fy.

A video of one of the early flights (not the maiden) can be found at
Peterf's BT Mosquito flight (2 min 37 sec)
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Old Sep 15, 2012, 06:31 AM
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United Kingdom, England, North York
Joined Nov 2004
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Conclusion

After 3 1/2 years of building (on and off) I am very pleased with the plane, it is not a scale scale plane but is a good stand off scale plane that has a lot of presence in the air and flies extremely well.

For my first build of this type of complex model it has turned out very well and I have to commend Brian Taylor for producing an excellent design that can be followed with limited head scratching and flies well even if you end up a lot heavier.

What would I do differently after completing the build.

1. Sheet the fuselage rather than planking it.
2. Fuel proof it with something else, the Poly C has turned out to be less fuel proof than advertised.
3. Not use nylon snakes without a steel inner on such long runs.
4. Use Gorilla glue to glue items to fibreglass cowls ratehr than epoxy.

and none of the above are major issues, which is pleasing.

Time to go and play.
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Old Sep 15, 2012, 04:29 PM
Build'em and Crash'em
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Narragansett, RI
Joined Oct 2000
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Very nicely done
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Old Sep 18, 2012, 06:56 PM
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Very impressive! Thanks for reposting your thread here, great videos and pictures! Have you been flying it much? Do the flaps help with landing speed vs your first flights? Are the engines evening out in performance? I wonder if the sound would be much different without the rpm balancing electronics. Any further experiments with propellers?
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Old Sep 18, 2012, 07:44 PM
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United Kingdom, England, North York
Joined Nov 2004
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Essar, Ken & Flyrod,

Thanks for the compliments, and this is certainly an easier forum to post pictures and video on.


Flyrod,

I have been flying a few times with it but the UK summer has been diabolical this year and work has taken me away a lot as well. I am finding that the flaps are very useful if there is little headwind to keep the approach speed down and I am still learning this part of the flight envelope. I have really got the hang of the take off, let the tailwheel rise early and it runs straight as a die.

The engines are coming closer together when the Twinsync is not running and when it is the max engine speed is increasing slightly as the Twinsync was keeping the fater running engine down to match the slower one, but these take some running in. I still have a tickover higher than I would like at 1,800-2,000 rpm when run in they should be stable at 1,500rpm. I have deicded to stay with the 16x12 props because they give lots of thrust and authority at take off and good scale like speed in the air, I was so happy with them I did not even try the 15x14 props and sold them on.

I have had some issues with the landing gear collapsing on me which was hard to understand. Originally I had a hand pump and pumped them up to 120psi. I then swapped to a small electric pumps and had some collapses. I eventually found that the pressure gauge on the electric pump was reading 60psi low so I only had 60psi on the retracts, no wonder the would not lock down.

Peter.
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Old Sep 19, 2012, 05:41 PM
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United States, PA, Sellersville
Joined Apr 2011
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Thanks for posting you beautiful build. Love the color scheem. I also am watching Bruces build. As far as joining the other site you were on, it took many tries but I finally was able to join. I am not impressed. This site is better. Good luck and many years flying that beauty.

Rick
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Old Sep 22, 2012, 09:43 PM
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Are you just using exhaust pressure to deliver fuel, or do you have any kind of a pump? Did you notice better performance with the genesis exhaust?
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Old Sep 23, 2012, 05:02 AM
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United Kingdom, England, North York
Joined Nov 2004
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No pump only exhaust pressure and that seems fine. I have not run a side by side exhuast comparison (which I should have), but they are no worse so far, the run in RPM gived by RCV for the 16x12 prop is 5350rpm and I have been getting 5,400rpm and do not consider the engines to be fully run in yet.
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Old Nov 14, 2012, 03:58 AM
Never too late
Australia, QLD, Eli Waters
Joined Nov 2012
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Traplet BT Mosquito kit arrived last week and I have been studying the plans, in conjunction with your thread. Seem to have a handle on most of it so far, but questions are cropping up all the time. I'm not sure my own thread would be useful, but I'll see. I have been following Bruce's thread for some time and admired his work as I have yours. So this is a touch base exercise for me, hoping that I can contact you when problems arise. This will be my first build for some years, I have been restoring old cars and technically model aircraft have moved on considerably, so I have some catching up to do. Please forgive stupid questions! At some stage in the future I would like a set of exhausts for the Merlins, would you please reserve me a set if possible.
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Old Dec 09, 2012, 10:38 PM
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Mosquito info

PeterF, Congragulations on your success! I have been watching your build and tests on RCSB for some time. My build schedule is much like yours, with work and things around the house I am about 3 1/2 years into a BT Mosquito. A few questions. Apparently your engine cooling is working out. I had planned to use a similar arrangement, but was concerned that it might not be suffcient. What was the average ambient temp when you were flying? Did you measure engine temps at all? You mentioned a gyro, is this a heli tail gyro hooked to the rudder? I know some people use this arrangement, but others suggest that the Mosquito rudder is not effective until substancial speed is attained.
I like the way you handled all the little bits that BT did not have much detail about. A photo is worth a thousand words. I'll be looking at your summary here as I complete my DH 98. I better get moving as the full size one is flying in NZ and soon to come here. I hope they send it round the airshow circuit!
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Old Dec 10, 2012, 09:42 AM
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Joined Nov 2004
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xfly-er, Thanks for the comments. The Gyro on the tailwheel and rudder is a normal rate gyro I have had for some time, I put one in my DC-3 and found it helped on take off. However, I now understand more about taking off with tail dragger twins so I am not sure how effective it is, but it does not cause a problem so I have kept the gyros in both planes.

I have not checked engine temps in either of the engnes, but the times I have flown here in the UK were late winter and through the spring and summer, temepratures in the range of 5-20C, 20C at most as the summer has been attrocius here this year.

I was at a local air museum today, The York Air Museum at Elvington and they have a night fighter version, I was amazed at actually how small the Mossie was, I was expecting something larger.
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Old Dec 10, 2012, 11:14 AM
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Yes the Mosquito is a compact airplane. I noticed that the seats are staggered so the pilot and JAFO don't bump shoulders. Also pilot has more armour plate in the seat so you know who's important..........http://www.mossie.org/images/W4050/d...ajd_d5_003.jpg
Probably needed a slender person well under 2M to crawl through to the bombsite.
http://www.mossie.org/images/W4050/proto_int_10.jpg
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Old Dec 10, 2012, 11:48 AM
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Joined Jan 2011
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Quote:
Originally Posted by xfly-er View Post
Yes the Mosquito is a compact airplane. I noticed that the seats are staggered so the pilot and JAFO don't bump shoulders. Also pilot has more armour plate in the seat so you know who's important..........http://www.mossie.org/images/W4050/d...ajd_d5_003.jpg
Probably needed a slender person well under 2M to crawl through to the bombsite.
http://www.mossie.org/images/W4050/proto_int_10.jpg
The reo had a shield that could be raised or lowered so he could reach the electronics and yes it helped if you were a smaller guy.

Bruce
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