DB Sopwith Pup

[Graff]

Hi all!

I obtained a quarter scale Sopwith Pup a while back.

It was equipped with a Saito fg33r3 radial with a faulty ignition system.....

I replaced the ignition system and installed the rest of the electrics.

I balanced it at 145 mm, and it works okay there.

I flew it today, and wow what an aircraft.

Sure, I had to trim a lot of down and a few clicks right aileron, but it flies very scale like.

The sound of the radial is very mesmerizing!

The loops were quite big, so the power is "enough"...

I use a wood 17X8 propeller. The fuel is alkylate petrol with 7% Stihl HP Ultra oil.

 

[Jon H]

Lovely model. I have two of these in storage (one kit and one uncovered airframe) waiting their turn on the building bench. I cant decide which one to work on which is part of the delay. 

 

I plan to use a laser 200 of some flavour and prop around 20-22x6. You might also find better performance using something like a 20x6 prop as you will get plenty of thrust out of it for loops etc but the fine pitch will keep the speed down and might help prevent the pitch up you mentioned. Your 17x8 is more suited to a WWII fighter. The saito manual suggests a maximum prop of 18x6 and minimum top end rpm of 8600. That seems small and fast to me, and certainly i would expect the engine to handle 19x6 at the very least, but maybe give macgregor a call and explain your use case. Most engines can be heavily loaded if you dont flog them. Given the nature of the model, a big prop and partial throttle use, i cannot see it doing any harm to the engine at all. Also as its spark ignition you could even retard the ignition a smidge to help it out with the bigger prop if it seems unhappy. I cant find many reviews of the engine, but if it will run a 19 or 20x6 at 7000rpm then that will be fine for performance and sound great too. 

 

Hope that is of use

[Outrunner]

3 hours ago, Jon - Laser Engines said:

Lovely model. I have two of these in storage (one kit and one uncovered airframe) waiting their turn on the building bench. I cant decide which one to work on which is part of the delay. 

 

I plan to use a laser 200 of some flavour and prop around 20-22x6. You might also find better performance using something like a 20x6 prop as you will get plenty of thrust out of it for loops etc but the fine pitch will keep the speed down and might help prevent the pitch up you mentioned. Your 17x8 is more suited to a WWII fighter. The saito manual suggests a maximum prop of 18x6 and minimum top end rpm of 8600. That seems small and fast to me, and certainly i would expect the engine to handle 19x6 at the very least, but maybe give macgregor a call and explain your use case. Most engines can be heavily loaded if you dont flog them. Given the nature of the model, a big prop and partial throttle use, i cannot see it doing any harm to the engine at all. Also as its spark ignition you could even retard the ignition a smidge to help it out with the bigger prop if it seems unhappy. I cant find many reviews of the engine, but if it will run a 19 or 20x6 at 7000rpm then that will be fine for performance and sound great too. 

 

Hope that is of use

If they were mine Jon I would finish the uncovered Pup and sell the other.

 

Nice Pup Graf.

[Graff]

Thanks, I will try a 20x6 and see how it works. The problem is that my suppliers has had the 6" pitch props on backorder....

[Frank Skilbeck]

Club mate has got one of these with the same engine, initially unbaffled. It ended up overheating, seizing and throwing a rod, pretty well mangled, Morris Mini Motors did the rebuild and fitted their improved cylinder distribution. Reinstalled, with baffles, and it now runs great.

 

Another friend has one with Os120 FS and I've flown it many times, it's a lovely flier.

[Jon H]

23 hours ago, Outrunner said:

If they were mine Jon I would finish the uncovered Pup and sell the other.

 

 

Slight digression but some explanation. 

 

I actually have 3 1/4 pups. The two DB's and a Mick Reeves new in box. It came about this way as i wanted a 1/4 pup that would be quick to finish for wings and wheels one year. A friend had one covered and, in my mind, nearly ready to go. The deal was done, but i then discovered the wings and tail were badly warped from how they were stored and whoever built it did it only for looks as much of the construction was not to an airworthy standard. This meant the airframe needed to be stripped, which it was, and once the size of the job became apparent i grabbed my 1/4 stampe airframe and finished that instead with the pup consigned to the rafters in the garage. Still wanting a 1/4 pup i grabbed a mick reeves kit when it came up on bmfa, but it looked over complicated for my use case so grabbed a new in box DB when that came up for sale. Having 3 i decided to sell the bent bare airframe as it was more work than new and i would rather spend covering money on a new build. i would then decide which kit to build when the time came. the reeves is very appealing due to its accuracy and might be an interesting future challenge, but the DB kit is like a giant flair model and the build well understood. So i got the bent one out of the rafters for the photos to sell it. To my surprise the 2 years or so it had spent laid flat in the damp rafters had completely straightened the wings and the job of fixing it was now not as big. my dad was muttering about his interest in it....so i kept it.

 

One day i will decide which one to build and the others will probably then be moved on to new homes. As i lack the space to store an operational example at the moment they are all hiding out at my dads. 

 

The Pup is my favoured WWI fighter in the same way as the Hurricane is my WWII favourite. I do have a pup problem though as i have 5 in total with a flair pup airframe bought cheap at old warden and a new in box balsa usa example. I also want the teeny tiny DB 40 inch pup for my little OS 26 4 stroke as it would be very sweet, but so far common sense has prevented me buying one. 

 

 

 

 

[Graff]

The first scale competition for the year was today, and I finished 5:th out of 9 contestants.

The Pup did its job wonderfully.

[Graff]

To summarize the season, I competed three times in F4H with the Pup, and it performed flawlessly everytime.

It was even good in winds up to 7-8 m/s.

I actually ended up fourth overall.

The only change I did was using a 20x6 "Sail" propeller. It flew much better with it.

 

For the next season I have a list of improvements to make.

 

1- Add a dummy engine

2- build a better cowl.

3- repaint in this scheme:

4- add details!

5- make a better scale documentation.

[Graff]

As promised, there are things being done on the Pup.

I moved the engine 25 mm to the rear and installed a scale cowling.

The wheels were replaced with DuBro wheels.

I made scale wheel locks for them.

 

I designed a lookalike Monosoupape dummy that would allow some cooling to the radial engine.

A few hours in Fusion 360 gave this:

 

I printed it on my trusty old Wanhao duplicator 4S using HiTemp ABS.

 

When test fitted it looks like this:

 

It left room for improvements, so version 2 is in the printer as I write this.

The repaint has also started.

I added rib tapes from Toni Clark before spraying on the custom mixed PC 10.

It's old Powermax Polykote paints that I mixed using black, beige yellow and blue. I added a dash of olive drab to get it perfect.

 

The first coat turned out too brown, hence the addition of olive drab.

 

Now it's just a matter of finishing it before the end of May.

Btw, I changed the prototype...

I model this one now:

Edited Monday at 09:06 by Graff

[Graff]

My dummy engine version 2.0 that I printed out is now glued on the plywood baffle (which will later be glued to the engine cowling).

 I've only primed it yet, but with some aluminum paint and detailing it will look better.

 The cooling of the engine will be so much better as a result.

[Graff]

The finished result: